SIP SIMPLE Client SDK

= Echo cancellation =

[[TOC(Design*, depth=1)]]

SIP SIMPLE client is a Python software library that allows for easy development of Internet communications end-points based on SIP and related protocols for voice, rich presence, session based instant messaging (IM), file transfers and desktop sharing. Other media types can be easily added by using an extensible high-level API. SIP SIMPLE client uses [http://www.pjsip.org/pjmedia/docs/html/index.htm PJSIP media library] for audio processing (sound card abstraction, audio codec and acoustic echo cancellation).

For more information see http://sipsimpleclient.com

== Background ==

The present implementation of the echo canceller from PJSIP media library is not performing to the desired level of quality. Practically, the speaker phone function of SIP SIMPLE client is not reliable and not performing satisfactory unless a headset is used.

[[Image(http://www.pjsip.org/images/media-flow.jpg)]]

== Project goal ==

Replace the existing AEC from Pjmedia library (what is displayed as echo.h in the above diagram) with a better solution to provide a high quality speakerphone user experience.

The developed software will be released under an open source licence and distributed with SIP SIMPLE client library.

The deliverable is C written program that can be applied to the pjsip  cvs trunk 1.0 with the '''patch''' command.

== Resources ==

General

 * Digital Signal Processing http://www.dsptutor.freeuk.com/

 * Graduation thesis about AEC  http://innovexpo.itee.uq.edu.au/2003/exhibits/s365914/

 * DSP concepts: http://www.bores.com/courses/intro/basics/index.htm

PJSIP media library

 * PJSIP media library http://pjsip.org, used by this project, AEC is implemented based on the Speex library, the code in pjsip/pjmedia/src/pjmedia/echo_speex.c 

 * Media flow - http://trac.pjsip.org/repos/wiki/media-flow

Speex AEC

 * Speex project http://speex.org, the echo canceller implements AEC based on the MDF algorithm, see speex/libspeex/mdf.c. A test client is available in speex/speexclient, this has been used for developing pjmedia equivalent

 * http://speex.org/docs/api/speex-api-reference/group__SpeexEchoState.html

Andree Adrian AEC

 * Draft AEC http://www.andreadrian.de/echo_cancel/draft-aec-03.txt

 * http://www.andreadrian.de/intercom/ implements AEC based on NLMS algorithm (not tested yet)

 * Kphone AEC implemented using above AEC http://www.andreadrian.de/echo_cancel/ (not tested)