What is the difference between a SIP trunk and a gateway?

• A. A gateway is a SIP trunk.
• B. A SIP trunk is a SIP connection; a gateway provides PSTN interfacing and routing.
• C. A SIP trunk performs media transcoding; a gateway does signaling only.
• D. A gateway is used for VoIP only.

Answer: (B)

Think about how voice traffic reaches the public telephone network. A SIP trunk is the IP-based connection to your service provider that carries SIP signaling and the actual voice payload over the Internet or IP network. It’s the service link used to place and receive calls through the provider, but it doesn’t itself connect you directly to the traditional PSTN hardware.

A gateway, on the other hand, is a device at your edge that interfaces with the PSTN. It provides the physical and protocol interworking needed to link the IP voice network to the legacy telephone network, handling signaling interworking and any necessary media conversion or transcoding as calls move between domains. In short, the SIP trunk is the service/connection over IP, while the gateway provides PSTN interfacing and routing.

That’s why this option is correct: it accurately separates the SIP trunk as a SIP connection to the service provider from the gateway’s role of connecting and interworking with the PSTN.