When terminating a call from an IP phone, what should you see in Wireshark?

When a call is terminated from an IP phone, observing a BYE message in Wireshark is indicative of the proper signaling involved in ending a session in the Session Initiation Protocol (SIP). The BYE request is a standard message used to indicate that a participant would like to end the call.

This message is sent from the device that initiated the call termination (in this case, the IP phone) to the other party involved in the call, as well as through any intermediate devices that may manage or route the call. When this BYE message is successfully transmitted, it not only terminates the call but also allows for an acknowledgment of the termination from the called party, ensuring both ends of the call are aware that the conversation has concluded.

The other options, such as a SIP INVITE, CANCEL, or ACK, relate to different stages of a call's lifecycle. The INVITE request is used to initiate a call, while a CANCEL message is sent to cancel an ongoing call request before it has been established. An ACK is used to acknowledge the receipt of a response to an INVITE. Thus, these messages do not pertain directly to the process of call termination as effectively as the BYE message does.