RFC 2509 (rfc2509) - Page 2 of 10
IP Header Compression over PPP
Alternative Format: Original Text Document
RFC 2509 IP Header Compression over PPP February 1999
used in both NCPs to negotiate parameters for the compression scheme.
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 [IPHC]
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 [MCML], 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. From the current specification of the
IPCP IP-Compression-Protocol configuration option [RFC 1332, p 6]
it follows that it can only be used to select a single compression
protocol at any time.
NOTE: [RFC 1332] is not explicit about whether the option
negotiates the capabilities of the receiver or of the sender. In
keeping with current practice, we assume that the option describes
the capabilities of the decompressor (receiving side) of the peer
that sends the Config-Req.
Engan, et. al. Standards Track