Transport Multiplexing Protocol (TMux)
RFC 1692

Document Type RFC - Historic (August 1994; No errata)
Was draft-cameron-tmux (individual)
Last updated 2018-06-09
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Network Working Group                                         P. Cameron
Request for Comments: 1692                  Xylogics, International Ltd.
Category: Standards Track                                     D. Crocker
                                                  Silicon Graphics, Inc.
                                                                D. Cohen
                                                               J. Postel
                                                             August 1994

                 Transport Multiplexing Protocol (TMux)

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.


   One of the problems with the use of terminal servers is the large
   number of small packets they can generate. Frequently, most of these
   packets are destined for only one or two hosts.  TMux is a protocol
   which allows multiple short transport segments, independent of
   application type, to be combined between a server and host pair.


   This specification is the result of the merger of two documents: the
   original TMux proposal which was the result of several discussions
   and related initiatives through IETF working groups; and IEN 90 [1]
   originally proposed by Danny Cohen and Jon Postel in May 1979.

Applicability Statement

   The TMux protocol is intended to optimize the transmission of large
   numbers of small data packets that are generated in situations where
   many interactive Telnet and Rlogin sessions are connected to a few
   hosts on the network.  In these situations, TMux can improve both
   network and host performance.  TMux is not intended for multiplexing
   long streams composed of large blocks of data that are typically
   transmitted by such applications as FTP.

   The TMux protocol may be applicable to other situations where small
   packets are generated, but this was not considered in the design.

Cameron, Crocker, Cohen & Postel                                [Page 1]
RFC 1692                          TMux                       August 1994

   The use of the TMux protocol in any other situation may require some

1. Introduction

   When network designers consider which protocols generate the most
   load, they naturally tend to consider protocols which transfer large
   blocks of data (e.g., FTP, NFS).  What is often not considered is the
   load generated by Telnet and Rlogin because of the assumption that
   users type slowly and the packets are very small.  This is a grave
   underestimation of the load on networks and hosts which have many
   Telnet and Rlogin ports on multiple terminal servers.

   The problem stems from the fact that the work a host must do to
   process a 1-octet packet is very nearly as much as the work it must
   do to process a 1500-octet packet.  That is, it is the overhead of
   processing a packet which consumes a host's resources, not the
   processing of the data.

   In particular, communication load is not measured only in bits per
   seconds but also in packets per seconds, and in many situation the
   latter is the true performance limit, not the former.  The proposed
   multiplexing is aimed at alleviating this situation.

   If one assumes that most users connected to a terminal server will be
   connecting to only a few hosts, then it should be obvious that the
   network and host load could be greatly reduced if traffic from
   multiple users, destined for the same host, could be sent in the same

   TMux is designed to improve network utilization and reduce the
   interrupt load on hosts which conduct multiple sessions involving
   many short packets.  It does this by multiplexing transport traffic
   onto a single IP datagram [2], thereby resulting in fewer, larger
   packets.  TMux is highly constrained in its method of accomplishing
   this task, seeking simplicity rather than sophistication.

2. Protocol Design

   IP hosts may engage in the use of TMux transparently, and may even
   switch back and forth between use of TMux and carriage of transport
   segments in the usual, independent IP datagrams.

   TMux operates by placing a set of transport segments into the same IP
   datagram.  Each segment is preceded by a TMux mini-header which
   specifies the segment length and the actual segment transport
   protocol.  The receiving host demultiplexes the individual transport
   segments and presents them to the transport layer as if they had been

Cameron, Crocker, Cohen & Postel                                [Page 2]
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