Description:

The LZS-DCP Stac Data Compression Protocol (LZS-DCP) provides an algorithm for compressing PPP encapsulated packets. This LZS version utilizes a DCP header.

RFC 1967:

This protocol is an enhanced version of the non-DCP (Option 17) PPP Stac LZS compression protocol, and will be referred to as the LZS-DCP Compression Protocol.

This publication of the LZS-DCP compression protocol is in the interest of providing a common compression protocol for Stac-LZS, and to provide features that are not available with the LZS compression protocol. Some of the differences between the LZS-DCP and LZS (compression type 17) protocols are as follows:

1. LZS-DCP provides an option which allows packets containing uncompressible data to be transferred without requiring the compression history to be cleared, potentially allowing a higher compression ratio. A bit is included in the DCP header to indicate whether the packet contains compressed or uncompressed data.
2. LZS-DCP uses reset request and acknowledgment bits in the DCP header that is included on each packet rather than using CCP's reset request and acknowledge packets, which may result in fewer discarded data packets during the REQ/ACK handshake.
3. LZS-DCP allows simultaneous use of both sequence numbers and the LCB for compression error detection.

The Stac LZS compression algorithm supports both single and multiple compression histories. A single compression history will require the minimum amount of memory to implement, but may not provide as much compression as a multiple history implementation.

Often, many streams of information are interleaved over the same physical link. Each virtual connection will transmit data that is independent of other virtual connections. Using multiple compression histories can improve the compression ratio of a communication link by associating separate compression histories with separate virtual links of communication.

Before any LZS-DCP packets are communicated, PPP MUST reach the Network-Layer Protocol phase, and the CCP Compression Control Protocol MUST reach the Opened state.

Packet format:

Glossary:

RFCs:

[RFC 1967] PPP LZS-DCP Stac Compression Protocol (LZS-DCP).