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Licklider Transmission Protocol - Specification
RFC 5326

Networking Working Group                                      M. Ramadas
Request for Comments: 5326                                  ISTRAC, ISRO
Category: Experimental                                       S. Burleigh
                                          NASA/Jet Propulsion Laboratory
                                                              S. Farrell
                                                  Trinity College Dublin
                                                          September 2008

            Licklider Transmission Protocol - Specification

Status of This Memo

   This memo defines an Experimental Protocol for the Internet
   community.  It does not specify an Internet standard of any kind.
   Discussion and suggestions for improvement are requested.
   Distribution of this memo is unlimited.

IESG Note

   This RFC is not a candidate for any level of Internet Standard.  It
   represents the consensus of the Delay Tolerant Networking (DTN)
   Research Group of the Internet Research Task Force (IRTF).  It may be
   considered for standardization by the IETF in the future, but the
   IETF disclaims any knowledge of the fitness of this RFC for any
   purpose and in particular notes that the decision to publish is not
   based on IETF review for such things as security, congestion control,
   or inappropriate interaction with deployed protocols.  See RFC 3932
   for more information.

Abstract

   This document describes the Licklider Transmission Protocol (LTP),
   designed to provide retransmission-based reliability over links
   characterized by extremely long message round-trip times (RTTs)
   and/or frequent interruptions in connectivity.  Since communication
   across interplanetary space is the most prominent example of this
   sort of environment, LTP is principally aimed at supporting "long-
   haul" reliable transmission in interplanetary space, but it has
   applications in other environments as well.

   This document is a product of the Delay Tolerant Networking Research
   Group and has been reviewed by that group.  No objections to its
   publication as an RFC were raised.

Ramadas, et al.               Experimental                      [Page 1]
RFC 5326                  LTP - Specification             September 2008

Table of Contents

   1. Introduction ....................................................3
   2. Terminology .....................................................4
   3. Segment Structure ...............................................9
      3.1. Segment Header ............................................10
           3.1.1. Segment Type Flags .................................11
           3.1.2. Segment Type Codes .................................13
           3.1.3. Segment Class Masks ................................14
           3.1.4. Extensions Field ...................................14
      3.2. Segment Content ...........................................16
           3.2.1. Data Segment (DS) ..................................16
           3.2.2. Report Segment (RS) ................................17
           3.2.3. Report Acknowledgment Segment ......................19
           3.2.4. Session Management Segments ........................20
      3.3. Segment Trailer ...........................................20
   4. Requests from Client Service ...................................20
      4.1. Transmission Request ......................................21
      4.2. Cancellation Request ......................................22
   5. Requirements from the Operating Environment ....................23
   6. Internal Procedures ............................................24
      6.1. Start Transmission ........................................25
      6.2. Start Checkpoint Timer ....................................25
      6.3. Start RS Timer ............................................25
      6.4. Stop Transmission .........................................25
      6.5. Suspend Timers ............................................26
      6.6. Resume Timers .............................................26
      6.7. Retransmit Checkpoint .....................................27
      6.8. Retransmit RS .............................................27
      6.9. Signify Red-Part Reception ................................28
      6.10. Signify Green-Part Segment Arrival .......................28
      6.11. Send Reception Report ....................................28
      6.12. Signify Transmission Completion ..........................30
      6.13. Retransmit Data ..........................................30
      6.14. Stop RS Timer ............................................31
      6.15. Start Cancel Timer .......................................32
      6.16. Retransmit Cancellation Segment ..........................32

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