Calls drop right after the called party tries to answer the call. Which of the below reasons is true?
A. Phone A is using SCCP and phone B is using SIP
B. Firewall is blocking RTP packets
C. An incompatible MTP type is allocated to the call
D. Codec are mismatched between phones
Kid says:
https://community.cisco.com/t5/ip-telephony-and-phones/incoming-call-drop-when-answer/td-p/3299657