x over a 4-wire ISDN Digital Subscriber Line (DSL). The circuit switched data service provides end-to-end digital service to pass data or video information over the public network. ISDN uses out-of-band signalling to establish and maintain data connections, which require special processing.
             ISDN lines are equipped with a Delta or D-channel connection, which is used to manage ISDN connections. The D channel is a 16Kbs X.25 connection that is also capable of offering a low speed packet service while also relaying call-processing information.
             ISDN lines are also equipped with two 64 Kb/s Bearer or B channels. Each B channel can be used for circuit switched voice, circuit switched data, or high-speed packet service. To provide a high-speed packet service one or both of the 64Kbs B channels are set up a
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