Call Quality Issues through SIP trunks

[plasticphone]

Hello - Running an up to date 3cx install - Debian server on Hyper-V with appropriate settings on premise. Current internet is a commercial fiber 50/5(up).

I am making outbound calls to PSTN numbers and the call quality is sub-par. Inbound calls from external numbers seem to suffer as well. What do I mean..sometime there is chop but it just doesn't sound like a call should. The system being replaced is on a POTS hunt group and the call quality is not comparable. It works, but I am not going live until I work this out.

I can make calls from my remote home office via HD codecs and the call quality is beautiful, but as soon as the SIP trunk is involved we have issues. Internal calls are great whether on the local network or not. External calls are the problem. I have tried both Flowroute and Callcentric but the results have been similar. I have a Sonicwall with QoS implemented. The external codecs are 711 with high priority. Through a Wireshark dump I noticed that the handset (Yealink T46S) on my remote office attempts to connect via 722 even on external calls. It hits the server with 722 and then the server hits the SIP provider with 711. I am wondering if this is an issue with transcoding? I refuse to lose the HD audio by downgrading to 711 all the time. The PBX does not deliver audio.

In a nutshell - the connection does not seem be an issue, the SIP provider does not seem to be the issue. Is transcoding the issue?

 

[leejor]

Through a Wireshark dump I noticed that the handset (Yealink T46S) on my remote office attempts to connect via 722 even on external calls. It hits the server with 722 and then the server hits the SIP provider with 711. I am wondering if this is an issue with transcoding? I refuse to lose the HD audio by downgrading to 711 all the time.

I think you have pinpointed the problem already. The set is using one Codec, and the trunk, another, therefore transcoding is probably a reality. There have been a number of posts about the same issue. To confirm, change the codec order on one set, so that the first choice Codec is the same as used by your provider.

https://www.3cx.com/community/threads/call-quality-transcoding.67494/

 

[JohnS_3CX]

The above thread link should give you all the information you need to be aware of.

 

[plasticphone]

I see this but it's not a solution for me.

Is there any phone or setup that can distinguish between internal / external and change to codec priority?

I can't imagine transcoding audio is very CPU intensive, but has anyone else seen improvement by upgrading CPU power? Can anyone tell me if the transcoding operation is multi-threaded?

 

[Alphabetic]

Settings > General

 

[JohnS_3CX]

The media server is multithreaded. As for the load, it's a relationship between how powerful the CPU is VS how many transcoded calls are going through at a given time.

 

[plasticphone]

Thanks for the feedback. I have re-aligned the codecs to see if there is any improvement. From my Yealink handset it is still trying to negotiate 722, but I will try on premise from a Grandstream handset.

I'm only using 1 call right now for testing so I doubt CPU should be an issue. @3cx, can you confirm many customers are using transcoding without issue for G711 calls?

 

[JohnS_3CX]

We can confirm that the system will successfully convert between our supported codecs when used as intended (with supported devices).

Note: transcoding a high quality codec to G.711 will probably sound worse to most people than a pure G.711 call. With this in mind, you may find you have better results if you remove G.722 from everywhere and set G.711 at the highest priority for all devices in their provisioning, all trunks in their options, and PBX General Settings under internal/external calls. Remember to reprovision phones to receive the changes. The above assumes that the provider will only go as high as G.711

If you set everything to run with the best codec your provider supports, transcoding will not even take place except in extreme cases. Read my last paragraph here again:
https://www.3cx.com/community/threads/call-quality-transcoding.67494/post-293490

 

[plasticphone]

So the end result is, if you want to make calls on a PSTN you cannot use HD on the rest of your system? Thats a pretty serious limitation.

 

[JohnS_3CX]

You can but, transcoding will take place. I would not call it a serious limitation.

 

[plasticphone]

Is there any way you can tell the handset to initiate G711 on outbound calls without making G711 the priority?