I've found a major problem when doing SIP REFER call transfer between two gateways.
Gateway A has a call (actually from FXS port) with gateway B, which runs CME.
Now gateway B wants to blind transfer this call, and attempts a call setup with callInfo(mode) set to redirect.
If the destination number is invalid, the transfer setup fails with ls_054.
That is fine but when re-conferencing the call to FXS port, there is one way audio, that is user on B cannot hear user on A.
That happens because in the early stage of the call transfer, gateway A sends SIP INVITE with SDP a=recvonly to B,
as confirmed by receiving an undocumented event ev_suspend_ack, and never sends a=sendrecv to resume two way audio.
When this happens, the leg state is lg_005.
If the call to be transferred is between users on GW A, there is no problem, as in fact there is no SIP at all.
How a script can resume audio in this scenario ?
I have tried few things to no avail, including a new transfer request toward the original endpoint, but it seems that IOS still consider the leg in transfer state:
%SIP-3-BADPAIR: Unexpected event 27 (SIPSPI_EV_CC_CALL_TRANSFER) in state 20 (SIP_STATE_INIT_XFER) substate 0 (SUBSTATE_NONE)
