All local lines, incoming and outgoing trunks, junctors, registers, senders and any special equipments such as coin box controller are connected one side (in figure left handside) of the switching network. The other side of the network shown are internal junctors. The functions of internal junctors are to provide a metallic path (through links) and to provide transmission bridge (local junctors).
The use of single network permits the interconnection of any devices on the traffic side of the switch and provides control of the system. This technique is called serial trunking. In serial switching, for one user to another user, seven stages of links are used is shown in Fig. 4.22.
Each through link or local junctor can be connected to any terminal on the traffic side by three stages of switches on one part and four stages on the other part.
Fig. 4.22. Serial trunking of local call in TXE-4.
The local junctor provides a ringing current, control, clean supervision and path release. For a local call a parallel path n established from the calling line to the called line via local junctor. Once the outgoing route has been determined, the sender part of the register sender is connected to an outgoing trunk junctors and conversation commences. The connection is then under the control of the outgoing trunk junctor. A, B, C and D are subunits.
The main control unit (up to 20) has number of register/senders (typically 36 in each). The cyclic and line scanner periodically broadcast all the fixed information relating to the system.
The first generation TEX 4 uses a diamond ring arrangement for the cyclic store. The information broadcasted by cyclic store includes the association between directory and equipment numbers between access codes and specific outgoing trunk junctors and so on. The line scanner broadcasts the state of line of the various high traffic items. The rate of broadcast ranges from minimum scanning rate of 156 ms to 36 ms for local calls.
The operation is as follows. Suppose that a subscriber initiates a call. With the reception of dialled pulses, within 156 m sec, the state of the associated line unit is broadcast with the information from the cyclic store also. The main control is designed in such a way that, at any time, it looks for next call. Once the calling condition is detected it instructs the switch network to connect the calling line to one of the registers controlled by the main control unit. The register detects when a significant number of digits has been dialled and itself calls in the main control unit by indicating a change of state to the scanner. The main control unit then selects the junctor and instructs the switch network to setup the required path.
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