What does the "INVITE" method do in SIP?

The "INVITE" method in SIP (Session Initiation Protocol) is specifically designed to create a new session by inviting another user to join. When a user wants to initiate a communication session, such as a voice call or video conference, they send an INVITE request to the intended recipient. This request not only indicates the desire to start the session but also includes details about the session parameters, such as media types, codecs, and other negotiation factors.

This process is fundamental to establishing a communication link in SIP, setting the stage for further signaling and media exchange once the invitation is accepted. It is the first step in a series of interactions that facilitate real-time communication over the internet.

The other choices pertain to different functionalities within SIP. For example, terminating a session is handled by the "BYE" method, retrieving user presence information typically involves the "PUBLISH" or "SUBSCRIBE" methods, and sending acknowledgments for received messages is done using the "ACK" method. These functionalities, while essential components of SIP, serve different purposes that do not align with the primary function of the INVITE method.