We have Freeswitch acting as a SIP platform, with internects with various UK carriers (including BT) on one side, with customer PBX connected from the other side. We have an intermittent problem where a call comes into FS from the PSTN and is routed to the customer PBX (and Avaya), with the call then transferred back, via Freeswitch, then the PSTN to another phone number. Sometimes the original caller continues to hear ringtone after the transfer-destination has answered (and no conversation is possible). I have attached Wireshark SIP flows for the scenario where this works and the one where transfer does not complete properly (labelled in red, above each ladder diagram, "BROKEN", on the left and "WORKING" on the right). In the working example, we see RTP BEFORE the REFER. In the non-working example, RTP is sent AFTER the BYE. 1. We don't understand why the Avaya sends messages in a different order, on different occasions, for the exact same operation? 2. Should Freeswitch be able to handle both the scenarios shown in the attached image? 3. Are there any config or dialplan settings which can be used to help fix this? NOTE: We also have other issues with call transfers in general, whereby the transfer succeeds, but there is no audio heard by the transferee. Thanks
