GB2038140A - Signalling systems - Google Patents

Abstract

In a modern telecommunication system of the "integrated network" type it is necessary for the individual telephone exchanges to be able to communicate signalling information to main centres such as group switching centres, and to such centres as centralised accounting centres. To enable this to be done an exchange has one or more signalling terminals, each of which provides several commonly-available signal channels for such communication. The signalling terminal or terminals is or are under the control of a processor (duplicated in the interest of security) with which there is associated a memory for the addresses of the centres to which messages are to be sent. This processor controls message assembly and transmission. In certain cases the processor may perform certain additional functions, such as those of the so-called management processor, described in our Patent No. 1 467 641.

Description

SPECIFICATION Signalling systems This invention relates to an automatic telecommunication exchange, and especially to such an exchange for use in a multiexchange network. For the interchange between exchanges of signalling information it is desirable to be able to provide one general purpose common channel signalling system optimised for a digital environment for operation in conjunction with stored program controlled exchanges, since such exchanges will ultimately be in the majority. In addition the signalling system should be suitable for serving the needs of an integrated services control network. The signalling system is assumed to be optimised for use with high bit-rate (e.g.

64 Kbits/s) channels, but would also be applicable over low speed digital channels and analogue links. The function of the system is to provide reliable land secure transfer of messages between processors in a telecommunications network. This is achieved by the use of sophisticated error control techniques and by the provision of duplicated signalling links with automatic change-over on failure. Error detection is provided by the inclusion of check bits in each signal unit and error correction is provided by retransmission.

The system must not introduce loss of information, out-of-sequence delivery of information or double delivery of information to the receiving end.

There are several reasons for adding common channel signalling to existing processorcontrolled systems such as TXE4 and TXE4A.

The common channel signalling link would enable call-charging data to be passed on towards a processing/billing centre if needed, and it would enable direct connection to a local maintenance centre to provide remote supervision and control of local exchanges. It would also allow such exchanges to end up more fully integrated with the evolving digital network by providing an interface suitable for signalling to other exchanges in the network.

This might be to a digital main network switching centre, for example. The possibilities are many and varied, and taken together provide good reasons for providing common channel signalling for such existing exchanges as TXE4 and TXE4A, and clearly the common channel signalling for TXE4A must be capable of being put to flexible use.

According to the present invention there is provided an automatic telecommunication exchange which when in use may be connected to one or other portions of a telecommunication system, which exchange includes a signalling terminal which serves the exchange and which provides one or more commonlyavailable signalling channels extending from the exchange to one or more other portions of the system, a memory associated with the signalling terminal and containing addresses of the destinations to which messages have to be sent from the exchange, control means associated with the exchange control equipment and responsive when a signalling message is to be sent to assemble the message, the process of assembly including obtaining from the memory the address or addresses to which the message is to be sent and the assembly of the message data, and means responsive to the assembly of said message to send it from the signalling terminal over channel therefrom appropriate to that message's destination.

An embodiment of the invention will now be described with reference to the accompanying drawing, which is a block schematic of a telephone exchange of the TXE4A type to which the invention has been applied. However, as already mentioned, the invention is applicable to other forms of telephone exchange.

Before describing the actual application of the invention the general operation of the exchange will be briefly described.

The exchange includes a four-stage switching network 1, which follows the principles of Patent No. 1 165 526 (G. Harland et all, which has local control equipment 2, which includes interrogators for testing speech paths for free or busy condiftions and markers for controlling speech path establishment. At the right hand or inlet side are a number of links such as 3, these including through links which do not have power feed and bridge links which do. One of these links is used for each call to be set up via the exchange. On the left-hand or outlet side are subscribers' line circuits such as 4, junction circuits such as 5 for incoming and outgoing junctions and registers such as 6.

Call establishment is effected by a number of main control units (MCU's) such as 7, plus scanner/cyclic store combination such as 8, and supervisory units (SPU's) such as 9.

Associated with the combinations 8, each of which serves a block of lines, junctions and registers (and other special facility circuits), we have a cyclic store controller 10, and the SPU's 9 have associated with them an SPU Handler 11.

The exchange has a further processor 12, which controls the common channel signalling terminal 13, and has associated with it a memory 14 for the addresses of distribution to which messages are sent over the common channel. There is also a direct memory address controller 16, and a device selector 1 7 to provide communications for signalling and other purposes between the processor 1 2 and various devices of the exchange shown. Note that this processor 1 2 can perform the functions of the so-called management processor which is described and claimed in our Patent No. 1 467 641 (G. G. Smith et al 7-5).

We now consider very briefly a typical call establishment apparatus. When a line assurnes a calling condition this is detected by that line's scanner 8. As a result an MCU such as 3 is seized for the call. The MCU receives from the cyclic store details of the calling line, and with the help of the appropriate ones of the markers 2 and SPU's 9 it connects the calling line via the switching network 1, a free bridge link 3 and the switching network 1 to a free register 6.

Proceed to send, often called dial tone, is now sent to the caller and the MCU withdraws from the connection.

On receiving the proceed to send the caller sends the wanted number, which is assembled in the register in use for the connection.

We assume that the call is a local one; when the number is complete the MCU, which regularly tests registers, detects this fact. The MCU then causes the wanted line to be tested. If it is busy, busy tone is applied, and the equipments release. If the line is free a new connection is set up from the caller to the wanted line, using a different link from that originally seized. The control equipment then drops out.

Further details of how the system functions may be found in British Patent No.

1 057 218 (Standard Telephones and Cables Limited, Her Majesty's Postmaster General and Automatic Telephone and Electric Company Limited).

There are two versions of signalling terminal contemplated at present to cover the range of sizes required. The larger version can handle from 1 6 up to 496 signalling links which may operate at 64 kbit/s or 4.8 kbit/s. The software for this version can be run on a multiprocessor arrangement. The smaller version can handle from 2 to 1 6 signalling links which may be 64 kbit/s or 4.8 kbit/s, and is designed for a small/medium local exchange with a both-way traffic capacity of up to 1000 erlangs. The software of this version is suitable for running on a duplicated processor operating in worker/standby mode.

TXE4A is a large local exchange for up to 10,000 erlangs of both-way traffic, and from this aspect the larger version of signalling terminal appears the most suitable choice for TXE4A. However, the choice of signalling terminal is not as simple for the following reasons, and it may be preferred to use the smaller terminal. One good reason for this is that TXE4A has sufficient processor power for call set-up and call supervision in its MCU's and SPU's. The additional processor 1 2 for the processing power for the signalling termi nal is only part of the total exchange processor power, so a duplicated processor arrange ment is sufficient.It is convenient to interface the smaller signalling terminal to the enhancement subsystem (when using the management processor of Patent No. 1 467 641) in this case as it is intended to work on a duplicated processor, while the larger version is structured to work on a multiprocessor arrangement.

Another point in favour of the smaller terminal is one derived from current equipment practice. The larger signalling terminal is too large physically for TXE4A enhancement even at the small end of its size range (two racks), whereas the smaller terminal is of a size which is more acceptable for use with the TXE4A.

The present estimate for a four link module is two shelves of equipment.

The smaller signalling terminal can handle up to 1 6 signalling links which will all be part of the same route. The hardware used is modular in steps of one, and the message carrying capacity of the terminal is limited by the processing time available (1 ms. in every 10 ms.) rather than the hardware, (receive and transmit queues etc.).

TXE4A needs several routes so that it can signal over a common channel to a digital main network switching centre, a digital junction switching centre and other large local exchanges. In addition it, may have to signal call charging information to a billing centre.

Connection to a local maintenance centre can also use a direct digital link. In the present systems, a typical TXE4A exchange has many small routes to adjacent exchanges with one large route to a group switching centre and possibly another large route to a tandem switching centre. Initially the local network may not include common channel signalling, but this must be catered for as it will come with the introduction of digital transmission and digital switching. Then the local network will evolve into more of a star network (arranged around a digital main network switching centre) instead of the present mesh network. One justification for providing common channel signalling for TXE4A is that digital transmission is available from local exchange to digital main exchange, or that a digital link to a local maintenance centre is required.

The smaller terminal can be made to work over more than one route, outgoing messages being allocated over the available links by the signalling terminal decoding part of the address field. The address field is inserted into the outgoing message by the user subsystem, which does not know that the address field is used by the signalling terminal in this way and allocated the address by using an algorithm. In the case of TXE4A, the user subsystem can use an algorithm which so inserts addresses that messages for each destination are allocated a particular group of signalling links, so that the signalling terminal automati cally sends messages to the correct destinations.

Using this method of identifying signalling links with routes it is possible to have up to four routes of four links each, or up to eight routes of two links each. This would be sufficient to allow TXE4A scope to develop into an exchange directly connected to the system X overlay network by common channel signalling at one or more points.

The smaller signalling terminal was initially developed as a four link module capable of carrying all messages necessary for the operation of a 1000 erlang local exchange. If 64 kbit/s signalling links are not available, then a larger number (up to 16) 4.8 kbit/s is necessary. In fact, depending upon exchange size and traffic handling capacity a quantity of between 4 and 20 links are necessary. Thus 1 6 links would be sufficient for the majority of TXE4A exchanges if the links were used at 64 kbit/s. The processor 1 2 must, of course, be capable of processing the signalling terminal at the required rate for the increased message rate.

At his point we revert to the drawing with special reference to the common channel and related matters. The processor 12, which as already mentioned may also serve the function of the "management" processor of the above-mentioned Patent No. 1 467 641, controls the selection of information to be signalled from the exchange. For this purpose it has access to the device selector 17, which in turn has access to the cyclic store controller 10, the scanner/cyclic store combinations such as 8, and the MCU's such as 7. The processor 1 2 also has access via the SPu handler 11 to the supervisory processing units 9. Thus the processor 12 can collect information for transmission via the common signalling channel from all parts of the exchange.

When such information has been collected, the message to be sent is assembled by the processor 1 2. The latter then notifies the DMA controller 1 6 that it needs an address to be attached to that message. Thus controller 1 6 has access to the device selector 1 7 and the SPU handler 11 so that when a message is to be sent it has such information as is available in the exchange which is relevant to the selection of the destination address.

Hence on this basis, assisted by such other information as the actual content of the message, the controller 1 6 selects from the memory 1 4 the address to be used for that message. The address thus selected is passed to the processor 12, so that assembly of the message has now been completed. The message is therefore sent out via the terminal 1 3 over the appropriate one of the signalling links to one of the destinations referred to above.

The processor 1 2 and its associated equipment items are duplicated in the interest of security, and can operate in this respect in various ways. Thus we can have load-sharing techniques, or the use of an active or passive stand-by processor.

In the present system the signalling terminal software operates on a duplicated preprocessor secured in the worker/stand-by method of operation. An operating system, which is a collection of software processes, runs on the processor as part of the user subsystem, and allocates the signalling terminal processes as necessary. The operating system is also responsible for inter-processor communication.

When there is a processor used to provide additional facilities, such an enhancement processor is to be a duplicated processor secured in a load sharing mode of operation.

Because of the large development effort needed for the signalling terminal software it is desirable to use it as it stands on the enhancement processor. Hence where the workload permits, the signalling software is run on the other processor. This will need some alteration to the software due to change from one machine to another, plus the fact that running software processes on a load sharing pair of processors differ from the use on worker/stand-by processors.

In the preceding descriptions references have been made to several earlier dated British Patent Specifications: the text of these specifications is to be considered as part of the disclosure in the present specification.

Claims (6)

1. An automatic telecommunication exchange which when in use may be connected to one or other portions of a telecommunication system, which exchange includes a signalling terminal which serves the exchange and which provides one or more commonly available signalling channels extending from the exchange to one or more other portions of the system, a memory associated with the signalling terminal and containing addresses of the destinations to which messages have to be sent from the exchange, control means associated with the exchange control equipment and responsive when a signalling message is to be sent to assemble the message, the process of assembly including obtaining from the memory the address or addresses to which the message is to be sent and the assembly of the message data, and means responsive to the assembly of said message to send it from the signalling terminal over a channel therefrom appropriate to that message's destination.

2. An exchange as claimed in claim 1, and in which the assembly of the messages and the transmission thereof via the signalling terminal are controlled by a processor additional to the processing means used for normal call setting operations.

3. An exchange as claimed in claim 2, and in which said additional processor also performs ancillary operations in respect of the exchange in the manner set out in our British Patent No. 1 467 641.

4. An exchange as claimed in claim 1, 2 or 3 in which the operations of the exchange are supervised by a device selector which has access to the control equipment of the exchange, and in which data to be assembled into a said massage is obtained from the said device selector.

5. An automatic telecommunication exchange substantially as described with reference to the accompanying drawings.

CLAIMS (22 Jan 1980)

6. An automatic telecommunication exchange which, when in use may be connected to one or more other telecommunication exchanges, which exchange includes a signalling terminal from which one or more commonly available signalling channels extend to said one or more other exchanges, a memory associated with the signalling terminal and containing addresses of the exchange destination to which messages have to be sent over said channel or channels, a processor additional to the exchange control equipment used for call establishment operations within the exchange, which processor is associated with said exchange control equipment and is responsive when a signalling message is to be sent to control the assembly of that message, the process of message assembly including obtaining from the memory the address to which the message is to be sent and the assembly of that address to the message data to form the message, a device selector which supervises the operations of the exchange and has access to the exchange control equipment, the message data to be assembled into a said message being obtained under the control of the device selector and applied therefrom to said processor, and means responsive to the assembly of a said message to transfer that message to the signalling terminal from which it is sent via the one channel appropriate to that message's destination.