GB2106752A - Concentrator - Google Patents

Abstract

In a telephone exchange the line circuits each of which is the interface between a subscribers' line and the exchange, are relatively complex and expensive units. Hence it would be useful to be able to reduce the number of such units needed. To do this a block of lines incoming to the exchange are connected to the nets of a plural-stage co-ordinate switching assembly (1), known as a pre-concentrator. The outlets from this assembly (1) give access to a number of line circuits (LCl, LCq), which are much less in number than the lines. Lines are scanned by scanners (3), which are modular in rating which scanners detect calling conditions, and cause, via a control unit (4), connections to be set up from calling lines to the line circuits (LCi, etc.). These give access to the main switch (2) of the exchange. For relatively low traffic lines, 64 line circuits may be provided for each block of 1000 lines, while for heavy traffic lines a block of 1000 lines may need 432 line circuits. With cheap cross-point devices a net economy results in spite of the need to place line protection elements and possibly also DC power feed on the line side of the switching assembly.

Description

SPECIFICATION Concentrator This invention relates to an automatic telecommunication exchange.

In such exchanges it is common practice to provide a subscribers' line circuit for each line served by the exchange, the line circuit acting as the interface between the line and the exchange. Such line circuits are expensive and in fact form a large proportion of the total cost of the exchange. It would thus be useful to find a method of reducing the number of such line circuits which have to be provided.

According to the present invention there is provided an automatic telecommunications exchange in which a group of subscribers' lines incoming to the exchange are connected to a number of subscibers' line circuits via a co-ordinate switching assembly, so that the number of line circuits is less than the number of subscriber's lines in the group, in which control means serving the subscriber's lines monitor the conditions of those lines in search of calling conditions, and in which when a calling condition on one of the lines is detected a connection is set up from that calling line via the switching assembly to a free one of the line circuits, whereafter that line circuit is marked as busy.

In most cases line protection will still need to be provided on a "per line" basis, and this also applies to the power feed for the line for at least some types of line. However, with the relatively cheap speech path switching devices currently available the use of the present invention does provide a useful economy in cost.

Embodiments of the invention will now be described with reference to the accompanying drawing, in which Figure lisa simplified block schematic of part of a telephone exchange embodying the present invention, Figure 2 is a generalised representation of a two-stage co-ordinate switching array for use in an arrangement such as that of Figure 1, and Figure 3 is a simplified schematic of a second embodiment of the invention.

In the arrangement shown in Figure 1, we have a switching array 1 which is herein referred to as a pre-concentrator which interconnects a block of n subscriber's lines and a group of q line circuits LC1 to LCq. These latter are connected to inlets to and outlets from the exchange's main switching network 2. The pre-concentrator 1 is served by scanning circuitry 3, which in the present case is modular in nature as it includes a group of p scanners each of which scans up to m lines, where m x p is at least equal to n.

Each scanner's output is in time division multiplex form, so p outputs from the scanners extend to control circuit 4 for the pre-concentrator 1. This control circuit, when a calling line is detected via one of the scanners, selects a free line circuit (if there is one), and causes a connection to be set up between that line circuit and the calling line. The control circuit 4 is also connected, as shown, to the exchange's central control (not shown) to pass thereto all relevant information about the newly initiated call. If all line circuits are busy, then the subscriber will hear nothing until such time as a line circuit becomes available or he hangs up. Alternatively, in the case of certain modern types of subscriber's terminal equipment a busy signal is sent to the caller's terminal, where it switches on a local busy tone generator.

When a call has to terminate on one of the lines served by the pre-concentrator, a message to that effect is sent to the control equipment 4, where it selects a free line circuit. It also, via the scanners 3, causes the wanted line to be tested. If it is found to be busy, then the central control causes busy tone to be sent back to the caller. However, if the wanted line is free, the control 4 is enabled so that it sets up a connection between the selected line circuit, one of LC1 to LCq, and the wanted line. Call completion then occurs in the usual manner.

As indicated by the little rings shown where the lines terminate on the pre-concentrator, line protection elements are provided on the 'line' side of the pre-concentrator. In the case of some lines, especially fully digital lines, power feeding arrangements also have to be provided on the 'line' side of the pre-concentrator.

Test access to the lines served uses additional outlets from the pre-concentrator 1, as shown, with control circuitry having access thereto so that access can be had to any of the lines served by the pre-concentrator. Alternatively test access can be achieved using conventional means (e.g. relays) on the line side of the pre-concentrator.

In most exchanges, a number of assemblies, each as shown in Figure 1, are needed, each serving a block of n lines. Thus if n = 1000, a large exchange may have 30 or more such assemblies.

Figure 2 shows in simplified form a two-stage co-ordinate network for use as a pre-concentrator, in which there are a first stage switches each serving "/d lines, and d second stage switches with q/d ports to which respective ones of the = line circuits are connected.

With such an arrangement we have considered two possible arrangements the characteristics of which are set out below.

(a) Average traffic lines, with both-way traffic 0.01E This has 1024 inlets to which the subscribers' lines are connected and 96 outlets. There are 16 first stage matrices each of which is a (64 x 16) matrix and 16 second stage matrices each of which is a (16 x 6) matrix. The allocation of the outlets from the second stage matrices is, per matrix, 6 for line circuits, 7 for scanners, 1 for test access and 2 spare. Thus for these relatively light traffic lines only 36 line circuits are needed. The switching array as just specified needs 17,920 cross points, which is 17.5 per line.

(b) Higher traffic lines averaging both-way traffic of OlE This has 1056 inlets to which the subscribers' lines are connected and 240 outlets. There are 24 first stage matrices each of which is a (44 x 24) matrix, and 24 second stage matrices each of which is a (24x10) matrix. The allocation of the outlets from the second stage matrices is, per matrix, 18 for line circuits, 4 for scanners, 1 test access and 1 spare.

Thus for this rather heavy traffic we need 31,104 cross-points, i.e. 29.5 per line. Note that, due to the fast action of the scanner, the number of scanner outlets needed is proportionally less than forthe light traffic case.

Thus as long as the cross-point cost is relatively low, we achieve a significant cost economy due to the saving in the relatively costly line circuits. If one uses a smaller pre-concentrator, e.g. one serving 500 lines, then the number of cross-points per line would be less, but the controller/scanner costs would have to be amortized over less lines.

Semi-conductor cross-points suitable for use in switching matrices are readily available commercially in 4 x 4 packages and 4 x 2 packages, and these can be assembled to make the larger matrices needed.

We now consider the function of some of the integers of Figure 1 in more detail, and consider their functions which would in many cases be performed under microprocessor control.

(i) The Scanners (a) Select next, subscribers' line terminal from a list, and if it is not in the busy, parked or not equipped condition, proceed to (b), then repeat (a) on the next terminal.

(b) Request from control a path to be set up across the pre-concentrator from the line found to be calling to a free line circuit.

(c) Await positive acknowledgement of path setup; if not received after a preset time, revert to (a) (d) Wait (settlement period for the various devices in the pre-concentrator and line circuit) (e) Test line, first time.

(f) Wait.

(g) Test line, second time.

(h) Compare tests and if both snow the line to be calling; advance to (i), if not, then back to (a).

(i) Inform control of calling state and terminal identity.

(j) Wait.

(k) If control returns a positive acknowledgement, mark busy and go to (1), else enter a fault routine.

(I) The call is now set up, and when the call is eventually terminated (or the wanted line found busy), then a request is sent to control to breakdown the path across the pre-concentrator and release the line circuit. Otherwise we enter the fault routine.

Note that while a call is in progress control equipment taken into use therefor is as far as possible released.

(m) On receipt of an acknowledgement from the pre-concentrator go back to (a), or enter fault routine.

The above is a "multi-threaded" operation since operations can be in progress at the same time for a number of lines.

The scanners have the following auxiliary functions; (i) Provide fault information (ii) Receive up-dating information of line status from central control (ii) Permit revision of the scan tables (used to control line scan from central control (iv) initialization routines (v) self checks (vi) Provide time outs, e.g. at the various waiting time referred to above (vii) Control overall phasing of the scan.

Typically a scanner includes a microprocessor with its own PROM and also with RAM, some of which is shared with the main processor. It also has an interface to the central controller, and line circuit equivalent, and it is connected to the preconcentrator as shown in Figure 1. The minimum number of scanners to be provided is two, operating in a load-sharing mode.

Pre-Concentrator controller The main functions of this control circuit are: (a) Maintain a map (or its equivalent) in a memory of the cross-point states.

(b) Receive messages from scanners and the central control to indicate the end points which need connections via the pre-concentrator.

(c) Determine a path to establish a wanted connection, and if this is not possible return a negative acknowledgement.

(d) Make a wanted connection, and return a positive acknowledgement.

(e) Receive a message from scanners and/or central control to break down paths between defined end points, or to do this from one specified end point.

(f) Break-down path, and acknowledge.

Auxiliary functions of this controller are: (i) Accept reload on the cross-point state map (ii) Provide fault information (iii) Perform initialization routines (iv) Handle security mechanisms (v) Provide time outs.

One type of semi-conductor cross-point switch visualised for use in the pre-concentrator consists of thyristors with associated control circuitry including latches. To switch a cross-point off in such a device, its latch is turned off and this controls the thyristor, whose current is reduced virtually to zero to effect the switch off. Such devices are available as packages each containing a 4 x 4 switch, and such packages can be assembled to form the larger-sized switches referred to above.

The arrangement shown in Figure 3 is intended to serve digital subscribers in an ISDN (Integrated Services Digital Network) system, in which case the transmission requirements to be taken into account are: (1) Ringing from the exchange is replaced by calling signals locally generated in the subscribers' terminal in response to the appropriate signal from the exchange. Hence high level AC signals do not have to be sent from the exchange.

(2) Although the information on the subscribers' loops is digital it is sent as analogue signals as "seen" by the transmission medium. Hence switching at subscriber loop level is analogue rather than digital.

(3) With the transmission method used, no low frequency components are involved, i.e. no signals less than 3.4 KHz, which means inductive line feed arrangements are smaller and cheaper than those in contemporary systems.

(4) Attenuation introduced by a switch affects error rate rather than the reference equivalent for the connection. Hence the requirements for series resistance of the cross-point elements are set by the performance of the local loop transmission systems rather than by the network loss as a whole. Hence the series resistance requirements for the crosspoints when switched on are less stringent than would otherwise be the case. This reduces cost.

In Figure 3, the incoming lines are connected to the main distribution frame 10, from which each line is connected to the distribution and power feed arrangements 11. Note that although this is shown as a separate block from the MDF, the protection elements and possibly also the power feed could well be incorporated into the MDF 10. From the block 11, the lines go to the pre-concentrator 12 which, as in the arrangement of Figure 1, is a two-stage co-ordinate switching array using electronic crosspoints. This gives access to a block of line transmission terminations 13 each of which effects conversion of the information between the "analogue" format on the line loops and the true digital format used within the exchange.The LTT block 13 is connected to block 14, which contains the subscribers' line circuits, and these are of course equal in number to the line transmission terminations in the block 13.

The line units 14 are connected to block 15, of digital line terminations, where conversion is effected to and from the 30 channel PCM formal used in the exchange proper.

Operations are controlled by a module controller 16, with a connection as shown to the main processors, and this module controller includes or controls line scanning means. This controller 16 controls the pre-concentrator 12 via a switch controller 17 and the line circuit and DLT blocks 14 and 15 via a line controller 18. The general operation of this equipment will be reasonably apparent in the light of the description given above of Figure 1.

The module controller 16 and possibly the other controllers, are duplicated in the interest of system security, and for the same reason the preconcentrator 12 may be triplicated.

In one example, the arrangement shown in Figure 3 has ISDN channels (e.g. 64Kb/s + 8Kb/s + 8 Kb/s), connected to the MDF 10 and therefrom to the pre-concentrator 12. The combined channels of 1024 such subscribers are concentrated without separation on to 256 channels at the LTT/SLU side. Further concentation once separation has taken place may not then be necessary, and if so one or more of the stages of the main switching network (2, Figure 1) can then be dispersed with. The number of crosspoints per subscribers' line is likely to be of the order of 20 to 30.

In the arrangements described hereinbefore we have assumed that the cross-point devices are thyristors. However, other types of semi-conductor device may be used as cross-point devices, one example being a MOS transistor.

CLAIMS (Filed on 22 Sept 1981) 1. An automatic telecommunication exchange, in which a group of subscribers' lines incoming to the exchange are connected to a number of subscribers' line circuits via a co-ordinate switching assembly, so that the number of line circuits is less than the number of subscribers' lines in the group, in which control means serving the subscribers' lines monitor the condition of those lines in search of calling conditions, and in which when a calling condition on one of the lines is detected a connection is set up from that calling line via the switching assembly to a free one of the line circuits, whereafter that line circuit is marked as busy.

2. An exchange as claimed in claim 1, and in which the co-ordinate switching assembly is a two stage assembly with the individual switch matrices made up of semi-conductor cross-points.

3. An exchange as claimed in claim 2, and in which the semi-conductor cross-points use thyristors whose on-off condition are controlled by latches.

4. An exchange as claimed in claim 2, and in which the semi-conductor cross-points use MOS devices whose on-off conditions are controlled by latches.

5. An exchange as claimed in claim 3 or 4, and in which the cross-points are in packages of 4 x 4 or 4 x 2 cross-points, the switch matrices each being assembled from a number of such packages.

6. An exchange as claimed in claims 1,2,3,4 or 5, and in which the line protection elements for the lines incoming to the exchange are connected to those lines on the line side of the co-ordinate switching assembly.

7. An exchange as claimed in claim 6, and in which the DC power feed arrangement for the subscribers' lines are also connected to those lines on the line side of the switching assembly.

8. An exchange as claimed in claims 1,2,3,4 or 5, in which the lines incoming to the exchange are connected to the line side of a main distribution frame (MDF) whose exchange side outlets are connected to the inlets to the co-ordinate switching assembly, and in which the line protection elements for the lines out the DC power feed arrangements therefor are installed at the MDF.

9. An exchange as claimed in any ome of the preceding claims, in which intelligence is conveyed over the incoming connections from the subscribers' lines in a digital form but with the digital elements conveyed in analogue form and in which the intelligence is maintained in such an analogue form within the co-ordinate switching assembly.

10. An exchange as claimed in claim 9, and in which for each incoming subscribers' line a plurality of digital channels is provided.

New claims or amendments to claims filed on 4 June 1982.

New or amended claims:

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (16)

**WARNING** start of CLMS field may overlap end of DESC **. (3) With the transmission method used, no low frequency components are involved, i.e. no signals less than 3.4 KHz, which means inductive line feed arrangements are smaller and cheaper than those in contemporary systems. (4) Attenuation introduced by a switch affects error rate rather than the reference equivalent for the connection. Hence the requirements for series resistance of the cross-point elements are set by the performance of the local loop transmission systems rather than by the network loss as a whole. Hence the series resistance requirements for the crosspoints when switched on are less stringent than would otherwise be the case. This reduces cost. In Figure 3, the incoming lines are connected to the main distribution frame 10, from which each line is connected to the distribution and power feed arrangements 11. Note that although this is shown as a separate block from the MDF, the protection elements and possibly also the power feed could well be incorporated into the MDF 10. From the block 11, the lines go to the pre-concentrator 12 which, as in the arrangement of Figure 1, is a two-stage co-ordinate switching array using electronic crosspoints. This gives access to a block of line transmission terminations 13 each of which effects conversion of the information between the "analogue" format on the line loops and the true digital format used within the exchange.The LTT block 13 is connected to block 14, which contains the subscribers' line circuits, and these are of course equal in number to the line transmission terminations in the block 13. The line units 14 are connected to block 15, of digital line terminations, where conversion is effected to and from the 30 channel PCM formal used in the exchange proper. Operations are controlled by a module controller 16, with a connection as shown to the main processors, and this module controller includes or controls line scanning means. This controller 16 controls the pre-concentrator 12 via a switch controller 17 and the line circuit and DLT blocks 14 and 15 via a line controller 18. The general operation of this equipment will be reasonably apparent in the light of the description given above of Figure 1. The module controller 16 and possibly the other controllers, are duplicated in the interest of system security, and for the same reason the preconcentrator 12 may be triplicated. In one example, the arrangement shown in Figure 3 has ISDN channels (e.g. 64Kb/s + 8Kb/s + 8 Kb/s), connected to the MDF 10 and therefrom to the pre-concentrator 12. The combined channels of 1024 such subscribers are concentrated without separation on to 256 channels at the LTT/SLU side. Further concentation once separation has taken place may not then be necessary, and if so one or more of the stages of the main switching network (2, Figure 1) can then be dispersed with. The number of crosspoints per subscribers' line is likely to be of the order of 20 to 30. In the arrangements described hereinbefore we have assumed that the cross-point devices are thyristors. However, other types of semi-conductor device may be used as cross-point devices, one example being a MOS transistor. CLAIMS (Filed on 22 Sept 1981)

1. An automatic telecommunication exchange, in which a group of subscribers' lines incoming to the exchange are connected to a number of subscribers' line circuits via a co-ordinate switching assembly, so that the number of line circuits is less than the number of subscribers' lines in the group, in which control means serving the subscribers' lines monitor the condition of those lines in search of calling conditions, and in which when a calling condition on one of the lines is detected a connection is set up from that calling line via the switching assembly to a free one of the line circuits, whereafter that line circuit is marked as busy.

2. An exchange as claimed in claim 1, and in which the co-ordinate switching assembly is a two stage assembly with the individual switch matrices made up of semi-conductor cross-points.

3. An exchange as claimed in claim 2, and in which the semi-conductor cross-points use thyristors whose on-off condition are controlled by latches.

4. An exchange as claimed in claim 2, and in which the semi-conductor cross-points use MOS devices whose on-off conditions are controlled by latches.

5. An exchange as claimed in claim 3 or 4, and in which the cross-points are in packages of 4 x 4 or 4 x 2 cross-points, the switch matrices each being assembled from a number of such packages.

6. An exchange as claimed in claims 1,2,3,4 or 5, and in which the line protection elements for the lines incoming to the exchange are connected to those lines on the line side of the co-ordinate switching assembly.

7. An exchange as claimed in claim 6, and in which the DC power feed arrangement for the subscribers' lines are also connected to those lines on the line side of the switching assembly.

8. An exchange as claimed in claims 1,2,3,4 or 5, in which the lines incoming to the exchange are connected to the line side of a main distribution frame (MDF) whose exchange side outlets are connected to the inlets to the co-ordinate switching assembly, and in which the line protection elements for the lines out the DC power feed arrangements therefor are installed at the MDF.

9. An exchange as claimed in any ome of the preceding claims, in which intelligence is conveyed over the incoming connections from the subscribers' lines in a digital form but with the digital elements conveyed in analogue form and in which the intelligence is maintained in such an analogue form within the co-ordinate switching assembly.

10. An exchange as claimed in claim 9, and in which for each incoming subscribers' line a plurality of digital channels is provided.

New claims or amendments to claims filed on 4 June 1982.

New or amended claims:

11. An automatic telecommunications exchange, in which a number of subscribers' lines incoming to the exchange have access to a number of subscribers' line circuits via a plural-stage co-ordinate switching assembly, the number q of said line circuits being less than the numbern of said subscribers' lines, in which the subscribers' lines are monitored via a set of p scanners each of which scans a number of said lines in search of calling conditions, where m x p is at least equal ton, in which a common control circuit is provided to which the outputs ofsaidp scanners are provided, which control circuit responds to the detection of a calling condition on one of said lines to select for use a free one of the line circuits, and in which when a free one of said line circuits has been selected a connection via said co-ordinate switching assembly is set up under the control of said common control circuit from the line on which a said calling condition was detected to the selected free line circuit, whereafter that line circuit is marked busy.

12. An exchange as claimed in claim 11, in which when a call is to be terminated at one of said lines a message to that effect is received by said common control circuit, which in response thereto selects a free one of said line circuits, in which the common control circuit also causes the wanted line to be tested and a connection via the co-ordinate switching assembly is set up to it from the selected line circuit if that line is free, whereafter the call is extended to that selected line circuit, and in which if the wanted line is found to be busy an indication to that effect is emitted and no connection is set up via the switching assembly.

New claims or amendments to claims filed on 17 June 1982.

New or amended claims:

13. An automatic telecommunication exchange, in which a number of subscribers' lines incoming to the exchange have access to a number of subscribers' line circuits via a plural-stage co-ordinate switching assembly, the number q of said line circuits being less than the number n of said subscribers' lines, in which the line protection elements for the lines incoming to the exchange are connected to those lines on the line side of the co-ordinate switching assembly, in which the subscribers' lines are monitored via a set ofp scanners each of which scans a number of said lines in search of calling conditions, where m x p is at least equal ton, in which the outputs of said p scanners are applied to a common control circuit which control circuit responds to the detection of a calling condition on a line to select for use for that line a free one of the line circuits, in which when a free one of said line circuits has been selected a connection via said switching assembly is set up underthe control of said common control circuit from the line on which a said calling condition was detected to the selected free line circuit, whereafterthat line circuit is marked busy, in which when a call is to be terminated at one of said lines a message to that effect is received by said common control circuit, which in response thereto selects a free one of said line circuits, in which the common control circuit also causes the wanted line to be tested and a connection to be set up via the co-ordinate switching assembly to the wanted line from the selected line circuit if that line is free, whereafter the call is extended to that selected line circuit, and in which if the wanted line is found to be busy an indication to that effect is emitted and no connection is set up via the switching assembly.

14. An exchange as claimed in claim 13, and in which the DC power feed arrangements for the lines are also connected to those lines on the line side of the switching assembly.

15. An exchange as claimed in claim 11, 12,13 or 14, in which intelligence is conveyed over the incoming connection from the subscribers' lines in a digital form but with the digital elements conveyed in analogue form, and in which the intelligence remains in said analogue form within the coordinate switching assembly.

16. An automatic telecommunication exchange substantially as described with reference to Figures 1 and 2, or Figures 2 and 3, of the accompanying drawings.