Delay Tolerant Networking B. Sipos
Internet-Draft RKF Engineering
Obsoletes: 7242 (if approved) M. Demmer
Intended status: Standards Track UC Berkeley
Expires: October 2, 2019 J. Ott
Aalto University
S. Perreault
March 31, 2019
Delay-Tolerant Networking TCP Convergence Layer Protocol Version 4
draft-ietf-dtn-tcpclv4-12
Abstract
This document describes a revised protocol for the TCP-based
convergence layer (TCPCL) for Delay-Tolerant Networking (DTN). The
protocol revision is based on implementation issues in the original
TCPCL Version 3 of RFC7242 and updates to the Bundle Protocol
contents, encodings, and convergence layer requirements in Bundle
Protocol Version 7. Specifically, the TCPCLv4 uses CBOR-encoded BPv7
bundles as its service data unit being transported and provides a
reliable transport of such bundles. 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
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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and may be updated, replaced, or obsoleted by other documents at any
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This Internet-Draft will expire on October 2, 2019.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Convergence Layer Services . . . . . . . . . . . . . . . 4
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 6
2.1. Definitions Specific to the TCPCL Protocol . . . . . . . 6
3. General Protocol Description . . . . . . . . . . . . . . . . 9
3.1. TCPCL Session Overview . . . . . . . . . . . . . . . . . 9
3.2. TCPCL States and Transitions . . . . . . . . . . . . . . 11
3.3. Transfer Segmentation Policies . . . . . . . . . . . . . 16
3.4. Example Message Exchange . . . . . . . . . . . . . . . . 17
4. Session Establishment . . . . . . . . . . . . . . . . . . . . 19
4.1. TCP Connection . . . . . . . . . . . . . . . . . . . . . 19
4.2. Contact Header . . . . . . . . . . . . . . . . . . . . . 19
4.3. Contact Validation and Negotiation . . . . . . . . . . . 20
4.4. Session Security . . . . . . . . . . . . . . . . . . . . 21
4.4.1. TLS Handshake Result . . . . . . . . . . . . . . . . 22
4.4.2. Example TLS Initiation . . . . . . . . . . . . . . . 22
4.5. Message Type Codes . . . . . . . . . . . . . . . . . . . 23
4.6. Session Initialization Message (SESS_INIT) . . . . . . . 24
4.7. Session Parameter Negotiation . . . . . . . . . . . . . . 26
4.8. Session Extension Items . . . . . . . . . . . . . . . . . 27
5. Established Session Operation . . . . . . . . . . . . . . . . 28
5.1. Upkeep and Status Messages . . . . . . . . . . . . . . . 28
5.1.1. Session Upkeep (KEEPALIVE) . . . . . . . . . . . . . 28
5.1.2. Message Rejection (MSG_REJECT) . . . . . . . . . . . 29
5.2. Bundle Transfer . . . . . . . . . . . . . . . . . . . . . 30
5.2.1. Bundle Transfer ID . . . . . . . . . . . . . . . . . 30
5.2.2. Data Transmission (XFER_SEGMENT) . . . . . . . . . . 31
5.2.3. Data Acknowledgments (XFER_ACK) . . . . . . . . . . . 33
5.2.4. Transfer Refusal (XFER_REFUSE) . . . . . . . . . . . 34
5.2.5. Transfer Extension Items . . . . . . . . . . . . . . 36
6. Session Termination . . . . . . . . . . . . . . . . . . . . . 38
6.1. Session Termination Message (SESS_TERM) . . . . . . . . . 38
6.2. Idle Session Shutdown . . . . . . . . . . . . . . . . . . 40
7. Implementation Status . . . . . . . . . . . . . . . . . . . . 40
8. Security Considerations . . . . . . . . . . . . . . . . . . . 41
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 42
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9.1. Port Number . . . . . . . . . . . . . . . . . . . . . . . 42
9.2. Protocol Versions . . . . . . . . . . . . . . . . . . . . 43
9.3. Session Extension Types . . . . . . . . . . . . . . . . . 43
9.4. Transfer Extension Types . . . . . . . . . . . . . . . . 44
9.5. Message Types . . . . . . . . . . . . . . . . . . . . . . 45
9.6. XFER_REFUSE Reason Codes . . . . . . . . . . . . . . . . 45
9.7. SESS_TERM Reason Codes . . . . . . . . . . . . . . . . . 46
9.8. MSG_REJECT Reason Codes . . . . . . . . . . . . . . . . . 47
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 48
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 48
11.1. Normative References . . . . . . . . . . . . . . . . . . 48
11.2. Informative References . . . . . . . . . . . . . . . . . 49
Appendix A. Significant changes from RFC7242 . . . . . . . . . . 49
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 50
1. Introduction
This document describes the TCP-based convergence-layer protocol for
Delay-Tolerant Networking. Delay-Tolerant Networking is an end-to-
end architecture providing communications in and/or through highly
stressed environments, including those with intermittent
connectivity, long and/or variable delays, and high bit error rates.
More detailed descriptions of the rationale and capabilities of these
networks can be found in "Delay-Tolerant Network Architecture"
[RFC4838].
An important goal of the DTN architecture is to accommodate a wide
range of networking technologies and environments. The protocol used
for DTN communications is the Bundle Protocol Version 7 (BPv7)
[I-D.ietf-dtn-bpbis], an application-layer protocol that is used to
construct a store-and-forward overlay network. BPv7 requires the
services of a "convergence-layer adapter" (CLA) to send and receive
bundles using the service of some "native" link, network, or Internet
protocol. This document describes one such convergence-layer adapter
that uses the well-known Transmission Control Protocol (TCP). This
convergence layer is referred to as TCP Convergence Layer Version 4
(TCPCLv4). For the remainder of this document, the abbreviation "BP"
without the version suffix refers to BPv7. For the remainder of this
document, the abbreviation "TCPCL" without the version suffix refers
to TCPCLv4.
The locations of the TCPCL and the BP in the Internet model protocol
stack (described in [RFC1122]) are shown in Figure 1. In particular,
when BP is using TCP as its bearer with TCPCL as its convergence
layer, both BP and TCPCL reside at the application layer of the
Internet model.
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+-------------------------+
| DTN Application | -\
+-------------------------| |
| Bundle Protocol (BP) | -> Application Layer
+-------------------------+ |
| TCP Conv. Layer (TCPCL) | |
+-------------------------+ |
| TLS (optional) | -/
+-------------------------+
| TCP | ---> Transport Layer
+-------------------------+
| IPv4/IPv6 | ---> Network Layer
+-------------------------+
| Link-Layer Protocol | ---> Link Layer
+-------------------------+
Figure 1: The Locations of the Bundle Protocol and the TCP
Convergence-Layer Protocol above the Internet Protocol Stack
This document describes the format of the protocol data units passed
between entities participating in TCPCL communications. This
document does not address:
o The format of protocol data units of the Bundle Protocol, as those
are defined elsewhere in [RFC5050] and [I-D.ietf-dtn-bpbis]. This
includes the concept of bundle fragmentation or bundle
encapsulation. The TCPCL transfers bundles as opaque data blocks.
o Mechanisms for locating or identifying other bundle entities
within an internet.
1.1. Convergence Layer Services
This version of the TCPCL provides the following services to support
the overlaying Bundle Protocol agent. In all cases, this is not an
API defintion but a logical description of how the CL may interact
with the BP agent. Each of these interactions may be associated with
any number of additional metadata items as necessary to support the
operation of the CL or BP agent.
Attempt Session The TCPCL allows a BP agent to pre-emptively attempt
to establish a TCPCL session with a peer entity. Each session
attempt can send a different set of session negotiation parameters
as directed by the BP agent.
Terminate Session The TCPCL allows a BP agent to pre-emptively
terminate an established TCPCL session with a peer entity. The
terminate request is on a per-session basis.
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Session State Changed The TCPCL supports indication when the session
state changes. The top-level session states indicated are:
Contact Negotating: A TCP connection has been made (as either
active or passive entity) and contact negotiation has begun.
Session Negotiating: Contact negotation has been completed
(including possible TLS use) and session negotiation has begun.
Established: The session has been fully established and is ready
for its first transfer.
Closing: The entity received a SESS_TERM message and is in the
closing state.
Terminated: The session has finished normal termination
sequencing..
Failed: The session ended without normal termination sequencing.
Session Idle Changed The TCPCL supports indication when the live/
idle sub-state changes. This occurs only when the top-level
session state is Established. Because TCPCL transmits serially
over a TCP connection, it suffers from "head of queue blocking"
this indication provides information about when a session is
available for immediate transfer start.
Begin Transmission The principal purpose of the TCPCL is to allow a
BP agent to transmit bundle data over an established TCPCL
session. Transmission request is on a per-session basis, the CL
does not necessarily perform any per-session or inter-session
queueing. Any queueing of transmissions is the obligation of the
BP agent.
Transmission Success The TCPCL supports positive indication when a
bundle has been fully transferred to a peer entity.
Transmission Intermediate Progress The TCPCL supports positive
indication of intermediate progress of transferr to a peer entity.
This intermediate progress is at the granularity of each
transferred segment.
Transmission Failure The TCPCL supports positive indication of
certain reasons for bundle transmission failure, notably when the
peer entity rejects the bundle or when a TCPCL session ends before
transferr success. The TCPCL itself does not have a notion of
transfer timeout.
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Reception Initialized The TCPCL supports indication to the reciver
just before any transmssion data is sent. This corresponds to
reception of the XFER_SEGMENT message with the START flag set.
Interrupt Reception The TCPCL allows a BP agent to interrupt an
individual transfer before it has fully completed (successfully or
not). Interruption can occur any time after the reception is
initialized.
Reception Success The TCPCL supports positive indication when a
bundle has been fully transferred from a peer entity.
Reception Intermediate Progress The TCPCL supports positive
indication of intermediate progress of transfer from the peer
entity. This intermediate progress is at the granularity of each
transferred segment. Intermediate reception indication allows a
BP agent the chance to inspect bundle header contents before the
entire bundle is available, and thus supports the "Reception
Interruption" capability.
Reception Failure The TCPCL supports positive indication of certain
reasons for reception failure, notably when the local entity
rejects an attempted transfer for some local policy reason or when
a TCPCL session ends before transfer success. The TCPCL itself
does not have a notion of transfer timeout.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2.1. Definitions Specific to the TCPCL Protocol
This section contains definitions specific to the TCPCL protocol.
TCPCL Entity: This is the notional TCPCL application that initiates
TCPCL sessions. This design, implementation, configuration, and
specific behavior of such an entity is outside of the scope of
this document. However, the concept of an entity has utility
within the scope of this document as the container and initiator
of TCPCL sessions. The relationship between a TCPCL entity and
TCPCL sessions is defined as follows:
A TCPCL Entity MAY actively initiate any number of TCPCL
Sessions and should do so whenever the entity is the initial
transmitter of information to another entity in the network.
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A TCPCL Entity MAY support zero or more passive listening
elements that listen for connection requests from other TCPCL
Entities operating on other entitys in the network.
A TCPCL Entity MAY passivley initiate any number of TCPCL
Sessions from requests received by its passive listening
element(s) if the entity uses such elements.
These relationships are illustrated in Figure 2. For most TCPCL
behavior within a session, the two entities are symmetric and
there is no protocol distinction between them. Some specific
behavior, particularly during session establishment, distinguishes
between the active entity and the passive entity. For the
remainder of this document, the term "entity" without the prefix
"TCPCL" refers to a TCPCL entity.
TCP Connection: The term Connection in this specification
exclusively refers to a TCP connection and any and all behaviors,
sessions, and other states association with that TCP connection.
TCPCL Session: A TCPCL session (as opposed to a TCP connection) is a
TCPCL communication relationship between two TCPCL entities.
Within a single TCPCL session there are two possible transfer
streams; one in each direction, with one stream from each entity
being the outbound stream and the other being the inbound stream.
The lifetime of a TCPCL session is bound to the lifetime of an
underlying TCP connection. A TCPCL session is terminated when the
TCP connection ends, due either to one or both entities actively
terminating the TCP connection or due to network errors causing a
failure of the TCP connection. For the remainder of this
document, the term "session" without the prefix "TCPCL" refers to
a TCPCL session.
Session parameters: These are a set of values used to affect the
operation of the TCPCL for a given session. The manner in which
these parameters are conveyed to the bundle entity and thereby to
the TCPCL is implementation dependent. However, the mechanism by
which two entities exchange and negotiate the values to be used
for a given session is described in Section 4.3.
Transfer Stream: A Transfer stream is a uni-directional user-data
path within a TCPCL Session. Messages sent over a transfer stream
are serialized, meaning that one set of user data must complete
its transmission prior to another set of user data being
transmitted over the same transfer stream. Each uni-directional
stream has a single sender entity and a single receiver entity.
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Transfer: This refers to the procedures and mechanisms for
conveyance of an individual bundle from one node to another. Each
transfer within TCPCL is identified by a Transfer ID number which
is unique only to a single direction within a single Session.
Transfer Segment: A subset of a transfer of user data being
communicated over a trasnfer stream.
Idle Session: A TCPCL session is idle while the only messages being
transmitted or received are KEEPALIVE messages.
Live Session: A TCPCL session is live while any messages are being
transmitted or received.
Reason Codes: The TCPCL uses numeric codes to encode specific
reasons for individual failure/error message types.
The relationship between connections, sessions, and streams is shown
in Figure 3.
+--------------------------------------------+
| TCPCL Entity |
| | +----------------+
| +--------------------------------+ | | |-+
| | Actively Inititated Session #1 +------------->| Other | |
| +--------------------------------+ | | TCPCL Entity's | |
| ... | | Passive | |
| +--------------------------------+ | | Listener | |
| | Actively Inititated Session #n +------------->| | |
| +--------------------------------+ | +----------------+ |
| | +-----------------+
| +---------------------------+ |
| +---| +---------------------------+ | +----------------+
| | | | Optional Passive | | | |-+
| | +-| Listener(s) +<-------------+ | |
| | +---------------------------+ | | | |
| | | | Other | |
| | +---------------------------------+ | | TCPCL Entity's | |
| +--->| Passively Inititated Session #1 +-------->| Active | |
| | +---------------------------------+ | | Initiator(s) | |
| | | | | |
| | +---------------------------------+ | | | |
| +--->| Passively Inititated Session #n +-------->| | |
| +---------------------------------+ | +----------------+ |
| | +-----------------+
+--------------------------------------------+
Figure 2: The relationships between TCPCL entities
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+----------------------------+ +--------------------------+
| TCPCL Session | | TCPCL "Other" Session |
| | | |
| +-----------------------+ | | +---------------------+ |
| | TCP Connection | | | | TCP Connection | |
| | | | | | | |
| | +-------------------+ | | | | +-----------------+ | |
| | | Optional Inbound | | | | | | Peer Outbound | | |
| | | Transfer Stream |<-[Seg]--[Seg]--[Seg]-| | Transfer Stream | | |
| | | ----- | | | | | | ----- | | |
| | | RECEIVER | | | | | | SENDER | | |
| | +-------------------+ | | | | +-----------------+ | |
| | | | | | | |
| | +-------------------+ | | | | +-----------------+ | |
| | | Optional Outbound | | | | | | Peer Inbound | | |
| | | Transfer Stream |------[Seg]---[Seg]---->| Transfer Stream | | |
| | | ----- | | | | | | ----- | | |
| | | SENDER | | | | | | RECEIVER | | |
| | +-------------------+ | | | | +-----------------+ | |
| +-----------------------+ | | +---------------------+ |
+----------------------------+ +--------------------------+
Figure 3: The relationship within a TCPCL Session of its two streams
3. General Protocol Description
The service of this protocol is the transmission of DTN bundles via
the Transmission Control Protocol (TCP). This document specifies the
encapsulation of bundles, procedures for TCP setup and teardown, and
a set of messages and node requirements. The general operation of
the protocol is as follows.
3.1. TCPCL Session Overview
First, one node establishes a TCPCL session to the other by
initiating a TCP connection in accordance with [RFC0793]. After
setup of the TCP connection is complete, an initial contact header is
exchanged in both directions to establish a shared TCPCL version and
possibly initiate TLS security. Once contact negotiation is
complete, TCPCL messaging is available and the session negotiation is
used to set parameters of the TCPCL session. One of these parameters
is a singleton endpoint identifier for each node (not the singleton
Endpoint Identifier (EID) of any application running on the node) to
denote the bundle-layer identity of each DTN node. This is used to
assist in routing and forwarding messages (e.g. to prevent loops).
Once negotiated, the parameters of a TCPCL session cannot change and
if there is a desire by either peer to transfer data under different
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parameters then a new session must be established. This makes CL
logic simpler but relies on the assumption that establishing a TCP
connection is lightweight enough that TCP connection overhead is
negligable compared to TCPCL data sizes.
Once the TCPCL session is established and configured in this way,
bundles can be transferred in either direction. Each transfer is
performed by an sequence of logical segments of data within
XFER_SEGMENT messages. Multiple bundles can be transmitted
consecutively in a single direction on a single TCPCL connection.
Segments from different bundles are never interleaved. Bundle
interleaving can be accomplished by fragmentation at the BP layer or
by establishing multiple TCPCL sessions between the same peers.
A feature of this protocol is for the receiving node to send
acknowledgment (XFER_ACK) messages as bundle data segments arrive.
The rationale behind these acknowledgments is to enable the sender
node to determine how much of the bundle has been received, so that
in case the session is interrupted, it can perform reactive
fragmentation to avoid re-sending the already transmitted part of the
bundle. In addition, there is no explicit flow control on the TCPCL
layer.
A TCPCL receiver can interrupt the transmission of a bundle at any
point in time by replying with a XFER_REFUSE message, which causes
the sender to stop transmission of the associated bundle (if it
hasn't already finished transmission) Note: This enables a cross-
layer optimization in that it allows a receiver that detects that it
already has received a certain bundle to interrupt transmission as
early as possible and thus save transmission capacity for other
bundles.
For sessions that are idle, a KEEPALIVE message is sent at a
negotiated interval. This is used to convey node live-ness
information during otherwise message-less time intervals.
A SESS_TERM message is used to start the closing of a TCPCL session
(see Section 6.1). During shutdown sequencing, in-progress transfers
can be completed but no new transfers can be initiated. A SESS_TERM
message can also be used to refuse a session setup by a peer (see
Section 4.3). It is an implementation matter to determine whether or
not to close a TCPCL session while there are no transfers queued or
in-progress.
Once a session is established established, TCPCL is a symmetric
protocol between the peers. Both sides can start sending data
segments in a session, and one side's bundle transfer does not have
to complete before the other side can start sending data segments on
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its own. Hence, the protocol allows for a bi-directional mode of
communication. Note that in the case of concurrent bidirectional
transmission, acknowledgment segments MAY be interleaved with data
segments.
3.2. TCPCL States and Transitions
The states of a nominal TCPCL session (i.e. without session failures)
are indicated in Figure 4.
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+-------+
| START |
+-------+
|
TCP Establishment
|
V
+-----------+ +---------------------+
| TCP |----------->| Contact / Session |
| Connected | | Negotiation |
+-----------+ +---------------------+
|
+-----Session Parameters-----+
| Negotiated
V
+-------------+ +-------------+
| Established |----New Transfer---->| Established |
| Session | | Session |
| Idle |<---Transfers Done---| Live |
+-------------+ +-------------+
| |
+------------------------------------+
|
SESS_TERM Exchange
|
V
+-------------+
| Established | +-------------+
| Session |----Transfers------>| TCP |
| Ending | Done | Terminating |
+-------------+ +-------------+
|
+------------Close Message------------+
|
V
+-------+
| END |
+-------+
Figure 4: Top-level states of a TCPCL session
Notes on Established Session states:
Session "Live" means transmitting or reeiving over a transfer
stream.
Session "Idle" means no transmission/reception over a transfer
stream.
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Session "Closing" means no new transfers will be allowed.
The contact negotiation sequencing is performed either as the active
or passive peer, and is illustrated in Figure 5 and Figure 6
respectively which both share the data validation and analyze final
states of Figure 7.
+-------+
| START |-----TCP-----+
+-------+ Connecting |
V
+-----------+ +---------+
| Connected |--OK-->| Send CH |--OK-->[PCH]
+-----------+ +---------+
| |
Error Error
| |
V |
[TCPTERM]<-------------+
Figure 5: Contact Initiation as Active peer
+-------+
| START |-----TCP----->[PCH]
+-------+ Connected
Figure 6: Contact Initiation as Passive peer
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+-------->[TCPTERM]<----------+
| |
Timeout Error
or Error |
| |
+-------+ +---------+ Contact +----------+
| START |---->| Waiting |---- Header --->| Validate |
+-------+ +---------+ Received +----------+
|
+---------------------------+
|
V
+---------+
+--Error--| Analyze |---No TLS---->[SI]
| | | ^
| +---------+ |
| | |
V TLS |
[TCPTERM] Negotiated |
^ | |
| V |
| +-----------+ |
| | Establish |---Success---+
+--Error--| TLS |
+-----------+
Figure 7: Processing of Contact Header (PCH)
The session negotiation sequencing is performed either as the active
or passive peer, and is illustrated in Figure 8 and Figure 9
respectively which both share the data validation and analyze final
states of Figure 10.
+-------+ TCPCL
| START |--Messaging--+
+-------+ Available |
V
+----------------+
| Send SESS_INIT |--OK-->[PSI]
+----------------+
|
Error
|
V
[SESSTERM]
Figure 8: Session Initiation as Active peer
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+-------+ TCPCL
| START |---Messaging-->[PSI]
+-------+ Available
Figure 9: Session Initiation as Passive peer
+------->[SESSTERM]<--------+
| |
Timeout Error
or Error |
| |
+-------+ +---------+ +----------+
| START |---->| Waiting |---SESS_INIT--->| Validate |
+-------+ +---------+ Received +----------+
|
+---------------------------+
|
V
+---------+ +--------------+
+--Error--| Analyze |---->| Established |
| | | | Session Idle |
| +---------+ +--------------+
V
[SESSTERM]
Figure 10: Processing of Session Initiation (PSI)
Transfers can occur after a session is established and it's not in
the ending state. Each transfer occurs within a single logical
transfer stream between a sender and a receiver, as illustrated in
Figure 11 and Figure 12 respectively.
+--Send XFER_SEGMENT--+
+--------+ | |
| Stream | +-------------+ |
| Idle |---Send XFER_SEGMENT-->| In Progress |<------------+
+--------+ +-------------+
|
+---------All segments sent-------+
|
V
+---------+ +--------+
| Waiting |---- Receive Final---->| Stream |
| for Ack | XFER_ACK | IDLE |
+---------+ +--------+
Figure 11: Transfer sender states
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Notes on transfer sending:
Pipelining of transfers can occur when the sending entity begins a
new transfer while in the "Waiting for Ack" state.
+-Receive XFER_SEGMENT-+
+--------+ | Send XFER_ACK |
| Stream | +-------------+ |
| IDLE |--Receive XFER_SEGMENT-->| In Progress |<-------------+
+--------+ +-------------+
|
+--------Sent Final XFER_ACK--------+
|
V
+--------+
| Stream |
| IDLE |
+--------+
Figure 12: Transfer receiver states
3.3. Transfer Segmentation Policies
Each TCPCL session allows a negotiated transfer segmentation polcy to
be applied in each transfer direction. A receiving node can set the
Segment MRU in its contact header to determine the largest acceptable
segment size, and a transmitting node can segment a transfer into any
sizes smaller than the receiver's Segment MRU. It is a network
administration matter to determine an appropriate segmentation policy
for entities operating TCPCL, but guidance given here can be used to
steer policy toward performance goals. It is also advised to
consider the Segment MRU in relation to chunking/packetization
performed by TLS, TCP, and any intermediate network-layer nodes.
Minimum Overhead For a simple network expected to exchange
relatively small bundles, the Segment MRU can be set to be
identical to the Transfer MRU which indicates that all transfers
can be sent with a single data segment (i.e. no actual
segmentation). If the network is closed and all transmitters are
known to follow a single-segment transfer policy, then receivers
can avoid the necessity of segment reassembly. Because this CL
operates over a TCP stream, which suffers from a form of head-of-
queue blocking between messages, while one node is transmitting a
single XFER_SEGMENT message it is not able to transmit any
XFER_ACK or XFER_REFUSE for any associated received transfers.
Predictable Message Sizing In situations where the maximum message
size is desired to be well-controlled, the Segment MRU can be set
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to the largest acceptable size (the message size less XFER_SEGMENT
header size) and transmitters can always segment a transfer into
maximum-size chunks no larger than the Segment MRU. This
guarantees that any single XFER_SEGMENT will not monopolize the
TCP stream for too long, which would prevent outgoing XFER_ACK and
XFER_REFUSE associated with received transfers.
Dynamic Segmentation Even after negotiation of a Segment MRU for
each receiving node, the actual transfer segmentation only needs
to guarantee than any individual segment is no larger than that
MRU. In a situation where network "goodput" is dynamic, the
transfer segmentation size can also be dynamic in order to control
message transmission duration.
Many other policies can be established in a TCPCL network between
these two extremes. Different policies can be applied to each
direction to/from any particular node. Additionally, future header
and transfer extension types can apply further nuance to transfer
policies and policy negotiation.
3.4. Example Message Exchange
The following figure depicts the protocol exchange for a simple
session, showing the session establishment and the transmission of a
single bundle split into three data segments (of lengths "L1", "L2",
and "L3") from Entity A to Entity B.
Note that the sending node can transmit multiple XFER_SEGMENT
messages without waiting for the corresponding XFER_ACK responses.
This enables pipelining of messages on a transfer stream. Although
this example only demonstrates a single bundle transmission, it is
also possible to pipeline multiple XFER_SEGMENT messages for
different bundles without necessarily waiting for XFER_ACK messages
to be returned for each one. However, interleaving data segments
from different bundles is not allowed.
No errors or rejections are shown in this example.
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Entity A Entity B
======== ========
+-------------------------+
| Contact Header | -> +-------------------------+
+-------------------------+ <- | Contact Header |
+-------------------------+
+-------------------------+
| SESS_INIT | -> +-------------------------+
+-------------------------+ <- | SESS_INIT |
+-------------------------+
+-------------------------+
| XFER_SEGMENT (start) | ->
| Transfer ID [I1] |
| Length [L1] |
| Bundle Data 0..(L1-1) |
+-------------------------+
+-------------------------+ +-------------------------+
| XFER_SEGMENT | -> <- | XFER_ACK (start) |
| Transfer ID [I1] | | Transfer ID [I1] |
| Length [L2] | | Length [L1] |
|Bundle Data L1..(L1+L2-1)| +-------------------------+
+-------------------------+
+-------------------------+ +-------------------------+
| XFER_SEGMENT (end) | -> <- | XFER_ACK |
| Transfer ID [I1] | | Transfer ID [I1] |
| Length [L3] | | Length [L1+L2] |
|Bundle Data | +-------------------------+
| (L1+L2)..(L1+L2+L3-1)|
+-------------------------+
+-------------------------+
<- | XFER_ACK (end) |
| Transfer ID [I1] |
| Length [L1+L2+L3] |
+-------------------------+
+-------------------------+
| SESS_TERM | -> +-------------------------+
+-------------------------+ <- | SESS_TERM |
+-------------------------+
Figure 13: An example of the flow of protocol messages on a single
TCP Session between two entities
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4. Session Establishment
For bundle transmissions to occur using the TCPCL, a TCPCL session
MUST first be established between communicating entities. It is up
to the implementation to decide how and when session setup is
triggered. For example, some sessions MAY be opened proactively and
maintained 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 transmission and the routing algorithm selects a
certain next-hop node.
4.1. TCP Connection
To establish a TCPCL session, an entity MUST first establish a TCP
connection with the intended peer entity, typically by using the
services provided by the operating system. Destination port number
4556 has been assigned by IANA as the Registered Port number for the
TCP convergence layer. Other destination port numbers MAY be used
per local configuration. Determining a peer's destination port
number (if different from the registered TCPCL port number) 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 entity is unable to establish a TCP connection for any reason,
then it is an implementation matter to determine how to handle the
connection failure. An entity MAY decide to re-attempt to establish
the connection. If it does so, it MUST NOT overwhelm its target with
repeated connection attempts. Therefore, the entity MUST retry the
connection setup no earlier than some delay time from the last
attempt, and it SHOULD use a (binary) exponential backoff mechanism
to increase this delay in case of repeated failures.
Once a TCP connection is established, each entity MUST immediately
transmit a contact header over the TCP connection. The format of the
contact header is described in Section 4.2.
4.2. Contact Header
Once a TCP connection is established, both parties exchange a contact
header. This section describes the format of the contact header and
the meaning of its fields.
Upon receipt of the contact header, both entities perform the
validation and negotiation procedures defined in Section 4.3. After
receiving the contact header from the other entity, either entity MAY
refuse the session by sending a SESS_TERM message with an appropriate
reason code.
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The format for the Contact Header is as follows:
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| magic='dtn!' |
+---------------+---------------+---------------+---------------+
| Version | Flags |
+---------------+---------------+
Figure 14: Contact Header Format
See Section 4.3 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
0x64 0x74 0x6E 0x21, i.e., the text string "dtn!" in US-ASCII (and
UTF-8).
Version: A one-octet field value containing the value 4 (current
version of the protocol).
Flags: A one-octet field of single-bit flags, interpreted according
to the descriptions in Table 1.
+----------+--------+-----------------------------------------------+
| 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
4.3. Contact Validation and Negotiation
Upon reception of the contact header, each node follows the following
procedures to ensure the validity of the TCPCL session and to
negotiate values for the session parameters.
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
some protection against an inadvertent TCP connection by a different
protocol than the one described in this document. To prevent a flood
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of repeated connections from a misconfigured application, an entity
MAY elect to hold an invalid connection open and idle for some time
before closing it.
The first negotiation is on the TCPCL protocol version to use. The
active node always sends its Contact Header first and waits for a
response from the passive node. The active node can repeatedly
attempt different protocol versions in descending order until the
passive node accepts one with a corresponding Contact Header reply.
Only upon response of a Contact Header from the passive node is the
TCPCL protocol version established and parameter negotiation begun.
During contact initiation, the active TCPCL node SHALL send the
highest TCPCL protocol version on a first session attempt for a TCPCL
peer. If the active node receives a Contact Header with a different
protocol version than the one sent earlier on the TCP connection, the
TCP connection SHALL be terminated. If the active node receives a
SESS_TERM message with reason of "Version Mismatch", that node MAY
attempt further TCPCL sessions with the peer using earlier protocol
version numbers in decreasing order. Managing multi-TCPCL-session
state such as this is an implementation matter.
If the passive node receives a contact header containing a version
that is greater than the current version of the protocol that the
node implements, then the node SHALL shutdown the session with a
reason code of "Version mismatch". If the passive node receives a
contact header with a version that is lower than the version of the
protocol that the node implements, the node MAY either terminate the
session (with a reason code of "Version mismatch") or the node MAY
adapt its operation to conform to the older version of the protocol.
The decision of version fall-back is an implementation matter.
4.4. Session Security
This version of the TCPCL supports establishing a Transport Layer
Security (TLS) session within an existing TCP connection. When TLS
is used within the TCPCL it affects the entire session. Once
established, there is no mechanism available to downgrade a TCPCL
session to non-TLS operation. If this is desired, the entire TCPCL
session MUST be terminated and a new non-TLS-negotiated session
established.
The use of TLS is negotated using the Contact Header as described in
Section 4.3. After negotiating an Enable TLS parameter of true, and
before any other TCPCL messages are sent within the session, the
session entities SHALL begin a TLS handshake in accordance with
[RFC5246]. The parameters within each TLS negotiation are
implementation dependent but any TCPCL node SHALL follow all
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recommended practices of [BCP195], or any updates or successors that
become part of [BCP195]. By convention, this protocol uses the node
which initiated the underlying TCP connection as the "client" role of
the TLS handshake request.
The TLS handshake, if it occurs, is considered to be part of the
contact negotiation before the TCPCL session itself is established.
Specifics about sensitive data exposure are discussed in Section 8.
4.4.1. TLS Handshake Result
If a TLS handshake cannot negotiate a TLS session, both entities of
the TCPCL session SHALL terminate the TCP connection. At this point
the TCPCL session has not yet been established so there is no TCPCL
session to terminate. This also avoids any potential security issues
assoicated with further TCP communication with an untrusted peer.
After a TLS session is successfully established, the active peer
SHALL send a SESS_INIT message to begin session negotiation. This
session negotation and all subsequent messaging are secured.
4.4.2. Example TLS Initiation
A summary of a typical CAN_TLS usage is shown in the sequence in
Figure 15 below.
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Entity A Entity B
======== ========
+-------------------------+
| Open TCP Connnection | ->
+-------------------------+ +-------------------------+
<- | Accept Connection |
+-------------------------+
+-------------------------+
| Contact Header | ->
+-------------------------+ +-------------------------+
<- | Contact Header |
+-------------------------+
+-------------------------+ +-------------------------+
| TLS Negotiation | -> <- | TLS Negotiation |
| (as client) | | (as server) |
+-------------------------+ +-------------------------+
... secured TCPCL messaging, starting with SESS_INIT ...
+-------------------------+ +-------------------------+
| SESS_TERM | -> <- | SESS_TERM |
+-------------------------+ +-------------------------+
Figure 15: A simple visual example of TCPCL TLS Establishment between
two entities
4.5. Message Type Codes
After the initial exchange of a contact header, all messages
transmitted over the session are identified by a one-octet header
with the following structure:
0 1 2 3 4 5 6 7
+---------------+
| Message Type |
+---------------+
Figure 16: Format of the Message Header
The message header fields are as follows:
Message Type: Indicates the type of the message as per Table 2
below. Encoded values are listed in Section 9.5.
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+--------------+------+---------------------------------------------+
| Name | Code | Description |
+--------------+------+---------------------------------------------+
| SESS_INIT | 0x07 | Contains the session parameter inputs from |
| | | one of the entities, as described in |
| | | Section 4.6. |
| | | |
| SESS_TERM | 0x05 | Indicates that one of the entities |
| | | participating in the session wishes to |
| | | cleanly terminate the session, as described |
| | | in Section 6. |
| | | |
| XFER_SEGMENT | 0x01 | Indicates the transmission of a segment of |
| | | bundle data, as described in Section 5.2.2. |
| | | |
| XFER_ACK | 0x02 | Acknowledges reception of a data segment, |
| | | as described in Section 5.2.3. |
| | | |
| XFER_REFUSE | 0x03 | Indicates that the transmission of the |
| | | current bundle SHALL be stopped, as |
| | | described in Section 5.2.4. |
| | | |
| KEEPALIVE | 0x04 | Used to keep TCPCL session active, as |
| | | described in Section 5.1.1. |
| | | |
| MSG_REJECT | 0x06 | Contains a TCPCL message rejection, as |
| | | described in Section 5.1.2. |
+--------------+------+---------------------------------------------+
Table 2: TCPCL Message Types
4.6. Session Initialization Message (SESS_INIT)
Before a session is established and ready to transfer bundles, the
session parameters are negotiated between the connected entities.
The SESS_INIT message is used to convey the per-entity parameters
which are used together to negotiate the per-session parameters as
described in Section 4.7.
The format of a SESS_INIT message is as follows in Figure 17.
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+-----------------------------+
| Message Header |
+-----------------------------+
| Keepalive Interval (U16) |
+-----------------------------+
| Segment MRU (U64) |
+-----------------------------+
| Transfer MRU (U64) |
+-----------------------------+
| EID Length (U16) |
+-----------------------------+
| EID Data (variable) |
+-----------------------------+
| Session Extension |
| Items Length (U32) |
+-----------------------------+
| Session Extension |
| Items (var.) |
+-----------------------------+
Figure 17: SESS_INIT Format
The fields of the SESS_INIT message are:
Keepalive Interval: A 16-bit unsigned integer indicating the
interval, in seconds, between any subsequent messages being
transmitted by the peer. The peer receiving this contact header
uses this interval to determine how long to wait after any last-
message transmission and a necessary subsequent KEEPALIVE message
transmission.
Segment MRU: A 64-bit unsigned integer indicating the largest
allowable single-segment data payload size to be received in this
session. Any XFER_SEGMENT sent to this peer SHALL have a data
payload no longer than the peer's Segment MRU. The two entities
of a single session MAY have different Segment MRUs, and no
relation between the two is required.
Transfer MRU: A 64-bit unsigned integer indicating the largest
allowable total-bundle data size to be received in this session.
Any bundle transfer sent to this peer SHALL have a Total Bundle
Length payload no longer than the peer's Transfer MRU. This value
can be used to perform proactive bundle fragmentation. The two
entities of a single session MAY have different Transfer MRUs, and
no relation between the two is required.
EID Length and EID Data: Together these fields represent a variable-
length text string. The EID Length is a 16-bit unsigned integer
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indicating the number of octets of EID Data to follow. A zero EID
Length SHALL be used to indicate the lack of EID rather than a
truly empty EID. This case allows an entity to avoid exposing EID
information on an untrusted network. A non-zero-length EID Data
SHALL contain the UTF-8 encoded EID of some singleton endpoint in
which the sending entity is a member, in the canonical format of
<scheme name>:<scheme-specific part>. This EID encoding is
consistent with [I-D.ietf-dtn-bpbis].
Session Extension Length and Session Extension Items: Together these
fields represent protocol extension data not defined by this
specification. The Session Extension Length is the total number
of octets to follow which are used to encode the Session Extension
Item list. The encoding of each Session Extension Item is within
a consistent data container as described in Section 4.8. The full
set of Session Extension Items apply for the duration of the TCPCL
session to follow. The order and mulitplicity of these Session
Extension Items MAY be significant, as defined in the associated
type specification(s).
4.7. Session Parameter Negotiation
An entity calculates the parameters for a TCPCL session by
negotiating the values from its own preferences (conveyed by the
contact header it sent to the peer) with the preferences of the peer
node (expressed in the contact header that it received from the
peer). The negotiated parameters defined by this specification are
described in the following paragraphs.
Transfer MTU and Segment MTU: The maximum transmit unit (MTU) for
whole transfers and individual segments are idententical to the
Transfer MRU and Segment MRU, respectively, of the recevied
contact header. A transmitting peer can send individual segments
with any size smaller than the Segment MTU, depending on local
policy, dynamic network conditions, etc. Determining the size of
each transmitted segment is an implementation matter.
Session Keepalive: Negotiation of the Session Keepalive parameter is
performed by taking the minimum of this two contact headers'
Keepalive Interval. The Session Keepalive interval is a parameter
for the behavior described in Section 5.1.1.
Enable TLS: Negotiation of the Enable TLS parameter is performed by
taking the logical AND of the two contact headers' CAN_TLS flags.
A local security policy is then applied to determine of the
negotated value of Enable TLS is acceptable. It can be a
reasonable security policy to both require or disallow the use of
TLS depending upon the desired network flows. If the Enable TLS
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state is unacceptable, the node SHALL terminate the session with a
reason code of "Contact Failure". Note that this contact failure
is different than a failure of TLS handshake after an agreed-upon
and acceptable Enable TLS state. If the negotiated Enable TLS
value is true and acceptable then TLS negotiation feature
(described in Section 4.4) begins immediately following the
contact header exchange.
Once this process of parameter negotiation is completed (which
includes a possible completed TLS handshake of the connection to use
TLS), this protocol defines no additional mechanism to change the
parameters of an established session; to effect such a change, the
TCPCL session MUST be terminated and a new session established.
4.8. Session Extension Items
Each of the Session Extension Items SHALL be encoded in an identical
Type-Length-Value (TLV) container form as indicated in Figure 18.
The fields of the Session Extension Item are:
Flags: A one-octet field containing generic bit flags about the
Item, which are listed in Table 3. If a TCPCL entity receives a
Session Extension Item with an unknown Item Type and the CRITICAL
flag set, the entity SHALL close the TCPCL session with SESS_TERM
reason code of "Contact Failure". If the CRITICAL flag is not
set, an entity SHALL skip over and ignore any item with an unknown
Item Type.
Item Type: A 16-bit unsigned integer field containing the type of
the extension item. This specification does not define any
extension types directly, but does allocate an IANA registry for
such codes (see Section 9.3).
Item Length: A 16-bit unsigned integer field containing the number
of Item Value octets to follow.
Item Value: A variable-length data field which is interpreted
according to the associated Item Type. This specification places
no restrictions on an extension's use of available Item Value
data. Extension specifications SHOULD avoid the use of large data
lengths, as no bundle transfers can begin until the full extension
data is sent.
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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... |
+---------------+---------------+---------------+---------------+
Figure 18: Session Extension Item Format
+----------+--------+-----------------------------------------------+
| Name | Code | Description |
+----------+--------+-----------------------------------------------+
| CRITICAL | 0x01 | If bit is set, indicates that the receiving |
| | | peer must handle the extension item. |
| | | |
| Reserved | others |
+----------+--------+-----------------------------------------------+
Table 3: Session Extension Item Flags
5. Established Session Operation
This section describes the protocol operation for the duration of an
established session, including the mechanism for transmitting bundles
over the session.
5.1. Upkeep and Status Messages
5.1.1. Session Upkeep (KEEPALIVE)
The protocol includes a provision for transmission of KEEPALIVE
messages over the TCPCL session to help determine if the underlying
TCP connection has been disrupted.
As described in Section 4.3, a negotiated parameter of each session
is the Session Keepalive interval. If the negotiated Session
Keepalive is zero (i.e. one or both contact headers contains a zero
Keepalive Interval), then the keepalive feature 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, entities 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. Entities SHOULD
choose a keepalive interval no longer than 10 minutes (600 seconds).
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Note: The Keepalive Interval SHOULD NOT be chosen too short as TCP
retransmissions MAY occur in case of packet loss. Those will have to
be triggered by a timeout (TCP retransmission timeout (RTO)), which
is dependent on the measured RTT for the TCP connection so that
KEEPALIVE messages MAY experience noticeable latency.
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
sides SHALL send a KEEPALIVE message whenever the negotiated interval
has elapsed with no transmission of any message (KEEPALIVE or other).
If no message (KEEPALIVE or other) has been received in a session
after some implementation-defined time duration, then the node SHALL
terminate the session by transmitting a SESS_TERM message (as
described in Section 6.1) with reason code "Idle Timeout". If
configurable, the idle timeout duration SHOULD be no shorter than
twice the keepalive interval. If not configurable, the idle timeout
duration SHOULD be exactly twice the keepalive interval.
5.1.2. Message Rejection (MSG_REJECT)
If a TCPCL node receives a message which is unknown to it (possibly
due to an unhandled protocol mismatch) or is inappropriate for the
current session state (e.g. a KEEPALIVE message received after
contact header negotiation has disabled that feature), there is a
protocol-level message to signal this condition in the form of a
MSG_REJECT reply.
The format of a MSG_REJECT message is as follows in Figure 19.
+-----------------------------+
| Message Header |
+-----------------------------+
| Reason Code (U8) |
+-----------------------------+
| Rejected Message Header |
+-----------------------------+
Figure 19: Format of MSG_REJECT Messages
The fields of the MSG_REJECT message are:
Reason Code: A one-octet refusal reason code interpreted according
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.
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+-------------+------+----------------------------------------------+
| Name | Code | Description |
+-------------+------+----------------------------------------------+
| Message | 0x01 | A message was received with a Message Type |
| Type | | code unknown to the TCPCL node. |
| Unknown | | |
| | | |
| Message | 0x02 | A message was received but the TCPCL node |
| Unsupported | | cannot comply with the message contents. |
| | | |
| Message | 0x03 | A message was received while the session is |
| Unexpected | | in a state in which the message is not |
| | | expected. |
+-------------+------+----------------------------------------------+
Table 4: MSG_REJECT Reason Codes
5.2. Bundle Transfer
All of the messages in this section are directly associated with
transferring a bundle between TCPCL entities.
A single TCPCL transfer results in a bundle (handled by the
convergence layer as opaque data) being exchanged from one node to
the other. In TCPCL a transfer is accomplished by dividing a single
bundle up into "segments" based on the receiving-side Segment MRU
(see Section 4.2). The choice of the length to use for segments is
an implementation matter, but each segment MUST be no larger than the
receiving node's maximum receive unit (MRU) (see the field "Segment
MRU" of Section 4.2). The first segment for a bundle MUST set the
'START' flag, and the last one MUST set the 'end' flag in the
XFER_SEGMENT message flags.
A single transfer (and by extension a single segment) SHALL NOT
contain data of more than a single bundle. This requirement is
imposed on the agent using the TCPCL rather than TCPCL itself.
If multiple bundles are transmitted on a single TCPCL connection,
they MUST be transmitted consecutively without interleaving of
segments from multiple bundles.
5.2.1. Bundle Transfer ID
Each of the bundle transfer messages contains a Transfer ID which is
used to correlate messages (from both sides of a transfer) for each
bundle. A Transfer ID does not attempt to address uniqueness of the
bundle data itself and has no relation to concepts such as bundle
fragmentation. Each invocation of TCPCL by the bundle protocol
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agent, requesting transmission of a bundle (fragmentary or
otherwise), results in the initiation of a single TCPCL transfer.
Each transfer entails the sending of a sequence of some number of
XFER_SEGMENT and XFER_ACK messages; all are correlated by the same
Transfer ID.
Transfer IDs from each node SHALL be unique within a single TCPCL
session. The initial Transfer ID from each node SHALL have value
zero. Subsequent Transfer ID values SHALL be incremented from the
prior Transfer ID value by one. Upon exhaustion of the entire 64-bit
Transfer ID space, the sending node SHALL terminate the session with
SESS_TERM reason code "Resource Exhaustion".
For bidirectional bundle transfers, a TCPCL node SHOULD NOT rely on
any relation between Transfer IDs originating from each side of the
TCPCL session.
5.2.2. Data Transmission (XFER_SEGMENT)
Each bundle is transmitted in one or more data segments. The format
of a XFER_SEGMENT message follows in Figure 20.
+------------------------------+
| Message Header |
+------------------------------+
| Message Flags (U8) |
+------------------------------+
| Transfer ID (U64) |
+------------------------------+
| Transfer Extension |
| Items Length (U32) |
| (only for START segment) |
+------------------------------+
| Transfer Extension |
| Items (var.) |
| (only for START segment) |
+------------------------------+
| Data length (U64) |
+------------------------------+
| Data contents (octet string) |
+------------------------------+
Figure 20: Format of XFER_SEGMENT Messages
The fields of the XFER_SEGMENT message are:
Message Flags: A one-octet field of single-bit flags, interpreted
according to the descriptions in Table 5.
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Transfer ID: A 64-bit unsigned integer identifying the transfer
being made.
Transfer Extension Length and Transfer Extension Items: Together
these fields represent protocol extension data for this
specification. The Transfer Extension Length and Transfer
Extension Item fields SHALL only be present when the 'START' flag
is set on the message. The Transfer Extension Length is the total
number of octets to follow which are used to encode the Transfer
Extension Item list. The encoding of each Transfer Extension Item
is within a consistent data container as described in
Section 5.2.5. The full set of transfer extension items apply
only to the assoicated single transfer. The order and
mulitplicity of these transfer extension items MAY be significant,
as defined in the associated type specification(s).
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
segments containing sequential portions of that bundle until it sends
a segment with the 'END' bit set. No interleaving of multiple
transfers from the same node is possible within a single TCPCL
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session. Simultaneous transfers between two entities MAY be achieved
using multiple TCPCL sessions.
5.2.3. Data Acknowledgments (XFER_ACK)
Although the TCP transport provides reliable transfer of data between
transport peers, the typical BSD sockets interface provides no means
to inform a sending application of when the receiving application has
processed some amount of transmitted data. Thus, after transmitting
some data, the TCPCL needs an additional mechanism to determine
whether the receiving agent has successfully received the segment.
To this end, the TCPCL protocol provides feedback messaging whereby a
receiving node transmits acknowledgments of reception of data
segments.
The format of an XFER_ACK message follows in Figure 21.
+-----------------------------+
| Message Header |
+-----------------------------+
| Message Flags (U8) |
+-----------------------------+
| Transfer ID (U64) |
+-----------------------------+
| Acknowledged length (U64) |
+-----------------------------+
Figure 21: Format of XFER_ACK Messages
The fields of the XFER_ACK message are:
Message Flags: A one-octet field of single-bit flags, interpreted
according to the descriptions in Table 5.
Transfer ID: A 64-bit unsigned integer identifying the transfer
being acknowledged.
Acknowledged length: A 64-bit unsigned integer indicating the total
number of octets in the transfer which are being acknowledged.
A receiving TCPCL node 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_SEGMENT
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.
The sending node SHOULD transmit multiple XFER_SEGMENT messages
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without waiting for the corresponding XFER_ACK responses. This
enables pipelining of messages on a transfer stream.
For example, suppose the sending node transmits four segments of
bundle data with lengths 100, 200, 500, and 1000, respectively.
After receiving the first segment, the node sends an acknowledgment
of length 100. After the second segment is received, the node sends
an acknowledgment of length 300. The third and fourth
acknowledgments are of length 800 and 1800, respectively.
5.2.4. Transfer Refusal (XFER_REFUSE)
The TCPCL supports a mechanism by which a receiving node can indicate
to the sender that it does not want to receive the corresponding
bundle. To do so, upon receiving an XFER_SEGMENT message, the node
MAY transmit a XFER_REFUSE message. As data segments and
acknowledgments MAY cross on the wire, the bundle that is being
refused SHALL be identified by the Transfer ID of the refusal.
There is no required relation between the Transfer MRU of a TCPCL
node (which is supposed to represent a firm limitation of what the
node will accept) and sending of a XFER_REFUSE message. A
XFER_REFUSE can be used in cases where the agent's bundle storage is
temporarily depleted or somehow constrained. A XFER_REFUSE can also
be used after the bundle header or any bundle data is inspected by an
agent and determined to be unacceptable.
A receiver MAY send an XFER_REFUSE message as soon as it receives any
XFER_SEGMENT message. The sender MUST be prepared for this and MUST
associate the refusal with the correct bundle via the Transfer ID
fields.
The format of the XFER_REFUSE message is as follows in Figure 22.
+-----------------------------+
| Message Header |
+-----------------------------+
| Reason Code (U8) |
+-----------------------------+
| Transfer ID (U64) |
+-----------------------------+
Figure 22: Format of XFER_REFUSE Messages
The fields of the XFER_REFUSE message are:
Reason Code: A one-octet refusal reason code interpreted according
to the descriptions in Table 6.
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Transfer ID: A 64-bit unsigned integer identifying the transfer
being refused.
+------------+------+-----------------------------------------------+
| Name | Code | Description |
+------------+------+-----------------------------------------------+
| Unknown | 0x00 | Reason for refusal is unknown or not |
| | | specified. |
| | | |
| Extension | 0x01 | A failure processing the Transfer Extension |
| Failure | | Items ha occurred. |
| | | |
| Completed | 0x02 | The receiver already has the complete bundle. |
| | | The sender MAY consider the bundle as |
| | | completely received. |
| | | |
| No | 0x03 | The receiver's resources are exhausted. The |
| Resources | | sender SHOULD apply reactive bundle |
| | | fragmentation before retrying. |
| | | |
| Retransmit | 0x04 | The receiver has encountered a problem that |
| | | requires the bundle to be retransmitted in |
| | | its entirety. |
+------------+------+-----------------------------------------------+
Table 6: XFER_REFUSE Reason Codes
The receiver MUST, for each transfer preceding the one to be refused,
have either acknowledged all XFER_SEGMENTs or refused the bundle
transfer.
The bundle transfer refusal MAY be sent before an entire data segment
is received. If a sender receives a XFER_REFUSE message, the sender
MUST complete the transmission of any partially sent XFER_SEGMENT
message. There is no way to interrupt an individual TCPCL message
partway through sending it. The sender MUST NOT commence
transmission of any further segments of the refused bundle
subsequently. Note, however, that this requirement does not ensure
that an entity will not receive another XFER_SEGMENT for the same
bundle after transmitting a XFER_REFUSE message since messages MAY
cross on the wire; if this happens, subsequent segments of the bundle
SHALL also be refused with a XFER_REFUSE message.
Note: If a bundle transmission is aborted in this way, the receiver
MAY not receive a segment with the 'END' flag set to '1' for the
aborted bundle. The beginning of the next bundle is identified by
the 'START' bit set to '1', indicating the start of a new transfer,
and with a distinct Transfer ID value.
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5.2.5. Transfer Extension Items
Each of the Transfer Extension Items SHALL be encoded in an identical
Type-Length-Value (TLV) container form as indicated in Figure 23.
The fields of the Transfer Extension Item are:
Flags: A one-octet field containing generic bit flags about the
Item, which are listed in Table 7. If a TCPCL node receives a
Transfer Extension Item with an unknown Item Type and the CRITICAL
flag set, the node SHALL refuse the transfer with an XFER_REFUSE
reason code of "Extension Failure". If the CRITICAL flag is not
set, an entity SHALL skip over and ignore any item with an unknown
Item Type.
Item Type: A 16-bit unsigned integer field containing the type of
the extension item. This specification allocates an IANA registry
for such codes (see Section 9.4).
Item Length: A 16-bit unsigned integer field containing the number
of Item Value octets to follow.
Item Value: A variable-length data field which is interpreted
according to the associated Item Type. This specification places
no restrictions on an extension's use of available Item Value
data. Extension specifications SHOULD avoid the use of large data
lengths, as the associated transfer cannot begin until the full
extension data is sent.
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
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... |
+---------------+---------------+---------------+---------------+
Figure 23: Transfer Extension Item Format
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+----------+--------+-----------------------------------------------+
| Name | Code | Description |
+----------+--------+-----------------------------------------------+
| CRITICAL | 0x01 | If bit is set, indicates that the receiving |
| | | peer must handle the extension item. |
| | | |
| Reserved | others |
+----------+--------+-----------------------------------------------+
Table 7: Transfer Extension Item Flags
5.2.5.1. Transfer Length Extension
The purpose of the Transfer Length extension is to allow entities to
preemptively refuse bundles that would exceed their resources or to
prepare storage on the receiving node for the upcoming bundle data.
Multiple Transfer Length extension items SHALL NOT occur within the
same transfer. The lack of a Transfer Length extension item in any
transfer SHALL NOT imply anything about the potential length of the
transfer. The Transfer Length extension SHALL be assigned transfer
extension type ID 0x0001.
If a transfer occupies exactly one segment (i.e. both START and END
bits are set) the Transfer Length extension SHOULD NOT be present.
The extension does not provide any additional information for single-
segment transfers.
The format of the Transfer Length data is as follows in Figure 24.
+----------------------+
| Total Length (U64) |
+----------------------+
Figure 24: Format of Transfer Length data
The fields of the Transfer Length extension are:
Total Length: A 64-bit unsigned integer indicating the size of the
data-to-be-transferred. The Total Length field SHALL be treated
as authoritative by the receiver. If, for whatever reason, the
actual total length of bundle data received differs from the value
indicated by the Total Length value, the receiver SHALL treat the
transmitted data as invalid.
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6. Session Termination
This section describes the procedures for ending a TCPCL session.
6.1. Session Termination Message (SESS_TERM)
To cleanly shut down a session, a SESS_TERM message SHALL be
transmitted by either node at any point following complete
transmission of any other message. When sent to initiate a
termination, the REPLY bit of a SESS_TERM message SHALL NOT be set.
Upon receiving a SESS_TERM message after not sending a SESS_TERM
message in the same session, an entity SHALL send an acknowledging
SESS_TERM message. When sent to acknowledge a termination, a
SESS_TERM message SHALL have identical data content from the message
being acknowledged except for the REPLY bit, which is set to indicate
acknowledgement.
After sending a SESS_TERM message, an entity MAY continue a possible
in-progress transfer in either direction. After sending a SESS_TERM
message, an entity SHALL NOT begin any new outgoing transfer (i.e.
send an XFER_SEGMENT message) for the remainder of the session.
After receving a SESS_TERM message, an entity SHALL NOT accept any
new incoming transfer for the remainder of the session.
Instead of following a clean shutdown sequence, after transmitting a
SESS_TERM message an entity MAY immediately close the associated TCP
connection. When performing an unclean shutdown, a receiving node
SHOULD acknowledge all received data segments before closing the TCP
connection. Not acknowledging received segments can result in
unnecessary retransmission. When performing an unclean shutodwn, a
transmitting node SHALL treat either sending or receiving a SESS_TERM
message (i.e. before the final acknowledgment) as a failure of the
transfer. 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 node.
The format of the SESS_TERM message is as follows in Figure 25.
+-----------------------------+
| Message Header |
+-----------------------------+
| Message Flags (U8) |
+-----------------------------+
| Reason Code (U8) |
+-----------------------------+
Figure 25: Format of SESS_TERM Messages
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The fields of the SESS_TERM message are:
Message Flags: A one-octet field of single-bit flags, interpreted
according to the descriptions in Table 8.
Reason Code: A one-octet refusal reason code interpreted according
to the descriptions in Table 9.
+----------+--------+-----------------------------------------------+
| Name | Code | Description |
+----------+--------+-----------------------------------------------+
| REPLY | 0x01 | If bit is set, indicates that this message is |
| | | an acknowledgement of an earlier SESS_TERM |
| | | message. |
| | | |
| Reserved | others |
+----------+--------+-----------------------------------------------+
Table 8: SESS_TERM Flags
+--------------+------+---------------------------------------------+
| Name | Code | Description |
+--------------+------+---------------------------------------------+
| Unknown | 0x00 | A termination reason is not available. |
| | | |
| Idle timeout | 0x01 | The session is being closed due to |
| | | idleness. |
| | | |
| Version | 0x02 | The node cannot conform to the specified |
| mismatch | | TCPCL protocol version. |
| | | |
| Busy | 0x03 | The node is too busy to handle the current |
| | | session. |
| | | |
| Contact | 0x04 | The node cannot interpret or negotiate |
| Failure | | contact header option. |
| | | |
| Resource | 0x05 | The node has run into some resource limit |
| Exhaustion | | and cannot continue the session. |
+--------------+------+---------------------------------------------+
Table 9: SESS_TERM Reason Codes
A session shutdown MAY occur immediately after transmission of a
contact header (and prior to any further message transmit). This
MAY, for example, be used to notify that the node is currently not
able or willing to communicate. However, an entity MUST always send
the contact header to its peer before sending a SESS_TERM message.
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If reception of the contact header itself somehow fails (e.g. an
invalid "magic string" is recevied), an entity SHALL close the TCP
connection without sending a SESS_TERM message. If the content of
the Session Extension Items data disagrees with the Session Extension
Length (i.e. the last Item claims to use more octets than are present
in the Session Extension Length), the reception of the contact header
is considered to have failed.
If a session is to be terminated before a protocol message has
completed being sent, then the node MUST NOT transmit the SESS_TERM
message but still SHALL close the TCP connection. Each TCPCL message
is contiguous in the octet stream and has no ability to be cut short
and/or preempted by an other message. This is particularly important
when large segment sizes are being transmitted; either entire
XFER_SEGMENT is sent before a SESS_TERM message or the connection is
simply terminated mid-XFER_SEGMENT.
6.2. Idle Session Shutdown
The protocol includes a provision for clean shutdown of 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
configuration matter.
If there is a configured time to close idle links and if no TCPCL
messages (other than KEEPALIVE messages) has been received for at
least that amount of time, then either node MAY terminate the session
by transmitting a SESS_TERM message indicating the reason code of
"Idle timeout" (as described in Table 9).
7. Implementation Status
[NOTE to the RFC Editor: please remove this section before
publication, as well as the reference to [RFC7942] and
[github-dtn-bpbis-tcpcl].]
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
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An example implementation of the this draft of TCPCLv4 has been
created as a GitHub project [github-dtn-bpbis-tcpcl] and is intented
to use as a proof-of-concept and as a possible source of
interoperability testing. This example implementation uses D-Bus as
the CL-BP Agent interface, so it only runs on hosts which provide the
Python "dbus" library.
8. Security Considerations
One security consideration for this protocol relates to the fact that
entities present their endpoint identifier as part of the contact
header exchange. It would be possible for an entity to fake this
value and present the identity of a singleton endpoint in which the
node is not a member, essentially masquerading as another DTN node.
If this identifier is used outside of a TLS-secured session or
without further verification as a means to determine which bundles
are transmitted over the session, then the node that has falsified
its identity would be able to obtain bundles that it otherwise would
not have. Therefore, an entity SHALL NOT use the EID value of an
unsecured contact header to derive a peer node's identity unless it
can corroborate it via other means. When TCPCL session security is
mandated by a TCPCL peer, that peer SHALL transmit initial unsecured
contact header values indicated in Table 10 in order. These values
avoid unnecessarily leaking session parameters and will be ignored
when secure contact header re-exchange occurs.
+--------------------+---------------------------------------------+
| Parameter | Value |
+--------------------+---------------------------------------------+
| Flags | The USE_TLS flag is set. |
| | |
| Keepalive Interval | Zero, indicating no keepalive. |
| | |
| Segment MRU | Zero, indicating all segments are refused. |
| | |
| Transfer MRU | Zero, indicating all transfers are refused. |
| | |
| EID | Empty, indicating lack of EID. |
+--------------------+---------------------------------------------+
Table 10: Recommended Unsecured Contact Header
TCPCL can be used to provide point-to-point transport security, but
does not provide security of data-at-rest and does not guarantee end-
to-end bundle security. The mechanisms defined in [RFC6257] and
[I-D.ietf-dtn-bpsec] are to be used instead.
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Even when using TLS to secure the TCPCL session, the actual
ciphersuite negotiated between the TLS peers MAY be insecure. TLS
can be used to perform authentication without data confidentiality,
for example. It is up to security policies within each TCPCL node to
ensure that the negotiated TLS ciphersuite meets transport security
requirements. This is identical behavior to STARTTLS use in
[RFC2595].
Another consideration for this protocol relates to denial-of-service
attacks. An entity MAY send a large amount of data over a TCPCL
session, requiring the receiving entity to handle the data, attempt
to stop the flood of data by sending a XFER_REFUSE message, or
forcibly terminate the session. This burden could cause denial of
service on other, well-behaving sessions. There is also nothing to
prevent a malicious entity from continually establishing sessions and
repeatedly trying to send copious amounts of bundle data. A
listening entity MAY take countermeasures such as ignoring TCP SYN
messages, closing TCP connections as soon as they are established,
waiting before sending the contact header, sending a SESS_TERM
message quickly or with a delay, etc.
9. IANA Considerations
In this section, registration procedures are as defined in [RFC8126].
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.
9.1. Port Number
Port number 4556 has been previously assigned as the default port for
the TCP convergence layer in [RFC7242]. This assignment is unchanged
by protocol version 4. Each TCPCL entity identifies its TCPCL
protocol version in its initial contact (see Section 9.2), so there
is no ambiguity about what protocol is being used.
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+------------------------+-------------------------------------+
| Parameter | Value |
+------------------------+-------------------------------------+
| Service Name: | dtn-bundle |
| | |
| Transport Protocol(s): | TCP |
| | |
| Assignee: | Simon Perreault <simon@per.reau.lt> |
| | |
| Contact: | Simon Perreault <simon@per.reau.lt> |
| | |
| Description: | DTN Bundle TCP CL Protocol |
| | |
| Reference: | [RFC7242] |
| | |
| Port Number: | 4556 |
+------------------------+-------------------------------------+
9.2. Protocol Versions
IANA has created, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer Version
Numbers" and initialize it with the following table. The
registration procedure is RFC Required.
+-------+-------------+---------------------+
| Value | Description | Reference |
+-------+-------------+---------------------+
| 0 | Reserved | [RFC7242] |
| | | |
| 1 | Reserved | [RFC7242] |
| | | |
| 2 | Reserved | [RFC7242] |
| | | |
| 3 | TCPCL | [RFC7242] |
| | | |
| 4 | TCPCLv4 | This specification. |
| | | |
| 5-255 | Unassigned |
+-------+-------------+---------------------+
9.3. Session Extension Types
EDITOR NOTE: sub-registry to-be-created upon publication of this
specification.
IANA will create, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer Version 4
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Session Extension Types" and initialize it with the contents of
Table 11. The registration procedure is RFC Required within the
lower range 0x0001--0x7FFF. Values in the range 0x8000--0xFFFF are
reserved for use on private networks for functions not published to
the IANA.
+----------------+--------------------------+
| Code | Session Extension Type |
+----------------+--------------------------+
| 0x0000 | Reserved |
| | |
| 0x0001--0x7FFF | Unassigned |
| | |
| 0x8000--0xFFFF | Private/Experimental Use |
+----------------+--------------------------+
Table 11: Session Extension Type Codes
9.4. Transfer Extension Types
EDITOR NOTE: sub-registry to-be-created upon publication of this
specification.
IANA will create, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer Version 4
Transfer Extension Types" and initialize it with the contents of
Table 12. The registration procedure is RFC Required within the
lower range 0x0001--0x7FFF. Values in the range 0x8000--0xFFFF are
reserved for use on private networks for functions not published to
the IANA.
+----------------+---------------------------+
| Code | Transfer Extension Type |
+----------------+---------------------------+
| 0x0000 | Reserved |
| | |
| 0x0001 | Transfer Length Extension |
| | |
| 0x0002--0x7FFF | Unassigned |
| | |
| 0x8000--0xFFFF | Private/Experimental Use |
+----------------+---------------------------+
Table 12: Transfer Extension Type Codes
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9.5. Message Types
EDITOR NOTE: sub-registry to-be-created upon publication of this
specification.
IANA will create, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer Version 4
Message Types" and initialize it with the contents of Table 13. The
registration procedure is RFC Required.
+-----------+--------------+
| Code | Message Type |
+-----------+--------------+
| 0x00 | Reserved |
| | |
| 0x01 | XFER_SEGMENT |
| | |
| 0x02 | XFER_ACK |
| | |
| 0x03 | XFER_REFUSE |
| | |
| 0x04 | KEEPALIVE |
| | |
| 0x05 | SESS_TERM |
| | |
| 0x06 | MSG_REJECT |
| | |
| 0x07 | SESS_INIT |
| | |
| 0x08--0xf | Unassigned |
+-----------+--------------+
Table 13: Message Type Codes
9.6. 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 initialize it with the contents of
Table 14. The registration procedure is RFC Required.
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+------------+---------------------------+
| Code | Refusal Reason |
+------------+---------------------------+
| 0x00 | Unknown |
| | |
| 0x01 | Extension Failure |
| | |
| 0x02 | Completed |
| | |
| 0x03 | No Resources |
| | |
| 0x04 | Retransmit |
| | |
| 0x05--0x07 | Unassigned |
| | |
| 0x08--0xFF | Reserved for future usage |
+------------+---------------------------+
Table 14: XFER_REFUSE Reason Codes
9.7. SESS_TERM 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
SESS_TERM Reason Codes" and initialize it with the contents of
Table 15. The registration procedure is RFC Required.
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+------------+---------------------+
| Code | Termination Reason |
+------------+---------------------+
| 0x00 | Unknown |
| | |
| 0x01 | Idle timeout |
| | |
| 0x02 | Version mismatch |
| | |
| 0x03 | Busy |
| | |
| 0x04 | Contact Failure |
| | |
| 0x05 | Resource Exhaustion |
| | |
| 0x06--0xFF | Unassigned |
+------------+---------------------+
Table 15: SESS_TERM Reason Codes
9.8. MSG_REJECT 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
MSG_REJECT Reason Codes" and initialize it with the contents of
Table 16. The registration procedure is RFC Required.
+-----------+----------------------+
| Code | Rejection Reason |
+-----------+----------------------+
| 0x00 | reserved |
| | |
| 0x01 | Message Type Unknown |
| | |
| 0x02 | Message Unsupported |
| | |
| 0x03 | Message Unexpected |
| | |
| 0x04-0xFF | Unassigned |
+-----------+----------------------+
Table 16: MSG_REJECT Reason Codes
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10. Acknowledgments
This specification is based on comments on implementation of
[RFC7242] provided from Scott Burleigh.
11. References
11.1. Normative References
[BCP195] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015.
[I-D.ietf-dtn-bpbis]
Burleigh, S., Fall, K., and E. Birrane, "Bundle Protocol
Version 7", draft-ietf-dtn-bpbis-12 (work in progress),
November 2018.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/info/rfc1122>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
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11.2. Informative References
[github-dtn-bpbis-tcpcl]
Sipos, B., "TCPCL Example Implementation",
<https://github.com/BSipos-RKF/dtn-bpbis-tcpcl/tree/
develop>.
[I-D.ietf-dtn-bpsec]
Birrane, E. and K. McKeever, "Bundle Protocol Security
Specification", draft-ietf-dtn-bpsec-09 (work in
progress), February 2019.
[RFC2595] Newman, C., "Using TLS with IMAP, POP3 and ACAP",
RFC 2595, DOI 10.17487/RFC2595, June 1999,
<https://www.rfc-editor.org/info/rfc2595>.
[RFC4838] Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst,
R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant
Networking Architecture", RFC 4838, DOI 10.17487/RFC4838,
April 2007, <https://www.rfc-editor.org/info/rfc4838>.
[RFC5050] Scott, K. and S. Burleigh, "Bundle Protocol
Specification", RFC 5050, DOI 10.17487/RFC5050, November
2007, <https://www.rfc-editor.org/info/rfc5050>.
[RFC6257] Symington, S., Farrell, S., Weiss, H., and P. Lovell,
"Bundle Security Protocol Specification", RFC 6257,
DOI 10.17487/RFC6257, May 2011,
<https://www.rfc-editor.org/info/rfc6257>.
[RFC7242] Demmer, M., Ott, J., and S. Perreault, "Delay-Tolerant
Networking TCP Convergence-Layer Protocol", RFC 7242,
DOI 10.17487/RFC7242, June 2014,
<https://www.rfc-editor.org/info/rfc7242>.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/info/rfc7942>.
Appendix A. Significant changes from RFC7242
The areas in which changes from [RFC7242] have been made to existing
headers and messages are:
o Split contact header into pre-TLS protocol negotiation and
SESS_INIT parameter negotiation. The contact header is now fixed-
length.
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o Changed contact header content to limit number of negotiated
options.
o Added contact option to negotiate maximum segment size (per each
direction).
o Added session extension capability.
o Added transfer extension capability. Moved transfer total length
into an extension item.
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-
related messages (XFER_SEGMENT, XFER_ACK, XFER_REFUSE).
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
fields.
o Renamed SHUTDOWN to SESS_TERM to deconflict term "shutdown".
o Removed the notion of a re-connection delay parameter.
The areas in which extensions from [RFC7242] have been made as new
messages and codes are:
o Added contact negotiation failure SESS_TERM reason code.
o Added MSG_REJECT message to indicate an unknown or unhandled
message was received.
o Added TLS session security mechanism.
o Added Resource Exhaustion SESS_TERM reason code.
Authors' Addresses
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Brian Sipos
RKF Engineering Solutions, LLC
7500 Old Georgetown Road
Suite 1275
Bethesda, MD 20814-6198
United States of America
Email: BSipos@rkf-eng.com
Michael Demmer
University of California, Berkeley
Computer Science Division
445 Soda Hall
Berkeley, CA 94720-1776
United States of America
Email: demmer@cs.berkeley.edu
Joerg Ott
Aalto University
Department of Communications and Networking
PO Box 13000
Aalto 02015
Finland
Email: ott@in.tum.de
Simon Perreault
Quebec, QC
Canada
Email: simon@per.reau.lt
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