RFC 1613 (rfc1613) - Page 2 of 13

cisco Systems X

RFC 1613                  X.25 Over TCP (XOT)                   May 1994


   length field, which is used to separate the X.25 packets within the
   TCP stream.

   In general, the normal X.25 protocol packet formats and state
   transition rules apply to the X.25 layer in XOT.  Exceptions to this
   are noted.

2. Conventions

   The following language conventions are used in the items of
   specification in this document:

      o   MUST, SHALL, or MANDATORY -- This item is an absolute
          requirement of the specification.

      o   SHOULD or RECOMMEND -- This item should generally be followed
          for all but exceptional circumstances.

      o   MAY or OPTIONAL -- This item is truly optional and may be
          followed or ignored according to the needs of the implementor.

   In some places in this document, there is parenthetical material
   labeled "DISCUSSION".  This material is intended to give
   clarification and explanation of the preceding text.

3. Relationship Between XOT and X.25

   When a networking device (a host, router, etc.) has an X.25 engine
   (i.e., protocol implementation), that engine  may be connected to
   interface(s) running LAPB, and/or to logical interface(s) running LLC
   or XOT/TCP/IP.  In general, the XOT layer itself is not at all
   sensitive to what kind of packets the X.25 engine passes to it.
   However, to improve interoperability between separate
   implementations, this document in some cases does specify behavior of
   the X.25 engine.

   While this document primarily discusses XOT from the perspective of
   switching X.25 traffic (i.e., connecting an X.25 Virtual Circuit
   between the local X.25 interfaces of two networking devices), this
   should not prevent a host from offering X.25 connectivity using XOT.

   The various X.25 standards may call a given packet type by a
   different name according to the assigned DTE/DCE role of the
   interface that originated the packet.  XOT is intended to be
   insensitive to the DTE/DCE role of the local interfaces at either end
   of an XOT TCP connection, so, for this document, the following terms
   are interchangeable unless stated otherwise:




Forster, Satz, Glick & Day