[asterisk-dev] AMR support in Asterisk-SVN (codec_amr.so)

Paul Bagyenda bagyenda at dsmagic.com
Mon Mar 5 19:26:12 MST 2007


  I've just done a first stab at AMR-NB (http://en.wikipedia.org/wiki/ 
Adaptive_Multi-Rate) support in Asterisk (SVN). It is tested with at  
least one device (Nokia E-series) and works fine. I hope this proves  
useful to people out there, comments/views welcome.

  Also I'd like to solicit views on how to get past one fairly  
significant issue: Asterisk does not seem to provide a clean way to  
get access to/provide out-of-band signalling info, such as what one  
gets via SDP on a SIP channel. For AMR this is important since this  
information tells us how the client intends to code the AMR packets  
(see RFC 3267, Sect. 8.1). A first glance seems to suggest we need  
some major surgery to some key modules to allow this...

  Because my implementation makes use of 3GPP TS 26.104, there is  
also the small matter of obtaining permission from 3GPP to 'publish'  
their code, if this ever makes it into Asterisk. (See http://www. 
3gpp.org/faq/faq_2005_2.htm#A3.8).  I am not including the 3GPP code  
in what is attached. Making things work is fairly simple:

- Get the code that is part of 3GPP TS 26.104
- Unpack it into a directory amr/ under the Asterisk codecs/ source  
- Add the attached Makefile to that directory.
- Apply the attached patch to Asterisk SVN code
- Unpack ast_amr.tgz over the asterisk source
- Type 'make' in the Asterisk top-level source tree

Will be glad to help privately on how to get things to work.


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