S20: Codec/transcoding problem with call transfer / forwarding

Hi, we have a massive problem with call transfer / call forwarding with a Yeastar S20. The scenario:

  1. Mobile1 calls Yeastar -> working
  2. Yeastar calls Mobile2 on Line2 -> working
  3. Transfer Mobile1 to Mobile2 -> One way audio, Mobile1 can't hear anything

The same thing happens when forwarding a client to a mobile number - when the call is recieved by Mobile2, the calling party can't hear anyhting.

We checked the PCAP trace as we thought of NAT problems, but all SIP and RTP packages look well and the Yeastar S20 gets all audio packages.

What we noticed: The two calls always use different codecs (eg. G.722 and G.711). When we only allow 1 codec in Yeastar trunk, everything works fine.

Yeastar LVL1 support told us this is a known bug. But how can this everyday scenario be a known unfixed bug?!

What kind of bug is this and how can we fix it (without only allowing 1 codec)?

Thanks for every help!


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