Which protocol is widely used for VoIP communications?

The correct answer is SIP (Session Initiation Protocol) because it is the primary signaling protocol used for initiating, maintaining, and terminating real-time sessions involving video, voice, messaging, and other communications over Internet Protocol (IP) networks. SIP is designed to establish connections and manage multimedia communication sessions such as voice calls and video conferences, making it particularly well-suited for Voice over Internet Protocol (VoIP) applications.

SIP facilitates the signaling process by providing the means to invite users to sessions, establish sessions between endpoints, and manage the session state. For instance, it can handle user registration, call setup, and call teardown, enabling seamless communication over IP networks. Consequently, SIP's role is essential in the realm of VoIP, where the goal is to transmit voice data effectively over the internet.

In contrast, other protocols mentioned serve very different purposes. RTSP (Real-Time Streaming Protocol) is focused on controlling streaming media servers, FTP (File Transfer Protocol) is utilized for transferring files across a network, and HTTP (Hypertext Transfer Protocol) is the foundation of data communication on the web. None of these protocols are designed for establishing and managing audio and video calling sessions in the same manner SIP does, which solidifies SIP's position as the