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5.1 | ISDN |
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5.1.2 | Basic ISDN components |
ISDN components include terminals,
terminal adapters (TAs), network-termination (NT) devices,
line-termination equipment, and exchange-termination equipment. The
table provides a summary of the ISDN components. Beyond the TE1 and TE2 devices, the next connection point in the ISDN network is the Network Termination type 1 (NT1) or Network Termination type 2 (NT2) device. These are network-termination devices that connect the four-wire subscriber wiring to the conventional two-wire local loop. In North America, the NT1 is a Customer Premises Equipment (CPE) device. In most parts of the world besides North America, the NT1 is part of the network provided by the carrier. The NT2 is a more complicated device, typically found in digital Private Branch eXchanges (PBXs), that performs Layer 2 and Layer 3 protocol services. An NT1/2 device also exists; it is a single device that combines the functions of an NT1 and an NT2.
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