GB2405055A

GB2405055A - A switching centre receiving data for or from a private user group terminal and translating between public and private network numbers

Info

Publication number: GB2405055A
Application number: GB0319159A
Authority: GB
Inventors: Danjan Cibej; Mihael Oman; Renata Stular
Original assignee: Siemens AG; Siemens Corp
Current assignee: Siemens AG; Siemens Corp
Priority date: 2003-08-15
Filing date: 2003-08-15
Publication date: 2005-02-16
Also published as: GB0319159D0

Abstract

There is described a switching centre 2 for operating in a telecommunications network 1. The switching centre 2 is capable of receiving a data message transmitted from a sending terminal 2a-2n of a private user group of terminals connected to the switching centre 2 and transmitting the message onwards in the telecommunications network 1 for delivery to an intended recipient terminal 3a-3n. The switching centre 2 is arranged to translate address information included in the message and which conforms with a private network numbering scheme, into corresponding address information which conforms with a public network numbering scheme, to enable the message to be routed to the recipient terminal 3a-3n.

Description

2003E01336 SL 2405055

MESSAGE SERVICE

Technical Field

This invention relates to a message service, in particularly a short message service in a Centrex environment.

Background

- Centrex As is known, Centrex (Central Office Exchange Service) is a service offered by telephone companies, normally to business or public organizations. A Centrex service is software implemented and in many ways emulates a private branch exchange. Normally, the telephone devices of a Centrex (CTX) group (for example, the workplace telephone devices of the employees of a company that subscribes for CTX) are directly connected to a CTX switch located in the local exchange of the telephone company providing the service.

Specific CTX functions are offered to the members of a CTX group for the set up of CTX connections or for the switching of CTX calls; these functions are essentially similar to the those functions that a subscriber connected to a hardware 2003E01336 SL implemented PBX is accustomed to. Typically, these CTX functions can comprise a private telephone number plan for the CTX group members, call redirection, call forwarding and use of an exit code (PNAC) (de, 'O') for dialling into the public telephone network.

The respective CTX groups of a plurality of CTX switches linked via the public telecommunications network may together form a distributed CTX private network known as a Centrex Business Group. Such a CTX private network may, for example, serve the various different premises of a company subscribing to Centrex, wherever the geographical locations of the premises.

The telephone devices of a CTX group are each assigned a CTX Directory Number (CTXDN) for use within the CTX group and also a Public Directory Number (PDN) for use in the public telephone network. A CTXDN of a device is typically two to seven digits long and is thus shorter than the PDN of the device. Users within a CTX business group may call each other's telephone devices using the relevant CTXDN's, and the CTXDN of a calling device may be displayed on a display at the called device. Thus the user of a called device may easily determine that the calling device is within the same CTX business group.

2003E01336 SL Short Message Service ( SMS) SMS allows a user of a terminal to compose a text message and to send it to a recipient terminal via a communications network. SMS was originally developed as part of the Global System for Mobile Communications (GSM), to enable text message to be sent between mobile telephones.

More recently, operators of fixed line PSTN/ISDN telephone networks have introduced services that enable their subscribers to transmit and receive SMS messages using fixed line telephones. To this end, fixed line telephones have been developed that support SMS. A user of such a phone may use the phone to compose a text message and send it to a recipient phone via the fixed telephone network. The fixed network includes a short message centre ( SMC) which handles the receipt of SMS messages from message originators and the forwarding of the messages to the intended recipients.

A known method of implementing SMS in fixed networks is a so called User Based Solution (UBS). This solution is a connection-oriented service. To send an SMS message to a recipient terminal a subscriber establishes a connection between the sending terminal and a short message centre and 2003E01336 SL sends the message to the short message centre in-band, on a speech channel. Likewise, a connection is established between the short message centre and the recipient terminal and the message is transmitted on from the short message centre to the recipient terminal in-band on a speech channel.

In this solution, no support for Centrex is available.

For a Centrex user this means that when sending and receiving SMS messages, the normal Centrex numbering plan cannot be used. This has a number of drawbacks. For example, a sender must address an SMS message to the Public Directory Number of the intended recipient terminal rather than the Centrex Directory Number of the recipient terminal. Furthermore, within a Centrex business group, the Centrex directory Number of a sending terminal is not available for presentation at the terminal that receives the SMS message.

The present invention aims to alleviate these problems.

According to the present invention there is provided, a switching centre for operating in a telecommunications network, the switching centre capable of receiving a data message transmitted from a sending terminal of a private user group of terminals connected to the switching centre and transmitting the message onwards in the telecommunications network for delivery to an intended recipient terminal, the 2003E01336 SL switching centre being arranged to translate address information included in the message and which conforms with a private network numbering scheme, into corresponding address information which conforms with a public network numbering scheme, to enable the message to be routed to the recipient terminal.

According to the invention there is also provided, a switching centre for operating in a telecommunications network, the switching centre being capable of receiving a data message transmitted from a sending terminal and intended for a recipient terminal of a private user group of terminals connected to the switching centre, and transmitting the message to the recipient terminal, the switching centre being arranged to translate address information included in the message and which conforms with a public network numbering scheme, into corresponding address information which conforms with a private numbering scheme.

Further features and advantages of the invention will become clear from the following description, which describes an embodiment of the invention, by way of example only, with reference to the accompanying drawings, wherein: Figure 1 illustrates a communications network; 2003E01336 SL Figure 2 illustrates signalling between elements in the communications network of Figure 1; Figure 3 illustrates message formats: Figure 1 illustrates a fixed line telecommunications network 1. The network 1 comprises a first Centrex switching centre 2, a second Centrex switching centre 3, a non-Centrex local exchange switch 4 and a short service message centre (SSMC) 5. These network elements are connected to each other as well as to other switches (not shown) in the remainder of the network via standard communications links (not shown).

The first Centrex switching centre 2 is connected to a first plurality of subscriber terminals 2a to 2n which form a first Centrex group. Likewise, the second Centrex switching centre is connected to a second plurality of subscriber terminals 3a to 3n which form a second Centrex group. The first and second Centrex groups together form a Centrex business group.

The non-Centrex switching centre 4 is connected to a non- Centrex terminal 6.

One example of a Centrex switching centre is the applicant's EWSD (Electronic Digital Dialling System). Such a system comprises a Centrex subscriber database as well as a Centrex 2003E01336 SL group database. Information about CTX subscribers is deposited in the CTX subscriber database, such as the internal telephone and public telephone numbers of the subscribers' telephone devices and also CTX functions that are available to the respective CTX subscribers.

Information about individual CTX groups within a business group is stored in a CTX group database, which contains; among other things, a group number plan and predetermined group functions that are available for the subscribers of the respective CTX group.

A further database is provided for depositing standard fixed network information that is required for call switching via the switch. This database comprises generally public data such as a number plan of subscribers.

A control processor is provided for processing calls to be switched via the switching centre.

In this embodiment, each of the first set of user terminals 2a to 2n and each of the second set of terminals 3a to 3n is an ISDN telephone. Each terminal 2a to 2n and 3a to 3n is connected to its respective CTX switching centre 2 and 3 via a respective CTX port. Each terminal 2a to 2n and 3a to an 2003E01336 SL is assigned via its CTX port a CTX Directory Number (CTXDN) and a public directory number (PDN), comprising a Local Area Code (LAC) and a Directory Number (DN).

Each terminal 2a to 2n, 3a to an and the non Centrex terminal 6 is an SMS enabled device. A user of a terminal 2a to 2n, 3a to 3n may generate an SMS message and transmit the message to the servicing CTX switching centre 2 or 3. From the servicing CTX switching centre the message is forwarded to the SSMC 5. The SSMC 5 generally holds the message and handles the onward transmission to the terminating terminal identified in the SMS message.

Contrary to user based solutions for sending SMS messages in fixed networks, in embodiments of the present invention, messages are transmitted from a sending terminal to a receiving terminal via the SSMC 5 using a connectionless service. This so called Network Based solution (NBS), is technically better than UBS, because in a connectionless service, the SSMC 5 need not be called by the terminal transmitting the message and the message is not transmitted through the network using speech channels.

The present invention enables CTX subscribers to use the same CTX numbering plan for sending SMS messages as is used to establish standard calls. Thus a CTX subscriber may transmit 2003E01336 SL an SMS message to another CTX subscriber using the CTXDN of the terminal of the message recipient. Furthermore, a CTX subscriber who receives an SMS message sent by another CTX subscriber is able to see the CTXDN of the sending terminal displayed on a display at the recipient terminal.

Referring now to Figure 2 of the accompanying drawings, which illustrates figuratively the process by which an SMS message may be transmitted from one CTX subscriber to another in the network 1. In a first example, the SMS message 10 is generated at one of the first set of user terminals 2a to 2n, say the terminal 2a, and is transmitted to one of the second set of user terminals 3a to 3n, say the terminal 3a. Digital Subscriber Signalling 1 (DSS1) is the access signalling used between the user terminals and the network 1.

The SMS message 10 generated at the terminal 2a comprises two parts, a DSS1 part (DSS1), and a GSM part (GSM). As is illustrated in Figure 2, the DSS1 part (DSS1) of the SMS message 10 comprises a number of data fields. A first of these data fields (ClgPN) contains the Centrex Directory Number CTXDN of the terminal used to send the SMS message. A second of these data fields (CldPN) contains the CTXDN of the terminal, which is to receive the SMS message. In this example, the CTXDN of the sending terminal = 100 and the 2003E01336 SL CTXDN of the receiving terminal = 101. The fields (ClgPN) and (CldPN) thus contain CTX specific data.

The GSM part (GSM) of the SMS message 10 contains the actual text message composed by the originator of the SMS message.

The GSM part (GSM) further contains CTX specific data, namely, the CTXDN of the sending terminal and the CTXDN of the intended recipient terminal. The format of the GSM part (GSM) of the SMS message 10 conforms to the SMS specifications defined in the technical specifications of the GSM system.

The signalling information included in the DSS1 part of the message is used to route the message through PSTN/ISDN parts of the network 1. The signalling information contained in the GSM part of the message is used to route the message through GSM parts of the network 1. For example, the SMSC 5 may be part of a GSM network rather than part of a fixed line network.

The first CTX switching centre 2 receives the SMS message 10 transmitted by the terminal 2a and is responsible for translating Centrex Directory Numbers contained in the message into their corresponding Public Directory Numbers for the onward routing of the SMS message 10 in the network 1.

2003E01336 SL The CTX switching centre 2 obtains from its database system the Public Directory Numbers of the sending terminal 2a and the intended recipient terminal 3a. The CTX switching centre 2 overwrites the CTX specific Directory Numbers contained in the first (ClgPN) and second (CldPN) data fields of the DSS1 part of the message 10 and the CTX specific Directory Numbers contained in the GSM part (GSM) part of the message 10 with the corresponding Public Directory Numbers. Thus, in this example, the CTXDN of the terminal 2a contained in the first field (ClgPN) and in the GSM part (GSM) of the message 10 is overwritten with the public directory number of the terminal 2a, namely, 4100. Likewise, the CTXDN of the terminal 3a contained in the second field (CldPN) and in the GSM part (GSM) of the message 10 is overwritten with the public directory number of the terminal 3a, namely, 4110.

In this example, the terminals 2a and 3a share a common Local Area Code (LAC) and so this need not be included in the public directory numbers included in the message 10. If the terminal 2a and 3a had different public LAC's, or indeed different public Country Codes, these codes would form part of the public directory numbers included in the message 10.

The first Centrex switching centre 2 is also responsible for putting into an additional information field (Add info) in 2003E01336 SL the DSS1 part of the message 10 CTX specific data. This CTX specific data consists of a generic number part and a business group identifier part. In this example, the generic number part includes the CTXDN of the sending terminal 2a and the CTXDN of the intended recipient terminal 3a.

The business group identifier part includes the CTX business group identifier number (BGID) of the CTX business group to which the sending terminal 2a belongs.

A format for the generic number part and the business group identifier part is schematically illustrated in Figure 3.

The message 10 is transmitted from the first Centrex switching centre 2 over the network 1 to the SSMC 4 using the Transactions Capability Application Part (TCAP) protocol.

Likewise, the message 10 is then forwarded from the SSMC 5 to the second Centrex switching centre 3. The SSMC 4 thus acts as a store and forward centre for the message.

The second Centrex switching centre 3 identifies from information contained in the business group identifier part that the sending terminal 2a and the intended recipient terminal 3a are in the same Centrex business group. The second Centrex switching centre 3 overwrites the Public Directory Numbers contained in the first (ClgPN) and second 2003E01336 SL (CldPN) data fields of the DSS1 part of the message 10 and the Public Directory Numbers contained in the GSM part (GSM) part of the message 10 with the corresponding CTX Directory Numbers. Thus, in this example, the public directory number of the terminal 2a contained in the first field (ClgPN) and in the GSM part (GSM) of the message 10 is overwritten with the CTXDN of the terminal 2a, namely, 100. Likewise, the public directory number of the terminal 3a contained in the second field (CldPN) and in the GSM part (GSM) of the message 10 is overwritten with the CTXDN of the terminal 3a, namely, 110. The additional information field (Add info) may be deleted.

The second Centrex switching centre 3 passes the message 10 to the terminal 3a. When a subscriber uses the terminal 3a to access the message content contained in the GSM part (GSM), the terminal 3a presents to the user the CTXDN of the terminal 2a from the first field (ClgPN) of the DSS1 part as being the number of the sending party.

The user of the terminal 3a may compose a reply message and in a procedure identical to that described above transmit the reply message to the terminal 2a using the CTXDN of the terminal 2a.

2003E01336 SL This process may also be used to send a SMS message from a terminal in one Centrex group, for example the terminal 2a, to a terminal in a different Centrex group, for example the terminal 3a, using so called,group dialling'. In group dialling, to send a message to a recipient terminal, the originator of the message must use a group dialling access code (AC) for calling from the Centrex group of the calling device to the Centrex group of the recipient device and the CXDN of the recipient terminal. Thus, if the group dialling access code for calling from the Centrex group of the terminal 2a to the Centrex group of the terminal 3a is, for example, *12, to send a message from the terminal 2a to the terminal 3a, the sender uses the number *12101.

This is the number contained in the second (CldPN) data field of the DSS1 part of the message 10 received at the first centrex switching centre 2. The first data field (ClgPN) contains the CTRX number of the terminal 2a, i.e 100. Again, these numbers are also contained in the GSM part of the message.

Again, to route the message 10 through the network 1, the first CTX switching centre 2 overwrites the CTX specific Directory Numbers contained in the first (ClgPN) and second (CldPN) data fields of the DSS1 part of the message 10 and 2003E01336 SL those numbers contained in the GSM part (GSM) part of the message 10 with the corresponding Public Directory Numbers, in this example, 4100 for the terminal 2a and 4110 for the terminal 3a.

The first Centrex switching centre 2 also puts into the generic number part of the additional information field (addinfo) the CTXDN of the sending terminal 2a and the CTXDN, (including the group dialling access code) of the intended recipient terminal 3a. Into the business group identifier part of the message the centre 2 inserts the CTX business group identifier number (BGID) of the CTX business group of the sending terminal 2a.

The message is transmitted from the first Centrex switching centre 2 to the SMSC 5 and then from the SMSC to the second Centrex switching centre 3.

On receiving the message 10 from the SMSC 5 the second Centrex switching centre 3 overwrites the Public Directory Number contained in the first (ClgPN) field, with a number comprising the group dialling access code for dialling from the Centrex group of the terminal 3a to that of the terminal 2a, for example, *21, followed by the CTXDN of the terminal 2a, i.e 100. The Public Directory number contained in the second (CldPN) data field is overwritten with the CTXDN of the terminal 3a. The corresponding Public Directory Numbers 2003E01336 SL contained in the GSM part (GSM) part of the message 10 are also overwritten with these CTX numbers and the data in the additional information field is deleted. The second Centrex switching centre 3 then passes the message 10 to the terminal 3a, which presents the number of the sending terminal 2a as being *21100. Thus, to send a reply SMS message to the terminal 2a, the user of the terminal 3a may simply use the number *21100.

The above described procedure may also be used to transmit an SMS message 10 between two terminals connected to the same Centrex switching centre, for example, the terminals 2a and 2b of the first set of terminals. This message 10 is transmitted from the terminal 2a to the first Centrex switching centre 2 and from there to the SMSC 5. From the SMSC 5 the message 10 is transmitted back to the first Centrex switching centre 2b and from there to the recipient terminal 2b.

The DSS1 part of the message 10 received at the first Centrex switching centre 2 from the terminal 2a contains in the first data field (ClgPN) the CTXDN of the terminal 2a, in this example 100, and in the second data field (CldPN) the CTXDN of the terminal 2b, in this example 102. Again, this information is also included in the GSM part (GSM) of the SMS 2003E01336 SL message 10 together with the actual text message composed by the originator of the SMS message.

Again, to route the message 10 through the network 1, the first CTX switching centre 2 overwrites the CTX specific Directory Numbers contained in the first (ClgPN) and second (CldPN) data fields of the DSS1 part of the message 10 and those numbers contained in the GSM part (GSM) part of the message 10 with the corresponding Public Directory Numbers, in this example,4100 for the terminal 2a and 4111 for the terminal 2b.

The first Centrex switching centre 2 again puts into the generic number part of the additional information field (addinfo) the CTXDN of the sending terminal 2a and the CTXDN of the intended recipient terminal 3a and into the business group identifier part the CTX business group identifier number (BGID) of the CTX business group to which the sending terminal 2a belongs.

The message is transmitted from the first Centrex switching centre 2 to the SMSC 5 and then from the SMSC back to the first Centrex switching centre 2.

2003E01336 SL On receiving the message 10 from the SMSC 5 the first Centrex switching centre 2 overwrites the Public Directory Numbers contained in the first (ClgPN) and second (CldPN) data fields of the DSS1 part of the message 10 and the Public Directory Numbers contained in the GSM part (GSM) part of the message with the corresponding CTX Directory Numbers and deletes the data additional information field. The first Centrex switching centre 2 then passes the message 10 to the terminal 2b. When a subscriber uses the terminal 2b to access the SMS message, the terminal 2b presents to the subscriber the CTXDN of the terminal 2a contained in the first field (ClgPN) of the DSS1 part as being the number of the sending party.

The above described procedure may also be used to transmit an SMS message 10 from a Centrex terminal, for example the terminal 2a, to a non Centrex SMS enabled terminal 6 connected to the non - Centrex switch 4.

This message 10 is transmitted from the terminal 2a to the first Centrex switching centre 2 and from there to the SMSC 5. From the SMSC 5 the message 10 is transmitted to the non- Centrex switching centre 5 from there to the recipient terminal 6.

2003E01336 SL The DSS1 part of the message 10 received at the first Centrex switching centre 2 from the terminal 2a contains in the first data field (ClgPN) the CTXDN of the terminal 2a, in this example 100. The second data field (CldPN) contains the number input by the user of the terminal 2a to send the message to the non - Centrex terminal 6.

This number comprises the Public Network Access Code (PNAC) of the Centrex numbering plan of the Centrex group of the terminal 2a, for example 0, followed by the Public Directory Number (PDN) of the terminal 6, in this example 4112. Again, this information is also included in the GSM part (GSM) of the SMS message 10 together with the actual text message composed by the originator of the SMS message.

To route the message 10 through the network 1, the first CTX switching centre 2 overwrites the CTX format numbers contained in the first (ClgPN) and second (CldPN) data fields in the DSS1 part of the message and those same numbers in the GSM part (GSM) part of the message 10 with the Public Directory Numbers of the terminals 2a and 6, in this example, 4100 and 4112 respectively.

In this example no information is put into the Add Info

field.

2003E01336 SL The message is transmitted from the first Centrex switching centre 2 to the SMSC 5 and then from the SMSC to the non Centrex switching centre 4.

The Non - Centrex switching centre 4 then passes the message to the terminal 6. When a subscriber uses the terminal 6 to access the SMS message, the terminal 6 presents to the subscriber the Public Directory Number of the terminal 2a contained in the first field (ClgPN) of the DSS1 part as being the number of the sending party.

The user of the terminal 6 may send a reply SMS message to the terminal 2a using the Public Directory Number of the terminal 2a.

This message 10 is transmitted from the terminal 6 to the non - Centrex switching centre 4 and from there to the SMSC 5.

From the SMSC 5 the message 10 is transmitted to the first Centrex switching centre 2 and from there to the recipient terminal 2a.

The DSS1 part of the message 10 received at the non - Centrex switching centre 4 from the terminal 6 contains in the first data field (ClgPN) the Public Directory Number of the 2003E01336 SL terminal 6, in this example 4112. The second data field (CldPN) contains the Public Directory Number (PDN) of the terminal 2a, in this example 4100. Again, this information is also included in the GSM part (GSM) of the SMS message 10 together with the actual text message composed by the originator of the SMS message.

In this example no information is put into the Add Info

field.

The message is transmitted from the non - Centrex switching centre 4 to the SMSC 5 and then from the SMSC 5 to the first Centrex switching centre 2.

On receiving the message 10 from the SMSC 5 the first Centrex switching centre 2 inserts at the front of the Public Directory Number contained in the first (ClgPN) data field, the PNAC code of the Centrex group, in this example, 0. The first Centrex switching centre 2 also overwrites the Public Directory Number of the terminal 2a contained in second (CldPN) data field with CTXDN of the terminal 2a, in this example, 100. Corresponding changes are also made in the GSM part (GSM) part of the message 10.

2003E01336 SL The first Centrex switching centre 2 then passes the message to the terminal 2a. When a subscriber uses the terminal 2a to access the SMS message, the terminal 2a presents to the subscriber the number 04112 i.e. the PDN of the terminal 6 preceded by the PNAC of the centrex group. The PNAC alerts the user that the SMS message has originated from an external phone that is not a member of the Centrex business group that the terminal 2a belongs to.

Other possibilities will be apparent to those skilled in the art, for example, an SMS message may be sent from one Centrex terminal to another by means of the sender using the Public Network Access Number of the Centrex group of the sending device and the Public directory number of the intended recipient device. At the recipient device the number of the sending device is presented as being the public directory number of the sending device preceded by the Public Network Access Number of the Centrex group of the recipient device.

The user of recipient device may simply use this number to send a reply message.

It will be appreciated that a CTX switching centre processing an SMS message formatted in the manner described above may apply to the message any of the CTX specific restrictions, commonly applied to standard CTX voice calls. For example, a 2003E01336 SL CTX subscriber may be prohibited from sending an SMS message to a recipient outside of the CTX group to which the subscriber belongs. Other such restrictions which may be applied, will be known to those skilled in the art.

In the above examples, the switching centre serving the intended recipient terminal may make use of any of the information contained in the DSS1 part of the message, including the Add info field, the GSM part of the message and its own databases to perform the number translations.

Although the invention has been described with reference to a Centrex environment it may also be used in other similar environments, for example, in a Private Branch Exchanges (PBX) environment.

The invention may also be used in respect of other types of discrete data messages, for example, picture messages.

Having thus described the present invention by reference to preferred embodiments, it is to be well understood that the embodiments in question are exemplary only and that modifications and variations such as will occur to those possessed of appropriate knowledge and skills may be made without departure from the scope of the invention as set forth in the appended claims.

Claims

A switching centre for operating in a telecommunications network, the switching centre capable of receiving a data message transmitted from a sending terminal of a private user group of terminals connected to the switching centre and transmitting the message onwards in the telecommunications network for delivery to an intended recipient terminal, the switching centre being arranged to translate address information included in the message and which conforms with a private network numbering scheme, into corresponding address information which conforms with a public network numbering scheme, to enable the message to be routed to the recipient terminal.
2. A switching centre according to claim 1, wherein the switching centre is arranged to translate an address of the recipient terminal included in the message and which conforms to a private network numbering scheme into a corresponding public network address of the recipient terminal.
3. A switching centre according to claim 1, the switching centre being further arranged to translate an address of the sending terminal included in the message and which conforms with a private network numbering scheme, into a corresponding public network address of the sending terminal. s
4. A switching centre according to claim 1, 2 3, wherein the message is transmitted from the switching centre to a message centre for onwards delivery to the intended recipient terminal.
5. A switching centre according to any preceding claim wherein the message is an SMS message.
6. A switching centre according to any preceding claim wherein the translated address information is included in a first part of the message that contains signalling information for routing the message in a fixed line network.
7. A switching centre according to claim 5 or 6, wherein the first part of the message conforms to DSS1.
8. A switching centre according to claim 7 or 8, wherein the translated address information is also included in a second part of the message that contains signalling information for routing the message in a mobile network.
9. A switching centre according to claim 8, wherein the second part of the message conforms to GSM.
10. A switching centre according to any preceding claim, wherein the is centre arranged to include the address information which conforms with a private numbering scheme in the message transmitted onwards by the centre.
11. A switching centre according to any preceding claim, wherein the centre is a Centrex switch and the address information which conforms with a private numbering scheme comprises one of, a Centrex directory number of the recipient terminal, a Centrex directory number of the recipient terminal combined with a Centrex group dialling code, or, a public directory number of the recipient terminal combined with a Centrex public network access code.
12. A switching centre according to any preceding claim wherein the switching centre is a Centrex switch and is arranged to include in the message, data identifying a Centrex business group to which the sending terminal belongs.
13. A switching centre for operating in a s telecommunications network, the switching centre capable of receiving a data message transmitted from a sending terminal and intended for a recipient terminal of a private user group of terminals connected to the switching centre, and transmitting the message to the recipient terminal, the switching centre being arranged to translate address information included in the message and which conforms with a public network numbering scheme, into corresponding address information which conforms with a private numbering scheme.
14. A switching centre according to claim 13, wherein the switching centre is arranged to translate an address of the recipient terminal included in the message and which conforms to a public network numbering scheme into a corresponding address of the recipient terminal which conforms with a private network numbering scheme.
15. A switching centre according to claim 13 or 14, wherein the switching centre is arranged to translate an address of the sending terminal included in the message and which conforms with a public network numbering scheme, into a corresponding address of the sending terminal which conforms with a private network numbering scheme.
16. A switching centre according to claim 13, 14 or 15, wherein the message is transmitted to the switching centre from a message centre for onwards delivery to the intended recipient terminal.
17. A switching centre according to any preceding claim wherein the message is an SMS message.
18. A switching centre according to any preceding claim wherein the translated address information is included in a first part of the message that contains signalling information for routing the message in a fixed line network.
19. A switching centre according to claim 18, wherein the first part of the message conforms to DSS1.
20. A switching centre according to claim 18 or 19, wherein the translated address information is also

I

included in a second part of the message that contains signalling information for routing the message in a mobile network.
21. A switching centre according to claim 20, wherein the second part of the message conforms to GSM.
22. A switching centre according to any of claims 13 to 21, wherein the centre is a Centrex switching center and wherein the address information which conforms with a private numbering scheme comprises one of, a Centrex directory number of the sending terminal terminal, a Centrex directory number of the sending terminal combined with a Centrex group dialling code, or, a public directory number of the sending terminal combined with a Centrex public network access code.