What does "SIP Re-INVITE" refer to?

"SIP Re-INVITE" specifically refers to an INVITE message that is used to modify an existing session. In the Session Initiation Protocol (SIP), a Re-INVITE can be sent by either party in a session to negotiate changes to the existing call parameters, such as changing codec information, updating the session description, or altering the media being used.

This mechanism allows for flexibility within established sessions, enabling modifications without establishing a new session entirely. It is particularly useful in scenarios where dynamic changes may occur during a call, such as adding video to an audio call or changing the media formats being utilized.

The other options do not accurately describe the function of a SIP Re-INVITE. For example, initiating a new session is done using a standard INVITE request, while a request to hang up a call is typically conveyed using a BYE message. Sending media streams falls under the RTP (Real-time Transport Protocol) and not directly related to the SIP Re-INVITE process.