1-) Phone1 calls a PSTN phone number (5555555)
Phone 1 (ext1001)-----SIP---->CUCM----SIP--->CUBE--- SIP-->PSTN
2-) Call is established and phone 1 initiates a transference to another PSTN number (6666666) putting 5555555 on hold
2-) phone 1 establishes the call with 666666 and when the transfer button is pushed:
a) with media temination point checked in the CUCM sip trunk to CUBE the transfer works and the call between 5555555 and 6666666 is connected.
b) without media termination point checked the transfer works and the call is connected but with no audio, just dead air.
Can somebody explain me how this comunication works? How is the call flow? Why I need MTP required checked?
I would aprecitte any help. Thank you in advance.
There are several reasons MTP can get invoked as described in the SRND, etc. Most common ones are:
Early Offer negotiation (i.e. not supported on gen1 phones)
Supplementary features not supported
To figure out why MTP is invoked you'd need to pull CCM logs and search for the call and reasons MTP is invoked.
Actually I found the fix in another thread.
On CUCM go to System--- Service Parameters and look for "Duplex Streaming Enabled" set this to TRUE and restart the CCM service
can you share the CUBE config?
also debug ccsip message for a failed call (MTP Unchecked) and a working call (MTP checked)?
does this issue occur when SCCP phones registered in CUCM trying to do the call transfer?
in the SIP profile applied to the involved SIP phones, RFC 2543 Hold is checked under 'Parameters used in Phone'? if so, can you uncheck and try once?
If RFC 2543 Hold is unchecked, then in the SIP profile applied to SIP Trunk to CUBE, can you check "Send send-receive SDP in mid-call INVITE" and check the behavior?
All these to be tried with MTP unchecked in the SIP Trunk.
If "Send send-receive SDP in mid-call INVITE" does not do the trick then you can set this option "Duplex Streaming Enabled" to True from the service parameter it will make CUCM to send a=sendrecv.
Sorry for late answer
I tried with MTP unchecked
RFC 2543 hold is unchecked, "send send-receive SDP in mid call INVITE" didn't work
No, that's not quite right, *ideally* you should not need any MTP to bridge the connections, and the one that handles the intelligence to allocate it, would be CUCM, not the GW. The GW can also only be used as MTP if it has been configured and registered as an MTP resource.