draft-ietf-dtn-tcpclv4-01.txt   draft-ietf-dtn-tcpclv4-02.txt 
Delay Tolerant Networking B. Sipos Delay Tolerant Networking B. Sipos
Internet-Draft RKF Engineering Internet-Draft RKF Engineering
Obsoletes: RFC7242 (if approved) M. Demmer Obsoletes: 7242 (if approved) M. Demmer
Intended status: Standards Track UC Berkeley Intended status: Standards Track UC Berkeley
Expires: May 31, 2017 J. Ott Expires: November 23, 2017 J. Ott
Aalto University Aalto University
S. Perreault S. Perreault
November 27, 2016 May 22, 2017
Delay-Tolerant Networking TCP Convergence Layer Protocol Version 4 Delay-Tolerant Networking TCP Convergence Layer Protocol Version 4
draft-ietf-dtn-tcpclv4-01 draft-ietf-dtn-tcpclv4-02
Abstract Abstract
This document describes a revised protocol for the TCP-based This document describes a revised protocol for the TCP-based
convergence layer for Delay-Tolerant Networking (DTN). The protocol convergence layer (TCPCL) for Delay-Tolerant Networking (DTN). The
revision is based on implementation issues in the original [RFC7242] protocol revision is based on implementation issues in the original
and updates to the Bundle Protocol contents, encodings, and TCPCL Version 3 and updates to the Bundle Protocol contents,
convergence layer requirements in [I-D.ietf-dtn-bpbis]. encodings, and convergence layer requirements in Bundle Protocl
Version 7. Several new IANA registries are defined for TCPCLv4 which
define some behaviors inherited from TCPCLv3 but with updated
encodings and/or semantics.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://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 May 31, 2017. This Internet-Draft will expire on November 23, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2017 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
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
2.1. Definitions Specific to the TCPCL Protocol . . . . . . . 4 2.1. Definitions Specific to the TCPCL Protocol . . . . . . . 4
3. General Protocol Description . . . . . . . . . . . . . . . . 5 3. General Protocol Description . . . . . . . . . . . . . . . . 5
3.1. Bidirectional Use of TCPCL Sessions . . . . . . . . . . . 6 3.1. Bidirectional Use of TCPCL Sessions . . . . . . . . . . . 6
3.2. Example Message Exchange . . . . . . . . . . . . . . . . 6 3.2. Example Message Exchange . . . . . . . . . . . . . . . . 7
4. Session Establishment . . . . . . . . . . . . . . . . . . . . 7 4. Session Establishment . . . . . . . . . . . . . . . . . . . . 8
4.1. Contact Header . . . . . . . . . . . . . . . . . . . . . 8 4.1. Contact Header . . . . . . . . . . . . . . . . . . . . . 10
4.2. Validation and Parameter Negotiation . . . . . . . . . . 10 4.1.1. Header Extension Items . . . . . . . . . . . . . . . 11
5. Established Session Operation . . . . . . . . . . . . . . . . 11 4.2. Validation and Parameter Negotiation . . . . . . . . . . 13
5.1. Message Type Codes . . . . . . . . . . . . . . . . . . . 11 5. Established Session Operation . . . . . . . . . . . . . . . . 14
5.2. Upkeep and Status Messages . . . . . . . . . . . . . . . 12 5.1. Message Type Codes . . . . . . . . . . . . . . . . . . . 14
5.2.1. Session Upkeep (KEEPALIVE) . . . . . . . . . . . . . 12 5.2. Upkeep and Status Messages . . . . . . . . . . . . . . . 15
5.2.2. Message Rejection (REJECT) . . . . . . . . . . . . . 13 5.2.1. Session Upkeep (KEEPALIVE) . . . . . . . . . . . . . 15
5.3. Session Security . . . . . . . . . . . . . . . . . . . . 14 5.2.2. Message Rejection (MSG_REJECT) . . . . . . . . . . . 16
5.3.1. TLS Handshake Result . . . . . . . . . . . . . . . . 14 5.3. Session Security . . . . . . . . . . . . . . . . . . . . 17
5.3.2. Example TLS Initiation . . . . . . . . . . . . . . . 15 5.3.1. TLS Handshake Result . . . . . . . . . . . . . . . . 17
5.4. Bundle Transfer . . . . . . . . . . . . . . . . . . . . . 15 5.3.2. Example TLS Initiation . . . . . . . . . . . . . . . 18
5.4.1. Bundle Transfer ID . . . . . . . . . . . . . . . . . 16 5.4. Bundle Transfer . . . . . . . . . . . . . . . . . . . . . 18
5.4.2. Bundle Length (LENGTH) . . . . . . . . . . . . . . . 16 5.4.1. Bundle Transfer ID . . . . . . . . . . . . . . . . . 19
5.4.3. Bundle Data Transmission (DATA_SEGMENT) . . . . . . . 17 5.4.2. Transfer initialization (XFER_INIT) . . . . . . . . . 19
5.4.4. Bundle Acknowledgments (ACK_SEGMENT) . . . . . . . . 18 5.4.3. Data Transmission (XFER_SEGMENT) . . . . . . . . . . 20
5.4.5. Bundle Refusal (REFUSE_BUNDLE) . . . . . . . . . . . 19 5.4.4. Data Acknowledgments (XFER_ACK) . . . . . . . . . . . 22
6. Session Termination . . . . . . . . . . . . . . . . . . . . . 21 5.4.5. Transfer Refusal (XFER_REFUSE) . . . . . . . . . . . 23
6.1. Shutdown Message (SHUTDOWN) . . . . . . . . . . . . . . . 21 6. Session Termination . . . . . . . . . . . . . . . . . . . . . 24
6.2. Idle Session Shutdown . . . . . . . . . . . . . . . . . . 23 6.1. Shutdown Message (SHUTDOWN) . . . . . . . . . . . . . . . 25
7. Security Considerations . . . . . . . . . . . . . . . . . . . 23 6.2. Idle Session Shutdown . . . . . . . . . . . . . . . . . . 27
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 7. Security Considerations . . . . . . . . . . . . . . . . . . . 27
8.1. Port Number . . . . . . . . . . . . . . . . . . . . . . . 25 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
8.2. Protocol Versions . . . . . . . . . . . . . . . . . . . . 25 8.1. Port Number . . . . . . . . . . . . . . . . . . . . . . . 29
8.3. Message Types . . . . . . . . . . . . . . . . . . . . . . 26 8.2. Protocol Versions . . . . . . . . . . . . . . . . . . . . 29
8.4. REFUSE_BUNDLE Reason Codes . . . . . . . . . . . . . . . 26 8.3. Header Extension Types . . . . . . . . . . . . . . . . . 30
8.5. SHUTDOWN Reason Codes . . . . . . . . . . . . . . . . . . 27 8.4. Message Types . . . . . . . . . . . . . . . . . . . . . . 31
8.6. REJECT Reason Codes . . . . . . . . . . . . . . . . . . . 27 8.5. XFER_REFUSE Reason Codes . . . . . . . . . . . . . . . . 31
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28 8.6. SHUTDOWN Reason Codes . . . . . . . . . . . . . . . . . . 32
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 8.7. MSG_REJECT Reason Codes . . . . . . . . . . . . . . . . . 33
10.1. Normative References . . . . . . . . . . . . . . . . . . 28 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 33
10.2. Informative References . . . . . . . . . . . . . . . . . 29 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 33
Appendix A. Significant changes from RFC7242 . . . . . . . . . . 29 10.1. Normative References . . . . . . . . . . . . . . . . . . 33
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30 10.2. Informative References . . . . . . . . . . . . . . . . . 34
Appendix A. Significant changes from RFC7242 . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35
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"
skipping to change at page 4, line 35 skipping to change at page 5, line 9
This section contains definitions that are interpreted to be specific This section contains definitions that are interpreted to be specific
to the operation of the TCPCL protocol, as described below. to the operation of the TCPCL protocol, as described below.
TCP Connection: A TCP connection refers to a transport connection TCP Connection: A TCP connection refers to a transport connection
using TCP as the transport protocol. using TCP as the transport protocol.
TCPCL Session: A TCPCL session (as opposed to a TCP connection) is a TCPCL Session: A TCPCL session (as opposed to a TCP connection) is a
TCPCL communication relationship between two bundle nodes. The TCPCL communication relationship between two bundle nodes. The
lifetime of a TCPCL session is bound to the lifetime of an lifetime of a TCPCL session is bound to the lifetime of an
underlying TCP connection. Therefore, a TCPCL session is underlying TCP connection. Therefore, a TCPCL session is
initiated when a bundle node initiates a TCP connection to be initiated after a bundle node establishes a TCP connection to for
established for the purposes of bundle communication. A TCPCL the purposes of bundle communication. A TCPCL session is
session is terminated when the TCP connection ends, due either to terminated when the TCP connection ends, due either to one or both
one or both nodes actively terminating the TCP connection or due nodes actively terminating the TCP connection or due to network
to network errors causing a failure of the TCP connection. For errors causing a failure of the TCP connection. For the remainder
the remainder of this document, the term "session" without the of this document, the term "session" without the prefix "TCPCL"
prefix "TCPCL" refer to a TCPCL session. refer to a TCPCL session.
Session parameters: The session parameters are a set of values used Session parameters: The session parameters are a set of values used
to affect the operation of the TCPCL for a given session. The to affect the operation of the TCPCL for a given session. The
manner in which these parameters are conveyed to the bundle node manner in which these parameters are conveyed to the bundle node
and thereby to the TCPCL is implementation dependent. However, and thereby to the TCPCL is implementation dependent. However,
the mechanism by which two bundle nodes exchange and negotiate the the mechanism by which two bundle nodes exchange and negotiate the
values to be used for a given session is described in Section 4.2. values to be used for a given session is described in Section 4.2.
Transmission: Transmission refers to the procedures and mechanisms Transfer Transfer refers to the procedures and mechanisms (described
(described below) for conveyance of a bundle from one node to below) for conveyance of an individual bundle from one node to
another. another. Each transfer within TCPCLv4 is identified by a Transfer
ID number which is unique only to a single direction within a
single Session.
3. General Protocol Description 3. General Protocol Description
The service of this protocol is the transmission of DTN bundles over The service of this protocol is the transmission of DTN bundles over
TCP. This document specifies the encapsulation of bundles, TCP. This document specifies the encapsulation of bundles,
procedures for TCP setup and teardown, and a set of messages and node procedures for TCP setup and teardown, and a set of messages and node
requirements. The general operation of the protocol is as follows. requirements. The general operation of the protocol is as follows.
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. After setup of the TCP connection is initiating a TCP connection. After setup of the TCP connection is
complete, an initial contact header is exchanged in both directions complete, an initial contact header is exchanged in both directions
to set parameters of the TCPCL session and exchange a singleton to set parameters of the TCPCL session and exchange a singleton
endpoint identifier for each node (not the singleton Endpoint endpoint identifier for each node (not the singleton Endpoint
Identifier (EID) of any application running on the node) to denote Identifier (EID) of any application running on the node) to denote
the bundle-layer identity of each DTN node. This is used to assist the bundle-layer identity of each DTN node. This is used to assist
in routing and forwarding messages, e.g., to prevent loops. in routing and forwarding messages, e.g., to prevent loops.
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 in one or more logical segments of data. Each logical data performed in one or more logical segments of data. Each logical data
segment consists of a DATA_SEGMENT message header, a count of the segment consists of a XFER_SEGMENT message header and flags, a count
length of the segment, and finally the octet range of the bundle of the length of the segment, and finally the octet range of the
data. The choice of the length to use for segments is an bundle data. The choice of the length to use for segments is an
implementation matter (but must be within the Segment MRU size of implementation matter (but must be within the Segment MRU size of
Section 4.1). The first segment for a bundle MUST set the 'start' Section 4.1). The first segment for a bundle MUST set the 'START'
flag, and the last one MUST set the 'end' flag in the DATA_SEGMENT flag, and the last one MUST set the 'end' flag in the XFER_SEGMENT
message header. message flags.
If multiple bundles are transmitted on a single TCPCL connection, If multiple bundles are transmitted on a single TCPCL connection,
they MUST be transmitted consecutively. Interleaving data segments they MUST be transmitted consecutively. Interleaving data segments
from different bundles is not allowed. Bundle interleaving can be from different bundles is not allowed. Bundle interleaving can be
accomplished by fragmentation at the BP layer or by establishing accomplished by fragmentation at the BP layer or by establishing
multiple TCPCL sessions. multiple TCPCL sessions.
A feature of this protocol is for the receiving node to send A feature of this protocol is for the receiving node to send
acknowledgments as bundle data segments arrive (ACK_SEGMENT). The acknowledgments as bundle data segments arrive (XFER_ACK). The
rationale behind these acknowledgments is to enable the sender node rationale behind these acknowledgments is to enable the sender node
to determine how much of the bundle has been received, so that in to determine how much of the bundle has been received, so that in
case the session is interrupted, it can perform reactive 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. For each data segment that is received, the receiving node bundle. For each data segment that is received, the receiving node
sends an ACK_SEGMENT code followed by an count containing the sends an XFER_ACK message containing the cumulative length of the
cumulative length of the bundle that has been received. The sending bundle that has been received. The sending node MAY transmit
node MAY transmit multiple DATA_SEGMENT messages without necessarily multiple XFER_SEGMENT messages without necessarily waiting for the
waiting for the corresponding ACK_SEGMENT responses. This enables corresponding XFER_ACK responses. This enables pipelining of
pipelining of messages on a channel. In addition, there is no messages on a channel. In addition, there is no explicit flow
explicit flow control on the TCPCL layer. control on the TCPCL layer.
Another feature is that a receiver MAY interrupt the transmission of Another feature is that a receiver MAY interrupt the transmission of
a bundle at any point in time by replying with a REFUSE_BUNDLE a bundle at any point in time by replying with a XFER_REFUSE message,
message, which causes the sender to stop transmission of the current which causes the sender to stop transmission of the current bundle,
bundle, after completing transmission of a partially sent data after completing transmission of a partially sent data segment.
segment. Note: This enables a cross-layer optimization in that it Note: This enables a cross-layer optimization in that it allows a
allows a receiver that detects that it already has received a certain receiver that detects that it already has received a certain bundle
bundle to interrupt transmission as early as possible and thus save to interrupt transmission as early as possible and thus save
transmission capacity for other bundles. transmission capacity for other 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 liveness information. negotiated interval. This is used to convey liveness information.
Finally, before sessions close, a SHUTDOWN message is sent to the Finally, before sessions close, a SHUTDOWN message is sent to the
session peer. After sending a SHUTDOWN message, the sender of this session peer. After sending a SHUTDOWN message, the sender of this
message MAY send further acknowledgments (ACK_SEGMENT or message MAY send further acknowledgments (XFER_ACK or XFER_REFUSE)
REFUSE_BUNDLE) but no further data messages (DATA_SEGMENT). A but no further data messages (XFER_SEGMENT). A SHUTDOWN message MAY
SHUTDOWN message MAY also be used to refuse a session setup by a also be used to refuse a session setup by a peer.
peer.
3.1. Bidirectional Use of TCPCL Sessions 3.1. Bidirectional Use of TCPCL Sessions
There are specific messages for sending and receiving operations (in There are specific messages for sending and receiving operations (in
addition to session setup/teardown). TCPCL is symmetric, i.e., both addition to session setup/teardown). TCPCL is symmetric, i.e., both
sides can start sending data segments in a session, and one side's sides can start sending data segments in a session, and one side's
bundle transfer does not have to complete before the other side can bundle transfer does not have to complete before the other side can
start sending data segments on its own. Hence, the protocol allows start sending data segments on its own. Hence, the protocol allows
for a bi-directional mode of communication. for a bi-directional mode of communication.
Note that in the case of concurrent bidirectional transmission, Note that in the case of concurrent bidirectional transmission,
acknowledgment segments MAY be interleaved with data segments. acknowledgment segments MAY be interleaved with data segments.
3.2. Example Message Exchange 3.2. Example Message Exchange
The following figure visually depicts the protocol exchange for a The following figure visually depicts the protocol exchange for a
simple session, showing the session establishment and the simple session, showing the session establishment and the
transmission of a single bundle split into three data segments (of transmission of a single bundle split into three data segments (of
lengths L1, L2, and L3) from Node A to Node B. lengths "L1", "L2", and "L3") from Node A to Node B.
Note that the sending node MAY transmit multiple DATA_SEGMENT Note that the sending node MAY transmit multiple XFER_SEGMENT
messages without necessarily waiting for the corresponding messages without necessarily waiting for the corresponding XFER_ACK
ACK_SEGMENT responses. This enables pipelining of messages on a responses. This enables pipelining of messages on a channel.
channel. Although this example only demonstrates a single bundle Although this example only demonstrates a single bundle transmission,
transmission, it is also possible to pipeline multiple DATA_SEGMENT it is also possible to pipeline multiple XFER_SEGMENT messages for
messages for different bundles without necessarily waiting for different bundles without necessarily waiting for XFER_ACK messages
ACK_SEGMENT messages to be returned for each one. However, to be returned for each one. However, interleaving data segments
interleaving data segments from different bundles is not allowed. from different bundles is not allowed.
No errors or rejections are shown in this example. No errors or rejections are shown in this example.
Node A Node B Node A Node B
====== ====== ====== ======
+-------------------------+ +-------------------------+ +-------------------------+ +-------------------------+
| Contact Header | -> <- | Contact Header | | Contact Header | -> <- | Contact Header |
+-------------------------+ +-------------------------+ +-------------------------+ +-------------------------+
+-------------------------+ +-------------------------+
| LENGTH | -> | XFER_INIT | ->
| Transfer ID [I1] | | Transfer ID [I1] |
| Total Length [L1] | | Total Length [L1] |
+-------------------------+ +-------------------------+
+-------------------------+ +-------------------------+
| DATA_SEGMENT (start) | -> | XFER_SEGMENT (start) | ->
| Transfer ID [I1] | | Transfer ID [I1] |
| Length [L1] | | Length [L1] |
| Bundle Data 0..(L1-1) | | Bundle Data 0..(L1-1) |
+-------------------------+ +-------------------------+
+-------------------------+ +-------------------------+ +-------------------------+ +-------------------------+
| DATA_SEGMENT | -> <- | ACK_SEGMENT (start) | | XFER_SEGMENT | -> <- | XFER_ACK (start) |
| Transfer ID [I1] | | Transfer ID [I1] | | Transfer ID [I1] | | Transfer ID [I1] |
| Length [L2] | | Length [L1] | | Length [L2] | | Length [L1] |
|Bundle Data L1..(L1+L2-1)| +-------------------------+ |Bundle Data L1..(L1+L2-1)| +-------------------------+
+-------------------------+ +-------------------------+
+-------------------------+ +-------------------------+ +-------------------------+ +-------------------------+
| DATA_SEGMENT (end) | -> <- | ACK_SEGMENT | | XFER_SEGMENT (end) | -> <- | XFER_ACK |
| Transfer ID [I1] | | Transfer ID [I1] | | Transfer ID [I1] | | Transfer ID [I1] |
| Length [L3] | | Length [L1+L2] | | Length [L3] | | Length [L1+L2] |
|Bundle Data | +-------------------------+ |Bundle Data | +-------------------------+
| (L1+L2)..(L1+L2+L3-1)| | (L1+L2)..(L1+L2+L3-1)|
+-------------------------+ +-------------------------+
+-------------------------+ +-------------------------+
<- | ACK_SEGMENT (end) | <- | XFER_ACK (end) |
| Transfer ID [I1] | | Transfer ID [I1] |
| Length [L1+L2+L3] | | Length [L1+L2+L3] |
+-------------------------+ +-------------------------+
+-------------------------+ +-------------------------+ +-------------------------+ +-------------------------+
| SHUTDOWN | -> <- | SHUTDOWN | | SHUTDOWN | -> <- | SHUTDOWN |
+-------------------------+ +-------------------------+ +-------------------------+ +-------------------------+
Figure 2: A Simple Visual Example of the Flow of Protocol Messages on Figure 2: A SL1e Visual Example of the Flow of Protocol Messages on a
a Single TCP Session between Two Nodes (A and B) Single TCP Session between Two Nodes (A and B)
4. Session Establishment 4. Session Establishment
For bundle transmissions to occur using the TCPCL, a TCPCL session For bundle transmissions to occur using the TCPCL, a TCPCL session
MUST first be established between communicating nodes. It is up to MUST first be established between communicating nodes. It is up to
the implementation to decide how and when session setup is triggered. the implementation to decide how and when session setup is triggered.
For example, some sessions MAY be opened proactively and maintained For example, some sessions MAY be opened proactively and maintained
for as long as is possible given the network conditions, while other for as long as is possible given the network conditions, while other
sessions MAY be opened only when there is a bundle that is queued for sessions MAY be opened only when there is a bundle that is queued for
transmission and the routing algorithm selects a certain next-hop transmission and the routing algorithm selects a certain next-hop
node. node.
To establish a TCPCL session, a node MUST first establish a TCP To establish a TCPCL session, a node MUST first establish a TCP
connection with the intended peer node, typically by using the connection with the intended peer node, typically by using the
services provided by the operating system. Port number 4556 has been services provided by the operating system. Destination port number
assigned by IANA as the well-known port number for the TCP 4556 has been assigned by IANA as the well-known port number for the
convergence layer. Other port numbers MAY be used per local TCP convergence layer. Other destination port numbers MAY be used
configuration. Determining a peer's port number (if different from per local configuration. Determining a peer's destination port
the well-known TCPCL port) is up to the implementation. number (if different from the well-known TCPCL port) is up to the
implementation. Any source port number MAY be used for TCPCL
sessions. Typically an operating system assigned number in the TCP
Ephemeral range (49152--65535) is used.
If the node is unable to establish a TCP connection for any reason, If the node is unable to establish a TCP connection for any reason,
then it is an implementation matter to determine how to handle the then it is an implementation matter to determine how to handle the
connection failure. A node MAY decide to re-attempt to establish the connection failure. A node MAY decide to re-attempt to establish the
connection. If it does so, it MUST NOT overwhelm its target with connection. If it does so, it MUST NOT overwhelm its target with
repeated connection attempts. Therefore, the node MUST retry the repeated connection attempts. Therefore, the node MUST retry the
connection setup only after some delay (a 1-second minimum is connection setup only after some delay (a 1-second minimum is
RECOMMENDED), and it SHOULD use a (binary) exponential backoff RECOMMENDED), and it SHOULD use a (binary) exponential backoff
mechanism to increase this delay in case of repeated failures. In mechanism to increase this delay in case of repeated failures. In
case a SHUTDOWN message specifying a reconnection delay is received, case a SHUTDOWN message specifying a reconnection delay is received,
skipping to change at page 9, line 24 skipping to change at page 10, line 30
| Segment MRU... | | Segment MRU... |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| contd. | | contd. |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| Transfer MRU... | | Transfer MRU... |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| contd. | | contd. |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| EID Length | EID Data... | | EID Length | EID Data... |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| contd. | | EID Data contd. |
+---------------+---------------+---------------+---------------+
| TCPCLv4 Header Extension Items... |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
Figure 3: Contact Header Format Figure 3: Contact Header Format
The fields of the contact header are: See Section 4.2 for details on the use of each of these contact
header fields. The fields of the contact header are:
magic: A four-octet field that always contains the octet sequence magic: A four-octet field that always contains the octet sequence
0x64 0x74 0x6e 0x21, i.e., the text string "dtn!" in US-ASCII (and 0x64 0x74 0x6e 0x21, i.e., the text string "dtn!" in US-ASCII (and
UTF-8). UTF-8).
Version: A one-octet field value containing the value 4 (current Version: A one-octet field value containing the value 4 (current
version of the protocol). version of the protocol).
Flags: A one-octet field of single-bit flags, interpreted according Flags: A one-octet field of single-bit flags, interpreted according
to the descriptions in Table 1. to the descriptions in Table 1.
Keepalive Interval: A 16-bit unsigned integer indicating the longest Keepalive Interval: A 16-bit unsigned integer indicating the longest
allowable interval in seconds between KEEPALIVE messages received allowable interval in seconds between KEEPALIVE messages received
in this session. in this session.
Segment MRU: A 64-bit unsigned integer indicating the largest Segment MRU: A 64-bit unsigned integer indicating the largest
allowable single-segment data payload size to be received in this allowable single-segment data payload size to be received in this
session. Any DATA_SEGMENT sent to this peer SHALL have a data session. Any XFER_SEGMENT sent to this peer SHALL have a data
payload no longer than the peer's Segment MRU. The two endpoints payload no longer than the peer's Segment MRU. The two endpoints
of a single session MAY have different Segment MRUs, and no of a single session MAY have different Segment MRUs, and no
relation between the two is required. relation between the two is required.
Transfer MRU: A 64-bit unsigned integer indicating the largest Transfer MRU: A 64-bit unsigned integer indicating the largest
allowable total-bundle data size to be received in this session. allowable total-bundle data size to be received in this session.
Any bundle transfer sent to this peer SHALL have a Total bundle Any bundle transfer sent to this peer SHALL have a Total bundle
data payload no longer than the peer's Transfer MRU. This value data 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
endpoints of a single session MAY have different Transfer MRUs, endpoints of a single session MAY have different Transfer MRUs,
and no relation between the two is required. and no relation between the two is required.
EID Length and EID Data: Together these fields represent a variable- EID Length and EID Data: Together these fields represent a variable-
length text string. The EID Length is a 16-bit unsigned integer length text string. The EID Length is a 16-bit unsigned integer
indicating the number of octets of EID Data to follow. A zero EID indicating the number of octets of EID Data to follow. A zero EID
Length is a special case which indicates the lack of EID rather Length SHALL be used to indicate the lack of EID rather than a
than a truly empty EID. A non-zero-length EID Data contains the truly empty EID. This case allows an endpoint to avoid exposing
UTF-8 encoded EID of some singleton endpoint in which the sending EID information on an untrusted network. A non-zero-length EID
node is a member, in the canonical format of <scheme Data SHALL contain the UTF-8 encoded EID of some singleton
name>:<scheme-specific part>. endpoint in which the sending node is a member, in the canonical
format of <scheme name>:<scheme-specific part>. This EID encoding
is consistent with [I-D.ietf-dtn-bpbis].
+---------+------+--------------------------------------------------+ Header Extension Values: The remaining items of the contact header
| Type | Code | Description | represent protocol extension data not defined by this
+---------+------+--------------------------------------------------+ specification. The encoding of each Header Extension Item is
| CAN_TLS | 0x01 | If bit is set, indicates that the sending peer | identical form as described in Section 4.1.1.
| | | is capable of TLS security. |
+---------+------+--------------------------------------------------+ +----------+--------+-----------------------------------------------+
| Name | Code | Description |
+----------+--------+-----------------------------------------------+
| CAN_TLS | 0x01 | If bit is set, indicates that the sending |
| | | peer is capable of TLS security. |
| | | |
| Reserved | others |
+----------+--------+-----------------------------------------------+
Table 1: Contact Header Flags Table 1: Contact Header Flags
4.1.1. Header Extension Items
Each of the Header Extension items SHALL be encoded in an identical
Type-Length-Value (TLV) container form as indicated in Figure 4. The
fields of the header extension item are:
Flags: A one-octet field containing generic bit flags about the
item, which are listed in Table 2. If a TCPCL endpoint receives
an extension item with an unknown Item Type and the CRITICAL flag
set, the endpoint SHALL close the TCPCL session with SHUTDOWN
reason code of "Contact Failure". If the CRITICAL flag is not
set, an endpoint SHALL skip over and ignore any item with an
unkonwn Item Type.
Item Type: A 16-bit unsigned integer field containing the type of
the extension item. Each type This specification does not define
any extension types directly, but does allocate an IANA registry
for such codes (see Section 8.3).
Item Length: A 32-bit unsigned integer field containing the number
of Item Value octets to follow.
Item Value: A variable-length data field which is interpreted
according to the associated Item Type. This specification places
no restrictions on an extensions use of available Item Value data.
Extension specification SHOULD avoid the use of large data
exchanges within the TCPCLv4 contact header as no bundle transfers
can begin until the a full contact exchange and negotiation has
been completed.
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Item Flags | Item Type | Item Length...|
+---------------+---------------+---------------+---------------+
| length contd. | Item Value... |
+---------------+---------------+---------------+---------------+
| value contd. |
+---------------+---------------+---------------+---------------+
Figure 4: Header Extention Item Format
+----------+--------+-----------------------------------------------+
| Name | Code | Description |
+----------+--------+-----------------------------------------------+
| CRITICAL | 0x01 | If bit is set, indicates that the receiving |
| | | peer must handle the extension item. |
| | | |
| Reserved | others |
+----------+--------+-----------------------------------------------+
Table 2: Header Extension Item Flags
4.2. Validation and Parameter Negotiation 4.2. Validation and Parameter Negotiation
Upon reception of the contact header, each node follows the following Upon reception of the contact header, each node follows the following
procedures to ensure the validity of the TCPCL session and to procedures to ensure the validity of the TCPCL session and to
negotiate values for the session parameters. negotiate values for the session parameters.
If the magic string is not present or is not valid, the connection If the magic string is not present or is not valid, the connection
MUST be terminated. The intent of the magic string is to provide MUST be terminated. The intent of the magic string is to provide
some protection against an inadvertent TCP connection by a different some protection against an inadvertent TCP connection by a different
protocol than the one described in this document. To prevent a flood protocol than the one described in this document. To prevent a flood
skipping to change at page 11, line 5 skipping to change at page 13, line 27
before closing it. before closing it.
If a node receives a contact header containing a version that is If a node receives a contact header containing a version that is
greater than the current version of the protocol that the node greater than the current version of the protocol that the node
implements, then the node SHALL shutdown the session with a reason implements, then the node SHALL shutdown the session with a reason
code of "Version mismatch". If a node receives a contact header with code of "Version mismatch". If a node receives a contact header with
a version that is lower than the version of the protocol that the a version that is lower than the version of the protocol that the
node implements, the node MAY either terminate the session (with a node implements, the node MAY either terminate the session (with a
reason code of "Version mismatch"). Otherwise, the node MAY adapt reason code of "Version mismatch"). Otherwise, the node MAY adapt
its operation to conform to the older version of the protocol. This its operation to conform to the older version of the protocol. This
decision is an implementation matter. decision is an implementation matter. When establishing the TCPCL
session, a node SHOULD send the contact header for the latest version
of TCPCL that it can use.
A node calculates the parameters for a TCPCL session by negotiating A node calculates the parameters for a TCPCL session by negotiating
the values from its own preferences (conveyed by the contact header the values from its own preferences (conveyed by the contact header
it sent to the peer) with the preferences of the peer node (expressed it sent to the peer) with the preferences of the peer node (expressed
in the contact header that it received from the peer). The in the contact header that it received from the peer). The
negotatiated parameters defined by this specification are described negotatiated parameters defined by this specification are described
in the following paragraphs. in the following paragraphs.
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. If the negotiated Session Keepalive is zero Keepalive Interval. If the negotiated Session Keepalive is zero
(i.e. one or both contact headers contains a zero Keepalive (i.e. one or both contact headers contains a zero Keepalive
Interval), then the keepalive feature (described in Section 5.2.1) Interval), then the keepalive feature (described in Section 5.2.1)
is disabled. is disabled. There is no logical minimum value for the keepalive
interval, but when used for many sessions on an open, shared
network a short interval could lead to excessive traffic. For
shared network use, endpoints SHOULD choose a keepalive interval
no shorter than 30 seconds. There is no logical maximum value for
the keepalive interval, but an idle TCP connection is liable for
closure by the host operating system if the keepalive time is
longer than tens-of-minutes. Endpoints SHOULD choose a keepalive
interval no longer than 10 minutes (600 seconds).
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.
If the negotiated Enable TLS value is true then TLS negotiation If the negotiated Enable TLS value is true then TLS negotiation
feature (described in Section 5.3) begins immediately following feature (described in Section 5.3) begins immediately following
the contact header exchange. the contact header exchange.
Once this process of parameter negotiation is completed, the protocol Once this process of parameter negotiation is completed, the protocol
defines no additional mechanism to change the parameters of an defines no additional mechanism to change the parameters of an
established session; to effect such a change, the session MUST be established session; to effect such a change, the session MUST be
skipping to change at page 11, line 45 skipping to change at page 14, line 29
established session, including the mechanism for transmitting bundles established session, including the mechanism for transmitting bundles
over the session. over the session.
5.1. Message Type Codes 5.1. Message Type Codes
After the initial exchange of a contact header, all messages After the initial exchange of a contact header, all messages
transmitted over the session are identified by a one-octet header transmitted over the session are identified by a one-octet header
with the following structure: with the following structure:
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+ +---------------+
| type | flags | | Message Type |
+-+-+-+-+-+-+-+-+ +---------------+
Figure 4: Format of the One-Octet Message Header Figure 5: Format of the Message Header
type: Indicates the type of the message as per Table 2 below. The message header fields are as follows:
flags: Optional flags defined based on message type. Message Type: Indicates the type of the message as per Table 3
below.
The types and values for the message type code are as follows. The message types defined in this specificaiton are listed in
Table 3. Encoded values are listed in Section 8.4.
+---------------+------+--------------------------------------------+ +--------------+----------------------------------------------------+
| Type | Code | Description | | Type | Description |
+---------------+------+--------------------------------------------+ +--------------+----------------------------------------------------+
| DATA_SEGMENT | 0x1 | Indicates the transmission of a segment of | | XFER_INIT | Contains the length (in octets) of the next |
| | | bundle data, as described in Section | | | transfer, as described in Section 5.4.2. |
| | | 5.4.3. | | | |
| | | | | XFER_SEGMENT | Indicates the transmission of a segment of bundle |
| ACK_SEGMENT | 0x2 | Acknowledges reception of a data segment, | | | data, as described in Section 5.4.3. |
| | | as described in Section 5.4.4. | | | |
| | | | | XFER_ACK | Acknowledges reception of a data segment, as |
| REFUSE_BUNDLE | 0x3 | Indicates that the transmission of the | | | described in Section 5.4.4. |
| | | current bundle SHALL be stopped, as | | | |
| | | described in Section 5.4.5. | | XFER_REFUSE | Indicates that the transmission of the current |
| | | | | | bundle SHALL be stopped, as described in Section |
| KEEPALIVE | 0x4 | KEEPALIVE message for the session, as | | | 5.4.5. |
| | | described in Section 5.2.1. | | | |
| | | | | KEEPALIVE | Used to keep TCPCL session active, as described in |
| SHUTDOWN | 0x5 | Indicates that one of the nodes | | | Section 5.2.1. |
| | | participating in the session wishes to | | | |
| | | cleanly terminate the session, as | | SHUTDOWN | Indicates that one of the nodes participating in |
| | | described in Section 6. | | | the session wishes to cleanly terminate the |
| | | | | | session, as described in Section 6. |
| LENGTH | 0x6 | Contains the length (in octets) of the | | | |
| | | next bundle, as described in Section | | MSG_REJECT | Contains a TCPCL message rejection, as described |
| | | 5.4.2. | | | in Section 5.2.2. |
| | | | +--------------+----------------------------------------------------+
| REJECT | TBD | Contains a TCPCL message rejection, as |
| | | described in Section 5.2.2. |
+---------------+------+--------------------------------------------+
Table 2: TCPCL Message Types Table 3: TCPCL Message Types
5.2. Upkeep and Status Messages 5.2. Upkeep and Status Messages
5.2.1. Session Upkeep (KEEPALIVE) 5.2.1. Session Upkeep (KEEPALIVE)
The protocol includes a provision for transmission of KEEPALIVE The protocol includes a provision for transmission of KEEPALIVE
messages over the TCPCL session to help determine if the underlying messages over the TCPCL session to help determine if the underlying
TCP connection has been disrupted. TCP connection has been disrupted.
As described in Section 4.1, one of the parameters in the contact As described in Section 4.1, one of the parameters in the contact
header is the Keepalive Interval. Both sides populate this field header is the Keepalive Interval. Both sides populate this field
with their requested intervals (in seconds) between KEEPALIVE with their requested intervals (in seconds) between KEEPALIVE
messages. messages.
The format of a KEEPALIVE message is a one-octet message type code of The format of a KEEPALIVE message is a one-octet message type code of
KEEPALIVE (as described in Table 2) with no additional data. Both KEEPALIVE (as described in Table 3) with no additional data. Both
sides SHOULD send a KEEPALIVE message whenever the negotiated sides SHOULD send a KEEPALIVE message whenever the negotiated
interval has elapsed with no transmission of any message (KEEPALIVE interval has elapsed with no transmission of any message (KEEPALIVE
or other). or other).
If no message (KEEPALIVE or other) has been received for at least If no message (KEEPALIVE or other) has been received for at least
twice the Keepalive Interval, then either party MAY terminate the twice the Keepalive Interval, then either party MAY terminate the
session by transmitting a one-octet SHUTDOWN message (as described in session by transmitting a one-octet SHUTDOWN message (as described in
Table 2, with reason code "Idle Timeout") and by closing the session. Section 6.1, with reason code "Idle Timeout") and by closing the
session.
Note: The Keepalive Interval SHOULD not be chosen too short as TCP Note: The Keepalive Interval SHOULD not be chosen too short as TCP
retransmissions MAY occur in case of packet loss. Those will have to retransmissions MAY occur in case of packet loss. Those will have to
be triggered by a timeout (TCP retransmission timeout (RTO)), which be triggered by a timeout (TCP retransmission timeout (RTO)), which
is dependent on the measured RTT for the TCP connection so that is dependent on the measured RTT for the TCP connection so that
KEEPALIVE messages MAY experience noticeable latency. KEEPALIVE messages MAY experience noticeable latency.
5.2.2. Message Rejection (REJECT) 5.2.2. Message Rejection (MSG_REJECT)
If a TCPCL endpoint receives a message which is unknown to it If a TCPCL endpoint receives a message which is unknown to it
(possibly due to an unhandled protocol mismatch) or is inappropriate (possibly due to an unhandled protocol mismatch) or is inappropriate
for the current session state (e.g. a KEEPALIVE message received for the current session state (e.g. a KEEPALIVE message received
after contact header negotation has disabled that feature), there is after contact header negotation has disabled that feature), there is
a protocol-level message to signal this condition in the form of a a protocol-level message to signal this condition in the form of a
REJECT reply. MSG_REJECT reply.
The format of a REJECT message follows: The format of a MSG_REJECT message follows:
+-----------------------------+ +-----------------------------+
| Message Header | | Message Header |
+-----------------------------+ +-----------------------------+
| Reason Code (U8) | | Reason Code (U8) |
+-----------------------------+ +-----------------------------+
| Rejected Message Header | | Rejected Message Header |
+-----------------------------+ +-----------------------------+
Figure 5: Format of REJECT Messages Figure 6: Format of MSG_REJECT Messages
The Rejected Message Header is a copy of the Message Header to which The fields of the MSG_REJECT message are:
the REJECT message is sent as a response. The REJECT Reason Code is
an 8-bit unsigned integer and indicates why the REJECT itself was Reason Code: A one-octet refusal reason code interpreted according
sent. The specified values of the reason code are: to the descriptions in Table 4.
Rejected Message Header: The Rejected Message Header is a copy of
the Message Header to which the MSG_REJECT message is sent as a
response.
+-------------+------+----------------------------------------------+ +-------------+------+----------------------------------------------+
| Name | Code | Description | | Name | Code | Description |
+-------------+------+----------------------------------------------+ +-------------+------+----------------------------------------------+
| Message | 0x01 | A message was received with a Message Type | | Message | 0x01 | A message was received with a Message Type |
| Type | | code unknown to the TCPCL endpoint. | | Type | | code unknown to the TCPCL endpoint. |
| Unknown | | | | Unknown | | |
| | | | | | | |
| Message | 0x02 | A message was received but the TCPCL | | Message | 0x02 | A message was received but the TCPCL |
| Unsupported | | endpoint cannot comply with the message | | Unsupported | | endpoint cannot comply with the message |
| | | contents. | | | | contents. |
| | | | | | | |
| Message | 0x03 | A message was received while the session is | | Message | 0x03 | A message was received while the session is |
| Unexpected | | in a state in which the message is not | | Unexpected | | in a state in which the message is not |
| | | expected. | | | | expected. |
+-------------+------+----------------------------------------------+ +-------------+------+----------------------------------------------+
Table 3: REJECT Reason Codes Table 4: MSG_REJECT Reason Codes
5.3. Session Security 5.3. Session Security
This version of the TCPCL supports establishing a session-level This version of the TCPCL supports establishing a session-level
Transport Layer Security (TLS) session within an existing TCPCL Transport Layer Security (TLS) session within an existing TCPCL
session. Negotation of whether or not to initiate TLS within TCPCL session. Negotation of whether or not to initiate TLS within TCPCL
session is part of the contact header as described in Section 4.2. session is part of the contact header as described in Section 4.2.
When TLS is used within the TCPCL it affects the entire session. By When TLS is used within the TCPCL it affects the entire session. By
convention, this protocol uses the endpoint which initiated the convention, this protocol uses the endpoint which initiated the
skipping to change at page 15, line 11 skipping to change at page 18, line 11
After a TLS session is successfuly established, both TCPCL endpoints After a TLS session is successfuly established, both TCPCL endpoints
SHALL re-exchange TCPCL Contact Header messages. Any information SHALL re-exchange TCPCL Contact Header messages. Any information
cached from the prior Contact Header exchange SHALL be discarded. cached from the prior Contact Header exchange SHALL be discarded.
This re-exchange avoids man-in-the-middle attack in identical fashion This re-exchange avoids man-in-the-middle attack in identical fashion
to [RFC2595]. to [RFC2595].
5.3.2. Example TLS Initiation 5.3.2. Example TLS Initiation
A summary of a typical CAN_TLS usage is shown in the sequence in A summary of a typical CAN_TLS usage is shown in the sequence in
Figure 6 below. Figure 7 below.
Node A Node B Node A Node B
====== ====== ====== ======
+-------------------------+ +-------------------------+
| Open TCP Connnection | -> | Open TCP Connnection | ->
+-------------------------+ +-------------------------+ +-------------------------+ +-------------------------+
<- | Accept Connection | <- | Accept Connection |
+-------------------------+ +-------------------------+
skipping to change at page 15, line 41 skipping to change at page 18, line 41
+-------------------------+ +-------------------------+ +-------------------------+ +-------------------------+
| Contact Header | -> <- | Contact Header | | Contact Header | -> <- | Contact Header |
+-------------------------+ +-------------------------+ +-------------------------+ +-------------------------+
... secured TCPCL messaging ... ... secured TCPCL messaging ...
+-------------------------+ +-------------------------+ +-------------------------+ +-------------------------+
| SHUTDOWN | -> <- | SHUTDOWN | | SHUTDOWN | -> <- | SHUTDOWN |
+-------------------------+ +-------------------------+ +-------------------------+ +-------------------------+
Figure 6: A simple visual example of TCPCL TLS Establishment between Figure 7: A simple visual example of TCPCL TLS Establishment between
two nodes two nodes
5.4. Bundle Transfer 5.4. Bundle Transfer
All of the message in this section are directly associated with All of the message in this section are directly associated with
tranfering a bundle between TCPCL endpoints. tranfering a bundle between TCPCL endpoints.
A single TCPCL transfer results in a bundle (handled by the A single TCPCL transfer results in a bundle (handled by the
convergence layer as opaque data) being exchanged from one endpoint convergence layer as opaque data) being exchanged from one endpoint
to the other. In TCPCL a transfer is accomplished by dividing a to the other. In TCPCL a transfer is accomplished by dividing a
skipping to change at page 16, line 20 skipping to change at page 19, line 20
5.4.1. Bundle Transfer ID 5.4.1. Bundle Transfer ID
Each of the bundle transfer messages contains a Transfer ID number Each of the bundle transfer messages contains a Transfer ID number
which is used to correlate messages originating from sender and which is used to correlate messages originating from sender and
receiver of a bundle. A Transfer ID does not attempt to address receiver of a bundle. A Transfer ID does not attempt to address
uniqueness of the bundle data itself and has no relation to concepts uniqueness of the bundle data itself and has no relation to concepts
such as bundle fragmentation. Each invocation of TCPCL by the bundle such as bundle fragmentation. Each invocation of TCPCL by the bundle
protocol agent, requesting transmission of a bundle (fragmentary or protocol agent, requesting transmission of a bundle (fragmentary or
otherwise), results in the initiation of a single TCPCL transfer. otherwise), results in the initiation of a single TCPCL transfer.
Each transfer entails the sending of a LENGTH message and some number Each transfer entails the sending of a XFER_INIT message and some
of DATA_SEGMENT and ACK_SEGMENT messages; all are correlated by the number of XFER_SEGMENT and XFER_ACK messages; all are correlated by
same Transfer ID. the same Transfer ID.
Transfer IDs from each endpoint SHALL be unique within a single TCPCL Transfer IDs from each endpoint SHALL be unique within a single TCPCL
session. The initial Transfer ID from each endpoint SHALL have value session. The initial Transfer ID from each endpoint SHALL have value
zero. Subsequent Transfer ID values SHALL be incremented from the zero. Subsequent Transfer ID values SHALL be incremented from the
prior Transfer ID value by one. Upon exhaustion of the entire 64-bit prior Transfer ID value by one. Upon exhaustion of the entire 64-bit
Transfer ID space, the sending endpoint SHALL terminate the session Transfer ID space, the sending endpoint SHALL terminate the session
with SHUTDOWN reason code "Resource Exhaustion". with SHUTDOWN reason code "Resource Exhaustion".
For bidirectional bundle transfers, a TCPCL endpoint SHOULD NOT rely For bidirectional bundle transfers, a TCPCL endpoint SHOULD NOT rely
on any relation between Transfer IDs originating from each side of on any relation between Transfer IDs originating from each side of
the TCPCL session. the TCPCL session.
5.4.2. Bundle Length (LENGTH) 5.4.2. Transfer initialization (XFER_INIT)
The LENGTH message contains the total length, in octets, of the The XFER_INIT message contains the total length, in octets, of the
bundle data in the associated transfer. The total length is bundle data in the associated transfer. The total length is
formatted as a 64-bit unsigned integer. formatted as a 64-bit unsigned integer.
The purpose of the LENGTH message is to allow nodes to preemptively The purpose of the XFER_INIT message is to allow nodes to
refuse bundles that would exceed their resources or to prepare preemptively refuse bundles that would exceed their resources or to
storage on the receiving node for the upcoming bundle data. See prepare storage on the receiving node for the upcoming bundle data.
Section 5.4.5 for details on when refusal based on LENGTH content is See Section 5.4.5 for details on when refusal based on XFER_INIT
acceptable. content is acceptable.
The Total Bundle Length field within a LENGTH message SHALL be used The Total Bundle Length field within a XFER_INIT message SHALL be
as informative data by the receiver. If, for whatever reason, the treated as authoritative by the receiver. If, for whatever reason,
actual total length of bundle data received differs from the value the actual total length of bundle data received differs from the
indicated by the LENGTH message, the receiver SHOULD accept the full value indicated by the XFER_INIT message, the receiver SHOULD treat
set of bundle data as valid. the transmitted data as invalid.
The format of the LENGTH message is as follows: The format of the XFER_INIT message is as follows:
+-----------------------------+ +-----------------------------+
| Message Header | | Message Header |
+-----------------------------+ +-----------------------------+
| Transfer ID (U64) | | Transfer ID (U64) |
+-----------------------------+ +-----------------------------+
| Total bundle length (U64) | | Total bundle length (U64) |
+-----------------------------+ +-----------------------------+
Figure 7: Format of LENGTH Messages Figure 8: Format of XFER_INIT Messages
LENGTH messages SHALL be sent immediately before transmission of any The fields of the XFER_INIT message are:
DATA_SEGMENT messages. LENGTH messages MUST NOT be sent unless the
next DATA_SEGMENT message has the 'S' bit set to "1" (i.e., just Transfer ID: A 64-bit unsigned integer identifying the transfer
before the start of a new transfer). about to begin.
Total bundle length: A 64-bit unsigned integer indicating the size
of the data-to-be-transferred.
XFER_INIT messages SHALL be sent immediately before transmission of
any XFER_SEGMENT messages. XFER_INIT messages MUST NOT be sent
unless the next XFER_SEGMENT message has the 'START' bit set to "1"
(i.e., just before the start of a new transfer).
A receiver MAY send a BUNDLE_REFUSE message as soon as it receives a A receiver MAY send a BUNDLE_REFUSE message as soon as it receives a
LENGTH message without waiting for the next DATA_SEGMENT message. XFER_INIT message without waiting for the next XFER_SEGMENT message.
The sender MUST be prepared for this and MUST associate the refusal The sender MUST be prepared for this and MUST associate the refusal
with the correct bundle via the Transfer ID fields. with the correct bundle via the Transfer ID fields.
Upon reception of a LENGTH message not immediately before the start Upon reception of a XFER_INIT message not immediately before the
of a starting DATA_SEGMENT the reciever SHALL send a REJECT message start of a starting XFER_SEGMENT the reciever SHALL send a MSG_REJECT
with a Reason Code of "Message Unexpected". message with a Reason Code of "Message Unexpected".
5.4.3. Bundle Data Transmission (DATA_SEGMENT) 5.4.3. Data Transmission (XFER_SEGMENT)
Each bundle is transmitted in one or more data segments. The format Each bundle is transmitted in one or more data segments. The format
of a DATA_SEGMENT message follows in Figure 8 and its use of header of a XFER_SEGMENT message follows in Figure 9.
flags is shown in Figure 9.
+------------------------------+ +------------------------------+
| Message Header | | Message Header |
+------------------------------+ +------------------------------+
| Message Flags (U8) |
+------------------------------+
| Transfer ID (U64) | | Transfer ID (U64) |
+------------------------------+ +------------------------------+
| Data length (U64) | | Data length (U64) |
+------------------------------+ +------------------------------+
| Data contents (octet string) | | Data contents (octet string) |
+------------------------------+ +------------------------------+
Figure 8: Format of DATA_SEGMENT Messages Figure 9: Format of XFER_SEGMENT Messages
4 5 6 7
+-+-+-+-+
|0|0|S|E|
+-+-+-+-+
Figure 9: Format of DATA_SEGMENT Header flags The fields of the XFER_SEGMENT message are:
The flags portion of the message header octet contains two optional Message Flags: A one-octet field of single-bit flags, interpreted
values in the two low-order bits, denoted 'S' and 'E' in Figure 9. according to the descriptions in Table 5.
The 'S' bit MUST be set to one if it precedes the transmission of the
first segment of a transfer. The 'E' bit MUST be set to one when
transmitting the last segment of a transfer. In the case where an
entire transfer is accomplished in a single segment, both the 'S' and
'E' bits MUST be set to one.
Following the message header, the length field is a 64-bit unsigned Transfer ID: A 64-bit unsigned integer identifying the transfer
integer containing the number of octets of bundle data that are being made.
transmitted in this segment. Following the length are the actual
data contents. Data length: A 64-bit unsigned integer indicating the number of
octets in the Data contents to follow.
Data contents: The variable-length data payload of the message.
+----------+--------+-----------------------------------------------+
| Name | Code | Description |
+----------+--------+-----------------------------------------------+
| END | 0x01 | If bit is set, indicates that this is the |
| | | last segment of the transfer. |
| | | |
| START | 0x02 | If bit is set, indicates that this is the |
| | | first segment of the transfer. |
| | | |
| Reserved | others |
+----------+--------+-----------------------------------------------+
Table 5: XFER_SEGMENT Flags
The flags portion of the message contains two optional values in the
two low-order bits, denoted 'START' and 'END' in Table 5. The
'START' bit MUST be set to one if it precedes the transmission of the
first segment of a transfer. The 'END' bit MUST be set to one when
transmitting the last segment of a transfer. In the case where an
entire transfer is accomplished in a single segment, both the 'START'
and 'END' bits MUST be set to one.
Once a transfer of a bundle has commenced, the node MUST only send Once a transfer of a bundle has commenced, the node MUST only send
segments containing sequential portions of that bundle until it sends segments containing sequential portions of that bundle until it sends
a segment with the 'E' bit set. No interleaving of multiple a segment with the 'END' bit set. No interleaving of multiple
transfers from the same endpoint is possible (within a single TCPCL transfers from the same endpoint is possible within a single TCPCL
session). session. Simultaneous transfers between two endpoints MAY be
achieved using multiple TCPCL sessions.
5.4.4. Bundle Acknowledgments (ACK_SEGMENT) 5.4.4. Data Acknowledgments (XFER_ACK)
Although the TCP transport provides reliable transfer of data between Although the TCP transport provides reliable transfer of data between
transport peers, the typical BSD sockets interface provides no means transport peers, the typical BSD sockets interface provides no means
to inform a sending application of when the receiving application has to inform a sending application of when the receiving application has
processed some amount of transmitted data. Thus, after transmitting processed some amount of transmitted data. Thus, after transmitting
some data, a Bundle Protocol agent needs an additional mechanism to some data, a Bundle Protocol agent needs an additional mechanism to
determine whether the receiving agent has successfully received the determine whether the receiving agent has successfully received the
segment. To this end, the TCPCL protocol provides feedback messaging segment. To this end, the TCPCL protocol provides feedback messaging
whereby a receiving node transmits acknowledgments of reception of whereby a receiving node transmits acknowledgments of reception of
data segments. data segments.
The format of an ACK_SEGMENT message follows in Figure 10 and its use The format of an XFER_ACK message follows in Figure 10.
of header flags is the same as for DATA_SEGMENT (shown in Figure 9).
The flags of an ACK_SEGMENT message SHALL be identical to the flags
of the DATA_SEGMENT message for which it is a reply.
+-----------------------------+ +-----------------------------+
| Message Header | | Message Header |
+-----------------------------+ +-----------------------------+
| Message Flags (U8) |
+-----------------------------+
| Transfer ID (U64) | | Transfer ID (U64) |
+-----------------------------+ +-----------------------------+
| Acknowledged length (U64) | | Acknowledged length (U64) |
+-----------------------------+ +-----------------------------+
Figure 10: Format of ACK_SEGMENT Messages Figure 10: Format of XFER_ACK Messages
A receving TCPCL endpoing SHALL send an ACK_SEGMENT message in The fields of the XFER_ACK message are:
response to each received DATA_SEGMENT message. The flags portion of
the ACK_SEGMENT header SHALL be set to match the corresponding Message Flags: A one-octet field of single-bit flags, interpreted
DATA_SEGEMNT message being acknowledged. The acknowledged length of according to the descriptions in Table 5.
each ACK_SEGMENT contains the sum of the data length fields of all
DATA_SEGMENT messages received so far in the course of the indicated Transfer ID: A 64-bit unsigned integer identifying the transfer
transfer. being acknowledged.
Acknowledged length: A 64-bit unsigned integer indicating the total
number of octets in the transfer which are being acknowledged.
A receving TCPCL endpoing SHALL send an XFER_ACK message in response
to each received XFER_SEGMENT message. The flags portion of the
XFER_ACK header SHALL be set to match the corresponding DATA_SEGEMNT
message being acknowledged. The acknowledged length of each XFER_ACK
contains the sum of the data length fields of all XFER_SEGMENT
messages received so far in the course of the indicated transfer.
For example, suppose the sending node transmits four segments of For example, suppose the sending node transmits four segments of
bundle data with lengths 100, 200, 500, and 1000, respectively. bundle data with lengths 100, 200, 500, and 1000, respectively.
After receiving the first segment, the node sends an acknowledgment After receiving the first segment, the node sends an acknowledgment
of length 100. After the second segment is received, the node sends of length 100. After the second segment is received, the node sends
an acknowledgment of length 300. The third and fourth an acknowledgment of length 300. The third and fourth
acknowledgments are of length 800 and 1800, respectively. acknowledgments are of length 800 and 1800, respectively.
5.4.5. Bundle Refusal (REFUSE_BUNDLE) 5.4.5. Transfer Refusal (XFER_REFUSE)
As bundles can be large, the TCPCL supports an optional mechanism by As bundles can be large, the TCPCL supports an optional mechanism by
which a receiving node MAY indicate to the sender that it does not which a receiving node MAY indicate to the sender that it does not
want to receive the corresponding bundle. want to receive the corresponding bundle.
To do so, upon receiving a LENGTH or DATA_SEGMENT message, the node To do so, upon receiving a XFER_INIT or XFER_SEGMENT message, the
MAY transmit a REFUSE_BUNDLE message. As data segments and node MAY transmit a XFER_REFUSE message. As data segments and
acknowledgments MAY cross on the wire, the bundle that is being acknowledgments MAY cross on the wire, the bundle that is being
refused SHALL be identified by the Transfer ID of the refusal. refused SHALL be identified by the Transfer ID of the refusal.
There is no required relation between the Transfer MRU of a TCPCL There is no required relation between the Transfer MRU of a TCPCL
endpoint (which is supposed to represent a firm limitation of what endpoint (which is supposed to represent a firm limitation of what
the endpoint will accept) and sending of a REFUSE_BUNDLE message. A the endpoint will accept) and sending of a XFER_REFUSE message. A
REFUSE_BUNDLE can be used in cases where the agent's bundle storage XFER_REFUSE can be used in cases where the agent's bundle storage is
is temporarily depleted or somehow constrained. A REFUSE_BUNDLE can temporarily depleted or somehow constrained. A XFER_REFUSE can also
also be used after the bundle header or any bundle data is inspected be used after the bundle header or any bundle data is inspected by an
by an agent and determined to be unacceptable. agent and determined to be unacceptable.
The format of the REFUSE_BUNDLE message is as follows: The format of the XFER_REFUSE message is as follows:
+-----------------------------+ +-----------------------------+
| Message Header | | Message Header |
+-----------------------------+ +-----------------------------+
| Reason Code (U8) |
+-----------------------------+
| Transfer ID (U64) | | Transfer ID (U64) |
+-----------------------------+ +-----------------------------+
Figure 11: Format of REFUSE_BUNDLE Messages Figure 11: Format of XFER_REFUSE Messages
4 5 6 7 The fields of the XFER_REFUSE message are:
+-+-+-+-+
| RCode |
+-+-+-+-+
Figure 12: Format of REFUSE_BUNDLE Header flags Reason Code: A one-octet refusal reason code interpreted according
to the descriptions in Table 6.
The RCode field, which stands for "reason code", contains a value Transfer ID: A 64-bit unsigned integer identifying the transfer
indicating why the bundle was refused. The following table contains being refused.
semantics for some values. Other values MAY be registered with IANA,
as defined in Section 8.
+------------+-------+----------------------------------------------+ +------------+------------------------------------------------------+
| Name | RCode | Semantics | | Name | Semantics |
+------------+-------+----------------------------------------------+ +------------+------------------------------------------------------+
| Unknown | 0x0 | Reason for refusal is unknown or not | | Unknown | Reason for refusal is unknown or not specified. |
| | | specified. | | | |
| | | | | Completed | The receiver now has the complete bundle. The sender |
| Completed | 0x1 | The receiver now has the complete bundle. | | | MAY now consider the bundle as completely received. |
| | | The sender MAY now consider the bundle as | | | |
| | | completely received. | | No | The receiver's resources are exhausted. The sender |
| | | | | Resources | SHOULD apply reactive bundle fragmentation before |
| No | 0x2 | The receiver's resources are exhausted. The | | | retrying. |
| Resources | | sender SHOULD apply reactive bundle | | | |
| | | fragmentation before retrying. | | Retransmit | The receiver has encountered a problem that requires |
| | | | | | the bundle to be retransmitted in its entirety. |
| Retransmit | 0x3 | The receiver has encountered a problem that | +------------+------------------------------------------------------+
| | | requires the bundle to be retransmitted in |
| | | its entirety. |
+------------+-------+----------------------------------------------+
Table 4: REFUSE_BUNDLE Reason Codes Table 6: XFER_REFUSE Reason Codes
The receiver MUST, for each transfer preceding the one to be refused, The receiver MUST, for each transfer preceding the one to be refused,
have either acknowledged all DATA_SEGMENTs or refused the bundle have either acknowledged all XFER_SEGMENTs or refused the bundle
transfer. transfer.
The bundle transfer refusal MAY be sent before an entire data segment The bundle transfer refusal MAY be sent before an entire data segment
is received. If a sender receives a REFUSE_BUNDLE message, the is received. If a sender receives a XFER_REFUSE message, the sender
sender MUST complete the transmission of any partially sent MUST complete the transmission of any partially sent XFER_SEGMENT
DATA_SEGMENT message. There is no way to interrupt an individual message. There is no way to interrupt an individual TCPCL message
TCPCL message partway through sending it. The sender MUST NOT partway through sending it. The sender MUST NOT commence
commence transmission of any further segments of the refused bundle transmission of any further segments of the refused bundle
subsequently. Note, however, that this requirement does not ensure subsequently. Note, however, that this requirement does not ensure
that a node will not receive another DATA_SEGMENT for the same bundle that a node will not receive another XFER_SEGMENT for the same bundle
after transmitting a REFUSE_BUNDLE message since messages MAY cross after transmitting a XFER_REFUSE message since messages MAY cross on
on the wire; if this happens, subsequent segments of the bundle the wire; if this happens, subsequent segments of the bundle SHOULD
SHOULD also be refused with a REFUSE_BUNDLE message. also be refused with a XFER_REFUSE message.
Note: If a bundle transmission is aborted in this way, the receiver Note: If a bundle transmission is aborted in this way, the receiver
MAY not receive a segment with the 'E' 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 'S' bit set to '1', indicating the start of a new transfer, and the 'START' bit set to '1', indicating the start of a new transfer,
with a distinct Transfer ID value. and with a distinct Transfer ID value.
6. Session Termination 6. Session Termination
This section describes the procedures for ending a TCPCL session. This section describes the procedures for ending a TCPCL session.
6.1. Shutdown Message (SHUTDOWN) 6.1. Shutdown Message (SHUTDOWN)
To cleanly shut down a session, a SHUTDOWN message MUST be To cleanly shut down a session, a SHUTDOWN message MUST be
transmitted by either node at any point following complete transmitted by either node at any point following complete
transmission of any other message. A receiving node SHOULD transmission of any other message. A receiving node SHOULD
acknowledge all received data segments before sending a SHUTDOWN acknowledge all received data segments before sending a SHUTDOWN
message to end the session. A transmitting node SHALL treat a message to end the session. A transmitting node SHALL treat a
SHUTDOWN message received mid-transfer (i.e. before the final SHUTDOWN message received mid-transfer (i.e. before the final
acknowledgement) as a failure of the transfer. acknowledgement) as a failure of the transfer.
After transmitting a SHUTDOWN message, an endpoint MAY immediately
close the associated TCP connection. Once the SHUTDOWN message is
sent, any further received data on the TCP connection SHOULD be
ignored. Any delay between request to terminate the TCP connection
and actual closing of the connection (a "half-closed" state) MAY be
ignored by the TCPCL endpoint.
The format of the SHUTDOWN message is as follows: The format of the SHUTDOWN message is as follows:
+-----------------------------------+ +-----------------------------------+
| Message Header | | Message Header |
+-----------------------------------+ +-----------------------------------+
| Message Flags (U8) |
+-----------------------------------+
| Reason Code (optional U8) | | Reason Code (optional U8) |
+-----------------------------------+ +-----------------------------------+
| Reconnection Delay (optional U16) | | Reconnection Delay (optional U16) |
+-----------------------------------+ +-----------------------------------+
Figure 13: Format of SHUTDOWN Messages Figure 12: Format of SHUTDOWN Messages
4 5 6 7 The fields of the SHUTDOWN message are:
+-+-+-+-+
|0|0|R|D|
+-+-+-+-+
Figure 14: Format of SHUTDOWN Header flags Message Flags: A one-octet field of single-bit flags, interpreted
according to the descriptions in Table 7.
Reason Code: A one-octet refusal reason code interpreted according
to the descriptions in Table 8. The Reason Code is present or
absent as indicated by one of the flags.
Reconnection Delay: A 16-bit unsigned integer indicating the desired
delay until further TCPCL sessions to the sending endpoint. The
Reconnection Delay is present or absent as indicated by one of the
flags.
+----------+--------+-----------------------------------------------+
| Name | Code | Description |
+----------+--------+-----------------------------------------------+
| D | 0x01 | If bit is set, indicates that a Reconnection |
| | | Delay field is present. |
| | | |
| R | 0x02 | If bit is set, indicates that a Reason Code |
| | | field is present. |
| | | |
| Reserved | others |
+----------+--------+-----------------------------------------------+
Table 7: SHUTDOWN Flags
It is possible for a node to convey additional information regarding It is possible for a node to convey additional information regarding
the reason for session termination. To do so, the node MUST set the the reason for session termination. To do so, the node MUST set the
'R' bit in the message header flags and transmit a one-octet reason 'R' bit in the message flags and transmit a one-octet reason code
code immediately following the message header. The specified values immediately following the message header. The specified values of
of the reason code are: the reason code are:
+--------------+------+---------------------------------------------+ +---------------+---------------------------------------------------+
| Name | Code | Description | | Name | Description |
+--------------+------+---------------------------------------------+ +---------------+---------------------------------------------------+
| Idle timeout | 0x00 | The session is being closed due to | | Idle timeout | The session is being closed due to idleness. |
| | | idleness. | | | |
| | | | | Version | The node cannot conform to the specified TCPCL |
| Version | 0x01 | The node cannot conform to the specified | | mismatch | protocol version. |
| mismatch | | TCPCL protocol version. | | | |
| | | | | Busy | The node is too busy to handle the current |
| Busy | 0x02 | The node is too busy to handle the current | | | session. |
| | | session. | | | |
| | | | | Contact | The node cannot interpret or negotiate contact |
| Contact | 0x03 | The node cannot interpret or negotiate | | Failure | header option. |
| Failure | | contact header option. | | | |
| | | | | TLS failure | The node failed to negotiate TLS session and |
| TLS failure | 0x04 | The node failed to negotiate TLS session | | | cannot continue the session. |
| | | and cannot continue the session. | | | |
| | | | | Resource | The node has run into some resoure limit and |
| Resource | 0x05 | The node has run into some resoure limit | | Exhaustion | cannot continue the session. |
| Exhaustion | | and cannot continue the session. | +---------------+---------------------------------------------------+
+--------------+------+---------------------------------------------+
Table 5: SHUTDOWN Reason Codes Table 8: SHUTDOWN Reason Codes
It is also possible to convey a requested reconnection delay to It is also possible to convey a requested reconnection delay to
indicate how long the other node MUST wait before attempting session indicate how long the other node MUST wait before attempting session
re-establishment. To do so, the node sets the 'D' bit in the message re-establishment. To do so, the node sets the 'D' bit in the message
header flags and then transmits an 16-bit unsigned integer specifying flags and then transmits an 16-bit unsigned integer specifying the
the requested delay, in seconds, following the message header (and requested delay, in seconds, following the message header (and
optionally, the SHUTDOWN reason code). The value 0 SHALL be optionally, the SHUTDOWN reason code). The value 0 SHALL be
interpreted as an infinite delay, i.e., that the connecting node MUST interpreted as an infinite delay, i.e., that the connecting node MUST
NOT re-establish the session. In contrast, if the node does not wish NOT re-establish the session. In contrast, if the node does not wish
to request a delay, it SHOULD omit the reconnection delay field (and to request a delay, it SHOULD omit the reconnection delay field (and
set the 'D' bit to zero). set the 'D' bit to zero).
A session shutdown MAY occur immediately after TCP connection A session shutdown MAY occur immediately after TCP connection
establishment or reception of a contact header (and prior to any establishment or reception of a contact header (and prior to any
further data exchange). This MAY, for example, be used to notify further data exchange). This MAY, for example, be used to notify
that the node is currently not able or willing to communicate. that the node is currently not able or willing to communicate.
skipping to change at page 23, line 32 skipping to change at page 27, line 44
The protocol includes a provision for clean shutdown of idle The protocol includes a provision for clean shutdown of idle
sessions. Determining the length of time to wait before closing idle sessions. Determining the length of time to wait before closing idle
sessions, if they are to be closed at all, is an implementation and sessions, if they are to be closed at all, is an implementation and
configuration matter. configuration matter.
If there is a configured time to close idle links and if no bundle If there is a configured time to close idle links and if no bundle
data (other than KEEPALIVE messages) has been received for at least data (other than KEEPALIVE messages) has been received for at least
that amount of time, then either node MAY terminate the session by that amount of time, then either node MAY terminate the session by
transmitting a SHUTDOWN message indicating the reason code of 'Idle transmitting a SHUTDOWN message indicating the reason code of 'Idle
timeout' (as described in Table 5). After receiving a SHUTDOWN timeout' (as described in Table 8). After receiving a SHUTDOWN
message in response, both sides MAY close the TCP connection. message in response, both sides MAY close the TCP connection.
7. Security Considerations 7. Security Considerations
One security consideration for this protocol relates to the fact that One security consideration for this protocol relates to the fact that
nodes present their endpoint identifier as part of the contact header nodes present their endpoint identifier as part of the contact header
exchange. It would be possible for a node to fake this value and exchange. It would be possible for a node to fake this value and
present the identity of a singleton endpoint in which the node is not present the identity of a singleton endpoint in which the node is not
a member, essentially masquerading as another DTN node. If this a member, essentially masquerading as another DTN node. If this
identifier is used outside of a TLS-secured session or without identifier is used outside of a TLS-secured session or without
further verification as a means to determine which bundles are further verification as a means to determine which bundles are
transmitted over the session, then the node that has falsified its transmitted over the session, then the node that has falsified its
identity would be able to obtain bundles that it otherwise would not identity would be able to obtain bundles that it otherwise would not
have. Therefore, a node SHALL NOT use the EID value of an unsecured have. Therefore, a node SHALL NOT use the EID value of an unsecured
contact header to derive a peer node's identity unless it can contact header to derive a peer node's identity unless it can
corroborate it via other means. When TCPCL session security is corroborate it via other means. When TCPCL session security is
mandatory, an endpoint SHALL transmit initial unsecured contact mandatory, an endpoint SHALL transmit initial unsecured contact
header values indicated in Table 6 in order. These values avoid header values indicated in Table 9 in order. These values avoid
unnecessarily leaking endpoing parameters and will be ignored when unnecessarily leaking endpoing parameters and will be ignored when
secure contact header re-exchange occurs. secure contact header re-exchange occurs.
+--------------------+---------------------------------------------+ +--------------------+---------------------------------------------+
| Parameter | Value | | Parameter | Value |
+--------------------+---------------------------------------------+ +--------------------+---------------------------------------------+
| Flags | The USE_TLS flag is set. | | Flags | The USE_TLS flag is set. |
| | | | | |
| Keepalive Interval | Zero, indicating no keepalive. | | Keepalive Interval | Zero, indicating no keepalive. |
| | | | | |
| Segment MRU | Zero, indicating all segments are refused. | | Segment MRU | Zero, indicating all segments are refused. |
| | | | | |
| Transfer MRU | Zero, indicating all transfers are refused. | | Transfer MRU | Zero, indicating all transfers are refused. |
| | | | | |
| EID | Empty, indating lack of EID. | | EID | Empty, indating lack of EID. |
+--------------------+---------------------------------------------+ +--------------------+---------------------------------------------+
Table 6: Recommended Unsecured Contact Header Table 9: 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 mechanisms defined in [RFC6257] and
[I-D.ietf-dtn-bpsec] are to be used instead. [I-D.ietf-dtn-bpsec] are to be used instead.
Even when using TLS to secure the TCPCL session, the actual Even when using TLS to secure the TCPCL session, the actual
ciphersuite negotiated between the TLS peers MAY be insecure. TLS ciphersuite negotiated between the TLS peers MAY be insecure. TLS
can be used to perform authentication without data confidentiality, can be used to perform authentication without data confidentiality,
for example. It is up to security policies within each TCPCL node to for example. It is up to security policies within each TCPCL node to
ensure that the negotiated TLS ciphersuite meets transport security ensure that the negotiated TLS ciphersuite meets transport security
requirements. This is identical behavior to STARTTLS use in requirements. This is identical behavior to STARTTLS use in
[RFC2595]. [RFC2595].
Another consideration for this protocol relates to denial-of-service Another consideration for this protocol relates to denial-of-service
attacks. A node MAY send a large amount of data over a TCPCL attacks. A node MAY send a large amount of data over a TCPCL
session, requiring the receiving node to handle the data, attempt to session, requiring the receiving node to handle the data, attempt to
stop the flood of data by sending a REFUSE_BUNDLE message, or stop the flood of data by sending a XFER_REFUSE message, or forcibly
forcibly terminate the session. This burden could cause denial of terminate the session. This burden could cause denial of service on
service on other, well-behaving sessions. There is also nothing to other, well-behaving sessions. There is also nothing to prevent a
prevent a malicious node from continually establishing sessions and malicious node from continually establishing sessions and repeatedly
repeatedly trying to send copious amounts of bundle data. A trying to send copious amounts of bundle data. A listening node MAY
listening node MAY take countermeasures such as ignoring TCP SYN take countermeasures such as ignoring TCP SYN messages, closing TCP
messages, closing TCP connections as soon as they are established, connections as soon as they are established, waiting before sending
waiting before sending the contact header, sending a SHUTDOWN message the contact header, sending a SHUTDOWN message quickly or with a
quickly or with a delay, etc. delay, etc.
8. IANA Considerations 8. IANA Considerations
In this section, registration procedures are as defined in [RFC5226] In this section, registration procedures are as defined in [RFC5226].
Some of the registries below are created new for TCPCLv4 but share
code values with TCPCLv3. This was done to disambiguate the use of
these values between TCPCLv3 and TCPCLv4 while preserving the
semantics of some values.
8.1. Port Number 8.1. 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. by protocol version 4. Each TCPCL endpoint identifies its TCPCL
protocol version in its initial contact (see Section 8.2), so there
is no ambiguity about what protocol is being used.
+------------------------+-------------------------------------+ +------------------------+-------------------------------------+
| Parameter | Value | | Parameter | Value |
+------------------------+-------------------------------------+ +------------------------+-------------------------------------+
| Service Name: | dtn-bundle | | Service Name: | dtn-bundle |
| | | | | |
| Transport Protocol(s): | TCP | | Transport Protocol(s): | TCP |
| | | | | |
| Assignee: | Simon Perreault <simon@per.reau.lt> | | Assignee: | Simon Perreault <simon@per.reau.lt> |
| | | | | |
skipping to change at page 26, line 5 skipping to change at page 30, line 23
| | | | | | | |
| 2 | Reserved | [RFC7242] | | 2 | Reserved | [RFC7242] |
| | | | | | | |
| 3 | TCPCL | [RFC7242] | | 3 | TCPCL | [RFC7242] |
| | | | | | | |
| 4 | TCPCLbis | This specification. | | 4 | TCPCLbis | This specification. |
| | | | | | | |
| 5-255 | Unassigned | | 5-255 | Unassigned |
+-------+-------------+---------------------+ +-------+-------------+---------------------+
8.3. Message Types 8.3. Header Extension Types
IANA has created, under the "Bundle Protocol" registry, a sub- EDITOR NOTE: sub-registry to-be-created upon publication of this
registry titled "Bundle Protocol TCP Convergence-Layer Message Types" specification.
and initialized it with the contents below. The registration
procedure is RFC Required.
+----------+---------------+ IANA will create, under the "Bundle Protocol" registry, a sub-
| Code | Message Type | registry titled "Bundle Protocol TCP Convergence-Layer Version 4
+----------+---------------+ Header Extension Types" and initialized it with the contents of
| 0x0 | Reserved | Table 10. The registration procedure is RFC Required within the
| | | lower range 0x0001--0x3fff. Values in the range 0x8000--0xffff are
| 0x1 | DATA_SEGMENT | resrved for use on private networks for functions not published to
| | | the IANA.
| 0x2 | ACK_SEGMENT |
| | |
| 0x3 | REFUSE_BUNDLE |
| | |
| 0x4 | KEEPALIVE |
| | |
| 0x5 | SHUTDOWN |
| | |
| 0x6 | LENGTH |
| | |
| TBD | REJECT |
| | |
| TBD--0xf | Unassigned |
+----------+---------------+
Message Type Codes +----------------+--------------------------+
| Code | Message Type |
+----------------+--------------------------+
| 0x0000 | Reserved |
| | |
| 0x0001--0x3fff | Unassigned |
| | |
| 0x8000--0xffff | Private/Experimental Use |
+----------------+--------------------------+
8.4. REFUSE_BUNDLE Reason Codes Table 10: Header Extension Type Codes
IANA has created, under the "Bundle Protocol" registry, a sub- 8.4. Message Types
registry titled "Bundle Protocol TCP Convergence-Layer REFUSE_BUNDLE
Reason Codes" and initialized it with the contents of Table 3. The EDITOR NOTE: sub-registry to-be-created upon publication of this
specification.
IANA will create, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer Version 4
Message Types" and initialized it with the contents of Table 11. The
registration procedure is RFC Required. registration procedure is RFC Required.
+-----------+--------------+
| Code | Message Type |
+-----------+--------------+
| 0x00 | Reserved |
| | |
| 0x01 | XFER_SEGMENT |
| | |
| 0x02 | XFER_ACK |
| | |
| 0x03 | XFER_REFUSE |
| | |
| 0x04 | KEEPALIVE |
| | |
| 0x05 | SHUTDOWN |
| | |
| 0x06 | XFER_INIT |
| | |
| 0x07 | MSG_REJECT |
| | |
| 0x08--0xf | Unassigned |
+-----------+--------------+
Table 11: Message Type Codes
8.5. XFER_REFUSE Reason Codes
EDITOR NOTE: sub-registry to-be-created upon publication of this
specification.
IANA will create, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer Version 4
XFER_REFUSE Reason Codes" and initialized it with the contents of
Table 12. The registration procedure is RFC Required.
+----------+---------------------------+ +----------+---------------------------+
| Code | Refusal Reason | | Code | Refusal Reason |
+----------+---------------------------+ +----------+---------------------------+
| 0x0 | Unknown | | 0x0 | Unknown |
| | | | | |
| 0x1 | Completed | | 0x1 | Completed |
| | | | | |
| 0x2 | No Resources | | 0x2 | No Resources |
| | | | | |
| 0x3 | Retransmit | | 0x3 | Retransmit |
| | | | | |
| 0x4--0x7 | Unassigned | | 0x4--0x7 | Unassigned |
| | | | | |
| 0x8--0xf | Reserved for future usage | | 0x8--0xf | Reserved for future usage |
+----------+---------------------------+ +----------+---------------------------+
REFUSE_BUNDLE Reason Codes Table 12: XFER_REFUSE Reason Codes
8.5. SHUTDOWN Reason Codes 8.6. SHUTDOWN Reason Codes
IANA has created, under the "Bundle Protocol" registry, a sub- EDITOR NOTE: sub-registry to-be-created upon publication of this
registry titled "Bundle Protocol TCP Convergence-Layer SHUTDOWN specification.
Reason Codes" and initialized it with the contents of Table 4. The
registration procedure is RFC Required.
+-----------+------------------+ IANA will create, under the "Bundle Protocol" registry, a sub-
| Code | Shutdown Reason | registry titled "Bundle Protocol TCP Convergence-Layer Version 4
+-----------+------------------+ SHUTDOWN Reason Codes" and initialized it with the contents of
| 0x00 | Idle timeout | Table 13. The registration procedure is RFC Required.
| | |
| 0x01 | Version mismatch |
| | |
| 0x02 | Busy |
| | |
| TBD | Contact Failure |
| | |
| TBD | TLS failure |
| | |
| TBD--0xFF | Unassigned |
+-----------+------------------+
SHUTDOWN Reason Codes +------------+------------------+
| Code | Shutdown Reason |
+------------+------------------+
| 0x00 | Idle timeout |
| | |
| 0x01 | Version mismatch |
| | |
| 0x02 | Busy |
| | |
| 0x03 | Contact Failure |
| | |
| 0x04 | TLS failure |
| | |
| 0x05--0xFF | Unassigned |
+------------+------------------+
8.6. REJECT Reason Codes Table 13: SHUTDOWN Reason Codes
8.7. 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 REJECT Reason registry titled "Bundle Protocol TCP Convergence-Layer Version 4
Codes" and initialized it with the contents of Table 4. The MSG_REJECT Reason Codes" and initialized it with the contents of
registration procedure is RFC Required. Table 14. The registration procedure is RFC Required.
+-----------+----------------------+ +-----------+----------------------+
| Code | Rejection Reason | | Code | Rejection Reason |
+-----------+----------------------+ +-----------+----------------------+
| 0x00 | reserved | | 0x00 | reserved |
| | | | | |
| 0x01 | Message Type Unknown | | 0x01 | Message Type Unknown |
| | | | | |
| 0x02 | Message Unsupported | | 0x02 | Message Unsupported |
| | | | | |
| 0x03 | Message Unexpected | | 0x03 | Message Unexpected |
| | | | | |
| 0x04-0xFF | Unassigned | | 0x04-0xFF | Unassigned |
+-----------+----------------------+ +-----------+----------------------+
REJECT Reason Codes Table 14: REJECT Reason Codes
9. Acknowledgments 9. Acknowledgments
This memo is based on comments on implementation of [RFC7242] This memo is based on comments on implementation of [RFC7242]
provided from Scott Burleigh. provided from Scott Burleigh.
10. References 10. References
10.1. Normative References 10.1. Normative References
skipping to change at page 29, line 41 skipping to change at page 34, line 46
DOI 10.17487/RFC6257, May 2011, DOI 10.17487/RFC6257, May 2011,
<http://www.rfc-editor.org/info/rfc6257>. <http://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,
<http://www.rfc-editor.org/info/rfc7242>. <http://www.rfc-editor.org/info/rfc7242>.
[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-03 (work in Specification", draft-ietf-dtn-bpsec-04 (work in
progress), October 2016. progress), March 2017.
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
messages are: headers and messages are:
o Changed contact header content to limit number of negotiated o Changed contact header content to limit number of negotiated
options. options.
o Added contact option to negotiate maximum segment size (per each o Added contact option to negotiate maximum segment size (per each
direction). direction).
o Added contact header extension capability.
o Defined new IANA registries for message / type / reason codes to
allow renaming some codes for clarity.
o Expanded Message Header to octet-aligned fields instead of bit-
packing.
o Added a bundle transfer identification number to all bundle- o Added a bundle transfer identification number to all bundle-
related messages (LENGTH, DATA_SEGMENT, ACK_SEGMENT, related messages (XFER_INIT, XFER_SEGMENT, XFER_ACK, XFER_REFUSE).
REFUSE_BUNDLE).
o Use flags in ACK_SEGMENT to mirror flags from DATA_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.
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 negotation failure SHUTDOWN reason code. o Added contact negotation failure SHUTDOWN reason code.
o Added REJECT message to indicate an unknown or unhandled message o Added MSG_REJECT message to indicate an unknown or unhandled
was received. message was received.
o Added TLS session security mechanism. o Added TLS session security mechanism.
o Added TLS failure SHUTDOWN reason code. o Added TLS failure SHUTDOWN reason code.
Authors' Addresses Authors' Addresses
Brian Sipos Brian Sipos
RKF Engineering Solutions, LLC RKF Engineering Solutions, LLC
1229 19th Street NW 7500 Old Georgetown Road
Wasington, DC 20036 Suite 1275
Bethesda, MD 20814-6198
US US
Email: BSipos@rkf-eng.com Email: BSipos@rkf-eng.com
Michael Demmer Michael Demmer
University of California, Berkeley University of California, Berkeley
Computer Science Division Computer Science Division
445 Soda Hall 445 Soda Hall
Berkeley, CA 94720-1776 Berkeley, CA 94720-1776
US US
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