GB2130050A

GB2130050A - Calling line identifier

Info

Publication number: GB2130050A
Application number: GB08230826A
Authority: GB
Inventors: Joseph Richard Cass; James Neil Pinnington
Original assignee: STC PLC; Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1982-10-28
Filing date: 1982-10-28
Publication date: 1984-05-23
Also published as: GB2130050B

Abstract

In a telephone exchange calling line identifier, a relatively long identification pulse is applied via drive means (6) to the P-wire of the switched path at a "concentration point" in the exchange. This pulse propagates back via the first selector (2) to the caller's line circuit (1). Here it is detected on scan by scan means (7), which scans a number of cycles of a block of lines during the persistence of the CLI pulse. Thus the calling line is detected, but this detection has to be repeated on eight successive scans to be accepted as valid. The identifier is an add-on assembly, and is modular in nature and is microprocessor controlled. As described, it forms part of a call logging system. <IMAGE>

Description

SPECIFICATION Calling line identifier This invention relates to a calling line identification system for use in an automatic telephone exchange.

For such purposes as metering and call logging it is necessary to be able to automatically identify a calling subscriber, and the need for providing this facility should be met in a reasonably economical manner.

According to the invention there is provided a calling line identification system, for use in an automatic telephone exchange, in which to effect an identification a driver circuit applies an electrical pulse to the switched path at a point within the exchange, which pulse is propagated via one or more switching stages to the line circuit connected to that point, in which a scanning circuit scans a block of line circuits which can be connected to the said point, the rate of scanning being such that all of the lines of that block are scanned a number n times within the duration of the identification pulse, in which when a said identification pulse is detected by the scanner the time in its cycle at which the detection is effected identifies that line circuit, which identification is temporarily stored, in which the successive detections of an identification pulse are assessed and the detection is accepted as valid if the identification pulse is detected on n successive scans by the scanning circuit, in which the application of the identical pulses to the switched paths, the scanning of the line circuits and the assessment of the scan results are effected under microprocessor control, in which the timing of the identification pulse and the timings of the scanning cycles are effected under control of the microprocessor, and in which when a successful detection is effected the result thereof is transmitted to recording equipment.

Such a system can be produced as an applique, or add-on circuit for addition to an existing telephone exchange, which in many cases is not of the processor controlled type.

An embodiment of the invention will now be described with reference to the accompanying drawings, in which Figure 1 is a simpiified block schematic which shows how a system embodying the invention is incorporated into a telephone exchange, while Figures 2, 3 and 4 are simplified block diagrams of parts of the system.

The general arrangement of a calling line identification system according to the invention is shown in Figure 1, where it is part of a call logging system installed as "add-on" equipment in an existing telephone exchange. This exchange is in the present instant assumed to be of the electro-mechanical type, e.g. a crossbar exchange such as the British Telecom BXB system.

In this exchange we have a number, typically ten thousand, of subscriber's line circuits such as 1, each of which has the usual three wires, the and + wires of the line to the subscriber's premises and the P wire. The line circuits are connected via a first switching stage 2 to the first selector 3, both of these, in the case of BXB, are crossbar switch stages.

The calling line identification (CLI) subsystem 4 contains a duplicated control arrangement 5, which is microprocessor based, and drive circuitry 6 and scan circuitry 7. As in many CLI arrangements, the basic principle is that when a calling line is to be identified, a pulse is applied by the drive circuitry 6 to the P wire of the selector input to which a calling line is connected. This pulse is propagated "backwards" via the first switching stage 2 to the line circuit, where it is detected by the scan circuitry 7, which monitors the line circuits such as 1 with access to the central drive point. This identification pulse is relatively long compared with the scan cycle, so that the scan circuitry 7 has time to find the drive pulse.

The output from the scan circuit 7 represents the calling line's identity by its time position in the scan cycle, and this information is applied to a CLI interface 8 on detection. To ensure that a spurious pulse is not interpreted as a CLI drive pulse, the scanner has to detect that pulse's condition on a line circuit's P wire eight times for it to be accepted as a valid detection. When this is done the result of the CLI operation is passed via an interface 8, the CLI interface, to the call logging subsystem 9.

The subsystem 9 has a number of line interfaces 10, 11 , five in this case, which receive call information from the drive point. In addition, it receives further call information from the CLI -interface 8 and also from the subscriber's private meter equipment 12. This meter equipment 12 is connected in the present case to the - and + wires, and collects from them information as to the line's condition, plus meter pulses. This information passes via the equipment 12, under control of an SPM (subscriber's private meter) control system 1 3 to another interface 14 from which it reaches the subsystem 9.

The subsystem 9 operates under control of a system control 1 5 and duplicate system control 1 6. There is a supplementary services interface 17, from which information as to such services in use is passed to the subsystem 9.

The information thus collected is recorded, either on disks or on tapes, as indicated at 1 8 and 19, under control of a data management subsystem 20. The connection ADC refers to the "Area Data Collection" facility.

The system is a distributed microprocessor system with duplicated control processors, and is modular, as will be seen below. It is intended to cater for a maximum size of ten thousand lines per main module, with up to two thousand drive points. The size quoted is only limited by the traffic that the system can handle, and this involves twenty line identifications per second, an identification rate which allows for two identification per call, one test identification per second, and a failure rate of 30%.

The system is divided into three main functional units, the monitors, which include the scanners 7, the drivers 6 which apply the CLI pulses to the drive points, and the control processors 1 5-1 6. The points to be monitored, i.e. the line circuit's P wires, are in blocks of 64, each block being handled by a monitor card.

Sixteen monitor cards are serviced by two buffer cards (duplication in the interest of system security), these eighteen cards making a fullyequipped equipment shelf. Hence for a tenthousand line exchange, ten such shelves are needed.

A monitor card samples each of its sixty four points eight times in every 1 6 millisec. cycle, and reports to both of its shelf buffers the results of those scans in the next clock cycle. This report is either a positive identification of a CLI pulse, a "watch dog" count, or an error message. Each buffer then assembles these reports for transmission to its associated control microprocessor during the next 1 6 millisec. cycle.

The points to be driven are also in blocks of sixty four, with each block handled by a driver.

Sixteen driver cards are serviced by two buffer cards, making a fully-equipped shelf of eighteen cards. Thus the system maximum of two thousand drive points takes four shelves, since each such point can be driven from two independent sources.

The control processors, in the blocks 1 5 and 16, are run one in a master mode and one in a standby mode. The master processor controls the drive of the CLI pulses and the communication of the CLI subsystem with the other subsystem, but both master and standby perform the monitoring and maintenance functions, with the standby reporting its results and status to the master.

Each of the scanner cards has a microprocessor which looks for a 2 millisec. pulse, and a frame pulse, of 1 6 millisec. On recognition of these pulses it scans all of its sixty four monitoring points, and stores the result. It repeats this scan every 2 ms. until the last scan, the eighth, of the frame pulse, and then applies to its output point either a "watch dog" count or the address of a monitoring point for which it has recognised a CLI pulse or a fauit report. The watch dog count is merely a count of the points scanned, and is used as a check that the scan has been performed.

To recognise a CLI pulse as valid, the scanner processor has to read the correct voltage level on a P wire for eight scans: failure of any one scan leads to failure to recognise a CLI pulse. In such case the system control causes another CLI pulse to be applied to the appropriate drive point.

The active bus buffer processors, in the duplicate control block 5, scan their sixteen shelf monitor cards for their previous frame output.

This scan is then followed by a similar scan by the standby buffer processor. The two processors then check their results, and when polled by the appropriate control, they report the status of their shelf and its sixteen scanner cards. The receipt of more than one CLI indication in a single frame causes the buffer processor to emit an error message which indicates the reason for that message.

Figure 2 shows the arrangement of the processors, buffers, drivers and monitors included in the CLI subsystem 4. Here there are two processors, A and B, connected to respective highways to the CLI interface 8, Figure 2, which processors control two bus drivers A and B, and a number of bus buffers 1A--l OA and 1 B-i OB.

The bus drivers control the drivers 1-16, one per card on a driver shelf, via the bus buffers A and B.

Similarly, but in reverse, the monitors, of which one set is shown, and which respond to the scan results, pass their results to the processors via the buffers 1 A-i OA and 1 B-1 OB. As already indicated, the processors compare the results of the scan for identity, only accepting a scan result as valid if both sources of that result agree. In addition, the processors only allow a scan result to be accepted as valid if it is repeated eight times without any discrepancy.

Figure 3 shows how the scan results are accepted. Here the subscribers' P wires are each connected to a line buffer, which responds to an identification pulse thereon when scanned. Eight such buffers are connected to the eight inputs of a multiplexer MUX, whose address inputs are controlled from the P2 outputs of the microprocessor.

The multiplexed scan results pass via a voltage window to the P 1 input of the processor, the voltage window being a pair of operational amplifiers so biassed that they pass a pulse whose value lies in a preset amplitude range. The processor pass the scan results, after the checks already mentioned, to the busses A and B to the call logging subsystem referred to above. Note that only one of the duplicated assemblies is shown in Figure 2.

In Figure 4, the bus buffer and latch are controlled from the CLI subsystem processor, and apply the CLI pulse via a 1 to 4 Demux and a 1 to 1 6 Demux, to respective line interfaces for 64 lines; as before, only one of the duplicated channels is shown.

Claims

1. A calling line identification system, for use in an automatic telephone exchange, in which to effect an identification a driver circuit applies an electrical pulse to the switched path at a point within the exchange, which pulse is propagated via one or more switching stages to the line circuit connected to that point, in which ascanning circuit scans a block of line circuits which can be connected to the said point, the rate of scanning being such that all of the lines of that block are scanned a number n times within the duration of the identification pulse, in which when a said identification pulse is detected by the scanner the time in its cycle at which the detection is effected identifies that line circuit, which identification is temporarily stored, in which the successive detections of an identification pulse are assessed and the detection is accepted as valid if the identification pulse is detected on n successive scans by the scanning circuit, in which the application of the identification pulses to the switched paths, the scanning of the line circuits and the assessment of the scan results are effected under microprocessor control, in which the timing of the identification pulse and the timings of the scanning cycles are effected under control of the microprocessor, and in which when a successful detection is effected the result thereof is transmitted to recording equipment.

2. A system as claimed in claim 1, in which the microprocessor, the driver circuits and the scanning circuits are all duplicated, and in which when a calling line identification is effected the results of the detection operations by the two sets of circuit elements are compared, the result being accepted as valid if the two results are identical.

3. A calling line identification system, for use in an automatic telephone exchange, substantially as described with reference to the accompanying drawings.