Session Initiation Protocol (SIP) is a signaling protocol used to initiate, maintain, and terminate real-time communication sessions, such as voice and video calls, over Internet Protocol (IP) networks. It is a text-based protocol that uses a client-server model, where a SIP client (e.g., a softphone or a VoIP phone) sends requests to a SIP server, which then processes the requests and sends responses back to the client.
SIP is an important protocol for VoIP and video conferencing because it allows users to establish and manage communication sessions in a standardized way. It is also used in other applications, such as instant messaging and presence, and can be used to provide services such as call forwarding, call waiting, and caller ID. SIP is a versatile protocol that is used in a wide range of applications, and it is an important part of the VoIP and video conferencing landscape.