RFC 3544 (rfc3544) - Page 2 of 14
IP Header Compression over PPP
Alternative Format: Original Text Document
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