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Circuit switching is a method of implementing a telecommunications network in which two network nodes establish a dedicated communications channel (circuit) through the network before the nodes may communicate. The circuit guarantees the full bandwidth of the channel and remains connected for the duration of the communication session.[1] The circuit functions as if the nodes were physically connected as with an electrical circuit.
Circuit switching originated in analog telephone networks where the network created a dedicated circuit between two telephones for the duration of a telephone call.[2] It contrasts with message switching and packet switching used in modern digital networks in which the trunklines between switching centres carry data between many different nodes in the form of data packets without dedicated circuits.
When you make a telephone call, for example, the telephone system establishes an electrical path between you and the person you're calling by joining available telephone cables -- circuits -- end-to-end. To complete your "connection", the telephone system's exchanges -- switching nodes -- allocate cable-miles in the form of circuits and maintain this allocation for the duration of your call. Thus, in circuit-switching, we say, circuits are allocated to carry connections. In pure circuit-switching, the making of a connection requires a number of distant switching nodes to piece together a continuous path from end to end; and, for the life of the connection, its constituent circuits are dedicated to carrying a conversation.
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