Which SIP method is primarily used to terminate a session?

The SIP method primarily used to terminate a session is the BYE method. This method is specifically designed to indicate the end of a session established by a previous INVITE request. When either participant in a SIP session wishes to terminate the call, they send a BYE request to the other participant, signaling that they want to close the session gracefully. This allows for proper session teardown and can include information about the reason for termination.

The INVITE method is used to initiate a session, while the OPTIONS method is typically used to query the capabilities of a user agent or server without establishing a session. The LEAVE method is not a standard part of the SIP repertoire. Therefore, BYE is the correct choice, as it fulfills the specific role of concluding a SIP session.