How is SIP related to VoIP?

SIP, which stands for Session Initiation Protocol, plays a crucial role in voice over IP (VoIP) communications. It is a signaling protocol used to initiate, maintain, modify, and terminate real-time sessions that involve video, voice, messaging, and other communications applications and services. In the context of VoIP, SIP is primarily responsible for establishing the connection between two parties who wish to communicate over the internet.

When a call is made using VoIP, SIP is used to set up the session by handling various tasks such as user location, session management, and end-to-end connection establishment. This protocol defines the way that components in a VoIP system interact and communicate, ensuring that sessions are established swiftly and reliably.

The other choices presented do not accurately reflect the function of SIP in relation to VoIP. For instance, SIP is not a physical phone, hardware, or a standalone application but rather an essential protocol that orchestrates the communication processes within a VoIP system. Understanding this fundamental connection underscores the significance of SIP in enabling seamless voice communication over internet networks.