GB2318020A

GB2318020A - Telecommunications exchanges

Info

Publication number: GB2318020A
Application number: GB9620816A
Authority: GB
Inventors: Brian Scally; Chris Philips; Ian Bernard Stewart
Original assignee: Roke Manor Research Ltd
Current assignee: Roke Manor Research Ltd
Priority date: 1996-10-05
Filing date: 1996-10-05
Publication date: 1998-04-08
Anticipated expiration: 2016-10-05
Also published as: GB2318020B; GB9620816D0

Abstract

A Private Automatic Branch Exchange (PABX) is provided by connecting a plurality of personal computers 1,2,3,4 via a local area network 6,7,8 to an interface unit 19 which serves to connect the local area network to a public switched telecommunication network 18. By connecting a telephone or similar communications apparatus 13-16 to the personal computer, and providing each personal computer with call processing means, an inexpensive distributed PABX is provided by a combination of said personal computers, said interface unit and said local area network.

Description

IMPROVEMENTS IN OR RELATING TO TELECOMMUNICATIONS EXCHANGES The present invention relates to telecommunications exchanges and in particular to telecommunications exchanges which provide call processing and inter-connection of telephones for private telecommunications networks.

Private Automatic Branch Exchanges (PABX) provide a facility for inter-connecting a plurality of telephones associated with a private telecommunications network. Typically, the telephones are provided at various points around a business premises and serve to provide communications for staff sited at remote locations. The PABX provides a means for connecting calls between telephones connected thereto, and for providing a means for connecting calls through telephones connected to the PABX, and telephones connected to a public telecommunications network.

Furthermore, such PABXs are provided with sophisticated call processing functions which provide facilities such as diverting calls when a telephone is not answered within a predetermined time limit, call re-routing on request, and voice mail etc. Some PABXs may also provide a facility for transmission of data, such as E-mail and the like.

Although PABXs have been manufactured and developed for a number of years, the cost of a PABX is typically still prohibitively large to a small business or private firm, in which only a relatively small number of telephones are to be connected.

In this case, call routing and inter-connection is performed manually by a dedicated operator. Alternatively each person in the business is provided with a dedicated line to the public telecommunications network. Since telecommunications companies charge a line rental for each line, a requirement for a dedicated line for each person is expensive for the small business.

In either case, the call processing facilities provided by PABXs are not available to small businesses. Furthermore, there is an increasing requirement for data as well as voice communications.

Such facilities will become increasingly desirable to a small business, further promoting a demand for a provision of advanced PABX type facilities to the small business.

Accordingly, it is an aim of the present invention to provide an inexpensive telecommunications exchange for a relatively small number of users.

According to the present invention, there is provided a telecommunications exchange for inter-connecting a plurality of communications apparatus so as to form therewith a private telecommunications network, comprising a plurality of personal computers to which said plurality of communications apparatus are connected, each of which personal computers being provided with a call processing means which operates in combination with the personal computer to provide call processing and connection facilities to at least one of said communications apparatus connected thereto, a local area network to which said personal computers are connected which provides a means for communicating data between said personal computers, and an interface unit connected to the local area network for providing an interface between a public telecommunications network and said telecommunications exchange.

The interface unit may comprise a data processor which operates to inter-work between the local area network and the public telecommunications network to which the data processor is connected via a telecommunications interface unit and a local area network interface unit.

The interface unit may be embodied within at least one of the personal computers.

The telecommunications network may be a public telecommunications network.

Personal computers are now common place in small businesses. Furthermore, such personal computers are typically networked and inter-connected via a local area network, such as an Ethernet. By providing an interface unit to effect communications between the public telecommunications network and data communicated via the local area network, a private branch exchange may be provided via a plurality of interconnected personal computers, wherein call processing facilities may be provided by a combination of software running on the PCs and the communications apparatus connected to the PCs providing a facility for users to communicate. A combination of personal computers inter-connected via a local area network and a distribution of data processing operations required to provide the facilities of a private branch exchange, serves to provide an inexpensive way of providing advanced facilities of a PABX to a small business.

One embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings, wherein, FIGURE 1 is a conceptual perspective view of a distributed telecommunications exchange; FIGURE 2 is a block diagram of apparatus embodied within personal computers of the telecommunications exchange shown in Figure 1; FIGURE 3 is a conceptual block diagram of elements which comprise the interface unit of the telecommunications exchange, and, FIGURES 4a - 4d are a set of four signal waveform diagrams, illustrative of the effects of processing operation performed by the interface unit shown in Figure 3.

An embodiment of the present invention will be illustrated with reference to a plurality of personal computers connected via a local area network. However, as will be appreciated, the present invention is not so limited to personal computers and the necessary apparatus for effecting the invention may be embodied with an alternative computer or data processing apparatus, which may be dedicated for this purpose.

Figure 1 shows a perspective view of a schematic representation of a plurality of personal computers connected via a local area network, which may, for example, be an Ethernet network. In Figure 1, four computers, 1, 2, 3, 4, are connected via an Ethernet formed by conductors 6, 7, 8. The Ethernet local area network (LAN) comprises the conductors 6, 7, 8, and an Ethernet interface card embodied within each of the computers 1, 2, 3, 4, which interface cards 9, 10, 11, 12, are inter-connected by the conductors 6, 7, 8, so as to form a 'BUS' architecture. Also shown connected to the computers 1, 2, 3, 4, are telephone receivers 13, 14, 15, 16, which serve to provide voice communications. Also connected into the Ethernet LAN is a PABX interface unit 19, which is connected to a Public Switched Telephone Network (PSTN) 18, via conductors 17 and 17'. The PABX interface unit 19 provides a means for inter-connecting the telecommunications network 18 with the local area network formed by the Ethernet and the personal computers 1, 2, 3, 4.

As will be appreciated, the embodiment of the present invention illustrated in Figure 1, with reference to telephone receivers 13, 14, 15, 16, may also be used to effect data communications from a source generated within the personal computers 1, 2, 3, 4. The personal computers 1, 2, 3, 4, may be distributed throughout a business premises and may for example be provided on each employee's desk. The telephone receivers 13, 14, 15, 16, thereby provide the employees with a means for voice communications. The personal computers 1, 2, 3, 4, are connected via the Ethernet LAN, which provides a means for transmitting data to any one of the other PCs connected to the Ethernet. Each of the personal computers 1, 2, 3, 4, is therefore provided with a means for converting data generated by, for example, the telephone receivers 13, 14, 15, 16, into an appropriate format for transmission over the Ethernet to one of the other PCs, whereat the data is re-transformed into a form which can be fed to the telephone receiver connected thereto, thereby providing a means for effecting voice communications over the Ethernet via the PCs.

The PABX interface unit 19, operates to inter-work between data and messaging information generated by the Ethernet and data and messaging information generated by the public switched telephone network 18. This inter-working provides a means whereby a call from a telephone connected to the public switched telephone network 18, may be routed via the PABX interface unit 19, to one of the telephone receivers 13, 14, 15, 16, connected to one of the personal computers 1, 2, 3, 4, via the Ethernet.

Similarly, a call made from one of the telephones 13, 14, 15, 16, may be placed with a corresponding telephone connected to the public switched telephone network 18 via the PABX interface unit 19, over the LAN. Call processing and signalling operations to effect this call connection from a telephone connected to one of the PCs, and a telephone connected to the public switched telephone network, is provided by apparatus embodied within each of the personal computers 1, 2, 3, 4. A diagram of such apparatus is shown in Figure 2, where parts also appearing in Figure 1 bear identical numerical designations.

In Figure 2, the Ethernet card 10, is shown to be connected to a central processing unit (CPU) 22, of the PC 1, via a conductor 23.

The central processing unit 22 of the PC 1, is also connected via a conductor 24, to a sound card 20, and also to a telephone receiver 13, via a conductor 26. The telephone receiver 13, is also connected to the sound card 20, via conductor 25.

The CPU 22, operates in accordance with an operating system installed on the personal computer to effect a Telephone Services Application Programme (TSAPI), or other standard telephone service provision which serves to generate and respond to call processing commands received from the Ethernet card 10, via the Ethernet LAN. In operation, therefore, TSAPI serves to respond to commands received from the Ethernet to establish a telephone connection between the telephone receiver 13 and a telephone receiver, either connected to the Ethernet via a corresponding PC (2, 3, 4) or connected to the public switched telephone network 18, via the PABX interface unit 19. The CPU 22, generates signalling commands in accordance with the TSAPI and generates control signals on conductors 26, 24, to control the sound card 20 and the telephone receiver 13. Data to be communicated to the telephone receiver 13 is thereby received by the Ethernet card 10, and where the data is audio information appertaining to an audio based telephone call, the data is fed from the Ethernet card 10, via the CPU 22 and conductor 24, to the sound card 20, which operates to generate analogue representations of audio signals in accordance with the data received, which are thereafter passed to the telephone receiver 13. The CPU may also serve to decode, uncompress or unencrypt the data. Where information is to be sent from the telephone receiver 13, analogue signals representative of audio signals generated by the telephone receiver 13, are fed via conductor 25, to the sound card 20, which thereafter generates digital data representative of the audio signals, which in conjunction with the CPU produces data in a format required for communication over the Ethernet via the Ethernet card 10. As will be appreciated the example shown in Figure 2 is for generation and transmission of voice communications, although equally data may be communicated and generated via the CPU 22, and transmitted over the Ethernet, via the Ethernet card 10, in accordance with for example an E-Mail communication.

In order to effect the connection of one of the telephone receivers 13, 14, 15, 16, with a telephone connected to the public switched telephone network (PSTN) 18, the PABX interface unit 19, must perform inter-working operations for signalling information as well as data. An example embodiment of the PABX interface unit 19, is shown in Figure 3, where parts also appearing in Figure 1 and 2, bear identical numerical designations. A general form of the interface unit 19, is shown in Figure 3 connected to the public switched telecommunications 18, and the Ethernet LAN via the conductors 7, 8, and the LAN interface unit 9. Also connected to the local area network interface unit 9 is a local area network signalling unit 30, which operates to inter-work and exchange local area network commands and corresponding commands received from the telecommunications network 18, in co-operation with the interface unit 9. The PABX interface unit 19, is conceptually comprised of two parts, which are a PSTN interface unit 39, and an inter-working unit 17. The PSTN interface unit 39, and interworking unit 17, are further conceptually comprised of two halves, the upper half associated with signalling and data received from the public switched telephone network via the PSTN interface unit 39, and a lower half associated with signalling and data received from the local area network, via the LAN interface unit 9. The upper half of the inter-working unit 17, is comprised of a signalling inter-working unit 31, connected to a compression and processing unit 32. Also connected to an input of the compression and processing unit 32, is a data re-clocking unit 33. The signalling inter-working unit 31, and data re-clock unit 33, are fed from signals received from a Public Switched Network Telephone (PSTN) receiver interface 34, which is correspondingly associated with an upper half of the PSTN interface unit 39. An output of the compression and processing unit 32, feeds the LAN interface 9.

Signals generated from the local area network are communicated to a de-compression and processing unit 35, which is part of the lower half of the inter-working unit 17. A first output from the de-compression and processing unit 35, feeds a data re-clocking unit 36, whereas a second output from the data de-compression and processing unit 35, feeds a second signalling inter-working unit 37. Outputs from the second data re-clocking unit 36, and second signalling inter-working unit 37, feed a PSTN transmit interface 38, which forms the lower half of the PSTN interface unit 19. The PSTN network receive interface 34, and PSTN network transmit interface 38, are connected to corresponding elements within the PSTN telecommunications network 18.

In operation, the PABX interface unit 19, forms a general purpose inter-working unit, which operates to self configure, during an initialisation phase, to the telecommunications network to which it has been connected. In this example embodiment, the PABX interface unit 19, is connected to a PSTN telecommunications network. In this case, the first and second signalling interworking units 31, 37, operate to interpret and exchange commands received from or transmitted to the PSTN in accordance with a call connection and routing operation. Similarly, the first and second data re-clocking units serve to translate data formats received from the PSTN and sent to the PSTN with those corresponding formats which must be provided to the local area network.

Furthermore, the compression and processing unit 32, provide appropriate compression for signalling and data transmitted from the PSTN to the local area network, whereas in the opposite direction, data and signalling transmitted from the local area network to the PSTN is de-compressed and processed by the decompression and processing unit 35.

The inter-working unit 17, PSTN interface unit 39, and LAN interface 9, in combination perform an inter-working function between the PSTN and the local area network, which operates in an asynchronous manner. The inter-working unit 17, provides a means for inter-working voice and combined voice and data and data only communications from a non-guaranteed quality of service network, which is in this case is the LAN, to a public switched telephone network. This operation is dependent upon the PSTN line type. The inter-working of voice and voice and data connections onto an PSTN line for example, require audio data samples from the local area network which are communicated asynchronously, to be re-clocked to allow their transport across the PSTN interface unit 39, thereafter to be communicated to the PSTN 18. The inter-working unit 17, operates to accommodate problems of delay, delay jitter, and different data rates associated with data transmitted to and received from the local area network.

To allow for high quality audio with low latency inter-working between the local area network and the PSTN, the inter-working unit 17, operates to provide a synchronised data stream for an ISDN interface, for example, with an appropriate received data stream for the local area network interface. In order to convert from the synchronised data streams to a non-guaranteed quality of service transport format, associated with the local area network, the data clocking units 33, 36, in combination with the signal inter-working units 31, 37, operate to effect the data transmission and translation. An example of re-clocking and translation between an asynchronous data format and the non-guaranteed quality of service format of the local area network, may be seen for example, by considering audio signals generated in accordance with voice communications. This is illustrated by four waveform diagrams with associated signal samples shown in Figures 4a to 4d.

In Figure 4a, an audio signal waveform is shown to be represented by a plurality of samples 41, which are generated by synchronous data stream received in accordance with an ISDN connection. Thus, the audio signal samples are transmitted from the PSTN receive interface 34, to the data re-clocking unit, and thereafter to the data compression and processing unit 32. These units in combination operate to re-clock and re-generate samples representative of the original audio signal as illustrated by the waveform diagram 40. As illustrated in Figure 4b, a first operation is to generate a plurality of interpolated over samples 42, of the audio signal in accordance with the original discrete time samples 41. Thereafter, and in accordance with a clocking rate appropriate to the local area network, the interpolated and over sampled audio signal 40 is re-sampled at a new clocking rate by appropriately selecting samples of the over sampled audio signal.

This is shown and illustrated in Figure 4c. Thereafter and in accordance with the new clocking and sampling rate, discrete time samples 43, representative of the audio signal 40 are passed to the local area network interface 9, for communication to one of the telephone receivers 13, 14, 15, 16, connected to one of the PC's 1, 2, 3, 4, and via the local area network. This is illustrated in Figure 4d.

As will be appreciated by those skilled in the art, various modifications may be made to the embodiment hereinbefore described without departing from the scope of the present invention. In particular, the telecommunications network to which the local area network is to be connected, may be an ATM network, in which case the PSTN interface unit 39, will be an ATM interface unit. Furthermore, the local area network may be a wireless local area network, or may be a local area network arranged in accordance with other variations of the Ethernet system.

Claims

1. A telecommunications exchange for inter-connecting a plurality of communications apparatus so as to form therewith a private telecommunications network, comprises a plurality of personal computers to which said plurality of communications apparatus are connected, each of which personal computers being provided with a call processing means which operates in combination with the personal computer to provide call processing and connection facilities to at least one of said communications apparatus connected thereto, a local area network to which said personal computers are connected which provides a means for communicating data between said personal computers, and an interface unit being connected to the local area network for providing an interface between a public telecommunications network and said telecommunications exchange.

2. A telecommunications exchange as claimed in Claim 1, wherein the interface unit comprises a data processor which operates to inter-work between the local area network and the public telecommunications network to which the data processor is connected via a telecommunications interface unit and a local area network interface unit.

3. A telecommunications exchange as claimed in Claim 2, wherein the data processor includes signalling inter-working means, which operates to convert messages and signalling information generated by the local area network into corresponding messages and signalling information for communication to the public telecommunications network, and to convert messages and signalling information generated from the public telecommunications network for communication to the local area network.

4. A telecommunications exchange as claimed in Claim 2 or 3, wherein the data processor further includes a data clocking means which operates to convert a sampling rate of data received from either the public telecommunications network or the local area network into a second sampling rate appropriate for communication on the other of the public telecommunications network or the local area network thereby effecting a transformation between discrete time representations of data generated from either the local area network or the public telecommunications network.

5. A telecommunications exchange as claimed in Claim 4, wherein the data processor further includes data compression means which operates to compress data received from said signalling inter-working means and said data re-clocking means, whereby said compressed data can be communicated via the local area network, and data de-compression means which operates to de-compress data received from the local area network for communication to the said clocking means and said signalling inter-working means.

6. A telecommunications exchange as claimed in any preceding Claim, wherein the personal computers include a local area network interface being connected to the local area network, which provides a means for communicating data via the local area network.

7. A telecommunications exchange as claimed in Claim 6, wherein said at least one communications apparatus is a telephone receiver and the personal computer further includes sound processing means which operates to convert data received via the local area network into analogue representations of audio signals fed to the telephone receiver, and for converting analogue representations of audio signals from the telephone receiver to data for transmission via the local area network.

8. A telecommunications network as claimed in any preceding Claim, wherein the interface unit comprises an initialisation means which operates to configure the data processor in dependence upon the telecommunications interface and the local area network interface to which said interface unit is connected.

9. A telecommunications exchange as claimed in any preceding Claim, wherein the public telecommunications network is a public switched telecommunications network.

10. A telecommunications exchange as claimed in any preceding Claim, wherein the local area network is an Ethernet.

11. A telecommunications exchange as hereinbefore described with reference to the accompanying drawings.