PPP Compression Plugins Overview

Purpose

This collection contains the three compression control protocols available for use with the Point-to-Point Protocol component.

Architecture

After a Point-to-Point Protocol link has been established, optional facilities such as data compression may be negotiated. Compression is used over a point-to-point link to increase throughput. Increasing the throughput is important when low bandwidth transport media is used. An example of low bandwidth transport media is GSM data at 9.6kbit/s.

The Point-to-Point Protocol includes the Compression Control Protocol (CCP) to handle the negotiation of the compression on the link. The Compression Control Protocol is defined by RFC1962.

The interface between the Symbian platform implementation of PPP and the compression plugins is not published. New compression plugins cannot be created.

Plugins are loaded when a config request packet is received which requests the plugin as part of the Compression Control Protocol. Each direction on the link can have zero or one plugins loaded. A different plugin can be used in each direction.

The plugins are configured in the ccp.ini file. The Point-to-Point Protocol component reads the ccp.ini file on startup and checks that the plugins exist. The Point-to-Point Protocol component does not load the plugins on startup.

Components

Symbian platform provides three compression plugins for use with the Point-to-Point Protocol component:

• Predictor-1 PPP compressor

  This compression control is used for high speed data and implements RFC 1978.

• Microsoft Point-To-Point Compression (MPPC)

  This compression control implements RFC 2118.

• Stac LZS Compression

  This compression control is optimised to compress efficiently and implements RFC 1974. The Symbian platform implementation does not include the multiple history buffers feature of the protocol.

Using PPP Compression Plugins

The components in this collection are not used directly by client application software. The components are loaded as part of the negotiation of the Point-to-Point protocol.