6. - SIP Messages

SIP messages are the communication units used by SIP endpoints to establish, modify, and terminate multimedia sessions. SIP messages are exchanged between SIP user agents, proxy servers, and redirect servers, and are used to initiate and control communication sessions between two or more parties. The messages consist of a request or response line, message headers, and a message body, and are used to exchange information about the session, including media types, codecs, addresses, and authentication credentials. SIP messages can be sent over UDP, TCP, or TLS transport protocols.