Adding iLBC to Asterisk
The Internet_Low_Bit_Rate_Codec is a freely-available stream processor that works really well with human voice compression. It typically delivers clear voice signals in ~16kb of bandwidth. For that reason, it has become very popular in Asterisk implementations. Unfortunately there have been license disputes in the open source community and the Asterisk maintainers have removed iLBC from the source tree. But you can still use it if you know a few tricks.
Build from Source
Depending on your distribution, you might need to build Asterisk from source. I'm using Red Hat Enterprise Linux 4, and Asterisk isn't one of the available packages. So here's how I did it. (I'm not going to detail how to install the kernel source, kernel headers, etc... See your distribution's instructions for that).
cd /usr/src
tar xzf asterisk-1.4.25.tar.gz
cd asterisk-1.4.25
# the following lines overcome a compile problem in
# RedHat Enterprise Linux 4 where the iLBC source isn't
# found by make, even after it is downloadeded.
# Your distro might not need this, so skip down as needed
# get the ILBC source
cd contrib/scripts/
./get_ilbc_source.sh
cd ../..
cd codecs
#the codecs/ilbc directory is empty, so make it a symlink to
#the contrib/scripts/codecs/ilbc directory
rm -rf ilbc
ln -s /usr/src/asterisk-1.4.25/contrib/scripts/codecs/ilbc ilbc
cd ..
Then...
./configure
make menuconfig
The menuconfig option gives a menu-based approach to configuring the source. ILBC is disabled by default, so we need to enable it. Here is what the main screen looks like:
**************************************************
Asterisk Module and Build Option Selection
**************************************************
Press 'h' for help.
1. Applications
2. Call Detail Recording
3. Channel Drivers
---> 4. Codec Translators
5. Format Interpreters
6. Dialplan Functions
7. PBX Modules
8. Resource Modules
9. Voicemail Build Options
10. Compiler Flags
11. Module Embedding
12. Core Sound Packages
13. Music On Hold File Packages
14. Extras Sound Packages
Go into option 4 and enable codec_ilbc, like this:
**************************************************
Asterisk Module and Build Option Selection
**************************************************
Press 'h' for help.
[*] 1. codec_adpcm
[*] 2. codec_alaw
[*] 3. codec_a_mu
[*] 4. codec_dahdi
[*] 5. codec_g726
[*] 6. codec_gsm
[*] 7. codec_ilbc
[*] 8. codec_lpc10
XXX 9. codec_speex
[*] 10. codec_ulaw
Adaptive Differential PCM Coder/Decoder
Then backout and goto option 5 to enable format_ilbc
**************************************************
Asterisk Module and Build Option Selection
**************************************************
Press 'h' for help.
[*] 1. format_g723
[*] 2. format_g726
[*] 3. format_g729
[*] 4. format_gsm
[*] 5. format_h263
[*] 6. format_h264
[*] 7. format_ilbc
[*] 8. format_jpeg
[*] 9. format_ogg_vorbis
[*] 10. format_pcm
... More ...
Raw iLBC data
After that, I recommend scanning through the other options to see if there are other things you need. In particular, options 12-14 contain some helpful soundfiles.
Exit out of the menuconfig and press 'S' to save your options. After that, its a fairly standard linux build process:
make
make install
make samples
make progdocs