What is a common use of the SIP "INVITE" message?

The "INVITE" message in the Session Initiation Protocol (SIP) is primarily used to initiate a new communication session. When a user wants to start a call or set up a media session, the SIP "INVITE" is sent to the recipient, indicating that the caller wishes to establish a connection. This message typically contains information about the media types and formats that the caller is willing to use, allowing the recipient to understand what capabilities are available for the session.

In addition, the "INVITE" message can also carry session description information in the form of an SDP (Session Description Protocol) payload, providing details about the codecs, transport addresses, and other necessary parameters for the session. This is crucial for setting up the session properly, and as a result, the "INVITE" message is foundational in the SIP protocol's operation for establishing real-time communication.

The other options refer to different functionalities within SIP, such as confirming the end of a session or modifying existing session parameters, which do not align with the primary purpose of the "INVITE" message. This clarity around the role of "INVITE" helps in understanding its nature and usage within SIP communications.