AT&T AT&T manual Tie Trunk TN760B

Tie Trunk (TN760B)

The Tie Trunk Circuit Pack interfaces four 6-wire tie trunks and the TDM bus. Two tip and ring pairs form a 4-wire analog transmission line. An E and M pair are used for signaling. The T and R pair transmit analog signals from the circuit pack. The T1 and RI pair receive analog signals from the tie trunk. The E and M pair are dc signaling leads used for call setup handshaking. The E lead receives signals from the tie trunk and the M lead provides signals from the circuit pack. The TN760Bs four port circuits support Type I, Type I Cornpatible, or Type V signaling. Incoming and outgoing trunks can be either automatic, immediate start, wink start, or delay dial. Figure 3-16shows the following Tie Trunk unique circuitry:

● Ground detector circuit

●Port Input/Output (1/0) circuit

●Four port circuits.

Ground Detector Circuit: This circuit determines if a ground has been applied to the E lead. Ground detector inputs come from the port circuits as an analog current to the -48 volt dc supply. Its output is a port control point to the port I/O circuit.

Port I/O Circuit: This circuit consists of bus expanders				for communication	between	the
on-board microprocessor and		the port circuits.	It receives	commands from	the on-board
microprocessor and	distributes	them to the individual port circuits. It also accesses the				port
circuit scan points	and passes the information to		the on-board microprocessor.

Port Circuits: The port circuits are identical, except for port 3 where part of the E-lead maintenance circuit is located. Each port circuit consists of a codec with associated input and output line transformers, analog operational amplifiers, a power filter, loop-around transistors, port control comparators, a relay driver, an electronic power feed device, an E- lead test maintenance circuit, and surge protection circuits.

The codec converts the incoming 4-wire analog signal from the tie trunk to a PCM data signal. The codec converts the incoming PCM data signal from the NPE to an analog signal. Outgoing and incoming line transformers provide de isolation to the tip and ring leads. Analog operational amplifiers provide amplification and buffering for the codec and network and loop-around gain compensation. Filtered power is provided to the codec and amplifiers.

The loop-around transistors are under control of the port control comparators and provide a loop-around path for the signal for testing purposes. The relay driver buffers and inverts the relay drive signals from the port 1/0 circuit so that a logic high input operates the appropriate relay. The relays and electronic power feed device control the M-lead circuitry to provide the proper signaling handshake for call progress tones and dial pulse dialing.

The	electronic feed device provides a -48			volt de		current to the M-lead		circuits. It		also tests
the	M-1ead circuits for	opens or	shorts and		prevents uncontrolled		operation		during	power-up.
The	E-lead test circuit	provides a	ground	to	the	ground detector	circuit	for	testing	purposes.

The surge protection circuitry provides lightning surge and power cross protection for the circuit pack. For each port circuit, E&M/Simplex and surge protection are selected by switch settings as shown on Figure 3-17.

The signaling type is administrable for each port. Table 3-Bsummarizes the conditions present as the transmit and receive control signals for each signaling type. Table 3-Clists the preferred TN760B tie trunk signaling format to be used in the likely-to-be-encountered installation situations.

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