Tag Archives: codecs

IP Telephony Codecs

My first stumbling block when installing and trying to get Asterisk PBX working were the codecs and mismatching. If both ends of a connection can’t negotiate the same codec, the call won’t complete.

I grabbed the recommended asterisk config for gizmo5 and when attempting to place a call to my gizmo call-in number which should have landed it into my PBX I got the following errors and it disconnected:

[Jan 14 01:40:20] WARNING[23334] channel.c: Unable to find a codec translation path from 0x400 (ilbc) to 0x4 (ulaw)
[Jan 14 01:40:21] WARNING[23334] channel.c: Unable to find a codec translation path from 0x400 (ilbc) to 0x2 (gsm)

When trying to determine what went wrong, I found that ilbc is no longer part of Asterisk config, and ulaw is actually G.711 using the  µ-law algorithm. I also found that one can add iLBC codec to Asterisk by agreeing to a license agreement and running a script.

So hence this blog post, so I can document what I’ve learned and hopefully prevent someone else from having same frustrations.

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