Network terminating terminal apparatus for integrated services digital network

DETAILED DESCRIPTION According to the present invention, network terminating terminal apparatus, for an integrated services digital network, comprises: a U-interface (412) for connection to the network and a U-transceiver (411) for extracting from signals received via said U-interface (412) B-channel data and D-channel data, a clock signal and framing signal; an S/T interface for connecting to remote terminal apparatus and a S/T transceiver (414) for transmitting signals to, and receiving signals from, said remote terminal apparatus via said S/T interface (426); a user interface and LAPD circuit (418) for interfacing local station apparatus (419, 422), including D-channel protocol means responsive to said user interface for generating a D-channel access signal (D.
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request, D.
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class) for securing access to said D-channel to enable said user interface to transmit data to said U-transceiver (411); D-channel monitoring and contention resolution means (427) for monitoring a D-channel in a data signal from said protocol means and signals received from said remote terminals by said S/T transceiver (414) and resolving contention between said user interface (418) and said remote terminal apparatus and for providing to said user interface (418) a signal enabling access and a D-channel control signal (D.
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b); D-channel access means responsive to said framing signal, said clock signal, said access enabling signal and said D-channel control signal (D.
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b) for controlling application to said U-transceiver 411 of B-channel data and D-channel data in said data signal (TX.
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LAPD) from said user interface and LAPD (418) selectively; said D-channel access means (423) serving to supply a D-channel control signal (D.
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b) to said S/T transceiver, said S/T transceiver being arranged to transmit said signal as an ECHO signal to said remote terminals.