draft-ietf-dtn-tcpclv4-12.txt   draft-ietf-dtn-tcpclv4-13.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: October 2, 2019 J. Ott Expires: February 21, 2020 J. Ott
Aalto University Aalto University
S. Perreault S. Perreault
March 31, 2019 August 20, 2019
Delay-Tolerant Networking TCP Convergence Layer Protocol Version 4 Delay-Tolerant Networking TCP Convergence Layer Protocol Version 4
draft-ietf-dtn-tcpclv4-12 draft-ietf-dtn-tcpclv4-13
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 of RFC7242 and updates to the Bundle Protocol TCPCL Version 3 of RFC7242 and updates to the Bundle Protocol
contents, encodings, and convergence layer requirements in Bundle contents, encodings, and convergence layer requirements in Bundle
Protocol Version 7. Specifically, the TCPCLv4 uses CBOR-encoded BPv7 Protocol Version 7. Specifically, the TCPCLv4 uses CBOR-encoded BPv7
bundles as its service data unit being transported and provides a bundles as its service data unit being transported and provides a
skipping to change at page 1, line 43 skipping to change at page 1, line 43
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 October 2, 2019. This Internet-Draft will expire on February 21, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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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. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 6 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 5
2.1. Definitions Specific to the TCPCL Protocol . . . . . . . 6 2.1. Definitions Specific to the TCPCL Protocol . . . . . . . 5
3. General Protocol Description . . . . . . . . . . . . . . . . 9 3. General Protocol Description . . . . . . . . . . . . . . . . 8
3.1. TCPCL Session Overview . . . . . . . . . . . . . . . . . 9 3.1. Convergence Layer Services . . . . . . . . . . . . . . . 8
3.2. TCPCL States and Transitions . . . . . . . . . . . . . . 11 3.2. TCPCL Session Overview . . . . . . . . . . . . . . . . . 10
3.3. Transfer Segmentation Policies . . . . . . . . . . . . . 16 3.3. TCPCL States and Transitions . . . . . . . . . . . . . . 12
3.4. Example Message Exchange . . . . . . . . . . . . . . . . 17 3.4. Transfer Segmentation Policies . . . . . . . . . . . . . 18
4. Session Establishment . . . . . . . . . . . . . . . . . . . . 19 3.5. Example Message Exchange . . . . . . . . . . . . . . . . 19
4.1. TCP Connection . . . . . . . . . . . . . . . . . . . . . 19 4. Session Establishment . . . . . . . . . . . . . . . . . . . . 21
4.2. Contact Header . . . . . . . . . . . . . . . . . . . . . 19 4.1. TCP Connection . . . . . . . . . . . . . . . . . . . . . 21
4.3. Contact Validation and Negotiation . . . . . . . . . . . 20 4.2. Contact Header . . . . . . . . . . . . . . . . . . . . . 22
4.4. Session Security . . . . . . . . . . . . . . . . . . . . 21 4.3. Contact Validation and Negotiation . . . . . . . . . . . 23
4.4.1. TLS Handshake Result . . . . . . . . . . . . . . . . 22 4.4. Session Security . . . . . . . . . . . . . . . . . . . . 24
4.4.2. Example TLS Initiation . . . . . . . . . . . . . . . 22 4.4.1. TLS Handshake . . . . . . . . . . . . . . . . . . . . 24
4.5. Message Type Codes . . . . . . . . . . . . . . . . . . . 23 4.4.2. TLS Authentication . . . . . . . . . . . . . . . . . 25
4.6. Session Initialization Message (SESS_INIT) . . . . . . . 24 4.4.3. Example TLS Initiation . . . . . . . . . . . . . . . 26
4.7. Session Parameter Negotiation . . . . . . . . . . . . . . 26 4.5. Message Header . . . . . . . . . . . . . . . . . . . . . 27
4.8. Session Extension Items . . . . . . . . . . . . . . . . . 27 4.6. Session Initialization Message (SESS_INIT) . . . . . . . 28
5. Established Session Operation . . . . . . . . . . . . . . . . 28 4.7. Session Parameter Negotiation . . . . . . . . . . . . . . 30
5.1. Upkeep and Status Messages . . . . . . . . . . . . . . . 28 4.8. Session Extension Items . . . . . . . . . . . . . . . . . 31
5.1.1. Session Upkeep (KEEPALIVE) . . . . . . . . . . . . . 28 5. Established Session Operation . . . . . . . . . . . . . . . . 32
5.1.2. Message Rejection (MSG_REJECT) . . . . . . . . . . . 29 5.1. Upkeep and Status Messages . . . . . . . . . . . . . . . 32
5.2. Bundle Transfer . . . . . . . . . . . . . . . . . . . . . 30 5.1.1. Session Upkeep (KEEPALIVE) . . . . . . . . . . . . . 32
5.2.1. Bundle Transfer ID . . . . . . . . . . . . . . . . . 30 5.1.2. Message Rejection (MSG_REJECT) . . . . . . . . . . . 33
5.2.2. Data Transmission (XFER_SEGMENT) . . . . . . . . . . 31 5.2. Bundle Transfer . . . . . . . . . . . . . . . . . . . . . 34
5.2.3. Data Acknowledgments (XFER_ACK) . . . . . . . . . . . 33 5.2.1. Bundle Transfer ID . . . . . . . . . . . . . . . . . 35
5.2.4. Transfer Refusal (XFER_REFUSE) . . . . . . . . . . . 34 5.2.2. Data Transmission (XFER_SEGMENT) . . . . . . . . . . 35
5.2.5. Transfer Extension Items . . . . . . . . . . . . . . 36 5.2.3. Data Acknowledgments (XFER_ACK) . . . . . . . . . . . 37
6. Session Termination . . . . . . . . . . . . . . . . . . . . . 38 5.2.4. Transfer Refusal (XFER_REFUSE) . . . . . . . . . . . 38
6.1. Session Termination Message (SESS_TERM) . . . . . . . . . 38 5.2.5. Transfer Extension Items . . . . . . . . . . . . . . 41
6.2. Idle Session Shutdown . . . . . . . . . . . . . . . . . . 40 6. Session Termination . . . . . . . . . . . . . . . . . . . . . 43
7. Implementation Status . . . . . . . . . . . . . . . . . . . . 40 6.1. Session Termination Message (SESS_TERM) . . . . . . . . . 43
8. Security Considerations . . . . . . . . . . . . . . . . . . . 41 6.2. Idle Session Shutdown . . . . . . . . . . . . . . . . . . 45
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 42 7. Implementation Status . . . . . . . . . . . . . . . . . . . . 45
9.1. Port Number . . . . . . . . . . . . . . . . . . . . . . . 42 8. Security Considerations . . . . . . . . . . . . . . . . . . . 46
9.2. Protocol Versions . . . . . . . . . . . . . . . . . . . . 43 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 47
9.3. Session Extension Types . . . . . . . . . . . . . . . . . 43 9.1. Port Number . . . . . . . . . . . . . . . . . . . . . . . 47
9.4. Transfer Extension Types . . . . . . . . . . . . . . . . 44 9.2. Protocol Versions . . . . . . . . . . . . . . . . . . . . 48
9.5. Message Types . . . . . . . . . . . . . . . . . . . . . . 45 9.3. Session Extension Types . . . . . . . . . . . . . . . . . 48
9.6. XFER_REFUSE Reason Codes . . . . . . . . . . . . . . . . 45 9.4. Transfer Extension Types . . . . . . . . . . . . . . . . 49
9.7. SESS_TERM Reason Codes . . . . . . . . . . . . . . . . . 46 9.5. Message Types . . . . . . . . . . . . . . . . . . . . . . 50
9.8. MSG_REJECT Reason Codes . . . . . . . . . . . . . . . . . 47 9.6. XFER_REFUSE Reason Codes . . . . . . . . . . . . . . . . 50
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 48 9.7. SESS_TERM Reason Codes . . . . . . . . . . . . . . . . . 51
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 48 9.8. MSG_REJECT Reason Codes . . . . . . . . . . . . . . . . . 52
11.1. Normative References . . . . . . . . . . . . . . . . . . 48 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 53
11.2. Informative References . . . . . . . . . . . . . . . . . 49 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 53
Appendix A. Significant changes from RFC7242 . . . . . . . . . . 49 11.1. Normative References . . . . . . . . . . . . . . . . . . 53
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 50 11.2. Informative References . . . . . . . . . . . . . . . . . 54
Appendix A. Significant changes from RFC7242 . . . . . . . . . . 55
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 56
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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| TCP | ---> Transport Layer | TCP | ---> Transport Layer
+-------------------------+ +-------------------------+
| IPv4/IPv6 | ---> Network Layer | IPv4/IPv6 | ---> Network Layer
+-------------------------+ +-------------------------+
| Link-Layer Protocol | ---> Link Layer | Link-Layer Protocol | ---> Link Layer
+-------------------------+ +-------------------------+
Figure 1: The Locations of the Bundle Protocol and the TCP Figure 1: The Locations of the Bundle Protocol and the TCP
Convergence-Layer Protocol above the Internet Protocol Stack Convergence-Layer Protocol above the Internet Protocol Stack
1.1. Scope
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 [I-D.ietf-dtn-bpbis]. This includes the
includes the concept of bundle fragmentation or bundle concept of bundle fragmentation or bundle encapsulation. The
encapsulation. The TCPCL transfers bundles as opaque data blocks. TCPCL transfers bundles as opaque data blocks.
o Mechanisms for locating or identifying other bundle entities o Mechanisms for locating or identifying other bundle entities
within an internet. (peers) within a network or across an internet. The mapping of
Node ID to potential CL protocol and network address is left to
1.1. Convergence Layer Services implementation and configuration of the BP Agent and its various
potential routing strategies.
This version of the TCPCL provides the following services to support
the overlaying Bundle Protocol agent. In all cases, this is not an
API defintion but a logical description of how the CL may interact
with the BP agent. Each of these interactions may be associated with
any number of additional metadata items as necessary to support the
operation of the CL or BP agent.
Attempt Session The TCPCL allows a BP agent to pre-emptively attempt
to establish a TCPCL session with a peer entity. Each session
attempt can send a different set of session negotiation parameters
as directed by the BP agent.
Terminate Session The TCPCL allows a BP agent to pre-emptively
terminate an established TCPCL session with a peer entity. The
terminate request is on a per-session basis.
Session State Changed The TCPCL supports indication when the session
state changes. The top-level session states indicated are:
Contact Negotating: A TCP connection has been made (as either
active or passive entity) and contact negotiation has begun.
Session Negotiating: Contact negotation has been completed
(including possible TLS use) and session negotiation has begun.
Established: The session has been fully established and is ready
for its first transfer.
Closing: The entity received a SESS_TERM message and is in the
closing state.
Terminated: The session has finished normal termination
sequencing..
Failed: The session ended without normal termination sequencing.
Session Idle Changed The TCPCL supports indication when the live/
idle sub-state changes. This occurs only when the top-level
session state is Established. Because TCPCL transmits serially
over a TCP connection, it suffers from "head of queue blocking"
this indication provides information about when a session is
available for immediate transfer start.
Begin Transmission The principal purpose of the TCPCL is to allow a
BP agent to transmit bundle data over an established TCPCL
session. Transmission request is on a per-session basis, the CL
does not necessarily perform any per-session or inter-session
queueing. Any queueing of transmissions is the obligation of the
BP agent.
Transmission Success The TCPCL supports positive indication when a
bundle has been fully transferred to a peer entity.
Transmission Intermediate Progress The TCPCL supports positive
indication of intermediate progress of transferr to a peer entity.
This intermediate progress is at the granularity of each
transferred segment.
Transmission Failure The TCPCL supports positive indication of
certain reasons for bundle transmission failure, notably when the
peer entity rejects the bundle or when a TCPCL session ends before
transferr success. The TCPCL itself does not have a notion of
transfer timeout.
Reception Initialized The TCPCL supports indication to the reciver
just before any transmssion data is sent. This corresponds to
reception of the XFER_SEGMENT message with the START flag set.
Interrupt Reception The TCPCL allows a BP agent to interrupt an
individual transfer before it has fully completed (successfully or
not). Interruption can occur any time after the reception is
initialized.
Reception Success The TCPCL supports positive indication when a o Logic for routing bundles along a path toward a bundle's endpoint.
bundle has been fully transferred from a peer entity. This CL protocol is involved only in transporting bundles between
adjacent nodes in a routing sequence.
Reception Intermediate Progress The TCPCL supports positive o Policies or mechanisms for assigning X.509 certificates,
indication of intermediate progress of transfer from the peer provisioning or deploying certificates and private keys, or
entity. This intermediate progress is at the granularity of each configuring security parameters on an individual BP node or across
transferred segment. Intermediate reception indication allows a a network.
BP agent the chance to inspect bundle header contents before the
entire bundle is available, and thus supports the "Reception
Interruption" capability.
Reception Failure The TCPCL supports positive indication of certain Any TCPCL implementation requires a BP agent to perform those above
reasons for reception failure, notably when the local entity listed functions in order to perform end-to-end bundle delivery.
rejects an attempted transfer for some local policy reason or when
a TCPCL session ends before transfer success. The TCPCL itself
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", "SHALLNOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
document are to be interpreted as described in [RFC2119]. "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2.1. Definitions Specific to the TCPCL Protocol 2.1. Definitions Specific to the TCPCL Protocol
This section contains definitions specific to the TCPCL protocol. This section contains definitions specific to the TCPCL protocol.
TCPCL Entity: This is the notional TCPCL application that initiates TCPCL Entity: This is the notional TCPCL application that initiates
TCPCL sessions. This design, implementation, configuration, and TCPCL sessions. This design, implementation, configuration, and
specific behavior of such an entity is outside of the scope of specific behavior of such an entity is outside of the scope of
this document. However, the concept of an entity has utility this document. However, the concept of an entity has utility
within the scope of this document as the container and initiator within the scope of this document as the container and initiator
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Figure 3: The relationship within a TCPCL Session of its two streams Figure 3: The relationship within a TCPCL Session of its two streams
3. General Protocol Description 3. General Protocol Description
The service of this protocol is the transmission of DTN bundles via The service of this protocol is the transmission of DTN bundles via
the Transmission Control Protocol (TCP). This document specifies the the Transmission Control Protocol (TCP). This document specifies the
encapsulation of bundles, procedures for TCP setup and teardown, and encapsulation of bundles, procedures for TCP setup and teardown, and
a set of messages and node requirements. The general operation of a set of messages and node requirements. The general operation of
the protocol is as follows. the protocol is as follows.
3.1. TCPCL Session Overview 3.1. Convergence Layer Services
This version of the TCPCL provides the following services to support
the overlaying Bundle Protocol agent. In all cases, this is not an
API defintion but a logical description of how the CL can interact
with the BP agent. Each of these interactions can be associated with
any number of additional metadata items as necessary to support the
operation of the CL or BP agent.
Attempt Session: The TCPCL allows a BP agent to pre-emptively
attempt to establish a TCPCL session with a peer entity. Each
session attempt can send a different set of session negotiation
parameters as directed by the BP agent.
Terminate Session: The TCPCL allows a BP agent to pre-emptively
terminate an established TCPCL session with a peer entity. The
terminate request is on a per-session basis.
Session State Changed: The TCPCL supports indication when the
session state changes. The top-level session states indicated
are:
Connecting: A TCP connection is being established. This state
only applies to the active entity.
Contact Negotating: A TCP connection has been made (as either
active or passive entity) and contact negotiation has begun.
Session Negotiating: Contact negotation has been completed
(including possible TLS use) and session negotiation has begun.
Established: The session has been fully established and is ready
for its first transfer.
Ending: The entity received a SESS_TERM message and is in the
ending state.
Terminated: The session has finished normal termination
sequencing.
Failed: The session ended without normal termination sequencing.
Session Idle Changed: The TCPCL supports indication when the live/
idle sub-state of the session changes. This occurs only when the
top-level session state is "Established". The session transitions
from Idle to Live at the at the start of a transfer in either
transfer stream; the session transitions from Live to Idle at the
end of a transfer when the other transfer stream does not have an
ongoing transfer. Because TCPCL transmits serially over a TCP
connection, it suffers from "head of queue blocking" this
indication provides information about when a session is available
for immediate transfer start.
Begin Transmission: The principal purpose of the TCPCL is to allow a
BP agent to transmit bundle data over an established TCPCL
session. Transmission request is on a per-session basis, the CL
does not necessarily perform any per-session or inter-session
queueing. Any queueing of transmissions is the obligation of the
BP agent.
Transmission Success: The TCPCL supports positive indication when a
bundle has been fully transferred to a peer entity.
Transmission Intermediate Progress: The TCPCL supports positive
indication of intermediate progress of transferr to a peer entity.
This intermediate progress is at the granularity of each
transferred segment.
Transmission Failure: The TCPCL supports positive indication of
certain reasons for bundle transmission failure, notably when the
peer entity rejects the bundle or when a TCPCL session ends before
transferr success. The TCPCL itself does not have a notion of
transfer timeout.
Reception Initialized: The TCPCL supports indication to the reciver
just before any transmssion data is sent. This corresponds to
reception of the XFER_SEGMENT message with the START flag set.
Interrupt Reception: The TCPCL allows a BP agent to interrupt an
individual transfer before it has fully completed (successfully or
not). Interruption can occur any time after the reception is
initialized.
Reception Success: The TCPCL supports positive indication when a
bundle has been fully transferred from a peer entity.
Reception Intermediate Progress: The TCPCL supports positive
indication of intermediate progress of transfer from the peer
entity. This intermediate progress is at the granularity of each
transferred segment. Intermediate reception indication allows a
BP agent the chance to inspect bundle header contents before the
entire bundle is available, and thus supports the "Reception
Interruption" capability.
Reception Failure: The TCPCL supports positive indication of certain
reasons for reception failure, notably when the local entity
rejects an attempted transfer for some local policy reason or when
a TCPCL session ends before transfer success. The TCPCL itself
does not have a notion of transfer timeout.
3.2. TCPCL Session Overview
First, one node establishes a TCPCL session to the other by First, one node establishes a TCPCL session to the other by
initiating a TCP connection in accordance with [RFC0793]. After initiating a TCP connection in accordance with [RFC0793]. After
setup of the TCP connection is complete, an initial contact header is setup of the TCP connection is complete, an initial contact header is
exchanged in both directions to establish a shared TCPCL version and exchanged in both directions to establish a shared TCPCL version and
possibly initiate TLS security. Once contact negotiation is possibly initiate TLS security. Once contact negotiation is
complete, TCPCL messaging is available and the session negotiation is complete, TCPCL messaging is available and the session negotiation is
used to set parameters of the TCPCL session. One of these parameters used to set parameters of the TCPCL session. One of these parameters
is a singleton endpoint identifier for each node (not the singleton is a Node ID of each TCPCL Entity. This is used to assist in routing
Endpoint Identifier (EID) of any application running on the node) to and forwarding messages by the BP Agent and is part of the
denote the bundle-layer identity of each DTN node. This is used to authentication capability provided by TLS.
assist in routing and forwarding messages (e.g. to prevent loops).
Once negotiated, the parameters of a TCPCL session cannot change and Once negotiated, the parameters of a TCPCL session cannot change and
if there is a desire by either peer to transfer data under different if there is a desire by either peer to transfer data under different
parameters then a new session must be established. This makes CL parameters then a new session must be established. This makes CL
logic simpler but relies on the assumption that establishing a TCP logic simpler but relies on the assumption that establishing a TCP
connection is lightweight enough that TCP connection overhead is connection is lightweight enough that TCP connection overhead is
negligable compared to TCPCL data sizes. negligable compared to TCPCL data sizes.
Once the TCPCL session is established and configured in this way, Once the TCPCL session is established and configured in this way,
bundles can be transferred in either direction. Each transfer is bundles can be transferred in either direction. Each transfer is
performed by an sequence of logical segments of data within performed by an sequence of logical segments of data within
XFER_SEGMENT messages. Multiple bundles can be transmitted XFER_SEGMENT messages. Multiple bundles can be transmitted
consecutively in a single direction on a single TCPCL connection. consecutively in a single direction on a single TCPCL connection.
Segments from different bundles are never interleaved. Bundle Segments from different bundles are never interleaved. Bundle
interleaving can be accomplished by fragmentation at the BP layer or interleaving can be accomplished by fragmentation at the BP layer or
by establishing multiple TCPCL sessions between the same peers. by establishing multiple TCPCL sessions between the same peers.
There is no fundamental limit on the number of TCPCL sessions which a
single node can establish beyond the limit imposed by the number of
available (ephemeral) TCP ports of the passive peer.
A feature of this protocol is for the receiving node to send A feature of this protocol is for the receiving node to send
acknowledgment (XFER_ACK) messages as bundle data segments arrive. acknowledgment (XFER_ACK) messages as bundle data segments arrive.
The rationale behind these acknowledgments is to enable the sender The rationale behind these acknowledgments is to enable the sender
node to determine how much of the bundle has been received, so that node to determine how much of the bundle has been received, so that
in case the session is interrupted, it can perform reactive in case the session is interrupted, it can perform reactive
fragmentation to avoid re-sending the already transmitted part of the fragmentation to avoid re-sending the already transmitted part of the
bundle. In addition, there is no explicit flow control on the TCPCL bundle. In addition, there is no explicit flow control on the TCPCL
layer. layer.
skipping to change at page 10, line 40 skipping to change at page 11, line 48
hasn't already finished transmission) Note: This enables a cross- hasn't already finished transmission) Note: This enables a cross-
layer optimization in that it allows a receiver that detects that it layer optimization in that it allows a receiver that detects that it
already has received a certain bundle to interrupt transmission as already has received a certain bundle to interrupt transmission as
early as possible and thus save transmission capacity for other early as possible and thus save transmission capacity for other
bundles. bundles.
For sessions that are idle, a KEEPALIVE message is sent at a For sessions that are idle, a KEEPALIVE message is sent at a
negotiated interval. This is used to convey node live-ness negotiated interval. This is used to convey node live-ness
information during otherwise message-less time intervals. information during otherwise message-less time intervals.
A SESS_TERM message is used to start the closing of a TCPCL session A SESS_TERM message is used to start the ending 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 SESS_TERM 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.
Once a session is established established, TCPCL is a symmetric Once a session is established, TCPCL is a symmetric protocol between
protocol between the peers. Both sides can start sending data the peers. Both sides can start sending data segments in a session,
segments in a session, and one side's bundle transfer does not have and one side's bundle transfer does not have to complete before the
to complete before the other side can start sending data segments on other side can start sending data segments on its own. Hence, the
its own. Hence, the protocol allows for a bi-directional mode of protocol allows for a bi-directional mode of communication. Note
communication. Note that in the case of concurrent bidirectional that in the case of concurrent bidirectional transmission,
transmission, acknowledgment segments MAY be interleaved with data acknowledgment segments MAY be interleaved with data segments.
segments.
3.2. TCPCL States and Transitions 3.3. TCPCL States and Transitions
The states of a nominal TCPCL session (i.e. without session failures) The states of a nominal TCPCL session (i.e. without session failures)
are indicated in Figure 4. are indicated in Figure 4.
+-------+ +-------+
| START | | START |
+-------+ +-------+
| |
TCP Establishment TCP Establishment
| |
skipping to change at page 12, line 28 skipping to change at page 13, line 28
| Negotiated | Negotiated
V V
+-------------+ +-------------+ +-------------+ +-------------+
| Established |----New Transfer---->| Established | | Established |----New Transfer---->| Established |
| Session | | Session | | Session | | Session |
| Idle |<---Transfers Done---| Live | | Idle |<---Transfers Done---| Live |
+-------------+ +-------------+ +-------------+ +-------------+
| | | |
+------------------------------------+ +------------------------------------+
| |
SESS_TERM Exchange [SESSTERM] Exchange
| |
V V
+-------------+ +-------------+
| Established | +-------------+ | Established | +-------------+
| Session |----Transfers------>| TCP | | Session |----Transfers------>| TCP |
| Ending | Done | Terminating | | Ending | Done | Terminating |
+-------------+ +-------------+ +-------------+ +-------------+
| |
+------------Close Message------------+ +----------TCP Close Message----------+
| |
V V
+-------+ +-------+
| END | | END |
+-------+ +-------+
Figure 4: Top-level states of a TCPCL session Figure 4: Top-level states of a TCPCL session
Notes on Established Session states: Notes on Established Session states:
Session "Live" means transmitting or reeiving over a transfer Session "Live" means transmitting or reeiving over a transfer
stream. stream.
Session "Idle" means no transmission/reception over a transfer Session "Idle" means no transmission/reception over a transfer
stream. stream.
Session "Closing" means no new transfers will be allowed. Session "Ending" means no new transfers will be allowed.
The contact negotiation sequencing is performed either as the active Contact negotation involves exchanging a Contact Header (CH) in both
or passive peer, and is illustrated in Figure 5 and Figure 6 directions and deriving a negotiated state from the two headers. The
contact negotiation sequencing is performed either as the active or
passive peer, and is illustrated in Figure 5 and Figure 6
respectively which both share the data validation and analyze final respectively which both share the data validation and analyze final
states of Figure 7. states of the "[PCH]" activity of Figure 7 and the "[TCPCLOSE]"
activity which indicates TCP connection close. Successful
negotiation results in one of the Session Initiation "[SI]"
activities being performed.
+-------+ +-------+
| START |-----TCP-----+ | START |
+-------+ Connecting | +-------+
V |
+-----------+ +---------+ TCP Connecting
| Connected |--OK-->| Send CH |--OK-->[PCH] V
+-----------+ +---------+ +-----------+
| | | TCP | +---------+
Error Error | Connected |--Send CH-->| Waiting |--Timeout-->[TCPCLOSE]
| | +-----------+ +---------+
V | |
[TCPTERM]<-------------+ Recevied CH
V
[PCH]
Figure 5: Contact Initiation as Active peer Figure 5: Contact Initiation as Active peer
+-------+ +-----------+ +---------+
| START |-----TCP----->[PCH] | TCP |--Wait for-->| Waiting |--Timeout-->[TCPCLOSE]
+-------+ Connected | Connected | CH +---------+
+-----------+ |
Received CH
V
+-----------------+
| Preparing reply |--Send CH-->[PSI]
+-----------------+
Figure 6: Contact Initiation as Passive peer Figure 6: Contact Initiation as Passive peer
+-------->[TCPTERM]<----------+
| |
Timeout Error
or Error |
| |
+-------+ +---------+ Contact +----------+
| START |---->| Waiting |---- Header --->| Validate |
+-------+ +---------+ Received +----------+
|
+---------------------------+
|
V
+---------+
+--Error--| Analyze |---No TLS---->[SI]
| | | ^
| +---------+ |
| | |
V TLS |
[TCPTERM] Negotiated |
^ | |
| V |
| +-----------+ |
| | Establish |---Success---+
+--Error--| TLS |
+-----------+
Figure 7: Processing of Contact Header (PCH) +-----------+
| Peer CH |
| available |
+-----------+
|
Validate and
Negotiate
V
+------------+
| Negotiated |----Failure---->[TCPCLOSE]
+------------+ ^
| | |
No TLS +----Negotiate---+ |
V TLS | Failure
+-----------+ V |
| TCPCL | +---------------+
| Messaging |<--Success--| TLS Finished |
| Available | +---------------+
+-----------+
The session negotiation sequencing is performed either as the active Figure 7: Processing of Contact Header [PCH]
or passive peer, and is illustrated in Figure 8 and Figure 9
respectively which both share the data validation and analyze final
states of Figure 10.
+-------+ TCPCL Session negotation involves exchanging a session initialization
| START |--Messaging--+ (SESS_INIT) message in both directions and deriving a negotiated
+-------+ Available | state from the two messages. The session negotiation sequencing is
V performed either as the active or passive peer, and is illustrated in
+----------------+ Figure 8 and Figure 9 respectively which both share the data
| Send SESS_INIT |--OK-->[PSI] validation and analyze final states of Figure 10. The validation
+----------------+ here includes certificate validation and authentication when TLS is
| used for the session.
Error
|
V
[SESSTERM]
Figure 8: Session Initiation as Active peer +-----------+
| TCPCL | +---------+
| Messaging |--Send SESS_INIT-->| Waiting |--Timeout-->[SESSTERM]
| Available | +---------+
+-----------+ |
Recevied SESS_INIT
|
V
[PSI]
+-------+ TCPCL Figure 8: Session Initiation [SI] as Active peer
| START |---Messaging-->[PSI]
+-------+ Available
Figure 9: Session Initiation as Passive peer +-----------+
| TCPCL | +---------+
| Messaging |----Wait for ---->| Waiting |--Timeout-->[SESSTERM]
| Available | SESS_INIT +---------+
+-----------+ |
Recevied SESS_INIT
|
+-----------------+
| Preparing reply |--Send SESS_INIT-->[PSI]
+-----------------+
+------->[SESSTERM]<--------+ Figure 9: Session Initiation [SI] as Passive peer
| |
Timeout Error
or Error |
| |
+-------+ +---------+ +----------+
| START |---->| Waiting |---SESS_INIT--->| Validate |
+-------+ +---------+ Received +----------+
|
+---------------------------+
|
V
+---------+ +--------------+
+--Error--| Analyze |---->| Established |
| | | | Session Idle |
| +---------+ +--------------+
V
[SESSTERM]
Figure 10: Processing of Session Initiation (PSI) +----------------+
| Peer SESS_INIT |
| available |
+----------------+
|
Validate and
Negotiate
V
+------------+
| Negotiated |---Failure--->[SESSTERM]
+------------+
|
Success
V
+--------------+
| Established |
| Session Idle |
+--------------+
Figure 10: Processing of Session Initiation [PSI]
Transfers can occur after a session is established and it's not in Transfers can occur after a session is established and it's not in
the ending state. Each transfer occurs within a single logical the ending state. Each transfer occurs within a single logical
transfer stream between a sender and a receiver, as illustrated in transfer stream between a sender and a receiver, as illustrated in
Figure 11 and Figure 12 respectively. Figure 11 and Figure 12 respectively.
+--Send XFER_SEGMENT--+ +--Send XFER_SEGMENT--+
+--------+ | | +--------+ | |
| Stream | +-------------+ | | Stream | +-------------+ |
| Idle |---Send XFER_SEGMENT-->| In Progress |<------------+ | Idle |---Send XFER_SEGMENT-->| In Progress |<------------+
skipping to change at page 16, line 13 skipping to change at page 17, line 29
Figure 11: Transfer sender states Figure 11: Transfer sender states
Notes on transfer sending: Notes on transfer sending:
Pipelining of transfers can occur when the sending entity begins a Pipelining of transfers can occur when the sending entity begins a
new transfer while in the "Waiting for Ack" state. new transfer while in the "Waiting for Ack" state.
+-Receive XFER_SEGMENT-+ +-Receive XFER_SEGMENT-+
+--------+ | Send XFER_ACK | +--------+ | Send XFER_ACK |
| Stream | +-------------+ | | Stream | +-------------+ |
| IDLE |--Receive XFER_SEGMENT-->| In Progress |<-------------+ | Idle |--Receive XFER_SEGMENT-->| In Progress |<-------------+
+--------+ +-------------+ +--------+ +-------------+
| |
+--------Sent Final XFER_ACK--------+ +--------Sent Final XFER_ACK--------+
| |
V V
+--------+ +--------+
| Stream | | Stream |
| IDLE | | Idle |
+--------+ +--------+
Figure 12: Transfer receiver states Figure 12: Transfer receiver states
3.3. Transfer Segmentation Policies Session termination involves one entity initiating the termination of
the session and the other entity acknowledging the termination. For
either entity, it is the sending of the SESS_TERM message which
transitions the session to the ending substate. While a session is
being terminated only in-progress transfers can be completed and no
new transfers can be started.
+-----------+ +---------+
| Session |--Send SESS_TERM-->| Session |
| Live/Idle | | Ending |
+-----------+ +---------+
Figure 13: Session Termination [SESSTERM] from the Initiator
+-----------+ +---------+
| Session |--Send SESS_TERM-->| Session |
| Live/Idle | | Ending |
+-----------+<------+ +---------+
| |
Receive SESS_TERM |
| |
+-------------+
Figure 14: Session Termination [SESSTERM] from the Responder
3.4. Transfer Segmentation Policies
Each TCPCL session allows a negotiated transfer segmentation polcy to Each TCPCL session allows a negotiated transfer segmentation polcy to
be applied in each transfer direction. A receiving node can set the be applied in each transfer direction. A receiving node can set the
Segment MRU in its contact header to determine the largest acceptable Segment MRU in its contact header to determine the largest acceptable
segment size, and a transmitting node can segment a transfer into any segment size, and a transmitting node can segment a transfer into any
sizes smaller than the receiver's Segment MRU. It is a network sizes smaller than the receiver's Segment MRU. It is a network
administration matter to determine an appropriate segmentation policy administration matter to determine an appropriate segmentation policy
for entities operating TCPCL, but guidance given here can be used to for entities operating TCPCL, but guidance given here can be used to
steer policy toward performance goals. It is also advised to steer policy toward performance goals. It is also advised to
consider the Segment MRU in relation to chunking/packetization consider the Segment MRU in relation to chunking/packetization
performed by TLS, TCP, and any intermediate network-layer nodes. performed by TLS, TCP, and any intermediate network-layer nodes.
Minimum Overhead For a simple network expected to exchange Minimum Overhead: For a simple network expected to exchange
relatively small bundles, the Segment MRU can be set to be relatively small bundles, the Segment MRU can be set to be
identical to the Transfer MRU which indicates that all transfers identical to the Transfer MRU which indicates that all transfers
can be sent with a single data segment (i.e. no actual can be sent with a single data segment (i.e. no actual
segmentation). If the network is closed and all transmitters are segmentation). If the network is closed and all transmitters are
known to follow a single-segment transfer policy, then receivers known to follow a single-segment transfer policy, then receivers
can avoid the necessity of segment reassembly. Because this CL can avoid the necessity of segment reassembly. Because this CL
operates over a TCP stream, which suffers from a form of head-of- operates over a TCP stream, which suffers from a form of head-of-
queue blocking between messages, while one node is transmitting a queue blocking between messages, while one node is transmitting a
single XFER_SEGMENT message it is not able to transmit any single XFER_SEGMENT message it is not able to transmit any
XFER_ACK or XFER_REFUSE for any associated received transfers. XFER_ACK or XFER_REFUSE for any associated received transfers.
Predictable Message Sizing In situations where the maximum message Predictable Message Sizing: In situations where the maximum message
size is desired to be well-controlled, the Segment MRU can be set size is desired to be well-controlled, the Segment MRU can be set
to the largest acceptable size (the message size less XFER_SEGMENT to the largest acceptable size (the message size less XFER_SEGMENT
header size) and transmitters can always segment a transfer into header size) and transmitters can always segment a transfer into
maximum-size chunks no larger than the Segment MRU. This maximum-size chunks no larger than the Segment MRU. This
guarantees that any single XFER_SEGMENT will not monopolize the guarantees that any single XFER_SEGMENT will not monopolize the
TCP stream for too long, which would prevent outgoing XFER_ACK and TCP stream for too long, which would prevent outgoing XFER_ACK and
XFER_REFUSE associated with received transfers. XFER_REFUSE associated with received transfers.
Dynamic Segmentation Even after negotiation of a Segment MRU for Dynamic Segmentation: Even after negotiation of a Segment MRU for
each receiving node, the actual transfer segmentation only needs each receiving node, the actual transfer segmentation only needs
to guarantee than any individual segment is no larger than that to guarantee than any individual segment is no larger than that
MRU. In a situation where network "goodput" is dynamic, the MRU. In a situation where network "goodput" is dynamic, the
transfer segmentation size can also be dynamic in order to control transfer segmentation size can also be dynamic in order to control
message transmission duration. message transmission duration.
Many other policies can be established in a TCPCL network between Many other policies can be established in a TCPCL network between the
these two extremes. Different policies can be applied to each two extremes of minimum overhead (large MRU, single-segment) and
direction to/from any particular node. Additionally, future header predictable message sizing (small MRU, highly segmented). Different
and transfer extension types can apply further nuance to transfer policies can be applied to each transfer stream to and from from any
policies and policy negotiation. particular node. Additionally, future header and transfer extension
types can apply further nuance to transfer policies and policy
negotiation.
3.4. Example Message Exchange 3.5. 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 Entity A to Entity B. and "L3") from Entity A to Entity B.
Note that the sending node can transmit multiple XFER_SEGMENT Note that the sending node can transmit multiple XFER_SEGMENT
messages without waiting for the corresponding XFER_ACK responses. messages without waiting for the corresponding XFER_ACK responses.
This enables pipelining of messages on a transfer stream. Although This enables pipelining of messages on a transfer stream. Although
this example only demonstrates a single bundle transmission, it is this example only demonstrates a single bundle transmission, it is
skipping to change at page 18, line 46 skipping to change at page 20, line 46
<- | XFER_ACK (end) | <- | XFER_ACK (end) |
| Transfer ID [I1] | | Transfer ID [I1] |
| Length [L1+L2+L3] | | Length [L1+L2+L3] |
+-------------------------+ +-------------------------+
+-------------------------+ +-------------------------+
| SESS_TERM | -> +-------------------------+ | SESS_TERM | -> +-------------------------+
+-------------------------+ <- | SESS_TERM | +-------------------------+ <- | SESS_TERM |
+-------------------------+ +-------------------------+
Figure 13: An example of the flow of protocol messages on a single Figure 15: An example of the flow of protocol messages on a single
TCP Session between two entities TCP Session between two entities
4. Session Establishment 4. Session Establishment
For bundle transmissions to occur using the TCPCL, a TCPCL session For bundle transmissions to occur using the TCPCL, a TCPCL session
MUST first be established between communicating entities. It is up MUST first be established between communicating entities. It is up
to the implementation to decide how and when session setup is to the implementation to decide how and when session setup is
triggered. For example, some sessions MAY be opened proactively and triggered. For example, some sessions MAY be opened proactively and
maintained for as long as is possible given the network conditions, maintained for as long as is possible given the network conditions,
while other sessions MAY be opened only when there is a bundle that while other sessions MAY be opened only when there is a bundle that
skipping to change at page 19, line 35 skipping to change at page 21, line 35
the implementation. Any source port number MAY be used for TCPCL the implementation. Any source port number MAY be used for TCPCL
sessions. Typically an operating system assigned number in the TCP sessions. Typically an operating system assigned number in the TCP
Ephemeral range (49152-65535) is used. Ephemeral range (49152-65535) is used.
If the entity is unable to establish a TCP connection for any reason, If the entity is unable to establish a TCP connection for any reason,
then it is an implementation matter to determine how to handle the then it is an implementation matter to determine how to handle the
connection failure. An entity MAY decide to re-attempt to establish connection failure. An entity MAY decide to re-attempt to establish
the connection. If it does so, it MUST NOT overwhelm its target with the connection. If it does so, it MUST NOT overwhelm its target with
repeated connection attempts. Therefore, the entity MUST retry the repeated connection attempts. Therefore, the entity MUST 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 back-off mechanism
to increase this delay in case of repeated failures. to increase this delay in case of repeated failures. The upper limit
on a re-attempt back-off is implementation defined but SHOULD be no
longer than one minute before signaling to the BP agent that a
connection cannot be made.
Once a TCP connection is established, each entity 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. Because the TCPCL
protocol version in use is part of the initial contact header, nodes
using TCPCL version 4 can coexist on a network with nodes using
earlier TCPCL versions (with some negotiation needed for
interoperation as described in Section 4.3).
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 entities perform the Upon receipt of the contact header, both entities perform the
validation and negotiation procedures defined in Section 4.3. After validation and negotiation procedures defined in Section 4.3. After
receiving the contact header from the other entity, either entity MAY receiving the contact header from the other entity, either entity MAY
skipping to change at page 20, line 15 skipping to change at page 22, line 27
The format for the Contact Header is as follows: The format for the Contact Header is as follows:
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| magic='dtn!' | | magic='dtn!' |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| Version | Flags | | Version | Flags |
+---------------+---------------+ +---------------+---------------+
Figure 14: Contact Header Format Figure 16: Contact Header Format
See Section 4.3 for details on the use of each of these contact See Section 4.3 for details on the use of each of these contact
header fields. header fields.
The fields of the contact header are: The fields of the contact header are:
magic: A four-octet field that always contains the octet sequence magic: A four-octet field that always contains the octet sequence
0x64 0x74 0x6E 0x21, i.e., the text string "dtn!" in US-ASCII (and 0x64 0x74 0x6E 0x21, i.e., the text string "dtn!" in US-ASCII (and
UTF-8). UTF-8).
Version: A one-octet field value containing the value 4 (current Version: A one-octet field value containing the value 4 (current
version of the protocol). version of the TCPCL).
Flags: A one-octet field of single-bit flags, interpreted according Flags: A one-octet field of single-bit flags, interpreted according
to the descriptions in Table 1. to the descriptions in Table 1. All reserved header flag bits
SHALL be not set by the sender. All reserved header flag bits
SHALL be ignored by the receiver.
+----------+--------+-----------------------------------------------+ +----------+--------+-----------------------------------------------+
| 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 |
+----------+--------+-----------------------------------------------+ +----------+--------+-----------------------------------------------+
skipping to change at page 21, line 6 skipping to change at page 23, line 28
Upon reception of the contact header, each node follows the following Upon reception of the contact header, each node follows the following
procedures to ensure the validity of the TCPCL session and to procedures to ensure the validity of the TCPCL session and to
negotiate values for the session parameters. negotiate values for the session parameters.
If the magic string is not present or is not valid, the connection If the magic string is not present or is not valid, the connection
MUST be terminated. The intent of the magic string is to provide MUST be terminated. The intent of the magic string is to provide
some protection against an inadvertent TCP connection by a different some protection against an inadvertent TCP connection by a different
protocol than the one described in this document. To prevent a flood protocol than the one described in this document. To prevent a flood
of repeated connections from a misconfigured application, an entity of repeated connections from a misconfigured application, an entity
MAY 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 ending it.
The first negotiation is on the TCPCL protocol version to use. The The first negotiation is on the TCPCL protocol version to use. The
active node always sends its Contact Header first and waits for a active node always sends its Contact Header first and waits for a
response from the passive node. The active node can repeatedly response from the passive node. The active node can repeatedly
attempt different protocol versions in descending order until the attempt different protocol versions in descending order until the
passive node accepts one with a corresponding Contact Header reply. passive node accepts one with a corresponding Contact Header reply.
Only upon response of a Contact Header from the passive node is the Only upon response of a Contact Header from the passive node is the
TCPCL protocol version established and parameter negotiation begun. TCPCL protocol version established and parameter negotiation begun.
During contact initiation, the active TCPCL node SHALL send the During contact initiation, the active TCPCL node SHALL send the
highest TCPCL protocol version on a first session attempt for a TCPCL highest TCPCL protocol version on a first session attempt for a TCPCL
peer. If the active node receives a Contact Header with a different peer. If the active node receives a Contact Header with a different
protocol version than the one sent earlier on the TCP connection, the protocol version than the one sent earlier on the TCP connection, the
TCP connection SHALL be terminated. If the active node receives a TCP connection SHALL be terminated. If the active node receives a
SESS_TERM message with reason of "Version Mismatch", that node MAY SESS_TERM message with reason of "Version Mismatch", that node MAY
attempt further TCPCL sessions with the peer using earlier protocol attempt further TCPCL sessions with the peer using earlier protocol
version numbers in decreasing order. Managing multi-TCPCL-session version numbers in decreasing order. Managing multi-TCPCL-session
state such as this is an implementation matter. state such as this is an implementation matter.
If the passive node receives a contact header containing a version If the passive node receives a contact header containing a version
that is greater than the current version of the protocol that the that is greater than the current version of the TCPCL that the node
node implements, then the node SHALL shutdown the session with a implements, then the node SHALL shutdown the session with a reason
reason code of "Version mismatch". If the passive node receives a code of "Version mismatch". If the passive node receives a contact
contact header with a version that is lower than the version of the header with a version that is lower than the version of the protocol
protocol that the node implements, the node MAY either terminate the that the node implements, the node MAY either terminate the session
session (with a reason code of "Version mismatch") or the node MAY (with a reason code of "Version mismatch") or the node MAY adapt its
adapt its operation to conform to the older version of the protocol. operation to conform to the older version of the protocol. The
The decision of version fall-back is an implementation matter. decision of version fall-back is an implementation matter.
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 terminated and a new non-TLS-negotiated session session MUST be terminated and a new non-TLS-negotiated session
established. established.
4.4.1. TLS Handshake
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 entities SHALL begin a TLS handshake in accordance with session entities SHALL begin a TLS handshake in accordance with TLS
[RFC5246]. The parameters within each TLS negotiation are 1.2 [RFC5246] or any successors that are compatible with TLS 1.2. By
implementation dependent but any TCPCL node SHALL follow all convention, this protocol uses the node which initiated the
recommended practices of [BCP195], or any updates or successors that underlying TCP connection as the "client" role of the TLS handshake
become part of [BCP195]. By convention, this protocol uses the node request.
which initiated the underlying TCP connection 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 8. Specifics about sensitive data exposure are discussed in Section 8.
4.4.1. TLS Handshake Result The parameters within each TLS negotiation are implementation
dependent but any TCPCL node SHALL follow all recommended practices
of BCP 195 [RFC7525], or any updates or successors that become part
of BCP 195. The TLS handshake SHOULD include a Server Name
Indication from the active peer. The TLS handshake SHALL request a
client-side certificate to allow authentication of the active peer.
The passive peer SHOULD supply a certificate within the TLS handshake
to allow authentication of its side of the session. The active peer
SHOULD supply a certificate within the TLS handshake to allow
authentication of its side of the session. All certificates supplied
during TLS handshake SHALL conform with the profile of [RFC5280].
When a certificate is supplied during TLS handshake, the full
certification chain SHOULD be included unless security policy
indicates that is unnecessary.
If a TLS handshake cannot negotiate a TLS session, both entities of If a TLS handshake cannot negotiate a TLS session, both entities of
the TCPCL session SHALL terminate the TCP connection. At this point the TCPCL session SHALL close the TCP connection. At this point the
the TCPCL session has not yet been established so there is no TCPCL TCPCL session has not yet been established so there is no TCPCL
session to terminate. This also avoids any potential security issues session to terminate. This also avoids any potential security issues
assoicated with further TCP communication with an untrusted peer. assoicated with further TCP communication with an untrusted peer.
After a TLS session is successfully established, the active peer After a TLS session is successfully established, the active peer
SHALL send a SESS_INIT message to begin session negotiation. This SHALL send a SESS_INIT message to begin session negotiation. This
session negotation and all subsequent messaging are secured. session negotation and all subsequent messaging are secured.
4.4.2. Example TLS Initiation 4.4.2. TLS Authentication
A summary of a typical CAN_TLS usage is shown in the sequence in Using X.509 certificates exchanged during the TLS handshake, each of
Figure 15 below. the entities can attempt to authenticate its peer at the network
layer (host name and address) and at the application layer (BP Node
ID). The Node ID exchanged in the Session Initialization is likely
to be used by the BP agent for making transfer and routing decisions,
so attempting host name validation is optional while attempting Node
ID validation is required. The logic for attempting validation is
separate from the logic for handling the result of validation, which
is based on local security policy.
Any certificate received during TLS handshake SHALL be validated up
to one or more trusted certificate authority (CA) certificates. If
certificate validation fails or if security policy disallows a
certificate for any reason, the entity SHOULD terminate the session
(with a reason code of "Contact Failure").
Immediately after the TLS handshake, each side of the TCP connection
SHOULD perform host name validation of its peer in accordance with
[RFC6125] unless it is not needed by security policy. The active
peer SHALL attempt to authenticate the host name (of the passive
peer) used to initiate the TCP connection. The active peer MAY
attempt to authenticate the IP address of the other side of the TCP
connection. The passive peer SHALL attempt to authenticate the IP
address of the other side of the TCP connection. The passive peer
MAY use the IP address to resolve one or more host names of the
active peer and attempt to authenticate those. If host name
validation fails (including failure because the certificate does not
contain any DNS-ID), the entity SHOULD terminate the session (with a
reason code of "Contact Failure") unless security policy allows an
unauthticated host.
Immediately before Session Parameter Negotiation, each side of the
session SHALL perform Node ID validation of its peer as described
below. Node ID validation SHALL succeed if the associated
certificate contains a subjectAltName entry of type
uniformResourceIdentifier whose value matches the Node ID of the
TCPCL entity. URI matching of Node IDs SHALL use the URI comparison
logic of [RFC3986] and scheme-based normalization of those schemes
specified in [I-D.ietf-dtn-bpbis]. This is similar to the URI-ID of
[RFC6125] but does not require any structure to the scheme-specific-
part of the URI. If Node ID validation fails (including failure
because the certificate does not contain any subjectAltName URI), the
entity SHOULD terminate the session (with a reason code of "Contact
Failure") unless security policy allows an unauthticated node.
4.4.3. Example TLS Initiation
A summary of a typical TLS use is shown in the sequence in Figure 17
below.
Entity A Entity B Entity A Entity B
======== ======== active peer passive peer
+-------------------------+ +-------------------------+
| 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 ... Host name validation occurs.
Secured TCPCL messaging can begin.
+-------------------------+ +-------------------------+ +-------------------------+ +-------------------------+
| SESS_TERM | -> <- | SESS_TERM | | SESS_INIT | -> <- | SESS_INIT |
+-------------------------+ +-------------------------+ +-------------------------+ +-------------------------+
Figure 15: A simple visual example of TCPCL TLS Establishment between Node ID validation occurs.
Session is established, transfers can begin.
+-------------------------+ +-------------------------+
| SESS_TERM | -> <- | SESS_TERM |
+-------------------------+ +-------------------------+
Figure 17: A simple visual example of TCPCL TLS Establishment between
two entities two entities
4.5. Message Type Codes 4.5. Message Header
After the initial exchange of a contact header, all messages After the initial exchange of a contact header, all messages
transmitted over the session are identified by a one-octet header transmitted over the session are identified by a one-octet header
with the following structure: with the following structure:
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---------------+ +---------------+
| Message Type | | Message Type |
+---------------+ +---------------+
Figure 16: Format of the Message Header Figure 18: 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 2 Message Type: Indicates the type of the message as per Table 2
below. Encoded values are listed in Section 9.5. below. Encoded values are listed in Section 9.5.
+--------------+------+---------------------------------------------+ +--------------+------+---------------------------------------------+
| Name | Code | Description | | Name | Code | Description |
+--------------+------+---------------------------------------------+ +--------------+------+---------------------------------------------+
| SESS_INIT | 0x07 | Contains the session parameter inputs from | | SESS_INIT | 0x07 | Contains the session parameter inputs from |
skipping to change at page 24, line 44 skipping to change at page 28, line 44
Table 2: TCPCL Message Types Table 2: TCPCL Message Types
4.6. Session Initialization Message (SESS_INIT) 4.6. Session Initialization Message (SESS_INIT)
Before a session is established and ready to transfer bundles, the Before a session is established and ready to transfer bundles, the
session parameters are negotiated between the connected entities. session parameters are negotiated between the connected entities.
The SESS_INIT message is used to convey the per-entity parameters The SESS_INIT message is used to convey the per-entity parameters
which are used together to negotiate the per-session parameters as which are used together to negotiate the per-session parameters as
described in Section 4.7. described in Section 4.7.
The format of a SESS_INIT message is as follows in Figure 17. The format of a SESS_INIT message is as follows in Figure 19.
+-----------------------------+ +-----------------------------+
| Message Header | | Message Header |
+-----------------------------+ +-----------------------------+
| Keepalive Interval (U16) | | Keepalive Interval (U16) |
+-----------------------------+ +-----------------------------+
| Segment MRU (U64) | | Segment MRU (U64) |
+-----------------------------+ +-----------------------------+
| Transfer MRU (U64) | | Transfer MRU (U64) |
+-----------------------------+ +-----------------------------+
skipping to change at page 25, line 25 skipping to change at page 29, line 25
+-----------------------------+ +-----------------------------+
| EID Data (variable) | | EID Data (variable) |
+-----------------------------+ +-----------------------------+
| Session Extension | | Session Extension |
| Items Length (U32) | | Items Length (U32) |
+-----------------------------+ +-----------------------------+
| Session Extension | | Session Extension |
| Items (var.) | | Items (var.) |
+-----------------------------+ +-----------------------------+
Figure 17: SESS_INIT Format Figure 19: SESS_INIT Format
The fields of the SESS_INIT message are: The fields of the SESS_INIT message are:
Keepalive Interval: A 16-bit unsigned integer indicating the Keepalive Interval: A 16-bit unsigned integer indicating the
interval, in seconds, between any subsequent messages being interval, in seconds, between any subsequent messages being
transmitted by the peer. The peer receiving this contact header transmitted by the peer. The peer receiving this contact header
uses this interval to determine how long to wait after any last- uses this interval to determine how long to wait after any last-
message transmission and a necessary subsequent KEEPALIVE message message transmission and a necessary subsequent KEEPALIVE message
transmission. transmission.
skipping to change at page 25, line 51 skipping to change at page 29, line 51
relation between the two is required. relation between the two is required.
Transfer MRU: A 64-bit unsigned integer indicating the largest Transfer MRU: A 64-bit unsigned integer indicating the largest
allowable total-bundle data size to be received in this session. allowable total-bundle data size to be received in this session.
Any bundle transfer sent to this peer SHALL have a Total Bundle Any bundle transfer sent to this peer SHALL have a Total Bundle
Length payload no longer than the peer's Transfer MRU. This value Length payload no longer than the peer's Transfer MRU. This value
can be used to perform proactive bundle fragmentation. The two can be used to perform proactive bundle fragmentation. The two
entities of a single session MAY have different Transfer MRUs, and entities of a single session MAY have different Transfer MRUs, and
no relation between the two is required. no relation between the two is required.
EID Length and EID Data: Together these fields represent a variable- Node ID Length and Node ID Data: Together these fields represent a
length text string. The EID Length is a 16-bit unsigned integer variable-length text string. The Node ID Length is a 16-bit
indicating the number of octets of EID Data to follow. A zero EID unsigned integer indicating the number of octets of Node ID Data
Length SHALL be used to indicate the lack of EID rather than a to follow. A zero-length Node ID SHALL be used to indicate the
truly empty EID. This case allows an entity to avoid exposing EID lack of Node ID rather than a truly empty Node ID. This case
information on an untrusted network. A non-zero-length EID Data allows an entity to avoid exposing Node ID information on an
SHALL contain the UTF-8 encoded EID of some singleton endpoint in untrusted network. A non-zero-length Node ID Data SHALL contain
which the sending entity is a member, in the canonical format of the UTF-8 encoded Node ID of the Entity which sent the SESS_INIT
<scheme name>:<scheme-specific part>. This EID encoding is message. Every Node ID SHALL be a URI consistent with the
consistent with [I-D.ietf-dtn-bpbis]. requirements of [RFC3986] and the URI schemes of
[I-D.ietf-dtn-bpbis]. The Node ID itself can be authenticated as
described in Section 4.4.2.
Session Extension Length and Session Extension Items: Together these Session Extension Length and Session Extension Items: Together these
fields represent protocol extension data not defined by this fields represent protocol extension data not defined by this
specification. The Session Extension Length is the total number specification. The Session Extension Length is the total number
of octets to follow which are used to encode the Session Extension of octets to follow which are used to encode the Session Extension
Item list. The encoding of each Session Extension Item is within Item list. The encoding of each Session Extension Item is within
a consistent data container as described in Section 4.8. The full a consistent data container as described in Section 4.8. The full
set of Session Extension Items apply for the duration of the TCPCL set of Session Extension Items apply for the duration of the TCPCL
session to follow. The order and mulitplicity of these Session session to follow. The order and mulitplicity of these Session
Extension Items MAY be significant, as defined in the associated Extension Items MAY be significant, as defined in the associated
skipping to change at page 26, line 51 skipping to change at page 31, line 5
Session Keepalive: Negotiation of the Session Keepalive parameter is Session Keepalive: Negotiation of the Session Keepalive parameter is
performed by taking the minimum of this two contact headers' performed by taking the minimum of this two contact headers'
Keepalive Interval. The Session Keepalive interval is a parameter Keepalive Interval. The Session Keepalive interval is a parameter
for the behavior described in Section 5.1.1. for the behavior described in Section 5.1.1.
Enable TLS: Negotiation of the Enable TLS parameter is performed by Enable TLS: Negotiation of the Enable TLS parameter is performed by
taking the logical AND of the two contact headers' CAN_TLS flags. taking the logical AND of the two contact headers' CAN_TLS flags.
A local security policy is then applied to determine of the A local security policy is then applied to determine of the
negotated value of Enable TLS is acceptable. It can be a negotated value of Enable TLS is acceptable. It can be a
reasonable security policy to both require or disallow the use of reasonable security policy to both require or disallow the use of
TLS depending upon the desired network flows. If the Enable TLS TLS depending upon the desired network flows. Because this state
state is unacceptable, the node SHALL terminate the session with a is negotiated over an unsecured medium, there is a risk of a TLS
reason code of "Contact Failure". Note that this contact failure Stripping as described in Section 8. If the Enable TLS state is
is different than a failure of TLS handshake after an agreed-upon unacceptable, the node SHALL terminate the session with a reason
and acceptable Enable TLS state. If the negotiated Enable TLS code of "Contact Failure". Note that this contact failure reason
value is true and acceptable then TLS negotiation feature is different than a failure of TLS handshake or TLS authentication
(described in Section 4.4) begins immediately following the after an agreed-upon and acceptable Enable TLS state. If the
contact header exchange. negotiated Enable TLS value is true and acceptable then TLS
negotiation feature (described in Section 4.4) begins immediately
following the contact header exchange.
Once this process of parameter negotiation is completed (which Once this process of parameter negotiation is completed (which
includes a possible completed TLS handshake of the connection to use includes a possible completed TLS handshake of the connection to use
TLS), this protocol defines no additional mechanism to change the TLS), this protocol defines no additional mechanism to change the
parameters of an established session; to effect such a change, the parameters of an established session; to effect such a change, the
TCPCL session MUST be terminated and a new session established. TCPCL session MUST be terminated and a new session established.
4.8. Session Extension Items 4.8. Session Extension Items
Each of the Session Extension Items SHALL be encoded in an identical Each of the Session Extension Items SHALL be encoded in an identical
Type-Length-Value (TLV) container form as indicated in Figure 18. Type-Length-Value (TLV) container form as indicated in Figure 20.
The fields of the Session Extension Item are: The fields of the Session Extension Item are:
Flags: A one-octet field containing generic bit flags about the Flags: A one-octet field containing generic bit flags about the
Item, which are listed in Table 3. If a TCPCL entity receives a Item, which are listed in Table 3. All reserved header flag bits
SHALL be not set by the sender. All reserved header flag bits
SHALL be ignored by the receiver. If a TCPCL entity receives a
Session Extension Item with an unknown Item Type and the CRITICAL Session Extension Item with an unknown Item Type and the CRITICAL
flag set, the entity SHALL close the TCPCL session with SESS_TERM flag set, the entity SHALL close the TCPCL session with SESS_TERM
reason code of "Contact Failure". If the CRITICAL flag is not reason code of "Contact Failure". If the CRITICAL flag is not
set, an entity SHALL skip over and ignore any item with an unknown set, an entity SHALL skip over and ignore any item with an unknown
Item Type. Item Type.
Item Type: A 16-bit unsigned integer field containing the type of Item Type: A 16-bit unsigned integer field containing the type of
the extension item. This specification does not define any the extension item. This specification does not define any
extension types directly, but does allocate an IANA registry for extension types directly, but does allocate an IANA registry for
such codes (see Section 9.3). such codes (see Section 9.3).
skipping to change at page 28, line 13 skipping to change at page 32, line 15
data is sent. data is sent.
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
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| Item Flags | Item Type | Item Length...| | Item Flags | Item Type | Item Length...|
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| length contd. | Item Value... | | length contd. | Item Value... |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
Figure 18: Session Extension Item Format Figure 20: Session Extension Item Format
+----------+--------+-----------------------------------------------+ +----------+--------+-----------------------------------------------+
| Name | Code | Description | | Name | Code | Description |
+----------+--------+-----------------------------------------------+ +----------+--------+-----------------------------------------------+
| CRITICAL | 0x01 | If bit is set, indicates that the receiving | | CRITICAL | 0x01 | If bit is set, indicates that the receiving |
| | | peer must handle the extension item. | | | | peer must handle the extension item. |
| | | | | | | |
| Reserved | others | | Reserved | others |
+----------+--------+-----------------------------------------------+ +----------+--------+-----------------------------------------------+
skipping to change at page 29, line 33 skipping to change at page 33, line 35
5.1.2. Message Rejection (MSG_REJECT) 5.1.2. Message Rejection (MSG_REJECT)
If a TCPCL node receives a message which is unknown to it (possibly 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 is as follows in Figure 19. The format of a MSG_REJECT message is as follows in Figure 21.
+-----------------------------+ +-----------------------------+
| Message Header | | Message Header |
+-----------------------------+ +-----------------------------+
| Reason Code (U8) | | Reason Code (U8) |
+-----------------------------+ +-----------------------------+
| Rejected Message Header | | Rejected Message Header |
+-----------------------------+ +-----------------------------+
Figure 19: Format of MSG_REJECT Messages Figure 21: 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 4. 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.
skipping to change at page 31, line 24 skipping to change at page 35, line 32
Transfer ID space, the sending node SHALL terminate the session with Transfer ID space, the sending node SHALL terminate the session with
SESS_TERM 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.
5.2.2. Data Transmission (XFER_SEGMENT) 5.2.2. Data Transmission (XFER_SEGMENT)
Each bundle is transmitted in one or more data segments. The format Each bundle is transmitted in one or more data segments. The format
of a XFER_SEGMENT message follows in Figure 20. of a XFER_SEGMENT message follows in Figure 22.
+------------------------------+ +------------------------------+
| Message Header | | Message Header |
+------------------------------+ +------------------------------+
| Message Flags (U8) | | Message Flags (U8) |
+------------------------------+ +------------------------------+
| Transfer ID (U64) | | Transfer ID (U64) |
+------------------------------+ +------------------------------+
| Transfer Extension | | Transfer Extension |
| Items Length (U32) | | Items Length (U32) |
skipping to change at page 31, line 46 skipping to change at page 36, line 25
+------------------------------+ +------------------------------+
| Transfer Extension | | Transfer Extension |
| Items (var.) | | Items (var.) |
| (only for START segment) | | (only for START segment) |
+------------------------------+ +------------------------------+
| Data length (U64) | | Data length (U64) |
+------------------------------+ +------------------------------+
| Data contents (octet string) | | Data contents (octet string) |
+------------------------------+ +------------------------------+
Figure 20: Format of XFER_SEGMENT Messages Figure 22: 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 5. according to the descriptions in Table 5. All reserved header
flag bits SHALL be not set by the sender. All reserved header
flag bits SHALL be ignored by the receiver.
Transfer ID: A 64-bit unsigned integer identifying the transfer Transfer ID: A 64-bit unsigned integer identifying the transfer
being made. being made.
Transfer Extension Length and Transfer Extension Items: Together Transfer Extension Length and Transfer Extension Items: Together
these fields represent protocol extension data for this these fields represent protocol extension data for this
specification. The Transfer Extension Length and Transfer specification. The Transfer Extension Length and Transfer
Extension Item fields SHALL only be present when the 'START' flag Extension Item fields SHALL only be present when the 'START' flag
is set on the message. The Transfer Extension Length is the total is set on the message. The Transfer Extension Length is the total
number of octets to follow which are used to encode the Transfer number of octets to follow which are used to encode the Transfer
skipping to change at page 33, line 19 skipping to change at page 37, line 48
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 21. The format of an XFER_ACK message follows in Figure 23.
+-----------------------------+ +-----------------------------+
| Message Header | | Message Header |
+-----------------------------+ +-----------------------------+
| Message Flags (U8) | | Message Flags (U8) |
+-----------------------------+ +-----------------------------+
| Transfer ID (U64) | | Transfer ID (U64) |
+-----------------------------+ +-----------------------------+
| Acknowledged length (U64) | | Acknowledged length (U64) |
+-----------------------------+ +-----------------------------+
Figure 21: Format of XFER_ACK Messages Figure 23: 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 5. according to the descriptions in Table 5. All reserved header
flag bits SHALL be not set by the sender. All reserved header
flag bits SHALL be ignored by the receiver.
Transfer ID: A 64-bit unsigned integer identifying the transfer Transfer ID: A 64-bit unsigned integer identifying the transfer
being acknowledged. being acknowledged.
Acknowledged length: A 64-bit unsigned integer indicating the total Acknowledged length: A 64-bit unsigned integer indicating the total
number of octets in the transfer which are being acknowledged. number of octets in the transfer which are being acknowledged.
A receiving TCPCL node SHALL send an XFER_ACK message in response to A receiving TCPCL node SHALL send an XFER_ACK message in response to
each received XFER_SEGMENT message. The flags portion of the each received XFER_SEGMENT message. The flags portion of the
XFER_ACK header SHALL be set to match the corresponding DATA_SEGMENT XFER_ACK header SHALL be set to match the corresponding DATA_SEGMENT
skipping to change at page 34, line 36 skipping to change at page 39, line 20
XFER_REFUSE can be used in cases where the agent's bundle storage is XFER_REFUSE can be used in cases where the agent's bundle storage is
temporarily depleted or somehow constrained. A XFER_REFUSE can also temporarily depleted or somehow constrained. A XFER_REFUSE can also
be used after the bundle header or any bundle data is inspected by an be used after the bundle header or any bundle data is inspected by an
agent and determined to be unacceptable. agent and determined to be unacceptable.
A receiver MAY send an XFER_REFUSE message as soon as it receives any A receiver MAY send an XFER_REFUSE message as soon as it receives any
XFER_SEGMENT message. The sender MUST be prepared for this and MUST XFER_SEGMENT message. The sender MUST be prepared for this and MUST
associate the refusal with the correct bundle via the Transfer ID associate the refusal with the correct bundle via the Transfer ID
fields. fields.
The format of the XFER_REFUSE message is as follows in Figure 22. The format of the XFER_REFUSE message is as follows in Figure 24.
+-----------------------------+ +-----------------------------+
| Message Header | | Message Header |
+-----------------------------+ +-----------------------------+
| Reason Code (U8) | | Reason Code (U8) |
+-----------------------------+ +-----------------------------+
| Transfer ID (U64) | | Transfer ID (U64) |
+-----------------------------+ +-----------------------------+
Figure 22: Format of XFER_REFUSE Messages Figure 24: 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 6. 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 refused. being refused.
+------------+------+-----------------------------------------------+ +------------+------+-----------------------------------------------+
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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.
5.2.5. Transfer Extension Items 5.2.5. Transfer Extension Items
Each of the Transfer Extension Items SHALL be encoded in an identical Each of the Transfer Extension Items SHALL be encoded in an identical
Type-Length-Value (TLV) container form as indicated in Figure 23. Type-Length-Value (TLV) container form as indicated in Figure 25.
The fields of the Transfer Extension Item are: The fields of the Transfer Extension Item are:
Flags: A one-octet field containing generic bit flags about the Flags: A one-octet field containing generic bit flags about the
Item, which are listed in Table 7. If a TCPCL node receives a Item, which are listed in Table 7. All reserved header flag bits
SHALL be not set by the sender. All reserved header flag bits
SHALL be ignored by the receiver. If a TCPCL node receives a
Transfer Extension Item with an unknown Item Type and the CRITICAL Transfer Extension Item with an unknown Item Type and the CRITICAL
flag set, the node SHALL refuse the transfer with an XFER_REFUSE flag set, the node SHALL refuse the transfer with an XFER_REFUSE
reason code of "Extension Failure". If the CRITICAL flag is not reason code of "Extension Failure". If the CRITICAL flag is not
set, an entity SHALL skip over and ignore any item with an unknown set, an entity SHALL skip over and ignore any item with an unknown
Item Type. Item Type.
Item Type: A 16-bit unsigned integer field containing the type of Item Type: A 16-bit unsigned integer field containing the type of
the extension item. This specification allocates an IANA registry the extension item. This specification allocates an IANA registry
for such codes (see Section 9.4). for such codes (see Section 9.4).
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extension data is sent. extension data is sent.
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
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| Item Flags | Item Type | Item Length...| | Item Flags | Item Type | Item Length...|
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| length contd. | Item Value... | | length contd. | Item Value... |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
Figure 23: Transfer Extension Item Format Figure 25: Transfer Extension Item Format
+----------+--------+-----------------------------------------------+ +----------+--------+-----------------------------------------------+
| Name | Code | Description | | Name | Code | Description |
+----------+--------+-----------------------------------------------+ +----------+--------+-----------------------------------------------+
| CRITICAL | 0x01 | If bit is set, indicates that the receiving | | CRITICAL | 0x01 | If bit is set, indicates that the receiving |
| | | peer must handle the extension item. | | | | peer must handle the extension item. |
| | | | | | | |
| Reserved | others | | Reserved | others |
+----------+--------+-----------------------------------------------+ +----------+--------+-----------------------------------------------+
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same transfer. The lack of a Transfer Length extension item in any same transfer. The lack of a Transfer Length extension item in any
transfer SHALL NOT imply anything about the potential length of the transfer SHALL NOT imply anything about the potential length of the
transfer. The Transfer Length extension SHALL be assigned transfer transfer. The Transfer Length extension SHALL be assigned transfer
extension type ID 0x0001. extension type ID 0x0001.
If a transfer occupies exactly one segment (i.e. both START and END If a transfer occupies exactly one segment (i.e. both START and END
bits are set) the Transfer Length extension SHOULD NOT be present. bits are set) the Transfer Length extension SHOULD NOT be present.
The extension does not provide any additional information for single- The extension does not provide any additional information for single-
segment transfers. segment transfers.
The format of the Transfer Length data is as follows in Figure 24. The format of the Transfer Length data is as follows in Figure 26.
+----------------------+ +----------------------+
| Total Length (U64) | | Total Length (U64) |
+----------------------+ +----------------------+
Figure 24: Format of Transfer Length data Figure 26: Format of Transfer Length data
The fields of the Transfer Length extension are: The fields of the Transfer Length extension are:
Total Length: A 64-bit unsigned integer indicating the size of the Total Length: A 64-bit unsigned integer indicating the size of the
data-to-be-transferred. The Total Length field SHALL be treated data-to-be-transferred. The Total Length field SHALL be treated
as authoritative by the receiver. If, for whatever reason, the as authoritative by the receiver. If, for whatever reason, the
actual total length of bundle data received differs from the value actual total length of bundle data received differs from the value
indicated by the Total Length value, the receiver SHALL treat the indicated by the Total Length value, the receiver SHALL treat the
transmitted data as invalid. transmitted data as invalid.
skipping to change at page 38, line 24 skipping to change at page 43, line 24
termination, the REPLY bit of a SESS_TERM message SHALL NOT be set. termination, the REPLY bit of a SESS_TERM message SHALL NOT be set.
Upon receiving a SESS_TERM message after not sending a SESS_TERM Upon receiving a SESS_TERM message after not sending a SESS_TERM
message in the same session, an entity SHALL send an acknowledging message in the same session, an entity SHALL send an acknowledging
SESS_TERM message. When sent to acknowledge a termination, a SESS_TERM message. When sent to acknowledge a termination, a
SESS_TERM message SHALL have identical data content from the message SESS_TERM message SHALL have identical data content from the message
being acknowledged except for the REPLY bit, which is set to indicate being acknowledged except for the REPLY bit, which is set to indicate
acknowledgement. acknowledgement.
After sending a SESS_TERM message, an entity MAY continue a possible After sending a SESS_TERM message, an entity MAY continue a possible
in-progress transfer in either direction. After sending a SESS_TERM in-progress transfer in either direction. After sending a SESS_TERM
message, an entity SHALL NOT begin any new outgoing transfer (i.e. message, an entity SHALL NOT begin any new outgoing transfer for the
send an XFER_SEGMENT message) for the remainder of the session. remainder of the session. After receving a SESS_TERM message, an
After receving a SESS_TERM message, an entity SHALL NOT accept any entity SHALL NOT accept any new incoming transfer for the remainder
new incoming transfer for the remainder of the session. of the session.
Instead of following a clean shutdown sequence, after transmitting a Instead of following a clean shutdown sequence, after transmitting a
SESS_TERM message an entity 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. Not acknowledging received segments can result in connection. Not acknowledging received segments can result in
unnecessary retransmission. When performing an unclean shutodwn, a unnecessary retransmission. When performing an unclean shutodwn, a
transmitting node SHALL treat either sending or receiving a SESS_TERM transmitting node SHALL treat either sending or receiving a SESS_TERM
message (i.e. before the final acknowledgment) as a failure of the message (i.e. before the final acknowledgment) as a failure of the
transfer. Any delay between request to terminate the TCP connection transfer. Any delay between request to terminate the TCP connection
and actual closing of the connection (a "half-closed" state) MAY be and actual closing of the connection (a "half-closed" state) MAY be
ignored by the TCPCL node. ignored by the TCPCL node.
The format of the SESS_TERM message is as follows in Figure 25. The format of the SESS_TERM message is as follows in Figure 27.
+-----------------------------+ +-----------------------------+
| Message Header | | Message Header |
+-----------------------------+ +-----------------------------+
| Message Flags (U8) | | Message Flags (U8) |
+-----------------------------+ +-----------------------------+
| Reason Code (U8) | | Reason Code (U8) |
+-----------------------------+ +-----------------------------+
Figure 25: Format of SESS_TERM Messages Figure 27: Format of SESS_TERM Messages
The fields of the SESS_TERM 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. All reserved header
flag bits SHALL be not set by the sender. All reserved header
flag bits SHALL be ignored by the receiver.
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. to the descriptions in Table 9.
+----------+--------+-----------------------------------------------+ +----------+--------+-----------------------------------------------+
| Name | Code | Description | | Name | Code | Description |
+----------+--------+-----------------------------------------------+ +----------+--------+-----------------------------------------------+
| REPLY | 0x01 | If bit is set, indicates that this message is | | REPLY | 0x01 | If bit is set, indicates that this message is |
| | | an acknowledgement of an earlier SESS_TERM | | | | an acknowledgement of an earlier SESS_TERM |
| | | message. | | | | message. |
skipping to change at page 40, line 25 skipping to change at page 45, line 27
message but still SHALL close the TCP connection. Each TCPCL message message but still SHALL close the TCP connection. Each TCPCL message
is contiguous in the octet stream and has no ability to be cut short is contiguous in the octet stream and has no ability to be cut short
and/or preempted by an other message. This is particularly important and/or preempted by an other message. This is particularly important
when large segment sizes are being transmitted; either entire when large segment sizes are being transmitted; either entire
XFER_SEGMENT is sent before a SESS_TERM message or the connection is XFER_SEGMENT is sent before a SESS_TERM message or the connection is
simply terminated mid-XFER_SEGMENT. simply terminated mid-XFER_SEGMENT.
6.2. Idle Session Shutdown 6.2. Idle Session Shutdown
The protocol includes a provision for clean shutdown of idle The protocol includes a provision for clean shutdown of idle
sessions. Determining the length of time to wait before closing idle sessions. Determining the length of time to wait before ending idle
sessions, if they are to be closed at all, is an implementation and sessions, if they are to be closed at all, is an implementation and
configuration matter. configuration matter.
If there is a configured time to close idle links and if no TCPCL If there is a configured time to close idle links and if no TCPCL
messages (other than KEEPALIVE messages) has been received for at messages (other than KEEPALIVE messages) has been received for at
least that amount of time, then either node MAY terminate the session least that amount of time, then either node MAY terminate the session
by transmitting a SESS_TERM message indicating the reason code of by transmitting a SESS_TERM message indicating the reason code of
"Idle timeout" (as described in Table 9). "Idle timeout" (as described in Table 9).
7. Implementation Status 7. Implementation Status
skipping to change at page 40, line 51 skipping to change at page 46, line 5
This section records the status of known implementations of the This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942]. Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may features. Readers are advised to note that other implementations can
exist. exist.
An example implementation of the this draft of TCPCLv4 has been An example implementation of the this draft of TCPCLv4 has been
created as a GitHub project [github-dtn-bpbis-tcpcl] and is intented created as a GitHub project [github-dtn-bpbis-tcpcl] and is intented
to use as a proof-of-concept and as a possible source of to use as a proof-of-concept and as a possible source of
interoperability testing. This example implementation uses D-Bus as interoperability testing. This example implementation uses D-Bus as
the CL-BP Agent interface, so it only runs on hosts which provide the the CL-BP Agent interface, so it only runs on hosts which provide the
Python "dbus" library. Python "dbus" library.
8. Security Considerations 8. Security Considerations
One security consideration for this protocol relates to the fact that
entities present their endpoint identifier as part of the contact
header exchange. It would be possible for an entity to fake this
value and present the identity of a singleton endpoint in which the
node is not a member, essentially masquerading as another DTN node.
If this identifier is used outside of a TLS-secured session or
without further verification as a means to determine which bundles
are transmitted over the session, then the node that has falsified
its identity would be able to obtain bundles that it otherwise would
not have. Therefore, an entity SHALL NOT use the EID value of an
unsecured contact header to derive a peer node's identity unless it
can corroborate it via other means. When TCPCL session security is
mandated by a TCPCL peer, that peer SHALL transmit initial unsecured
contact header values indicated in Table 10 in order. These values
avoid unnecessarily leaking session parameters and will be ignored
when secure contact header re-exchange occurs.
+--------------------+---------------------------------------------+
| Parameter | Value |
+--------------------+---------------------------------------------+
| Flags | The USE_TLS flag is set. |
| | |
| Keepalive Interval | Zero, indicating no keepalive. |
| | |
| Segment MRU | Zero, indicating all segments are refused. |
| | |
| Transfer MRU | Zero, indicating all transfers are refused. |
| | |
| EID | Empty, indicating lack of EID. |
+--------------------+---------------------------------------------+
Table 10: Recommended Unsecured Contact Header
TCPCL can be used to provide point-to-point transport security, but TCPCL can be used to provide point-to-point transport security, but
does not provide security of data-at-rest and does not guarantee end- does not provide security of data-at-rest and does not guarantee end-
to-end bundle security. The mechanisms defined in [RFC6257] and to-end bundle security. The bundle security mechanisms defined in
[I-D.ietf-dtn-bpsec] are to be used instead. [I-D.ietf-dtn-bpsec] are to be used instead.
When negotating whether to use TLS security as part of the contact
header exchange, it is possible for a man-in-the-middle attacker to
unset the CAN_TLS flag on either side of the exchange. This leads to
the "SSL Stripping" attack described in [RFC7457]. If TLS is desired
for use on any TCPCL network, it is strongly encouraged that the
security policy disallow use of TCPCL when "Enable TLS" is negotiated
to false. This requires that the TLS handshake occurs, regardless of
the policy-driven parameters of the handshake and policy-driven
handling of the handshake outcome.
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].
The certificates exchanged by TLS enable authentication of peer host
name and Node ID, but it is possible that a peer either not provide a
valid certificate or that the certificate does not validate either
the host name or Node ID of the peer. Having a CA-validated
certificate does not alone guarantee the identity of the network host
or BP node from which the certificate is provided; additional
validation procedures bind the host name or node ID based on the
contents of the certificate. The host name validation is a weaker
form of authentication, because even if a peer is operating on an
authenticated network host name it can provide an invalid Node ID and
cause bundles to be "leaked" to an invalid node. Especially in DTN
environments, network names and addresses of nodes can be time-
variable so binding a certificate to a Node ID is a more stable
identity. Node ID validation ensures that the peer to which a bundle
is transferred is in fact the node which the BP Agent expects it to
be. It is a reasonable policy to skip host name validation if
certificates can be guaranteed to validate the peer's Node ID. In
circumstances where certificates can only be issued to network host
names, Node ID validation is not possible but it could be reasonable
to assume that a trusted host is not going to present an invalid Node
ID. Trusting an authenticated host name can be feasable on a network
secured by a private CA but is not advisable on the Internet when
using a variety of public CAs.
Another consideration for this protocol relates to denial-of-service Another consideration for this protocol relates to denial-of-service
attacks. An entity 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 entity to handle the data, attempt session, requiring the receiving entity to handle the data, attempt
to stop the flood of data by sending a XFER_REFUSE message, or to stop the flood of data by sending a XFER_REFUSE message, or
forcibly terminate the session. This burden could cause denial of forcibly terminate the session. This burden could cause denial of
service on other, well-behaving sessions. There is also nothing to service on other, well-behaving sessions. There is also nothing to
prevent a malicious entity from continually establishing sessions and prevent a malicious entity from continually establishing sessions and
repeatedly trying to send copious amounts of bundle data. A repeatedly trying to send copious amounts of bundle data. A
listening entity MAY take countermeasures such as ignoring TCP SYN listening entity MAY take countermeasures such as ignoring TCP SYN
messages, closing TCP connections as soon as they are established, messages, closing TCP connections as soon as they are established,
waiting before sending the contact header, sending a SESS_TERM waiting before sending the contact header, sending a SESS_TERM
message quickly or with a delay, etc. message quickly or with a delay, etc.
9. IANA Considerations 9. IANA Considerations
In this section, registration procedures are as defined in [RFC8126]. Registration procedures referred to in this section are defined in
[RFC8126].
Some of the registries below are created new for TCPCLv4 but share Some of the registries have been defined as version specific to
code values with TCPCLv3. This was done to disambiguate the use of TCPCLv4, and imports some or all codepoints from TCPCLv3. This was
these values between TCPCLv3 and TCPCLv4 while preserving the done to disambiguate the use of these codepoints between TCPCLv3 and
semantics of some values. TCPCLv4 while preserving the semantics of some of the codepoints.
9.1. 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 entity identifies its TCPCL by protocol version 4. Each TCPCL entity identifies its TCPCL
protocol version in its initial contact (see Section 9.2), so there protocol version in its initial contact (see Section 9.2), so there
is no ambiguity about what protocol is being used. is no ambiguity about what protocol is being used.
+------------------------+-------------------------------------+ +------------------------+-------------------------------------+
skipping to change at page 44, line 5 skipping to change at page 49, line 5
+-------+-------------+---------------------+ +-------+-------------+---------------------+
9.3. Session 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
Session 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 10. The registration procedure is Expert Review within the
lower range 0x0001--0x7FFF. 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 | Session Extension Type | | Code | Session Extension Type |
+----------------+--------------------------+ +----------------+--------------------------+
| 0x0000 | Reserved | | 0x0000 | Reserved |
| | | | | |
| 0x0001--0x7FFF | Unassigned | | 0x0001--0x7FFF | Unassigned |
| | | | | |
| 0x8000--0xFFFF | Private/Experimental Use | | 0x8000--0xFFFF | Private/Experimental Use |
+----------------+--------------------------+ +----------------+--------------------------+
Table 11: Session Extension Type Codes Table 10: Session Extension Type Codes
9.4. Transfer Extension Types 9.4. Transfer 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
Transfer Extension Types" and initialize it with the contents of Transfer Extension Types" and initialize it with the contents of
Table 12. The registration procedure is RFC Required within the Table 11. The registration procedure is Expert Review within the
lower range 0x0001--0x7FFF. 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 | Transfer Extension Type | | Code | Transfer Extension Type |
+----------------+---------------------------+ +----------------+---------------------------+
| 0x0000 | Reserved | | 0x0000 | Reserved |
| | | | | |
| 0x0001 | Transfer Length Extension | | 0x0001 | Transfer Length Extension |
| | | | | |
| 0x0002--0x7FFF | Unassigned | | 0x0002--0x7FFF | Unassigned |
| | | | | |
| 0x8000--0xFFFF | Private/Experimental Use | | 0x8000--0xFFFF | Private/Experimental Use |
+----------------+---------------------------+ +----------------+---------------------------+
Table 12: Transfer Extension Type Codes Table 11: Transfer Extension Type Codes
9.5. 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 13. The Message Types" and initialize it with the contents of Table 12. The
registration procedure is RFC Required. registration procedure is RFC Required within the lower range 0x01--
0xEF. Values in the range 0xF0--0xFF are reserved for use on private
networks for functions not published to the IANA.
+-----------+--------------+ +------------+--------------------------+
| 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 | SESS_TERM | | 0x05 | SESS_TERM |
| | | | | |
| 0x06 | MSG_REJECT | | 0x06 | MSG_REJECT |
| | | | | |
| 0x07 | SESS_INIT | | 0x07 | SESS_INIT |
| | | | | |
| 0x08--0xf | Unassigned | | 0x08--0xEF | Unassigned |
+-----------+--------------+ | | |
| 0xF0--0xFF | Private/Experimental Use |
+------------+--------------------------+
Table 13: Message Type Codes Table 12: Message Type Codes
9.6. 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 14. The registration procedure is RFC Required. Table 13. The registration procedure is Specification Required
within the lower range 0x00--0xEF. Values in the range 0xF0--0xFF
are reserved for use on private networks for functions not published
to the IANA.
+------------+---------------------------+ +------------+--------------------------+
| Code | Refusal Reason | | Code | Refusal Reason |
+------------+---------------------------+ +------------+--------------------------+
| 0x00 | Unknown | | 0x00 | Unknown |
| | | | | |
| 0x01 | Extension Failure | | 0x01 | Extension Failure |
| | | | | |
| 0x02 | Completed | | 0x02 | Completed |
| | | | | |
| 0x03 | No Resources | | 0x03 | No Resources |
| | | | | |
| 0x04 | Retransmit | | 0x04 | Retransmit |
| | | | | |
| 0x05--0x07 | Unassigned | | 0x05--0xEF | Unassigned |
| | | | | |
| 0x08--0xFF | Reserved for future usage | | 0xF0--0xFF | Private/Experimental Use |
+------------+---------------------------+ +------------+--------------------------+
Table 14: XFER_REFUSE Reason Codes Table 13: XFER_REFUSE Reason Codes
9.7. SESS_TERM Reason Codes 9.7. SESS_TERM Reason Codes
EDITOR NOTE: sub-registry to-be-created upon publication of this EDITOR NOTE: sub-registry to-be-created upon publication of this
specification. specification.
IANA will create, under the "Bundle Protocol" registry, 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
SESS_TERM Reason Codes" and initialize it with the contents of SESS_TERM Reason Codes" and initialize it with the contents of
Table 15. The registration procedure is RFC Required. Table 14. The registration procedure is Specification Required
within the lower range 0x00--0xEF. Values in the range 0xF0--0xFF
are reserved for use on private networks for functions not published
to the IANA.
+------------+---------------------+ +------------+--------------------------+
| Code | Termination Reason | | Code | Termination Reason |
+------------+---------------------+ +------------+--------------------------+
| 0x00 | Unknown | | 0x00 | Unknown |
| | | | | |
| 0x01 | Idle timeout | | 0x01 | Idle timeout |
| | | | | |
| 0x02 | Version mismatch | | 0x02 | Version mismatch |
| | | | | |
| 0x03 | Busy | | 0x03 | Busy |
| | | | | |
| 0x04 | Contact Failure | | 0x04 | Contact Failure |
| | | | | |
| 0x05 | Resource Exhaustion | | 0x05 | Resource Exhaustion |
| | | | | |
| 0x06--0xFF | Unassigned | | 0x06--0xEF | Unassigned |
+------------+---------------------+ | | |
| 0xF0--0xFF | Private/Experimental Use |
+------------+--------------------------+
Table 15: SESS_TERM Reason Codes Table 14: SESS_TERM Reason Codes
9.8. 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 16. The registration procedure is RFC Required. Table 15. The registration procedure is Specification Required
within the lower range 0x01--0xEF. Values in the range 0xF0--0xFF
are reserved for use on private networks for functions not published
to the IANA.
+-----------+----------------------+ +------------+--------------------------+
| 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--0xEF | Unassigned |
+-----------+----------------------+ | | |
| 0xF0--0xFF | Private/Experimental Use |
+------------+--------------------------+
Table 16: MSG_REJECT Reason Codes Table 15: MSG_REJECT Reason Codes
10. 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.
11. References 11. References
11.1. Normative References 11.1. Normative References
[BCP195] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015.
[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-12 (work in progress), Version 7", draft-ietf-dtn-bpbis-14 (work in progress),
November 2018. August 2019.
[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>.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989, DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/info/rfc1122>. <https://www.rfc-editor.org/info/rfc1122>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(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>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <https://www.rfc-editor.org/info/rfc6125>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26, Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>. <https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
11.2. Informative References 11.2. Informative References
[github-dtn-bpbis-tcpcl] [github-dtn-bpbis-tcpcl]
Sipos, B., "TCPCL Example Implementation", Sipos, B., "TCPCL Example Implementation",
<https://github.com/BSipos-RKF/dtn-bpbis-tcpcl/tree/ <https://github.com/BSipos-RKF/dtn-bpbis-tcpcl/tree/
develop>. 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-09 (work in Specification", draft-ietf-dtn-bpsec-10 (work in
progress), February 2019. progress), April 2019.
[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>.
[RFC4838] Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst, [RFC4838] Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst,
R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant
Networking Architecture", RFC 4838, DOI 10.17487/RFC4838, Networking Architecture", RFC 4838, DOI 10.17487/RFC4838,
April 2007, <https://www.rfc-editor.org/info/rfc4838>. April 2007, <https://www.rfc-editor.org/info/rfc4838>.
[RFC5050] Scott, K. and S. Burleigh, "Bundle Protocol
Specification", RFC 5050, DOI 10.17487/RFC5050, November
2007, <https://www.rfc-editor.org/info/rfc5050>.
[RFC6257] Symington, S., Farrell, S., Weiss, H., and P. Lovell,
"Bundle Security Protocol Specification", RFC 6257,
DOI 10.17487/RFC6257, May 2011,
<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>.
[RFC7457] Sheffer, Y., Holz, R., and P. Saint-Andre, "Summarizing
Known Attacks on Transport Layer Security (TLS) and
Datagram TLS (DTLS)", RFC 7457, DOI 10.17487/RFC7457,
February 2015, <https://www.rfc-editor.org/info/rfc7457>.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running [RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205, Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016, RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/info/rfc7942>. <https://www.rfc-editor.org/info/rfc7942>.
Appendix A. Significant changes from RFC7242 Appendix A. Significant changes from RFC7242
The areas in which changes from [RFC7242] have been made to existing The areas in which changes from [RFC7242] have been made to existing
headers and messages are: headers and messages are:
o Split contact header into pre-TLS protocol negotiation and o Split contact header into pre-TLS protocol negotiation and
SESS_INIT parameter negotiation. The contact header is now fixed- SESS_INIT parameter negotiation. The contact header is now fixed-
length. length.
o Changed contact header content to limit number of negotiated o Changed contact header content to limit number of negotiated
options. options.
o Added contact option to negotiate maximum segment size (per each o Added session option to negotiate maximum segment size (per each
direction). direction).
o Renamed "Endpoint ID" to "Node ID" to conform with BPv7
terminology.
o Added session extension capability. o Added session extension capability.
o Added transfer extension capability. Moved transfer total length o Added transfer extension capability. Moved transfer total length
into an extension item. into an extension item.
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 Segments of all new IANA registries are reserved for private/
experimental use.
o Expanded Message Header to octet-aligned fields instead of bit- o Expanded Message Header to octet-aligned fields instead of bit-
packing. packing.
o Added a bundle transfer identification number to all bundle- o Added a bundle transfer identification number to all bundle-
related messages (XFER_SEGMENT, XFER_ACK, XFER_REFUSE). related messages (XFER_SEGMENT, XFER_ACK, XFER_REFUSE).
o Use flags in XFER_ACK to mirror flags from XFER_SEGMENT. o Use flags in XFER_ACK to mirror flags from XFER_SEGMENT.
o Removed all uses of SDNV fields and replaced with fixed-bit-length o Removed all uses of SDNV fields and replaced with fixed-bit-length
fields. fields.
o Renamed SHUTDOWN to SESS_TERM to deconflict term "shutdown". o Renamed SHUTDOWN to SESS_TERM to deconflict term "shutdown"
related to TCP connections.
o Removed the notion of a re-connection delay parameter. o Removed the notion of a re-connection delay parameter.
The areas in which extensions from [RFC7242] have been made as new The areas in which extensions from [RFC7242] have been made as new
messages and codes are: messages and codes are:
o Added contact negotiation failure SESS_TERM reason code. o Added contact negotiation failure SESS_TERM reason code.
o Added MSG_REJECT message to indicate an unknown or unhandled o Added MSG_REJECT message to indicate an unknown or unhandled
message was received. message was received.
 End of changes. 124 change blocks. 
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