draft-ietf-dtn-tcpclv4-18.txt   draft-ietf-dtn-tcpclv4-19.txt 
Delay Tolerant Networking B. Sipos Delay Tolerant Networking B. Sipos
Internet-Draft RKF Engineering Internet-Draft RKF Engineering
Intended status: Standards Track M. Demmer Intended status: Standards Track M. Demmer
Expires: July 30, 2020 UC Berkeley Expires: September 8, 2020 UC Berkeley
J. Ott J. Ott
Aalto University Aalto University
S. Perreault S. Perreault
January 27, 2020 March 7, 2020
Delay-Tolerant Networking TCP Convergence Layer Protocol Version 4 Delay-Tolerant Networking TCP Convergence Layer Protocol Version 4
draft-ietf-dtn-tcpclv4-18 draft-ietf-dtn-tcpclv4-19
Abstract Abstract
This document describes a TCP-based convergence layer (TCPCL) for This document describes a TCP-based convergence layer (TCPCL) for
Delay-Tolerant Networking (DTN). This version of the TCPCL protocol Delay-Tolerant Networking (DTN). This version of the TCPCL protocol
is based on implementation issues in the earlier TCPCL Version 3 of resolves implementation issues in the earlier TCPCL Version 3 of
RFC7242 and updates to the Bundle Protocol (BP) contents, encodings, RFC7242 and updates to the Bundle Protocol (BP) contents, encodings,
and convergence layer requirements in BP Version 7. Specifically, and convergence layer requirements in BP Version 7. Specifically,
the TCPCLv4 uses CBOR-encoded BPv7 bundles as its service data unit the TCPCLv4 uses CBOR-encoded BPv7 bundles as its service data unit
being transported and provides a reliable transport of such bundles. being transported and provides a reliable transport of such bundles.
This version of TCPCL also includes security and extensibility
mechanisms.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 30, 2020. This Internet-Draft will expire on September 8, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 17 skipping to change at page 2, line 21
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 5 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 5
2.1. Definitions Specific to the TCPCL Protocol . . . . . . . 5 2.1. Definitions Specific to the TCPCL Protocol . . . . . . . 5
3. General Protocol Description . . . . . . . . . . . . . . . . 8 3. General Protocol Description . . . . . . . . . . . . . . . . 9
3.1. Convergence Layer Services . . . . . . . . . . . . . . . 8 3.1. Convergence Layer Services . . . . . . . . . . . . . . . 9
3.2. TCPCL Session Overview . . . . . . . . . . . . . . . . . 10 3.2. TCPCL Session Overview . . . . . . . . . . . . . . . . . 11
3.3. TCPCL States and Transitions . . . . . . . . . . . . . . 12 3.3. TCPCL States and Transitions . . . . . . . . . . . . . . 13
3.4. Transfer Segmentation Policies . . . . . . . . . . . . . 18 3.4. Transfer Segmentation Policies . . . . . . . . . . . . . 19
3.5. Example Message Exchange . . . . . . . . . . . . . . . . 19 3.5. Example Message Exchange . . . . . . . . . . . . . . . . 20
4. Session Establishment . . . . . . . . . . . . . . . . . . . . 20 4. Session Establishment . . . . . . . . . . . . . . . . . . . . 21
4.1. TCP Connection . . . . . . . . . . . . . . . . . . . . . 21 4.1. TCP Connection . . . . . . . . . . . . . . . . . . . . . 22
4.2. Contact Header . . . . . . . . . . . . . . . . . . . . . 22 4.2. Contact Header . . . . . . . . . . . . . . . . . . . . . 23
4.3. Contact Validation and Negotiation . . . . . . . . . . . 23 4.3. Contact Validation and Negotiation . . . . . . . . . . . 24
4.4. Session Security . . . . . . . . . . . . . . . . . . . . 24 4.4. Session Security . . . . . . . . . . . . . . . . . . . . 25
4.4.1. TLS Handshake . . . . . . . . . . . . . . . . . . . . 24 4.4.1. Entity Identification . . . . . . . . . . . . . . . . 26
4.4.2. TLS Authentication . . . . . . . . . . . . . . . . . 26 4.4.2. TLS Handshake . . . . . . . . . . . . . . . . . . . . 27
4.4.3. Example TLS Initiation . . . . . . . . . . . . . . . 27 4.4.3. TLS Authentication . . . . . . . . . . . . . . . . . 28
4.5. Message Header . . . . . . . . . . . . . . . . . . . . . 28 4.4.4. Example TLS Initiation . . . . . . . . . . . . . . . 30
4.6. Session Initialization Message (SESS_INIT) . . . . . . . 30 4.5. Message Header . . . . . . . . . . . . . . . . . . . . . 31
4.7. Session Parameter Negotiation . . . . . . . . . . . . . . 31 4.6. Session Initialization Message (SESS_INIT) . . . . . . . 32
4.8. Session Extension Items . . . . . . . . . . . . . . . . . 32 4.7. Session Parameter Negotiation . . . . . . . . . . . . . . 34
5. Established Session Operation . . . . . . . . . . . . . . . . 33 4.8. Session Extension Items . . . . . . . . . . . . . . . . . 35
5.1. Upkeep and Status Messages . . . . . . . . . . . . . . . 33 5. Established Session Operation . . . . . . . . . . . . . . . . 36
5.1.1. Session Upkeep (KEEPALIVE) . . . . . . . . . . . . . 34 5.1. Upkeep and Status Messages . . . . . . . . . . . . . . . 36
5.1.2. Message Rejection (MSG_REJECT) . . . . . . . . . . . 34 5.1.1. Session Upkeep (KEEPALIVE) . . . . . . . . . . . . . 36
5.2. Bundle Transfer . . . . . . . . . . . . . . . . . . . . . 35 5.1.2. Message Rejection (MSG_REJECT) . . . . . . . . . . . 37
5.2.1. Bundle Transfer ID . . . . . . . . . . . . . . . . . 36 5.2. Bundle Transfer . . . . . . . . . . . . . . . . . . . . . 38
5.2.2. Data Transmission (XFER_SEGMENT) . . . . . . . . . . 36 5.2.1. Bundle Transfer ID . . . . . . . . . . . . . . . . . 39
5.2.3. Data Acknowledgments (XFER_ACK) . . . . . . . . . . . 38 5.2.2. Data Transmission (XFER_SEGMENT) . . . . . . . . . . 39
5.2.4. Transfer Refusal (XFER_REFUSE) . . . . . . . . . . . 39 5.2.3. Data Acknowledgments (XFER_ACK) . . . . . . . . . . . 41
5.2.5. Transfer Extension Items . . . . . . . . . . . . . . 42 5.2.4. Transfer Refusal (XFER_REFUSE) . . . . . . . . . . . 42
6. Session Termination . . . . . . . . . . . . . . . . . . . . . 44 5.2.5. Transfer Extension Items . . . . . . . . . . . . . . 45
6.1. Session Termination Message (SESS_TERM) . . . . . . . . . 44 6. Session Termination . . . . . . . . . . . . . . . . . . . . . 47
6.2. Idle Session Shutdown . . . . . . . . . . . . . . . . . . 46 6.1. Session Termination Message (SESS_TERM) . . . . . . . . . 47
7. Implementation Status . . . . . . . . . . . . . . . . . . . . 46 6.2. Idle Session Shutdown . . . . . . . . . . . . . . . . . . 50
8. Security Considerations . . . . . . . . . . . . . . . . . . . 47
8.1. Threat: Passive Leak of Node Data . . . . . . . . . . . . 47 7. Implementation Status . . . . . . . . . . . . . . . . . . . . 50
8.2. Threat: Passive Leak of Bundle Data . . . . . . . . . . . 47 8. Security Considerations . . . . . . . . . . . . . . . . . . . 50
8.3. Threat: TCPCL Version Downgrade . . . . . . . . . . . . . 47 8.1. Threat: Passive Leak of Node Data . . . . . . . . . . . . 51
8.4. Threat: Transport Security Stripping . . . . . . . . . . 47 8.2. Threat: Passive Leak of Bundle Data . . . . . . . . . . . 51
8.5. Threat: Weak Ciphersuite Downgrade . . . . . . . . . . . 48 8.3. Threat: TCPCL Version Downgrade . . . . . . . . . . . . . 51
8.6. Threat: Invalid Certificate Use . . . . . . . . . . . . . 48 8.4. Threat: Transport Security Stripping . . . . . . . . . . 51
8.7. Threat: Symmetric Key Overuse . . . . . . . . . . . . . . 48 8.5. Threat: Weak Ciphersuite Downgrade . . . . . . . . . . . 52
8.8. Threat: BP Node Impersonation . . . . . . . . . . . . . . 48 8.6. Threat: Invalid Certificate Use . . . . . . . . . . . . . 52
8.9. Threat: Denial of Service . . . . . . . . . . . . . . . . 49 8.7. Threat: Symmetric Key Overuse . . . . . . . . . . . . . . 52
8.10. Alternate Uses of TLS . . . . . . . . . . . . . . . . . . 50 8.8. Threat: BP Node Impersonation . . . . . . . . . . . . . . 52
8.10.1. TLS Without Authentication . . . . . . . . . . . . . 50 8.9. Threat: Denial of Service . . . . . . . . . . . . . . . . 53
8.10.2. Non-Certificate TLS Use . . . . . . . . . . . . . . 50 8.10. Alternate Uses of TLS . . . . . . . . . . . . . . . . . . 54
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 50 8.10.1. TLS Without Authentication . . . . . . . . . . . . . 54
9.1. Port Number . . . . . . . . . . . . . . . . . . . . . . . 51 8.10.2. Non-Certificate TLS Use . . . . . . . . . . . . . . 54
9.2. Protocol Versions . . . . . . . . . . . . . . . . . . . . 51 8.11. Predictability of Transfer IDs . . . . . . . . . . . . . 54
9.3. Session Extension Types . . . . . . . . . . . . . . . . . 52 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 55
9.4. Transfer Extension Types . . . . . . . . . . . . . . . . 53 9.1. Port Number . . . . . . . . . . . . . . . . . . . . . . . 55
9.5. Message Types . . . . . . . . . . . . . . . . . . . . . . 54 9.2. Protocol Versions . . . . . . . . . . . . . . . . . . . . 55
9.6. XFER_REFUSE Reason Codes . . . . . . . . . . . . . . . . 55 9.3. Session Extension Types . . . . . . . . . . . . . . . . . 56
9.7. SESS_TERM Reason Codes . . . . . . . . . . . . . . . . . 56 9.4. Transfer Extension Types . . . . . . . . . . . . . . . . 57
9.8. MSG_REJECT Reason Codes . . . . . . . . . . . . . . . . . 57 9.5. Message Types . . . . . . . . . . . . . . . . . . . . . . 58
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 58 9.6. XFER_REFUSE Reason Codes . . . . . . . . . . . . . . . . 59
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 58 9.7. SESS_TERM Reason Codes . . . . . . . . . . . . . . . . . 60
11.1. Normative References . . . . . . . . . . . . . . . . . . 58 9.8. MSG_REJECT Reason Codes . . . . . . . . . . . . . . . . . 61
11.2. Informative References . . . . . . . . . . . . . . . . . 60 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 62
Appendix A. Significant changes from RFC7242 . . . . . . . . . . 61 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 62
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 62 11.1. Normative References . . . . . . . . . . . . . . . . . . 62
11.2. Informative References . . . . . . . . . . . . . . . . . 64
Appendix A. Significant changes from RFC7242 . . . . . . . . . . 65
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 66
1. Introduction 1. Introduction
This document describes the TCP-based convergence-layer protocol for This document describes the TCP-based convergence-layer protocol for
Delay-Tolerant Networking. Delay-Tolerant Networking is an end-to- Delay-Tolerant Networking. Delay-Tolerant Networking is an end-to-
end architecture providing communications in and/or through highly end architecture providing communications in and/or through highly
stressed environments, including those with intermittent stressed environments, including those with intermittent
connectivity, long and/or variable delays, and high bit error rates. connectivity, long and/or variable delays, and high bit error rates.
More detailed descriptions of the rationale and capabilities of these More detailed descriptions of the rationale and capabilities of these
networks can be found in "Delay-Tolerant Network Architecture" networks can be found in "Delay-Tolerant Network Architecture"
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between entities participating in TCPCL communications. This between entities participating in TCPCL communications. This
document does not address: document does not address:
o The format of protocol data units of the Bundle Protocol, as those o The format of protocol data units of the Bundle Protocol, as those
are defined elsewhere in [I-D.ietf-dtn-bpbis]. This includes the are defined elsewhere in [I-D.ietf-dtn-bpbis]. This includes the
concept of bundle fragmentation or bundle encapsulation. The concept of bundle fragmentation or bundle encapsulation. The
TCPCL transfers bundles as opaque data blocks. TCPCL transfers bundles as opaque data blocks.
o Mechanisms for locating or identifying other bundle entities o Mechanisms for locating or identifying other bundle entities
(peers) within a network or across an internet. The mapping of (peers) within a network or across an internet. The mapping of
Node ID to potential CL protocol and network address is left to Node ID to potential convergence layer (CL) protocol and network
implementation and configuration of the BP Agent and its various address is left to implementation and configuration of the BP
potential routing strategies. Agent and its various potential routing strategies.
o Logic for routing bundles along a path toward a bundle's endpoint. o Logic for routing bundles along a path toward a bundle's endpoint.
This CL protocol is involved only in transporting bundles between This CL protocol is involved only in transporting bundles between
adjacent nodes in a routing sequence. adjacent nodes in a routing sequence.
o Policies or mechanisms for assigning X.509 certificates, o Policies or mechanisms for creating X.509 certificates;
provisioning, deploying, or accessing certificates and private provisioning, deploying, or accessing certificates and private
keys, deploying or accessing certificate revocation lists (CRLs), keys; deploying or accessing certificate revocation lists (CRLs);
or configuring security parameters on an individual entity or or configuring security parameters on an individual entity or
across a network. across a network.
o Uses of TLS which are not based on X.509 certificate o Uses of TLS which are not based on X.509 certificate
authentication (see Section 8.10.2) or in which authentication is authentication (see Section 8.10.2) or in which authentication of
not available (see Section 8.10.1). both entities is not possible (see Section 8.10.1).
Any TCPCL implementation requires a BP agent to perform those above Any TCPCL implementation requires a BP agent to perform those above
listed functions in order to perform end-to-end bundle delivery. listed functions in order to perform end-to-end bundle delivery.
2. Requirements Language 2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
2.1. Definitions Specific to the TCPCL Protocol 2.1. Definitions Specific to the TCPCL Protocol
This section contains definitions specific to the TCPCL protocol. This section contains definitions specific to the TCPCL protocol.
Network Byte Order: Most significant byte first, a.k.a., big endian.
All of the integer encodings in this protocol SHALL be transmitted
in network byte order.
TCPCL Entity: This is the notional TCPCL application that initiates TCPCL Entity: This is the notional TCPCL application that initiates
TCPCL sessions. This design, implementation, configuration, and TCPCL sessions. This design, implementation, configuration, and
specific behavior of such an entity is outside of the scope of specific behavior of such an entity is outside of the scope of
this document. However, the concept of an entity has utility this document. However, the concept of an entity has utility
within the scope of this document as the container and initiator within the scope of this document as the container and initiator
of TCPCL sessions. The relationship between a TCPCL entity and of TCPCL sessions. The relationship between a TCPCL entity and
TCPCL sessions is defined as follows: TCPCL sessions is defined as follows:
A TCPCL Entity MAY actively initiate any number of TCPCL * A TCPCL Entity MAY actively initiate any number of TCPCL
Sessions and should do so whenever the entity is the initial Sessions and should do so whenever the entity is the initial
transmitter of information to another entity in the network. transmitter of information to another entity in the network.
A TCPCL Entity MAY support zero or more passive listening * A TCPCL Entity MAY support zero or more passive listening
elements that listen for connection requests from other TCPCL elements that listen for connection requests from other TCPCL
Entities operating on other entitys in the network. Entities operating on other entities in the network.
A TCPCL Entity MAY passivley initiate any number of TCPCL * A TCPCL Entity MAY passively initiate any number of TCPCL
Sessions from requests received by its passive listening Sessions from requests received by its passive listening
element(s) if the entity uses such elements. element(s) if the entity uses such elements.
These relationships are illustrated in Figure 2. For most TCPCL These relationships are illustrated in Figure 2. For most TCPCL
behavior within a session, the two entities are symmetric and behavior within a session, the two entities are symmetric and
there is no protocol distinction between them. Some specific there is no protocol distinction between them. Some specific
behavior, particularly during session establishment, distinguishes behavior, particularly during session establishment, distinguishes
between the active entity and the passive entity. For the between the active entity and the passive entity. For the
remainder of this document, the term "entity" without the prefix remainder of this document, the term "entity" without the prefix
"TCPCL" refers to a TCPCL entity. "TCPCL" refers to a TCPCL entity.
TCP Connection: The term Connection in this specification TCP Connection: The term Connection in this specification
exclusively refers to a TCP connection and any and all behaviors, exclusively refers to a TCP connection and any and all behaviors,
sessions, and other states associated with that TCP connection. sessions, and other states associated with that TCP connection.
TCPCL Session: A TCPCL session (as opposed to a TCP connection) is a TCPCL Session: A TCPCL session (as opposed to a TCP connection) is a
TCPCL communication relationship between two TCPCL entities. TCPCL communication relationship between two TCPCL entities. A
Within a single TCPCL session there are two possible transfer TCPCL session operates within a single underlying TCP connection
streams; one in each direction, with one stream from each entity and the lifetime of a TCPCL session is bound to the lifetime of
being the outbound stream and the other being the inbound stream. that TCP connection. A TCPCL session is terminated when the TCP
The lifetime of a TCPCL session is bound to the lifetime of an connection ends, due either to one or both entities actively
underlying TCP connection. A TCPCL session is terminated when the
TCP connection ends, due either to one or both entities actively
closing the TCP connection or due to network errors causing a closing the TCP connection or due to network errors causing a
failure of the TCP connection. For the remainder of this failure of the TCP connection. Within a single TCPCL session
document, the term "session" without the prefix "TCPCL" refers to there are two possible transfer streams; one in each direction,
a TCPCL session. with one stream from each entity being the outbound stream and the
other being the inbound stream (see Figure 3). From the
perspective of a TCPCL session, the two transfer streams do not
logically interact with each other. The streams do operate over
the same TCP connection and between the same BP agents, so there
are logical relationships at those layers (message and bundle
interleaving respectively). For the remainder of this document,
the term "session" without the prefix "TCPCL" refers to a TCPCL
session.
Session parameters: These are a set of values used to affect the Session parameters: These are a set of values used to affect the
operation of the TCPCL for a given session. The manner in which operation of the TCPCL for a given session. The manner in which
these parameters are conveyed to the bundle entity and thereby to these parameters are conveyed to the bundle entity and thereby to
the TCPCL is implementation dependent. However, the mechanism by the TCPCL is implementation dependent. However, the mechanism by
which two entities exchange and negotiate the values to be used which two entities exchange and negotiate the values to be used
for a given session is described in Section 4.3. for a given session is described in Section 4.3.
Transfer Stream: A Transfer stream is a uni-directional user-data Transfer Stream: A Transfer stream is a uni-directional user-data
path within a TCPCL Session. Messages sent over a transfer stream path within a TCPCL Session. Transfers sent over a transfer
are serialized, meaning that one set of user data must complete stream are serialized, meaning that one transfer must complete its
its transmission prior to another set of user data being transmission prior to another transfer being started over the same
transmitted over the same transfer stream. Each uni-directional transfer stream. At the stream layer there is no logical
stream has a single sender entity and a single receiver entity. relationship between transfers in that stream; it's only within
the BP agent that transfers are fully decoded as bundles. Each
uni-directional stream has a single sender entity and a single
receiver entity.
Transfer: This refers to the procedures and mechanisms for Transfer: This refers to the procedures and mechanisms for
conveyance of an individual bundle from one node to another. Each conveyance of an individual bundle from one node to another. Each
transfer within TCPCL is identified by a Transfer ID number which transfer within TCPCL is identified by a Transfer ID number which
is unique only to a single direction within a single Session. is guaranteed to be unique only to a single direction within a
single Session.
Transfer Segment: A subset of a transfer of user data being Transfer Segment: A subset of a transfer of user data being
communicated over a trasnfer stream. communicated over a transfer stream.
Idle Session: A TCPCL session is idle while the only messages being Idle Session: A TCPCL session is idle while there is no transmission
transmitted or received are KEEPALIVE messages. in-progress in either direction. While idle, the only messages
being transmitted or received are KEEPALIVE messages.
Live Session: A TCPCL session is live while any messages are being Live Session: A TCPCL session is live while there is a transmission
transmitted or received. in-progress in either direction.
Reason Codes: The TCPCL uses numeric codes to encode specific Reason Codes: The TCPCL uses numeric codes to encode specific
reasons for individual failure/error message types. reasons for individual failure/error message types.
The relationship between connections, sessions, and streams is shown The relationship between connections, sessions, and streams is shown
in Figure 3. in Figure 3.
+--------------------------------------------+ +--------------------------------------------+
| TCPCL Entity | | TCPCL Entity |
| | +----------------+ | | +----------------+
| +--------------------------------+ | | |-+ | +--------------------------------+ | | |-+
| | Actively Inititated Session #1 +------------->| Other | | | | Actively Initiated Session #1 +------------->| Other | |
| +--------------------------------+ | | TCPCL Entity's | | | +--------------------------------+ | | TCPCL Entity's | |
| ... | | Passive | | | ... | | Passive | |
| +--------------------------------+ | | Listener | | | +--------------------------------+ | | Listener | |
| | Actively Inititated Session #n +------------->| | | | | Actively Initiated Session #n +------------->| | |
| +--------------------------------+ | +----------------+ | | +--------------------------------+ | +----------------+ |
| | +-----------------+ | | +-----------------+
| +---------------------------+ | | +---------------------------+ |
| +---| +---------------------------+ | +----------------+ | +---| +---------------------------+ | +----------------+
| | | | Optional Passive | | | |-+ | | | | Optional Passive | | | |-+
| | +-| Listener(s) +<-------------+ | | | | +-| Listener(s) +<-------------+ | |
| | +---------------------------+ | | | | | | +---------------------------+ | | | |
| | | | Other | | | | | | Other | |
| | +---------------------------------+ | | TCPCL Entity's | | | | +---------------------------------+ | | TCPCL Entity's | |
| +--->| Passively Inititated Session #1 +-------->| Active | | | +--->| Passively Initiated Session #1 +-------->| Active | |
| | +---------------------------------+ | | Initiator(s) | | | | +---------------------------------+ | | Initiator(s) | |
| | | | | | | | | | | |
| | +---------------------------------+ | | | | | | +---------------------------------+ | | | |
| +--->| Passively Inititated Session #n +-------->| | | | +--->| Passively Initiated Session #n +-------->| | |
| +---------------------------------+ | +----------------+ | | +---------------------------------+ | +----------------+ |
| | +-----------------+ | | +-----------------+
+--------------------------------------------+ +--------------------------------------------+
Figure 2: The relationships between TCPCL entities Figure 2: The relationships between TCPCL entities
+----------------------------+ +--------------------------+ +---------------------------+ +---------------------------+
| "Own" TCPCL Session | | "Other" TCPCL Session | | "Own" TCPCL Session | | "Other" TCPCL Session |
| | | | | | | |
| +-----------------------+ | | +---------------------+ | | +----------------------+ | | +----------------------+ |
| | TCP Connection | | | | TCP Connection | | | | TCP Connection | | | | TCP Connection | |
| | | | | | | | | | | | | | | |
| | +-------------------+ | | | | +-----------------+ | | | | +-----------------+ | | Messages | | +-----------------+ | |
| | | Optional Inbound | | | | | | Peer Outbound | | | | | | Own Inbound | +--------------------+ | Peer Outbound | | |
| | | Transfer Stream |<-[Seg]--[Seg]--[Seg]-| | Transfer Stream | | | | | | Transfer Stream | | Transfer Stream | | |
| | | ----- |--[Ack]----[Ack]------->| ----- | | | | | | ----- |<---[Seg]--[Seg]--[Seg]---| ----- | | |
| | | RECEIVER | | | | | | SENDER | | | | | | RECEIVER |---[Ack]----[Ack]-------->| SENDER | | |
| | +-------------------+ | | | | +-----------------+ | | | | +-----------------+ +-----------------+ | |
| | | | | | | | | | | |
| | +-------------------+ | | | | +-----------------+ | | | | +-----------------+ +-----------------+ | |
| | | Optional Outbound | | | | | | Peer Inbound | | | | | | Own Outbound |-------[Seg]---[Seg]----->| Peer Inbound | | |
| | | Transfer Stream |------[Seg]---[Seg]---->| Transfer Stream | | | | | | Transfer Stream |<---[Ack]----[Ack]-[Ack]--| Transfer Stream | | |
| | | ----- |<--[Ack]----[Ack]-[Ack]-| ----- | | | | | | ----- | | ----- | | |
| | | SENDER | | | | | | RECEIVER | | | | | | SENDER | +--------------------+ | RECEIVER | | |
| | +-------------------+ | | | | +-----------------+ | | | | +-----------------+ | | | | +-----------------+ | |
| +-----------------------+ | | +---------------------+ | | +-----------------------+ | | +---------------------+ |
+----------------------------+ +--------------------------+ +----------------------------+ +--------------------------+
Figure 3: The relationship within a TCPCL Session of its two streams Figure 3: The relationship within a TCPCL Session of its two streams
3. General Protocol Description 3. General Protocol Description
The service of this protocol is the transmission of DTN bundles via The service of this protocol is the transmission of DTN bundles via
the Transmission Control Protocol (TCP). This document specifies the the Transmission Control Protocol (TCP). This document specifies the
encapsulation of bundles, procedures for TCP setup and teardown, and encapsulation of bundles, procedures for TCP setup and teardown, and
a set of messages and node requirements. The general operation of a set of messages and node requirements. The general operation of
the protocol is as follows. the protocol is as follows.
3.1. Convergence Layer Services 3.1. Convergence Layer Services
This version of the TCPCL provides the following services to support This version of the TCPCL provides the following services to support
the overlaying Bundle Protocol agent. In all cases, this is not an the overlaying Bundle Protocol agent. In all cases, this is not an
API defintion but a logical description of how the CL can interact API definition but a logical description of how the CL can interact
with the BP agent. Each of these interactions can be associated with with the BP agent. Each of these interactions can be associated with
any number of additional metadata items as necessary to support the any number of additional metadata items as necessary to support the
operation of the CL or BP agent. operation of the CL or BP agent.
Attempt Session: The TCPCL allows a BP agent to pre-emptively Attempt Session: The TCPCL allows a BP agent to preemptively attempt
attempt to establish a TCPCL session with a peer entity. Each to establish a TCPCL session with a peer entity. Each session
session attempt can send a different set of session negotiation attempt can send a different set of session negotiation parameters
parameters as directed by the BP agent. as directed by the BP agent.
Terminate Session: The TCPCL allows a BP agent to pre-emptively Terminate Session: The TCPCL allows a BP agent to preemptively
terminate an established TCPCL session with a peer entity. The terminate an established TCPCL session with a peer entity. The
terminate request is on a per-session basis. terminate request is on a per-session basis.
Session State Changed: The TCPCL supports indication when the Session State Changed: The TCPCL entity indicates to the BP agent
session state changes. The top-level session states indicated when the session state changes. The top-level session states
are: indicated are:
Connecting: A TCP connection is being established. This state Connecting: A TCP connection is being established. This state
only applies to the active entity. only applies to the active entity.
Contact Negotiating: A TCP connection has been made (as either Contact Negotiating: A TCP connection has been made (as either
active or passive entity) and contact negotiation has begun. active or passive entity) and contact negotiation has begun.
Session Negotiating: Contact negotiation has been completed Session Negotiating: Contact negotiation has been completed
(including possible TLS use) and session negotiation has begun. (including possible TLS use) and session negotiation has begun.
Established: The session has been fully established and is ready Established: The session has been fully established and is ready
for its first transfer. for its first transfer.
Ending: The entity received a SESS_TERM message and is in the Ending: The entity sent SESS_TERM message and is in the ending
ending state. state.
Terminated: The session has finished normal termination Terminated: The session has finished normal termination
sequencing. sequencing.
Failed: The session ended without normal termination sequencing. Failed: The session ended without normal termination sequencing.
Session Idle Changed: The TCPCL supports indication when the live/ Session Idle Changed: The TCPCL entity indicates to the BP agent
idle sub-state of the session changes. This occurs only when the when the live/idle sub-state of the session changes. This occurs
top-level session state is "Established". The session transitions only when the top-level session state is "Established". The
from Idle to Live at the at the start of a transfer in either session transitions from Idle to Live at the at the start of a
transfer stream; the session transitions from Live to Idle at the transfer in either transfer stream; the session transitions from
end of a transfer when the other transfer stream does not have an Live to Idle at the end of a transfer when the other transfer
ongoing transfer. Because TCPCL transmits serially over a TCP stream does not have an ongoing transfer. Because TCPCL transmits
connection, it suffers from "head of queue blocking" this serially over a TCP connection it suffers from "head of queue
indication provides information about when a session is available blocking," so a transfer in either direction can block an
for immediate transfer start. immediate start of a new transfer in the session.
Begin Transmission: The principal purpose of the TCPCL is to allow a Begin Transmission: The principal purpose of the TCPCL is to allow a
BP agent to transmit bundle data over an established TCPCL BP agent to transmit bundle data over an established TCPCL
session. Transmission request is on a per-session basis, the CL session. Transmission request is on a per-session basis and the
does not necessarily perform any per-session or inter-session CL does not necessarily perform any per-session or inter-session
queueing. Any queueing of transmissions is the obligation of the queueing. Any queueing of transmissions is the obligation of the
BP agent. BP agent.
Transmission Success: The TCPCL supports positive indication when a Transmission Success: The TCPCL entity indicates to the BP agent
bundle has been fully transferred to a peer entity. when a bundle has been fully transferred to a peer entity.
Transmission Intermediate Progress: The TCPCL supports positive Transmission Intermediate Progress: The TCPCL entity indicates to
indication of intermediate progress of transfer to a peer entity. the BP agent on intermediate progress of transfer to a peer
This intermediate progress is at the granularity of each entity. This intermediate progress is at the granularity of each
transferred segment. transferred segment.
Transmission Failure: The TCPCL supports positive indication of Transmission Failure: The TCPCL entity indicates to the BP agent on
certain reasons for bundle transmission failure, notably when the certain reasons for bundle transmission failure, notably when the
peer entity rejects the bundle or when a TCPCL session ends before peer entity rejects the bundle or when a TCPCL session ends before
transfer success. The TCPCL itself does not have a notion of transfer success. The TCPCL itself does not have a notion of
transfer timeout. transfer timeout.
Reception Initialized: The TCPCL supports indication to the reciver Reception Initialized: The TCPCL entity indicates to the receiving
just before any transmssion data is sent. This corresponds to BP agent just before any transmission data is sent. This
reception of the XFER_SEGMENT message with the START flag of 1. corresponds to reception of the XFER_SEGMENT message with the
START flag of 1.
Interrupt Reception: The TCPCL allows a BP agent to interrupt an Interrupt Reception: The TCPCL entity allows a BP agent to interrupt
individual transfer before it has fully completed (successfully or an individual transfer before it has fully completed (successfully
not). Interruption can occur any time after the reception is or not). Interruption can occur any time after the reception is
initialized. initialized.
Reception Success: The TCPCL supports positive indication when a Reception Success: The TCPCL entity indicates to the BP agent when a
bundle has been fully transferred from a peer entity. bundle has been fully transferred from a peer entity.
Reception Intermediate Progress: The TCPCL supports positive Reception Intermediate Progress: The TCPCL entity indicates to the
indication of intermediate progress of transfer from the peer BP agent on intermediate progress of transfer from the peer
entity. This intermediate progress is at the granularity of each entity. This intermediate progress is at the granularity of each
transferred segment. Intermediate reception indication allows a transferred segment. Intermediate reception indication allows a
BP agent the chance to inspect bundle header contents before the BP agent the chance to inspect bundle header contents before the
entire bundle is available, and thus supports the "Reception entire bundle is available, and thus supports the "Reception
Interruption" capability. Interruption" capability.
Reception Failure: The TCPCL supports positive indication of certain Reception Failure: The TCPCL entity indicates to the BP agent on
reasons for reception failure, notably when the local entity certain reasons for reception failure, notably when the local
rejects an attempted transfer for some local policy reason or when entity rejects an attempted transfer for some local policy reason
a TCPCL session ends before transfer success. The TCPCL itself or when a TCPCL session ends before transfer success. The TCPCL
does not have a notion of transfer timeout. itself does not have a notion of transfer timeout.
3.2. TCPCL Session Overview 3.2. TCPCL Session Overview
First, one node establishes a TCPCL session to the other by First, one node establishes a TCPCL session to the other by
initiating a TCP connection in accordance with [RFC0793]. After initiating a TCP connection in accordance with [RFC0793]. After
setup of the TCP connection is complete, an initial contact header is setup of the TCP connection is complete, an initial Contact Header is
exchanged in both directions to establish a shared TCPCL version and exchanged in both directions to establish a shared TCPCL version and
negotiate the use of TLS security (as described in Section 4). Once negotiate the use of TLS security (as described in Section 4). Once
contact negotiation is complete, TCPCL messaging is available and the contact negotiation is complete, TCPCL messaging is available and the
session negotiation is used to set parameters of the TCPCL session. session negotiation is used to set parameters of the TCPCL session.
One of these parameters is a Node ID of each TCPCL Entity. This is One of these parameters is a Node ID that each TCPCL Entity is acting
used to assist in routing and forwarding messages by the BP Agent and as. This is used to assist in routing and forwarding messages by the
is part of the authentication capability provided by TLS. BP Agent and is part of the authentication capability provided by
TLS.
Once negotiated, the parameters of a TCPCL session cannot change and Once negotiated, the parameters of a TCPCL session cannot change and
if there is a desire by either peer to transfer data under different if there is a desire by either peer to transfer data under different
parameters then a new session must be established. This makes CL parameters then a new session must be established. This makes CL
logic simpler but relies on the assumption that establishing a TCP logic simpler but relies on the assumption that establishing a TCP
connection is lightweight enough that TCP connection overhead is connection is lightweight enough that TCP connection overhead is
negligable compared to TCPCL data sizes. negligible compared to TCPCL data sizes.
Once the TCPCL session is established and configured in this way, Once the TCPCL session is established and configured in this way,
bundles can be transferred in either direction. Each transfer is bundles can be transferred in either direction. Each transfer is
performed by an sequence of logical segments of data within performed by segmenting the transfer data into one or more
XFER_SEGMENT messages. Multiple bundles can be transmitted XFER_SEGMENT messages. Multiple bundles can be transmitted
consecutively in a single direction on a single TCPCL connection. consecutively in a single direction on a single TCPCL connection.
Segments from different bundles are never interleaved. Bundle Segments from different bundles are never interleaved. Bundle
interleaving can be accomplished by fragmentation at the BP layer or interleaving can be accomplished by fragmentation at the BP layer or
by establishing multiple TCPCL sessions between the same peers. by establishing multiple TCPCL sessions between the same peers.
There is no fundamental limit on the number of TCPCL sessions which a There is no fundamental limit on the number of TCPCL sessions which a
single node can establish beyond the limit imposed by the number of single node can establish beyond the limit imposed by the number of
available (ephemeral) TCP ports of the passive entity. available (ephemeral) TCP ports of the active entity.
A feature of this protocol is for the receiving node to send A feature of this protocol is for the receiving node to send
acknowledgment (XFER_ACK) messages as bundle data segments arrive. acknowledgment (XFER_ACK) messages as bundle data segments arrive.
The rationale behind these acknowledgments is to enable the sender The rationale behind these acknowledgments is to enable the sender
node to determine how much of the bundle has been received, so that node to determine how much of the bundle has been received, so that
in case the session is interrupted, it can perform reactive in case the session is interrupted, it can perform reactive
fragmentation to avoid re-sending the already transmitted part of the fragmentation to avoid re-sending the already transmitted part of the
bundle. In addition, there is no explicit flow control on the TCPCL bundle. In addition, there is no explicit flow control on the TCPCL
layer. layer.
skipping to change at page 11, line 48 skipping to change at page 12, line 49
hasn't already finished transmission) Note: This enables a cross- hasn't already finished transmission) Note: This enables a cross-
layer optimization in that it allows a receiver that detects that it layer optimization in that it allows a receiver that detects that it
already has received a certain bundle to interrupt transmission as already has received a certain bundle to interrupt transmission as
early as possible and thus save transmission capacity for other early as possible and thus save transmission capacity for other
bundles. bundles.
For sessions that are idle, a KEEPALIVE message is sent at a For sessions that are idle, a KEEPALIVE message is sent at a
negotiated interval. This is used to convey node live-ness negotiated interval. This is used to convey node live-ness
information during otherwise message-less time intervals. information during otherwise message-less time intervals.
A SESS_TERM message is used to start the ending of a TCPCL session A SESS_TERM message is used to initiate the ending of a TCPCL session
(see Section 6.1). During shutdown sequencing, in-progress transfers (see Section 6.1). During termination sequencing, in-progress
can be completed but no new transfers can be initiated. A SESS_TERM transfers can be completed but no new transfers can be initiated. A
message can also be used to refuse a session setup by a peer (see SESS_TERM message can also be used to refuse a session setup by a
Section 4.3). Regardless of the reason, session termination is peer (see Section 4.3). Regardless of the reason, session
initiated by one of the entities and responded-to by the other as termination is initiated by one of the entities and responded-to by
illustrated by Figure 13 and Figure 14. Even when there are no the other as illustrated by Figure 13 and Figure 14. Even when there
transfers queued or in-progress, the session termination procedure are no transfers queued or in-progress, the session termination
allows each entity to distinguish between a clean end to a session procedure allows each entity to distinguish between a clean end to a
and the TCP connection being closed because of some underlying session and the TCP connection being closed because of some
network issue. underlying network issue.
Once a session is established, TCPCL is a symmetric protocol between Once a session is established, TCPCL is a symmetric protocol between
the peers. Both sides can start sending data segments in a session, the peers. Both sides can start sending data segments in a session,
and one side's bundle transfer does not have to complete before the and one side's bundle transfer does not have to complete before the
other side can start sending data segments on its own. Hence, the other side can start sending data segments on its own. Hence, the
protocol allows for a bi-directional mode of communication. Note protocol allows for a bi-directional mode of communication. Note
that in the case of concurrent bidirectional transmission, that in the case of concurrent bidirectional transmission,
acknowledgment segments MAY be interleaved with data segments. acknowledgment segments MAY be interleaved with data segments.
3.3. TCPCL States and Transitions 3.3. TCPCL States and Transitions
The states of a nominal TCPCL session (i.e. without session failures) The states of a normal TCPCL session (i.e., without session failures)
are indicated in Figure 4. are indicated in Figure 4.
+-------+ +-------+
| START | | START |
+-------+ +-------+
| |
TCP Establishment TCP Establishment
| |
V V
+-----------+ +---------------------+ +-----------+ +---------------------+
skipping to change at page 13, line 46 skipping to change at page 14, line 46
| |
V V
+-------+ +-------+
| END | | END |
+-------+ +-------+
Figure 4: Top-level states of a TCPCL session Figure 4: Top-level states of a TCPCL session
Notes on Established Session states: Notes on Established Session states:
Session "Live" means transmitting or reeiving over a transfer Session "Live" means transmitting or receiving over a transfer
stream. stream.
Session "Idle" means no transmission/reception over a transfer Session "Idle" means no transmission/reception over a transfer
stream. stream.
Session "Ending" means no new transfers will be allowed. Session "Ending" means no new transfers will be allowed.
Contact negotiation involves exchanging a Contact Header (CH) in both Contact negotiation involves exchanging a Contact Header (CH) in both
directions and deriving a negotiated state from the two headers. The directions and deriving a negotiated state from the two headers. The
contact negotiation sequencing is performed either as the active or contact negotiation sequencing is performed either as the active or
passive entity, and is illustrated in Figure 5 and Figure 6 passive entity, and is illustrated in Figure 5 and Figure 6
respectively which both share the data validation and analyze final respectively which both share the data validation and negotiation of
states of the "[PCH]" activity of Figure 7 and the "[TCPCLOSE]" the Processing of Contact Header "[PCH]" activity of Figure 7 and the
activity which indicates TCP connection close. Successful "[TCPCLOSE]" activity which indicates TCP connection close.
negotiation results in one of the Session Initiation "[SI]" Successful negotiation results in one of the Session Initiation
activities being performed. To avoid data loss, a Session "[SI]" activities being performed. To avoid data loss, a Session
Termination "[ST]" exchange allows cleanly finishing transfers before Termination "[ST]" exchange allows cleanly finishing transfers before
a session is ended. a session is ended.
+-------+ +-------+
| START | | START |
+-------+ +-------+
| |
TCP Connecting TCP Connecting
V V
+-----------+ +-----------+
| TCP | +---------+ | TCP | +---------+
| Connected |--Send CH-->| Waiting |--Timeout-->[TCPCLOSE] | Connected |--Send CH-->| Waiting |--Timeout-->[TCPCLOSE]
+-----------+ +---------+ +-----------+ +---------+
| |
Recevied CH Received CH
V V
[PCH] [PCH]
Figure 5: Contact Initiation as Active Entity Figure 5: Contact Initiation as Active Entity
+-----------+ +---------+ +-----------+ +---------+
| TCP |--Wait for-->| Waiting |--Timeout-->[TCPCLOSE] | TCP |--Wait for-->| Waiting |--Timeout-->[TCPCLOSE]
| Connected | CH +---------+ | Connected | CH +---------+
+-----------+ | +-----------+ |
Received CH Received CH
V V
+-----------------+ +-----------------+
| Preparing reply |--Send CH-->[PSI] | Preparing reply |--Send CH-->[PCH]
+-----------------+ +-----------------+
Figure 6: Contact Initiation as Passive Entity Figure 6: Contact Initiation as Passive Entity
+-----------+ +-----------+
| Peer CH | | Peer CH |
| available | | available |
+-----------+ +-----------+
| |
Validate and Validate and
skipping to change at page 15, line 32 skipping to change at page 16, line 32
| Available | +---------------+ | Available | +---------------+
+-----------+ +-----------+
Figure 7: Processing of Contact Header [PCH] Figure 7: Processing of Contact Header [PCH]
Session negotiation involves exchanging a session initialization Session negotiation involves exchanging a session initialization
(SESS_INIT) message in both directions and deriving a negotiated (SESS_INIT) message in both directions and deriving a negotiated
state from the two messages. The session negotiation sequencing is state from the two messages. The session negotiation sequencing is
performed either as the active or passive entity, and is illustrated performed either as the active or passive entity, and is illustrated
in Figure 8 and Figure 9 respectively which both share the data in Figure 8 and Figure 9 respectively which both share the data
validation and analyze final states of Figure 10. The validation validation and negotiation of Figure 10. The validation here
here includes certificate validation and authentication when TLS is includes certificate validation and authentication when TLS is used
used for the session. for the session.
+-----------+ +-----------+
| TCPCL | +---------+ | TCPCL | +---------+
| Messaging |--Send SESS_INIT-->| Waiting |--Timeout-->[ST] | Messaging |--Send SESS_INIT-->| Waiting |--Timeout-->[ST]
| Available | +---------+ | Available | +---------+
+-----------+ | +-----------+ |
Recevied SESS_INIT Received SESS_INIT
| |
V V
[PSI] [PSI]
Figure 8: Session Initiation [SI] as Active Entity Figure 8: Session Initiation [SI] as Active Entity
+-----------+ +-----------+
| TCPCL | +---------+ | TCPCL | +---------+
| Messaging |----Wait for ---->| Waiting |--Timeout-->[ST] | Messaging |----Wait for ---->| Waiting |--Timeout-->[ST]
| Available | SESS_INIT +---------+ | Available | SESS_INIT +---------+
+-----------+ | +-----------+ |
Recevied SESS_INIT Received SESS_INIT
| |
+-----------------+ +-----------------+
| Preparing reply |--Send SESS_INIT-->[PSI] | Preparing reply |--Send SESS_INIT-->[PSI]
+-----------------+ +-----------------+
Figure 9: Session Initiation [SI] as Passive Entity Figure 9: Session Initiation [SI] as Passive Entity
+----------------+ +----------------+
| Peer SESS_INIT | | Peer SESS_INIT |
| available | | available |
skipping to change at page 16, line 40 skipping to change at page 17, line 40
Success Success
V V
+--------------+ +--------------+
| Established | | Established |
| Session Idle | | Session Idle |
+--------------+ +--------------+
Figure 10: Processing of Session Initiation [PSI] Figure 10: Processing of Session Initiation [PSI]
Transfers can occur after a session is established and it's not in Transfers can occur after a session is established and it's not in
the ending state. Each transfer occurs within a single logical the Ending state. Each transfer occurs within a single logical
transfer stream between a sender and a receiver, as illustrated in transfer stream between a sender and a receiver, as illustrated in
Figure 11 and Figure 12 respectively. Figure 11 and Figure 12 respectively.
+--Send XFER_SEGMENT--+ +--Send XFER_SEGMENT--+
+--------+ | | +--------+ | |
| Stream | +-------------+ | | Stream | +-------------+ |
| Idle |---Send XFER_SEGMENT-->| In Progress |<------------+ | Idle |---Send XFER_SEGMENT-->| In Progress |<------------+
+--------+ +-------------+ +--------+ +-------------+
| |
+---------All segments sent-------+ +---------All segments sent-------+
skipping to change at page 17, line 45 skipping to change at page 18, line 45
+--------+ +--------+
| Stream | | Stream |
| Idle | | Idle |
+--------+ +--------+
Figure 12: Transfer receiver states Figure 12: Transfer receiver states
Session termination involves one entity initiating the termination of Session termination involves one entity initiating the termination of
the session and the other entity acknowledging the termination. For the session and the other entity acknowledging the termination. For
either entity, it is the sending of the SESS_TERM message which either entity, it is the sending of the SESS_TERM message which
transitions the session to the ending substate. While a session is transitions the session to the Ending substate. While a session is
being terminated only in-progress transfers can be completed and no in the Ending state only in-progress transfers can be completed and
new transfers can be started. no new transfers can be started.
+-----------+ +---------+ +-----------+ +---------+
| Session |--Send SESS_TERM-->| Session | | Session |--Send SESS_TERM-->| Session |
| Live/Idle | | Ending | | Live/Idle | | Ending |
+-----------+ +---------+ +-----------+ +---------+
Figure 13: Session Termination [ST] from the Initiator Figure 13: Session Termination [ST] from the Initiator
+-----------+ +---------+ +-----------+ +---------+
| Session |--Send SESS_TERM-->| Session | | Session |--Send SESS_TERM-->| Session |
skipping to change at page 18, line 27 skipping to change at page 19, line 27
Receive SESS_TERM | Receive SESS_TERM |
| | | |
+-------------+ +-------------+
Figure 14: Session Termination [ST] from the Responder Figure 14: Session Termination [ST] from the Responder
3.4. Transfer Segmentation Policies 3.4. Transfer Segmentation Policies
Each TCPCL session allows a negotiated transfer segmentation polcy to Each TCPCL session allows a negotiated transfer segmentation polcy to
be applied in each transfer direction. A receiving node can set the be applied in each transfer direction. A receiving node can set the
Segment MRU in its contact header to determine the largest acceptable Segment MRU in its SESS_INIT message to determine the largest
segment size, and a transmitting node can segment a transfer into any acceptable segment size, and a transmitting node can segment a
sizes smaller than the receiver's Segment MRU. It is a network transfer into any sizes smaller than the receiver's Segment MRU. It
administration matter to determine an appropriate segmentation policy is a network administration matter to determine an appropriate
for entities operating TCPCL, but guidance given here can be used to segmentation policy for entities operating TCPCL, but guidance given
steer policy toward performance goals. It is also advised to here can be used to steer policy toward performance goals. It is
consider the Segment MRU in relation to chunking/packetization also advised to consider the Segment MRU in relation to chunking/
performed by TLS, TCP, and any intermediate network-layer nodes. packetization performed by TLS, TCP, and any intermediate network-
layer nodes.
Minimum Overhead: For a simple network expected to exchange Minimum Overhead: For a simple network expected to exchange
relatively small bundles, the Segment MRU can be set to be relatively small bundles, the Segment MRU can be set to be
identical to the Transfer MRU which indicates that all transfers identical to the Transfer MRU which indicates that all transfers
can be sent with a single data segment (i.e. no actual can be sent with a single data segment (i.e., no actual
segmentation). If the network is closed and all transmitters are segmentation). If the network is closed and all transmitters are
known to follow a single-segment transfer policy, then receivers known to follow a single-segment transfer policy, then receivers
can avoid the necessity of segment reassembly. Because this CL can avoid the necessity of segment reassembly. Because this CL
operates over a TCP stream, which suffers from a form of head-of- operates over a TCP stream, which suffers from a form of head-of-
queue blocking between messages, while one node is transmitting a queue blocking between messages, while one node is transmitting a
single XFER_SEGMENT message it is not able to transmit any single XFER_SEGMENT message it is not able to transmit any
XFER_ACK or XFER_REFUSE for any associated received transfers. XFER_ACK or XFER_REFUSE for any associated received transfers.
Predictable Message Sizing: In situations where the maximum message Predictable Message Sizing: In situations where the maximum message
size is desired to be well-controlled, the Segment MRU can be set size is desired to be well-controlled, the Segment MRU can be set
to the largest acceptable size (the message size less XFER_SEGMENT to the largest acceptable size (the message size less XFER_SEGMENT
header size) and transmitters can always segment a transfer into header size) and transmitters can always segment a transfer into
maximum-size chunks no larger than the Segment MRU. This maximum-size chunks no larger than the Segment MRU. This
guarantees that any single XFER_SEGMENT will not monopolize the guarantees that any single XFER_SEGMENT will not monopolize the
TCP stream for too long, which would prevent outgoing XFER_ACK and TCP stream for too long, which would prevent outgoing XFER_ACK and
XFER_REFUSE associated with received transfers. XFER_REFUSE associated with received transfers.
Dynamic Segmentation: Even after negotiation of a Segment MRU for Dynamic Segmentation: Even after negotiation of a Segment MRU for
each receiving node, the actual transfer segmentation only needs each receiving node, the actual transfer segmentation only needs
to guarantee than any individual segment is no larger than that to guarantee than any individual segment is no larger than that
MRU. In a situation where network "goodput" is dynamic, the MRU. In a situation where TCP throughput is dynamic, the transfer
transfer segmentation size can also be dynamic in order to control segmentation size can also be dynamic in order to control message
message transmission duration. transmission duration.
Many other policies can be established in a TCPCL network between the Many other policies can be established in a TCPCL network between the
two extremes of minimum overhead (large MRU, single-segment) and two extremes of minimum overhead (large MRU, single-segment) and
predictable message sizing (small MRU, highly segmented). Different predictable message sizing (small MRU, highly segmented). Different
policies can be applied to each transfer stream to and from any policies can be applied to each transfer stream to and from any
particular node. Additionally, future header and transfer extension particular node. Additionally, future header and transfer extension
types can apply further nuance to transfer policies and policy types can apply further nuance to transfer policies and policy
negotiation. negotiation.
3.5. Example Message Exchange 3.5. Example Message Exchange
skipping to change at page 19, line 44 skipping to change at page 20, line 45
also possible to pipeline multiple XFER_SEGMENT messages for also possible to pipeline multiple XFER_SEGMENT messages for
different bundles without necessarily waiting for XFER_ACK messages different bundles without necessarily waiting for XFER_ACK messages
to be returned for each one. However, interleaving data segments to be returned for each one. However, interleaving data segments
from different bundles is not allowed. from different bundles is not allowed.
No errors or rejections are shown in this example. No errors or rejections are shown in this example.
Entity A Entity B Entity A Entity B
======== ======== ======== ========
+-------------------------+ +-------------------------+
| Open TCP Connnection | -> +-------------------------+ | Open TCP Connection | -> +-------------------------+
+-------------------------+ <- | Accept Connection | +-------------------------+ <- | Accept Connection |
+-------------------------+ +-------------------------+
+-------------------------+ +-------------------------+
| Contact Header | -> +-------------------------+ | Contact Header | -> +-------------------------+
+-------------------------+ <- | Contact Header | +-------------------------+ <- | Contact Header |
+-------------------------+ +-------------------------+
+-------------------------+ +-------------------------+
| SESS_INIT | -> +-------------------------+ | SESS_INIT | -> +-------------------------+
+-------------------------+ <- | SESS_INIT | +-------------------------+ <- | SESS_INIT |
+-------------------------+ +-------------------------+
+-------------------------+ +-------------------------+
| XFER_SEGMENT (start) | -> | XFER_SEGMENT (start) | ->
| Transfer ID [I1] | | Transfer ID [I1] |
| Length [L1] | | Length [L1] |
| Bundle Data 0..(L1-1) | | Bundle Data 0..(L1-1) |
skipping to change at page 20, line 49 skipping to change at page 21, line 51
+-------------------------+ +-------------------------+ +-------------------------+ +-------------------------+
Figure 15: An example of the flow of protocol messages on a single Figure 15: An example of the flow of protocol messages on a single
TCP Session between two entities TCP Session between two entities
4. Session Establishment 4. Session Establishment
For bundle transmissions to occur using the TCPCL, a TCPCL session For bundle transmissions to occur using the TCPCL, a TCPCL session
MUST first be established between communicating entities. It is up MUST first be established between communicating entities. It is up
to the implementation to decide how and when session setup is to the implementation to decide how and when session setup is
triggered. For example, some sessions MAY be opened proactively and triggered. For example, some sessions can be opened proactively and
maintained for as long as is possible given the network conditions, maintained for as long as is possible given the network conditions,
while other sessions MAY be opened only when there is a bundle that while other sessions are be opened only when there is a bundle that
is queued for transmission and the routing algorithm selects a is queued for transmission and the routing algorithm selects a
certain next-hop node. certain next-hop node.
4.1. TCP Connection 4.1. TCP Connection
To establish a TCPCL session, an entity MUST first establish a TCP To establish a TCPCL session, an entity MUST first establish a TCP
connection with the intended peer entity, typically by using the connection with the intended peer entity, typically by using the
services provided by the operating system. Destination port number services provided by the operating system. Destination port number
4556 has been assigned by IANA as the Registered Port number for the 4556 has been assigned by IANA as the Registered Port number for the
TCP convergence layer. Other destination port numbers MAY be used TCP convergence layer. Other destination port numbers MAY be used
per local configuration. Determining a peer's destination port per local configuration. Determining a peer's destination port
number (if different from the registered TCPCL port number) is up to number (if different from the registered TCPCL port number) is up to
the implementation. Any source port number MAY be used for TCPCL the implementation. Any source port number MAY be used for TCPCL
sessions. Typically an operating system assigned number in the TCP sessions. Typically an operating system assigned number in the TCP
Ephemeral range (49152-65535) is used. Ephemeral range (49152-65535) is used.
If the entity is unable to establish a TCP connection for any reason, If the entity is unable to establish a TCP connection for any reason,
then it is an implementation matter to determine how to handle the then it is an implementation matter to determine how to handle the
connection failure. An entity MAY decide to re-attempt to establish connection failure. An entity MAY decide to re-attempt to establish
the connection. If it does so, it MUST NOT overwhelm its target with the connection. If it does so, it MUST NOT overwhelm its target with
repeated connection attempts. Therefore, the entity MUST retry the repeated connection attempts. Therefore, the entity MUST NOT retry
connection setup no earlier than some delay time from the last the connection setup earlier than some delay time from the last
attempt, and it SHOULD use a (binary) exponential back-off mechanism attempt, and it SHOULD use a (binary) exponential back-off mechanism
to increase this delay in case of repeated failures. The upper limit to increase this delay in case of repeated failures. The upper limit
on a re-attempt back-off is implementation defined but SHOULD be no on a re-attempt back-off is implementation defined but SHOULD be no
longer than one minute before signaling to the BP agent that a longer than one minute (60 seconds) before signaling to the BP agent
connection cannot be made. that a connection cannot be made.
Once a TCP connection is established, the active entity SHALL Once a TCP connection is established, the active entity SHALL
immediately transmit its contact header. Upon reception of a contact immediately transmit its Contact Header. Once a TCP connection is
header, the passive entity SHALL transmit its contact header. If the established, the passive entity SHALL wait for the peer's Contact
passive entity does not receive a Contact Header after some Header. If the passive entity does not receive a Contact Header
implementation-defined time duration after TCP connection is after some implementation-defined time duration after TCP connection
established, the entity SHALL close the TCP connection. The ordering is established, the entity SHALL close the TCP connection. Entities
of the contact header exchange allows the passive entity to avoid SHOULD choose a Contact Header reception timeout interval no longer
than 10 minutes (600 seconds). Upon reception of a Contact Header,
the passive entity SHALL transmit its Contact Header. The ordering
of the Contact Header exchange allows the passive entity to avoid
allocating resources to a potential TCPCL session until after a valid allocating resources to a potential TCPCL session until after a valid
contact header has been received from the passive entity. This Contact Header has been received from the active entity. This
ordering also allows the passive peer to adapt to alternate TCPCL ordering also allows the passive peer to adapt to alternate TCPCL
protocol versions. protocol versions.
The format of the contact header is described in Section 4.2. The format of the Contact Header is described in Section 4.2.
Because the TCPCL protocol version in use is part of the initial Because the TCPCL protocol version in use is part of the initial
contact header, nodes using TCPCL version 4 can coexist on a network Contact Header, nodes using TCPCL version 4 can coexist on a network
with nodes using earlier TCPCL versions (with some negotiation needed with nodes using earlier TCPCL versions (with some negotiation needed
for interoperation as described in Section 4.3). for interoperation as described in Section 4.3).
4.2. Contact Header 4.2. Contact Header
This section describes the format of the contact header and the This section describes the format of the Contact Header and the
meaning of its fields. meaning of its fields.
If an entity is capable of exchanging messages according to TLS 1.2 If an entity is capable of exchanging messages according to TLS 1.3
[RFC5246] or any successors [RFC8446] that are compatible with TLS [RFC8446] or any successors which are compatible with that TLS
1.2, the CAN_TLS flag within its contanct header SHALL be set to 1. ClientHello, the the CAN_TLS flag within its Contact Header SHALL be
This behavor prefers the use of TLS when possible, even if security set to 1. This behavior prefers the use of TLS when possible, even
policy does not allow or require authentication. This follows the if security policy does not allow or require authentication. This
opportunistic security model of [RFC7435]. follows the opportunistic security model of [RFC7435].
Upon receipt of the contact header, both entities perform the Upon receipt of the Contact Header, both entities perform the
validation and negotiation procedures defined in Section 4.3. After validation and negotiation procedures defined in Section 4.3. After
receiving the contact header from the other entity, either entity MAY receiving the Contact Header from the other entity, either entity MAY
refuse the session by sending a SESS_TERM message with an appropriate refuse the session by sending a SESS_TERM message with an appropriate
reason code. reason code.
The format for the Contact Header is as follows: The format for the Contact Header is as follows:
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| magic='dtn!' | | magic='dtn!' |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| Version | Flags | | Version | Flags |
+---------------+---------------+ +---------------+---------------+
Figure 16: Contact Header Format Figure 16: Contact Header Format
See Section 4.3 for details on the use of each of these contact See Section 4.3 for details on the use of each of these Contact
header fields. Header fields.
The fields of the contact header are: The fields of the Contact Header are:
magic: A four-octet field that always contains the octet sequence magic: A four-octet field that always contains the octet sequence
0x64 0x74 0x6E 0x21, i.e., the text string "dtn!" in US-ASCII (and 0x64 0x74 0x6E 0x21, i.e., the text string "dtn!" in US-ASCII (and
UTF-8). UTF-8).
Version: A one-octet field value containing the value 4 (current Version: A one-octet field value containing the value 4 (current
version of the TCPCL). version of the TCPCL).
Flags: A one-octet field of single-bit flags, interpreted according Flags: A one-octet field of single-bit flags, interpreted according
to the descriptions in Table 1. All reserved header flag bits to the descriptions in Table 1. All reserved header flag bits
skipping to change at page 23, line 18 skipping to change at page 24, line 20
| CAN_TLS | 0x01 | If bit is set, indicates that the sending | | CAN_TLS | 0x01 | If bit is set, indicates that the sending |
| | | peer is capable of TLS security. | | | | peer is capable of TLS security. |
| | | | | | | |
| Reserved | others | | Reserved | others |
+----------+--------+-----------------------------------------------+ +----------+--------+-----------------------------------------------+
Table 1: Contact Header Flags Table 1: Contact Header Flags
4.3. Contact Validation and Negotiation 4.3. Contact Validation and Negotiation
Upon reception of the contact header, each node follows the following Upon reception of the Contact Header, each node follows the following
procedures to ensure the validity of the TCPCL session and to procedures to ensure the validity of the TCPCL session and to
negotiate values for the session parameters. negotiate values for the session parameters.
If the magic string is not present or is not valid, the connection If the magic string is not present or is not valid, the connection
MUST be terminated. The intent of the magic string is to provide MUST be terminated. The intent of the magic string is to provide
some protection against an inadvertent TCP connection by a different some protection against an inadvertent TCP connection by a different
protocol than the one described in this document. To prevent a flood protocol than the one described in this document. To prevent a flood
of repeated connections from a misconfigured application, an entity of repeated connections from a misconfigured application, a passive
MAY elect to hold an invalid connection open and idle for some time entity MAY deny new TCP connections from a specific peer address for
before ending it. a period of time after one or more connections fail to provide a
decodable Contact Header.
The first negotiation is on the TCPCL protocol version to use. The The first negotiation is on the TCPCL protocol version to use. The
active entity always sends its Contact Header first and waits for a active entity always sends its Contact Header first and waits for a
response from the passive entity. The active entity can repeatedly response from the passive entity. During contact initiation, the
attempt different protocol versions in descending order until the active TCPCL node SHALL send the highest TCPCL protocol version on a
passive entity accepts one with a corresponding Contact Header reply. first session attempt for a TCPCL peer. If the active entity
Only upon response of a Contact Header from the passive entity is the receives a Contact Header with a lower protocol version than the one
TCPCL protocol version established and parameter negotiation begun. sent earlier on the TCP connection, the TCP connection SHALL be
closed. If the active entity receives a SESS_TERM message with
reason of "Version Mismatch", that node MAY attempt further TCPCL
sessions with the peer using earlier protocol version numbers in
decreasing order. Managing multi-TCPCL-session state such as this is
an implementation matter.
During contact initiation, the active TCPCL node SHALL send the If the passive entity receives a Contact Header containing a version
highest TCPCL protocol version on a first session attempt for a TCPCL that is not a version of the TCPCL that the entity implements, then
peer. If the active entity receives a Contact Header with a the entity SHALL send its Contact Header and immediately terminate
different protocol version than the one sent earlier on the TCP the session with a reason code of "Version mismatch". If the passive
connection, the TCP connection SHALL be closed. If the active entity entity receives a Contact Header with a version that is lower than
receives a SESS_TERM message with reason of "Version Mismatch", that the latest version of the protocol that the entity implements, the
node MAY attempt further TCPCL sessions with the peer using earlier entity MAY either terminate the session (with a reason code of
protocol version numbers in decreasing order. Managing multi-TCPCL- "Version mismatch") or adapt its operation to conform to the older
session state such as this is an implementation matter. version of the protocol. The decision of version fall-back is an
implementation matter.
If the passive entity receives a contact header containing a version The negotiated contact parameters defined by this specification are
that is greater than the current version of the TCPCL that the node described in the following paragraphs.
implements, then the node SHALL shutdown the session with a reason
code of "Version mismatch". If the passive entity receives a contact TCPCL Version: Both Contact Headers of a successful contact
header with a version that is lower than the version of the protocol negotiation have identical TCPCL Version numbers as described
that the node implements, the node MAY either terminate the session above. Only upon response of a Contact Header from the passive
(with a reason code of "Version mismatch") or the node MAY adapt its entity is the TCPCL protocol version established and session
operation to conform to the older version of the protocol. The negotiation begun.
decision of version fall-back is an implementation matter.
Enable TLS: Negotiation of the Enable TLS parameter is performed by
taking the logical AND of the two Contact Headers' CAN_TLS flags.
A local security policy is then applied to determine of the
negotiated value of Enable TLS is acceptable. It can be a
reasonable security policy to require or disallow the use of TLS
depending upon the desired network flows. Because this state is
negotiated over an unsecured medium, there is a risk of a TLS
Stripping as described in Section 8. If the Enable TLS state is
unacceptable, the entity SHALL terminate the session with a reason
code of "Contact Failure". Note that this contact failure reason
is different than a failure of TLS handshake or TLS authentication
after an agreed-upon and acceptable Enable TLS state. If the
negotiated Enable TLS value is true and acceptable then TLS
negotiation feature (described in Section 4.4) begins immediately
following the Contact Header exchange.
4.4. Session Security 4.4. Session Security
This version of the TCPCL supports establishing a Transport Layer This version of the TCPCL supports establishing a Transport Layer
Security (TLS) session within an existing TCP connection. When TLS Security (TLS) session within an existing TCP connection. When TLS
is used within the TCPCL it affects the entire session. Once is used within the TCPCL it affects the entire session. Once TLS is
established, there is no mechanism available to downgrade a TCPCL established, there is no mechanism available to downgrade the TCPCL
session to non-TLS operation. If this is desired, the entire TCPCL session to non-TLS operation.
session MUST be terminated and a new non-TLS-negotiated session
established.
Once established, the lifetime of a TLS session SHALL be bound to the Once established, the lifetime of a TLS connection SHALL be bound to
lifetime of the underlying TCP connection. Immediately prior to the lifetime of the underlying TCP connection. Immediately prior to
actively ending a TLS session after TCPCL session termination, the actively ending a TLS connection after TCPCL session termination, the
peer which sent the original (non-reply) SESS_TERM message SHOULD peer which sent the original (non-reply) SESS_TERM message SHOULD
follow the Closure Alert procedure of [RFC5246] to cleanly terminate follow the Closure Alert procedure of [RFC8446] to cleanly terminate
the TLS session. Because each TCPCL message is either fixed-length the TLS connection. Because each TCPCL message is either fixed-
or self-indicates its length, the lack of a TLS Closure Alert will length or self-indicates its length, the lack of a TLS Closure Alert
not cause data truncation or corruption. will not cause data truncation or corruption.
Subsequent TCPCL session attempts to the same passive entity MAY Subsequent TCPCL session attempts to the same passive entity MAY
attempt use the TLS session resumption feature. There is no attempt use the TLS connection resumption feature. There is no
guarantee that the passive entity will accept the request to resume a guarantee that the passive entity will accept the request to resume a
TLS session, and the active entity cannot assume any resumption TLS session, and the active entity cannot assume any resumption
outcome. outcome.
4.4.1. TLS Handshake 4.4.1. Entity Identification
The TCPCL uses the TLS for certificate exchange in both directions to
identify each entity and to allow each entity to authenticate its
peer. Each certificate can potentially identify multiple entities
and there is no problem using such a certificate as long as the
identifiers are sufficient to meet authentication policy (as
described in later sections) for the entity which presents it.
The public key infrastructure (PKI) Certificate Authority (CA) or
authorities available within a network are likely not controlled by
the certificate end users and CA policies vary widely between
networks and PKI management tools. For this reason, the TCPCL
defines a prioritized list of what a certificate can identify about a
TCPCL entity:
Node ID: The ideal certificate identity is the Node ID of the entity
using the NODE-ID definition below. When the Node ID is
identified, there is no need for any lower-level identification to
take place.
Host Name: If CA policy forbids a certificate to contain an
arbitrary NODE-ID but allows a DNS-ID to be identified then one or
more stable host names can be identified in the certificate. The
use of wildcard DNS-ID is discouraged due to the complex rules for
matching and dependence on implementation support for wildcard
matching.
Network Address: If no stable host name is available but a stable
network address is available and CA policy allows a certificate to
contain a NETWORK-ID (as defined below) then one or more network
addresses can be identified in the certificate. There is no
wildcard-type address matching defined, so this is the least
robust
When only a DNS-ID or NETWORK-ID can be identified by a certificate,
it is implied that an entity which authenticates using that
certificate is trusted to provide a valid Node ID in its SESS_INIT;
the certificate itself does not actually authenticate that Node ID.
The RECOMMENDED security policy of an entity is to validate a peer
which authenticates its Node ID regardless of an authenticated host
name or address, and only consider the host/address authentication in
the absence of an authenticated Node ID.
This specification defines a NODE-ID of a certificate as being the
subjectAltName entry of type uniformResourceIdentifier whose value is
a URI consistent with the requirements of [RFC3986] and the URI
schemes of the IANA "Bundle Protocol URI Scheme Type" registry. This
is similar to the URI-ID of [RFC6125] but does not require any
structure to the scheme-specific-part of the URI. Unless specified
otherwise by the definition of the URI scheme being authenticated,
URI matching of a NODE-ID SHALL use the URI comparison logic of
[RFC3986] and scheme-based normalization of those schemes specified
in [I-D.ietf-dtn-bpbis]. A URI scheme can refine this "exact match"
logic with rules about how Node IDs within that scheme are to be
compared with the certificate-authenticated NODE-ID.
This specification defines a NETWORK-ID of a certificate as being the
subjectAltName entry of type iPAddress whose value is encoded
according to [RFC5280].
4.4.2. TLS Handshake
The use of TLS is negotiated using the Contact Header as described in The use of TLS is negotiated using the Contact Header as described in
Section 4.3. After negotiating an Enable TLS parameter of true, and Section 4.3. After negotiating an Enable TLS parameter of true, and
before any other TCPCL messages are sent within the session, the before any other TCPCL messages are sent within the session, the
session entities SHALL begin a TLS handshake in accordance with TLS session entities SHALL begin a TLS handshake in accordance with
1.2 [RFC5246] or any successors that are compatible with TLS 1.2. By [RFC8446]. By convention, this protocol uses the entity which
convention, this protocol uses the node which initiated the initiated the underlying TCP connection (the active peer) as the
underlying TCP connection as the "client" role of the TLS handshake "client" role of the TLS handshake request.
request.
The TLS handshake, if it occurs, is considered to be part of the The TLS handshake, if it occurs, is considered to be part of the
contact negotiation before the TCPCL session itself is established. contact negotiation before the TCPCL session itself is established.
Specifics about sensitive data exposure are discussed in Section 8. Specifics about sensitive data exposure are discussed in Section 8.
The parameters within each TLS negotiation are implementation The parameters within each TLS negotiation are implementation
dependent but any TCPCL node SHALL follow all recommended practices dependent but any TCPCL node SHALL follow all recommended practices
of BCP 195 [RFC7525], or any updates or successors that become part of BCP 195 [RFC7525], or any updates or successors that become part
of BCP 195. Within each TLS handshake, the following requirements of BCP 195. Within each TLS handshake, the following requirements
apply (using the rough order in which they occur): apply (using the rough order in which they occur):
Client Hello: When a resolved host name was used to establish the Client Hello: When a resolved host name was used to establish the
TCP connection, the TLS ClientHello SHOULD include a Server Name TCP connection, the TLS ClientHello SHOULD include a Server Name
Indication (SNI) from the active entity in accordance with Indication (SNI) in accordance with [RFC6066] containing that host
[RFC6066]. When present, the SNI SHALL contain the same host name name (of the passive entity) which was resolved. Note: The SNI
used to establish the TCP connection. Note: The SNI text is the text is the network-layer name for the passive entity, which is
network-layer name for the passive entity, which is not the Node not the Node ID of that entity.
ID of that entity.
Server Certificate: The passive entity SHALL supply a certificate Server Certificate: The passive entity SHALL supply a certificate
within the TLS handshake to allow authentication of its side of within the TLS handshake to allow authentication of its side of
the session. When assigned a stable host name or address, the the session. Unless prohibited by CA policy, the passive entity
passive entity certificate SHOULD contain a subjectAltName entry certificate SHALL contain a NODE-ID which authenticates the Node
which authenticates that host name or address. The passive entity ID of the peer. When assigned a stable host name, the passive
certificate SHOULD contain a subjectAltName entry of type entity certificate SHOULD contain a DNS-ID which authenticates
uniformResourceIdentifier which authenticates the Node ID of the that (fully qualified) name. When assigned a stable network
peer. The passive entity MAY use the SNI host name to choose an address, the passive entity certificate MAY contain a NETWORK-ID
appropriate server-side certificate which authenticates that host which authenticates that address. The passive entity MAY use the
name and corresponding Node ID. SNI host name to choose an appropriate server-side certificate
which authenticates that host name.
Certificate Request: During TLS handshake, the passive entity SHALL Certificate Request: During TLS handshake, the passive entity SHALL
request a client-side certificate. request a client-side certificate.
Client Certificate: The active entity SHALL supply a certificate Client Certificate: The active entity SHALL supply a certificate
chain within the TLS handshake to allow authentication of its side chain within the TLS handshake to allow authentication of its side
of the session. When assigned a stable host name or address, the of the session. Unless prohibited by CA policy, the active entity
active entity certificate SHOULD contain a subjectAltName entry certificate SHALL contain a NODE-ID which authenticates the Node
which authenticates that host name or address. The active entity ID of the peer. When assigned a stable host name, the active
certificate SHOULD contain a subjectAltName entry of type entity certificate SHOULD contain a DNS-ID which authenticates
uniformResourceIdentifier which authenticates the Node ID of the that (fully qualified) name. When assigned a stable network
peer. address, the active entity certificate MAY contain a NETWORK-ID
which authenticates that address.
All certificates supplied during TLS handshake SHALL conform with the All certificates supplied during TLS handshake SHALL conform to
profile of [RFC5280], or any updates or successors to that profile. [RFC5280], or any updates or successors to that profile. When a
When a certificate is supplied during TLS handshake, the full certificate is supplied during TLS handshake, the full certification
certification chain SHOULD be included unless security policy chain SHOULD be included unless security policy indicates that is
indicates that is unnecessary. unnecessary.
If a TLS handshake cannot negotiate a TLS session, both entities of If a TLS handshake cannot negotiate a TLS connection, both entities
the TCPCL session SHALL close the TCP connection. At this point the of the TCPCL session SHALL close the TCP connection. At this point
TCPCL session has not yet been established so there is no TCPCL the TCPCL session has not yet been established so there is no TCPCL
session to terminate. This also avoids any potential security issues session to terminate.
assoicated with further TCP communication with an untrusted peer.
After a TLS session is successfully established, the active entity After a TLS connection is successfully established, the active entity
SHALL send a SESS_INIT message to begin session negotiation. This SHALL send a SESS_INIT message to begin session negotiation. This
session negotiation and all subsequent messaging are secured. session negotiation and all subsequent messaging are secured.
4.4.2. TLS Authentication 4.4.3. TLS Authentication
Using X.509 certificates exchanged during the TLS handshake, each of Using X.509 certificates exchanged during the TLS handshake, each of
the entities can attempt to authenticate its peer at the network the entities can attempt to authenticate its peer Node ID directly or
layer (host name and address) and at the application layer (BP Node authenticate the peer host name or network address. The Node ID
ID). The Node ID exchanged in the Session Initialization is likely exchanged in the Session Initialization is likely to be used by the
to be used by the BP agent for making transfer and routing decisions, BP agent for making transfer and routing decisions, so attempting
so attempting host name validation is optional while attempting Node Node ID validation is required while attempting host name validation
ID validation is required. The logic for attempting validation is is optional. The logic for attempting validation is separate from
separate from the logic for handling the result of validation, which the logic for handling the result of validation, which is based on
is based on local security policy. local security policy.
By using the SNI host name (see Section 4.4.1) a single passive By using the SNI host name (see Section 4.4.2) a single passive
entity can act as a convergence layer for multiple BP agents with entity can act as a convergence layer for multiple BP agents with
distinct Node IDs. When this "virtual host" behavior is used, the distinct Node IDs. When this "virtual host" behavior is used, the
host name is used as the indication of which BP Node the passive host name is used as the indication of which BP Node the active
entity is attempting to communicate with. A virtual host CL entity entity is attempting to communicate with. A virtual host CL entity
can be authenticated by a certificate containing all of the host can be authenticated by a certificate containing all of the host
names and/or Node IDs being hosted or by several certificates each names and/or Node IDs being hosted or by several certificates each
authenticating a single host name and/or Node ID. authenticating a single host name and/or Node ID, using the SNI value
from the peer to select which certificate to use.
Any certificate received during TLS handshake SHALL be validated up Any certificate received during TLS handshake SHALL be validated up
to one or more trusted certificate authority (CA) certificates. If to one or more trusted CA certificates. If certificate validation
certificate validation fails or if security policy disallows a fails or if security policy disallows a certificate for any reason,
certificate for any reason, the entity SHALL terminate the session the entity SHALL terminate the session (with a reason code of
(with a reason code of "Contact Failure"). "Contact Failure").
Either during or immediately after the TLS handshake, each side of Either during or immediately after the TLS handshake, the active
the TCP connection SHOULD perform host name validation of its peer in entity SHALL attempt to authenticate the host name (of the passive
accordance with [RFC6125] unless it is not needed by security policy. entity) used to initiate the TCP connection using any DNS-ID of the
The active entity SHALL attempt to authenticate the host name (of the peer certificate. If host name validation fails (including failure
passive entity) used to initiate the TCP connection. The active because the certificate does not contain any DNS-ID) and security
entity MAY attempt to authenticate the IP address of the other side policy disallows an unauthenticated host, the entity SHALL terminate
of the TCP connection. The passive entity SHALL attempt to the session (with a reason code of "Contact Failure").
authenticate the IP address of the other side of the TCP connection.
The passive entity MAY use the IP address to resolve one or more host Either during or immediately after the TLS handshake, the active
names of the active entity and attempt to authenticate those. If entity SHALL attempt to authenticate the IP address of the other side
host name validation fails (including failure because the certificate of the TCP connection using any NETWORK-ID of the peer certificate.
does not contain any DNS-ID) and security policy disallows an Either during or immediately after the TLS handshake, the passive
unauthticated host, the entity SHALL terminate the session (with a entity SHALL attempt to authenticate the IP address of the other side
reason code of "Contact Failure"). of the TCP connection using any NETWORK-ID of the peer certificate.
If host address validation fails (including failure because the
certificate does not contain any NETWORK-ID) and security policy
disallows an unauthenticated host, the entity SHALL terminate the
session (with a reason code of "Contact Failure").
Immediately before Session Parameter Negotiation, each side of the Immediately before Session Parameter Negotiation, each side of the
session SHALL perform Node ID validation of its peer as described session SHALL perform Node ID validation of its peer as described
below. Node ID validation SHALL succeed if the associated below. Node ID validation SHALL succeed if the associated
certificate contains a subjectAltName entry of type certificate includes a NODE-ID whose value matches the Node ID of the
uniformResourceIdentifier whose value matches the Node ID of the TCPCL entity. If Node ID validation fails (including failure because
TCPCL entity. Unless specified otherwise by the definition of the the certificate does not contain any NODE-ID) and security policy
URI scheme being authenticated, URI matching of Node IDs SHALL use disallows an unauthenticated Node ID, the entity SHALL terminate the
the URI comparison logic of [RFC3986] and scheme-based normalization session (with a reason code of "Contact Failure").
of those schemes specified in [I-D.ietf-dtn-bpbis]. This is similar
to the URI-ID of [RFC6125] but does not require any structure to the
scheme-specific-part of the URI. A URI scheme can refine this "exact
match" logic with rules about how Node IDs within that scheme are to
be compared with the certificate-authenticated URI. If Node ID
validation fails (including failure because the certificate does not
contain any subjectAltName URI) and security policy disallows an
unauthticated Node ID, the entity SHALL terminate the session (with a
reason code of "Contact Failure").
4.4.3. Example TLS Initiation 4.4.4. Example TLS Initiation
A summary of a typical TLS use is shown in the sequence in Figure 17 A summary of a typical TLS use is shown in the sequence in Figure 17
below. below. In this example the active peer terminates the session but
termination can be initiated from either peer.
Entity A Entity B Entity A Entity B
active peer passive peer active peer passive peer
+-------------------------+ +-------------------------+
| Open TCP Connnection | -> +-------------------------+ | Open TCP Connection | -> +-------------------------+
+-------------------------+ <- | Accept Connection | +-------------------------+ <- | Accept Connection |
+-------------------------+ +-------------------------+
+-------------------------+ +-------------------------+
| Contact Header | -> +-------------------------+ | Contact Header | -> +-------------------------+
+-------------------------+ <- | Contact Header | +-------------------------+ <- | Contact Header |
+-------------------------+ +-------------------------+
+-------------------------+ +-------------------------+ +-------------------------+ +-------------------------+
| TLS Negotiation | -> <- | TLS Negotiation | | TLS Negotiation | -> <- | TLS Negotiation |
| (as client) | | (as server) | | (as client) | | (as server) |
skipping to change at page 28, line 50 skipping to change at page 31, line 7
+-------------------------+ +-------------------------+
+-------------------------+ +-------------------------+ +-------------------------+ +-------------------------+
| TCP Close | -> <- | TCP Close | | TCP Close | -> <- | TCP Close |
+-------------------------+ +-------------------------+ +-------------------------+ +-------------------------+
Figure 17: A simple visual example of TCPCL TLS Establishment between Figure 17: A simple visual example of TCPCL TLS Establishment between
two entities two entities
4.5. Message Header 4.5. Message Header
After the initial exchange of a contact header, all messages After the initial exchange of a Contact Header, all messages
transmitted over the session are identified by a one-octet header transmitted over the session are identified by a one-octet header
with the following structure: with the following structure:
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---------------+ +---------------+
| Message Type | | Message Type |
+---------------+ +---------------+
Figure 18: Format of the Message Header Figure 18: Format of the Message Header
skipping to change at page 29, line 27 skipping to change at page 32, line 15
+--------------+------+---------------------------------------------+ +--------------+------+---------------------------------------------+
| Name | Code | Description | | Name | Code | Description |
+--------------+------+---------------------------------------------+ +--------------+------+---------------------------------------------+
| SESS_INIT | 0x07 | Contains the session parameter | | SESS_INIT | 0x07 | Contains the session parameter |
| | | inputs from one of the entities, | | | | inputs from one of the entities, |
| | | as described in Section 4.6. | | | | as described in Section 4.6. |
| | | | | | | |
| SESS_TERM | 0x05 | Indicates that one of the | | SESS_TERM | 0x05 | Indicates that one of the |
| | | entities participating in the session | | | | entities participating in the session |
| | | wishes to cleanly terminate the session, as | | | | wishes to cleanly terminate the session, as |
| | | described in Section 6. | | | | described in Section 6.1. |
| | | | | | | |
| XFER_SEGMENT | 0x01 | Indicates the transmission of | | XFER_SEGMENT | 0x01 | Indicates the transmission of |
| | | a segment of bundle data, as described in | | | | a segment of bundle data, as described in |
| | | Section 5.2.2. | | | | Section 5.2.2. |
| | | | | | | |
| XFER_ACK | 0x02 | Acknowledges reception of a | | XFER_ACK | 0x02 | Acknowledges reception of a |
| | | data segment, as described in | | | | data segment, as described in |
| | | Section 5.2.3. | | | | Section 5.2.3. |
| | | | | | | |
| XFER_REFUSE | 0x03 | Indicates that the | | XFER_REFUSE | 0x03 | Indicates that the |
| | | transmission of the current bundle SHALL be | | | | transmission of the current bundle SHALL be |
| | | stopped, as described in | | | | stopped, as described in |
| | | Section 5.2.4. | | | | Section 5.2.4. |
| | | | | | | |
| KEEPALIVE | 0x04 | Used to keep TCPCL session | | KEEPALIVE | 0x04 | Used to keep TCPCL session |
| | | active, as described in Section | | | | active, as described in |
| | | 5.1.1. | | | | Section 5.1.1. |
| | | | | | | |
| MSG_REJECT | 0x06 | Contains a TCPCL message | | MSG_REJECT | 0x06 | Contains a TCPCL message |
| | | rejection, as described in | | | | rejection, as described in |
| | | Section 5.1.2. | | | | Section 5.1.2. |
+--------------+------+---------------------------------------------+ +--------------+------+---------------------------------------------+
Table 2: TCPCL Message Types Table 2: TCPCL Message Types
4.6. Session Initialization Message (SESS_INIT) 4.6. Session Initialization Message (SESS_INIT)
skipping to change at page 30, line 39 skipping to change at page 33, line 29
| Items Length (U32) | | Items Length (U32) |
+-----------------------------+ +-----------------------------+
| Session Extension | | Session Extension |
| Items (var.) | | Items (var.) |
+-----------------------------+ +-----------------------------+
Figure 19: SESS_INIT Format Figure 19: SESS_INIT Format
The fields of the SESS_INIT message are: The fields of the SESS_INIT message are:
Keepalive Interval: A 16-bit unsigned integer indicating the Keepalive Interval: A 16-bit unsigned integer indicating the minimum
interval, in seconds, between any subsequent messages being interval, in seconds, to negotiate the Session Keepalive using the
transmitted by the peer. The peer receiving this contact header method of Section 4.7.
uses this interval to determine how long to wait after any last-
message transmission and a necessary subsequent KEEPALIVE message
transmission.
Segment MRU: A 64-bit unsigned integer indicating the largest Segment MRU: A 64-bit unsigned integer indicating the largest
allowable single-segment data payload size to be received in this allowable single-segment data payload size to be received in this
session. Any XFER_SEGMENT sent to this peer SHALL have a data session. Any XFER_SEGMENT sent to this peer SHALL have a data
payload no longer than the peer's Segment MRU. The two entities payload no longer than the peer's Segment MRU. The two entities
of a single session MAY have different Segment MRUs, and no of a single session MAY have different Segment MRUs, and no
relation between the two is required. relation between the two is required.
Transfer MRU: A 64-bit unsigned integer indicating the largest Transfer MRU: A 64-bit unsigned integer indicating the largest
allowable total-bundle data size to be received in this session. allowable total-bundle data size to be received in this session.
skipping to change at page 31, line 22 skipping to change at page 34, line 8
Node ID Length and Node ID Data: Together these fields represent a Node ID Length and Node ID Data: Together these fields represent a
variable-length text string. The Node ID Length is a 16-bit variable-length text string. The Node ID Length is a 16-bit
unsigned integer indicating the number of octets of Node ID Data unsigned integer indicating the number of octets of Node ID Data
to follow. A zero-length Node ID SHALL be used to indicate the to follow. A zero-length Node ID SHALL be used to indicate the
lack of Node ID rather than a truly empty Node ID. This case lack of Node ID rather than a truly empty Node ID. This case
allows an entity to avoid exposing Node ID information on an allows an entity to avoid exposing Node ID information on an
untrusted network. A non-zero-length Node ID Data SHALL contain untrusted network. A non-zero-length Node ID Data SHALL contain
the UTF-8 encoded Node ID of the Entity which sent the SESS_INIT the UTF-8 encoded Node ID of the Entity which sent the SESS_INIT
message. Every Node ID SHALL be a URI consistent with the message. Every Node ID SHALL be a URI consistent with the
requirements of [RFC3986] and the URI schemes of requirements of [RFC3986] and the URI schemes of the IANA "Bundle
[I-D.ietf-dtn-bpbis]. The Node ID itself can be authenticated as Protocol URI Scheme Type" registry. The Node ID itself can be
described in Section 4.4.2. authenticated as described in Section 4.4.3.
Session Extension Length and Session Extension Items: Session Extension Length and Session Extension Items:
Together these fields represent protocol extension data not Together these fields represent protocol extension data not
defined by this specification. The Session Extension Length is defined by this specification. The Session Extension Length is
the total number of octets to follow which are used to encode the the total number of octets to follow which are used to encode the
Session Extension Item list. The encoding of each Session Session Extension Item list. The encoding of each Session
Extension Item is within a consistent data container as described Extension Item is within a consistent data container as described
in Section 4.8. The full set of Session Extension Items apply for in Section 4.8. The full set of Session Extension Items apply for
the duration of the TCPCL session to follow. The order and the duration of the TCPCL session to follow. The order and
mulitplicity of these Session Extension Items MAY be significant, multiplicity of these Session Extension Items is significant, as
as defined in the associated type specification(s). defined in the associated type specification(s).
4.7. Session Parameter Negotiation 4.7. Session Parameter Negotiation
An entity calculates the parameters for a TCPCL session by An entity calculates the parameters for a TCPCL session by
negotiating the values from its own preferences (conveyed by the negotiating the values from its own preferences (conveyed by the
contact header it sent to the peer) with the preferences of the peer SESS_INIT it sent to the peer) with the preferences of the peer node
node (expressed in the contact header that it received from the (expressed in the SESS_INIT that it received from the peer). The
peer). The negotiated parameters defined by this specification are negotiated parameters defined by this specification are described in
described in the following paragraphs. the following paragraphs.
Transfer MTU and Segment MTU: The maximum transmit unit (MTU) for Transfer MTU and Segment MTU: The maximum transmit unit (MTU) for
whole transfers and individual segments are idententical to the whole transfers and individual segments are identical to the
Transfer MRU and Segment MRU, respectively, of the recevied Transfer MRU and Segment MRU, respectively, of the received
contact header. A transmitting peer can send individual segments Contact Header. A transmitting peer can send individual segments
with any size smaller than the Segment MTU, depending on local with any size smaller than the Segment MTU, depending on local
policy, dynamic network conditions, etc. Determining the size of policy, dynamic network conditions, etc. Determining the size of
each transmitted segment is an implementation matter. If the each transmitted segment is an implementation matter. If either
either Transfer MRU or Segment MRU is unacceptable, the node SHALL the Transfer MRU or Segment MRU is unacceptable, the entity SHALL
terminate the session with a reason code of "Contact Failure". terminate the session with a reason code of "Contact Failure".
Session Keepalive: Negotiation of the Session Keepalive parameter is Session Keepalive: Negotiation of the Session Keepalive parameter is
performed by taking the minimum of this two contact headers' performed by taking the minimum of the two Contact Headers'
Keepalive Interval. The Session Keepalive interval is a parameter Keepalive Interval values. The Session Keepalive interval is a
for the behavior described in Section 5.1.1. If the Session parameter for the behavior described in Section 5.1.1. If the
Keepalive interval is unacceptable, the node SHALL terminate the Session Keepalive interval is unacceptable, the entity SHALL
session with a reason code of "Contact Failure". terminate the session with a reason code of "Contact Failure".
Note: a negotiated Session Keepalive of zero indicates that
Enable TLS: Negotiation of the Enable TLS parameter is performed by KEEPALIVEs are disabled.
taking the logical AND of the two contact headers' CAN_TLS flags.
A local security policy is then applied to determine of the
negotiated value of Enable TLS is acceptable. It can be a
reasonable security policy to both require or disallow the use of
TLS depending upon the desired network flows. Because this state
is negotiated over an unsecured medium, there is a risk of a TLS
Stripping as described in Section 8. If the Enable TLS state is
unacceptable, the node SHALL terminate the session with a reason
code of "Contact Failure". Note that this contact failure reason
is different than a failure of TLS handshake or TLS authentication
after an agreed-upon and acceptable Enable TLS state. If the
negotiated Enable TLS value is true and acceptable then TLS
negotiation feature (described in Section 4.4) begins immediately
following the contact header exchange.
Once this process of parameter negotiation is completed (which Once this process of parameter negotiation is completed (which
includes a possible completed TLS handshake of the connection to use includes a possible completed TLS handshake of the connection to use
TLS), this protocol defines no additional mechanism to change the TLS), this protocol defines no additional mechanism to change the
parameters of an established session; to effect such a change, the parameters of an established session; to effect such a change, the
TCPCL session MUST be terminated and a new session established. TCPCL session MUST be terminated and a new session established.
4.8. Session Extension Items 4.8. Session Extension Items
Each of the Session Extension Items SHALL be encoded in an identical Each of the Session Extension Items SHALL be encoded in an identical
Type-Length-Value (TLV) container form as indicated in Figure 20. Type-Length-Value (TLV) container form as indicated in Figure 20.
The fields of the Session Extension Item are: The fields of the Session Extension Item are:
Flags: A one-octet field containing generic bit flags about the Item Flags: A one-octet field containing generic bit flags about the
Item, which are listed in Table 3. All reserved header flag bits Item, which are listed in Table 3. All reserved header flag bits
SHALL be set to 0 by the sender. All reserved header flag bits SHALL be set to 0 by the sender. All reserved header flag bits
SHALL be ignored by the receiver. If a TCPCL entity receives a SHALL be ignored by the receiver. If a TCPCL entity receives a
Session Extension Item with an unknown Item Type and the CRITICAL Session Extension Item with an unknown Item Type and the CRITICAL
flag of 1, the entity SHALL close the TCPCL session with SESS_TERM flag of 1, the entity SHALL close the TCPCL session with SESS_TERM
reason code of "Contact Failure". If the CRITICAL flag is 0, an reason code of "Contact Failure". If the CRITICAL flag is 0, an
entity SHALL skip over and ignore any item with an unknown Item entity SHALL skip over and ignore any item with an unknown Item
Type. Type.
Item Type: A 16-bit unsigned integer field containing the type of Item Type: A 16-bit unsigned integer field containing the type of
the extension item. This specification does not define any the extension item. This specification does not define any
extension types directly, but does allocate an IANA registry for extension types directly, but does create an IANA registry for
such codes (see Section 9.3). such codes (see Section 9.3).
Item Length: A 16-bit unsigned integer field containing the number Item Length: A 16-bit unsigned integer field containing the number
of Item Value octets to follow. of Item Value octets to follow.
Item Value: A variable-length data field which is interpreted Item Value: A variable-length data field which is interpreted
according to the associated Item Type. This specification places according to the associated Item Type. This specification places
no restrictions on an extension's use of available Item Value no restrictions on an extension's use of available Item Value
data. Extension specifications SHOULD avoid the use of large data data. Extension specifications SHOULD avoid the use of large data
lengths, as no bundle transfers can begin until the full extension lengths, as no bundle transfers can begin until the full extension
skipping to change at page 34, line 4 skipping to change at page 36, line 23
Table 3: Session Extension Item Flags Table 3: Session Extension Item Flags
5. Established Session Operation 5. Established Session Operation
This section describes the protocol operation for the duration of an This section describes the protocol operation for the duration of an
established session, including the mechanism for transmitting bundles established session, including the mechanism for transmitting bundles
over the session. over the session.
5.1. Upkeep and Status Messages 5.1. Upkeep and Status Messages
5.1.1. Session Upkeep (KEEPALIVE) 5.1.1. Session Upkeep (KEEPALIVE)
The protocol includes a provision for transmission of KEEPALIVE The protocol includes a provision for transmission of KEEPALIVE
messages over the TCPCL session to help determine if the underlying messages over the TCPCL session to help determine if the underlying
TCP connection has been disrupted. TCP connection has been disrupted.
As described in Section 4.3, a negotiated parameter of each session As described in Section 4.3, a negotiated parameter of each session
is the Session Keepalive interval. If the negotiated Session is the Session Keepalive interval. If the negotiated Session
Keepalive is zero (i.e. one or both contact headers contains a zero Keepalive is zero (i.e., one or both contact headers contains a zero
Keepalive Interval), then the keepalive feature is disabled. There Keepalive Interval), then the keepalive feature is disabled. There
is no logical minimum value for the keepalive interval, but when used is no logical minimum value for the keepalive interval (within the
for many sessions on an open, shared network a short interval could minimum imposed by the positive-value encoding), but when used for
lead to excessive traffic. For shared network use, entities SHOULD many sessions on an open, shared network a short interval could lead
choose a keepalive interval no shorter than 30 seconds. There is no to excessive traffic. For shared network use, entities SHOULD choose
logical maximum value for the keepalive interval, but an idle TCP a keepalive interval no shorter than 30 seconds. There is no logical
connection is liable for closure by the host operating system if the maximum value for the keepalive interval (within the maximum imposed
keepalive time is longer than tens-of-minutes. Entities SHOULD by the fixed-size encoding), but an idle TCP connection is liable for
choose a keepalive interval no longer than 10 minutes (600 seconds). closure by the host operating system if the keepalive time is longer
than tens-of-minutes. Entities SHOULD choose a keepalive interval no
longer than 10 minutes (600 seconds).
Note: The Keepalive Interval SHOULD NOT be chosen too short as TCP Note: The Keepalive Interval SHOULD NOT be chosen too short as TCP
retransmissions MAY occur in case of packet loss. Those will have to retransmissions MAY occur in case of packet loss. Those will have to
be triggered by a timeout (TCP retransmission timeout (RTO)), which be triggered by a timeout (TCP retransmission timeout (RTO)), which
is dependent on the measured RTT for the TCP connection so that is dependent on the measured RTT for the TCP connection so that
KEEPALIVE messages MAY experience noticeable latency. KEEPALIVE messages can experience noticeable latency.
The format of a KEEPALIVE message is a one-octet message type code of The format of a KEEPALIVE message is a one-octet message type code of
KEEPALIVE (as described in Table 2) with no additional data. Both KEEPALIVE (as described in Table 2) with no additional data. Both
sides SHALL send a KEEPALIVE message whenever the negotiated interval sides SHALL send a KEEPALIVE message whenever the negotiated interval
has elapsed with no transmission of any message (KEEPALIVE or other). has elapsed with no transmission of any message (KEEPALIVE or other).
If no message (KEEPALIVE or other) has been received in a session If no message (KEEPALIVE or other) has been received in a session
after some implementation-defined time duration, then the node SHALL after some implementation-defined time duration, then the entity
terminate the session by transmitting a SESS_TERM message (as SHALL terminate the session by transmitting a SESS_TERM message (as
described in Section 6.1) with reason code "Idle Timeout". If described in Section 6.1) with reason code "Idle Timeout". If
configurable, the idle timeout duration SHOULD be no shorter than configurable, the idle timeout duration SHOULD be no shorter than
twice the keepalive interval. If not configurable, the idle timeout twice the keepalive interval. If not configurable, the idle timeout
duration SHOULD be exactly twice the keepalive interval. duration SHOULD be exactly twice the keepalive interval.
5.1.2. Message Rejection (MSG_REJECT) 5.1.2. Message Rejection (MSG_REJECT)
If a TCPCL node receives a message which is unknown to it (possibly This message type is not expected to be seen in a well-functioning
due to an unhandled protocol mismatch) or is inappropriate for the session. Its purpose is to aid in troubleshooting bad entity
current session state (e.g. a KEEPALIVE message received after behavior by allowing the peer to observe why an entity is not
contact header negotiation has disabled that feature), there is a responding as expected to its messages.
protocol-level message to signal this condition in the form of a
MSG_REJECT reply. If a TCPCL entity receives a message type which is unknown to it
(possibly due to an unhandled protocol version mismatch or a
incorrectly-negotiated session extension which defines a new message
type), the entity SHALL send a MSG_REJECT message with a Reason Code
of "Message Type Unknown" and close the TCP connection. If a TCPCL
entity receives a message type which is known but is inappropriate
for the negotiated session parameters (possibly due to incorrectly-
negotiated session extension), the entity SHALL send a MSG_REJECT
message with a Reason Code of "Message Unsupported". If a TCPCL
entity receives a message which is inappropriate for the current
session state (e.g., a SESS_INIT after the session has already been
established or an XFER_ACK message with an unknown Transfer ID), the
entity SHALL send a MSG_REJECT message with a Reason Code of "Message
Unexpected".
The format of a MSG_REJECT message is as follows in Figure 21. The format of a MSG_REJECT message is as follows in Figure 21.
+-----------------------------+ +-----------------------------+
| Message Header | | Message Header |
+-----------------------------+ +-----------------------------+
| Reason Code (U8) | | Reason Code (U8) |
+-----------------------------+ +-----------------------------+
| Rejected Message Header | | Rejected Message Header |
+-----------------------------+ +-----------------------------+
skipping to change at page 35, line 32 skipping to change at page 38, line 20
response. response.
+-------------+------+----------------------------------------------+ +-------------+------+----------------------------------------------+
| Name | Code | Description | | Name | Code | Description |
+-------------+------+----------------------------------------------+ +-------------+------+----------------------------------------------+
| Message | 0x01 | A message was received with a | | Message | 0x01 | A message was received with a |
| Type | | Message Type code unknown to the TCPCL node. | | Type | | Message Type code unknown to the TCPCL node. |
| Unknown | | | | Unknown | | |
| | | | | | | |
| Message | 0x02 | A message was received but the | | Message | 0x02 | A message was received but the |
| Unsupported | | TCPCL node cannot comply with the message | | Unsupported | | TCPCL entity cannot comply with the message |
| | | contents. | | | | contents. |
| | | | | | | |
| Message | 0x03 | A message was received while the | | Message | 0x03 | A message was received while the |
| Unexpected | | session is in a state in which the message | | Unexpected | | session is in a state in which the message |
| | | is not expected. | | | | is not expected. |
+-------------+------+----------------------------------------------+ +-------------+------+----------------------------------------------+
Table 4: MSG_REJECT Reason Codes Table 4: MSG_REJECT Reason Codes
5.2. Bundle Transfer 5.2. Bundle Transfer
All of the messages in this section are directly associated with All of the messages in this section are directly associated with
transferring a bundle between TCPCL entities. transferring a bundle between TCPCL entities.
A single TCPCL transfer results in a bundle (handled by the A single TCPCL transfer results in a bundle (handled by the
convergence layer as opaque data) being exchanged from one node to convergence layer as opaque data) being exchanged from one node to
the other. In TCPCL a transfer is accomplished by dividing a single the other. In TCPCL a transfer is accomplished by dividing a single
bundle up into "segments" based on the receiving-side Segment MRU bundle up into "segments" based on the receiving-side Segment MRU
(see Section 4.2). The choice of the length to use for segments is (see Section 4.2). The choice of the length to use for segments is
an implementation matter, but each segment MUST be no larger than the an implementation matter, but each segment MUST NOT be larger than
receiving node's maximum receive unit (MRU) (see the field Segment the receiving node's maximum receive unit (MRU) (see the field
MRU of Section 4.2). The first segment for a bundle is indicated by Segment MRU of Section 4.2). The first segment for a bundle is
the 'START' flag and the last segment is indicated by the 'END' flag. indicated by the 'START' flag and the last segment is indicated by
the 'END' flag.
A single transfer (and by extension a single segment) SHALL NOT A single transfer (and by extension a single segment) SHALL NOT
contain data of more than a single bundle. This requirement is contain data of more than a single bundle. This requirement is
imposed on the agent using the TCPCL rather than TCPCL itself. imposed on the agent using the TCPCL rather than TCPCL itself.
If multiple bundles are transmitted on a single TCPCL connection, If multiple bundles are transmitted on a single TCPCL connection,
they MUST be transmitted consecutively without interleaving of they MUST be transmitted consecutively without interleaving of
segments from multiple bundles. segments from multiple bundles.
5.2.1. Bundle Transfer ID 5.2.1. Bundle Transfer ID
Each of the bundle transfer messages contains a Transfer ID which is Each of the bundle transfer messages contains a Transfer ID which is
used to correlate messages (from both sides of a transfer) for each used to correlate messages (from both sides of a transfer) for each
bundle. A Transfer ID does not attempt to address uniqueness of the bundle. A Transfer ID does not attempt to address uniqueness of the
bundle data itself and has no relation to concepts such as bundle bundle data itself and has no relation to concepts such as bundle
fragmentation. Each invocation of TCPCL by the bundle protocol fragmentation. Each invocation of TCPCL by the bundle protocol
agent, requesting transmission of a bundle (fragmentary or agent, requesting transmission of a bundle (fragmentary or
otherwise), results in the initiation of a single TCPCL transfer. otherwise), results in the initiation of a single TCPCL transfer.
Each transfer entails the sending of a sequence of some number of Each transfer entails the sending of a sequence of some number of
XFER_SEGMENT and XFER_ACK messages; all are correlated by the same XFER_SEGMENT and XFER_ACK messages; all are correlated by the same
Transfer ID. Transfer ID. The sending entity originates a transfer ID and the
receiving entity uses that same Transfer ID in acknowledgements.
Transfer IDs from each node SHALL be unique within a single TCPCL Transfer IDs from each node SHALL be unique within a single TCPCL
session. The initial Transfer ID from each node SHALL have value session. Upon exhaustion of the entire 64-bit Transfer ID space, the
zero. Subsequent Transfer ID values SHALL be incremented from the sending node SHALL terminate the session with SESS_TERM reason code
prior Transfer ID value by one. Upon exhaustion of the entire 64-bit "Resource Exhaustion". For bidirectional bundle transfers, a TCPCL
Transfer ID space, the sending node SHALL terminate the session with node SHOULD NOT rely on any relation between Transfer IDs originating
SESS_TERM reason code "Resource Exhaustion". from each side of the TCPCL session.
For bidirectional bundle transfers, a TCPCL node SHOULD NOT rely on Although there is not a strict requirement for Transfer ID initial
any relation between Transfer IDs originating from each side of the values or ordering (see Section 8.11), in the absence of any other
TCPCL session. mechanism for generating Transfer IDs an entity SHALL use the
following algorithm: The initial Transfer ID from each node is zero
and subsequent Transfer ID values are incremented from the prior
Transfer ID value by one.
5.2.2. Data Transmission (XFER_SEGMENT) 5.2.2. Data Transmission (XFER_SEGMENT)
Each bundle is transmitted in one or more data segments. The format Each bundle is transmitted in one or more data segments. The format
of a XFER_SEGMENT message follows in Figure 22. of a XFER_SEGMENT message follows in Figure 22.
+------------------------------+ +------------------------------+
| Message Header | | Message Header |
+------------------------------+ +------------------------------+
| Message Flags (U8) | | Message Flags (U8) |
skipping to change at page 37, line 46 skipping to change at page 40, line 46
Transfer Extension Length and Transfer Extension Items: Transfer Extension Length and Transfer Extension Items:
Together these fields represent protocol extension data for this Together these fields represent protocol extension data for this
specification. The Transfer Extension Length and Transfer specification. The Transfer Extension Length and Transfer
Extension Item fields SHALL only be present when the 'START' flag Extension Item fields SHALL only be present when the 'START' flag
is set to 1 on the message. The Transfer Extension Length is the is set to 1 on the message. The Transfer Extension Length is the
total number of octets to follow which are used to encode the total number of octets to follow which are used to encode the
Transfer Extension Item list. The encoding of each Transfer Transfer Extension Item list. The encoding of each Transfer
Extension Item is within a consistent data container as described Extension Item is within a consistent data container as described
in Section 5.2.5. The full set of transfer extension items apply in Section 5.2.5. The full set of transfer extension items apply
only to the assoicated single transfer. The order and only to the associated single transfer. The order and
mulitplicity of these transfer extension items MAY be significant, multiplicity of these transfer extension items is significant, as
as defined in the associated type specification(s). defined in the associated type specification(s).
Data length: A 64-bit unsigned integer indicating the number of Data length: A 64-bit unsigned integer indicating the number of
octets in the Data contents to follow. octets in the Data contents to follow.
Data contents: The variable-length data payload of the message. Data contents: The variable-length data payload of the message.
+----------+--------+-----------------------------------------------+ +----------+--------+-----------------------------------------------+
| Name | Code | Description | | Name | Code | Description |
+----------+--------+-----------------------------------------------+ +----------+--------+-----------------------------------------------+
| END | 0x01 | If bit is set, indicates that this is the | | END | 0x01 | If bit is set, indicates that this is the |
| | | last segment of the transfer. | | | | last segment of the transfer. |
| | | | | | | |
| START | 0x02 | If bit is set, indicates that this is the | | START | 0x02 | If bit is set, indicates that this is the |
| | | first segment of the transfer. | | | | first segment of the transfer. |
| | | | | | | |
| Reserved | others | | Reserved | others |
+----------+--------+-----------------------------------------------+ +----------+--------+-----------------------------------------------+
Table 5: XFER_SEGMENT Flags Table 5: XFER_SEGMENT Flags
The flags portion of the message contains two optional values in the The flags portion of the message contains two flag values in the two
two low-order bits, denoted 'START' and 'END' in Table 5. The low-order bits, denoted 'START' and 'END' in Table 5. The 'START'
'START' flag SHALL be set to 1 when transmitting the first segment of flag SHALL be set to 1 when transmitting the first segment of a
a transfer. The 'END' flag SHALL be set to 1 when transmitting the transfer. The 'END' flag SHALL be set to 1 when transmitting the
last segment of a transfer. In the case where an entire transfer is last segment of a transfer. In the case where an entire transfer is
accomplished in a single segment, both the 'START' and 'END' flags accomplished in a single segment, both the 'START' and 'END' flags
SHALL be set to 1. SHALL be set to 1.
Once a transfer of a bundle has commenced, the node MUST only send Once a transfer of a bundle has commenced, the entity MUST only send
segments containing sequential portions of that bundle until it sends segments containing sequential portions of that bundle until it sends
a segment with the 'END' flag set to 1. No interleaving of multiple a segment with the 'END' flag set to 1. No interleaving of multiple
transfers from the same node is possible within a single TCPCL transfers from the same node is possible within a single TCPCL
session. Simultaneous transfers between two entities MAY be achieved session. Simultaneous transfers between two entities MAY be achieved
using multiple TCPCL sessions. using multiple TCPCL sessions.
5.2.3. Data Acknowledgments (XFER_ACK) 5.2.3. Data Acknowledgments (XFER_ACK)
Although the TCP transport provides reliable transfer of data between Although the TCP transport provides reliable transfer of data between
transport peers, the typical BSD sockets interface provides no means transport peers, the typical BSD sockets interface provides no means
to inform a sending application of when the receiving application has to inform a sending application of when the receiving application has
processed some amount of transmitted data. Thus, after transmitting processed some amount of transmitted data. Thus, after transmitting
some data, the TCPCL needs an additional mechanism to determine some data, the TCPCL needs an additional mechanism to determine
whether the receiving agent has successfully received the segment. whether the receiving agent has successfully received and fully
To this end, the TCPCL protocol provides feedback messaging whereby a processed the segment. To this end, the TCPCL protocol provides
receiving node transmits acknowledgments of reception of data feedback messaging whereby a receiving node transmits acknowledgments
segments. of reception of data segments.
The format of an XFER_ACK message follows in Figure 23. The format of an XFER_ACK message follows in Figure 23.
+-----------------------------+ +-----------------------------+
| Message Header | | Message Header |
+-----------------------------+ +-----------------------------+
| Message Flags (U8) | | Message Flags (U8) |
+-----------------------------+ +-----------------------------+
| Transfer ID (U64) | | Transfer ID (U64) |
+-----------------------------+ +-----------------------------+
skipping to change at page 39, line 31 skipping to change at page 42, line 31
flag bits SHALL be set to 0 by the sender. All reserved header flag bits SHALL be set to 0 by the sender. All reserved header
flag bits SHALL be ignored by the receiver. flag bits SHALL be ignored by the receiver.
Transfer ID: A 64-bit unsigned integer identifying the transfer Transfer ID: A 64-bit unsigned integer identifying the transfer
being acknowledged. being acknowledged.
Acknowledged length: A 64-bit unsigned integer indicating the total Acknowledged length: A 64-bit unsigned integer indicating the total
number of octets in the transfer which are being acknowledged. number of octets in the transfer which are being acknowledged.
A receiving TCPCL node SHALL send an XFER_ACK message in response to A receiving TCPCL node SHALL send an XFER_ACK message in response to
each received XFER_SEGMENT message. The flags portion of the each received XFER_SEGMENT message after the segment has been fully
XFER_ACK header SHALL be set to match the corresponding DATA_SEGMENT processed. The flags portion of the XFER_ACK header SHALL be set to
message being acknowledged. The acknowledged length of each XFER_ACK match the corresponding XFER_SEGMENT message being acknowledged
contains the sum of the data length fields of all XFER_SEGMENT (including flags not decodable to the entity). The acknowledged
messages received so far in the course of the indicated transfer. length of each XFER_ACK contains the sum of the data length fields of
The sending node SHOULD transmit multiple XFER_SEGMENT messages all XFER_SEGMENT messages received so far in the course of the
without waiting for the corresponding XFER_ACK responses. This indicated transfer. The sending node SHOULD transmit multiple
enables pipelining of messages on a transfer stream. XFER_SEGMENT messages without waiting for the corresponding XFER_ACK
responses. This enables pipelining of messages on a transfer stream.
For example, suppose the sending node transmits four segments of For example, suppose the sending node transmits four segments of
bundle data with lengths 100, 200, 500, and 1000, respectively. bundle data with lengths 100, 200, 500, and 1000, respectively.
After receiving the first segment, the node sends an acknowledgment After receiving the first segment, the entity sends an acknowledgment
of length 100. After the second segment is received, the node sends of length 100. After the second segment is received, the entity
an acknowledgment of length 300. The third and fourth sends an acknowledgment of length 300. The third and fourth
acknowledgments are of length 800 and 1800, respectively. acknowledgments are of length 800 and 1800, respectively.
5.2.4. Transfer Refusal (XFER_REFUSE) 5.2.4. Transfer Refusal (XFER_REFUSE)
The TCPCL supports a mechanism by which a receiving node can indicate The TCPCL supports a mechanism by which a receiving node can indicate
to the sender that it does not want to receive the corresponding to the sender that it does not want to receive the corresponding
bundle. To do so, upon receiving an XFER_SEGMENT message, the node bundle. To do so, upon receiving an XFER_SEGMENT message, the entity
MAY transmit a XFER_REFUSE message. As data segments and MAY transmit a XFER_REFUSE message. As data segments and
acknowledgments MAY cross on the wire, the bundle that is being acknowledgments can cross on the wire, the bundle that is being
refused SHALL be identified by the Transfer ID of the refusal. refused SHALL be identified by the Transfer ID of the refusal.
There is no required relation between the Transfer MRU of a TCPCL There is no required relation between the Transfer MRU of a TCPCL
node (which is supposed to represent a firm limitation of what the node (which is supposed to represent a firm limitation of what the
node will accept) and sending of a XFER_REFUSE message. A node will accept) and sending of a XFER_REFUSE message. A
XFER_REFUSE can be used in cases where the agent's bundle storage is XFER_REFUSE can be used in cases where the agent's bundle storage is
temporarily depleted or somehow constrained. A XFER_REFUSE can also temporarily depleted or somehow constrained. A XFER_REFUSE can also
be used after the bundle header or any bundle data is inspected by an be used after the bundle header or any bundle data is inspected by an
agent and determined to be unacceptable. agent and determined to be unacceptable.
A receiver MAY send an XFER_REFUSE message as soon as it receives any A transfer receiver MAY send an XFER_REFUSE message as soon as it
XFER_SEGMENT message. The sender MUST be prepared for this and MUST receives any XFER_SEGMENT message. The transfer sender MUST be
associate the refusal with the correct bundle via the Transfer ID prepared for this and MUST associate the refusal with the correct
fields. bundle via the Transfer ID fields.
The TCPCL itself does not have any required behavior to respond to an
XFER_REFUSE based on its Reason Code; the refusal is passed up as an
indication to the BP agent that the transfer has been refused. If a
transfer refusal has a Reason Code which is not decodable to the BP
agent, the agent SHOULD treat the refusal as having an Unknown
reason.
The format of the XFER_REFUSE message is as follows in Figure 24. The format of the XFER_REFUSE message is as follows in Figure 24.
+-----------------------------+ +-----------------------------+
| Message Header | | Message Header |
+-----------------------------+ +-----------------------------+
| Reason Code (U8) | | Reason Code (U8) |
+-----------------------------+ +-----------------------------+
| Transfer ID (U64) | | Transfer ID (U64) |
+-----------------------------+ +-----------------------------+
skipping to change at page 41, line 11 skipping to change at page 44, line 11
Transfer ID: A 64-bit unsigned integer identifying the transfer Transfer ID: A 64-bit unsigned integer identifying the transfer
being refused. being refused.
+------------+------+-----------------------------------------------+ +------------+------+-----------------------------------------------+
| Name | Code | Description | | Name | Code | Description |
+------------+------+-----------------------------------------------+ +------------+------+-----------------------------------------------+
| Unknown | 0x00 | Reason for refusal is unknown or not | | Unknown | 0x00 | Reason for refusal is unknown or not |
| | | specified. | | | | specified. |
| | | | | | | |
| Extension | 0x01 | A failure processing the Transfer Extension | | Completed | 0x01 | The receiver already has the complete bundle. |
| Failure | | Items ha occurred. |
| | | |
| Completed | 0x02 | The receiver already has the complete bundle. |
| | | The sender MAY consider the bundle as | | | | The sender MAY consider the bundle as |
| | | completely received. | | | | completely received. |
| | | | | | | |
| No | 0x03 | The receiver's resources are exhausted. The | | No | 0x02 | The receiver's resources are exhausted. The |
| Resources | | sender SHOULD apply reactive bundle | | Resources | | sender SHOULD apply reactive bundle |
| | | fragmentation before retrying. | | | | fragmentation before retrying. |
| | | | | | | |
| Retransmit | 0x04 | The receiver has encountered a problem that | | Retransmit | 0x03 | The receiver has encountered a problem that |
| | | requires the bundle to be retransmitted in | | | | requires the bundle to be retransmitted in |
| | | its entirety. | | | | its entirety. |
| | | |
| Not | 0x04 | Some issue with the bundle data or the |
| Acceptable | | transfer extension data was encountered. The |
| | | sender SHOULD NOT retry the same bundle with |
| | | the same extensions. |
| | | |
| Extension | 0x05 | A failure processing the Transfer Extension |
| Failure | | Items has occurred. |
+------------+------+-----------------------------------------------+ +------------+------+-----------------------------------------------+
Table 6: XFER_REFUSE Reason Codes Table 6: XFER_REFUSE Reason Codes
The receiver MUST, for each transfer preceding the one to be refused, The receiver MUST, for each transfer preceding the one to be refused,
have either acknowledged all XFER_SEGMENTs or refused the bundle have either acknowledged all XFER_SEGMENT messages or refused the
transfer. bundle transfer.
The bundle transfer refusal MAY be sent before an entire data segment The bundle transfer refusal MAY be sent before an entire data segment
is received. If a sender receives a XFER_REFUSE message, the sender is received. If a sender receives a XFER_REFUSE message, the sender
MUST complete the transmission of any partially sent XFER_SEGMENT MUST complete the transmission of any partially sent XFER_SEGMENT
message. There is no way to interrupt an individual TCPCL message message. There is no way to interrupt an individual TCPCL message
partway through sending it. The sender MUST NOT commence partway through sending it. The sender MUST NOT commence
transmission of any further segments of the refused bundle transmission of any further segments of the refused bundle
subsequently. Note, however, that this requirement does not ensure subsequently. Note, however, that this requirement does not ensure
that an entity will not receive another XFER_SEGMENT for the same that an entity will not receive another XFER_SEGMENT for the same
bundle after transmitting a XFER_REFUSE message since messages MAY bundle after transmitting a XFER_REFUSE message since messages can
cross on the wire; if this happens, subsequent segments of the bundle cross on the wire; if this happens, subsequent segments of the bundle
SHALL also be refused with a XFER_REFUSE message. SHALL also be refused with a XFER_REFUSE message.
Note: If a bundle transmission is aborted in this way, the receiver Note: If a bundle transmission is aborted in this way, the receiver
MAY not receive a segment with the 'END' flag set to 1 for the does not receive a segment with the 'END' flag set to 1 for the
aborted bundle. The beginning of the next bundle is identified by aborted bundle. The beginning of the next bundle is identified by
the 'START' flag set to 1, indicating the start of a new transfer, the 'START' flag set to 1, indicating the start of a new transfer,
and with a distinct Transfer ID value. and with a distinct Transfer ID value.
5.2.5. Transfer Extension Items 5.2.5. Transfer Extension Items
Each of the Transfer Extension Items SHALL be encoded in an identical Each of the Transfer Extension Items SHALL be encoded in an identical
Type-Length-Value (TLV) container form as indicated in Figure 25. Type-Length-Value (TLV) container form as indicated in Figure 25.
The fields of the Transfer Extension Item are: The fields of the Transfer Extension Item are:
Flags: A one-octet field containing generic bit flags about the Item Flags: A one-octet field containing generic bit flags about the
Item, which are listed in Table 7. All reserved header flag bits Item, which are listed in Table 7. All reserved header flag bits
SHALL be set to 0 by the sender. All reserved header flag bits SHALL be set to 0 by the sender. All reserved header flag bits
SHALL be ignored by the receiver. If a TCPCL node receives a SHALL be ignored by the receiver. If a TCPCL node receives a
Transfer Extension Item with an unknown Item Type and the CRITICAL Transfer Extension Item with an unknown Item Type and the CRITICAL
flag is 1, the node SHALL refuse the transfer with an XFER_REFUSE flag is 1, the entity SHALL refuse the transfer with an
reason code of "Extension Failure". If the CRITICAL flag is 0, an XFER_REFUSE reason code of "Extension Failure". If the CRITICAL
entity SHALL skip over and ignore any item with an unknown Item flag is 0, an entity SHALL skip over and ignore any item with an
Type. unknown Item Type.
Item Type: A 16-bit unsigned integer field containing the type of Item Type: A 16-bit unsigned integer field containing the type of
the extension item. This specification allocates an IANA registry the extension item. This specification creates an IANA registry
for such codes (see Section 9.4). for such codes (see Section 9.4).
Item Length: A 16-bit unsigned integer field containing the number Item Length: A 16-bit unsigned integer field containing the number
of Item Value octets to follow. of Item Value octets to follow.
Item Value: A variable-length data field which is interpreted Item Value: A variable-length data field which is interpreted
according to the associated Item Type. This specification places according to the associated Item Type. This specification places
no restrictions on an extension's use of available Item Value no restrictions on an extension's use of available Item Value
data. Extension specifications SHOULD avoid the use of large data data. Extension specifications SHOULD avoid the use of large data
lengths, as the associated transfer cannot begin until the full lengths, as the associated transfer cannot begin until the full
skipping to change at page 43, line 28 skipping to change at page 46, line 28
The purpose of the Transfer Length extension is to allow entities to The purpose of the Transfer Length extension is to allow entities to
preemptively refuse bundles that would exceed their resources or to preemptively refuse bundles that would exceed their resources or to
prepare storage on the receiving node for the upcoming bundle data. prepare storage on the receiving node for the upcoming bundle data.
Multiple Transfer Length extension items SHALL NOT occur within the Multiple Transfer Length extension items SHALL NOT occur within the
same transfer. The lack of a Transfer Length extension item in any same transfer. The lack of a Transfer Length extension item in any
transfer SHALL NOT imply anything about the potential length of the transfer SHALL NOT imply anything about the potential length of the
transfer. The Transfer Length extension SHALL be assigned transfer transfer. The Transfer Length extension SHALL be assigned transfer
extension type ID 0x0001. extension type ID 0x0001.
If a transfer occupies exactly one segment (i.e. both START and END If a transfer occupies exactly one segment (i.e., both START and END
flags are 1) the Transfer Length extension SHOULD NOT be present. flags are 1) the Transfer Length extension SHOULD NOT be present.
The extension does not provide any additional information for single- The extension does not provide any additional information for single-
segment transfers. segment transfers.
The format of the Transfer Length data is as follows in Figure 26. The format of the Transfer Length data is as follows in Figure 26.
+----------------------+ +----------------------+
| Total Length (U64) | | Total Length (U64) |
+----------------------+ +----------------------+
Figure 26: Format of Transfer Length data Figure 26: Format of Transfer Length data
The fields of the Transfer Length extension are: The fields of the Transfer Length extension are:
Total Length: A 64-bit unsigned integer indicating the size of the Total Length: A 64-bit unsigned integer indicating the size of the
data-to-be-transferred. The Total Length field SHALL be treated data-to-be-transferred. The Total Length field SHALL be treated
as authoritative by the receiver. If, for whatever reason, the as authoritative by the receiver. If, for whatever reason, the
actual total length of bundle data received differs from the value actual total length of bundle data received differs from the value
indicated by the Total Length value, the receiver SHALL treat the indicated by the Total Length value, the receiver SHALL treat the
transmitted data as invalid. transmitted data as invalid and send an XFER_REFUSE with a Reason
Code of "Not Acceptable".
6. Session Termination 6. Session Termination
This section describes the procedures for ending a TCPCL session. This section describes the procedures for terminating a TCPCL
session. The purpose of terminating a session is to allow transfers
to complete before the session is closed but not allow any new
transfers to start. A session state change is necessary for this to
happen because transfers can be in-progress in either direction
(transfer stream) within a session. Waiting for a transfer to
complete in one direction does not control or influence the
possibility of a transfer in the other direction. Either peer of a
session can terminate an established session at any time.
6.1. Session Termination Message (SESS_TERM) 6.1. Session Termination Message (SESS_TERM)
To cleanly shut down a session, a SESS_TERM message SHALL be To cleanly terminate a session, a SESS_TERM message SHALL be
transmitted by either node at any point following complete transmitted by either node at any point following complete
transmission of any other message. When sent to initiate a transmission of any other message. When sent to initiate a
termination, the REPLY flag of a SESS_TERM message SHALL be 0. Upon termination, the REPLY flag of a SESS_TERM message SHALL be 0. Upon
receiving a SESS_TERM message after not sending a SESS_TERM message receiving a SESS_TERM message after not sending a SESS_TERM message
in the same session, an entity SHALL send an acknowledging SESS_TERM in the same session, an entity SHALL send an acknowledging SESS_TERM
message. When sent to acknowledge a termination, a SESS_TERM message message. When sent to acknowledge a termination, a SESS_TERM message
SHALL have identical data content from the message being acknowledged SHALL have identical data content from the message being acknowledged
except for the REPLY flag, which is set to 1 to indicate except for the REPLY flag, which is set to 1 to indicate
acknowledgement. acknowledgement.
After sending a SESS_TERM message, an entity MAY continue a possible Once a SESS_TERM message is sent the state of that TCPCL session
in-progress transfer in either direction. After sending a SESS_TERM changes to Ending. While the session is in the Ending state, an
message, an entity SHALL NOT begin any new outgoing transfer for the entity MAY finish an in-progress transfer in either direction. While
remainder of the session. After receving a SESS_TERM message, an the session is in the Ending state, an entity SHALL NOT begin any new
entity SHALL NOT accept any new incoming transfer for the remainder outgoing transfer for the remainder of the session. While the
of the session. session is in the Ending state, an entity SHALL NOT accept any new
incoming transfer for the remainder of the session.
Instead of following a clean shutdown sequence, after transmitting a Instead of following a clean termination sequence, after transmitting
SESS_TERM message an entity MAY immediately close the associated TCP a SESS_TERM message an entity MAY immediately close the associated
connection. When performing an unclean shutdown, a receiving node TCP connection. When performing an unclean termination, a receiving
SHOULD acknowledge all received data segments before closing the TCP node SHOULD acknowledge all received XFER_SEGMENTs with an XFER_ACK
connection. Not acknowledging received segments can result in before closing the TCP connection. Not acknowledging received
unnecessary retransmission. When performing an unclean shutodwn, a segments can result in unnecessary bundle or bundle fragment
retransmission. When performing an unclean termination, a
transmitting node SHALL treat either sending or receiving a SESS_TERM transmitting node SHALL treat either sending or receiving a SESS_TERM
message (i.e. before the final acknowledgment) as a failure of the message (i.e., before the final acknowledgment) as a failure of the
transfer. Any delay between request to close the TCP connection and transfer. Any delay between request to close the TCP connection and
actual closing of the connection (a "half-closed" state) MAY be actual closing of the connection (a "half-closed" state) MAY be
ignored by the TCPCL node. ignored by the TCPCL entity.
The TCPCL itself does not have any required behavior to respond to an
SESS_TERM based on its Reason Code; the termination is passed up as
an indication to the BP agent that the session state has changed. If
a termination has a Reason Code which is not decodable to the BP
agent, the agent SHOULD treat the termination as having an Unknown
reason.
The format of the SESS_TERM message is as follows in Figure 27. The format of the SESS_TERM message is as follows in Figure 27.
+-----------------------------+ +-----------------------------+
| Message Header | | Message Header |
+-----------------------------+ +-----------------------------+
| Message Flags (U8) | | Message Flags (U8) |
+-----------------------------+ +-----------------------------+
| Reason Code (U8) | | Reason Code (U8) |
+-----------------------------+ +-----------------------------+
skipping to change at page 45, line 41 skipping to change at page 49, line 19
| | | | | | | |
| Idle timeout | 0x01 | The session is being closed due to | | Idle timeout | 0x01 | The session is being closed due to |
| | | idleness. | | | | idleness. |
| | | | | | | |
| Version | 0x02 | The node cannot conform to the specified | | Version | 0x02 | The node cannot conform to the specified |
| mismatch | | TCPCL protocol version. | | mismatch | | TCPCL protocol version. |
| | | | | | | |
| Busy | 0x03 | The node is too busy to handle the current | | Busy | 0x03 | The node is too busy to handle the current |
| | | session. | | | | session. |
| | | | | | | |
| Contact | 0x04 | The node cannot interpret or negotiate | | Contact | 0x04 | The node cannot interpret or negotiate a |
| Failure | | contact header option. | | Failure | | Contact Header or SESS_INIT option. |
| | | | | | | |
| Resource | 0x05 | The node has run into some resource limit | | Resource | 0x05 | The node has run into some resource limit |
| Exhaustion | | and cannot continue the session. | | Exhaustion | | and cannot continue the session. |
+--------------+------+---------------------------------------------+ +--------------+------+---------------------------------------------+
Table 9: SESS_TERM Reason Codes Table 9: SESS_TERM Reason Codes
A session shutdown MAY occur immediately after transmission of a A session termination MAY occur immediately after transmission of a
contact header (and prior to any further message transmit). This Contact Header (and prior to any further message transmit). This
MAY, for example, be used to notify that the node is currently not can, for example, be used to notify that the entity is currently not
able or willing to communicate. However, an entity MUST always send able or willing to communicate. However, an entity MUST always send
the contact header to its peer before sending a SESS_TERM message. the Contact Header to its peer before sending a SESS_TERM message.
If reception of the contact header itself somehow fails (e.g. an If reception of the Contact Header itself somehow fails (e.g., an
invalid "magic string" is recevied), an entity SHALL close the TCP invalid "magic string" is received), an entity SHALL close the TCP
connection without sending a SESS_TERM message. If the content of connection without sending a SESS_TERM message. If the content of
the Session Extension Items data disagrees with the Session Extension the Session Extension Items data disagrees with the Session Extension
Length (i.e. the last Item claims to use more octets than are present Length (i.e., the last Item claims to use more octets than are
in the Session Extension Length), the reception of the contact header present in the Session Extension Length), the reception of the
is considered to have failed. SESS_INIT is considered to have failed.
If a session is to be terminated before a protocol message has If a session is to be terminated before a protocol message has
completed being sent, then the node MUST NOT transmit the SESS_TERM completed being sent, then the entity MUST NOT transmit the SESS_TERM
message but still SHALL close the TCP connection. Each TCPCL message message but still SHALL close the TCP connection. Each TCPCL message
is contiguous in the octet stream and has no ability to be cut short is contiguous in the octet stream and has no ability to be cut short
and/or preempted by an other message. This is particularly important and/or preempted by an other message. This is particularly important
when large segment sizes are being transmitted; either entire when large segment sizes are being transmitted; either entire
XFER_SEGMENT is sent before a SESS_TERM message or the connection is XFER_SEGMENT is sent before a SESS_TERM message or the connection is
simply terminated mid-XFER_SEGMENT. simply terminated mid-XFER_SEGMENT.
6.2. Idle Session Shutdown 6.2. Idle Session Shutdown
The protocol includes a provision for clean shutdown of idle The protocol includes a provision for clean termination of idle
sessions. Determining the length of time to wait before ending idle sessions. Determining the length of time to wait before ending idle
sessions, if they are to be closed at all, is an implementation and sessions, if they are to be closed at all, is an implementation and
configuration matter. configuration matter.
If there is a configured time to close idle links and if no TCPCL If there is a configured time to close idle links and if no TCPCL
messages (other than KEEPALIVE messages) has been received for at messages (other than KEEPALIVE messages) has been received for at
least that amount of time, then either node MAY terminate the session least that amount of time, then either node MAY terminate the session
by transmitting a SESS_TERM message indicating the reason code of by transmitting a SESS_TERM message indicating the reason code of
"Idle timeout" (as described in Table 9). "Idle timeout" (as described in Table 9).
skipping to change at page 47, line 9 skipping to change at page 50, line 38
assist the IETF in its decision processes in progressing drafts to assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations can features. Readers are advised to note that other implementations can
exist. exist.
An example implementation of the this draft of TCPCLv4 has been An example implementation of the this draft of TCPCLv4 has been
created as a GitHub project [github-dtn-bpbis-tcpcl] and is intented created as a GitHub project [github-dtn-bpbis-tcpcl] and is intended
to use as a proof-of-concept and as a possible source of to use as a proof-of-concept and as a possible source of
interoperability testing. This example implementation uses D-Bus as interoperability testing. This example implementation uses D-Bus as
the CL-BP Agent interface, so it only runs on hosts which provide the the CL-BP Agent interface, so it only runs on hosts which provide the
Python "dbus" library. Python "dbus" library.
8. Security Considerations 8. Security Considerations
This section separates security considerations into threat categories This section separates security considerations into threat categories
based on guidance of BCP 72 [RFC3552]. based on guidance of BCP 72 [RFC3552].
skipping to change at page 47, line 42 skipping to change at page 51, line 27
to-end bundle security. The bundle security mechanisms defined in to-end bundle security. The bundle security mechanisms defined in
[I-D.ietf-dtn-bpsec] are to be used instead. [I-D.ietf-dtn-bpsec] are to be used instead.
When used without TLS security, the TCPCL exposes all bundle data to When used without TLS security, the TCPCL exposes all bundle data to
passive eavesdroppers. This can be avoided by always using TLS, even passive eavesdroppers. This can be avoided by always using TLS, even
if authentication is not available (see Section 8.10). if authentication is not available (see Section 8.10).
8.3. Threat: TCPCL Version Downgrade 8.3. Threat: TCPCL Version Downgrade
When a TCPCL entity supports multiple versions of the protocol it is When a TCPCL entity supports multiple versions of the protocol it is
possible for a malicious or misconfigued peer to use an older version possible for a malicious or misconfigured peer to use an older
of TCPCL which does not support transport security. It is up to version of TCPCL which does not support transport security. A man-
security policies within each TCPCL node to ensure that the TCPCL in-the-middle attacker can also manipulate a Contact Header to
version in use meets transport security requirements. present a lower protocol version than desired.
It is up to security policies within each TCPCL node to ensure that
the negotiated TCPCL version meets transport security requirements.
8.4. Threat: Transport Security Stripping 8.4. Threat: Transport Security Stripping
When security policy allows non-TLS sessions, TCPCL does not protect When security policy allows non-TLS sessions, TCPCL does not protect
against active network attackers. It is possible for a man-in-the- against active network attackers. It is possible for a man-in-the-
middle attacker to set the CAN_TLS flag to 0 on either side of the middle attacker to set the CAN_TLS flag to 0 on either side of the
Contact Header exchange. This leads to the "SSL Stripping" attack Contact Header exchange. This leads to the "SSL Stripping" attack
described in [RFC7457]. described in [RFC7457].
The purpose of the CAN_TLS flag is to allow the use of TCPCL on The purpose of the CAN_TLS flag is to allow the use of TCPCL on
skipping to change at page 48, line 28 skipping to change at page 52, line 16
Even when using TLS to secure the TCPCL session, the actual Even when using TLS to secure the TCPCL session, the actual
ciphersuite negotiated between the TLS peers can be insecure. ciphersuite negotiated between the TLS peers can be insecure.
Recommendations for ciphersuite use are included in BCP 195 Recommendations for ciphersuite use are included in BCP 195
[RFC7525]. It is up to security policies within each TCPCL node to [RFC7525]. It is up to security policies within each TCPCL node to
ensure that the negotiated TLS ciphersuite meets transport security ensure that the negotiated TLS ciphersuite meets transport security
requirements. requirements.
8.6. Threat: Invalid Certificate Use 8.6. Threat: Invalid Certificate Use
There are many reasons, described in [RFC5280], why a certificate can Even when TLS itself is operating properly an attacker can attempt to
fail to validate, including using the certificate outside of its exploit vulnerabilities within certificate check algorithms or
valid time interval, using purposes for which it was not authorized, configuration to establish a secure TCPCL session using an invalid
or using it after it has been revoked by its CA. Validating a certificate. A BP agent treats the peer Node ID within a TCPCL
certificate is a complex task and may require network connectivity if session as authoritative and an invalid certificate exploit could
lead to bundle data leaking and/or denial of service to the Node ID
being impersonated. There are many reasons, described in [RFC5280],
why a certificate can fail to validate, including using the
certificate outside of its valid time interval, using purposes for
which it was not authorized, or using it after it has been revoked by
its CA. Validating a certificate is a complex task and can require
network connectivity outside of the primary TCPCL network path(s) if
a mechanism such as the Online Certificate Status Protocol (OCSP) is a mechanism such as the Online Certificate Status Protocol (OCSP) is
used by the CA. The configuration and use of particular certificate used by the CA. The configuration and use of particular certificate
validation methods are outside of the scope of this document. validation methods are outside of the scope of this document.
8.7. Threat: Symmetric Key Overuse 8.7. Threat: Symmetric Key Overuse
Even with a secure block cipher and securely-established session Even with a secure block cipher and securely-established session
keys, there are limits to the amount of plaintext which can be safely keys, there are limits to the amount of plaintext which can be safely
encrypted with a given set of keys as described in [AEAD-LIMITS]. encrypted with a given set of keys as described in [AEAD-LIMITS].
When permitted by the negotiated TLS version (see [RFC8446]), it is When permitted by the negotiated TLS version (see [RFC8446]), it is
advisable to take advantage of session key updates to avoid those advisable to take advantage of session key updates to avoid those
limits. When key updates are not possible, establishing new TCPCL/ limits. When key updates are not possible, renegotiation of the TLS
TLS session is an alternative to limit session key use. connection or establishing new TCPCL/TLS session are alternatives to
limit session key use.
8.8. Threat: BP Node Impersonation 8.8. Threat: BP Node Impersonation
The certificates exchanged by TLS enable authentication of peer host The certificates exchanged by TLS enable authentication of peer host
name and Node ID, but it is possible that a peer either not provide a name and Node ID, but it is possible that a peer either not provide a
valid certificate or that the certificate does not validate either valid certificate or that the certificate does not validate either
the host name or Node ID of the peer. Having a CA-validated the host name or Node ID of the peer. Having a CA-validated
certificate does not alone guarantee the identity of the network host certificate does not alone guarantee the identity of the network host
or BP node from which the certificate is provided; additional or BP node from which the certificate is provided; additional
validation procedures in Section 4.4.1 bind the host name or node ID validation procedures in Section 4.4.2 bind the host name or node ID
based on the contents of the certificate. based on the contents of the certificate.
The host name validation is a weaker form of authentication, because The host name validation is a weaker form of authentication, because
even if a peer is operating on an authenticated network host name it even if a peer is operating on an authenticated network host name it
can provide an invalid Node ID and cause bundles to be "leaked" to an can provide an invalid Node ID and cause bundles to be "leaked" to an
invalid node. Especially in DTN environments, network names and invalid node. Especially in DTN environments, network names and
addresses of nodes can be time-variable so binding a certificate to a addresses of nodes can be time-variable so binding a certificate to a
Node ID is a more stable identity. Trusting an authenticated host Node ID is a more stable identity. Trusting an authenticated host
name can be feasable on a network secured by a private CA but is not name can be feasible on a network secured by a private CA but is not
advisable on the Internet when using a variety of public CAs. advisable on the Internet when using a variety of public CAs.
Node ID validation ensures that the peer to which a bundle is Node ID validation ensures that the peer to which a bundle is
transferred is in fact the node which the BP Agent expects it to be. transferred is in fact the node which the BP Agent expects it to be.
It is a reasonable policy to skip host name validation if It is a reasonable policy to skip host name validation if
certificates can be guaranteed to validate the peer's Node ID. In certificates can be guaranteed to validate the peer's Node ID. In
circumstances where certificates can only be issued to network host circumstances where certificates can only be issued to network host
names, Node ID validation is not possible but it could be reasonable names, Node ID validation is not possible but it could be reasonable
to assume that a trusted host is not going to present an invalid Node to assume that a trusted host is not going to present an invalid Node
ID. ID. Determining of when a host name authentication can be trusted to
validate a Node ID is also a policy matter outside the scope of this
document.
8.9. Threat: Denial of Service 8.9. Threat: Denial of Service
The behaviors described in this section all amount to a potential The behaviors described in this section all amount to a potential
denial-of-service to a TCPCL entity. The denial-of-service could be denial-of-service to a TCPCL entity. The denial-of-service could be
limited to an individual TCPCL session, could affect other well- limited to an individual TCPCL session, could affect other well-
behaving sessions on an entity, or could affect all sessions on a behaving sessions on an entity, or could affect all sessions on a
host. host.
A malicious entity can continually establish TCPCL sessions and delay A malicious entity can continually establish TCPCL sessions and delay
skipping to change at page 49, line 49 skipping to change at page 53, line 46
to be incorrectly behaving within TCPCL. to be incorrectly behaving within TCPCL.
An entity can send a large amount of data over a TCPCL session, An entity can send a large amount of data over a TCPCL session,
requiring the receiving entity to handle the data. The victim entity requiring the receiving entity to handle the data. The victim entity
can attempt to stop the flood of data by sending an XFER_REFUSE can attempt to stop the flood of data by sending an XFER_REFUSE
message, or forcibly terminate the session. message, or forcibly terminate the session.
There is the possibility of a "data dribble" attack in which an There is the possibility of a "data dribble" attack in which an
entity presents a very small Segment MRU which causes transfers to be entity presents a very small Segment MRU which causes transfers to be
split among an large number of very small segments and causes the split among an large number of very small segments and causes the
segmentation overhead to overwhelm the network througput. Similarly, segmentation overhead to overwhelm the actual bundle data segments.
an entity can present a very small Transfer MRU which will cause Similarly, an entity can present a very small Transfer MRU which will
resources to be wasted on establishing and upkeeping a TCPCL session cause resources to be wasted on establishment and upkeep of a TCPCL
over which a bundle could never be transferred. The victim entity session over which a bundle could never be transferred. The victim
can terminate the session during the negotiation of Section 4.7 if entity can terminate the session during the negotiation of
the MRUs are unacceptable. Section 4.7 if the MRUs are unacceptable.
The keepalive mechanism can be abused to waste throughput within a The keepalive mechanism can be abused to waste throughput within a
network link which would otherwise be usable for bundle network link which would otherwise be usable for bundle
transmissions. Due to the quantization of the Keepalive Interval transmissions. Due to the quantization of the Keepalive Interval
parameter the smallest Session Keepalive is one second, which should parameter the smallest Session Keepalive is one second, which should
be long enough to not flood the link. The victim entity can be long enough to not flood the link. The victim entity can
terminate the session during the negotiation of Section 4.7 if the terminate the session during the negotiation of Section 4.7 if the
Keepalive Interval is unacceptable. Keepalive Interval is unacceptable.
Finally, an attacker or a misconfigured entity can cause issues at
the TCP connection which will cause unnecessary TCP retransmissions
or connection resets, effectively denying the use of the overlying
TCPCL session.
8.10. Alternate Uses of TLS 8.10. Alternate Uses of TLS
This specification makes use of public key infrastructure (PKI) This specification makes use of X.509 PKI certificate validation and
certificate validation and authentication within TLS. There are authentication within TLS. There are alternate uses of TLS which are
alternate uses of TLS which are not necessarily incompatible with the not necessarily incompatible with the security goals of this
security goals of this specification, but are outside of the scope of specification, but are outside of the scope of this document. The
this document. following subsections give examples of alternate TLS uses.
8.10.1. TLS Without Authentication 8.10.1. TLS Without Authentication
In environments where PKI is available but there are restrictions on In environments where PKI is available but there are restrictions on
the issuance of certificates (including the contents of the issuance of certificates (including the contents of
certificates), it may be possible to make use of TLS in a way which certificates), it may be possible to make use of TLS in a way which
authenticates only the passive entity of a TCPCL session or which authenticates only the passive entity of a TCPCL session or which
does not authenticate either entity. Using TLS in a way which does does not authenticate either entity. Using TLS in a way which does
not authenticate both peer entities of each TCPCL session is outside not authenticate both peer entities of each TCPCL session is outside
of the scope of this document. of the scope of this document.
8.10.2. Non-Certificate TLS Use 8.10.2. Non-Certificate TLS Use
In environments where PKI is unavailable, alternate uses of TLS which In environments where PKI is unavailable, alternate uses of TLS which
do not require certificates such as [RFC5489] are available and can do not require certificates such as pre-shared key (PSK)
be used to ensure confidentality within TCPCL. Using non-PKI node authentication [RFC5489] and the use of raw public keys [RFC7250] are
authentication methods is outside of the scope of this document. available and can be used to ensure confidentiality within TCPCL.
Using non-PKI node authentication methods is outside of the scope of
this document.
8.11. Predictability of Transfer IDs
The only requirement on Transfer IDs is that they be unique with each
session from the sending peer only. The trivial algorithm of the
first transfer starting at zero and later transfers incrementing by
one causes absolutely predictable Transfer IDs. Even when a TCPCL
session is not TLS secured and there is a man-in-the-middle attacker
causing denial of service with XFER_REFUSE messages, it is not
possible to preemptively refuse a transfer so there is no benefit in
having unpredictable Transfer IDs within a session.
9. IANA Considerations 9. IANA Considerations
Registration procedures referred to in this section are defined in Registration procedures referred to in this section are defined in
[RFC8126]. [RFC8126].
Some of the registries have been defined as version specific to Some of the registries have been defined as version specific to
TCPCLv4, and imports some or all codepoints from TCPCLv3. This was TCPCLv4, and imports some or all codepoints from TCPCLv3. This was
done to disambiguate the use of these codepoints between TCPCLv3 and done to disambiguate the use of these codepoints between TCPCLv3 and
TCPCLv4 while preserving the semantics of some of the codepoints. TCPCLv4 while preserving the semantics of some of the codepoints.
skipping to change at page 54, line 36 skipping to change at page 58, line 36
4 Message Types" and initialize it with the contents of Table 12. 4 Message Types" and initialize it with the contents of Table 12.
The registration procedure is RFC Required within the lower range The registration procedure is RFC Required within the lower range
0x01--0xEF. Values in the range 0xF0--0xFF are reserved for use on 0x01--0xEF. Values in the range 0xF0--0xFF are reserved for use on
private networks for functions not published to the IANA. private networks for functions not published to the IANA.
Specifications of new message types need to define the encoding of Specifications of new message types need to define the encoding of
the message data as well as the purpose and relationship of the new the message data as well as the purpose and relationship of the new
message to existing session/transfer state within the baseline message to existing session/transfer state within the baseline
message sequencing. The use of new message types need to be message sequencing. The use of new message types need to be
negotiated between TCPCL entities within a session (using the session negotiated between TCPCL entities within a session (using the session
extension mechanism) so that the receving entity can properly decode extension mechanism) so that the receiving entity can properly decode
all message types used in the session. all message types used in the session.
Expert(s) are encouraged to favor new session/transfer extension Expert(s) are encouraged to favor new session/transfer extension
types over new message types. TCPCL messages are not self- types over new message types. TCPCL messages are not self-
delimiting, so care must be taken in introducing new message types. delimiting, so care must be taken in introducing new message types.
If an entity receives an unknown message type the only thing that can If an entity receives an unknown message type the only thing that can
be done is to send a MSG_REJECT and close the TCP connection; not be done is to send a MSG_REJECT and close the TCP connection; not
even a clean termination can be done at that point. even a clean termination can be done at that point.
+------------+--------------------------+ +------------+--------------------------+
skipping to change at page 55, line 45 skipping to change at page 59, line 45
IANA will create, under the "Bundle Protocol" registry [IANA-BUNDLE], IANA will create, under the "Bundle Protocol" registry [IANA-BUNDLE],
a sub-registry titled "Bundle Protocol TCP Convergence-Layer Version a sub-registry titled "Bundle Protocol TCP Convergence-Layer Version
4 XFER_REFUSE Reason Codes" and initialize it with the contents of 4 XFER_REFUSE Reason Codes" and initialize it with the contents of
Table 13. The registration procedure is Specification Required Table 13. The registration procedure is Specification Required
within the lower range 0x00--0xEF. Values in the range 0xF0--0xFF within the lower range 0x00--0xEF. Values in the range 0xF0--0xFF
are reserved for use on private networks for functions not published are reserved for use on private networks for functions not published
to the IANA. to the IANA.
Specifications of new XFER_REFUSE reason codes need to define the Specifications of new XFER_REFUSE reason codes need to define the
meaning of the reason and disambiguate it with pre-exisiting reasons. meaning of the reason and disambiguate it with pre-existing reasons.
Each refusal reason needs to be usable by the receving BP Agent to Each refusal reason needs to be usable by the receiving BP Agent to
make retransmission or re-routing decisions. make retransmission or re-routing decisions.
Expert(s) are encouraged to be biased towards approving registrations Expert(s) are encouraged to be biased towards approving registrations
unless they are abusive, frivolous, or actively harmful (not merely unless they are abusive, frivolous, or actively harmful (not merely
aesthetically displeasing, or architecturally dubious). aesthetically displeasing, or architecturally dubious).
+------------+--------------------------+ +------------+--------------------------+
| Code | Refusal Reason | | Code | Refusal Reason |
+------------+--------------------------+ +------------+--------------------------+
| 0x00 | Unknown | | 0x00 | Unknown |
| | | | | |
| 0x01 | Extension Failure | | 0x01 | Completed |
| | | | | |
| 0x02 | Completed | | 0x02 | No Resources |
| | | | | |
| 0x03 | No Resources | | 0x03 | Retransmit |
| | | | | |
| 0x04 | Retransmit | | 0x04 | Not Acceptable |
| | | | | |
| 0x05--0xEF | Unassigned | | 0x05 | Extension Failure |
| | |
| 0x06--0xEF | Unassigned |
| | | | | |
| 0xF0--0xFF | Private/Experimental Use | | 0xF0--0xFF | Private/Experimental Use |
+------------+--------------------------+ +------------+--------------------------+
Table 13: XFER_REFUSE Reason Codes Table 13: XFER_REFUSE Reason Codes
9.7. SESS_TERM Reason Codes 9.7. SESS_TERM Reason Codes
EDITOR NOTE: sub-registry to-be-created upon publication of this EDITOR NOTE: sub-registry to-be-created upon publication of this
specification. specification.
IANA will create, under the "Bundle Protocol" registry [IANA-BUNDLE], IANA will create, under the "Bundle Protocol" registry [IANA-BUNDLE],
a sub-registry titled "Bundle Protocol TCP Convergence-Layer Version a sub-registry titled "Bundle Protocol TCP Convergence-Layer Version
4 SESS_TERM Reason Codes" and initialize it with the contents of 4 SESS_TERM Reason Codes" and initialize it with the contents of
Table 14. The registration procedure is Specification Required Table 14. The registration procedure is Specification Required
within the lower range 0x00--0xEF. Values in the range 0xF0--0xFF within the lower range 0x00--0xEF. Values in the range 0xF0--0xFF
are reserved for use on private networks for functions not published are reserved for use on private networks for functions not published
to the IANA. to the IANA.
Specifications of new SESS_TERM reason codes need to define the Specifications of new SESS_TERM reason codes need to define the
meaning of the reason and disambiguate it with pre-exisiting reasons. meaning of the reason and disambiguate it with pre-existing reasons.
Each termination reason needs to be usable by the receving BP Agent Each termination reason needs to be usable by the receiving BP Agent
to make re-connection decisions. to make re-connection decisions.
Expert(s) are encouraged to be biased towards approving registrations Expert(s) are encouraged to be biased towards approving registrations
unless they are abusive, frivolous, or actively harmful (not merely unless they are abusive, frivolous, or actively harmful (not merely
aesthetically displeasing, or architecturally dubious). aesthetically displeasing, or architecturally dubious).
+------------+--------------------------+ +------------+--------------------------+
| Code | Termination Reason | | Code | Termination Reason |
+------------+--------------------------+ +------------+--------------------------+
| 0x00 | Unknown | | 0x00 | Unknown |
skipping to change at page 57, line 41 skipping to change at page 61, line 41
IANA will create, under the "Bundle Protocol" registry [IANA-BUNDLE], IANA will create, under the "Bundle Protocol" registry [IANA-BUNDLE],
a sub-registry titled "Bundle Protocol TCP Convergence-Layer Version a sub-registry titled "Bundle Protocol TCP Convergence-Layer Version
4 MSG_REJECT Reason Codes" and initialize it with the contents of 4 MSG_REJECT Reason Codes" and initialize it with the contents of
Table 15. The registration procedure is Specification Required Table 15. The registration procedure is Specification Required
within the lower range 0x01--0xEF. Values in the range 0xF0--0xFF within the lower range 0x01--0xEF. Values in the range 0xF0--0xFF
are reserved for use on private networks for functions not published are reserved for use on private networks for functions not published
to the IANA. to the IANA.
Specifications of new MSG_REJECT reason codes need to define the Specifications of new MSG_REJECT reason codes need to define the
meaning of the reason and disambiguate it with pre-exisiting reasons. meaning of the reason and disambiguate it with pre-existing reasons.
Each rejection reason needs to be usable by the receving TCPCL Entity Each rejection reason needs to be usable by the receiving TCPCL
to make message sequencing and/or session termination decisions. Entity to make message sequencing and/or session termination
decisions.
Expert(s) are encouraged to be biased towards approving registrations Expert(s) are encouraged to be biased towards approving registrations
unless they are abusive, frivolous, or actively harmful (not merely unless they are abusive, frivolous, or actively harmful (not merely
aesthetically displeasing, or architecturally dubious). aesthetically displeasing, or architecturally dubious).
+------------+--------------------------+ +------------+--------------------------+
| Code | Rejection Reason | | Code | Rejection Reason |
+------------+--------------------------+ +------------+--------------------------+
| 0x00 | reserved | | 0x00 | reserved |
| | | | | |
skipping to change at page 58, line 34 skipping to change at page 62, line 34
This specification is based on comments on implementation of This specification is based on comments on implementation of
[RFC7242] provided from Scott Burleigh. [RFC7242] provided from Scott Burleigh.
11. References 11. References
11.1. Normative References 11.1. Normative References
[I-D.ietf-dtn-bpbis] [I-D.ietf-dtn-bpbis]
Burleigh, S., Fall, K., and E. Birrane, "Bundle Protocol Burleigh, S., Fall, K., and E. Birrane, "Bundle Protocol
Version 7", draft-ietf-dtn-bpbis-19 (work in progress), Version 7", draft-ietf-dtn-bpbis-23 (work in progress),
January 2020. February 2020.
[IANA-BUNDLE] [IANA-BUNDLE]
IANA, "Bundle Protocol", IANA, "Bundle Protocol",
<https://www.iana.org/assignments/bundle/>. <https://www.iana.org/assignments/bundle/>.
[IANA-PORTS] [IANA-PORTS]
IANA, "Service Name and Transport Protocol Port Number IANA, "Service Name and Transport Protocol Port Number
Registry", <https://www.iana.org/assignments/service- Registry", <https://www.iana.org/assignments/service-
names-port-numbers/>. names-port-numbers/>.
skipping to change at page 59, line 20 skipping to change at page 63, line 20
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005, RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>. <https://www.rfc-editor.org/info/rfc3986>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>. <https://www.rfc-editor.org/info/rfc5280>.
[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS) [RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066, Extensions: Extension Definitions", RFC 6066,
DOI 10.17487/RFC6066, January 2011, DOI 10.17487/RFC6066, January 2011,
<https://www.rfc-editor.org/info/rfc6066>. <https://www.rfc-editor.org/info/rfc6066>.
skipping to change at page 60, line 26 skipping to change at page 64, line 22
Luykx, A. and K. Paterson, "Limits on Authenticated Luykx, A. and K. Paterson, "Limits on Authenticated
Encryption Use in TLS", August 2017, Encryption Use in TLS", August 2017,
<http://www.isg.rhul.ac.uk/~kp/TLS-AEbounds.pdf>. <http://www.isg.rhul.ac.uk/~kp/TLS-AEbounds.pdf>.
[github-dtn-bpbis-tcpcl] [github-dtn-bpbis-tcpcl]
Sipos, B., "TCPCL Example Implementation", Sipos, B., "TCPCL Example Implementation",
<https://github.com/BSipos-RKF/dtn-bpbis-tcpcl/>. <https://github.com/BSipos-RKF/dtn-bpbis-tcpcl/>.
[I-D.ietf-dtn-bpsec] [I-D.ietf-dtn-bpsec]
Birrane, E. and K. McKeever, "Bundle Protocol Security Birrane, E. and K. McKeever, "Bundle Protocol Security
Specification", draft-ietf-dtn-bpsec-15 (work in Specification", draft-ietf-dtn-bpsec-21 (work in
progress), January 2020. progress), March 2020.
[RFC2595] Newman, C., "Using TLS with IMAP, POP3 and ACAP", [RFC2595] Newman, C., "Using TLS with IMAP, POP3 and ACAP",
RFC 2595, DOI 10.17487/RFC2595, June 1999, RFC 2595, DOI 10.17487/RFC2595, June 1999,
<https://www.rfc-editor.org/info/rfc2595>. <https://www.rfc-editor.org/info/rfc2595>.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC [RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552, Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003, DOI 10.17487/RFC3552, July 2003,
<https://www.rfc-editor.org/info/rfc3552>. <https://www.rfc-editor.org/info/rfc3552>.
skipping to change at page 61, line 17 skipping to change at page 65, line 17
Networking (DTN) Bundle Protocol and Licklider Networking (DTN) Bundle Protocol and Licklider
Transmission Protocol (LTP)", RFC 7122, Transmission Protocol (LTP)", RFC 7122,
DOI 10.17487/RFC7122, March 2014, DOI 10.17487/RFC7122, March 2014,
<https://www.rfc-editor.org/info/rfc7122>. <https://www.rfc-editor.org/info/rfc7122>.
[RFC7242] Demmer, M., Ott, J., and S. Perreault, "Delay-Tolerant [RFC7242] Demmer, M., Ott, J., and S. Perreault, "Delay-Tolerant
Networking TCP Convergence-Layer Protocol", RFC 7242, Networking TCP Convergence-Layer Protocol", RFC 7242,
DOI 10.17487/RFC7242, June 2014, DOI 10.17487/RFC7242, June 2014,
<https://www.rfc-editor.org/info/rfc7242>. <https://www.rfc-editor.org/info/rfc7242>.
[RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
Weiler, S., and T. Kivinen, "Using Raw Public Keys in
Transport Layer Security (TLS) and Datagram Transport
Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
June 2014, <https://www.rfc-editor.org/info/rfc7250>.
[RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection [RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection
Most of the Time", RFC 7435, DOI 10.17487/RFC7435, Most of the Time", RFC 7435, DOI 10.17487/RFC7435,
December 2014, <https://www.rfc-editor.org/info/rfc7435>. December 2014, <https://www.rfc-editor.org/info/rfc7435>.
[RFC7457] Sheffer, Y., Holz, R., and P. Saint-Andre, "Summarizing [RFC7457] Sheffer, Y., Holz, R., and P. Saint-Andre, "Summarizing
Known Attacks on Transport Layer Security (TLS) and Known Attacks on Transport Layer Security (TLS) and
Datagram TLS (DTLS)", RFC 7457, DOI 10.17487/RFC7457, Datagram TLS (DTLS)", RFC 7457, DOI 10.17487/RFC7457,
February 2015, <https://www.rfc-editor.org/info/rfc7457>. February 2015, <https://www.rfc-editor.org/info/rfc7457>.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running [RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205, Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016, RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/info/rfc7942>. <https://www.rfc-editor.org/info/rfc7942>.
Appendix A. Significant changes from RFC7242 Appendix A. Significant changes from RFC7242
The areas in which changes from [RFC7242] have been made to existing The areas in which changes from [RFC7242] have been made to existing
headers and messages are: headers and messages are:
o Split contact header into pre-TLS protocol negotiation and o Split Contact Header into pre-TLS protocol negotiation and
SESS_INIT parameter negotiation. The contact header is now fixed- SESS_INIT parameter negotiation. The Contact Header is now fixed-
length. length.
o Changed contact header content to limit number of negotiated o Changed Contact Header content to limit number of negotiated
options. options.
o Added session option to negotiate maximum segment size (per each o Added session option to negotiate maximum segment size (per each
direction). direction).
o Renamed "Endpoint ID" to "Node ID" to conform with BPv7 o Renamed "Endpoint ID" to "Node ID" to conform with BPv7
terminology. terminology.
o Added session extension capability. o Added session extension capability.
skipping to change at page 62, line 20 skipping to change at page 66, line 28
o Expanded Message Header to octet-aligned fields instead of bit- o Expanded Message Header to octet-aligned fields instead of bit-
packing. packing.
o Added a bundle transfer identification number to all bundle- o Added a bundle transfer identification number to all bundle-
related messages (XFER_SEGMENT, XFER_ACK, XFER_REFUSE). related messages (XFER_SEGMENT, XFER_ACK, XFER_REFUSE).
o Use flags in XFER_ACK to mirror flags from XFER_SEGMENT. o Use flags in XFER_ACK to mirror flags from XFER_SEGMENT.
o Removed all uses of SDNV fields and replaced with fixed-bit-length o Removed all uses of SDNV fields and replaced with fixed-bit-length
fields. (network byte order) fields.
o Renamed SHUTDOWN to SESS_TERM to deconflict term "shutdown" o Renamed SHUTDOWN to SESS_TERM to deconflict term "shutdown"
related to TCP connections. related to TCP connections.
o Removed the notion of a re-connection delay parameter. o Removed the notion of a re-connection delay parameter.
The areas in which extensions from [RFC7242] have been made as new The areas in which extensions from [RFC7242] have been made as new
messages and codes are: messages and codes are:
o Added contact negotiation failure SESS_TERM reason code. o Added contact negotiation failure SESS_TERM reason code.
o Added MSG_REJECT message to indicate an unknown or unhandled o Added MSG_REJECT message to indicate an unknown or unhandled
message was received. message was received.
o Added TLS session security mechanism. o Added TLS connection security mechanism.
o Added Resource Exhaustion SESS_TERM reason code. o Added Resource Exhaustion SESS_TERM reason code.
Authors' Addresses Authors' Addresses
Brian Sipos Brian Sipos
RKF Engineering Solutions, LLC RKF Engineering Solutions, LLC
7500 Old Georgetown Road 7500 Old Georgetown Road
Suite 1275 Suite 1275
Bethesda, MD 20814-6198 Bethesda, MD 20814-6198
United States of America United States of America
Email: BSipos@rkf-eng.com Email: BSipos@rkf-eng.com
Michael Demmer Michael Demmer
University of California, Berkeley University of California, Berkeley
Computer Science Division Computer Science Division
445 Soda Hall 445 Soda Hall
Berkeley, CA 94720-1776 Berkeley, CA 94720-1776
United States of America United States of America
Email: demmer@cs.berkeley.edu Email: demmer@cs.berkeley.edu
Joerg Ott Joerg Ott
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