RFC 3153 (rfc3153) - Page 1 of 9

PPP Multiplexing

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Network Working Group                                      R. Pazhyannur
Request for Comments: 3153                                        I. Ali
Category: Standards Track                                       Motorola
                                                                  C. Fox
                                                           Cisco Systems
                                                             August 2001


                           PPP Multiplexing

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.

Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

   This document describes a method to reduce the PPP (Point-to-Point
   Protocol) framing overhead used to transport small packets over slow
   links.

1. Description

   The method, PPP Multiplexing, sends multiple PPP encapsulated packets
   in a single PPP frame.  As a result, the PPP overhead per packet is
   reduced.  PPP encapsulation (for example with PPP in HDLC framing)
   adds several bytes of overhead: a HDLC flag (at least one to separate
   adjacent packets), the Address (0xFF) and Control (0x03) field bytes,
   a two byte PPP Protocol ID, and the two byte CRC field.  Even with
   the Address and Control Fields negotiated off and the PPP Protocol ID
   compressed, each PPP encapsulated frame will include four bytes of
   overhead.  When PPP frames are tunneled, as in L2TP [1], the L2TP
   overhead per PPP frame is significant.

   The key idea is to concatenate multiple PPP encapsulated frames into
   a single PPP multiplexed frame by inserting a delimiter before the
   beginning of each frame.  The description of the delimiters is
   provided in Subsection 1.1.  The delimiters are used by the
   demultiplexor to separate the PPP frames within the multiplexed
   frame.  Each PPP encapsulated frame within the multiplexed frame is
   called a PPP subframe.



Pazhyannur, et al.          Standards Track
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