Last time I was troubleshooting for soft phone call failure issue, where it gets a busy after a ring.
IP Communicator --> CUCM 9.1 --> SIP Trunk (early offer) --> SME 9.1 --> MGCP GW --> PBX
In the CCM traces I see soft phone was looking for an MTP resource, I added a MTP in MRGL and the issue got resolved. The SRND also suggest to add an MTP in MRGL for soft phone like legacy devices to make calls work with SIP early offer.
1. Could someone tell me what's the exact reason for the soft phone requires an MTP?
2. An MTP is in place, when there is an capabilities mismatch, most likely a DTMF issue. But considering we don't require DTMF and all for a basic voice call, can we make the call work without an MTP?