RFC 1613 (rfc1613) - Page 1 of 13

cisco Systems X

Network Working Group                                         J. Forster
Request for Comments: 1613                                       G. Satz
Category: Informational                                         G. Glick
                                                     cisco Systems, Inc.
                                                                  R. Day
                                                                   JANET
                                                                May 1994


                   cisco Systems X.25 over TCP (XOT)

Status of this Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.

Table of Contents

   1.  Introduction....................................................1
   2.  Conventions.....................................................2
   3.  Relationship Between XOT and X.25...............................2
   4.  Overall Packet Format...........................................3
   4.1   XOT Header....................................................4
   5.  TCP Connection, Port Number, and Logical Channel Numbers (LCNs).4
   6.  XOT Packets.....................................................5
   6.1   Virtual Circuit Setup and Clearing............................5
   6.2   Data and Flow Control.........................................6
   6.3   Interrupt, and Reset Packets..................................8
   6.4   Restart, DTE Reject, Diagnostics, and Registration............8
   6.5   PVC Setup.....................................................8
   7.  Acknowledgments................................................12
   8.  Security Considerations........................................12
   9.  References.....................................................12
  10.  Authors' Addresses.............................................13

1. Introduction

   It is sometimes desirable to transport X.25 over IP internets.  The
   X.25 Packet Level requires a reliable link level below it and
   normally uses LAPB.  This memo documents a method of sending X.25
   packets over IP internets by encapsulating the X.25 Packet Level in
   TCP packets.

   TCP provides a reliable byte stream.  X.25 requires that the layer
   below it provide message semantics, in particular the boundary
   between packets.  To provide this, a small (4-byte) XOT header is
   used between TCP and X.25.  The primary content of this header is a



Forster, Satz, Glick & Day