Which of the following is a packet switching WAN technology?

Frame Relay is a Layer 2 packet-switching WAN protocol that uses Permanent Virtual Circuits (PVCs) or Switched Virtual Circuits (SVCs) to forward variable-length frames across a shared provider network, making it the textbook example of packet-switching WAN.

T1 is a dedicated leased-line circuit-switching technology that provides a fixed 1.544 Mbps point-to-point connection, not packet switching.

Asynchronous Transfer Mode (ATM) uses fixed 53-byte cells, classifying it as cell switching rather than traditional variable-length packet switching.

ISDN (Integrated Services Digital Network) is a circuit-switching technology that establishes a dedicated end-to-end circuit for the duration of a call.