WO2001041466A1

WO2001041466A1 - A switching device

Info

Publication number: WO2001041466A1
Application number: PCT/GB2000/004599
Authority: WO
Inventors: Neil Berrington; Andrew Martyn Draper
Original assignee: Initia, Inc
Priority date: 1999-12-03
Filing date: 2000-12-01
Publication date: 2001-06-07
Also published as: AU1540301A; GB9928671D0

Abstract

The present invention relates to a switching device (A, B) for use in a switched telephone communications system (1) which is configured to interconnect communications devices (2, 3, 4, 5) coupled thereto. The switching device includes a number of interconnectable ports (10, 11, 12, 13, 14), a store (A) for storing routing information indicating the communications devices (2, 3, 4, 5) which are coupled to the ports and a processor (16) for controlling the interconnection of the ports.

Description

A SWITCHING DEVICE

The present invention relates to a switching device for use in a communications system the system being configured to interconnect communications devices, with each communications device having a respective address. This is particularly useful for systems in which the communications devices are telephones and the addresses comprise telephone numbers. Currently, in the telecommunications industry, communication is achieved by routing signals through a number of switching devices. Thus, for example, computers communicate with each other via communications networks which include a number of switching units . The manner in which data is transferred between the communications devices coupled to the network will depend upon the communications protocol that the network uses .

Thus, for example, in transparent bridging type networks, the network is configured such that a single path exists between any two destinations on the network. Data is then transferred between communications devices along this designated path. Alternatively, source routing type networks include many paths between any two given destinations. However, in this case, an indication of the preferred route through the network is stored in the data to be transferred.

As far as telephone systems are concerned, these generally include a number of interconnected exchanges. A signal indicating that a call is to be made along with the telephone number of the intended destination telephone is received by a first local exchange. This examines at least a portion of the telephone number to determine the next exchange to which the call signals should be transferred. Thus for example, the exchange may examine only the STD code portion of the telephone number to determine the exchange which is local for that code. The next exchange will then similarly examine the next portion of the number, thereby allowing the call to be routed in stages.

In order to do this, data must be stored at each exchange indicating which output ports the signal should be sent to depending on the destination telephone number indicated in the signal. Currently this information is updated locally for each exchange. Accordingly, each exchange must be manually updated with information concerning which telephones are connected to the entire network, along with information regarding how calls should be routed to the specified destination phone. This typically has the disadvantage that if an exchange is updated with an incorrect number then this will only be on a specific local exchange. It is therefore possible that the mistake will not be noticed as the incorrect number will not be obvious to all users of the network.

In accordance with a first aspect of the present invention, we provide a switching device for use in a switched telephone communications system, the system being configured to interconnect communications devices coupled thereto, each communications device having a respective address, the switching device comprising: a number of interconnectable ports, including at least one switching port for coupling to another switching device, and a number of communications ports for coupling to communications devices ; a store for storing routing information indicating the communications devices which are coupled to the communications ports in accordance with the respective address; and, a processor for controlling the interconnection of the ports, the processor being adapted to perform the following in use : a. obtain routing information from another switching device coupled to the switching port in use; b. determine from the obtained routing information the addresses of communications devices coupled to the switching port via the other switching device; c. update the routing information stored in memory in accordance with the addresses of communications devices coupled to the switching port via the other switching device; d. monitor signals received from a first communications device via a first port and determine therefrom an address of a second communications device; e. select a second port via which signals can be transferred to the second communications device in accordance with the routing information; and, f . interconnect the first and second ports so as to interconnect the first and second communications devices .

In accordance with a second aspect of the present invention, we provide a switching device for use in a communications system, the system being configured to interconnect communications devices, each communications device having a respective address, the switching device comprising: a number of interconnectable ports, including at least one switching port for coupling to another switching device, and a number of communications ports for coupling to communications devices; a store for storing routing information indicating the communications devices which are coupled to the communications ports in accordance with the respective address; and, a processor for controlling the interconnection of the ports, the processor being adapted to perform the following in use: a. obtain routing information from another switching device coupled to the switching port in use; b. determine from the obtained routing information the addresses of communications devices coupled to the switching port via the other switching device ; c. update the routing information stored in memory in accordance with the addresses of communications devices coupled to the switching port via the other switching device; d. monitor signals received from a first communications device via a first port and determine therefrom an address of a second communications device; e. determine all the ports via which signals can be transferred to the second communications device in accordance with the address of the second communications device ; f. select a second port from the determined ports in accordance with the routing information; and, g. interconnect the first and second ports so as to interconnect the first and second communications devices . In accordance with a third aspect of the present invention, we provide a method of operating a switched telephone communications system to interconnect at least first and second communications devices coupled thereto, each communications device having a respective address, the communications system having at least two switching devices, each switching device having a number of interconnectable ports, including at least one switching port for coupling to the other switching device, and a number of communications ports for coupling to the communications devices, and a memory for storing routing information, the method comprising: a. causing each switching device to obtain routing information from the other switching device via the respective switching port; b. determining from the obtained routing information the addresses of communications devices coupled to the switching port via the other switching device; c. updating the routing information stored in memory in accordance with the addresses of communications devices coupled to the switching port via the other switching device ; d. monitoring signals received from a first communications device via a first port and determining therefrom an address of a second communications device ; e. selecting a second port via which signals can be transferred to the second communications device in accordance with the routing information; and, f . interconnecting the first and second ports so as to interconnect the first and second communications devices. In accordance with a fourth aspect of the present invention, we provide a method of operating a communications system to interconnect at least first and second communications devices coupled thereto, each communications device having a respective address, the communications system having at least two switching devices, each switching device having a number of interconnectable ports, including at least one switching port for coupling to the other switching device, and a number of communications ports for coupling to the communications devices, and a memory for storing routing information, the method comprising: a. causing each switching device to obtain routing information from the other switching device via the respective switching port; b. determining from the obtained routing information the addresses of communications devices coupled to the switching port via the other switching device; c. updating the routing information stored in memory in accordance with the addresses of communications devices coupled to the switching port via the other switching device; d. monitoring signals received from a first communications device via a first port and determining therefrom an address of a second communications device ; e. determining all the ports via which signals can be transferred to the second communications device ; f. selecting a second port from the determined ports in accordance with the routing information; and, g. interconnecting the first and second ports so as to interconnect the first and second communications devices. In accordance with a fifth aspect of the present invention, we provide a method of configuring a switching device for use in a communications system, the communications system including at least two switching devices and a number of communications devices, each switching device having a number of interconnectable ports, including at least one switching port for coupling to the other switching device, and a number of communications ports for coupling to the communications devices, and a memory for storing routing information, the method comprising: a. inputting routing information indicating the communications devices which are coupled to the communications ports in accordance with the address of the respective communications device; b. obtaining routing information from the other switching device coupled to the switching port in use; c. determining from the obtained routing information the addresses of communications devices coupled to the switching port via the other switching device ; d. updating the routing information stored in memory in accordance with the addresses of the communications devices coupled to the switching port via the other switching device.

Thus, the present invention provides a switching device for use in a communications system, together with a method of operating the communications system and a method of configuring the switching device. In this case, the switching device includes a store which stores routing information indicating which communications devices are coupled to which ports of the switching device. This information is however only provided locally to each switching device regarding the communications devices which are directly coupled to that switching device. The switching device then downloads routing information from other switching devices in the communications system to determine the addresses of other communications devices coupled to the network. This therefore allows each exchange to be configured locally and still obtain information regarding the overall configuration of the communications system from other switching devices . This advantageously means that should a number be incorrectly entered for a particular switching unit, this mistake will then be propagated throughout the entire communications network thereby making the mistake easier to discover and correct .

In the present invention, the term switched telephone communications system is intended to refer to any system in which communications devices are interconnected via a link in use. This link may be physical, or it may be virtual in the sense that the system acts as though a physical link were in place. Thus the communications devices are effectively connected so that once the link is established, the entire call is routed by that link. This is in contrast to data transfer techniques in which each packet of data is routed separately so that the different data packets may be transferred via different routes.

This therefore includes systems such as the Public Switched Telephone Network (PSTN) , the International Switched Digital Network (ISDN) , or Private Branch Exchanges (PBX or PABX) , as well as mobile and cordless phone systems. However, this could also be extended to the transfer of E-mails over such systems as E-mail addresses can also be used for longest match first searching. In addition to this, it is possible for a portion of the link to include transfer via a data communications network, such as the Internet. In this situation, the network is consider as a portion of the link and the manner in which the data is transferred via this link is irrelevant. Thus for example if the Internet is used, the link will be maintained for the duration of the call in the sense that the call will always be transferred via the Internet, with the actual route taken across the Internet being irrelevant for the purposes of the call . Any such implementation would be achieved by replacing one of the telephones with a gatekeeper which is then connected to the Internet or other appropriate data communications system. In these circumstances, the telephone exchanges will continue to operate in accordance with the invention, simply transferring the telephone calls to the gatekeeper. The gatekeeper will then cause the calls to be transferred across the Internet to the other communications system. Accordingly, this does not affect the operation of the telephone exchange in any way. Typically, at least some of the signals received at or transmitted from the switching device include an address, the address being in one of a number of predetermined formats and typically at least some of the signals transferred through the switching device include an address, the address being any one of a number of standard formats. In this case, each port preferably includes a translator for translating the format of addresses from/to one of the predetermined formats to/from one of the standard formats. This advantageously allows all numbers to be transferred through the switching device in a standard format thus ensuring that the switching device is able to correctly determine the intended destination represented by the respective address. This also reduces the amount of processing required to determine which ports should be interconnected. Furthermore, the addresses are then translated such that addresses received or output from certain ports can be a selected one of a number of predetermined formats which are suitable for transfer to the given destination. Thus for example if the destination communication device is a private telephone, this may be a different number format than if the communications device is coupled directly to a communications network, such as a

PSTN exchange, or a public telephone. Alternatively, however, a standard format could be used throughout although this would require configuration of the entire network. Typically the translator comprises a translation store for storing translation information indicating the translation that is required to translate the format of the address; and, a processor for translating the address in accordance with the translation information. However, any suitable form of translator may be used.

Preferably, when routing information is transferred by a switching port, the addresses contained in the routing information are translated as required by the translation information. Alternatively however the exchanges could be configured to having routing information in a format which is identical for all switching devices, in which case translation of the routing information would not be required.

Typically the routing information includes cost information indicating the cost of transferring signals to a given address via a respective port. In this case, the processor is adapted to select the second port by determining all the ports via which signals can be transferred to the second communications device; determining the cost of transferring signals to the second communications device for each of the determined ports in accordance with the cost information; and, selecting the second port to be the port with the lowest cost. However, whilst this is based on the financial cost of transferring the signals, alternative systems of determining the preferred port may be used. This may be based on bandwidth requirements for the connection and the bandwidth available via certain ports. In this case, the cost indication will be based on bandwidth considerations as opposed to the financial cost of transferring the signals. The switching device may also further comprise an input coupled to the store for inputting the routing information. However, the store may alternatively be preprogrammed before it is inserted into the switching device. Typically a communications system according to the invention will include at least two switching devices according to the first or second aspects of the present invention, the switching devices being interconnected by the switching ports, and at least two communications devices coupled to the switching devices . Typically the communications devices are telephones and the addresses comprise telephone numbers. However, the system is also applicable to E-mail addresses. Accordingly, the communications devices may comprise E-mail terminals. As will be appreciated by a person skilled in the art, this is not meant to be limiting and it will be realized that the present invention may also be applied to other forms of address. Typically at least one of the communication ports of the switching device is coupled to a communications network, the communications network having at least one communications device coupled thereto. In this case, this allows multiple communications devices to be connected to any one communications port of the switching device.

Typically the communications network comprises a PBX network or a PSTN. However, any suitable form of communications network may be used and this will typically depend on the communications devices using the system. Thus, for example, if telephones are used, then the communications network may comprise a public telephone network. Alternatively, however if E-mail devices are used, the communications network could comprise the Internet.

Typically each switching device has a respective standard format. The switching devices may alternatively each have an identical standard format in which case the addresses can be transferred between the switching devices in the standard format thereby obviating the need for translation of addresses between the switching devices. However, the present invention is implementable on currently available systems and typically these systems utilize different standard formats. Thus, it is possible for the switching devices to operate in accordance with different standard formats.

The routing information is usually in the form of a look-up table (LUT) including for each port of the switching device an indication of the address of communications devices coupled to the port. In this case, the method of determining all the ports via which signals can be transferred to the second communications device preferably comprises comparing the address of the second communications device to the addresses contained in the LUT. The routing LUT may be in the form of a single LUT stored centrally in a store of the switching device. Alternatively, however a respective routing LUT may be associated with each port. It will be realized that the term LUT is intended to cover any form of data accessing system in which the respective address is used to access an indication of the intended destination port. In use, at least some signals received at, or transmitted from, each switching device include an address, the address being in one of a number of predetermined formats, and wherein in use at least some signals transferred through each switching device include an address, the address being in one of a number of standard formats. In this case, the method preferably further comprises causing the ports to translate the format of addresses from/to one of the predetermined formats to/from one of the standard formats. Translation information is usually provided for each port, the translation information indicating the translation that is required to translate the format of the address. However, translation information may not be required for every port in the case where the numbers are not to be transferred from the port, or if the numbers are not to be translated.

In the case where translation is required, the method of translating the address usually comprises : a. determining the current format of the address,• b. determining the translated format of the address from the translation information; and, c. translating the address.

The translation information is usually in the form of an LUT, although as mentioned above, any suitable look-up system can be used. Typically the step of determining the current format of the address comprises comparing the address to the list of address contained in the LUT using a longest match first technique.

When routing information is transferred by a switching port, the method preferably further comprises translating the addresses contained in the routing information in accordance with the translation information. This may not be needed if the addresses contained in the routing information have the same format that is used by the switching device that receives the transferred routing information. However, even in this case, the routing information can be translated when output from a first switching device and then translated again when received at a second switching device. This ensures that the routing information transferred between the switching devices is always in a form or can be converted into a form suitable for use by the receiving switching device.

Typically when the routing information includes cost information, the method of configuring the switching device further comprises determining a cost associated with the coupling of communications devices via any given port, and generating cost information for each port indicating the cost of coupling to a communications device in accordance with the respective address.

Preferably at least some signals received at or transmitted from each switching device include an address, the address being in one of a number of predetermined formats, and wherein in use at least some signals transferred through each switching device include an address, the address being in one of a number of standard formats, wherein the method further comprises determining the standard format associated with each one of the predetermined number of formats for each port and generating translation information accordingly.

Examples of the present invention will now be described with reference to the accompanying drawings, in which :-

Figure 1 is a schematic diagram of a communications system according to the present invention;

Figure 2 is a schematic diagram of one of the telephone exchanges shown in Figure 1; Figure 3 is a schematic diagram of a second communications system according to the present invention; and, Figure 4 is a schematic diagram of one of the telephone exchanges shown in Figure 3.

Figure 1 shows a first telephone exchange A coupled to a second telephone exchange B and a telephone network 1, which in this example is a Public Switched Telephone Network (PSTN) . The second telephone exchange B is also coupled to the telephone network 1. A number of telephones 2,3,4,5,6,7 are also provided which are coupled to the first and second telephone exchanges A,B and the telephone network 1, as shown.

It will be realized that the telephone exchanges may also form part of the telephone network 1. However, in the present example, the telephone exchanges A,B and the telephones 2,3,4,5 form part of an internal network, for example as part of the internal telephone system of a company.

An example of one of the telephone exchanges A is shown in more detail in Figure 2. The telephone exchange includes ports 10A, 11A which are coupled to the telephones 2 and 3 respectively. The exchange A also includes a port

12A which is coupled to the telephone network 1 and a port 13A which is coupled to the other telephone exchange B. Each of the ports 10A, 11A, 12A, 13A is coupled to a bus 15A. Also coupled to the bus 15A is a processor 16A and a memory 17A. Each of the ports includes a processor and a memory (not shown) .

The telephone exchange B similarly includes ports 10B,11B coupled to the telephones 4,5 respectively. A port 12B is coupled to the telephone network 1 and a port 13B is coupled to the telephone exchange A. Internally, the telephone exchange B includes a processor 16B, a bus 15B and a memory 17B configured in a manner similar to that shown in Figure 2 for telephone exchange A.

Operation of the system will now be described with reference to Figures 1 and 2.

Firstly, if the user is to make a telephone call from the telephone 2 to the telephone 6, the user would activate the telephone 2 and input the telephone number of the telephone 6. An initialization signal is sent via the port 10A to the telephone exchange A. This signal would be transferred via the bus 15A to the processor 16A which would determine that connection to the telephone 6 is required.

The processor 16A then accesses a routing look-up table (LUT) stored in the memory 17A to determine via which port 11A, 12A, 13A the signal should be output. The routing LUT, which will be explained in more detail below, indicates one of the ports 11A, 12A, 13A and the processor will accordingly interconnect the port 10A with the appropriate port 11A,12A,13A.

In the present example, the routing LUT indicates the port 13A and accordingly, the processor 16A interconnects the port 10A and the port 13A. The signal is then transferred from the port 10A, via the bus 15A and the port

13A to the telephone exchange B.

The telephone exchange B will receive the signal via the port 13B and again perform a similar procedure. Thus, the processor 16B will determine from a routing LUT stored in the memory 17B which port the signal should be output from. In this case, the routing LUT indicates the port 12B and accordingly, the processor 16B operates to interconnect the ports 13B and 12B via the bus 15B. The signal is then transferred to the telephone network 1 where it will be routed in accordance with the standard telephone network protocol to the telephone 6.

The format of the telephone number will vary depending on the telephone 2,3,4,5,6,7 from which it originates.

Thus, in the present example, the telephones 2,3,4,5 are private internal phones. Accordingly, the telephone number dialed to connect to the telephone 6 will be of the form:

[T 9 w x y]

where: T - indication of the type of call

9 - digit dialed to indicate outside line w - leading zeros

00 - international 0 - national x - area code of telephone 6 y - telephone number of telephone 6

The types of calls available include "international" and "private". However, in general, the telephone network 1 does not use the indication of the type of call T when routing calls but instead relies solely on the telephone number itself. Accordingly, in this case the call type T is "unknown". As the majority of telephones are adapted to be used with any type of telephone exchange A,B or network 1, the telephones will usually specify the call type T as "unknown" .

However, the telephone exchanges A,B can utilize the call type information when routing calls and therefore the telephone exchanges utilize this option when data is transferred therethrough as will be explained in more detail below.

Thus, for example, if one of the private internal telephones 2,3,4,5 was to call one of the other telephones, the called number would be of the form:

[unknown y]

In this case, none of the codes "w" or "x" are needed. It will be realized however, that in this case if specially configured private phones are used, the call type T could alternatively be specified as "private", as follows: [private y]

If the telephone 6 were to dial the number of one of the telephones 2,3,4,5, then the number would be of the form: [unknown 0 x y] In this case, the "9" which is used to indicate an outside line is not required and the call type is left as "unknown" .

The telephone exchanges A,B are not necessarily able to output numbers as they are received. This is because the network may not be able to handle the number format . Thus, for example, the telephone network 1 does not require the presence of the number 9 to indicate an outside line. The telephone network 1 is therefore unable to interpret numbers including the additional leading 9 of the form:

[T 9 0 x y]

Accordingly, it is necessary to alter the number format before the signals are output from the telephone exchange. Furthermore, it is advantageous if this is done by placing telephone numbers in a standard internal number format for transfer through each telephone exchange A,B, particularly as numbers may also be received from telephones in a number of formats . In order to achieve this, the ports 10,11,12,13 of the telephone exchanges A,B are adapted to translate any telephone numbers received in signals from any external device (i.e. any telephone 2,3,4,5,6,7, any other telephone exchange A,B or any telephone network 1) . This is done by the port processor of the respective port 10,11,12,13 in accordance with translation information which is stored in a translation LUT in the respective port memory. In this example, a respective translation LUT is provided for each port. However, alternatively a single translation LUT could be provided in the central memory 17. In this case, the translation could be carried out either by the port processors or by the central processor 16.

Examples of the translation LUTs are shown in Table 1 and Table 2 on the following page. Table 1

Table 2

Table 1 shows four translation LUTs, one for each of the ports 10A, 11A, 12A, 13A of the telephone exchange A, whilst Table 2 shows four translation LUTs for the ports 10B, 11B, 12B, 13B of the telephone exchange B. The port numbers indicate which port the translation LUT relates to.

The connection type, which is only included for explanation purposes, indicates to what form of external device (i.e. the telephone network 1, the telephones 2,3,4,5,6,7 or the other telephone exchange B,A) the respective port is connected to. Thus, for example, Table 1 indicates that ports 10A and 11A are connected to the telephones 2 and 3 respectively via internal connections. The internal connections are intended to refer to the fact that the telephones 2,3,4,5 and the telephone exchanges A,B form part of a private network as described above .

For the purposes of this example, the telephone exchange A is located in a region having the national dialing code (0)1753, whereas the telephone exchange B is located in an area having the national dialing code

(0)1472. Similarly, the telephone network 1 spans both of these areas, in addition to a number of other areas. For the purposes of the present example, the telephone network

1 is therefore considered to be divided into two portions 1A,1B with the portion 1A being located in the area having the national dialing code (0)1753 and the portion IB being located in the area having the national dialing code

(0) 1472.

In addition to the port number and connection type each Table 1 and 2 includes an input number column, an internal number format column and an output number column. The input number column represents the format of the telephone numbers which can be received by the port from an external devices. Thus, in the case of the port 10A this represents the format of the telephone numbers which can be dialed by the telephone 2, and therefore input to the port 10A. The internal number format represents the format of the number as it is transferred through the telephone exchange AB. Thus, the input number represents the format of the number as it is received from the respective telephone 2, whereas the internal number format represents the format of the number as it is transferred from the port 10A to the bus 15A.

The output number column represents the format of the telephone number as it is output from the port 10A to the respective telephone 2. Thus, a telephone number received at the port 10A from the bus 15A in the internal number format will be translated into the output number format, as shown, before it is output from the port 10A to the telephone 2. In practice, the telephone number rarely needs to be output from the telephone exchange A,B directly to the telephones 2,3,4,5. Accordingly, it is not always necessary for an entry to be included in the output number column, as shown for example with respect to port 10A in table 1.

However, in some circumstances telephone numbers are transferred to the telephone. This may occur for example, if a single telephone is used to answer calls directed to a number of different telephone numbers, such as when a single phone is used as the contact point for different companies. In this case each company could use a different phone number with the phone being adapted to allow the intended recipient company to be identified for example by a different tonal ring. The information that makes up the translation LUT of each of the ports 10,11,12,13 is determined and input into the appropriate memory by an operator. This must be done for each telephone exchange A,B locally. Thus, an operator of the telephone exchange A must determine Table 1 for each of the ports 10A, 11A, 12A, 13A whilst an operator of the telephone exchange B must determine the equivalent Table 2. In order to determine the translation LUTs for the telephone exchange A, the operator must be aware of the format of numbers which can be generated and received by the telephones 2, 3, the telephone network 1A and the telephone exchange B. The operator then simply places the internal number format in the appropriate column, together with the appropriate input and output number formats.

As the numbers generally have set prefixes, such as the national dialing codes, which represent the intended destination in broad terms, then the format of the number can often be specified in terms of the prefix only.

However, full number matching may also be included.

As mentioned above, the input and output numbers for the ports 10A, 11A, 10B, 11B are determined based on the capabilities of the respective telephones 2,3,4,5. Thus, in this example, the telephones 2,4,5 are adapted to generate numbers in a format suitable for transfer directly onto the telephone network 1, whereas the telephone 3 is adapted specifically for use with the telephone exchange A, so that no translation of number format is required.

Furthermore, in this example the two telephone exchanges are adapted to operate in accordance with the same internal number format. Accordingly, translation of the number formats is not required as the number are transferred between the two telephone exchanges A,B.

Finally, in this example, it is not possible to transfer telephone calls to private phones via the telephone network 1 and accordingly, there is no entry corresponding the internal number format [private y] for the port 12A,12B. However, if suitable longest matching techniques which match the entire number were used, this could be implemented, in which case appropriate translations would be added.

Operation of the system to translate call numbers for the call described above will now be described. Firstly, the user will input the telephone number of the telephone 6 into the telephone 2. In this case, the input number will be of the form [unknown 9 0 x y] , as described above. The connection signal generated by the telephone is transferred to the port 10A, as described above. The port 10A receives the signal and determines the telephone number indicated therein. The telephone number is then compared to the input numbers in the translation LUT for port 10A using a longest match first procedure.

Accordingly, the processor first compares the number [unknown 9 0 0 x y] to the number contained in the signal received from the telephone 2. In this case the prefix does not match, so the processor then compares the number

[unknown 9 0 x y] to the input number. In this case, the port processor determines a match and therefore outputs a signal from the port 10A, to the bus 15A including the telephone number in the internal number format i.e.

[international +44 x y] .

The call signals are then routed by the processor 16A, as will be explained in more detail below, to the port 13A. In this case, the port 13A will again perform a longest match first in comparison with the internal number formats stored in the translation LUT for the port 13A.

Thus, the port processor will firstly compare the number [international +44 1753 y] to the received number. In this case, there is no match so the number then compares the number [international +44 x y] and determines a match. Accordingly, the port 13A outputs the signal including the number [international +44 x y] .

This is transferred to the port 13B of the telephone exchange B. In this case, it is important to remember that the [x] in the number output from the port 13A is 1472. Accordingly, when the signals including the telephone number of the telephone 6 are received at the port 13B this carries out a longest match comparison with the input numbers stored in the respective translation LUT and determines that the number [international +44 1472 y] is the longest match. As this matches the internal number format of the telephone exchange B no effective translation is carried out. The call signals are then routed to the processor 16B which determines that a connection is to be made to the port 12B.

Accordingly, the call signals are transferred to the port 12B including the number in the format [international +44 1472 y]

The number included in the call signals received by the port 12B will then be translated to the output number format [unknown y] which is simply the telephone number of the telephone 6. In this case, because the telephone 6 is on a local exchange IB, the national area code [1472] is not required. A second example in which a call is made from the telephone 4 to the telephone 2 will now be described. In this case, because the call is between private phones on the internal network, no area code or outside line number 9 is required. Accordingly, the call signals generated by the telephone 4 will include the telephone number in the format [unknown y] .

As signals including this number are received at the port 10B, the port processor will compare the number [unknown y] to the input number list in the respective translation LUT for the port 10B. Again, carrying out a longest number match the port processor will compare the numbers [unknown 9 0 0 x y] , [unknown 9 0 x y] and [unknown 9 y] before determining a match with the number [unknown y] . In this case the internal number format is the number [private y] .

The signals are then transferred through the telephone exchange B by the bus 15B to the port 13B. The port 13B carries out an appropriate look up operation and outputs the call signals including the number [private y] . These signals are received by the port 13A and transferred through the telephone exchange A in the format [private y] . As set out above, the call signals containing the telephone number will not be transferred to the telephone 2 and accordingly no further translation will occur.

Operation of the system to determine the routing of the call signals will now be described with reference to Tables 3 and 4 which are shown below. These represent routing LUTs which are stored in the processors 16A, 16B of the telephone exchanges A,B.

The Table 3, which is the routing LUT for telephone exchange A, includes a port number indicating the ports to which the relevant information refers. A connection type is included for the purposes of the present explanation and this indicates, as in Tables 1 and 2 the external device to which the port is connected. The internal number formats are also provided, along with a cost indication. Table 4 provides similar information for the telephone exchange B.

The cost indication represents the total financial cost of transferring a call received at one of the ports

10A, 11A, 12A, 13A to the final destination specified by the call number contained in the call signals.

Table 3

Table 4

It will be realized that if the respective telephone exchange A,B receives a call intended for one of the telephones 2,3,4,5 connected thereto, the call should be transferred directly to the telephone. Accordingly, the internal number format for each of the ports 10A, 10B, 11A, 11B is specific to the respective telephone number .

In this case the actual telephone numbers of the telephones 2,3,4,5 are represented as y2,y3,y4,y5 respectively. Thus, as shown, the routing LUT includes the address of the telephone 2,3,4,5 connected to the port 10A, 10B, 11A, 11B within the internal number format entry corresponding to the respective port .

Thus, when a call signal is received by the telephone exchange A and a longest match first search procedure carried out, if the telephone number indicated is either y2 or y3 , then a match will be found and the call transferred to the appropriate port 10A,10B.

Accordingly, as this is the desired call transfer, the cost of transferring a call to a telephone directly from the respective telephone exchange A,B is set to zero. In this example, this is achieved by not providing a valid cost indication. However, for internal private call a negligible cost indication is provided. As far as the remaining costs are concerned, the cost of transferring a call between the ports 13A, 13B is determined depending on the nature of the connection. In this example, the connection represents a link between two exchanges within a private company network and accordingly this will be given a low cost of 0.100 pence per minute. In the event in which transfer of a call across this link is effectively free, a minimal cost indication will still be provided to prevent calls being routed in perpetual loops . The cost of transferring calls to the telephone network 1 depends on the charges levied by the operator of the telephone network 1. Thus in this example, if the intended destination telephone is situated on a local portion of the telephone network 1, the cost is 1.000 pence per minute. Thus, the cost of transferring a call from the telephone exchange A to a telephone 7 on the communications network 1A is 1.000 pence per minute.

In this example, the cost of transferring a call to a non-local portion of the telephone network 1 is set to 5.000 pence per minute, whilst the cost of transferring a call to an international portion of the telephone network is 10.000 pence per minute.

These cost values are input manually for the ports 10A, 11A, 12A, 10B, 11B, 12B which are coupled to the telephones 2,3,4,5 or the telephone network 1. In order to do this, the operator must determine the nature of the external device to which the ports are connected. The operator can the determine the cost of transferring calls to given telephone numbers accordingly. The extent to which this is done automatically by the operator will depend on the situation. Thus, for example for the ports 10A, 11A which are only coupled to the telephones 2,3 the operator will be aware of the telephone number of the respective telephone and also of the cost of transferring the call via the respective telephone exchange A,B. Accordingly, this information can be input manually by the operator. This means that the operator can set the cost of the calls as desired for the internal transfers.

As far as the connection to telephone network 1A, IB is concerned, for the respective ports 12A, 12B the list of telephone numbers which can be reached and the associated costs are extensive and therefore could initially be determined by the operator of the telephone network 1. Thus, it may be that the telephone network operator has a set price list which is published. In this case, this information can then be input manually, as required. Alternatively, the price list may be available for download from an appropriate Internet webpage, or the like. However, as far as the ports 13A, 13B are concerned, whilst the operator will know the format in which numbers are to be transferred and can therefore input the translation LUT, the operator will not know the numbers of the telephones which are connected to the other exchange. Accordingly, for the telephone exchange A, this information is derived by download from the telephone exchange B.

Accordingly, when the telephone exchange A is to be configured the operator causes the telephone exchange A to download a portion of the routing LUT of the telephone exchange B via the ports 13A,13B. In order to do this, the processor 15A sends a request to the processor 15B which accesses the routing LUT stored in the memory 16B.

The processor 15B downloads any routing information which has an associated non-zero cost as shown in Table 5 below. This shows the relative costs for transferring calls from the exchange B to the appropriate destination based on the respective internal number format .

In this case, there should be a respective entry for the [private y4] and the [private y5] telephone numbers.

However, because the routing of calls to the either the telephone 4 or the telephone 5 is determined within the telephone exchange B, no distinction needs to be made outside the telephone exchange B. Accordingly, a single entry based on the internal number [private y] is provided. As mentioned above, there is a notional cost of .100 pence per minute for transferring calls via the link between the ports 13A and 13B. Accordingly, as the Table 5 is transferred over this link, the additional costings are added as required. Table 5

Table 6

Table 7

Furthermore, the appropriate translation rules associated with the ports 13B,13A are also applied to the numbers as the routing LUT shown in Table 5 is transferred. Thus, as the LUT is output from the port 13B, the translation rules defined by the translation LUT are applied to the telephone numbers contained therein. In this example, as the two telephone exchanges A,B operate in accordance with the same internal number format then no change is noticeable when the LUT is output from the port 13B, as shown in Table 6. When the Table 6 is received at the port 13A, the telephone numbers are again translated, in accordance with the respective translation LUT associated with the port 13A, although in this example this again has no effect. However, at this point the above mentioned cost of 0.1 pence per minute is added to each cost indication, resulting in the routing LUT shown in Table 7. This is then transferred to the processor 15A and incorporated in the routing LUT of the exchange A, resulting in the routing LUT shown in Table 3.

Thus, in the example described above, when the telephone 2 is to make a call to the telephone 6, the call signals will be received at the port 10A. These are then transferred to the processor 15A and translated into the internal number format [international +44 x y] (where x is 1472) as described above. This is then transferred to the processor 15A. The processor 15A then accesses the routing LUT, using the internal number format to determine to which port the call signals should be transferred. In the present example, this can be achieved by performing a longest match first search technique to search the internal number format numbers stored in the routing LUT. In this case, the longest match occurs for the internal number format [international +44 1472 y] which is associated with the port 13A, as shown in Table 3.

Accordingly, the processor interconnects the ports 10A, 13A and transfers the call signals to the telephone exchange B via the port 13B.

Once the call signals are received by the telephone exchange B, the processor 15B will again compare the number in its internal number format [international +44 1472 y] for each of the ports 10B, 11B, 12B, 13B in the routing LUT. From this the processor 15B determines that the port 12B represents the longest match and accordingly operates to interconnect the ports 13B,12B so that the call is transferred to the telephone network IB and hence to the telephone 6, as required. A variation on this technique can be implemented by defining that the length of the internal number format [international +44 x y] is equal for the longest match searching techniques to the number [international +44 1472 y] . In this example, the number [international +44 x y] can be transferred from the telephone exchange A in two ways. The first is as in the example described above, via port 13A, the second is via the port 12A and then the telephone network 1. In the first case, the call would be transferred between the ports 13A,13B, which incurs a 0.100 pence per minute cost , and then via the exchange B to the local exchange IB, which incurs a further 1.000 pence per minute cost. Accordingly the total cost would be 1.100 pence per minute, as indicated for the port 13A in the [international +44 1472 y international] internal number format row.

However, in the second case the call is transferred directly to the telephone network 1. This would involve a national rate call directly to the network IB and accordingly, this would cost 5.000 pence per minute. This is indicated by the [international +44 x y] internal number format row for the port 12A.

Accordingly, when the call is to be transferred, the processor 15A can be configured to perform a search for the cheapest connection which can be made in accordance with the internal number format of the telephone number which is included in the call signals. Thus the internal number format for the call to be made is used to look-up the respective cost. In this case, the processor 15A would determine that the cheapest cost is to transfer the call via the port 13A, to the telephone exchange B and the port

13A would be interconnected with the port 13B accordingly.

Once the call signals are received by the telephone exchange B, the processor 15B will again compare the number in its internal number format [international +44 1472 y] for each of the ports 10B, 11B, 12B, 13B in the routing LUT.

From this the processor 15B determines that the port 12B represents the cheapest route for the call. Accordingly, the processor 15B interconnects the ports 13B,12B so that the call is transferred to the telephone network IB and hence to the telephone 6, as required. Additionally, the alternative routes are maintained in the routing LUTs. Thus, although the processors 15A,15B are configured to perform a longest match first and then select the cheapest route, should the route fail, then the processors 15A,15B can determine a second route in accordance with the additional cost information.

In the case in which a private call is made between the two telephones 2,4 then the call signal generated by the telephone 2 will include the telephone number [unknown y4] . This is translated into the internal number format of [private y4] .

A longest match is carried out by the processor 15A which determines the longest match to be the number

[private y] , so the processor interconnects the ports

10A,13A and transfers the call signals via the ports 13A,13B to the processor 15B. Again a longest match procedure is performed, resulting in the determination of the port 10B. The ports 13B,10B are interconnected and the call can proceed as required.

A second example of a network including a number of telephone exchanges according to the present invention is shown in Figure 3. In this case, a third telephone exchange C has been added which is coupled to the telephone exchanges A,B, as well as to the telephone network 1. In this case, the telephone exchange C is coupled to a portion of the telephone network 1C which is located in the same area as the telephone exchange C and therefore has the same national dialing code. The telephone exchange C and the telephone network are coupled to respective telephones 9,8. In order to allow for the number of connections between the respective telephone exchanges, each telephone exchange A,B,C is modified as shown in Figure 4 by the addition of a further port 14. This allows each telephone exchange to be coupled to the other two exchanges via the respective ports 13,14.

In this example, the ports 14A, 14B of the telephone exchanges A,B are coupled to the ports 13C,14C of the telephone exchange C, as shown.

The modified system will function in the general manner described above with respect to Figures 1 and 2, although the routing and translation LUTs become more complicated with the addition of an extra port in the telephone exchange.

A further variation over the previous example is that in this case the telephone exchange C uses a different internal number format to the telephone exchanges A,B. As a result it is necessary to translate telephone numbers which are transferred between the ports 14A, 13C and the ports 14B,14C.

In this example the internal number format of the telephone exchange C is identical to the number format used by the telephone network 1. As a result the translation LUTs of the telephone exchanges B,C are as shown in Tables 8 and 9 below. The translation LUT of the telephone exchange A would be modified in a similar manner to that of the telephone exchange B. Accordingly, the operation of the telephone exchange A is similar to that of the telephone exchange B which will be described in more detail below.

As shown in Table 9, the national code of the network portion 1C is (0)171.

Table 8

Table 9

Furthermore, as shown in Table 8, the translation LUT of the telephone exchange B is set up so that telephone numbers transferred via the port 14B are in the internal number format of the telephone exchange B. As a result the translation LUT of the telephone exchange C is set up so that the port processor of the port 14C translates the format of telephone numbers to/from the internal number format of telephone exchange B from/to the internal number format of telephone exchange C when telephone numbers are output and received respectively.

Alternatively however, the translation LUTs could be configured such that the port processor of the port 14B performs the translation. A further alternative is for the translation LUT of each telephone exchange A,B,C to be configured so that the telephone exchanges A,B,C output telephone numbers in their own respective internal number formats. In this case, the translation LUTs are configured so that the format of telephone numbers received from the other telephone exchanges are translated.

The exact method used will depend on how the system is initially configured by the input of the number formats into the translation LUTs.

Furthermore, because of the additional connections, there are also a greater number of routes by which various telephones can connect. Thus, for example, the telephone 2 can connect to the telephone 6 via the telephone network 1; or via the telephone exchange B and the telephone network 1; or via the telephone exchange C and the telephone network 1; or via the telephone exchange B, the telephone exchange C and the telephone network 1.

This leads to a significant increase in the complexity of the routing LUTs. Tables 10 and 11 are examples of the routing LUTs for the telephone exchanges B and C and these indicate that multiple routes exist to specified destinations . Table 10

Table 11

Thus for example, if a call having the destination telephone number [international +44 1753 y] is made from the telephone 4 then when the processor 15B performs a longest match procedure in the routing LUT, two identical matches will be located. These correspond to the two possible routes via which the call signals having the telephone number [international +44 1753 y] can be routed. The first route is directly via the telephone exchange A onto the telephone network 1A and the second is via the telephone exchange C, the telephone exchange A and then on to the telephone network 1A.

Accordingly, if only the longest match first technique is used, this will not allow a unique route to be identified. However, by then analyzing the cost information as described above, the processor 15B will determine that to transfer the call via the port 13B will cost 1.100 pence per minute. This is due to 0.100 p per minute cost of using the link between the ports 13A,13B, and the 1.000 p per minute cost of transferring the call via the network 1A. In contrast, to transfer the call via the port 14B will cost 1.200 pence per minute. This higher price results from the fact that call must be transferred via the link between the ports 14B,14C and the link between the ports 14A,13C, which costs 0.100 pence per minute each, together with the 1.000 pence per minute charge for transferring the call via the telephone network 1A.

Again, all alternative routes are maintained in the information transferred between the telephone exchanges A,B,C. The processors 15A,15B,15C are configured to select the cheapest route. However, should the route fail, then the processors can determine a second route in accordance with the additional cost information.

It will be realized that although the routing LUTs do not define the entire route to a given destination, once the call has been transferred to the telephone exchange, then the respective processor can then perform a similar analysis to determine the route. Again, as in the previous example, the routing LUTs are established by having an operator enter cost values for each internal number format for the ports which are connected either directly to telephones, or the telephone network 1. For ports connected to other telephone exchanges the information is downloaded by exchanging a portion of the routing LUTs. An example of the routing LUT portion that is generated within the telephone exchange C for transfer to the telephone exchange B is shown in Table 12.

As shown, the routing LUT already contains details of the routes via the telephone exchange A and this would be achieved by previous transfer of appropriate routing LUT portions between the telephone exchanges A,C. It will be realized from this, that in this example further transfers will be required between the telephone exchanges A,C to reflect any updating following the communication of the routing LUT information between the telephone exchanges B,C. Thus the processors can be arranged to periodically transfer routing LUT portions to ensure that the respective routing LUT is up to date. Alternatively, when the system is initially configured, each telephone exchange could transmit its own routing LUT portion to each other telephone exchange, allowing all the routes to be calculated by considering all the received routing LUT portions .

As the portion of the routing LUT is output from the port 14C, the telephone numbers contained therein are translated in accordance with the translation LUT.

Accordingly, the telephone numbers are translated from the internal number format of the telephone exchange C into the internal number format of the telephone exchange B, as shown in Table 13, below. This table is then transferred over the link between the ports 14C,14B to the telephone exchange B. The cost component of 0.100 pence per minute is added representing the cost of transferring calls over the link, as shown in Table 14. This is then incorporated into the routing LUT of the telephone exchange B by the processor 15B, as shown by the port 14B row of Table 10.

A similar situation exists for the transfer of the portion of the LUT from the telephone exchange B to the telephone exchange C. The routing LUT portion generated by the processor 15B is shown as Table 15, the portion as it is output from the port 14B is shown as Table 16, whilst the portion as it is received by the processor 15C is shown as Table 17.

Table 12

Table 13

Table 14

10

15 Table 15

20

25

Table 16

30

35

40 Table 17

It will be realized that in the above mentioned examples, any of the telephones may be replaced by any other appropriate communications device. In particular, the telephones may be replaced by a gatekeeper which is in turn connected to a network such as a LAN, a WAN, or the Internet . The network is in turn connected to a communications device, such as a computer or the like, adapted for making voice type calls, thereby allowing telephone calls to be routed over the network.

In this case, the gatekeeper simulates telephone operation so that telephone exchanges can operate in the normal way. Thus when the telephone number of the communications device is entered, the routing LUTs are adapted to transfer the call to the gatekeeper. This is achieved by having the telephone number of the communications device associated with the port to which the gatekeeper is connected, in the respective routing LUT. The gatekeeper can then translate call signals and voice signals contained within the telephone call into a format suitable for transfer over the network to the communications device.

A further option is for the links between the telephone exchanges to be formed from a link via a network. In this case, some of the ports 13A, 14A, 13B, 14B, 13C, 14C could be connected to respective gatekeepers, with the gatekeepers being connected via a network, such as the Internet. This allows the telephone exchanges to be connected via the Internet so as to allow the connection of a telephone over a global system. Other networks systems such as companies' internal LANs or WANs could also be used.

Claims

1. A switching device for use in a switched telephone communications system, the system being configured to interconnect communications devices coupled thereto, each communications device having a respective address, the switching device comprising: a number of interconnectable ports, including at least one switching port for coupling to another switching device, and a number of communications ports for coupling to communications devices ; a store for storing routing information indicating the communications devices which are coupled to the communications ports in accordance with the respective address; and, a processor for controlling the interconnection of the ports, the processor being adapted to perform the following in use : a. obtain routing information from another switching device coupled to the switching port in use; b. determine from the obtained routing information the addresses of communications devices coupled to the switching port via the other switching device; c. update the routing information stored in memory in accordance with the addresses of communications devices coupled to the switching port via the other switching device; d. monitor signals received from a first communications device via a first port and determine therefrom an address of a second communications device ; e. select a second port via which signals can be transferred to the second communications device in accordance with the routing information; and, f . interconnect the first and second ports so as to interconnect the first and second communications devices .

2. A switching device according to claim 1, wherein the routing information includes cost information indicating the cost of transferring signals to a given address via a respective port, and wherein the processor is adapted to select the second port by: a. determining all the ports via which signals can be transferred to the second communications device; b. determining the cost of transferring signals to the second communications device for each of the determined ports in accordance with the cost information; and, c. selecting the second port to be the port with the lowest cost .

3. A switching device for use in a communications system, the system being configured to interconnect communications devices, each communications device having a respective address, the switching device comprising: a number of interconnectable ports, including at least one switching port for coupling to another switching device, and a number of communications ports for coupling to communications devices; a store for storing routing information indicating the communications devices which are coupled to the communications ports in accordance with the respective address; and, a processor for controlling the interconnection of the ports, the processor being adapted to perform the following in use: a. obtain routing information from another switching device coupled to the switching port in use; b. determine from the obtained routing information the addresses of communications devices coupled to the switching port via the other switching device; c. update the routing information stored in memory in accordance with the addresses of communications devices coupled to the switching port via the other switching device; d. monitor signals received from a first communications device via a first port and determine therefrom an address of a second communications device; e. determine all the ports via which signals can be transferred to the second communications device in accordance with the address of the second communications device; f. select a second port from the determined ports in accordance with the routing information; and, g. interconnect the first and second ports so as to interconnect the first and second communications devices .

4. A switching device according to claim 3, wherein the routing information includes cost information indicating the cost of transferring signals to a given address via a respective port, and wherein the processor is adapted to select the second port by: a. determining the cost of transferring signals to the second communications device for each of the determined ports in accordance with the cost information; and, b. selecting the second port to be the port with the lowest cost.

5. A switching device according to any of the preceding claims, wherein at least some of the signals received at or transmitted from the switching device include an address, the address being in one of a number of predetermined formats, and wherein at least some of the signals transferred through the switching device include an address, the address being in one of a number of standard formats, wherein each port includes a translator for translating the format of addresses from/to one of the predetermined formats to/from one of the standard formats.

6. A switching device according to claim 5, wherein the translator comprises: a translation store for storing translation information indicating the translation that is required to translate the format of the address; and, a processor for translating the address in accordance with the translation information.

7. A switching device according to claim 5 or claim 6, wherein when routing information is transferred by a switching port, the addresses contained in the routing information are translated as required by the translation information.

8. A switching device according to any of the preceding claims, the switching device further comprising an input coupled to the store for inputting the routing information.

9. A communication system comprising at least two switching devices according to any of the preceding claims, the switching devices being interconnected by the switching ports, and at least two communications devices coupled to the switching devices.

10. A communication system according to claim 9, wherein the communications devices are telephones and the addresses comprise telephone numbers.

11. A communication system according to claim 9 or claim 10, wherein at least one of the communications ports of the switching device is coupled to a communications network, the communications network having at least one communications device connected thereto.

12. A communication system according to claim 11, wherein the communications network comprises a PBX network or a PSTN.

13. A communications system according to any of claims 9 to 12, when dependent on at least claim 5, wherein each switching device has a respective standard format.

14. A method of operating a switched telephone communications system to interconnect at least first and second communications devices coupled thereto, each communications device having a respective address, the communications system having at least two switching devices, each switching device having a number of interconnectable ports, including at least one switching port for coupling to the other switching device, and a number of communications ports for coupling to the communications devices, and a memory for storing routing information, the method comprising: a. causing each switching device to obtain routing information from the other switching device via the respective switching port; b. determining from the obtained routing information the addresses of communications devices coupled to the switching port via the other switching device; c. updating the routing information stored in memory in accordance with the addresses of communications devices coupled to the switching port via the other switching device; d. monitoring signals received from a first communications device via a first port and determining therefrom an address of a second communications device; e. selecting a second port via which signals can be transferred to the second communications device in accordance with the routing information; and, f . interconnecting the first and second ports so as to interconnect the first and second communications devices.

15. A method according to claim 14, wherein the routing information includes cost information indicating the cost of transferring signals to a given address via a respective port, and wherein the method of selecting a second port comprises : a. determining all the ports via which signals can be transferred to the second communications device ; b. determining the cost of transferring signals to the second communications device for each of the determined ports in accordance with the cost information; and, c. selecting the second port to be the port with the lowest cost .

16. A method of operating a communications system to interconnect at least first and second communications devices coupled thereto, each communications device having a respective address, the communications system having at least two switching devices, each switching device having a number of interconnectable ports, including at least one switching port for coupling to the other switching device, and a number of communications ports for coupling to the communications devices, and a memory for storing routing information, the method comprising: a. causing each switching device to obtain routing information from the other switching device via the respective switching port; b. determining from the obtained routing information the addresses of communications devices coupled to the switching port via the other switching device; c. updating the routing information stored in memory in accordance with the addresses of communications devices coupled to the switching port via the other switching device; d. monitoring signals received from a first communications device via a first port and determining therefrom an address of a second communications device; e. determining all the ports via which signals can be transferred to the second communications device; f. selecting a second port from the determined ports in accordance with the routing information; and, g. interconnecting the first and second ports so as to interconnect the first and second communications devices.

17. A method according to claim 16, wherein the routing information includes cost information indicating the cost of transferring signals to a given address via a respective port, and wherein the method of selecting a second port comprises : a. determining the cost of transferring signals to the second communications device for each of the determined ports in accordance with the cost information; and, b. selecting the second port to be the port with the lowest cost .

18. A method according to claim 15 or claim 17, wherein the routing information comprises a look-up table including for each port of the switching device an indication of the address of communications devices coupled to the port, wherein the method of determining all the ports via which signals can be transferred to the second communications device comprises comparing the address of the second communications device to the addresses contained in the LUT.

19. A method according to claim 15, claim 17 or claim 18, wherein in use at least some signals received at or transmitted from each switching device include an address, the address being in one of a number of predetermined formats, and wherein in use at least some signals transferred through each switching device include an address, the address being in one of a number of standard formats, wherein the method further comprises causing the ports to translate the format of addresses from/to one of the predetermined formats to/from one of the standard formats .

20. A method according to claim 19, wherein translation information is provided for each port, the translation information indicating the translation that is required to translate the format of the address, and wherein the method of translating the address comprises: a. determining the current format of the address; b. determining the translated format of the address from the translation information; and, c. translating the address.

21. A method according to claim 20, wherein the translation information comprises a look-up table and wherein the step of determining the current format of the address comprises comparing the address to the list of address contained in the LUT using a longest match first technique.

22. A method according to any of claims 19 to 21, wherein when routing information is transferred by a switching port, the method further comprises translating the addresses contained in the routing information in accordance with the translation information.

23. A method according to any of claims 14 to 22, wherein the communications devices are telephones and the addresses comprise telephone numbers.

24. A method according to any of claims 14 to 23, for operating a communication system according to any of claims

9 to 13.

25. A method of configuring a switching device for use in a communications system, the communications system including at least two switching devices and a number of communications devices, each switching device having a number of interconnectable ports, including at least one switching port for coupling to the other switching device, and a number of communications ports for coupling to the communications devices, and a memory for storing routing information, the method comprising: a. inputting routing information indicating the communications devices which are coupled to the communications ports in accordance with the address of the respective communications device; b. obtaining routing information from the other switching device coupled to the switching port in use ; c. determining from the obtained routing information the addresses of communications devices coupled to the switching port via the other switching device; d. updating the routing information stored in memory in accordance with the addresses of the communications devices coupled to the switching port via the other switching device.

26. A method according to claim 25, wherein the routing information includes cost information, the method further comprising determining a cost associated with the coupling of communications devices via any given port, and generating cost information for each port indicating the cost of coupling to a communications device in accordance with the respective address.

27. A method according to claim 25 or claim 26, wherein in use at least some signals received at or transmitted from each switching device include an address, the address being in one of a number of predetermined formats, and wherein in use at least some signals transferred through each switching device include an address, the address being in one of a number of standard formats, wherein the method further comprises determining the standard format associated with each one of the predetermined number of formats for each port and generating translation information accordingly.

28. A method according to any of claims 25 to 27, for configuring a switching device according to any of claims 1 to 8.