General Information on 3cx Codecs

[markpoulding]

Hi

We currently use 3cx phone system Version5.1.4510.0.

We currently have snom320 phones on the system.

I was wondering you can modify the codec on the phone system and the phones. Which takes perfence? should you keep them the same? Which codecs does anybody recommend?

Sorry for being very general on the message, however I did not feel you would need to much information on the server logs on this one. However if this is not the case my appologies in advance

Any help appricated

Many Thanks

Mark

 

[acrumpton]

The phone and system negotiate until they agree on a common codec.

We use G.711 and also use Snom 320's and have no issues.
I am looking at bandwidth conservation for our remote uses so would be interested in performance experience regarding G.729 or FR.GSM if anybody has it.

 

[SY]

Hi,

Technical manual is available. There is detailed description how PBX handles RTP streams.
You can find description of codec negotiations in RFCs: 3264, 3555, 4566. We don't break these rules and we are tolerant to interpretations except cases if rules are completelly ignored by remote party (device, VoIP provider etc.)
Codecs are handled by PBX automatically and you don't need to take care about it, until you have problems.
Default codec order is:
PCMU (most preffered)
PCMA
GSM
then
G729, iLBC, SPEEX

Default order(set) of codecs is configurable for VoIP provider lines (property of "VoIP provider" object).

Regards

 

[xray]

Stepan,

Regarding your statement about codec order, we're finding that 3CX will not allow our VOIP clients (we've tried several) to select the GSM codec. We've even configured the VOIP client to ONLY allow/offer the GSM codec during negotiations, but then the calls simply have NO audio whatsoever. The 3CX system seems to "want" to use PCMU.

Is there a configuration step that we missed on the 3CX end to allow the use of this codec?

Thank you.

 

[SY]

Stepan,

Regarding your statement about codec order, we're finding that 3CX will not allow our VOIP clients (we've tried several) to select the GSM codec. We've even configured the VOIP client to ONLY allow/offer the GSM codec during negotiations, but then the calls simply have NO audio whatsoever. The 3CX system seems to "want" to use PCMU.

Is there a configuration step that we missed on the 3CX end to allow the use of this codec?

Thank you.

xray,

These statements are true and they are true since v3.0 (~May, 2007 except statement regarding G729, it supported since v5).
3CXMediaServer.trace.log (in verbose mode) still shows everything related to SDP negotiations. You can post it here and then we will be able to find the reason of this issue.
Please don't post the megabytes of information. Just stop media server service, wait for few seconds then start it again and replicate problematic call scenario.

Thanks