<?xml version="1.0" encoding="utf-8"?>

<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->

<!-- This component and the accompanying materials are made available under the terms of the License 

"Eclipse Public License v1.0" which accompanies this distribution, 

and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->

<!-- Initial Contributors:

    Nokia Corporation - initial contribution.

Contributors: 

-->

<!DOCTYPE concept

  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

<concept id="GUID-BAFF62FA-55D9-5CEE-8747-FF4E4BEC4042" xml:lang="en"><title>PPP

Compression Plugins Overview</title><shortdesc>This topic describes the Point-to-Point Protocol (PPP) Compression

Plugins collection. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<section id="GUID-D4738F9B-3C83-47A8-A4E2-042E75A55457"><title>Purpose</title> <p>This collection contains the three compression

control protocols available for use with the <xref href="GUID-602026AB-ABD6-5937-A8FB-EFB21EBEEEC3.dita">Point-to-Point

Protocol</xref> component. </p> </section>

<section id="GUID-1A342A77-AA6C-44C1-893A-E42E103B9B04"><title>Architecture</title> <p>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. </p> <p>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. </p> <p>The interface between the Symbian

platform implementation of PPP and the compression plugins is not published.

New compression plugins cannot be created. </p> <p>Plugins are loaded when

a <i>config request</i> 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. </p> <p>The

plugins are configured in the <filepath>ccp.ini</filepath> file. The Point-to-Point

Protocol component reads the <filepath>ccp.ini</filepath> file on startup

and checks that the plugins exist. The Point-to-Point Protocol component does

not load the plugins on startup. </p> </section>

<section id="GUID-63A9C70B-380A-4296-9730-AECFB830D1EE"><title>Components</title> <p>Symbian platform provides three compression

plugins for use with the Point-to-Point Protocol component: </p> <ul>

<li id="GUID-52E0A1C0-E43B-5960-BBEA-BD0C6CDFB6F3"><p>Predictor-1 PPP compressor </p> <p>This

compression control is used for high speed data and implements RFC 1978. </p> </li>

<li id="GUID-725A7F96-BD81-5E08-B0AC-AEDF5BD32042"><p>Microsoft Point-To-Point

Compression (MPPC) </p> <p>This compression control implements RFC 2118. </p> </li>

<li id="GUID-6B1A4C56-C5EC-5B49-8D29-2A7DC70A1B1F"><p>Stac LZS Compression </p> <p>This

compression control is optimised to compress efficiently and implements RFC

1974. The Symbian platform implementation does not include the <i>multiple

history buffers</i> feature of the protocol. </p> </li>

</ul> </section>

<section id="GUID-78E5697B-23D5-4425-970C-ECCB44CA9D20"><title>Using PPP Compression Plugins</title> <p>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. </p> </section>

</conbody></concept>