Which of the following mediums is circuit switched?

The PSTN (Public Switched Telephone Network) uses circuit switching, meaning a dedicated physical circuit is established between the caller and receiver for the entire duration of the call, guaranteeing consistent bandwidth. This dedicated path remains reserved even during silence, which is the defining characteristic that distinguishes circuit switching from packet switching.

ATM (Asynchronous Transfer Mode) is a cell-switching (packet-switched) technology that breaks data into fixed 53-byte cells and routes them across shared network paths.

Frame Relay is a packet-switched WAN technology that routes variable-length frames across a shared network without dedicating a fixed circuit.

MPLS (Multiprotocol Label Switching) is a packet-switched technique that uses short path labels rather than long network addresses to forward packets efficiently across a shared network.