Codec Order Question

[MAWWICT]

Hi all,

Just a quick question. Our new SIP provider has told us that their preferred voice Codec is G711-alaw (Which I believe is called PCMA in some areas of the 3CX admin area)
For the best audio performance is it recommended that I set the preferred Codec as G711-alaw/PCMA in all areas of the 3CX admin area? (On the SIP trunk itself, Under 'Settings' / 'Codecs' and on each desk phone) Or can the order be mixed to ensure that any internal calls always have the best voice quality?
Our 3CX is installed on our private Azure environment, with an SBC running within our on-site server room, if that makes any difference.

Thanks

 

[Alphabetic]

Check this out if you havent see it already https://www.3cx.com/docs/sip-trunk-codecs-sdp/

 

[SteveITS]

@MAWWICT You can adjust codecs, just be aware that transcoding (from one code to another) happens in real time on the 3CX server, and generally impacts quality. So usually one wants to use the codec your trunk provider is using. It would be handy if there were separate options for internal or external calls but that's not how it works.

 

[N_G]

Edit: OK, so i have a better answer for you.

You just have to set the codec priority at trunk level to G711. No need to do it at endpoint level.

This document about Codecs and Codec negotiation has been updated.

 

[SteveITS]

There is no need to adjust anything because if your provider prefers this codec then during negotiation it will sate this and it will be used automatically. So try first without changing anything

Hi Nick, just to clarify, that's the case for outbound calls also? So if a 3CX mobile app or phone is set to use Opus but the SIP trunk does not have Opus and is set to use PCMU, then the outbound call will negotiate PCMU on the app and trunk?

In other posts here I've seen advice to reorder the extensions to match the trunk.
Thanks,

 

[N_G]

@SteveITS I am working on getting you a detailed answer, possibly a blog post to explain exactly how it works.