rfc994.txt

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   --------------------+--- ISO NETWORK SERVICE PROVIDER -----^-----------------
                       |                                      |
                       |                                      |
                       |                                      |
           PROTOCOL    |  REFERENCE TO AIMS  -----------------+
                       |
        SPECIFICATION  |  REFERENCE TO ASSUMPTIONS -----------+
                       |                                      |
                       |                                      |
                       |                                      |
   --------------------+---SUBNETWORK SERVICE DEFINITION(S)---v-----------------

                 Figure 1: Interrelationship of Standards


1     Scope and Field of Application

   This International Standard specifies a protocol which is used to
   provide the Connectionless-mode Network Service as described in Ad-
   dendum 1 to the Network Service Definition Covering Connectionless-
   mode Transmission.  The protocol relies upon the provision of an
   underlying connectionless-mode service by real subnetworks and/or
   data links. The underlying connectionless-mode service assumed by the
   protocol may be obtained either directly, from a connectionless-mode
   real subnetwork, or indirectly, through the operation of an appropri-
   ate Subnetwork Dependent Convergence Function (SNDCF) or Protocol
   (SNDCP) over a connection-mode real subnetwork as described in ISO
   8648, Internal Organization of the Network Layer.






ISO 8473                                                        [Page 6]

RFC 994                                                    December 1986


      This Standard specifies:

      a)  procedures for the connectionless transmission of data and
          control information from one network-entity to a peer
          network-entity;

      b)  the encoding of the protocol data units (PDUs) used for the
          transmission of data and control information, comprising a
          variable-length protocol header format;

      c)  procedures for the correct interpretation of protocol control
          information; and

      d)  the functional requirements for implementations claiming
          conformance to the Standard.

      The procedures are defined in terms of:

      a)  the interactions among peer network-entities through the
          exchange of protocol data units;

      b)  the interactions between a network-entity and a Network Service
          user through the exchange of Network Service primitives; and

      c)  the interactions between a network-entity and an underlying
          service provider through the exchange of service primitives.

2     References

   ISO 7498, Information Processing Systems --- Open Systems Intercon-
   nection --- Basic Reference Model

   DIS 7498/AD1, Information Processing Systems --- Open Systems In-
   terconnection --- Addendum to ISO 7498 Covering Connectionless-mode
   Transmission

   ISO 8348, Information Processing Systems --- Telecommunications and
   Information Exchange between Systems --- Network Service Definition

   ISO 8348/AD1, Information Processing Systems --- Telecommunications
   and Information Exchange between Systems --- Addendum to the Net-
   work Service Definition Covering Connectionless-mode Transmission

   ISO 8348/AD2, Information Processing Systems --- Telecommunications
   and Information Exchange between Systems --- Addendum to the Net-
   work Service Definition Covering Network Layer Addressing*

   DIS 8648, Information Processing Systems --- Telecommunications and
   Information Exchange between Systems --- Internal Organization of the
   Network Layer




ISO 8473                                                        [Page 7]

RFC 994                                                    December 1986


   ISO 8509, Technical Report --- OSI Service Conventions

   ISO 9074, A Formal Description Technique based on an Extended State
   Transition Model
________________________________
     *At present, at the stage of Draft; publication anticipated in
      due course.















































ISO 8473                                                        [Page 8]

RFC 994                                                    December 1986


                          SECTION  ONE.  GENERAL

3     Definitions

3.1   Reference Model Definitions

   This document makes use of the following concepts defined in ISO 7498:

     (a)  End system

     (b)  Network entity

     (c)  Network layer

     (d)  Network protocol

     (e)  Network protocol data unit

     (f)  Network relay

     (g)  Network service

     (h)  Network service access point

     (i)  Network service access point address

     (j)  Routing

     (k)  Service

     (l)  Service data unit

3.2   Service Conventions Definitions

   This Protocol Standard makes use of the following terms from the OSI
   Service Conventions Technical Report (ISO TR 8509):

     (a)  Service provider

     (b)  Service user

3.3   Network Layer Architecture Definitions

   This Protocol Standard makes use of the following terms from the
   Internal Organization of the Network Layer (ISO 8648):

     (a)  Intermediate system

     (b)  Relay system

     (c)  Subnetwork



ISO 8473                                                        [Page 9]

RFC 994                                                    December 1986


3.4   Network Layer Addressing Definitions

   This Protocol Standard makes use of the following terms from ISO 8348/AD2,
   Addendum to the Network Service Definition Covering Network Layer
   addressing:

     (a)  Network addressing domain

     (b)  Network protocol address information

     (c)  Subnetwork point of attachment

3.5   Additional Definitions

   For the purposes of this Protocol Standard, the following definitions
   apply:

     (a)  derived PDU --- a protocol data unit whose fields are identical
          to those of an initial PDU, except that it carries only a segment
          of the user data from an N-UNITDATA request.

     (b)  initial PDU --- a protocol data unit carrying the whole of the
          userq data from an N-UNITDATA request.

     (c)  local matter --- a decision made by a system concerning its
          behavior in the Network Layer that is not prescribed or
          constrained by this Protocol Standard.

     (d)  network-entity title --- an identifier for a network-entity
          which has the same abstract syntax as an NSAP address, and which
          can be used to unambiguously identify a network-entity in an end
          or intermediate system.

     (e)  reassembly --- the act of regenerating an initial PDU from two
          or more derived PDUs.

     (f)  segment --- a distinct unit of data consisting of part or all
          of the user data provided in the N-UNITDATA request and delivered
          in the N-UNITDATA indication.

     (g)  segmentation --- the act of generating two or more derived PDUs
          from an initial or derived PDU. The derived PDUs together carry
          the entire user data of the initial or derived PDU from which they
          were generated.

                                       Note:
          It is possible that such an initial PDU will never actually be
          generated for a particular N-UNITDATA request, owing to the
          immediate application of segmentation.





ISO 8473                                                       [Page 10]

RFC 994                                                    December 1986


4     Symbols and Abbreviations

4.1   Data Units

     NSDU      Network Service Data Unit
     PDU       Protocol Data Unit
     SNSDU     Subnetwork Service Data Unit

4.2     Protocol Data Units
     DT PDU    Data Protocol Data Unit
     ER PDU    Error Report Protocol Data Unit

4.3     Protocol Data Unit Fields

     CS        Checksum
     DA        Destination Address
     DAL       Destination Address Length
     DUID      Data Unit Identifier
     E/R       Error Report Flag
     LI        Length Indicator
     LT        Lifetime
     MS        More Segments Flag
     NLPID     Network Layer Protocol Identifier
     SA        Source Address
     SAL       Source Address Length
     SL        Segment Length
     SO        Segment Offset
     SP        Segmentation Permitted Flag
     TL        Total Lengt
     TP        Type
     V/P       Version/Protocol Identifier Extension

4.4     Parameters

     DA      Destination Address
     QOS     Quality of Service
     SA      Source Address

4.5     Miscellaneous

     CLNP       Connectionless-mode Network Protocol
     NS         Network Service