a result, datagram packet switching networks do not require a circuit to be established and allow many pairs of nodes to communicate concurrently over the same channel. Multiplexing multiple telecommunications connections over the same physical conductor has been possible for a long time, but each channel on the multiplexed link was either dedicated to one call at a time, or it was idle between calls. Examples of circuit-switched networks Public switched telephone network (PSTN) B channel of ISDN Circuit Switched Data (CSD) and High-Speed Circuit-Switched Data (HSCSD) service in cellular systems such as GSM Datakit X.21 (Used in the German DATEX-L and Scandinavian DATEX circuit switched data network) Optical mesh network See also Clos network Switching circuit theory Time-driven switching – a circuit-switching variant References External links Netheads vs Bellheads by Steve Steinberg University of Virginia RFC 3439 Some Internet Architectural Guidelines and Philopsophy Teletraffic Network architecture Physical layer protocols