What happens during SIP call teardown?

• A. The signaling session remains active until manual termination
• B. A BYE transaction ends the dialog and both sides release media resources
• C. Media is renegotiated automatically without teardown
• D. The session is upgraded to a video call

Answer: (B)

In SIP, call teardown is performed with a BYE request. When a BYE is sent and processed, the SIP dialog is terminated, the other side responds with a 200 OK, and both endpoints release the associated media resources (stop the RTP streams, free up ports, and cleanup codecs). This BYE mechanism is the explicit signal to end the session and to clean up everything tied to that call.

Why this is the best fit: the BYE transaction is designed specifically to terminate an active dialog in SIP, ensuring that both signaling state and media state are properly torn down. Other concepts don’t describe the termination flow correctly: simply letting the signaling session linger would leave resources in use, and automatic media renegotiation without teardown doesn’t end the call, it just changes parameters if negotiated. Upgrading to a video call is a separate renegotiation, not the teardown of the current session.