RFC 3544 (rfc3544) - Page 2 of 14


IP Header Compression over PPP



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RFC 3544             IP Header Compression over PPP            July 2003


   In order to establish compression of IP datagrams sent over a PPP
   link each end of the link must agree on a set of configuration
   parameters for the compression.  The process of negotiating link
   parameters for network layer protocols is handled in PPP by a family
   of network control protocols (NCPs).  Since there are separate NCPs
   for IPv4 and IPv6, this document defines configuration options to be
   used in both NCPs to negotiate parameters for the compression scheme.

   This document obsoletes RFC 2509, adding two new suboptions to the IP
   header compression configuration option.  One suboption negotiates
   usage of Enhanced RTP-Compression (specified in [RFC 3545]), and the
   other suboption negotiates header compression for only TCP or only
   non-TCP packets.

   IPHC relies on the link layer's ability to indicate the types of
   datagrams carried in the link layer frames.  In this document nine
   new types for the PPP Data Link Layer Protocol Field are defined
   along with their meaning.

   In general, header compression schemes that use delta encoding of
   compressed packets require that the lower layer does not reorder
   packets between compressor and decompressor.  IPHC uses delta
   encoding of compressed packets for TCP and RTP.  The IPHC
   specification [RFC 2507] includes methods that allow link layers that
   may reorder packets to be used with IPHC.  Since PPP does not reorder
   packets these mechanisms are disabled by default.  When using
   reordering mechanisms such as multiclass multilink PPP [RFC 2686],
   care must be taken so that packets that share the same compression
   context are not reordered.

2.  Configuration Option

   This document specifies a new compression protocol value for the IPCP
   IP-Compression-Protocol option as specified in [RFC 1332].  The new
   value and the associated option format are described in section 2.1.

   The option format is structured to allow future extensions to the
   IPHC scheme.

   NOTE: The specification of link and network layer parameter
      negotiation for PPP [RFC 1661], [RFC 1331], [RFC 1332] does not
      prohibit multiple instances of one configuration option but states
      that the specification of a configuration option must explicitly
      allow multiple instances.  [RFC 3241] updates RFC 1332 by
      explicitly allowing the sending of multiple instances of the IP-
      Compression-Protocol configuration option, each with a different
      value for IP-Compression-Protocol.  Each type of compression
      protocol may independently establish its own parameters.



Koren, et al.               Standards Track


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