ISDN customer access points

To allow for a wide range of uses the network termination equipment for ISDN has a number of network terminations, terminal adapters and associated alternative access points. These are illustrated in Figure 6.12.

Figure 6.12

ISDN customer access points

The ISDN standards define five groups of functional devices: The NT1, NT2, TE1, TE2 and the TA. After defining the functional devices, the standards define the protocol that each device uses to speak with the devices on either side of it. These protocols are assigned the letters R, S, T and U as identifiers, and are termed reference points. The function of each of these devices is as follows:

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