Cloud PBX only uses G711 codec on Polycom, can't change to anything else


Our users are complaining that calls using Polycom VVX 501 phones (with the latest firmware, sound much worse than calls through the desktop Skype app. We're not 100% sure how to debugg this -- one thought is that it's different codecs.


The Call Analytics portal shows that the desktop app uses modern codecs (e.g. x-msrta) but the Polycom phones only use G711Mu/G711A (and Cloud PBX / Cloud Voice rejects calls with any other codec).


e.g. here's our Polycom config that enables every single codec except 711Mu/G711A:




Calling using this always fails with error "FAILED - RESPONSE CODE: 488, Proxy side Media negotiation failed":




We've tried changing the "PrioritizedCodecsList" but it's not clear that does anything -- or even what the valid possible parameters are:

e.g. Set-CsIPPhonePolicy -PrioritizedCodecsList "ThisIsNotACodec" is accepted just fine.


Has anyone else seen this? (Or had very bad call quality on Polycom phones; but great quality on the desktop Skype app?)

5 Replies

Hi Nicholas,


It's currently on the Polycom VVX roadmap to add the SILK audio codec (which is predominantly the codec used in SfB Online). This is the codec Microsoft picked up in the Skype consumer acquisition.


Check out the following blog that covers what codecs to keep on VVX phones and what can be removed: 


Hope this helps,




Thanks -- though still unlear why Polycom phones with Skype for Business Online / Cloud Voice / Cloud PBX only seem to support PSTN calling with G.711 (they won't use G.722 at all). 


(And Polycom supports Opus -- which the SILK codec was rolled into -- I would be surprised if they ever added support for SILK.)


Based on the following screen grab (sandbox feature at the moment, NOT on GA code), they will:

SILK Support.JPG





Whoa; cool find!


Still odd that we can't call using anything but G.711 (and that the PrioritizedCodecsList preference for G.722 is essentially ignored).


Just updating this thread; we still can't get our Polycoms to use any codec other than G.711; and our users are complaining a lot about poor call quality.


Has anyone been able to get the PrioritizedCodecsList to work (that is, to prefer G.722, or use any other codec?)?