rfc938.txt

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Network Working Group                                       Trudy Miller
Request for Comments: 938                                            ACC
                                                           February 1985

                 Internet Reliable Transaction Protocol
                 Functional and Interface Specification


STATUS OF THIS MEMO

   This RFC is being distributed to members of the DARPA research
   community in order to solicit their reactions to the proposals
   contained in it.  While the issues discussed may not be directly
   relevant to the research problems of the DARPA community, they may be
   interesting to a number of researchers and implementors.  This RFC
   suggests a proposed protocol for the ARPA-Internet community, and
   requests discussion and suggestions for improvements.  Distribution
   of this memo is unlimited.

ABSTRACT

   The Internet Reliable Transaction Protocol (IRTP) is a transport
   level host to host protocol designed for an internet environment.  It
   provides reliable, sequenced delivery of packets of data between
   hosts and multiplexes/demultiplexes streams of packets from/to user
   processes representing ports.  It is simple to implement, with a
   minimum of connection management, at the possible expense of
   efficiency.

























Miller                                                          [Page i]



RFC 938                                                    February 1985
Internet Reliable Transaction Protocol


TABLE OF CONTENTS

   INTRODUCTION

      1.1   Purpose .........................................  1
      1.2   Underlying Mechanisms ...........................  1
      1.3   Relationship to Other Protocols .................  2

   IRTP HEADERS

      2.1   Header Format ...................................  3
      2.2   Packet Type .....................................  3
      2.3   Port Number .....................................  3
      2.4   Sequence Number .................................  4
      2.5   Length ..........................................  4
      2.6   Checksum ........................................  4

   INTERFACES

      3.1   User Services Provided By IRTP ..................  5
      3.2   IP Services Expected by IRTP ....................  5

   MODEL OF OPERATION

      4.1   State Variables .................................  6
      4.2   IRTP Initialization .............................  7
      4.3   Host-to-Host Synchronization ....................  7
      4.3.1   Response to SYNCH Packets .....................  7
      4.3.2   Response to SYNCH ACK Packet ..................  8
      4.4   Transmitting Data ...............................  8
      4.4.1   Receiving Data From Using Processes ...........  8
      4.4.2   Packet Retransmission ......................... 10
      4.5   Receiving Data .................................. 10
      4.5.1   Receive and Acknowledgment Windows ............ 11
      4.5.2   Invalid Packets ............................... 12
      4.5.3   Sequence Numbers Within Acknowledge Window .... 12
      4.5.4   Sequence Numbers Within the Receive Window .... 12
      4.5.5   Forwarding Data to Using Processes ............ 13

   IMPLEMENTATION ISSUES

      5.1   Retransmission Strategies ....................... 14
      5.2   Pinging ......................................... 14
      5.3   Deleting Connection Tables ...................... 16





Miller                                                         [Page ii]



RFC 938                                                    February 1985
Internet Reliable Transaction Protocol


   LIST OF FIGURES

      Figure 1-1    Relationship of IRTP to Other Protocols .  2
      Figure 2-1    IRTP Header Format ......................  3
      Figure 4-1    SYNCH Packet Format .....................  8
      Figure 4-2    SYNCH ACK Packet Format .................  8
      Figure 4-3    DATA Packet Format ......................  9
      Figure 4-4    DATA ACK Packet Format .................. 11
      Figure 4-5    PORT NAK Packet Format .................. 11

   ABBREVIATIONS

      ICMP        Internet Control Message Protocol
      IP          Internet Protocol
      IRTP        Internet Reliable Transaction Protocol
      RDP         Reliable Data Protocol
      TCP         Transmission Control Protocol
      UDP         User Datagram Protocol































Miller                                                        [Page iii]



RFC 938                                                    February 1985
Internet Reliable Transaction Protocol


CHAPTER 1 - INTRODUCTION

   The Internet Reliable Transaction Protocol (IRTP) is a full duplex,
   transaction oriented, host to host protocol which provides reliable
   sequenced delivery of packets of data, called transaction packets.

   Note: throughout this document the terms host and internet address
   are used interchangeably.

   1.1 Purpose

      The IRTP was designed for an environment in which one host will
      have to maintain reliable communication with many other hosts.  It
      is assumed that there is a (relatively) sporadic flow of
      information with each destination host, however information flow
      may be initiated at any time at either end of the connection.  The
      nature of the information is in the form of transactions, i.e.
      small, self contained messages.  There may be times at which one
      host will want to communicate essentially the same information to
      all of its known destinations as rapidly as possible.

      In effect, the IRTP defines a constant underlying connection
      between two hosts. This connection is not established and broken
      down, rather it can be resynchronized with minimal loss of data
      whenever one of the hosts has been rebooted.

      Due to the lack of connection management, it is desirable that all
      IRTP processes keep static information about all possible remote
      hosts. However, the IRTP has been designed such that minimal state
      information needs to be associated with each host to host pair,
      thereby allowing one host to communicate with many remote hosts.

      The IRTP is more complex than UDP in that it provides reliable,
      sequenced delivery of packets, but it is less complex than TCP in
      that sequencing is done on a packet by packet (rather than
      character stream) basis, and there is only one connection defined
      between any two internet addresses (that is, it is not a process
      to process protocol.)

   1.2 Underlying Mechanisms

      The IRTP uses retransmission and acknowledgments to guarantee
      delivery. Checksums are used to guarantee data integrity and to
      protect against misrouting.  There is a host to host
      synchronization mechanism and packet sequencing to provide
      duplicate detection and ordered delivery to the user process.  A
      simple mechanism allows IRTP to multiplex and demultiplex streams


Miller                                                          [Page 1]



RFC 938                                                    February 1985
Internet Reliable Transaction Protocol


      of transaction packets being exchanged between multiple IRTP users
      on this host and statically paired IRTP users on the same remote
      host.

   1.3 Relationship to Other Protocols

      The IRTP is designed for use in a potentially lossy internet
      environment.  It requires that IP be under it.  The IP protocol
      number of IRTP is 28.

      Conversely, IRTP provides a reliable transport protocol for one or
      more user processes.  User processes must have well-known IRTP
      port numbers, and can communicate only with matching processes
      with the same port number.  (Note that the term port refers to a
      higher level protocol.  IRTP connections exists between two hosts,
      not between a host/port and another host/port.)

      These relationships are depicted below.

         +--------+    +--------+   +-----------+
         | port a |....| port x |   | TCP users |   Application Level
         +--------+    +--------+   +-----------+
               |          |            | ... |
             +--------------+       +-----------+
             |     IRTP     |       |    TCP    |   Host Level
             +--------------+       +-----------+
                    |                     |
         +--------------------------------------+
         |    Internet Protocol and ICMP        |   Internet Level
         +--------------------------------------+
                          |
         +--------------------------------------+
         |      Local Network Protocol          |   Network Level
         +--------------------------------------+

         Figure 1-1.  Relationship of IRTP to Other Protocols













Miller                                                          [Page 2]



RFC 938                                                    February 1985
Internet Reliable Transaction Protocol


CHAPTER 2 - IRTP HEADERS

   2.1 Header Format

      Each IRTP packet is preceded by an eight byte header depicted
      below. The individual fields are described in the following
      sections.

         0      7 8     15 16             31
         +--------+--------+--------+--------+
         | packet |  port  |     sequence    |
         |  type  | number |      number     |
         +--------+--------+--------+--------+
         |      length     |    checksum     |
         |                 |                 |
         +-----------------+-----------------+
         |                                   |
         |       optional data octets        |
         + . . . . . . . . . . . . . . . . . |

         Figure 2-1.  IRTP Header Format

   2.2 Packet Type

      Five packet types are defined by the IRTP. These are:

      packet type   numeric code

      SYNCH              0
      SYNCH ACK          1
      DATA               2
      DATA ACK           3
      PORT NAK           4

      The use of individual packet types is discussed in MODEL OF
      OPERATION.

   2.3 Port Number

      This field is used for the multiplexing and demultiplexing of
      packets from multiple user processes across a single IRTP
      connection.  Processes which desire to use IRTP must claim port
      numbers.  A port number represents a higher level protocol, and
      data to/from this port may be exchanged only with a process which
      has claimed the same port number at a remote host.  A process can
      claim multiple port numbers, however, only one process may claim
      an individual port number.  All port numbers are well-known.


Miller                                                          [Page 3]



RFC 938                                                    February 1985
Internet Reliable Transaction Protocol


   2.4 Sequence Number

      For each communicating pair of hosts, there are two sequence
      numbers defined, which are the send sequence numbers for the two
      ends.  Sequence numbers are treated as unsigned 16 bit integers.
      Each time a new transaction packet is sent, the sender increases
      the sequence number by one.  Initial sequence numbers are
      established when the connection is resynchronized (see Section
      4.3.)

   2.5 Length

      The length is the number of octets in this transaction packet,
      including the header and the data.  (This means that the minimum