Which protocol is commonly associated with Voice over IP (VoIP) communications?

The Session Initiation Protocol (SIP) is a protocol that is fundamentally connected to VoIP communications as it is specifically designed for initiating, maintaining, and terminating real-time sessions that involve video, voice, messaging, and other communications services. SIP facilitates the signalling necessary to set up and control VoIP calls and establishes and manages the sessions between the endpoints, allowing users to make phone calls over the internet.

While other protocols like UDP are often used in conjunction with SIP for the transport of voice packets, SIP itself plays a crucial role in managing the initiation and termination of those calls. It provides the mechanisms necessary for handling call setup requests, user availability, and call routing information, making it an integral component of VoIP technology.

In contrast, TCP is a connection-oriented protocol that ensures reliable data transmission but does not handle the signaling and session management aspects that SIP specializes in. ICMP, on the other hand, is primarily used for network diagnostics and error messaging rather than for VoIP communication. Overall, SIP stands out as the protocol that directly supports the core functionalities required for VoIP services.