How does PSTN differ from VoIP in terms of network type and signaling?

• A. PSTN uses circuit-switched networks with SS7 signaling; VoIP uses packet-switched networks with IP-based signaling such as SIP.
• B. PSTN uses packet-switched networks with IP-based signaling; VoIP uses circuit-switched with SS7.
• C. PSTN uses satellite links with IP signaling; VoIP uses wireless networks with proprietary signaling.
• D. PSTN and VoIP both use packet-switched networks and IP signaling.

Answer: (A)

PSTN and VoIP differ in how they carry calls and how signaling is used to set them up. The PSTN uses circuit-switched networks, which establish a dedicated path for the entire duration of a call. The signaling that coordinates this path, routing, and features runs over SS7, a separate signaling network that handles call setup, teardown, and feature exchange.

VoIP, by contrast, travels over packet-switched IP networks. Voice is sent as packets over the Internet or an IP network, and the signaling to establish and control the call is IP-based, with SIP being a common protocol used to set up the session, negotiate codecs, and manage call parameters. This fundamental shift—from a dedicated circuit with SS7 signaling to an IP-based, packet-switched approach with SIP—drives the major differences between PSTN and VoIP.