Alcatel Carrier Internetworking Solutions Omni Switch/Router - Manual (Page 940)

Page 30-2
Data Compression
RFC 1974 specifies the use of STAC-LZS compression with PPP. Data compression allows the
payload of a PPP packet, including the protocol ID, to be compressed, saving valuable
bandwidth. Compression is negotiated during the Network phase using Compression Control
Protocol (CCP), which includes the negotiation of a data compression algorithm and any
parameters specific to the algorithm. Once negotiated, all data packets (i.e., non-control
protocol packets) from all successfully negotiated protocols are compressed before
transmission. The compression algorithm negotiated includes any mechanism for
synchronizing the compressor and decompressor.
STAC-LZS’s maximum data compression ratio is 30:1. The LZS algorithm is optimized to
compress all file types as efficiently as possible. Even string matches as short as two octets are
effectively compressed. The STAC-LZS compression algorithm supports both single
compression history communication and multiple compression history communication.
Often, many streams of information are interleaved over the same link. Each virtual link will
transmit data that is independent of other virtual links. Using multiple compression histories
can improve the compression ratio of a communication link.
Multi-Link PPP
The main limitation of PPP is implicit in its name: Point-to-Point Protocol, meaning that it is
limited to connecting two points over a single physical connection. Multi-Link PPP (MLPPP)
extends the functionality of PPP by combining multiple PPP links into a single logical data
pipeline, called a “bundle.” Unlike standard PPP, MLPPP is not limited to individual links;
both physical and virtual connections can be bundled.
Traditional vs. Multilink PPP
Traditional PPP Multilink PPP
PPP
Entity
PPP
Entity
ISDN
Link 1
ISDN
Link 2
ISDN
Link N
Direct
Link 1
Direct
Link 2
Overflow
Link 1
Overflow
Link 2
T1/E1
ISDN
T1/E1
ISDN
PPP
Entity
Perm.
Link
- or -
T1/E1,
USP
Rotary
Links