[asterisk-users] Why doesn't Asterisk try to prevent transcoding

Ryan Wagoner rswagoner at gmail.com
Sat Dec 14 21:31:31 CST 2013

Let's say I have two devices configured and the follow call scenarios occur.


Polycom phone with g722,ulaw,alaw,g729


Polycom phone with g722,ulaw,alaw,g729

101 dials 100 -> ulaw to ulaw is chosen
100 dials 101 -> g722 to ulaw is chosen

Ideally when 100 dials 101 ulaw would be chosen since it is the common
format. Looking into this deeper

Device 100 sends INVITE to Asterisk offering g722,ulaw,alaw,g729
Asterisk sends INVITE to device 101 offering ulaw
Device 101 sends 200 OK to Asterisk offering ulaw
Asterisk sends 200 OK to device 100 offering g722,ulaw

I can prevent transcoding by adding SIP_CODEC_INBOUND=ulaw to the dialplan
for extension 101. This causes Asterisk to send 200 OK to device 100
offering ulaw. Am I missing why Asterisk wouldn't just offer the highest
priority codec they have in common to prevent transcoding?

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