At times, you might see the following warning message in the report of your test:
Channel without SSRC information (probably issue with SDP) limited/skewed stats
This stems from a longstanding known issue in Chrome itself: When the Answer SDP doesn’t include SSRC information for the incoming channels, Chrome doesn’t produce any interesting/relevant statistics for that channel. This in turn means that testRTC cannot access the statistics of that channel to show meaningful information.
We’ve seen this happen mainly with PBX and SBC systems that connect WebRTC to SIP, and mainly on audio channels.
The approach we took in such a case, is to glean the most amount of data Chrome provides (which looks more like control channel stats and no media attached to it) and show the warning.
What can you do about it?
- Live with it. You can still check that the channel got open and validate that data is passing through that audio channel (though not how much and not find any network issues about it)
- Fix it on your end – make sure the SDP includes that missing SSRC