draft-ietf-dtn-tcpclv4-07.txt   draft-ietf-dtn-tcpclv4-08.txt 
Delay Tolerant Networking B. Sipos Delay Tolerant Networking B. Sipos
Internet-Draft RKF Engineering Internet-Draft RKF Engineering
Obsoletes: 7242 (if approved) M. Demmer Obsoletes: 7242 (if approved) M. Demmer
Intended status: Standards Track UC Berkeley Intended status: Standards Track UC Berkeley
Expires: September 21, 2018 J. Ott Expires: November 21, 2018 J. Ott
Aalto University Aalto University
S. Perreault S. Perreault
Mar 20, 2018 May 20, 2018
Delay-Tolerant Networking TCP Convergence Layer Protocol Version 4 Delay-Tolerant Networking TCP Convergence Layer Protocol Version 4
draft-ietf-dtn-tcpclv4-07 draft-ietf-dtn-tcpclv4-08
Abstract Abstract
This document describes a revised protocol for the TCP-based This document describes a revised protocol for the TCP-based
convergence layer (TCPCL) for Delay-Tolerant Networking (DTN). The convergence layer (TCPCL) for Delay-Tolerant Networking (DTN). The
protocol revision is based on implementation issues in the original protocol revision is based on implementation issues in the original
TCPCL Version 3 and updates to the Bundle Protocol contents, TCPCL Version 3 and updates to the Bundle Protocol contents,
encodings, and convergence layer requirements in Bundle Protocol encodings, and convergence layer requirements in Bundle Protocol
Version 7. Specifically, the TCPCLv4 uses CBOR-encoded BPv7 bundles Version 7. Specifically, the TCPCLv4 uses CBOR-encoded BPv7 bundles
as its service data unit being transported and provides a reliable as its service data unit being transported and provides a reliable
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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 September 21, 2018. This Internet-Draft will expire on November 21, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 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
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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. Convergence Layer Services . . . . . . . . . . . . . . . 4 1.1. Convergence Layer Services . . . . . . . . . . . . . . . 4
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 6 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 6
2.1. Definitions Specific to the TCPCL Protocol . . . . . . . 6 2.1. Definitions Specific to the TCPCL Protocol . . . . . . . 6
3. General Protocol Description . . . . . . . . . . . . . . . . 7 3. General Protocol Description . . . . . . . . . . . . . . . . 8
3.1. TCPCL Session Overview . . . . . . . . . . . . . . . . . 7 3.1. TCPCL Session Overview . . . . . . . . . . . . . . . . . 8
3.2. Example Message Exchange . . . . . . . . . . . . . . . . 8 3.2. Transfer Segmentation Policies . . . . . . . . . . . . . 10
4. Session Establishment . . . . . . . . . . . . . . . . . . . . 10 3.3. Example Message Exchange . . . . . . . . . . . . . . . . 11
4.1. TCP Connection . . . . . . . . . . . . . . . . . . . . . 11 4. Session Establishment . . . . . . . . . . . . . . . . . . . . 13
4.2. Contact Header . . . . . . . . . . . . . . . . . . . . . 11 4.1. TCP Connection . . . . . . . . . . . . . . . . . . . . . 13
4.2.1. Header Extension Items . . . . . . . . . . . . . . . 14 4.2. Contact Header . . . . . . . . . . . . . . . . . . . . . 13
4.3. Validation and Parameter Negotiation . . . . . . . . . . 15 4.3. Contact Validation and Negotiation . . . . . . . . . . . 14
4.3.1. Reactive Fragmentation Extension . . . . . . . . . . 16 4.4. Session Security . . . . . . . . . . . . . . . . . . . . 15
4.4. Session Security . . . . . . . . . . . . . . . . . . . . 17 4.4.1. TLS Handshake Result . . . . . . . . . . . . . . . . 16
4.4.1. TLS Handshake Result . . . . . . . . . . . . . . . . 18 4.4.2. Example TLS Initiation . . . . . . . . . . . . . . . 16
4.4.2. Example TLS Initiation . . . . . . . . . . . . . . . 18 4.5. Message Type Codes . . . . . . . . . . . . . . . . . . . 17
5. Established Session Operation . . . . . . . . . . . . . . . . 19 4.6. Session Initialization Message (SESS_INIT) . . . . . . . 18
5.1. Message Type Codes . . . . . . . . . . . . . . . . . . . 19 4.6.1. Session Extension Items . . . . . . . . . . . . . . . 20
5.2. Upkeep and Status Messages . . . . . . . . . . . . . . . 20 4.7. Session Parameter Negotiation . . . . . . . . . . . . . . 21
5.2.1. Session Upkeep (KEEPALIVE) . . . . . . . . . . . . . 20 5. Established Session Operation . . . . . . . . . . . . . . . . 22
5.2.2. Message Rejection (MSG_REJECT) . . . . . . . . . . . 21 5.1. Upkeep and Status Messages . . . . . . . . . . . . . . . 22
5.3. Bundle Transfer . . . . . . . . . . . . . . . . . . . . . 22 5.1.1. Session Upkeep (KEEPALIVE) . . . . . . . . . . . . . 22
5.3.1. Bundle Transfer ID . . . . . . . . . . . . . . . . . 23 5.1.2. Message Rejection (MSG_REJECT) . . . . . . . . . . . 23
5.3.2. Transfer Initialization (XFER_INIT) . . . . . . . . . 23 5.2. Bundle Transfer . . . . . . . . . . . . . . . . . . . . . 24
5.3.3. Data Transmission (XFER_SEGMENT) . . . . . . . . . . 24 5.2.1. Bundle Transfer ID . . . . . . . . . . . . . . . . . 24
5.3.4. Data Acknowledgments (XFER_ACK) . . . . . . . . . . . 26 5.2.2. Transfer Initialization (XFER_INIT) . . . . . . . . . 25
5.3.5. Transfer Refusal (XFER_REFUSE) . . . . . . . . . . . 27 5.2.3. Data Transmission (XFER_SEGMENT) . . . . . . . . . . 28
6. Session Termination . . . . . . . . . . . . . . . . . . . . . 29 5.2.4. Data Acknowledgments (XFER_ACK) . . . . . . . . . . . 29
6.1. Shutdown Message (SHUTDOWN) . . . . . . . . . . . . . . . 29 5.2.5. Transfer Refusal (XFER_REFUSE) . . . . . . . . . . . 30
6.2. Idle Session Shutdown . . . . . . . . . . . . . . . . . . 32 6. Session Termination . . . . . . . . . . . . . . . . . . . . . 32
7. Security Considerations . . . . . . . . . . . . . . . . . . . 32 6.1. Session Termination Message (SESS_TERM) . . . . . . . . . 32
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33 6.2. Idle Session Shutdown . . . . . . . . . . . . . . . . . . 35
8.1. Port Number . . . . . . . . . . . . . . . . . . . . . . . 34 7. Implementation Status . . . . . . . . . . . . . . . . . . . . 35
8.2. Protocol Versions . . . . . . . . . . . . . . . . . . . . 34 8. Security Considerations . . . . . . . . . . . . . . . . . . . 35
8.3. Header Extension Types . . . . . . . . . . . . . . . . . 35 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
8.4. Message Types . . . . . . . . . . . . . . . . . . . . . . 35 9.1. Port Number . . . . . . . . . . . . . . . . . . . . . . . 37
8.5. XFER_REFUSE Reason Codes . . . . . . . . . . . . . . . . 36 9.2. Protocol Versions . . . . . . . . . . . . . . . . . . . . 37
8.6. SHUTDOWN Reason Codes . . . . . . . . . . . . . . . . . . 37 9.3. Session Extension Types . . . . . . . . . . . . . . . . . 38
8.7. MSG_REJECT Reason Codes . . . . . . . . . . . . . . . . . 38 9.4. Transfer Extension Types . . . . . . . . . . . . . . . . 38
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 38 9.5. Message Types . . . . . . . . . . . . . . . . . . . . . . 39
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 38 9.6. XFER_REFUSE Reason Codes . . . . . . . . . . . . . . . . 40
10.1. Normative References . . . . . . . . . . . . . . . . . . 38 9.7. SESS_TERM Reason Codes . . . . . . . . . . . . . . . . . 41
10.2. Informative References . . . . . . . . . . . . . . . . . 39 9.8. MSG_REJECT Reason Codes . . . . . . . . . . . . . . . . . 42
Appendix A. Significant changes from RFC7242 . . . . . . . . . . 40 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 42
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 42
11.1. Normative References . . . . . . . . . . . . . . . . . . 42
11.2. Informative References . . . . . . . . . . . . . . . . . 43
Appendix A. Significant changes from RFC7242 . . . . . . . . . . 44
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 45
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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This document describes the format of the protocol data units passed This document describes the format of the protocol data units passed
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 [RFC5050] and [I-D.ietf-dtn-bpbis]. This are defined elsewhere in [RFC5050] and [I-D.ietf-dtn-bpbis]. This
includes the concept of bundle fragmentation or bundle includes the concept of bundle fragmentation or bundle
encapsulation. The TCPCL transfers bundles as opaque data blocks. encapsulation. The TCPCL transfers bundles as opaque data blocks.
o Mechanisms for locating or identifying other bundle nodes within o Mechanisms for locating or identifying other bundle entities
an internet. within an internet.
1.1. Convergence Layer Services 1.1. 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: the overlaying Bundle Protocol agent:
Attempt Session The TCPCL allows a BP agent to pre-emptively attempt Attempt Session The TCPCL allows a BP agent to pre-emptively attempt
to establish a TCPCL session with a peer node. Each session to establish a TCPCL session with a peer entity. Each session
attempt can send a different set of contact header parameters as attempt can send a different set of contact header parameters as
directed by the BP agent. directed by the BP agent.
Shutdown Session The TCPCL allows a BP agent to pre-emptively Shutdown Session The TCPCL allows a BP agent to pre-emptively
shutdown an established TCPCL session with a peer node. The shutdown an established TCPCL session with a peer entity. The
shutdown request is on a per-session basis. shutdown request is on a per-session basis.
Session is Started The TCPCL supports indication when a new TCP Session is Started The TCPCL supports indication when a new TCP
connection has been started (as either client or server) before connection has been started (as either client or server) before
the TCPCL handshake has begun. the TCPCL handshake has begun.
Session is Established The TCPCL supports indication when a new Session is Established The TCPCL supports indication when a new
session has been fully established and is ready for its first session has been fully established and is ready for its first
transfer. transfer.
Session is Shutdown The TCPCL supports indication when an Session is Shutdown The TCPCL supports indication when an
established session has been ended by normal exchange of SHUTDOWN established session has been ended by normal exchange of SESS_TERM
messages with all transfers completed. messages with all transfers completed.
Session is Failed The TCPCL supports indication when a session Session is Failed The TCPCL supports indication when a session
fails, either during contact negotiation, TLS negotiation, or fails, either during contact negotiation, TLS negotiation, or
after establishement for any reason other than normal shutdown. after establishement for any reason other than normal shutdown.
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, the CL
does not necessarily perform any per-session or inter-session 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 Availability Because TCPCL transmits serially over a Transmission Availability Because TCPCL transmits serially over a
TCP connection, it suffers from "head of queue blocking" and TCP connection, it suffers from "head of queue blocking" and
supports indication of when an established session is live-but- supports indication of when an established session is live-but-
idle (i.e. available for immediate transfer start) or live-and- idle (i.e. available for immediate transfer start) or live-and-
not-idle. not-idle.
Transmission Success The TCPCL supports positive indication when a Transmission Success The TCPCL supports positive indication when a
bundle has been fully transferred to a peer node. bundle has been fully transferred to a peer entity.
Transmission Intermediate Progress The TCPCL supports positive Transmission Intermediate Progress The TCPCL supports positive
indication of intermediate progress of transferr to a peer node. indication of intermediate progress of transferr to a peer entity.
This intermediate progress is at the granularity of each 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 supports positive indication of
certain reasons for bundle transmission failure, notably when the certain reasons for bundle transmission failure, notably when the
peer node rejects the bundle or when a TCPCL session ends before peer entity rejects the bundle or when a TCPCL session ends before
transferr success. The TCPCL itself does not have a notion of transferr success. The TCPCL itself does not have a notion of
transfer timeout. transfer timeout.
Interrupt Reception The TCPCL allows a BP agent to interrupt an Interrupt Reception The TCPCL allows a BP agent to interrupt an
individual transfer before it has fully completed (successfully or individual transfer before it has fully completed (successfully or
not). not).
Reception Success The TCPCL supports positive indication when a Reception Success The TCPCL supports positive indication when a
bundle has been fully transferred from a peer node. bundle has been fully transferred from a peer entity.
Reception Intermediate Progress The TCPCL supports positive Reception Intermediate Progress The TCPCL supports positive
indication of intermediate progress of transfer from the peer indication of intermediate progress of transfer from the peer
node. 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 supports positive indication of certain
reasons for reception failure, notably when the local node rejects reasons for reception failure, notably when the local entity
an attempted transfer for some local policy reason or when a TCPCL rejects an attempted transfer for some local policy reason or when
session ends before transfer success. The TCPCL itself does not a TCPCL session ends before transfer success. The TCPCL itself
have a notion of transfer timeout. does not have a notion of transfer timeout.
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", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
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.
TCPCL Node: This term refers to either side of a negotiating or in- TCPCL Entity: This is the notional TCPCL application that initiates
service TCPCL Session. For most TCPCL behavior, the two nodes are TCPCL sessions. This design, implementation, configuration, and
specific behavior of such an entity is outside of the scope of
this document. However, the concept of an entity has utility
within the scope of this document as the container and initiator
of TCPCL sessions. The relationship between a TCPCL entity and
TCPCL sessions is defined as follows:
A TCPCL Entity MAY actively initiate any number of TCPCL
Sessions and should do so whenever the entity is the initial
transmitter of information to another entity in the network.
A TCPCL Entity MAY support zero or more passive listening
elements that listen for connection requests from other TCPCL
Entities operating on other entitys in the network.
A TCPCL Entity MAY passivley initiate any number of TCPCL
Sessions from requests received by its passive listening
element(s) if the entity uses such elements.
For most TCPCL behavior within a session, the two entities are
symmetric and there is no protocol distinction between them. Some symmetric and there is no protocol distinction between them. Some
specific behavior, particularly during negotiation, distinguishes specific behavior, particularly during session establishment,
between the connecting node and the connected-to node. For the distinguishes between the active entity and the passive entity.
remainder of this document, the term "node" without the prefix For the remainder of this document, the term "entity" without the
"TCPCL" refers to a TCPCL node. prefix "TCPCL" refers to a TCPCL entity.
TCP Connection: This term refers to a transport connection using TCP TCP Connection: The term Connection in this specification
as the transport protocol. exclusively refers to a TCP connection and any and all behaviors,
sessions, and other states association 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 bundle nodes. The TCPCL communication relationship between two TCPCL entities.
lifetime of a TCPCL session is bound to the lifetime of an Within a single TCPCL session there are two possible transfer
streams; one in each direction, with one stream from each entity
being the outbound stream and the other being the inbound stream.
The lifetime of a TCPCL session is bound to the lifetime of an
underlying TCP connection. A TCPCL session is terminated when the underlying TCP connection. A TCPCL session is terminated when the
TCP connection ends, due either to one or both nodes actively TCP connection ends, due either to one or both entities actively
terminating the TCP connection or due to network errors causing a terminating 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. For the remainder of this
document, the term "session" without the prefix "TCPCL" refers to document, the term "session" without the prefix "TCPCL" refers to
a TCPCL session. 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 node 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 bundle nodes exchange and negotiate the values to be which two entities exchange and negotiate the values to be used
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
path within a TCPCL Session. Messages sent over a transfer stream
are serialized, meaning that one set of user data must complete
its transmission prior to another set of user data being
transmitted over the same transfer stream. 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 unique only to a single direction within a single Session.
Transfer Segment: A subset of a transfer of user data being
communicated over a trasnfer stream.
Idle Session: A TCPCL session is idle while the only messages being Idle Session: A TCPCL session is idle while the only messages being
transmitted or received are KEEPALIVE messages. 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 any messages are being
transmitted or received. transmitted or received.
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
in Figure 2.
+----------------------------+ +--------------------------+
| TCPCL Session | | TCPCL "Other" Session |
| | | |
| +-----------------------+ | | +---------------------+ |
| | TCP Connection | | | | TCP Connection | |
| | | | | | | |
| | +-------------------+ | | | | +-----------------+ | |
| | | Optional Inbound | | | | | | Peer Outbound | | |
| | | Transfer Stream |<-[Seg]--[Seg]--[Seg]-| | Transfer Stream | | |
| | | ----- | | | | | | ----- | | |
| | | RECEIVER | | | | | | SENDER | | |
| | +-------------------+ | | | | +-----------------+ | |
| | | | | | | |
| | +-------------------+ | | | | +-----------------+ | |
| | | Optional Outbound | | | | | | Peer Inbound | | |
| | | Transfer Stream |------[Seg]---[Seg]---->| Transfer Stream | | |
| | | ----- | | | | | | ----- | | |
| | | SENDER | | | | | | RECEIVER | | |
| | +-------------------+ | | | | +-----------------+ | |
| +-----------------------+ | | +---------------------+ |
+----------------------------+ +--------------------------+
Figure 2: 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. TCPCL Session Overview 3.1. TCPCL Session Overview
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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 SHUTDOWN message is used to start the closing of a TCPCL session A SESS_TERM message is used to start the closing of a TCPCL session
(see Section 6.1). During shutdown sequencing, in-progress transfers (see Section 6.1). During shutdown sequencing, in-progress transfers
can be completed but no new transfers can be initiated. A SHUTDOWN can be completed but no new transfers can be initiated. A SESS_TERM
message can also be used to refuse a session setup by a peer (see message can also be used to refuse a session setup by a peer (see
Section 4.3). It is an implementation matter to determine whether or Section 4.3). It is an implementation matter to determine whether or
not to close a TCPCL session while there are no transfers queued or not to close a TCPCL session while there are no transfers queued or
in-progress. in-progress.
TCPCL is a symmetric protocol between the peers of a session. Both TCPCL is a symmetric protocol between the peers of a session. Both
sides can start sending data segments in a session, and one side's sides can start sending data segments in a session, and one side's
bundle transfer does not have to complete before the other side can bundle transfer does not have to complete before the other side can
start sending data segments on its own. Hence, the protocol allows start sending data segments on its own. Hence, the protocol allows
for a bi-directional mode of communication. Note that in the case of for a bi-directional mode of communication. Note that in the case of
concurrent bidirectional transmission, acknowledgment segments MAY be concurrent bidirectional transmission, acknowledgment segments MAY be
interleaved with data segments. interleaved with data segments.
3.2. Example Message Exchange 3.2. Transfer Segmentation Policies
Each TCPCL session allows a negotiated transfer segmentation polcy to
be applied in each transfer direction. A receiving node can set the
Segment MRU in its contact header to determine the largest acceptable
segment size, and a transmitting node can segment a transfer into any
sizes smaller than the receiver's Segment MRU. It is a network
administration matter to determine an appropriate segmentation policy
for entities operating TCPCL, but guidance given here can be used to
steer policy toward performance goals.
Minimum Overhead For a simple network expected to exchange
relatively small bundles, the Segment MRU can be set to be
identical to the Transfer MRU which indicates that all transfers
can be sent with a single data segment (i.e. no actual
segmentation). If the network is closed and all transmitters are
known to follow a single-segment transfer policy, then receivers
can avoid the necessity of segment reassembly. Because this CL
operates over a TCP stream, which suffers from a form of head-of-
queue blocking between messages, while one node is transmitting a
single XFER_SEGMENT message it is not able to transmit any
XFER_ACK or XFER_REFUSE for any associated received transfers.
Predictable Message Sizing In situations where the maximum message
size is desired to be well-controlled, the Segment MRU can be set
to the largest acceptable size (the message size less XFER_SEGMENT
header size) and transmitters can always segment a transfer into
maximum-size chunks no larger than the Segment MRU. This
guarantees that any single XFER_SEGMENT will not monopolize the
TCP stream for too long, which would prevent outgoing XFER_ACK and
XFER_REFUSE associated with received transfers.
Dynamic Segmentation Even after negotiation of a Segment MRU for
each receiving node, the actual transfer segmentation only needs
to guarantee than any individual segment is no larger than that
MRU. In a situation where network "goodput" is dynamic, the
transfer segmentation size can also be dynamic in order to control
message transmission duration.
Many other policies can be established in a TCPCL network between
these two extremes. Different policies can be applied to each
direction to/from any particular node. Additionally, future header
and transfer extension types can apply further nuance to transfer
policies and policy negotiation.
3.3. Example Message Exchange
The following figure depicts the protocol exchange for a simple The following figure depicts the protocol exchange for a simple
session, showing the session establishment and the transmission of a session, showing the session establishment and the transmission of a
single bundle split into three data segments (of lengths "L1", "L2", single bundle split into three data segments (of lengths "L1", "L2",
and "L3") from Node A to Node B. and "L3") from Entity A to Entity B.
Note that the sending node MAY transmit multiple XFER_SEGMENT Note that the sending node MAY transmit multiple XFER_SEGMENT
messages without necessarily waiting for the corresponding XFER_ACK messages without necessarily waiting for the corresponding XFER_ACK
responses. This enables pipelining of messages on a channel. responses. This enables pipelining of messages on a channel.
Although this example only demonstrates a single bundle transmission, Although this example only demonstrates a single bundle transmission,
it is also possible to pipeline multiple XFER_SEGMENT messages for it is 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.
Node A Node B Entity A Entity B
====== ====== ======== ========
+-------------------------+ +-------------------------+ +-------------------------+
| Contact Header | -> <- | Contact Header | | Contact Header | -> +-------------------------+
+-------------------------+ +-------------------------+ +-------------------------+ <- | Contact Header |
+-------------------------+
+-------------------------+
| SESS_INIT | -> +-------------------------+
+-------------------------+ <- | SESS_INIT |
+-------------------------+
+-------------------------+ +-------------------------+
| XFER_INIT | -> | XFER_INIT | ->
| Transfer ID [I1] | | Transfer ID [I1] |
| Total Length [L1] | | Total Length [L1] |
+-------------------------+ +-------------------------+
+-------------------------+ +-------------------------+
| XFER_SEGMENT (start) | -> | XFER_SEGMENT (start) | ->
| Transfer ID [I1] | | Transfer ID [I1] |
| Length [L1] | | Length [L1] |
skipping to change at page 10, line 41 skipping to change at page 12, line 46
| Length [L3] | | Length [L1+L2] | | Length [L3] | | Length [L1+L2] |
|Bundle Data | +-------------------------+ |Bundle Data | +-------------------------+
| (L1+L2)..(L1+L2+L3-1)| | (L1+L2)..(L1+L2+L3-1)|
+-------------------------+ +-------------------------+
+-------------------------+ +-------------------------+
<- | XFER_ACK (end) | <- | XFER_ACK (end) |
| Transfer ID [I1] | | Transfer ID [I1] |
| Length [L1+L2+L3] | | Length [L1+L2+L3] |
+-------------------------+ +-------------------------+
+-------------------------+ +-------------------------+ +-------------------------+
| SHUTDOWN | -> <- | SHUTDOWN | | SESS_TERM | -> +-------------------------+
+-------------------------+ +-------------------------+ +-------------------------+ <- | SESS_TERM |
+-------------------------+
Figure 2: An Example of the Flow of Protocol Messages on a Single TCP Figure 3: An example of the flow of protocol messages on a single TCP
Session between Two Nodes (A and B) 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 nodes. It is up to MUST first be established between communicating entities. It is up
the implementation to decide how and when session setup is triggered. to the implementation to decide how and when session setup is
triggered. For example, some sessions MAY be opened proactively and
For example, some sessions MAY be opened proactively and maintained maintained for as long as is possible given the network conditions,
for as long as is possible given the network conditions, while other while other sessions MAY be opened only when there is a bundle that
sessions MAY be opened only when there is a bundle that is queued for is queued for transmission and the routing algorithm selects a
transmission and the routing algorithm selects a certain next-hop certain next-hop node.
node.
4.1. TCP Connection 4.1. TCP Connection
To establish a TCPCL session, a node MUST first establish a TCP To establish a TCPCL session, an entity MUST first establish a TCP
connection with the intended peer node, 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 node 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. A node MAY decide to re-attempt to establish the connection failure. An entity MAY decide to re-attempt to establish
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 node MUST retry the repeated connection attempts. Therefore, the entity MUST retry the
connection setup no earlier than some delay time from the last connection setup no earlier than some delay time from the last
attempt, and it SHOULD use a (binary) exponential backoff mechanism attempt, and it SHOULD use a (binary) exponential backoff mechanism
to increase this delay in case of repeated failures. In case a to increase this delay in case of repeated failures.
SHUTDOWN message specifying a reconnection delay is received, that
delay is used as the initial delay. The default initial re-attempt
delay SHOULD be no shorter than 1 second and SHOULD be configurable
since it will be application and network type dependent.
Once a TCP connection is established, each node MUST immediately Once a TCP connection is established, each entity MUST immediately
transmit a contact header over the TCP connection. The format of the transmit a contact header over the TCP connection. The format of the
contact header is described in Section 4.2. contact header is described in Section 4.2.
4.2. Contact Header 4.2. Contact Header
Once a TCP connection is established, both parties exchange a contact Once a TCP connection is established, both parties exchange a contact
header. This section describes the format of the contact header and header. This section describes the format of the contact header and
the meaning of its fields. the meaning of its fields.
Upon receipt of the contact header, both nodes perform the validation Upon receipt of the contact header, both entities perform the
and negotiation procedures defined in Section 4.3. After receiving validation and negotiation procedures defined in Section 4.3. After
the contact header from the other node, either node MAY refuse the receiving the contact header from the other entity, either entity MAY
session by sending a SHUTDOWN message with an appropriate reason refuse the session by sending a SESS_TERM message with an appropriate
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 | Keepalive Interval | | Version | Flags |
+---------------+---------------+---------------+---------------+ +---------------+---------------+
| Segment MRU... |
+---------------+---------------+---------------+---------------+
| contd. |
+---------------+---------------+---------------+---------------+
| Transfer MRU... |
+---------------+---------------+---------------+---------------+
| contd. |
+---------------+---------------+---------------+---------------+
| EID Length | EID Data... |
+---------------+---------------+---------------+---------------+
| EID Data contd. |
+---------------+---------------+---------------+---------------+
| Header Extension Length... |
+---------------+---------------+---------------+---------------+
| contd. |
+---------------+---------------+---------------+---------------+
| Header Extension Items... |
+---------------+---------------+---------------+---------------+
Figure 3: Contact Header Format Figure 4: 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. The fields of the contact header are: header fields. 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 protocol). version of the protocol).
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. to the descriptions in Table 1.
Keepalive Interval: A 16-bit unsigned integer indicating the
interval, in seconds, between any subsequent messages being
transmitted by the peer. The peer receiving this contact header
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
allowable single-segment data payload size to be received in this
session. Any XFER_SEGMENT sent to this peer SHALL have a data
payload no longer than the peer's Segment MRU. The two nodes of a
single session MAY have different Segment MRUs, and no relation
between the two is required.
Transfer MRU: A 64-bit unsigned integer indicating the largest
allowable total-bundle data size to be received in this session.
Any bundle transfer sent to this peer SHALL have a Total Bundle
Length payload no longer than the peer's Transfer MRU. This value
can be used to perform proactive bundle fragmentation. The two
nodes of a single session MAY have different Transfer MRUs, and no
relation between the two is required.
EID Length and EID Data: Together these fields represent a variable-
length text string. The EID Length is a 16-bit unsigned integer
indicating the number of octets of EID Data to follow. A zero EID
Length SHALL be used to indicate the lack of EID rather than a
truly empty EID. This case allows a node to avoid exposing EID
information on an untrusted network. A non-zero-length EID Data
SHALL contain the UTF-8 encoded EID of some singleton endpoint in
which the sending node is a member, in the canonical format of
<scheme name>:<scheme-specific part>. This EID encoding is
consistent with [I-D.ietf-dtn-bpbis].
Header Extension Length and Header Extension Items: Together these
fields represent protocol extension data not defined by this
specification. The Header Extension Length is the total number of
octets to follow which are used to encode the Header Extension
Item list. The encoding of each Header Extension Item is within a
consistent data container as described in Section 4.2.1.
+----------+--------+-----------------------------------------------+ +----------+--------+-----------------------------------------------+
| Name | Code | Description | | Name | Code | Description |
+----------+--------+-----------------------------------------------+ +----------+--------+-----------------------------------------------+
| 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
4.2.1. Header Extension Items 4.3. Contact Validation and Negotiation
Each of the Header Extension Items SHALL be encoded in an identical
Type-Length-Value (TLV) container form as indicated in Figure 4. The
fields of the Header Extension Item are:
Flags: A one-octet field containing generic bit flags about the
Item, which are listed in Table 2. If a TCPCL node receives a
Header Extension Item with an unknown Item Type and the CRITICAL
flag set, the node SHALL close the TCPCL session with SHUTDOWN
reason code of "Contact Failure". If the CRITICAL flag is not
set, a node SHALL skip over and ignore any item with an unknown
Item Type.
Item Type: A 16-bit unsigned integer field containing the type of
the extension item. This specification does not define any
extension types directly, but does allocate an IANA registry for
such codes (see Section 8.3).
Item Length: A 32-bit unsigned integer field containing the number
of Item Value octets to follow.
Item Value: A variable-length data field which is interpreted
according to the associated Item Type. This specification places
no restrictions on an extension's use of available Item Value
data. Extension specification SHOULD avoid the use of large data
exchanges within the TCPCL contact header as no bundle transfers
can begin until the full contact exchange and negotiation has been
completed.
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
+---------------+---------------+---------------+---------------+
| Item Flags | Item Type | Item Length...|
+---------------+---------------+---------------+---------------+
| length contd. | Item Value... |
+---------------+---------------+---------------+---------------+
| value contd. |
+---------------+---------------+---------------+---------------+
Figure 4: Header Extension Item Format
+----------+--------+-----------------------------------------------+
| Name | Code | Description |
+----------+--------+-----------------------------------------------+
| CRITICAL | 0x01 | If bit is set, indicates that the receiving |
| | | peer must handle the extension item. |
| | | |
| Reserved | others |
+----------+--------+-----------------------------------------------+
Table 2: Header Extension Item Flags
4.3. Validation and Parameter 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, a node MAY of repeated connections from a misconfigured application, an entity
elect to hold an invalid connection open and idle for some time MAY elect to hold an invalid connection open and idle for some time
before closing it. before closing it.
A connecting TCPCL node SHALL send the highest TCPCL protocol version A connecting TCPCL node SHALL send the highest TCPCL protocol version
on a first session attempt for a TCPCL peer. If a connecting node on a first session attempt for a TCPCL peer. If a connecting node
receives a SHUTDOWN message with reason of "Version Mismatch", that receives a SESS_TERM message with reason of "Version Mismatch", that
node MAY attempt further TCPCL sessions with the peer using earlier node MAY attempt further TCPCL sessions with the peer using earlier
protocol version numbers in decreasing order. Managing multi-TCPCL- protocol version numbers in decreasing order. Managing multi-TCPCL-
session state such as this is an implementation matter. session state such as this is an implementation matter.
If a node receives a contact header containing a version that is If an entity receives a contact header containing a version that is
greater than the current version of the protocol that the node greater than the current version of the protocol that the node
implements, then the node SHALL shutdown the session with a reason implements, then the node SHALL shutdown the session with a reason
code of "Version mismatch". If a node receives a contact header with code of "Version mismatch". If an entity receives a contact header
a version that is lower than the version of the protocol that the with a version that is lower than the version of the protocol that
node implements, the node MAY either terminate the session (with a the node implements, the node MAY either terminate the session (with
reason code of "Version mismatch") or the node MAY adapt its a reason code of "Version mismatch") or the node MAY adapt its
operation to conform to the older version of the protocol. The operation to conform to the older version of the protocol. The
decision of version fall-back is an implementation matter. decision of version fall-back is an implementation matter.
A node calculates the parameters for a TCPCL session by negotiating
the values from its own preferences (conveyed by the contact header
it sent to the peer) with the preferences of the peer node (expressed
in the contact header that it received from the peer). The
negotiated parameters defined by this specification are described in
the following paragraphs.
Transfer MTU and Segment MTU: The maximum transmit unit (MTU) for
whole transfers and individual segments are idententical to the
Transfer MRU and Segment MRU, respectively, of the recevied
contact header. A transmitting peer can send individual segments
with any size smaller than the Segment MTU, depending on local
policy, dynamic network conditions, etc. Determining the size of
each transmitted segment is an implementation matter.
Session Keepalive: Negotiation of the Session Keepalive parameter is
performed by taking the minimum of this two contact headers'
Keepalive Interval. The Session Keepalive interval is a parameter
for the behavior described in Section 5.2.1.
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
negotated value of Enable TLS is acceptable. If not, the node
SHALL shutdown the session with a reason code of "Contact
Failure". Note that this contact failure is different than a "TLS
Failure" 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
includes a possible completed TLS handshake of the connection to use
TLS), this protocol defines no additional mechanism to change the
parameters of an established session; to effect such a change, the
TCPCL session MUST be terminated and a new session established.
4.3.1. Reactive Fragmentation Extension
In order to allow BP agents to use this reliable convergence layer to
perform reactive fragmentation, a header extension type
REACTIVE_FRAGMENT is defined to negotate the fragmentation
capabilities of the node sending the extension item. If either node
does not send a REACTIVE_FRAGMENT item then no reactive fragmentation
is allowed to be initiated within that session. Reactive
fragmentation is performed after a failed transfer, so it necessarily
spans more than a single TCPCL session. In fact, follow-on bundle
fragments may be sent via an entirely different convergence layer.
For these reasons, details of how reactive fragmentation and
reassembly takes place are outside the scope of this specification.
Within a single contact header there SHALL be no more than one item
with an extension type of REACTIVE_FRAGMENT. If no REACTIVE_FRAGMENT
item is received from a peer, all REACTIVE_FRAGMENT flags of that
peer SHALL be considered to be not set. The CRITICAL flag of the
REACTIVE_FRAGMENT item MAY be set to indicate that the peer node has
to interpret and negotiate the reactive fragmentation capability.
The order of the REACTIVE_FRAGMENT item within the extension items is
not significant. The Item Length of a REACTIVE_FRAGMENT item SHALL
be a single octet. The contents of the REACTIVE_FRAGMENT item shall
be interpreted as a bit mask, with flags interpreted according to
Table 3.
When a transfer-sending node has set the CAN_GENERATE flag and the
peer node has set the CAN_RECEIVE flag, the sending node SHALL use
acknowledged data segment information to reactively fragment a failed
transfer within some later transfers. When a transfer-receving node
has set the CAN_RECEIVE flag and the peer node has set the
CAN_GENERATE flag, the receving node SHALL treat partial received
transfers as reactively fragmented bundles and use the partial
transfer to reassemble future fragments of that bundle.
+--------------+--------+-------------------------------------------+
| Name | Code | Description |
+--------------+--------+-------------------------------------------+
| CAN_GENERATE | 0x01 | If bit is set, indicates that the sending |
| | | node is capable of generating reactively |
| | | fragmented bundles. |
| | | |
| CAN_RECEIVE | 0x02 | If bit is set, indicates that the sending |
| | | node is capable of receving and |
| | | reassembling reactively fragmented |
| | | bundles. |
| | | |
| Reserved | others |
+--------------+--------+-------------------------------------------+
Table 3: REACTIVE_FRAGMENT Flags
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
established, there is no mechanism available to downgrade a TCPCL established, there is no mechanism available to downgrade a TCPCL
session to non-TLS operation. If this is desired, the entire TCPCL session to non-TLS operation. If this is desired, the entire TCPCL
session MUST be shutdown and a new non-TLS-negotiated session session MUST be shutdown and a new non-TLS-negotiated session
established. established.
The use of TLS is negotated using the Contact Header as described in The use of TLS is negotated 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 nodes SHALL begin a TLS handshake in accordance with session entities SHALL begin a TLS handshake in accordance with
[RFC5246]. The parameters within each TLS negotiation are [RFC5246]. The parameters within each TLS negotiation are
implementation dependent but any TCPCL node SHOULD follow all implementation dependent but any TCPCL node SHOULD follow all
recommended best practices of [RFC7525]. By convention, this recommended best practices of [RFC7525]. By convention, this
protocol uses the node which initiated the underlying TCP connection protocol uses the node which initiated the underlying TCP connection
as the "client" role of the TLS handshake request. as the "client" role of the TLS handshake 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 7. Specifics about sensitive data exposure are discussed in Section 8.
4.4.1. TLS Handshake Result 4.4.1. TLS Handshake Result
If a TLS handshake cannot negotiate a TLS session, both nodes of the If a TLS handshake cannot negotiate a TLS session, both entities of
TCPCL session SHALL start a TCPCL shutdown with reason "TLS Failure". the TCPCL session SHALL start a TCPCL shutdown with reason "TLS
Failure".
After a TLS session is successfully established, both TCPCL nodes After a TLS session is successfully established, both TCPCL entities
SHALL re-exchange TCPCL Contact Header messages. Any information SHALL re-exchange TCPCL Contact Header messages. Any information
cached from the prior Contact Header exchange SHALL be discarded. cached from the prior Contact Header exchange SHALL be discarded.
This re-exchange avoids a "man-in-the-middle" attack in identical This re-exchange avoids a "man-in-the-middle" attack in identical
fashion to [RFC2595]. Each re-exchange header CAN_TLS flag SHALL be fashion to [RFC2595]. Each re-exchange header CAN_TLS flag SHALL be
identical to the original header CAN_TLS flag from the same node. identical to the original header CAN_TLS flag from the same node.
The CAN_TLS logic (TLS negotiation) SHALL NOT apply during header re- The CAN_TLS logic (TLS negotiation) SHALL NOT apply during header re-
exchange. This reinforces the fact that there is no TLS downgrade exchange. This reinforces the fact that there is no TLS downgrade
mechanism. mechanism.
4.4.2. Example TLS Initiation 4.4.2. Example TLS Initiation
A summary of a typical CAN_TLS usage is shown in the sequence in A summary of a typical CAN_TLS usage is shown in the sequence in
Figure 5 below. Figure 5 below.
Node A Node B Entity A Entity B
====== ====== ======== ========
+-------------------------+ +-------------------------+
| Open TCP Connnection | -> | Open TCP Connnection | ->
+-------------------------+ +-------------------------+ +-------------------------+ +-------------------------+
<- | 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) |
+-------------------------+ +-------------------------+ +-------------------------+ +-------------------------+
+-------------------------+ +-------------------------+ ... secured TCPCL messaging, starting with SESS_INIT ...
| Contact Header | -> <- | Contact Header |
+-------------------------+ +-------------------------+
... secured TCPCL messaging ...
+-------------------------+ +-------------------------+ +-------------------------+ +-------------------------+
| SHUTDOWN | -> <- | SHUTDOWN | | SESS_TERM | -> <- | SESS_TERM |
+-------------------------+ +-------------------------+ +-------------------------+ +-------------------------+
Figure 5: A simple visual example of TCPCL TLS Establishment between Figure 5: A simple visual example of TCPCL TLS Establishment between
two nodes two entities
5. Established Session Operation
This section describes the protocol operation for the duration of an
established session, including the mechanism for transmitting bundles
over the session.
5.1. Message Type Codes 4.5. Message Type Codes
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 6: Format of the Message Header Figure 6: Format of the Message Header
The message header fields are as follows: The message header fields are as follows:
Message Type: Indicates the type of the message as per Table 4 Message Type: Indicates the type of the message as per Table 2
below. Encoded values are listed in Section 8.4. below. Encoded values are listed in Section 9.5.
+--------------+----------------------------------------------------+ +--------------+----------------------------------------------------+
| Type | Description | | Type | Description |
+--------------+----------------------------------------------------+ +--------------+----------------------------------------------------+
| SESS_INIT | Contains the session parameter inputs from one of |
| | the entities, as described in Section 4.6. |
| | |
| XFER_INIT | Contains the length (in octets) of the next | | XFER_INIT | Contains the length (in octets) of the next |
| | transfer, as described in Section 5.3.2. | | | transfer, as described in Section 5.2.2. |
| | | | | |
| XFER_SEGMENT | Indicates the transmission of a segment of bundle | | XFER_SEGMENT | Indicates the transmission of a segment of bundle |
| | data, as described in Section 5.3.3. | | | data, as described in Section 5.2.3. |
| | | | | |
| XFER_ACK | Acknowledges reception of a data segment, as | | XFER_ACK | Acknowledges reception of a data segment, as |
| | described in Section 5.3.4. | | | described in Section 5.2.4. |
| | | | | |
| XFER_REFUSE | Indicates that the transmission of the current | | XFER_REFUSE | Indicates that the transmission of the current |
| | bundle SHALL be stopped, as described in Section | | | bundle SHALL be stopped, as described in Section |
| | 5.3.5. | | | 5.2.5. |
| | | | | |
| KEEPALIVE | Used to keep TCPCL session active, as described in | | KEEPALIVE | Used to keep TCPCL session active, as described in |
| | Section 5.2.1. | | | Section 5.1.1. |
| | | | | |
| SHUTDOWN | Indicates that one of the nodes participating in | | SESS_TERM | Indicates that one of the entities participating |
| | the session wishes to cleanly terminate the | | | in the session wishes to cleanly terminate the |
| | session, as described in Section 6. | | | session, as described in Section 6. |
| | | | | |
| MSG_REJECT | Contains a TCPCL message rejection, as described | | MSG_REJECT | Contains a TCPCL message rejection, as described |
| | in Section 5.2.2. | | | in Section 5.1.2. |
+--------------+----------------------------------------------------+ +--------------+----------------------------------------------------+
Table 4: TCPCL Message Types Table 2: TCPCL Message Types
5.2. Upkeep and Status Messages 4.6. Session Initialization Message (SESS_INIT)
5.2.1. Session Upkeep (KEEPALIVE) Before a session is established and ready to transfer bundles, the
session parameters are negotiated between the connected entities.
The SESS_INIT message is used to convey the per-entity parameters
which are used together to negotiate the per-session parameters.
The format of a SESS_INIT message is as follows in Figure 7.
+-------------------------------+
| Message Header |
+-------------------------------+
| Keepalive Interval (U16) |
+-------------------------------+
| Segment MRU (U64) |
+-------------------------------+
| Transfer MRU (U64) |
+-------------------------------+
| EID Length (U16) |
+-------------------------------+
| EID Data (variable) |
+-------------------------------+
| Session Extension Length (U64)|
+-------------------------------+
| Session Extension Items (var.)|
+-------------------------------+
Figure 7: SESS_INIT Format
A 16-bit unsigned integer indicating the interval, in seconds,
between any subsequent messages being transmitted by the peer.
The peer receiving this contact header uses this interval to
determine how long to wait after any last-message transmission and
a necessary subsequent KEEPALIVE message transmission.
A 64-bit unsigned integer indicating the largest allowable single-
segment data payload size to be received in this session. Any
XFER_SEGMENT sent to this peer SHALL have a data payload no longer
than the peer's Segment MRU. The two entities of a single session
MAY have different Segment MRUs, and no relation between the two
is required.
A 64-bit unsigned integer indicating the largest allowable total-
bundle data size to be received in this session. Any bundle
transfer sent to this peer SHALL have a Total Bundle Length
payload no longer than the peer's Transfer MRU. This value can be
used to perform proactive bundle fragmentation. The two entities
of a single session MAY have different Transfer MRUs, and no
relation between the two is required.
Together these fields represent a variable-length text string.
The EID Length is a 16-bit unsigned integer indicating the number
of octets of EID Data to follow. A zero EID Length SHALL be used
to indicate the lack of EID rather than a truly empty EID. This
case allows an entity to avoid exposing EID information on an
untrusted network. A non-zero-length EID Data SHALL contain the
UTF-8 encoded EID of some singleton endpoint in which the sending
entity is a member, in the canonical format of <scheme
name>:<scheme-specific part>. This EID encoding is consistent
with [I-D.ietf-dtn-bpbis].
Together these fields represent protocol extension data not
defined by this specification. The Session Extension Length is
the total number of octets to follow which are used to encode the
Session Extension Item list. The encoding of each Session
Extension Item is within a consistent data container as described
in Section 4.6.1. The full set of Session Extension Items apply
for the duration of the TCPCL session to follow. The order and
mulitplicity of these Session Extension Items MAY be significant,
as defined in the associated type specification(s).
4.6.1. Session Extension Items
Each of the Session Extension Items SHALL be encoded in an identical
Type-Length-Value (TLV) container form as indicated in Figure 8. The
fields of the Session Extension Item are:
Flags: A one-octet field containing generic bit flags about the
Item, which are listed in Table 3. If a TCPCL entity receives a
Session Extension Item with an unknown Item Type and the CRITICAL
flag set, the entity SHALL close the TCPCL session with SESS_TERM
reason code of "Contact Failure". If the CRITICAL flag is not
set, an entity SHALL skip over and ignore any item with an unknown
Item Type.
Item Type: A 16-bit unsigned integer field containing the type of
the extension item. This specification does not define any
extension types directly, but does allocate an IANA registry for
such codes (see Section 9.3).
Item Length: A 32-bit unsigned integer field containing the number
of Item Value octets to follow.
Item Value: A variable-length data field which is interpreted
according to the associated Item Type. This specification places
no restrictions on an extension's use of available Item Value
data. Extension specification SHOULD avoid the use of large data
exchanges within the TCPCL contact header as no bundle transfers
can begin until the full contact exchange and negotiation has been
completed.
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
+---------------+---------------+---------------+---------------+
| Item Flags | Item Type | Item Length...|
+---------------+---------------+---------------+---------------+
| length contd. | Item Value... |
+---------------+---------------+---------------+---------------+
| value contd. |
+---------------+---------------+---------------+---------------+
Figure 8: Session Extension Item Format
+----------+--------+-----------------------------------------------+
| Name | Code | Description |
+----------+--------+-----------------------------------------------+
| CRITICAL | 0x01 | If bit is set, indicates that the receiving |
| | | peer must handle the extension item. |
| | | |
| Reserved | others |
+----------+--------+-----------------------------------------------+
Table 3: Session Extension Item Flags
4.7. Session Parameter Negotiation
An entity calculates the parameters for a TCPCL session by
negotiating the values from its own preferences (conveyed by the
contact header it sent to the peer) with the preferences of the peer
node (expressed in the contact header that it received from the
peer). The negotiated parameters defined by this specification are
described in the following paragraphs.
Transfer MTU and Segment MTU: The maximum transmit unit (MTU) for
whole transfers and individual segments are idententical to the
Transfer MRU and Segment MRU, respectively, of the recevied
contact header. A transmitting peer can send individual segments
with any size smaller than the Segment MTU, depending on local
policy, dynamic network conditions, etc. Determining the size of
each transmitted segment is an implementation matter.
Session Keepalive: Negotiation of the Session Keepalive parameter is
performed by taking the minimum of this two contact headers'
Keepalive Interval. The Session Keepalive interval is a parameter
for the behavior described in Section 5.1.1.
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
negotated value of Enable TLS is acceptable. If not, the node
SHALL shutdown the session with a reason code of "Contact
Failure". Note that this contact failure is different than a "TLS
Failure" 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
includes a possible completed TLS handshake of the connection to use
TLS), this protocol defines no additional mechanism to change the
parameters of an established session; to effect such a change, the
TCPCL session MUST be terminated and a new session established.
5. Established Session Operation
This section describes the protocol operation for the duration of an
established session, including the mechanism for transmitting bundles
over the session.
5.1. Upkeep and Status Messages
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, but when used
for many sessions on an open, shared network a short interval could for many sessions on an open, shared network a short interval could
lead to excessive traffic. For shared network use, nodes SHOULD lead to excessive traffic. For shared network use, entities SHOULD
choose a keepalive interval no shorter than 30 seconds. There is no choose a keepalive interval no shorter than 30 seconds. There is no
logical maximum value for the keepalive interval, but an idle TCP logical maximum value for the keepalive interval, but an idle TCP
connection is liable for closure by the host operating system if the connection is liable for closure by the host operating system if the
keepalive time is longer than tens-of-minutes. Nodes SHOULD choose a keepalive time is longer than tens-of-minutes. Entities SHOULD
keepalive interval no longer than 10 minutes (600 seconds). 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 MAY 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 4) with no additional data. Both KEEPALIVE (as described in Table 2) with no additional data. Both
sides SHOULD send a KEEPALIVE message whenever the negotiated sides SHOULD send a KEEPALIVE message whenever the negotiated
interval has elapsed with no transmission of any message (KEEPALIVE interval has elapsed with no transmission of any message (KEEPALIVE
or other). 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 MAY after some implementation-defined time duration, then the node MAY
terminate the session by transmitting a one-octet SHUTDOWN message terminate the session by transmitting a SESS_TERM message (as
(as described in Section 6.1) with reason code "Idle Timeout. described in Section 6.1) with reason code "Idle Timeout.
5.2.2. Message Rejection (MSG_REJECT) 5.1.2. Message Rejection (MSG_REJECT)
If a TCPCL node receives a message which is unknown to it (possibly If a TCPCL node receives a message which is unknown to it (possibly
due to an unhandled protocol mismatch) or is inappropriate for the due to an unhandled protocol mismatch) or is inappropriate for the
current session state (e.g. a KEEPALIVE message received after current session state (e.g. a KEEPALIVE message received after
contact header negotiation has disabled that feature), there is a contact header negotiation has disabled that feature), there is a
protocol-level message to signal this condition in the form of a protocol-level message to signal this condition in the form of a
MSG_REJECT reply. MSG_REJECT reply.
The format of a MSG_REJECT message follows: The format of a MSG_REJECT message is as follows in Figure 9.
+-----------------------------+ +-----------------------------+
| Message Header | | Message Header |
+-----------------------------+ +-----------------------------+
| Reason Code (U8) | | Reason Code (U8) |
+-----------------------------+ +-----------------------------+
| Rejected Message Header | | Rejected Message Header |
+-----------------------------+ +-----------------------------+
Figure 7: Format of MSG_REJECT Messages Figure 9: Format of MSG_REJECT Messages
The fields of the MSG_REJECT message are: The fields of the MSG_REJECT message are:
Reason Code: A one-octet refusal reason code interpreted according Reason Code: A one-octet refusal reason code interpreted according
to the descriptions in Table 5. to the descriptions in Table 4.
Rejected Message Header: The Rejected Message Header is a copy of Rejected Message Header: The Rejected Message Header is a copy of
the Message Header to which the MSG_REJECT message is sent as a the Message Header to which the MSG_REJECT message is sent as a
response. response.
+-------------+------+----------------------------------------------+ +-------------+------+----------------------------------------------+
| Name | Code | Description | | Name | Code | Description |
+-------------+------+----------------------------------------------+ +-------------+------+----------------------------------------------+
| Message | 0x01 | A message was received with a Message Type | | Message | 0x01 | A message was received with a Message Type |
| Type | | code unknown to the TCPCL node. | | Type | | code unknown to the TCPCL node. |
| Unknown | | | | Unknown | | |
| | | | | | | |
| Message | 0x02 | A message was received but the TCPCL node | | Message | 0x02 | A message was received but the TCPCL node |
| Unsupported | | cannot comply with the message contents. | | Unsupported | | cannot comply with the message contents. |
| | | | | | | |
| Message | 0x03 | A message was received while the session is | | Message | 0x03 | A message was received while the session is |
| Unexpected | | in a state in which the message is not | | Unexpected | | in a state in which the message is not |
| | | expected. | | | | expected. |
+-------------+------+----------------------------------------------+ +-------------+------+----------------------------------------------+
Table 5: MSG_REJECT Reason Codes Table 4: MSG_REJECT Reason Codes
5.3. 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 nodes. 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 be no larger than the
receiving node's maximum receive unit (MRU) (see the field "Segment receiving node's maximum receive unit (MRU) (see the field "Segment
MRU" of Section 4.2). The first segment for a bundle MUST set the MRU" of Section 4.2). The first segment for a bundle MUST set the
'START' flag, and the last one MUST set the 'end' flag in the 'START' flag, and the last one MUST set the 'end' flag in the
XFER_SEGMENT message flags. XFER_SEGMENT message flags.
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.
5.3.1. 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 XFER_INIT message and some Each transfer entails the sending of a XFER_INIT message and some
number of XFER_SEGMENT and XFER_ACK messages; all are correlated by number of XFER_SEGMENT and XFER_ACK messages; all are correlated by
the same Transfer ID. the same Transfer ID.
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. The initial Transfer ID from each node SHALL have value
zero. Subsequent Transfer ID values SHALL be incremented from the zero. Subsequent Transfer ID values SHALL be incremented from the
prior Transfer ID value by one. Upon exhaustion of the entire 64-bit prior Transfer ID value by one. Upon exhaustion of the entire 64-bit
Transfer ID space, the sending node SHALL terminate the session with Transfer ID space, the sending node SHALL terminate the session with
SHUTDOWN reason code "Resource Exhaustion". SESS_TERM reason code "Resource Exhaustion".
For bidirectional bundle transfers, a TCPCL node SHOULD NOT rely on For bidirectional bundle transfers, a TCPCL node SHOULD NOT rely on
any relation between Transfer IDs originating from each side of the any relation between Transfer IDs originating from each side of the
TCPCL session. TCPCL session.
5.3.2. Transfer Initialization (XFER_INIT) 5.2.2. Transfer Initialization (XFER_INIT)
The XFER_INIT message contains the total length, in octets, of the The XFER_INIT message contains the total length, in octets, of the
bundle data in the associated transfer. The total length is bundle data in the associated transfer. The total length is
formatted as a 64-bit unsigned integer. formatted as a 64-bit unsigned integer.
The purpose of the XFER_INIT message is to allow nodes to The purpose of the XFER_INIT message 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.
See Section 5.3.5 for details on when refusal based on XFER_INIT See Section 5.2.5 for details on when refusal based on XFER_INIT
content is acceptable. content is acceptable.
The Total Bundle Length field within a XFER_INIT message SHALL be The Total Bundle Length field within a XFER_INIT message SHALL be
treated as authoritative by the receiver. If, for whatever reason, treated as authoritative by the receiver. If, for whatever reason,
the actual total length of bundle data received differs from the the actual total length of bundle data received differs from the
value indicated by the XFER_INIT message, the receiver SHOULD treat value indicated by the XFER_INIT message, the receiver SHOULD treat
the transmitted data as invalid. the transmitted data as invalid.
The format of the XFER_INIT message is as follows: The format of the XFER_INIT message is as follows in Figure 10.
+-----------------------------+ +-----------------------------+
| Message Header | | Message Header |
+-----------------------------+ +-----------------------------+
| Transfer ID (U64) | | Transfer ID (U64) |
+-----------------------------+ +-----------------------------+
| Total Bundle Length (U64) | | Total Bundle Length (U64) |
+-----------------------------+ +-----------------------------+
| Transfer Extension |
| Length (U64) |
+-----------------------------+
| Transfer Extension Items... |
+-----------------------------+
Figure 8: Format of XFER_INIT Messages Figure 10: Format of XFER_INIT Messages
The fields of the XFER_INIT message are: The fields of the XFER_INIT message are:
Transfer ID: A 64-bit unsigned integer identifying the transfer Transfer ID: A 64-bit unsigned integer identifying the transfer
about to begin. about to begin.
Total Bundle Length: A 64-bit unsigned integer indicating the size Total Bundle Length: A 64-bit unsigned integer indicating the size
of the data-to-be-transferred. of the data-to-be-transferred.
Transfer Extension Length and Transfer Extension Items: Together
these fields represent protocol extension data not defined by this
specification. The Transfer Extension Length is the total number
of octets to follow which are used to encode the Transfer
Extension Item list. The encoding of each Transfer Extension Item
is within a consistent data container as described in
Section 5.2.2.1. The full set of transfer extension items apply
only to the assoicated single transfer. The order and
mulitplicity of these transfer extension items MAY be significant,
as defined in the associated type specification(s).
An XFER_INIT message SHALL be sent as the first message in a transfer An XFER_INIT message SHALL be sent as the first message in a transfer
sequence, before transmission of any XFER_SEGMENT messages for the sequence, before transmission of any XFER_SEGMENT messages for the
same Transfer ID. XFER_INIT messages MUST NOT be sent unless the same Transfer ID. XFER_INIT messages MUST NOT be sent unless the
next XFER_SEGMENT message has the 'START' bit set to "1" (i.e., just next XFER_SEGMENT message has the 'START' bit set to "1" (i.e., just
before the start of a new transfer). before the start of a new transfer).
5.3.3. Data Transmission (XFER_SEGMENT) 5.2.2.1. Transfer Extension Items
Each of the Transfer Extension Items SHALL be encoded in an identical
Type-Length-Value (TLV) container form as indicated in Figure 11.
The fields of the Transfer Extension Item are:
Flags: A one-octet field containing generic bit flags about the
Item, which are listed in Table 5. If a TCPCL node receives a
Transfer Extension Item with an unknown Item Type and the CRITICAL
flag set, the node SHALL close the TCPCL session with SESS_TERM
reason code of "Contact Failure". If the CRITICAL flag is not
set, an entity SHALL skip over and ignore any item with an unknown
Item Type.
Item Type: A 16-bit unsigned integer field containing the type of
the extension item. This specification does not define any
extension types directly, but does allocate an IANA registry for
such codes (see Section 9.4).
Item Length: A 32-bit unsigned integer field containing the number
of Item Value octets to follow.
Item Value: A variable-length data field which is interpreted
according to the associated Item Type. This specification places
no restrictions on an extension's use of available Item Value
data. Extension specification SHOULD avoid the use of large data
exchanges within the XFER_INIT as the associated transfer cannot
begin until the full initialization message is sent.
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
+---------------+---------------+---------------+---------------+
| Item Flags | Item Type | Item Length...|
+---------------+---------------+---------------+---------------+
| length contd. | Item Value... |
+---------------+---------------+---------------+---------------+
| value contd. |
+---------------+---------------+---------------+---------------+
Figure 11: Transfer Extension Item Format
+----------+--------+-----------------------------------------------+
| Name | Code | Description |
+----------+--------+-----------------------------------------------+
| CRITICAL | 0x01 | If bit is set, indicates that the receiving |
| | | peer must handle the extension item. |
| | | |
| Reserved | others |
+----------+--------+-----------------------------------------------+
Table 5: Transfer Extension Item Flags
5.2.3. 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 9. of a XFER_SEGMENT message follows in Figure 12.
+------------------------------+ +------------------------------+
| Message Header | | Message Header |
+------------------------------+ +------------------------------+
| Message Flags (U8) | | Message Flags (U8) |
+------------------------------+ +------------------------------+
| Transfer ID (U64) | | Transfer ID (U64) |
+------------------------------+ +------------------------------+
| Data length (U64) | | Data length (U64) |
+------------------------------+ +------------------------------+
| Data contents (octet string) | | Data contents (octet string) |
+------------------------------+ +------------------------------+
Figure 9: Format of XFER_SEGMENT Messages Figure 12: Format of XFER_SEGMENT Messages
The fields of the XFER_SEGMENT message are: The fields of the XFER_SEGMENT message are:
Message Flags: A one-octet field of single-bit flags, interpreted Message Flags: A one-octet field of single-bit flags, interpreted
according to the descriptions in Table 6. according to the descriptions in Table 6.
Transfer ID: A 64-bit unsigned integer identifying the transfer Transfer ID: A 64-bit unsigned integer identifying the transfer
being made. being made.
Data length: A 64-bit unsigned integer indicating the number of Data length: A 64-bit unsigned integer indicating the number of
skipping to change at page 26, line 9 skipping to change at page 29, line 14
'START' bit MUST be set to one if it precedes the transmission of the 'START' bit MUST be set to one if it precedes the transmission of the
first segment of a transfer. The 'END' bit MUST be set to one when first segment of a transfer. The 'END' bit MUST be set to one when
transmitting the last segment of a transfer. In the case where an transmitting the last segment of a transfer. In the case where an
entire transfer is accomplished in a single segment, both the 'START' entire transfer is accomplished in a single segment, both the 'START'
and 'END' bits MUST be set to one. and 'END' bits MUST be set to one.
Once a transfer of a bundle has commenced, the node MUST only send Once a transfer of a bundle has commenced, the node 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' bit set. No interleaving of multiple a segment with the 'END' bit set. 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 nodes MAY be achieved session. Simultaneous transfers between two entities MAY be achieved
using multiple TCPCL sessions. using multiple TCPCL sessions.
5.3.4. Data Acknowledgments (XFER_ACK) 5.2.4. 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 the segment.
To this end, the TCPCL protocol provides feedback messaging whereby a To this end, the TCPCL protocol provides feedback messaging whereby a
receiving node transmits acknowledgments of reception of data receiving node transmits acknowledgments of reception of data
segments. segments.
The format of an XFER_ACK message follows in Figure 10. The format of an XFER_ACK message follows in Figure 13.
+-----------------------------+ +-----------------------------+
| Message Header | | Message Header |
+-----------------------------+ +-----------------------------+
| Message Flags (U8) | | Message Flags (U8) |
+-----------------------------+ +-----------------------------+
| Transfer ID (U64) | | Transfer ID (U64) |
+-----------------------------+ +-----------------------------+
| Acknowledged length (U64) | | Acknowledged length (U64) |
+-----------------------------+ +-----------------------------+
Figure 10: Format of XFER_ACK Messages Figure 13: Format of XFER_ACK Messages
The fields of the XFER_ACK message are: The fields of the XFER_ACK message are:
Message Flags: A one-octet field of single-bit flags, interpreted Message Flags: A one-octet field of single-bit flags, interpreted
according to the descriptions in Table 6. according to the descriptions in Table 6.
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
skipping to change at page 27, line 17 skipping to change at page 30, line 25
necessarily waiting for the corresponding XFER_ACK responses. This necessarily waiting for the corresponding XFER_ACK responses. This
enables pipelining of messages on a channel. enables pipelining of messages on a channel.
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 node 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 node sends
an acknowledgment of length 300. The third and fourth 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.
5.3.5. Transfer Refusal (XFER_REFUSE) 5.2.5. 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 a XFER_INIT or XFER_SEGMENT bundle. To do so, upon receiving a XFER_INIT or XFER_SEGMENT
message, the node MAY transmit a XFER_REFUSE message. As data message, the node MAY transmit a XFER_REFUSE message. As data
segments and acknowledgments MAY cross on the wire, the bundle that segments and acknowledgments MAY cross on the wire, the bundle that
is being refused SHALL be identified by the Transfer ID of the is being refused SHALL be identified by the Transfer ID of the
refusal. 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
skipping to change at page 27, line 40 skipping to change at page 30, line 48
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 a A receiver MAY send an XFER_REFUSE message as soon as it receives a
XFER_INIT message without waiting for the next XFER_SEGMENT message. XFER_INIT message without waiting for the next XFER_SEGMENT message.
The sender MUST be prepared for this and MUST associate the refusal The sender MUST be prepared for this and MUST associate the refusal
with the correct bundle via the Transfer ID fields. with the correct bundle via the Transfer ID fields.
The format of the XFER_REFUSE message is as follows: The format of the XFER_REFUSE message is as follows in Figure 14.
+-----------------------------+ +-----------------------------+
| Message Header | | Message Header |
+-----------------------------+ +-----------------------------+
| Reason Code (U8) | | Reason Code (U8) |
+-----------------------------+ +-----------------------------+
| Transfer ID (U64) | | Transfer ID (U64) |
+-----------------------------+ +-----------------------------+
Figure 11: Format of XFER_REFUSE Messages Figure 14: Format of XFER_REFUSE Messages
The fields of the XFER_REFUSE message are: The fields of the XFER_REFUSE message are:
Reason Code: A one-octet refusal reason code interpreted according Reason Code: A one-octet refusal reason code interpreted according
to the descriptions in Table 7. to the descriptions in Table 7.
Transfer ID: A 64-bit unsigned integer identifying the transfer Transfer ID: A 64-bit unsigned integer identifying the transfer
being refused. being refused.
+------------+------------------------------------------------------+ +------------+------------------------------------------------------+
skipping to change at page 28, line 43 skipping to change at page 32, line 4
have either acknowledged all XFER_SEGMENTs or refused the bundle have either acknowledged all XFER_SEGMENTs or refused the bundle
transfer. 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 a node will not receive another XFER_SEGMENT for the same bundle that an entity will not receive another XFER_SEGMENT for the same
after transmitting a XFER_REFUSE message since messages MAY cross on bundle after transmitting a XFER_REFUSE message since messages MAY
the wire; if this happens, subsequent segments of the bundle SHOULD cross on the wire; if this happens, subsequent segments of the bundle
also be refused with a XFER_REFUSE message. SHOULD 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 MAY 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' bit set to '1', indicating the start of a new transfer, the 'START' bit set to '1', indicating the start of a new transfer,
and with a distinct Transfer ID value. and with a distinct Transfer ID value.
6. Session Termination 6. Session Termination
This section describes the procedures for ending a TCPCL session. This section describes the procedures for ending a TCPCL session.
6.1. Shutdown Message (SHUTDOWN) 6.1. Session Termination Message (SESS_TERM)
To cleanly shut down a session, a SHUTDOWN message SHALL be To cleanly shut down 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. Upon receiving a SHUTDOWN message transmission of any other message. Upon receiving a SESS_TERM
after not sending a SHUTDOWN message in the same session, a node message after not sending a SESS_TERM message in the same session, an
SHOULD send a confirmation SHUTDOWN message with identical content to entity SHOULD send a confirmation SESS_TERM message with identical
the SHUTDOWN for which it is confirming. content to the SESS_TERM for which it is confirming.
After sending a SHUTDOWN message, a node MAY continue a possible in- After sending a SESS_TERM message, an entity MAY continue a possible
progress transfer in either direction. After sending a SHUTDOWN in-progress transfer in either direction. After sending a SESS_TERM
message, a node SHALL NOT begin any new outgoing transfer (i.e. send message, an entity SHALL NOT begin any new outgoing transfer (i.e.
an XFER_INIT message) for the remainder of the session. After send an XFER_INIT message) for the remainder of the session. After
receving a SHUTDOWN message, a node SHALL NOT accept any new incoming receving a SESS_TERM message, an entity SHALL NOT accept any new
transfer for the remainder of the session. incoming transfer for the remainder of the session.
Instead of following a clean shutdown sequence, after transmitting a Instead of following a clean shutdown sequence, after transmitting a
SHUTDOWN message a node MAY immediately close the associated TCP SESS_TERM message an entity MAY immediately close the associated TCP
connection. When performing an unclean shutdown, a receiving node connection. When performing an unclean shutdown, a receiving node
SHOULD acknowledge all received data segments before closing the TCP SHOULD acknowledge all received data segments before closing the TCP
connection. When performing an unclean shutodwn, a transmitting node connection. When performing an unclean shutodwn, a transmitting node
SHALL treat either sending or receiving a SHUTDOWN message (i.e. SHALL treat either sending or receiving a SESS_TERM message (i.e.
before the final acknowledgment) as a failure of the transfer. Any before the final acknowledgment) as a failure of the transfer. Any
delay between request to terminate the TCP connection and actual delay between request to terminate the TCP connection and actual
closing of the connection (a "half-closed" state) MAY be ignored by closing of the connection (a "half-closed" state) MAY be ignored by
the TCPCL node. the TCPCL node.
The format of the SHUTDOWN message is as follows: The format of the SESS_TERM message is as follows in Figure 15.
+-----------------------------------+ +-----------------------------------+
| Message Header | | Message Header |
+-----------------------------------+ +-----------------------------------+
| Message Flags (U8) | | Message Flags (U8) |
+-----------------------------------+ +-----------------------------------+
| Reason Code (optional U8) | | Reason Code (optional U8) |
+-----------------------------------+ +-----------------------------------+
| Reconnection Delay (optional U16) |
+-----------------------------------+
Figure 12: Format of SHUTDOWN Messages Figure 15: Format of SESS_TERM Messages
The fields of the SHUTDOWN message are: The fields of the SESS_TERM message are:
Message Flags: A one-octet field of single-bit flags, interpreted Message Flags: A one-octet field of single-bit flags, interpreted
according to the descriptions in Table 8. according to the descriptions in Table 8.
Reason Code: A one-octet refusal reason code interpreted according Reason Code: A one-octet refusal reason code interpreted according
to the descriptions in Table 9. The Reason Code is present or to the descriptions in Table 9. The Reason Code is present or
absent as indicated by one of the flags. absent as indicated by one of the flags.
Reconnection Delay: A 16-bit unsigned integer indicating the desired
delay, in seconds, before re-attepmting a TCPCL session to the
sending node. The Reconnection Delay is present or absent as
indicated by one of the flags.
+----------+--------+-----------------------------------------------+ +----------+--------+-----------------------------------------------+
| Name | Code | Description | | Name | Code | Description |
+----------+--------+-----------------------------------------------+ +----------+--------+-----------------------------------------------+
| D | 0x01 | If bit is set, indicates that a Reconnection |
| | | Delay field is present. |
| | | |
| R | 0x02 | If bit is set, indicates that a Reason Code | | R | 0x02 | If bit is set, indicates that a Reason Code |
| | | field is present. | | | | field is present. |
| | | | | | | |
| Reserved | others | | Reserved | others |
+----------+--------+-----------------------------------------------+ +----------+--------+-----------------------------------------------+
Table 8: SHUTDOWN Flags Table 8: SESS_TERM Flags
It is possible for a node to convey optional information regarding It is possible for an entity to convey optional information regarding
the reason for session termination. To do so, the node MUST set the the reason for session termination. To do so, the node MUST set the
'R' bit in the message flags and transmit a one-octet reason code 'R' bit in the message flags and transmit a one-octet reason code
immediately following the message header. The specified values of immediately following the message header. The specified values of
the reason code are: the reason code are:
+---------------+---------------------------------------------------+ +---------------+---------------------------------------------------+
| Name | Description | | Name | Description |
+---------------+---------------------------------------------------+ +---------------+---------------------------------------------------+
| Idle timeout | The session is being closed due to idleness. | | Idle timeout | The session is being closed due to idleness. |
| | | | | |
skipping to change at page 31, line 26 skipping to change at page 34, line 26
| Contact | The node cannot interpret or negotiate contact | | Contact | The node cannot interpret or negotiate contact |
| Failure | header option. | | Failure | header option. |
| | | | | |
| TLS Failure | The node failed to negotiate TLS session and | | TLS Failure | The node failed to negotiate TLS session and |
| | cannot continue the session. | | | cannot continue the session. |
| | | | | |
| Resource | The node has run into some resource limit and | | Resource | The node has run into some resource limit and |
| Exhaustion | cannot continue the session. | | Exhaustion | cannot continue the session. |
+---------------+---------------------------------------------------+ +---------------+---------------------------------------------------+
Table 9: SHUTDOWN Reason Codes Table 9: SESS_TERM Reason Codes
If a node does not want its peer to reopen a connection immediately,
it SHALL set the 'D' bit in the flags and include a reconnection
delay to indicate when the peer is allowed to attempt another session
setup. The Reconnection Delay value 0 SHALL be interpreted as an
infinite delay, i.e., that the connecting node MUST NOT re-establish
the session.
A session shutdown MAY occur immediately after transmission of a A session shutdown 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 MAY, for example, be used to notify that the node is currently not
able or willing to communicate. However, a node MUST always send the able or willing to communicate. However, an entity MUST always send
contact header to its peer before sending a SHUTDOWN 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), a node SHOULD close the TCP invalid "magic string" is recevied), an entity SHOULD close the TCP
connection without sending a SHUTDOWN message. If the content of the connection without sending a SESS_TERM message. If the content of
Header Extension Items data disagrees with the Header 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 present
in the Header Extension Length), the reception of the contact header in the Session Extension Length), the reception of the contact header
is considered to have failed. 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 SHUTDOWN completed being sent, then the node MUST NOT transmit the SESS_TERM
message but still SHOULD close the TCP connection. Each TCPCL message but still SHOULD close the TCP connection. Each TCPCL
message is contiguous in the octet stream and has no ability to be message is contiguous in the octet stream and has no ability to be
cut short and/or preempted by an other message. This is particularly cut short and/or preempted by an other message. This is particularly
important when large segment sizes are being transmitted; either important when large segment sizes are being transmitted; either
entire XFER_SEGMENT is sent before a SHUTDOWN message or the entire XFER_SEGMENT is sent before a SESS_TERM message or the
connection is simply terminated mid-XFER_SEGMENT. connection is 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 shutdown of idle
sessions. Determining the length of time to wait before closing idle sessions. Determining the length of time to wait before closing 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 SHUTDOWN 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).
7. Security Considerations 7. Implementation Status
[NOTE to the RFC Editor: please remove this section before
publication, as well as the reference to [RFC7942] and
[github-dtn-bpbis-tcpcl].]
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
An example implementation of the this draft of TCPCLv4 has been
created as a GitHub project [github-dtn-bpbis-tcpcl] and is intented
to use as a proof-of-concept and as a possible source of
interoperability testing. This example implementation uses D-Bus as
the CL-BP Agent interface, so it only runs on hosts which provide the
Python "dbus" library.
8. Security Considerations
One security consideration for this protocol relates to the fact that One security consideration for this protocol relates to the fact that
nodes present their endpoint identifier as part of the contact header entities present their endpoint identifier as part of the contact
exchange. It would be possible for a node to fake this value and header exchange. It would be possible for an entity to fake this
present the identity of a singleton endpoint in which the node is not value and present the identity of a singleton endpoint in which the
a member, essentially masquerading as another DTN node. If this node is not a member, essentially masquerading as another DTN node.
identifier is used outside of a TLS-secured session or without If this identifier is used outside of a TLS-secured session or
further verification as a means to determine which bundles are without further verification as a means to determine which bundles
transmitted over the session, then the node that has falsified its are transmitted over the session, then the node that has falsified
identity would be able to obtain bundles that it otherwise would not its identity would be able to obtain bundles that it otherwise would
have. Therefore, a node SHALL NOT use the EID value of an unsecured not have. Therefore, an entity SHALL NOT use the EID value of an
contact header to derive a peer node's identity unless it can unsecured contact header to derive a peer node's identity unless it
corroborate it via other means. When TCPCL session security is can corroborate it via other means. When TCPCL session security is
mandated by a TCPCL peer, that peer SHALL transmit initial unsecured mandated by a TCPCL peer, that peer SHALL transmit initial unsecured
contact header values indicated in Table 10 in order. These values contact header values indicated in Table 10 in order. These values
avoid unnecessarily leaking session parameters and will be ignored avoid unnecessarily leaking session parameters and will be ignored
when secure contact header re-exchange occurs. when secure contact header re-exchange occurs.
+--------------------+---------------------------------------------+ +--------------------+---------------------------------------------+
| Parameter | Value | | Parameter | Value |
+--------------------+---------------------------------------------+ +--------------------+---------------------------------------------+
| Flags | The USE_TLS flag is set. | | Flags | The USE_TLS flag is set. |
| | | | | |
skipping to change at page 33, line 35 skipping to change at page 36, line 44
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 MAY be insecure. TLS ciphersuite negotiated between the TLS peers MAY be insecure. TLS
can be used to perform authentication without data confidentiality, can be used to perform authentication without data confidentiality,
for example. It is up to security policies within each TCPCL node to for example. 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. This is identical behavior to STARTTLS use in requirements. This is identical behavior to STARTTLS use in
[RFC2595]. [RFC2595].
Another consideration for this protocol relates to denial-of-service Another consideration for this protocol relates to denial-of-service
attacks. A node MAY send a large amount of data over a TCPCL attacks. An entity MAY send a large amount of data over a TCPCL
session, requiring the receiving node to handle the data, attempt to session, requiring the receiving entity to handle the data, attempt
stop the flood of data by sending a XFER_REFUSE message, or forcibly to stop the flood of data by sending a XFER_REFUSE message, or
terminate the session. This burden could cause denial of service on forcibly terminate the session. This burden could cause denial of
other, well-behaving sessions. There is also nothing to prevent a service on other, well-behaving sessions. There is also nothing to
malicious node from continually establishing sessions and repeatedly prevent a malicious entity from continually establishing sessions and
trying to send copious amounts of bundle data. A listening node MAY repeatedly trying to send copious amounts of bundle data. A
take countermeasures such as ignoring TCP SYN messages, closing TCP listening entity MAY take countermeasures such as ignoring TCP SYN
connections as soon as they are established, waiting before sending messages, closing TCP connections as soon as they are established,
the contact header, sending a SHUTDOWN message quickly or with a waiting before sending the contact header, sending a SESS_TERM
delay, etc. message quickly or with a delay, etc.
8. IANA Considerations 9. IANA Considerations
In this section, registration procedures are as defined in [RFC5226]. In this section, registration procedures are as defined in [RFC5226].
Some of the registries below are created new for TCPCLv4 but share Some of the registries below are created new for TCPCLv4 but share
code values with TCPCLv3. This was done to disambiguate the use of code values with TCPCLv3. This was done to disambiguate the use of
these values between TCPCLv3 and TCPCLv4 while preserving the these values between TCPCLv3 and TCPCLv4 while preserving the
semantics of some values. semantics of some values.
8.1. Port Number 9.1. Port Number
Port number 4556 has been previously assigned as the default port for Port number 4556 has been previously assigned as the default port for
the TCP convergence layer in [RFC7242]. This assignment is unchanged the TCP convergence layer in [RFC7242]. This assignment is unchanged
by protocol version 4. Each TCPCL node identifies its TCPCL protocol by protocol version 4. Each TCPCL entity identifies its TCPCL
version in its initial contact (see Section 8.2), so there is no protocol version in its initial contact (see Section 9.2), so there
ambiguity about what protocol is being used. is no ambiguity about what protocol is being used.
+------------------------+-------------------------------------+ +------------------------+-------------------------------------+
| Parameter | Value | | Parameter | Value |
+------------------------+-------------------------------------+ +------------------------+-------------------------------------+
| Service Name: | dtn-bundle | | Service Name: | dtn-bundle |
| | | | | |
| Transport Protocol(s): | TCP | | Transport Protocol(s): | TCP |
| | | | | |
| Assignee: | Simon Perreault <simon@per.reau.lt> | | Assignee: | Simon Perreault <simon@per.reau.lt> |
| | | | | |
| Contact: | Simon Perreault <simon@per.reau.lt> | | Contact: | Simon Perreault <simon@per.reau.lt> |
| | | | | |
| Description: | DTN Bundle TCP CL Protocol | | Description: | DTN Bundle TCP CL Protocol |
| | | | | |
| Reference: | [RFC7242] | | Reference: | [RFC7242] |
| | | | | |
| Port Number: | 4556 | | Port Number: | 4556 |
+------------------------+-------------------------------------+ +------------------------+-------------------------------------+
8.2. Protocol Versions 9.2. Protocol Versions
IANA has created, under the "Bundle Protocol" registry, a sub- IANA has created, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer Version registry titled "Bundle Protocol TCP Convergence-Layer Version
Numbers" and initialize it with the following table. The Numbers" and initialize it with the following table. The
registration procedure is RFC Required. registration procedure is RFC Required.
+-------+-------------+---------------------+ +-------+-------------+---------------------+
| Value | Description | Reference | | Value | Description | Reference |
+-------+-------------+---------------------+ +-------+-------------+---------------------+
| 0 | Reserved | [RFC7242] | | 0 | Reserved | [RFC7242] |
skipping to change at page 35, line 21 skipping to change at page 38, line 21
| | | | | | | |
| 2 | Reserved | [RFC7242] | | 2 | Reserved | [RFC7242] |
| | | | | | | |
| 3 | TCPCL | [RFC7242] | | 3 | TCPCL | [RFC7242] |
| | | | | | | |
| 4 | TCPCLbis | This specification. | | 4 | TCPCLbis | This specification. |
| | | | | | | |
| 5-255 | Unassigned | | 5-255 | Unassigned |
+-------+-------------+---------------------+ +-------+-------------+---------------------+
8.3. Header Extension Types 9.3. Session Extension Types
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, a sub- IANA will create, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer Version 4 registry titled "Bundle Protocol TCP Convergence-Layer Version 4
Header Extension Types" and initialize it with the contents of Session Extension Types" and initialize it with the contents of
Table 11. The registration procedure is RFC Required within the Table 11. The registration procedure is RFC Required within the
lower range 0x0001--0x3fff. Values in the range 0x8000--0xffff are lower range 0x0001--0x7fff. Values in the range 0x8000--0xffff are
reserved for use on private networks for functions not published to reserved for use on private networks for functions not published to
the IANA. the IANA.
+----------------+--------------------------+ +----------------+--------------------------+
| Code | Message Type | | Code | Message Type |
+----------------+--------------------------+ +----------------+--------------------------+
| 0x0000 | Reserved | | 0x0000 | Reserved |
| | | | | |
| 0x0001 | REACTIVE_FRAGMENT | | 0x0001--0x7fff | Unassigned |
| | | | | |
| 0x0002--0x3fff | Unassigned | | 0x8000--0xffff | Private/Experimental Use |
+----------------+--------------------------+
Table 11: Session Extension Type Codes
9.4. Transfer Extension Types
EDITOR NOTE: sub-registry to-be-created upon publication of this
specification.
IANA will create, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer Version 4
Transfer Extension Types" and initialize it with the contents of
Table 12. The registration procedure is RFC Required within the
lower range 0x0001--0x7fff. Values in the range 0x8000--0xffff are
reserved for use on private networks for functions not published to
the IANA.
+----------------+--------------------------+
| Code | Message Type |
+----------------+--------------------------+
| 0x0000 | Reserved |
| | |
| 0x0001--0x7fff | Unassigned |
| | | | | |
| 0x8000--0xffff | Private/Experimental Use | | 0x8000--0xffff | Private/Experimental Use |
+----------------+--------------------------+ +----------------+--------------------------+
Table 11: Header Extension Type Codes Table 12: Transfer Extension Type Codes
8.4. Message Types 9.5. Message Types
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, a sub- IANA will create, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer Version 4 registry titled "Bundle Protocol TCP Convergence-Layer Version 4
Message Types" and initialize it with the contents of Table 12. The Message Types" and initialize it with the contents of Table 13. The
registration procedure is RFC Required. registration procedure is RFC Required.
+-----------+--------------+ +-----------+--------------+
| Code | Message Type | | Code | Message Type |
+-----------+--------------+ +-----------+--------------+
| 0x00 | Reserved | | 0x00 | Reserved |
| | | | | |
| 0x01 | XFER_SEGMENT | | 0x01 | XFER_SEGMENT |
| | | | | |
| 0x02 | XFER_ACK | | 0x02 | XFER_ACK |
| | | | | |
| 0x03 | XFER_REFUSE | | 0x03 | XFER_REFUSE |
| | | | | |
| 0x04 | KEEPALIVE | | 0x04 | KEEPALIVE |
| | | | | |
| 0x05 | SHUTDOWN | | 0x05 | SESS_TERM |
| | | | | |
| 0x06 | XFER_INIT | | 0x06 | XFER_INIT |
| | | | | |
| 0x07 | MSG_REJECT | | 0x07 | MSG_REJECT |
| | | | | |
| 0x08--0xf | Unassigned | | 0x08--0xf | Unassigned |
+-----------+--------------+ +-----------+--------------+
Table 12: Message Type Codes Table 13: Message Type Codes
8.5. XFER_REFUSE Reason Codes 9.6. XFER_REFUSE 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, a sub- IANA will create, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer Version 4 registry titled "Bundle Protocol TCP Convergence-Layer Version 4
XFER_REFUSE Reason Codes" and initialize it with the contents of XFER_REFUSE Reason Codes" and initialize it with the contents of
Table 13. The registration procedure is RFC Required. Table 14. The registration procedure is RFC Required.
+----------+---------------------------+ +----------+---------------------------+
| Code | Refusal Reason | | Code | Refusal Reason |
+----------+---------------------------+ +----------+---------------------------+
| 0x0 | Unknown | | 0x0 | Unknown |
| | | | | |
| 0x1 | Completed | | 0x1 | Completed |
| | | | | |
| 0x2 | No Resources | | 0x2 | No Resources |
| | | | | |
| 0x3 | Retransmit | | 0x3 | Retransmit |
| | | | | |
| 0x4--0x7 | Unassigned | | 0x4--0x7 | Unassigned |
| | | | | |
| 0x8--0xf | Reserved for future usage | | 0x8--0xf | Reserved for future usage |
+----------+---------------------------+ +----------+---------------------------+
Table 13: XFER_REFUSE Reason Codes Table 14: XFER_REFUSE Reason Codes
8.6. SHUTDOWN 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, a sub- IANA will create, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer Version 4 registry titled "Bundle Protocol TCP Convergence-Layer Version 4
SHUTDOWN Reason Codes" and initialize it with the contents of SESS_TERM Reason Codes" and initialize it with the contents of
Table 14. The registration procedure is RFC Required. Table 15. The registration procedure is RFC Required.
+------------+---------------------+ +------------+---------------------+
| Code | Shutdown Reason | | Code | Shutdown Reason |
+------------+---------------------+ +------------+---------------------+
| 0x00 | Idle timeout | | 0x00 | Idle timeout |
| | | | | |
| 0x01 | Version mismatch | | 0x01 | Version mismatch |
| | | | | |
| 0x02 | Busy | | 0x02 | Busy |
| | | | | |
| 0x03 | Contact Failure | | 0x03 | Contact Failure |
| | | | | |
| 0x04 | TLS failure | | 0x04 | TLS failure |
| | | | | |
| 0x05 | Resource Exhaustion | | 0x05 | Resource Exhaustion |
| | | | | |
| 0x06--0xFF | Unassigned | | 0x06--0xFF | Unassigned |
+------------+---------------------+ +------------+---------------------+
Table 14: SHUTDOWN Reason Codes Table 15: SESS_TERM Reason Codes
8.7. MSG_REJECT Reason Codes 9.8. MSG_REJECT 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, a sub- IANA will create, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer Version 4 registry titled "Bundle Protocol TCP Convergence-Layer Version 4
MSG_REJECT Reason Codes" and initialize it with the contents of MSG_REJECT Reason Codes" and initialize it with the contents of
Table 15. The registration procedure is RFC Required. Table 16. The registration procedure is RFC Required.
+-----------+----------------------+ +-----------+----------------------+
| Code | Rejection Reason | | Code | Rejection Reason |
+-----------+----------------------+ +-----------+----------------------+
| 0x00 | reserved | | 0x00 | reserved |
| | | | | |
| 0x01 | Message Type Unknown | | 0x01 | Message Type Unknown |
| | | | | |
| 0x02 | Message Unsupported | | 0x02 | Message Unsupported |
| | | | | |
| 0x03 | Message Unexpected | | 0x03 | Message Unexpected |
| | | | | |
| 0x04-0xFF | Unassigned | | 0x04-0xFF | Unassigned |
+-----------+----------------------+ +-----------+----------------------+
Table 15: REJECT Reason Codes Table 16: REJECT Reason Codes
9. Acknowledgments 10. Acknowledgments
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.
10. References 11. References
10.1. 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-10 (work in progress), Version 7", draft-ietf-dtn-bpbis-10 (work in progress),
November 2017. November 2017.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, [RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981, RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>. <https://www.rfc-editor.org/info/rfc793>.
skipping to change at page 39, line 30 skipping to change at page 43, line 30
(TLS) Protocol Version 1.2", RFC 5246, (TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008, DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>. <https://www.rfc-editor.org/info/rfc5246>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, [RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer "Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>. 2015, <https://www.rfc-editor.org/info/rfc7525>.
10.2. Informative References 11.2. Informative References
[github-dtn-bpbis-tcpcl]
Sipos, B., "TCPCL Example Implementation",
<https://github.com/BSipos-RKF/dtn-bpbis-tcpcl/tree/
develop>.
[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-06 (work in Specification", draft-ietf-dtn-bpsec-06 (work in
progress), October 2017. progress), October 2017.
[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>.
skipping to change at page 40, line 10 skipping to change at page 44, line 15
[RFC6257] Symington, S., Farrell, S., Weiss, H., and P. Lovell, [RFC6257] Symington, S., Farrell, S., Weiss, H., and P. Lovell,
"Bundle Security Protocol Specification", RFC 6257, "Bundle Security Protocol Specification", RFC 6257,
DOI 10.17487/RFC6257, May 2011, DOI 10.17487/RFC6257, May 2011,
<https://www.rfc-editor.org/info/rfc6257>. <https://www.rfc-editor.org/info/rfc6257>.
[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>.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<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
SESS_INIT parameter negotiation.
o Changed contact header content to limit number of negotiated o Changed contact header content to limit number of negotiated
options. options.
o Added contact option to negotiate maximum segment size (per each o Added contact option to negotiate maximum segment size (per each
direction). direction).
o Added contact header extension capability. o Added session extension capability.
o Added transfer extension capability.
o Defined new IANA registries for message / type / reason codes to o Defined new IANA registries for message / type / reason codes to
allow renaming some codes for clarity. allow renaming some codes for clarity.
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_INIT, XFER_SEGMENT, XFER_ACK, XFER_REFUSE). related messages (XFER_INIT, 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. fields.
o Renamed SHUTDOWN to SESS_TERM to deconflict term "shutdown".
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 SHUTDOWN 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 session security mechanism.
o Added TLS failure and Resource Exhaustion SHUTDOWN reason code. o Added TLS failure and Resource Exhaustion SESS_TERM reason code.
o Added extension for reactive fragmentation negotiation
(REACTIVE_FRAGMENT).
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
US US
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