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Delay-Tolerant Networking Working Group                     S. Burleigh
Internet Draft                          JPL, Calif. Inst. Of Technology
Intended status: Standards Track                     September 14, 2018
Expires: March 2019


                   Simple TCP Convergence-Layer Protocol
                      draft-burleigh-dtn-stcp-00.txt


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Abstract

   This document describes a Simple TCP (STCP) "convergence-layer"
   protocol for the Delay-Tolerant Networking (DTN) Bundle Protocol
   (BP).  STCP uses Transmission Control Protocol (TCP) to transmit BP
   "bundles" from one BP node to another node to which it is
   topologically adjacent in the BP network. The services provided by
   the STCP convergence-layer protocol adapter utilize a standard TCP
   connection for the purposes of bundle transmission.

Table of Contents


   1. Introduction...................................................2
   2. Conventions used in this document..............................3
   3. STCP Design Elements...........................................3
      3.1. STCP Endpoints............................................3
      3.2. STCP Protocol Data Units..................................4
      3.3. Custody Signals................Error! Bookmark not defined.
      3.4. Custody Transfer Status ReportsError! Bookmark not defined.
   4. STCP Procedures................................................4
      4.1. SPDU Transmission.........................................4
      4.2. SPDU Reception.................Error! Bookmark not defined.
      4.3. Retransmission Timer ExpirationError! Bookmark not defined.
      4.4. Custody Signal Reception.......Error! Bookmark not defined.
   5. Security Considerations........................................6
   6. IANA Considerations............................................6
   7. References.....................................................6
      7.1. Normative References......................................6
      7.2. Informative References....................................6
   8. Acknowledgments................................................6
   Appendix A. For More Information..................................7
   Appendix B. CDDL expression............Error! Bookmark not defined.

1. Introduction

   This document describes the Simple TCP (STCP) protocol, a Delay-
   Tolerant Networking (DTN) Bundle Protocol (BP) [RFC5050]
   "convergence layer" protocol that uses a standard TCP connection to
   transmit bundles from one BP node to another node to which it is
   topologically adjacent in the BP network.

   Conformance to the STCP convergence-layer protocol specification is
   OPTIONAL for BP nodes.





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   Each BP node that conforms to the STCP specification includes an
   STCP convergence-layer adapter (SCLA).  Every SCLA engages in
   communication via the Transmission Control Protocol [RFC0793].

   Like any convergence-layer adapter, the STCP CLA provides:

     . A transmission service that sends an outbound bundle (from the
        bundle protocol agent) to a peer CLA via the STCP convergence
        layer protocol.
     . A reception service that delivers to the bundle protocol agent
        an inbound bundle that was sent by a peer CLA via the STCP
        convergence layer protocol.

   Transmission of bundles via STCP is "reliable" to the extent that
   TCP itself is reliable.  STCP provides no supplementary error
   detection and recovery procedures.  In particular, STCP does not
   provide to the sender any intermediate reporting of reception
   progress.

2. Conventions used in this document

   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 RFC-2119 [RFC2119].

   In this document, these words will appear with that interpretation
   only when in ALL CAPS. Lower case uses of these words are not to be
   interpreted as carrying RFC-2119 significance.

3. STCP Design Elements

3.1. STCP Sessions

   An STCP "session" is formed when a TCP connection is established by
   the matching of an active TCP OPEN request issued by some SCLA,
   termed the session's "sender", with a passive TCP OPEN request
   issued by some SCLA, termed the session's "receiver".  That portion
   of the state of a session that is exposed to the session's sender is
   termed the "transmission element" of the session.  That portion of
   the state of a session that is exposed to the session's receiver is
   termed the "reception element" of the session.

   The values of the parameters constraining STCP's TCP connection
   establishment, including the establishment of Transport Layer
   Security (TLS; [RFC8446]) sessions within the connections, are
   assumed to be provided by management.  At some point a discovery
   protocol may be developed that enables these values to be declared


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   automatically; such protocol is beyond the scope of this
   specification.

   STCP sessions are unidirectional; that is, bundles transmitted via
   an STCP session are transmitted only from the session's sender to
   its receiver.  When bidirectional exchange of bundles between SCLAs
   via STCP is required, two sessions are formed, one in each
   direction.

   Closure of either element of a session MAY occur either upon request
   of the bundle protocol agent or upon detection of any error.
   Closure of either element of an STCP session SHALL cause the
   corresponding TCP connection to be terminated (unless termination of
   that connection was in fact the cause of the closure of that session
   element).  Since termination of the associated TCP connection will
   result in errors at the other element of the session, termination of
   either element of the session will effectively terminate the
   session.

3.2. STCP Protocol Data Units

   An STCP protocol data unit (SPDU) is simply a serialized bundle
   preceded by an integer indicating the length of that serialized
   bundle.  An SPDU is constructed as follows.

   Each SPDU SHALL be represented as a CBOR array. The number of items
   in the array SHALL be 2.

   The first item of the SPDU array SHALL be the length of the
   serialized bundle that is encapsulated in the SPDU, represented as a
   CBOR unsigned integer.

   The second item of the SPDU array SHALL be a single serialized BP
   bundle, termed the "encapsulated bundle", represented as a CBOR byte
   string.

4. STCP Procedures

4.1. SPDU Transmission

   When an SCLA is requested by the bundle protocol agent to send a
   bundle to a peer SCLA identified by some IP address and port number:

     . If no STCP session enabling transmission to that SCLA has been
        formed, the SCLA SHALL attempt to form that session.  If this
        attempt is unsuccessful, the SCLA SHALL inform the bundle
        protocol agent that its data sending procedures with regard to


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        this bundle have concluded and transmission of the bundle was
        unsuccessful; no further steps of this procedure will be
        attempted.
     . The SCLA SHALL form an SPDU from the subject bundle.
     . The SCLA SHALL attempt to send this SPDU to the peer SCLA by
        TCP via the transmission element of the session formed for this
        purpose.
          o If that transmission is completed without error, the SCLA
             SHALL inform the bundle protocol agent that its data
             sending procedures with regard to this bundle have
             concluded and transmission of the bundle was successful.
          o Otherwise:
               . The transmission element SHALL be closed.
               . The SCLA SHALL inform the bundle protocol agent that
                  its data sending procedures with regard to this
                  bundle have concluded and transmission of the bundle
                  was unsuccessful.

4.2. Reception Session Formation

   An SCLA that is required to receive (rather than only transmit)
   bundles SHALL issue a passive TCP OPEN.  Whenever TCP matches that
   passive OPEN with an active TCP OPEN issued by some SCLA, an STCP
   session is formed as noted earlier; SPDUs may be received via the
   reception element of such session.

4.3. SPDU Reception

   From the moment at which an STCP session reception element is first
   exposed to the moment at which it is closed, in a continuous cycle,
   the corresponding session's receiver SHALL:

     . Attempt to receive, by TCP via the corresponding session, the
        length of the next bundle sent via this session.  If this
        attempt fails for any reason, the reception element SHALL be
        closed and no further steps of this procedure will be
        attempted.
     . Attempt to receive, by TCP via the corresponding session, a
        serialized bundle of the indicated length.  If this attempt
        fails for any reason, the reception element SHALL be closed and
        no further steps of this procedure will be attempted.
     . Deliver the received serialized bundle to the bundle protocol
        agent.






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5. Security Considerations

   Because STCP constitutes a nearly negligible extension of TCP, it
   introduces virtually no security considerations beyond the well-
   known TCP security considerations.

   An adversary could mount a denial-of-service attack by repeatedly
   establishing and terminating STCP sessions; well-understood DOS
   attack mitigations would apply.

   Maliciously formed bundle lengths could disrupt the operation of
   STCP session receivers, but STCP implementations need to be robust
   against incorrect bundle lengths in any case.

   Maliciously crafted serialized bundles could be received and
   delivered to the bundle protocol agent, but that is not an STCP-
   specific security consideration: all bundles delivered to the BPA by
   all convergence-layer adapters need to be processed in awareness of
   this possibility.

6. IANA Considerations

   No new IANA considerations apply.

7. References

7.1. Normative References

   [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC
   793, DOI 10.17487/RFC0793, September 1981.

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
   Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
   Version 1.3", RFC 8446, August 2018.

7.2. Informative References

   [RFC5050] Scott, M. and S. Burleigh, "Bundle Protocol
   Specification", RFC 5050, November 2007.

8. Acknowledgments

   This document was prepared using 2-Word-v2.0.template.dot.




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Appendix A.                 For More Information

   Please refer comments to dtn@ietf.org. The Delay Tolerant Networking
   Research Group (DTNRG) Web site is located at http://www.dtnrg.org.

   Copyright (c) 2018 IETF Trust and the persons identified as authors
   of the code. All rights reserved.

   Redistribution and use in source and binary forms, with or without
   modification, is permitted pursuant to, and subject to the license
   terms contained in, the Simplified BSD License set forth in Section
   4.c of the IETF Trust's Legal Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info).

Authors' Address

   Scott Burleigh
   Jet Propulsion Laboratory, California Institute of Technology
   4800 Oak Grove Dr.
   Pasadena, CA 91109-8099
   US
   Phone: +1 818 393 3353
   Email: Scott.Burleigh@jpl.nasa.gov


























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