Exam 350-801 topic 1 question 315 discussion

the source phone doesn't "ring". it receives a "ringing" packet from the CUCM which receives it from the destination phone. that's why there are 2 messages.

The device that sends the 180 Ringing signal is the phone you're calling, the "destination" phone, not the source phone (when you call somebody, their phone rings, not yours).

It's C. If you've ever looked at a SIP trace for a call, you would see this. The first packet you see is from the destination phone, which sends a "180 Ringing" to CUCM, to advise it that the phone is physically ringing. The second one is from CUCM relaying it to the source phone that placed the call, so it can provide Ringback tone to the calling user.

Looks like A: https://www.cisco.com/c/en/us/support/docs/unified-communications/unified-communications-manager-callmanager/213583-procedure-to-analyse-call-flow-of-sip-ca.html

Documentation on how to analyze a SIP call point to A https://www.cisco.com/c/en/us/support/docs/unified-communications/unified-communications-manager-callmanager/213583-procedure-to-analyse-call-flow-of-sip-ca.html

The correct answer is B

C is correct

B. The source phone must signal to the destination phone that it is ringing, and the destination phone signals back with a 180 Ringing message. The same process applies to 11 BYE messages. When a call is made, the source phone sends a SIP INVITE message to the Cisco UCM, which sends a SIP INVITE message to the destination phone. The destination phone signals back with a 180 Ringing message to the Cisco UCM, which signals back with a 180 Ringing message to the source phone. This process happens twice, resulting in two 180 Ringing messages in the SIP trace. Similarly, when the call ends, both phones send a BYE message to the Cisco UCM, resulting in two BYE messages in the SIP trace.

C is the correct