GB2131652A - Telecommunications exchanges - Google Patents

Abstract

A telecommunications exchange includes line identification apparatus in which signals on additional wires (the 'p' wires) (1) which are switched in parallel with the speech pairs are used to identify an originating exchange line circuit. On detection of seizure of the 'p' wire (1) at one of a number of call logging points (11) a data signal is transmitted by a transmitter circuit (9). On detection of such a signal a receive circuit (2) adds a plurality of data bits to the signal identifying one of a number of associated 'p' wires (1) on which the signal was received and transmits the modified data signal to a receiver multiplexer (4, 4'). On receipt of the modified data signal the receiver multiplexer (4, 4') adds a respective plurality of data bits to the signal identifying one of a plurality of receivers (2) connected thereto and retransmits the signal to a further multiplexer (5, 5'). The further multiplexer (5, 5') adds a respective plurality of bits and transmits the signal to a control circuit (6, 6') which adds further bits identifying the further multiplexer (5, 5'). The complete signal is then transmitted to call logging apparatus. <IMAGE>

Description

SPECIFICATION Telecommunication exchanges The present invention relates to telecommunication exchanges and in particular to line identification apparatus used in such exchanges.

Call logging requires an identification of the origi nating line of each call to be passed to a call logger associated at some concentration point of a telephone exchange-for example at a register or at a line connection.

In conventional designs of line identification apparatus the identification data is generated completely on a per subscriber basis by using for example hardwired transformer cores. Alternatively the identification data may be individually strapped on a strapping field in the subscriber line circuit. Such line identification apparatus is not easily added to an existing' exchange.

It is an object of the present invention to provide improved line identification apparatus for use in telecommunications exchanges which is capable inter-alia of use to provide line identification without significantly affecting the mode of operation of a conventional exchange.

According to the present invention in a telecommunications exchange ofthe kind having switched speech pairs and additional wires ('P' wires) which are switched in parallel with the speech pairs, detection means is responsive to changes in the electrical state of connections through the exchange at each of a plurality of call logging points to cause a data signal to be supplied to the additional wires at each call logging point at which such a change is detected, the data signal comprising a plurality of data bits identifying the particular call logging point, a plurality of receivers are each arranged to scan the addition wires of a plurality of line circuits individualtothatreceiverto detect the presence of a data signal as aforesaid supplied thereto over an additional wire path through the exchange, each of said receivers being arranged to modify the data signal so detected by the addition of a plurality of data bits which identify the particular additional wire of those scanned by the receiver and to transmit the modified data to a receiver multiplexer which is common to said plurality of receivers and which further modifies the data signal bythe addition of a plurality of data bits identifying the particular receiver supplying the modified data signal, the further modified data signal being utilised to identify the line circuit to which the particular call logging point is connected.

Preferably a plurality of receiver multiplexers are each arranged to receive modified data from a respective plurality of receivers and to transmit the further modified data signal to afurther multiplexer which is common to said plurality of receiver multiplexers and which modifies said data bythe addition of a further plurality of data bits identifying the particular receiver multiplexer supplying the further modified data signal.

There may be a plurality of said further multiplexers each operating as aforesaid and each connected to control means which is arranged to add to the data signal a respective plurality of data bits identifying the particular one of said further multiplexers supplying said data signal.

The control means may be arranged to transmit the data to call logging means, which may be a computer which also acts as said detection means. Said detection means may be arranged to detect seizure of the speech pair at each of said logging points and to forward data identifying the seized call logging point to control means.

On receipt of such data said control means may be arranged to forward a corresponding data signal to a first demultiplexerwhich determines from a first plurality of the data bits therein which of a plurality of second demultiplexers is to receive the signal. Each of said second demultiplexers may be arrariged to determine from a second different plurality of data bits which of a respective plurality of transmitters to which each of said second demultiplexers are connected is to receive said data signal. Each of said transmitters may be arranged to forward a corresponding data signal in dependence on a further plurality of data bits to the particular one of a respective plurality of additional wire call logging points to which it is connected.

Data transfer between said receivers and said receiver multiplexers and between said receiver multiplexers and said further multiplexers and between said further multiplexes and said control means may be in channels of respective time - division multiplex (TDM) signals. Similarly data transfer between said control means,firstdemultiplexer,second demultiplexer and transmitters may be in channels of respective TDM signals between them.

The data rate of the respective TDM signals towards the system centre may be increased in comparison with the data rate of respective TDM channels towards the receivers orthetransmitters. There may be less logging points than line circuits by a factor of at least two.

Line identification apparatus for use in a telecommunications exchange in accordancewiththe invention will now be described by way of example only with reference to the accompanying drawings of which: Figure lisa schematic diagram ofthe apparatus; Figure 2 is a circuit diagram of a receiverofthe apparatus of Figure 1; Figure 3 is a schematic diagram of one ofthe receiver highways of Figure 1; Figure 4 is a schematic diagram of another of the receiver highways of Figure 1; Figures 5 and 6 when assembled as shown in Figure 7 show a schematic diagram ofthe control of Figure 1; Figure 8 is a schematic diagram of one ofthe transmit highways of Figure 1; Figure 9 is a schematic diagram of another ofthe transmit highways of Figure 1;; Figure loins a schematic diagram of a transmitter of Figure 1; and Figures 11 and 12 are diagrams showing the data format of signals at various points in the diagram of Figure 1.

Referring to Figure 1 in which one of the switched 'P' wires 1 of an exchange is shown diagrammatically, the apparatus comprises a number of receivers 2 (only one of which is shown) each connected to the'P' wires ofuptothirty-two line circuits (not shown) buy a respective connection 3.

Each receiver 2 is connected to two 'highway one' circuits 4 and 4' for security reasons, each of the highway one circuits 4 and 4' having four groups of connections each from eight receivers 2. Each highway one circuit4 and 4' is connected to two 'highway two' circuits 5 and 5' and the two highway circuits 5 and 5' are connected to respective control circuits 6 and 6'. It is here noted that although for clarity only two highway one circuits 4,4' are shown, eight such circuits are connected to each highway two circuit 5,5'. Similarly eight highway two circuits 5,5' are connected to each control circuit 6,6'.

On the other side the control circuits 6,6' are each connected to four highway three circuits 7, 7', each of which are connected to eight highway four circuits 8,8' each of which may be connected to up to eight transmitter circuits 9. Each of the transmitter circuits 9 may supply up to thirty-two selectable points 11 on different 'P' wires 1 ofthe exchange.

Briefly the apparatus functions inthefollowing manner. On detection of a seize of the speech pair of the exchange (not shown) at a point corresponding to one of the points 11, a call logger (not shown) forwards a request to one of the controls 6 by way of a connection 12. The control 6 causes a signal to be sent to the transmitter 9 which is connected to the appropriate point 11, which transmitter will forward a signal on the 'P' wire 1. When the signal which inter-alia identifies the call logger is detected by the receiver 2 it adds 5 bits to the message (identifying in binary one ofthirty-two line circuits connected thereto), and forwards the message in a manner hereinafter described to oneofthe highway one circuits, say, 4.

When the message is received by the highway one circuit 4 it adds a further five bits before the message is forwarded to one of the highway two circuits, say, 5.

Thefurtherfive bits identify the receiver2fromwhich the message was received.

The highway two circuitS adds a further'three bits to the message (identifying one of weight highway one circuits 4 and the now complete message is returned to the control circuit 6. Having received a first message the control circuit 6 causes the transmitter 9 to repeat its request on the 'P' wire 1 and the process is repeated.

When two identical messages have been received in this manner, the control circuit 6 forwards the data defining the originating line circuit (not shown) to the call logger.

Before considering thefunctioning of the circuit in detail it is necessary to considertheformat ofthe message sent bythe transmitter 9 on the 'P' wire 1.

Thus referring to Figure 11(a) the message comprises twenty-five data bits each offour milliseconds duration the first six of which define a prefix. Fourteen further bits define the identity of the loggerwhilsta furtherfive bits are provided to give a parity check on the whole message when it is received.

Atypical 'P' wire message is shown in figure 11(b) in which it will be seen that each bit consists of a one millisecond period atzero voltage followed by either a two millisecond period at fifteen volts (representing data bit value 'one') or a furthertwo milliseconds at zero volts (data bit value 'zero') and a further one millisecond period at zero volts.

Thus it will be seen fro Figure 11 (a) and (b) thatthe prefix consists of six 'one's forwhich the receiver 2 will scan each of its associated line circuit'P'wires 1.

Referring now to Figure 2, the thirty4wo 'P' wire connections 3 each have feed and balancing resistors 14, 14' and are serviced in four groups of eight. Each group is connected to a one out of eight selector 15 each of which feeds a respective comparator 16 The selectors 15 are driven at 32 kilohertz. Thus each two millisecond bit of an input message will be sampled eighttimes.

The comparators 16 are in turn sampled by a four-to-one selector 17 which is driven at 256 kilohertz such that a receiverldecoder 18 receives at eight times the bit rate. The receiver/decoder 18 is arranged to identifythetwenty-five bits in each message and performs a parity check on each message using the five parity bits. When a correctly received message is identified by the receiver/decoder 18 it is stored in a random-access memory (RAM) 19 priortoforwarding to the highway one circuit 4.

It is noted that each receiver 2 is connected to two highway one circuits 4,4' by respective serial transmit paths 20,20'. Each highway one card 4,4' provides respective 500 Hertz and 16 Kilohertz clock signals on respective clock leads 21,21' and 22,22'.

The respective clock signals being used by the receiver/decoder 18 are selected by a selector 23, the seclected 500 Hertz clock determining the scanning of the 'P' wire connections 3 and the 16 kilohertz clock determining transmission of data on either lead 20 or lead 20'.

It is here noted that if the clock signal on lead 22 is selected to control the transmission of data to the highway one circuit 4, the data is transmitted on lead 20. Similarly if lead 22' is selected, data will be transmitted on lead 20' to highway one circuit 4'.

The transmitted data may conveniently be divided into four bytes each comprising eight bits. The four bytes are shown schematically in Figure 12 and are as follows, the first bit of byte one is a free/busy bit which indicates whetherthe time slot is in use, this being followedbytheupperseven bits of the logger identity received by the receiver 2. The next byte comprises the lower seven bits ofthe logger identity received and a parity bit on the complete logger identity. The remaining two bytes are for a sixteen bit line identity.

Although all 32 bits are transmitted by the receiver 2 to the highway one circuit4 only the lower five bits of the line identity are provided bythe receiver2. As has been previously stated the bit rate between the receiver 2 and the highway one circuit 4 is 16 kilohertz.

Thus if all thirty-two 'P' wire connections 3 are in use at the same time it will take 64 milliseconds to forward all messages to the highway one circuit. For the avoidance of doubt each timeslot is used on a first-come first-served basis such that no message will take more than 64 milliseconds to be forwarded regardless of the number of 'P' wires. The format of a complete message in onetimeslot is shown in Figure 12 and this format is retained throughout subsequent transmis sion of the message.

Referring to Figure 3 each highway one circuit 4 receives data from 32 receiver circuits 2 on the respective data leads 20. The 32 receivers are connected in four groups of eight and each is selected in turn in a similar mannerto the selection in the receiver by a one out of eight selector 24 and a one out of four selector 25. As each message is received a parity check is carried out and the next five bits ofthe line identification (the five bits identifying the respective receiver 2) are added by receiver circuit 26. The received and modified messages are stored in a RAM 27 and are transmitted to one ofthe highway two circuits 5 over respective transmit leads 28,28'.

Since the highway one circuit receives up to 32 messages in each 2 ms period (16 kHz bit rate) it is arrangedto forward these messages at a bit rate of 512 kHz under control of a transmit clock signal which is transmitted to the highway two circuits 5 or 5' on respective clock leads 29,29'.

The transmit clock signal and the 500 Hz and 16 kHz clock signals returned on leads 21 and 22 are derived from a 2 megahertz signal received from the two highway two circuits 5and 5' over respective leads 30, 30' buy a clock generatorcircuit 31.

To avoid difficulties which could araisefrom phase differences in the two clocks all of the highway one circuits 4 are arranged to selectthe same clock signal using a clock selector 32 which is connected to all of the other highway one clock selectors by respective leads33.

Referring nowto Figure 4 each highwaytwo circuit5 receives messagesfrom eight of the highway one circuits 4. The messages are again multiplexed by a one out of eight selector 34 and stored in a RAM store 35 for onward transmission. The nextthree bits of the line identity are added to the data prior to storage. The timing ofthe receiver is taken from the transmit clock received over lead 27 in case the highway one circuit is working to a master clock signal from a different highway two circuit, say, 4'. The messages now have thirteen of the sixteen required line identification bits andareforwardedovera link36to the control circuit 6 again at 512kHz.

The control circuit 6 provides an 8 magahertz clock signal on lead 37 from which the necessary highway two clocks are derived by a clock generator 38 together with the two megahertzmasterclocksignal previously mentioned.

Eight highway two circuits 5 are connected to one of the control circuits 6 and, referrng to Figures 5 and 6, as the messages are received from each highway two circuit the final three bits are added to the line identification before storage in a RAM 39. These messagesaretransferred under control of a microprocessor40 by way of an interface 41 to the requesting data logger.

It is now necessary to consider the request from the data loggerwhich is received by the control 6 by way of an interface 42. The request will be stored in a respective RAM and forwarded to one of four highway three circuits 7 in dependence upon the first two bits of the logger identity.

As shown in Figure 8the highway three circuits 7 analyse the nextthree bits to determine which of eight highway four circuits 8 is to receive this message.

The highwayfour circuit8 as shown in Figure 9 analyses a further four bits ofthe message to determine which of sixteen transmitters 9 are to receive the message.

Finallythetransmitter 9 shown in Figure 10 analyses the last for bits ofthe logger identity and outputs the received message to the appropriate one out of thirty-two 'P' wire connections 10.

Thus the logger which may be a computer such as a miniprocessorfor example may have up to 16000 logging points associated with up to 64000 originating points.

Each of the circuits 2,4,5,6,7,8 and 9 may be standard regardless of the exchange in which the apparatus is fitted since no exchange dependent strapping is required.

It will be appreciated that where a system is required for an exchange having fewer lines, the highway two circuits 5 may be omitted whilst if less logging points are required the highway circuitthree 7 may be omitted without materially affecting the mode of operation.

Claims (14)

1. Atelecommunications exchange of the kind having switched speech pairs and additional wires which are switched in parallel with the speech pairs wherein detection means is responsive to changes in the electrical state of connections through the exchange at each of a pluralityofcall logging pointsto cause a data signal to be supplied to the additional wires at each call logging point at which such a change is detected,the data signal comprising a plurality of data bits identifying the particular call logging point, a plurality of receivers are each arranged to scan the additional wires of a plurality of line circuits individual tothatreceivertodetectthe presence of a data signal as aforesaid supplied thereto over an additional wire path through the exchange, each of said receivers being arranged to modify the data signal so detected bytheaddition of a pluralityofdata bits which identify the particular additional wire of those scanned by the receiver and to transmit the modified data to a receiver multiplexerwhich is common to said plurality of receivers and which further modifies the data signal by the addition of a plurality of data bits identifying the particular receiver supplying the modified data signal, thefurthermodifiedsignal being utilised to identify the line circuitto which the particular call logging point is connected.

2. Atelecommunications exchange as claimed in claim 1 wherein a plurality of receiver multiplexers are each arranged to receive modified data from a respective plurality of receivers and to transmit the further modified data signal to a further multiplexer which is common to said plurality of receiver multiplexers and which modifies said data by the addition of a further plurality of data bits identifying the particular receiver multiplexer supplying the further modified data signal.

3. Atelecommunications exchange as claimed in Claim 2 wherein a plurality offurther multiplexers each operating in the manner of said further multiplexer are each connected to control means which is arranged to add to the data signal a respective plurality of data bits identifying the one of said plurality of further multiplexers through which the data signal is received.

4. Atelecommunications exchange as claimed in Claim 1, Claim 2 or Claim 3 in whichthedata signal as completely modified by preceding apparatus is transmitted to call logging means.

5. Atelecommunications exchange as claimed in Claim 4 in which the call logging means is a computer.

6. Atelecommunications exchange as claimed in Claim 5 in which said computer is also the detection means.

7. Atelecommunications exchange as claimed in any preceding claim wherein said detection means is arranged to detect seizure of a speech pair at each of said call logging points and to forward data identifying the seized call logging point to control means.

8. Atelecommunications exchange as claimed in Claim 7 wherein on receipt of such data said control means forwards a corresponding data signal to a first demultiplexerwhich determines from a first plurality ofthe data bits therein which of a plurality of second demultiplexersisto receive that data signal.

9. Atelecommunications exchange as claimed in Claim 8 wherein each of said second demultiplexers on receiving a data signal from the first demultiplexer to which it is connected determines from a second different plurality of data bits which of a respective plurality of transmitters connected thereto is to receive that data signal.

10. Atelecommunications exchange as claimed in Claim 9 wherein on receipt of such a data signal each of said transmitters is arranged to forward a corres ponding data signal to one of a plurality of said call logging points to which it is connected in dependence upon a further plurality of data bits ofthat data signal.

11. Atelecommunications exchange as claimed in any preceding claim wherein data transfer between the call logging units is in channels of respective time division multiplex (TDM) signals.

12. Atelecommunications exchange as claimed in Claim 11 in which the data rate of the respective TDM signals towards the system centre is increased with respect to the data rate toward the receivers and/or the transmitters.

13. Atelecommunications exchange as claimed in any preceding claim in which the ratio of exchange line circuits to call logging points is less than 0.5.

14. Atelecommunications exchange including line identification apparatus substantially as hereinbefore described with reference to the accompanying drawings.