Hey folks,
another quick one that came „into my way“…
Ribbon adds the parameter a=maxptime:60 into each SDP of each call going through the SBC Edge series.
Reason for that:
They are adding maxptime, because there were some rogue devices that would start a call using a ptime=20ms, put the call on hold and then start sending ptime=80ms.
This resulted in one-way audio and a ot of complaints from partners and customers. The SBC DSPs can only support a maximum ptime of 60ms and that is what Ribbon Edge SBCs are advertising to keep rogue devices from trying send RTP larger than 60ms.
Side info: maxptime does tell the peer device what the SBC maximum is. It is in no way telling the peer device to use a fixed ptime of 60ms.
If this maxptime:60 inserted by the SBC is causing trouble with your peer devices or PBXes… ->There is no way to replace this parameter with „nothing“ to get rid of it.
A confirmed and tested way from Ribbon would be to replace it with another SDP line, like a=ptime:20
In the usual case there are going to be two lines in SDP with „a=ptime:20“ in the SDP then. But in our testings I had no issues with that.
Hope this might help if you come accross an Edge SBC „forcing“ the maxptime of 60 😉
Cheers,
Enrico
