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Delay-Tolerant Networking Working Group                     S. Burleigh
Internet Draft                          JPL, Calif. Inst. Of Technology
Intended status: Standards Track                         April 23, 2019
Expires: September 2019


                  Minimal TCP Convergence-Layer Protocol
                       draft-ietf-dtn-mtcpcl-01.txt


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Abstract

   This document describes a Minimal TCP (MTCP) "convergence-layer"
   protocol for the Delay-Tolerant Networking (DTN) Bundle Protocol
   (BP).  MTCP 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 MTCP 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. MTCP Design Elements...........................................3
      3.1. MTCP Sessions.............................................3
      3.2. MTCP Protocol Data Units..................................4
   4. MTCP Procedures................................................4
      4.1. MPDU Transmission.........................................4
      4.2. Reception Session Formation...............................5
      4.3. MPDU Reception............................................5
   5. Security Considerations........................................5
   6. IANA Considerations............................................6
   7. References.....................................................6
      7.1. Normative References......................................6
      7.2. Informative References....................................7
   8. Acknowledgments................................................7
   Appendix A. For More Information..................................8

1. Introduction

   This document describes the Minimal TCP (MTCP) 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 MTCP convergence-layer protocol specification is
   OPTIONAL for BP nodes.

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

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



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     . A transmission service that sends an outbound bundle (from the
        bundle protocol agent) to a peer CLA via the MTCP 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 MTCP
        convergence layer protocol.

   Transmission of bundles via MTCP is "reliable" to the extent that
   TCP itself is reliable.  MTCP provides no supplementary error
   detection and recovery procedures.  In particular, MTCP does not
   provide to the sender any interim 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. MTCP Design Elements

3.1. MTCP Sessions

   An MTCP "session" is formed when a TCP connection is established by
   the matching of an active TCP OPEN request issued by some MCLA,
   termed the session's "sender", with a passive TCP OPEN request
   issued by some MCLA, 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 MTCP's TCP connection
   establishment, including the establishment of Transport Layer
   Security (TLS; [RFC8446]) sessions within the connections, SHALL be
   provided by management, by means that are beyond the scope of this
   specification.  No TCP port number will be reserved for MTCP
   connection purposes.

   The use of TLS to secure MTCP sessions is optional but is strongly
   recommended.  When it is determined, by management, that an MTCP
   session between a given sender and receiver is to be secured by TLS:




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     . Following establishment of the session's TCP connection, the
        sender and receiver SHALL undertake a TLS handshake in
        accordance with [RFC8446] with the sender acting in the role of
        "client". The parameter settings governing each such handshake
        (again, determined by management) are an implementation matter,
        but the handshake SHOULD conform to all recommended best
        practices of [RFC7525] and its updates and successors.
     . If the handshake does not result in successful establishment of
        a TLS session, then the session's TCP connection SHALL be
        terminated and the attempt to form an MTCP session SHALL be
        abandoned.

   MTCP sessions are unidirectional; that is, bundles transmitted via
   an MTCP session are transmitted only from the session's sender to
   its receiver.  When bidirectional exchange of bundles between MCLAs
   via MTCP is required, two MTCP 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 MTCP 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. MTCP Protocol Data Units

   An MTCP protocol data unit (MPDU) is simply a serialized bundle in a
   CBOR representation that indicates the length of that serialized
   bundle.  An MPDU is constructed as follows.

   Each MPDU SHALL be a single serialized BP bundle, termed the
   "encapsulated bundle", represented as a CBOR byte string of definite
   length (NOT an indefinite-length byte string).

4. MTCP Procedures

4.1. MPDU Transmission

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

     . If no MTCP session enabling transmission to that MCLA has been
        formed, the MCLA SHALL attempt to form that session.  If this


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        attempt is unsuccessful, the MCLA 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; no further steps of this procedure will be
        attempted.
     . The MCLA SHALL form an MPDU from the subject bundle.
     . The MCLA SHALL attempt to send this MPDU to the peer MCLA by
        TCP via the transmission element of the session formed for this
        purpose.
          o If that transmission is completed without error, the MCLA
             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 MCLA 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 MCLA 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 MCLA, an MTCP
   session is formed as noted earlier; MPDUs may be received via the
   reception element of such session.

4.3. MPDU Reception

   From the moment at which an MTCP 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, a
        serialized BP bundle represented as a CBOR byte string of
        definite 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.

5. Security Considerations

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



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   known TCP security considerations.  To address these considerations,
   the use of TLS to secure MTCP sessions is strongly recommended.

   Even when TLS is used to secure an MTCP session, the ciphersuite
   specified for the TLS session may be insecure. For example, TLS can
   be configured to support authentication without confidentiality.
   MCLA management MUST ensure that the ciphersuites employed to secure
   MTCP sessions meet transport security requirements. This constraint
   echoes constraints on STARTTLS in [RFC2595].

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

   Maliciously formed bundle lengths could disrupt the operation of
   MTCP session receivers, but MTCP 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 MTCP-
   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

   [RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
   "Recommendations for Secure Use of Transport Layer Security (TLS)
   and Datagram Transport Layer Security (DTLS)", BCP 195, RFC 7525,
   May 2015.

   [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.




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7.2. Informative References

   [RFC2595] Newman, C., "Using TLS with IMAP, POP3 and ACAP", RFC
   2595, August 2018.

   [RFC5050] Scott, K. 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) 2019 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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