I'm testing SIP Trunking with SIP early offer.
I use CUCM 184.108.40.20600-1, with CUBE 15.1(4)M.
If I tick 'MTP required' on the SIP Trunk, it works fine. This always use MTP for every call so not scalable.
But, if I tick "Early Offer support ...(insert MTP if needed)" and "Send send-receive SDP in mid-call INVITE" on SIP Profile, then Call Forward completes but no speech both ways.
What I notice is CUCM doesn't invoke MTP for call forward at all.
When I test Call Transfer, CUCM invokes MTP briefly and release it after the call is transfered.
Is it a CUCM bug or did I miss any configuration for it to work?