I’m a contractor trying to fix an integration the previous team left half-finished. We have a BYOC-Premises trunk connecting Genesys Cloud to a very old legacy PBX. The PBX only supports the G.729 codec due to bandwidth constraints.
Inbound calls from the PBX to Genesys work fine. However, when a Genesys agent tries to blind-transfer a call back to the PBX, the transfer fails instantly with a ‘SIP 488 Not Acceptable Here’ error. Looking at the Edge PCAP, the initial inbound leg negotiates G.729, but on the transfer, the Edge’s INVITE to the PBX forces an SDP offer with only PCMU (G.711). I have G.729 set as the only allowed codec in the Trunk configuration! Why is the Edge ignoring the Trunk setting and forcing G.711 on transfers?
This sounds like a transcoder exhaustion issue or a ‘Media Bypass’ conflict. When we built our custom agent desktop, we noticed that if ‘Media Bypass’ is enabled on the WebRTC phone trunk, the Edge tries to pass the agent’s browser codec (which is usually Opus or G.711) directly to the destination.
If your PBX strictly requires G.729, the Edge must anchor the media to transcode it. If the Edge doesn’t have available DSP resources to transcode Opus to G.729 at that exact moment, it might just offer G.711 hoping the PBX will accept it. Disable Media Bypass on the agent phones and see if the Edge starts offering G.729 again.
I run a local user group and this came up last month! There’s actually a hidden setting on the BYOC Trunk under the ‘Media’ tab called ‘Transcoding’.
By default, Genesys Cloud tries to avoid transcoding if possible. If the original caller (e.g., from the PSTN carrier) came in on G.711, and the agent transfers the call to the PBX, the Edge might try to pass that original G.711 stream through. You need to ensure the ‘Transcoding’ flag on the PBX trunk is set to ‘Always’ (or strictly enforce the codec list) so the Edge knows it’s obligated to convert that G.711 caller leg into G.729 before sending it to the legacy PBX.