AU4094993A - Communication methods and apparatus - Google Patents

Description

CO MU ICATION METHODS AND APPARATUS

Technical Field

The present invention relates to telecommunication apparatus suitable for connecting subscribers to a high data rate digital communications network, directly or via a radio link. More particularly, but not exclusively, the invention relates to a communications apparatus including network, subscriber and radio transceiver interface modules interconnected by a cross connect switch, wherein at least some time slots are allocated dynamically.

Background of the Invention

For a small number of subscribers of a telecommunications network it is not economic to provide a full exchange. To date two options have been available for communicating to remote areas via low capacity radio links. The first option is a low rate radio link coupled to a phone or data multiplexer card. This allows communication from a radio source directly to a phone line of a telecommunication network. The alternative option is a low rate radio link coupled with a framing unit to allow interfacing to a microwave link or the like at a standard primary rate (i.e. 2Mbps) . Such units have been regarded as separate stand alone units and not part of an integrated telecommunications network. These systems have a fixed configuration and a limited non- expandible capacity. There has existed a need for a flexible and expandible system having up to 30 circuits which can interface between subscribers, radio links and a national telecommunications network.

A further problem with prior ^rt systems relates to wastage of the radio link capacity. Where two subscribers are connected to a common radio link prior art systems have routed communications through the radio link and local exchange, wasting the available capacity of the radio link. Prior art systems have also been inefficient in their use of the available radio spectrum.

Disclosure of the Invention

It is an object of the present invention to provide a system which mitigates these disadvantages or at least provides the public with a useful choice.

According to a first aspect of the invention there is provided a multi-channel digital communication apparatus comprising:

i) a control module including processing means and a cross connect switch; and two or more of the following interface modules:

ii) a network interface module which interfaces communications between the control module and a high data rate digital communications network;

iii) a subscriber interface module which interfaces data or voice communications from a subscriber to the control module; and iv) a radio transceiver module which interfaces radio communications between the control module and the remote radio transceiver, characterised in that the interface modules are linked to the cross connect switch of the control module by data highways with the control module allocating time slots for communications between the modules; wherein at least some time slots are allocated dynamically as required by the interface modules.

Preferably connectors are provided in the data highways connecting at least some of the interface modules to the control module to allow easy configuration of an apparatus to suit network requirements.

According to a further aspect of the invention there is provided a method of communicating between first and second subscribers connected to a first —__ communications apparatus, said first communications apparatus being linked to an exchange by a communications link; said method comprising:

i) upon said first subscriber placing a call, said first communications apparatus sending a call request including a unique identifier to the exchange,

ii) the exchange sending the unique identifier back to the first communications apparatus when routing the call to the second subscriber; and

iϋ) the first communications apparatus comparing the received identifier with its own identifier and, if identifiers match, routing communications directly between the first and second subscriber and releasing the communications link.

The communications link may include a radio link to a second communication apparatus, which is directly connected to the exchange by a high data rate link. When matching identifiers are detected the link between the first and second communications apparatus may be released, with the second communications apparatus maintaining an off-hook status whilst the call continues. At the end of the call a signal may be sent by the first communications apparatus to the second communications apparatus indicating that the call has finished.

The unique identifiers may be compared by cross correlation. The unique identifier may be in the form of an audio frequency carrier wave phase shift modulated, a band limited waveform or a swept frequency chirp.

Brief Description of the Drawings

The invention will now be described by way of example with reference to the accompanying drawings in which:

Figure 1: shows the communication apparatus of the invention in block form.

Figure 2: shows a typical integrated telecommunications network using a number of the apparatus of figure 1.

Figure 3: shows two apparatus as shown in figure 1 connecting two remote subscribers to a telecommunications network via a radio link.

Best Mode for Carrying out the Invention

Referring to figure 1 the communications apparatus is seen to comprise a control module 2 (including cross connect switch 5, CPU 20, memory 22 and optionally multi-party conferencing unit 23) connected to 3 interface modules: network interfaces 1 and la; subscriber interfaces 3 (interfaces 9-12) and radio transceiver 4. The interface modules are connected by data highways, preferably 2Mbps (megabits per second) 32 time slot PCM highways, through cross connect switch 5. Cross connect switch 5 assigns time slots for communications between the interface modules.

In the embodiment ^hown in figure 1 connectors 25 to 29 are interposed in the data highways 13 and 15 connecting modules 4, 9, 10, 11 and 12 to the control module 2. In the embodiment shown in figure 1 the network interfaces 1 and la are included in the control module. Network interfaces 1 and la may be separate modules and connectors may be interposed in the data highway 6a and 6 between the network interface modules 1 and la and cross connection switch 5. By providing connectors 25 to 29 interface modules may be added to or removed from the system as required for a particular configuration.

Network interfaces 1 and la are connected to cross connect switch 5 via data highways 6 and 6a, which may operate at a data rate of about 2Mbps. Network interfaces 1 and la may communicate with a high data rate communications network using G.703 or G.704 protocol operating at 2Mbps. Network interfaces 1 and la may be based on the Mitel Semiconducor MT8979 integrated circuit. Outputs 7 and 7a and inputs 8 and 8a of network interfaces 1 and la may be connected to high data rate digital communications networks, such as telephone exchanges, microwave links, fibre optic links etc. It is envisaged that the communications apparatus will typically be connected to the national telecommunication network at at least 1 point.

Both network interfaces 1 and la are used when communications are to be sent both up and down a telecommunications network. Where the communications apparatus is at the end of a network only one network interface 1 need be provided. Network interfaces 1 and la may also enable back-to-back interconnection of two units as shown in figure 2.

Referring now to the subscriber interface modules 3 a number of subscriber modules 9 to 12 are seen to be connected to cross connect switch 5 via a 2 Mbps data highway 13. Each module 9 to 12 being connected to the data highway 13 via a connector 26 to 29.

Module 9 is a 4 wire E & M trunk interface, typically providing five circuits. Module 10 is a two wire trunk and subscriber interface. This may be divided into a two wire exchange module and a two wire subscriber module, providing five circuits per module. Module 11 may be a rate adaptor allowing synchronous or asynchronous communication (RS232 or RS422) (X.21)) with data equipment, typically providing two circuits. Module 12 may be a 64 Kbps digital interface or ISDN interface providing five circuits. Modules 9 and 10 which allow voice communication use 64Kbps PCM coding to allow communication via the 2Mbps PCM highway. A G721 ADPCM coding module may be added to double the voice circuit capacity.

Trunk and subscriber interface module 10 may be provided with the necessary circuitry and/or software to enable coin box operation. For military applications card 10 may support central battery (CD) and magneto telephone operation. Modules 9 and 10 may include an SGS Thompson TS5070 integrated circuit to convert analog interface signals to digital PCM format. Module 10 may include SGS Thompson L3000 and L3010 integrated circuits to interface standard 2 wire analog telephone instruments to the apparatus.

Referring now to radio transceiver 4, the transceiver is seen to include a modem 14 which communicates with cross connect switch 5 via a 2 Mbps data highway 15. Modem 14 performs the necessary framing operations to enable communications between the radio and cross connect switch 5. Signals received by antenna 16 are supplied to duplexer 17 which routes the signals to receiver 18. Signals received by modem 14 from receiver 18 will be framed and placed in an appropriate time slot on data highway 15. Communications received on the data highway to be transmitted by the radio will be extracted by modem 14 and sent to transmitter 19, which will transmit the signals to duplexer 17 for transmission by aerial 16. The radio may typically operate at frequencies between 600 to 2500 MHz.

Cross connect switch 5 may suitably be based on a Mitel Semiconductor MT8980 integrated cirucit controlled by a central processing unit 20 (suitably a Motorola 68302) connected to cross connect switch 5 via a 2mbps data highway 21. CPU 20 and cross connect switch 5 are both connected to memory 22. CPU 20 controls the operation of cross connect switch 5 in accordance with software stored in memory 22.

Cross connect switch 5 routes time division multiplexed information between network interfaces 1, la; subscriber modules 3 and radio transceiver module 4. Time slots may be allocated on a static basis (i.e: a certain number of time slots are allocated for certain routes) or time slots may be allocated on a dynamic basis (i.e: time slots are allocated dynamically in response to time slot requests form each module) .

For example under static time slot allocation 14 time slots may be allocated for communications between network interfaces 1 and la and subscriber modules 3, 14 time slots may be allocated for communications between radio transceiver module 4 and network interfaces 1 and la and 4 time slots allocated for communications between radio transceiver 4 and subscriber modules 3. Under such static allocation a further subscriber of a subscriber module 3 may be unable to communicate with radio transceiver 4 if all 4 time slots are in use, despite the fact that the remaining 28 time slots may be unused.

Under Dynamic time slot allocation the modules request a time slot, and the CPU allocates a time slot if one is available. Under fully dynamic allocation all time slots could be allocated to a single communication path. A mixture of dynamic and static allocation may be used to ensure a minimum number of time slots are allocated to each path with the balance being assigned dynamically as requested. Routing may be controlled by software (discussed later) or in response to user commands (e.g. dial tones or computer generated commands) . Dynamic routing controlled by appropriate software will enable the system to provide PABX-like operation. The dynamic allocation of time slots enables much greater flexibility and increased data handling capacity. According to the invention at least a portion of time slots are allocated dynamically.

It is envisaged that the communications apparatus of the invention will be of a rack construction allowing interchangeable modules to be inserted or removed in accordance with user requirements. Connectors 25 to 29 may be 2 part connectors with one section being mounted to the rack, enabling the data highways of the interface modules to be connected to the data highways of the cross connect switch 5 when the modules are inserted in the rack and both sections of the connectors are engaged.

A rack construction allows great flexibility in configuring a system for users requirements. For example the most simple system may consist of a two wire trunk and subscriber interface card 10, radio transceiver 4 and a cross connect switch 5. Such a configuration would allow communications to a telephone subscriber terminal over a radio link.

If the system is to be connected to a telephone exchange a network interface 1 may be provided. If the communications apparatus is to form an intermediate link of the microwave link a further network interface la may be provided. As subscriber demands increase further subscriber cards 9, 10, 11 or 12 may be added to the system.

Likewise, radio transceiver 4 may be upgraded as data capacity is increased. Where microwave frequencies of greater than 3 GHZ are required a replacement card may be provided which supplies an intermediate frequency signal to an RF amplifier at the rear of a microwave antennae. Cards including band up/down converters may also be provided to enable satellite links to be established.

For long radio links two systems may be connected back to back to form a repeater. Each system would include a radio transceiver 4 and a network interface 1. The network interfaces 1 would be simply interconnected to provide a repeater.

Figure 2 shows a typical communications network including apparatus of the form shown in figure 1. A central exchange 30 is connected to a high capacity digital backbone consisting of microwave repeaters 31 to 34. The communications apparatus indicated by the numerals 35, 36, 38, 39, 41, 42, 44 and 45 are communications apparatus as shown in figure 1, configured for their position in the network.

Communications apparatus 35 consists of the apparatus shown in figure 1 without any of the subscriber interfaces 9 to 12. Apparatus 35 is connected to microwave repeater 32 by a 2Mbps link. Link 46 may be connected to the ports 7 and 8 of network interface 1. Network interface la of apparatus 35 may connect to network interface 1 of apparatus 38 via 2Mbps link 47. Likewise, apparatus 41 is linked to apparatus 38 via 2Mbps link 48. Apparatus 35 is connected to communication apparatus 36 at a first site A via a radio link 49. This would typically be a .7Mbps link having up to 10 circuits. Apparatus 36 may be provided with a radio transceiver 4 and an interface module 10 to allow the connection of 5 subscribers 37 to the national network via the radio link.

Communications apparatus 39-links site B to communications apparatus 38 via a .7 Mbps radio link 50 (10 circuits). A digital rural switch 40 may be connected to communications apparatus 39 to provide 10 local line connections. Communications apparatus 44 is connected to communications apparatus 39 via a 2Mbps link 51 and provides a radio link 52 to the communications apparatus 45 at site C. Communications apparatus 45 includes interface modules 9 or 10 to provide local circuits at site C. Communications apparatus 42 is connected to communications apparatus 41 via a .7 Mbps radio link providing 10 circuits. Communications apparatus 42 is connected to an analogue PABX 43.

It will be seen that various configurations of the apparatus shown in figure 1 are employed at different points in the network. For example, communications apparatus 36 does not require network interfaces 1 and la and cormunications apparatus 35 does not require subscriber interfaces 9 to 12. The communications apparatus of the present invention gives the flexibility to configure each communications apparatus for the requirements of a particular network link. This makes the communications apparatus of the invention cost effective and flexible.

A method of communicating between a first communication apparatus and a second communication apparatus to increase the available capacity of the system will now be described^ Although the advantages are greatest where a radio link is employed, the method may be used advantageously for any link.

Referring to figure 3 a typical configuration is shown. First and second subscribers 64 and 65 are connected to a first communications apparatus 63 of the form shown in figure 1. The first communications apparatus 63 includes a subscriber interface 10 and radio transceiver 4 (see figure 1). First communications apparatus 63 communicates with second communications apparatus 62 over a radio link 66. Second communications apparatus 62 communicates with exchange 60 via a high data rate communications link 61. Second communications apparatus 62 includes a network interface 1 and transceiver 4 (see figure 1).

In normal operation first subscriber 64 places a call, which is communicated from first communications apparatus 63 to second communications apparatus 62 over radio link 66, and on to exchange 60 over high data rate link 61. The exchange then routes the call back through second communications apparatus 62 and first communications apparatus 63 to second subscriber 65. The communication over the radio link is however wasted as the two subscribers could have been connected directly without using the radio link. As the radio link has only a data carrying capacity of 700Kbps (compared to 2Mbps for the other links) it is important not to waste the capacity of this link.

The problem can be overcome by directly connecting the two subscribers. This however requires the system to identify internal calls. This would require a table of subscriber telephone numbers to be maintained listing the communications link to which each subscriber is connected. Problems also arise in that for billing purposes the network cannot monitor the length of the call between the subscribers. Call diversion must also be allowed for.

These problems may be overcome by employing the following method. A call from first subscriber 64 is sent over radio link 66 to second terminal 62 connected to exchange 60. With the call is transmitted a unique identifier identifying communication apparatus 63. The call is processed at the exchange and is routed back through communications apparatus 62 and radio link 66 to first communications apparatus 63. The unique identifier is sent back to the first communications apparatus with this transmission. When the second subscriber 65 answers the call the first communications apparatus 63 compares the unique identifier received with its own unique identifier stored in memory. If the unique identifiers match the first communications apparatus knows that both subscribers are connected to it. If the unique identifiers do not match the call continues in the nrmal way. Likewise, if call diversion has been en__ led, then normal operation continues through the exchange. If however both subscribers are connected to the same communications apparatus and call diversion is not enabled then the first communications apparatus effects a direct connection between first and second subscribers 64 and 65. The first communications apparatus 63 sends a message to second communications apparatus 62 instructing it to maintain the "off hook" status and release the link between first communications apparatus 63 and second communications apparatus 62. Second communications apparatus 62 maintains an "off hook" status during the call so that the exchange continues to bill the call in the normal way. When the call has been completed the first communications apparatus 63 sends a signal to second communications apparatus 62 informing it -- that the call has terminated. Second communications apparatus 62 changes the "off hook" status for the call so that the exchange knows that the call has been terminated.

The preferred means of comparing the unique identification codes is cross correlation. This would allow signal identification with a high degree of confidence, even though an exact match is not possible due to distortions introduced by possible digital-to- analogue-to-digital conversion introduced by the exchange. __

The unique identification signal which will be embedded in the PCM structure has to be made compatible with the possible conversion to an analogue audio signal. In one embodiment a digital sequence may be used that is equivalent to an audio frequency carrier wave phase shift modulated. Alternatively, an arbitrary band limited waveform or a swept frequency chirp may be generated, where the specific parameters of these waveforms can be described and identified.

Referring again to figure 1, modem 14 of radio transceiver 4 may be a variable rate modem. For spectral efficiency the modem uses only that portion of spectrum necessary to handle the data of a given configuration. As further channels are added further spectrum may bemused by the radio transceiver 4. This ensures that energy is not wasted on unused capacity and the transmitted data is transmitted with the maximum energy per bit for a given transmitter power. This also ensures efficient use of the available spectrum.

Public services and safety services such as the police typically operate on VHF or UHF radio. VHF and/or UHF cards may be provided to enable VHF or UHF radio systems to be interfaced to the national telecommunications system. In this way mobile VHF and UHF radios can be linked to a control centre via the national telecommunications network.

It is thus seen that the present invention provides an integrated system allowing easy configuration and expansion to meet user requirements. Dynamic allocation of time slots increases the effective capacity of the system and gives flexibility. The invention also provides a method of local connection that releases a long distance communications link whilst not interfering with call billing.

Although this invention has been described by way of example and with reference to possible embodiments thereof it is to be understood that improvements and/ or modifications may be made thereto without departing from the scope of the invention as defined in the appended claims.

Industrial Applicability

The methods and apparatus of the invention are applicable in telecommunication systems including mobile radio base repeater systems, trunked mobile radio networks, railway communication systems, oil and gas production systems, telemetry and SCADA systems, electricity authorities, police communications networks, remote control of airport communications and STL broadcast program sound links. The apparatus of the invention is particularly suited to private and rural telecommunication systems.

Claims (12)

1. A multi-channel digital communications apparatus comprising:

i) a control module including processing means and a cross connect switch; and two or more of the following interface modules:

ii) a network interface module which interfaces communications between the control module and a high rate digital communications network;

iii) a subscriber interface module which interfaces data or voice communications from a subscriber to the control module; and

iv) a radio transceiver module which interfaces radio communications between the control module and a remote radio transceiver, characterised in that the interface modules are linked to the cross connect switch of the control module by data highways with the control module allocating time slots for communications between the modules, wherein at least some time slots are allocated dynamically as required by the interface modules.

2. An apparatus as claimed in claim 1 wherein a number of time slots are allocated statically, with the remainder being allocated dynamically.

3. An apparatus as claimed in claim 1 or claim 2 wherein connectors are provided in the data highways connecting the radio transceiver and subscriber interface modules to the cross connect switch, enabling these modules to be easily added or removed.

4. An apparatus as claimed in claim 3 wherein the modules are mounted in a rack, the rack being provided with connectors engageable with complementary connectors of the modules linking the data highways between the modules.

5. A communications apparatus as claimed in claim 1 including a network interface module, a subscriber interface module and a radio transceiver module.

6. A method of communicating between first and second subscribers connected to a first communications apparatus, said first communications apparatus being linked to an exchange by a communications link; said method comprising:

i) upon said first subscriber placing a call, said first communications apparatus sending a call request including a unique identifier to the exchange; ii) the exchange sending the unique identifier back to the first communications apparatus when routing the call to the second subscriber, and iii) the first communications apparatus comparing the unique identifier with its own identifier and, if identifiers match, routing communications directly between the first and second subscriber and releasing the communications link.

7. A method as claimed in claim 6 wherein the first communications apparatus is the apparatus of claim 1.

8. A method as claimed in claim 6 or claim 7 wherein a second communications apparatus is provided in the communications link between said first commmunication apparatus and said exchange and, if a match occurs in step (iii), said first communications apparatus sends a signal to said second communications apparatus directing it to maintain an off hook status, and at the termination of the call sends a signal to said second communication apparatus indicating that the call has been terminated.

9. A method as claimed in claim 8 wherein the first and second communications apparatus are linked by a radio link.

10. A method as claimed in claim 6 wherein the comparison in step (iii) is by cross correlation.

11. A method as claimed in claim 6 wherein the unique identifier is the equivalent of an audio frequency carrier wave phase shift modulated or a band limited waveform or a swept frequency chirp.

12. An apparatus operating in accordance with the method of any one of claims 6 to 11.