IE20020415A1 - A mobile network number transparency system and method - Google Patents

Abstract

A platform ("Ulyssees") supports a signalling relay function (SRF), a number portability location register (NPLR), and a number portability database (NPDB). The signalling relay function receives signals from an MSC and routes as appropriate for the number portability and with relevant protocol conversion. The relay translates a MAP operation between networks so that a call is routed directly from an MSC of an originating network to an MSC of the destination network.

Description

"A mobile network number transparency system and method" INTRODUCTION Field of the Invention The invention is directed towards providing improved number transparency, particularly between networks operating according to different standards such as ANSI41 and GSM.

Prior Art Discussion It is generally desirable, and indeed mandatory in some countries, that network operators provide a service whereby a subscriber may be migrated form one network to another without changing their telephone number. Migration must be seamless from the subscriber’s perspective to the extent that the subscriber must receive all services that are addressed by directory number from any source, including: voice and data calls; short messages; GPRS (General Packet Radio System); and At present there are some number portability techniques available, as follows: • Call Forwarding. A simple migration facility can be implemented using the call forwarding unconditional features of the GSM and ANSI 41 networks. This involves retaining an HLR entry for a migrated subscriber, with call forward unconditional (CFU) set to an appropriate number (e.g. prefix plus number) to cause the call to be re-routed to the other network.

This is an inefficient and inflexible approach and is not realistic if there are more than a few migrated subscribers.

• Re-direct on release. If an MSC receives an "unknown subscriber" response from an HLR, it can assume the number is migrated and route the call to the other network urn secret ££.

X Ha, ΠΓ& op g ?) 11 -2(typically with a routing prefix). This only works when there is only one other possible network.

The disadvantages of the switch-based approach is that the necessary switch enhancements are non-standard, can be expensive, and, like the CFU approach, can be inefficient and inflexible.

• Intelligent network-like query of a migration database. For ANSI 41 networks, MAP messages and procedures have been defined for querying a Number Portability DataBase (NPDB) in GSM networks CS-1 INAP can be used.

The disadvantages of the IN approach is that appropriate IN facilities need to be installed on all switches (which can be expensive) and IN queries can have a significant impact on switch performance.

PCT Patent Specification No. W001/03446 (Nokia) describes a system for number portability, in which a routing regular is queried for routing information of a ported mobile subscriber.

The invention is directed towards providing an improved system and method to implement number portability (transparency) between two or more networks using different core network signalling standards, for example GSM and ANSI41.

SUMMARY OF THE INVENTION According to the invention, there is provided a method for handling a mobile network call or short message to provide number portability between mobile networks that use different signalling standards, the method comprising the steps of: routing the signal to a signalling relay, and the signalling relay translating the signal and relaying the translated signal to a destination network. -3By handling the translation and routing itself, the relay takes considerable processing overhead from the requesting network element.

In one embodiment, the signal is routed as a query from an MSC or an SMSC for routing a call or a short message.

In another embodiment, the signalling relay relays a MAP message to the HLR of the destination network.

In one embodiment, the signalling relay comprises a number portability database and it accesses said database to determine how the signal should be relayed.

In another embodiment, the signalling relay invokes a number portability location register (NPLR) function to return a routing number that causes the call to be sent to the destination network.

In another embodiment, the signalling relay translates a MAP operation between networks so that a call is routed directly from an MSC or an SMSC of an originating network to an MSC or an SMSC of the destination network.

In one embodiment, the signalling relay resides on a platform, and there is a relay on the platform associated with both networks co-operating for number portability services.

In another embodiment, the platform inspects the MAP payload of an SS7 SCCP message to determine the operation type and subscriber number.

In one embodiment, the platform assigns a default number for numbers not in the number portability database.

According to another aspect, the invention provides a number portability platform comprising means for performing the signalling relay operations of the method as defined above. -4DETAILED DESCRIPTION OF THE INVENTION Brief Description of the Drawings The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings in which:Fig. 1 is a diagram showing a number portability process for ANSI41-GSM migration; Fig. 2 is a diagram showing how calls to ANSI41 subscribers roaming in a GSM network are handled; Fig. 3 is a diagram showing handling of calls from ANSI41 to GSM subscribers; Fig. 4 is a diagram showing handling of calls from GSM to ANSI41 subscribers; Fig. 5 is a diagram showing SMS delivery using SMSC relaying; Fig. 6 is a diagram illustrating protocol translation for inter-technology SMS (ANSI41-GSM); and Figs. 7 to 17 are diagrams illustrating signalling for different number transparency scenarios.

Description of the Embodiments The invention provides a system and method to implement number portability (transparency) which operates simultaneously in both systems, for example GSM and ANSI41.

The method and system uses an approach called a signalling relay, MAP-based approach.

The MSC routes queries to possibly migrated numbers through a signalling relay, which includes a migration (number portability) database. If the call is for a subscriber of that y l y 4¾. -5network, the signalling relay function (SRF) relays the SCCP message to the appropriate HLR. If the call is for a subscriber of another network, the technique is to invoke a Number Portability Location Register (NPLR) function to return a routing number that causes the call to be sent to the other network. Typically the routing number is the original dialled number with a routing prefix.

The basic signalling relay approach entails no impact on other network elements, other than SS7 configuration changes. There are no performance impacts on the switches or the HLRs.

The signalling relay architecture is supplemented by a feature to translate the MAP operation between ANSI 41 and GSM, so that in most cases a call can be routed directly from an MSC in one technology to a serving MSC in the other, thus avoiding unnecessary trunking.

Call Relaying Between Networks The approach is illustrated in Fig. 1. A platform (called "Ulyssees") has two SRFs, a number portability database (NPDB) and a NPLR. In this method, the signalling relay function is being performed in the GSM network. This is the general case. Ulysses-NP always relays queries to the HLR if it is in same network. The relay is at the SCCP (Signalling Connection Control Part) level, so the reply can be sent directly to the querying network element.

In this case, as the call will have been received with a routing prefix, indicating that the subscriber is a GSM subscriber, the relay through the SRF is unnecessary. However it can be useful when there are multiple HLRs as the use of an SRF allows MSISDNs/MDNs to be assigned to any HLR (the actual HLR for any MSISDN or MDN can be specified).

As shown in Fig. 2, for calls originating in the GSM network that are for ANSI 41 numbers, a similar scenario is implemented. The GSM MSCs will route HLR queries through the SRF. If the number has been migrated to GSM, it will be relayed to the required HLR.

Otherwise, for non-migrated numbers, it will return a routing number that sends the call to the ANSI 41 network. This technique avoids thromboning calls between the networks. -6Ulysses-NP is capable of inspecting the MAP payload of an SCCP message in order to determine the operation type and the subscriber number (MSISDN in GSM, or MIN/MDN for ANSI 41). This means that the network operator is free to use any form of SCCP addressing. Operations may be sent to the SRF using global title (with the directory number as the global title) or they may be sent just using the SRF point code (DPC/SSN).

Only directory number oriented operations (such as GSM SRI or ANSI 41 LOCREQ) are handled by the SRF. All mobility management operations associated with the IMSI (or MIN) will be sent directly to the HLRs.

Protocol Translation Approach If the GSM and ANSI 41 networks are folly meshed at the ISUP level and providing a subscriber does not require IN or CAMEL services, it would be possible to perform direct routing from the ANSI 41 network to the GSM network (and vice versa).

A flag indicating that direct routing is allowed is associated with a network and, optionally with an individual number. It is possible to include protocol translation and directly query GSM PILRs from ANSI 41 (and vice versa). If the ANSI 41 and GSM MSCs are folly meshed at the ISUP level, the call can be routed directly to the serving MSC, and therefore there is no unnecessary trunking involved. This is shown in Fig. 3.

Similarly the GSM MSCs can route HLR queries through the SRF, which, if the number has not been migrated to GSM, will translate the query to the IS41 form, as shown in Fig. 4.

Hybrid Approach An issue with the direct routing, protocol translation approach is that mobile terminated IN or CAMEL services for a subscriber cannot be invoked by the ANSI 41 MSC and they will not be invoked by the GSM service MSCs, when routing on MSRN; similarly IS41 WIN services cannot be invoked by a GSM MSC. The question of IN services is one of the reasons why the GSM 03.66 standard does not recommend direct routing of calls by a donor MSC to a serving MSC for ported subscribers. -7Typically an operator will deploy a "hybrid approach" using protocol translation and direct routing, but supplemented by call relaying if the subscriber profile indicates that there are IN services that must be handled by an MSC in the subscription network.

All "ported" numbers will include an indication as to whether direct routing is allowed. The network operator would need to consider this in the planning and implementation of any mobile terminated IN, CAMEL or WIN services. Note that the necessary information is not available in an SRI or LOCREQ response, so it cannot be done automatically and must be provisioned in the number portability database.

Mobile Terminated Short Messages For migration with number transparency, a method is required for the SMSCs to have access to the migration database. The platform is able to support a number of different techniques. The actual one chosen will depend on an operator’s SMSC approach to inter-technology messaging.

Whilst it is possible to maintain a database of migrated subscribers in the SMSCs, this means replicated copies of the migration database, which has a significant impact on operations support and provisioning systems, not to mention the SMSCs themselves. The invention addresses this problem.

A very simple approach is, when delivering a message, the SMSC would first query an HLR in the network suggested by the numbering plan, if this results in an "unknown subscriber" indication, it could then try the other network or relay to the other SMSC (depending on the inter-technology technique used). Care must, of course, be taken to avoid looping if the number is unknown in either network. However this will be inefficient if there are a lot of ported numbers.

Inter-SMSC Relaying SMSCs in both networks send an HLR query for all numbers in the ANSI 41 and GSM number space via a signalling relay function. If the subscription network is the same as the querying network (i.e. the same technology), the query is simply relayed to the appropriate HLR. If, however, the number has been migrated to the other network, there are two options: a. Act as a pseudo HLR and give a response that indicates to the SMSC that relaying to the other network is needed. This only works when the querying SMSC is the network operator’s (and can be appropriately adapted). b. Provide protocol translation and gateway facilities. After routing the query to the HLR in the other network and receiving a positive response, a reply is given to the querying SMSC that causes the short message to be sent via a translation gateway. This approach can support short messages from other GSM operators to ANSI 41 subscribers.

As in the call related case, the HLR query in the technology B network is shown as being relayed through the SRF. As implied in the diagram, the SMSCs could in fact be combined.

Dual Mode SMSC For the dual mode SMSC approach, the platform could determine the network from the number portability database. If the subscription network is the same as the standard MAP query message, the MAP query is simply relayed to the appropriate HLR. If it is a different technology, Ulysses-NP can translate the MAP query into the appropriate standard, in the same way as we have proposed for call related queries. Typically all queries would be in the same format (GSM being the recommended one).

In addition to the basic rerouting query, the relay translates all other SMS delivery associated messages, such as those used for alerting The technique relies on the SMSC being able to determine technology from the serving MSC address.

Fig. 6 shows translation for successful message delivery.

In summary, the invention provides a system in which a high availability network element is shared between the ANSI 41 and GSM networks, with a common migration database. This database comprises all numbers that have migrated ("ported") to the other technology. The invention provides a number analysis facility that is used to assign the default (number owner network) for numbers that are not in the database.

There are considerable savings in directly routing a call to the serving MSC. An enhancement may be made to the platform to translate between the ANSI 41 and GSM HLR queries. This includes a facility for specifying whether such direct routing were allowed for each subscriber.

To support the various scenarios for short messages, the platform supports the option to perform the pseudo HLR function for short message relaying and is, therefore, capable of implementing the inter-technology SMS scenarios described above. If required, this can also be enhanced to translate a short message MAP query (SRI or SMSREQ) into the appropriate subscription network standard and return the serving MSC. The following sections describe the main signalling scenarios.

Call Related Signalling Normal Call to ANSI 41 Subscriber (Fig. 7) This shows the basic call scenario to an un-migrated ANSI 41 subscriber. It also shows the scenario that would be used for an ANSI 41 subscriber calling a GSM number that has been migrated to ANSI 41 if that is ever done. a. Call is received by an ANSI 41 switch, b. Which sends a LOCREQ to the HLRs. SS7 configuration is such that this is sent through the Ulysses SRF (signalling relay function). - 10c. Ulysses-NP determines that the subscriber should be an ANSI 41 subscriber and relays the operation to the appropriate HLR. The SRF can chose the HLR depending on the actual MIN/MDN. d. The PILR responds with the routing number (after interacting with the VLR, etc). This response is sent directly to the MSC as the Ulysses relaying function is just an SCCP redirection. e. The call is set up.

Normal Call to GSM Subscriber (Fig. 8) This shows the basic call scenario to a normal GSM subscriber. It also shows the scenario for a GSM subscriber calling an ANSI 41 number that has been migrated to GSM (avoiding tromboning back to the ANSI 41 network). a. Call is received by a GSM switch, b. Which sends a MAP-Send-Routeing-Information (SRI) towards the HLRs. SS7 configuration is such that this is sent through the Ulysses SRF (signalling relay function). c. Ulysses-NP determines that the subscriber should be a GSM subscriber (either a "native" subscriber or a migrated ANSI 41 number) and relays the operation to the appropriate HLR. The SRF can chose the HLR depending on the actual MSISDN. d. The HLR responds with the routing number (after interacting with the VLR, etc). This response is sent directly to the MSC as the Ulysses relaying function is just an SCCP redirection. e. The call is set up.

Call To Migrated ANSI 41 Number - Direct Routing (Fig. 9) This shows the scenario where direct routing is supported. The platform translates the HLR query into the GSM form, relays it to the GSM HLR and re-translated the response. a,b. Call is received by a ANSI 41 switch, which sends a LOCREQ towards the - 11 HLRs, via the SRF. c. Ulysses-NP determines that the subscriber is a GSM subscriber (e.g. a migrated ANSI 41 number or a native GSM number), for which direct routing is allowed. It translates the LOCREQ into the GSM equivalent (Send Routing Information), which it relays to the GSM HLR. d. The GSM HLR responds with a routing number (MSRN). e. Ulysses-NP uses the MSRN to form the ANSI 41 routing number (TLDN). f. The ANSI 41 MSC routes the call to the serving GSM MSC. g. which delivers the call to the GSM handset. The serving MSC can be in any network.

GSM Call to ANSI 41 Subscriber, Direct Routing (Fig. 10) In order to avoid tromboning calls through the ANSI 41 network, it is recommended that the GSM network be configured to treat all calls to ANSI 41 number blocks as ordinary mobile calls and send an HLR query through the SRF. This shows the scenario where direct routing is supported for routing from GSM to ANSI 41 subscribers. The platform translates the HLR query into the ANSI 41 form, relays it to the ANSI 41 HLR and re-translates the response. Just as with routing to GSM subscribers, direct routing is not possible if there are any WIN (or other IN) services associated with the subscriber, a,b. Call is received by a GSM switch, which sends an SRI towards the HLRs, via the SRF. c. Ulysses-NP determines that the subscriber is an ANSI 41 subscriber (e.g. a native ANSI 41 number or a GSM number migrated to ANSI 41 - if that is possible), for which direct routing is allowed. It translates the SRI into the ANSI 41 equivalent (LOCREQ), which it relays to the ANSI 41 HLR. d. The ANSI 41 HLR responds with a routing number (TLDN). e. The platform uses the TLDN to form the GSM routing number (MSRN). This is a straightforward mapping. f. The GSM MSC routes the call to the serving ANSI 41 MSC. - 12g. which delivers the call to the ANSI 41 handset. The serving MSC can be in any network.

Call To Migrated ANSI 41 Number - Indirect Routing (Fig. 11) This shows the scenario for a call to an ANSI 41 number that has been migrated to GSM. It also shows the scenario for an ANSI 41 subscriber calling a real GSM subscriber if it is possible to migrate GSM numbers to ANSI 41. This scenario is used if direct routing is prohibited by the routing profile. a,b. Call is received by an ANSI 41 switch, which sends a LOCREQ towards the HLRs, via the SRF. c. Ulysses-NP determines that the subscriber is a GSM subscriber (e.g. a migrated ANSI 41 number or a native GSM number). It invokes a pseudo HLR function that returns a reply with a routing number comprising the original number and a routing prefix (). The real ANSI 41 HLRs are not used at all. d. The routing prefix causes the call to be routed to the GSM network. The prefixes are fully configurable, with control over Nature-of-Address (NoA), and they may also contain non-decadic digits. e. The GSM gateway MSC treats the call as a call to a GSM number and sends a MAPSend-Routeing-Information (SRI) towards the GSM HLRs. As far as the prefix is concerned, it can do one of the following: 1. Strip the prefix completely and use the original dialled number as the MSISDN. This is straightforward - all switches can do this. 2. Retain the prefix and use the whole routing number as the MSISDN. In this case the SRF will strip the prefix (from the MAP message). 3. Strip the prefix from the MAP message, but retain it, or some other indicator, in the SCCP global title (perhaps sending it directly to the HLR).

In the general case, to prevent circular routing, it is desirable that some indication of the prefix is received by the SRF. As we propose a unified SRF, it should be impossible for - 13there to be an inconsistency between the ANSI 41 and GSM routing databases and thus the simple prefix stripping option (1) is probably acceptable. Nevertheless, for robustness, either (2) or (3) is recommended. f. Ulysses-NP determines that the subscriber is a migrated ANSI 41 number) and relays the operation to the appropriate HLR (fixing the MSISDN if necessary). g, h. The HLR responds with the routing number and the call is set up.

GSM Call to ANSI 41 Subscriber, Indirect Routing (Fig. 12) In order to avoid tromboning calls through the ANSI 41 network, it is recommended that the GSM network be configured to treat all calls to ANSI 41 number blocks as ordinary mobile calls and send an HLR query through the SRF. If the number has been migrated then the SRF will relay it directly to the appropriate HLR. If it is a native ANSI 41 number (or a subscriber migrated from GSM to ANSI 41) the following scenario will be used if direct routing has been disabled for the subscriber. a,b. Call is received by a GSM switch, which sends a MAP-Send-RoutingInformation(SRI) towards the HLRs. c. Ulysses-NP determines that the subscriber should be an ANSI 41 subscriber (either a "native" subscriber or a migrated GSM number). It invokes a pseudo HLR function that returns a reply with a routing number comprising the original directory number and a routing prefix (shown as ). The real GSM HLRs are not used at all. d. The routing prefix causes the call to be routed to the ANSI 41 network. e. The ANSI 41 gateway MSC treats the call as a call to a GSM number and sends a LOCREQ to the ANSI 41 HLRs. f. Ulysses-NP determines that the subscriber is a migrated ANSI 41 number) and relays the operation to the appropriate HLR (fixing the MDN/MIN if necessary). g. h. The HLR responds with the routing number and the call is set up. -14Short Message Scenarios The following scenarios are based on the use of inter-SMSC relaying. For clarity the SMSCs are shown as separate, however, they could be combined into a single, network entity, in which case the relaying is purely internal. If a unified SMSC is used, it would be possible to bypass the SRF completely. In this case the SMSC would first query the HLR in the network suggested by the numbering plan, if it received a "no subscriber" indication, it could try the other network.

Ordinary Short Message to ANSI 41 Subscriber (Fig. 13) This shows the basic short message scenario to an un-migrated ANSI 41 subscriber. It also shows the scenario for an ANSI 41 SMSC sending a message to a GSM number that has been migrated to ANSI 41. a. Message is received by an ANSI 41 oriented SMSC, b. Which sends an SMSREQ to the HLRs. SS7 configuration is such that this is sent through the Ulysses SRF (signalling relay function). c. Ulysses-NP determines that the subscriber should be an ANSI 41 subscriber and relays the operation to the appropriate HLR. The SRF can chose the HLR depending on the actual MIN/MDN. d. The HLR responds with the serving MSC information. This response is sent directly to the MSC as the Ulysses relaying function is just an SCCP redirection. e. The SMSC attempts to deliver the message.

Ordinary Short Message to GSM Subscriber (Fig. 14) This shows the basic short message scenario to a normal GSM subscriber. It also shows the scenario for a GSM subscriber sending a message to a ANSI 41 number that has been migrated to GSM. - 15a. Message is received by a GSM oriented SMSC. b. Which sends a MAP-Send-Routeing-Information-For-Short-Message (SRI-SM) towards the HLRs. SS7 configuration is such that this is sent through the Ulysses SRF (signalling relay function). c. Ulysses-NP determines that the subscriber should be a GSM subscriber (either a "native" subscriber or a migrated ANSI 41 number) and relays the operation to the appropriate HLR. The SRF can chose the HLR depending on the actual MSISDN. d. The HLR responds with the serving MSC information. This response is sent directly to the MSC as the Ulysses relaying function is just an SCCP redirection. e. The SMSC attempts message delivery.

ANSI 41 Originated Short Message To Migrated ANSI 41 Number (Fig. 15) This shows the scenario for an ANSI 41 originated short message to an ANSI 41 number that has been migrated to GSM. It also shows the scenario for an ANSI 41-originated short message to a GSM number. a,b. Message is received by an ANSI 41 SMSC, which sends an SMSREQ towards the HLRs, via the SRF. c. Ulysses-NP determines that the subscriber is a GSM subscriber (e.g. a migrated ANSI 41 number or a native GSM number). It invokes a pseudo HLR function that returns a reply with a special, pseudo serving MSC address. d. This special MSC address causes the SMSC to send the message to the GSM SMSC (which could be part ofthe same system). e. The GSM oriented SMSC treats it as a message to a GSM number and sends a MAPSend-ROUTEING-Information-FOR-Short-Message (SRI-SM) towards the GSM HLRs. f. Ulysses-NP determines that the subscriber is a migrated ANSI 41 number) and relays the operation to the appropriate HLR. g. h. The HLR responds with the serving MSC information and the message is delivered. - 16GSM Message to ANSI 41 Subscriber (Fig. 16) a,b. Message is received by a GSM oriented SMSC, which sends an SRI-SM to the HLRs. c. Ulysses-NP determines that the subscriber should be a ANSI 41 subscriber (either a "native" subscriber or a migrated GSM number). It invokes a pseudo HLR function that returns a reply with a special, pseudo serving MSC address. d. This special MSC address causes the SMSC to send the message to the ANSI 41 SMSC (which could be part of the same system). e. The ANSI 41 oriented SMSC treats it as a message to a GSM number and sends an SMSREQ to the ANSI 41 HLRs. f. Ulysses-NP determines that the subscriber is a migrated ANSI 41 number) and relays the operation to the appropriate HLR. g. h. The HLR responds with the routing number and the message is delivered.

Dual Mode SMSC Integrated Scenario (Fig. 17) The SMSC may translate a HLR query for short message delivery. This scenario shows how this would work for a GSM oriented query. In this scenario all queries are in the GSM format; this means that Ulysses-NP+ will only need to do a one way translation. a,b. Message is received by the SMSC, which sends a GSM SRI-SM query towards towards the HLRs. c. Ulysses-NP determines that the subscriber should be a ANSI 41 subscriber (either a "native" subscriber or a migrated GSM number). It translates the SRI-SM into the ANSI-41 equivalent and sends an SMSREQ towards the ANSI 41 HLRs. d. The ANSI 41 HLR responds with the serving MSC information. e. Ulysses-NP translates the result back into GSM format and sends the response to the SMSC -17f. The SMSC determines that the serving MSC is an ANSI 41 element and sends the message in ANSI 41 format.

This is only a simple view of the multi-mode scenario. Alerting functions, needed when a message cannot be delivered immediately are also handled and translated. Furthermore, when delivering from GSM to ANSI 41, additional handling is needed if the ANSI 41 message size maximum is exceeded.

Other GSM Phase 2+ Non Call Related Signalling In GSM phase 2+ a number of other MAP operations are defined that are addressed by MSISDN. These include the CAMEL Map-Any-Time-Interrogation (ATI) operation and Map-Send-Routing-Information-for-Location-Services (SRI-LCS). Provided the subscriber is a GSM subscriber, such operations will be routed by Ulysses-NP to the appropriate HLR. If the subscriber is an ANSI 41 subscriber they will be rejected.

In the case of the GSM optimised routing service (SOR). When the database indicates that the destination subscriber uses a non-GSM technology (i.e. is an ANSI 41 subscriber), Ulysses-NP ignores the SOR indicator in a GSM phase 2+ MAP operation and, if the query comes from a network that can understand the routing prefix, treats the query as an ordinary SRI. If the query comes from another network, it has to be rejected.

The following sets out some of the advantages of the invention.

• The solution is vendor independent and, apart from reconfiguration of the SS7 routing, requires no modifications to the operator’s MSCs or HLRs and only minimal changes to the SMSCs.

• Optimal use of signalling and trunks between the two networks.

• If and when number portability is mandated in an operator’s country, The invention can be used as a complete solution for both GSM and ANSI 41 networks.

The invention is not limited to the embodiments described but may be varied in construction and detail.

Claims (11)

Claims

1. A method for handling a mobile network call or short message signal to provide number portability and transparency between mobile networks that use different signalling standards, the method comprising the steps of: routing the signal to a signalling relay, and the signalling relay translating the signal and relaying the translated signal to a destination network.

2. A method as claimed in claim 1, wherein the signal is routed as a query from an MSC or an SMSC for routing a call or short message.

3. A method as claimed in claim 1 or 2, wherein the signalling relay relays a MAP message to the HLR of the destination network.

4. A method as claimed in any preceding claim, wherein the signalling relay comprises a number portability database and it accesses said database to determine how the signal should be relayed.

5. A method as claimed in any preceding claim, wherein the signalling relay invokes a number portability location register (NPLR) function to return a routing number that causes the call to be sent to the destination network.

6. A method as claimed in any preceding claim, wherein the signalling relay translates a MAP operation between networks so that a call or a short message is routed directly from an MSC or an SMSC of an originating network to an MSC or an SMSC of the destination network.

7. A method as claimed in any preceding claim, wherein the signalling relay resides on a platform, and there is a relay on the platform associated with both networks cooperating for number portability services. -198.

8.A method, as claimed in claim 7, wherein the platform comprises means for inspecting the MAP payload of an SS7 SCCP message to determine the operation type and subscriber number.

9. A method as claimed in claim 7 or 8, wherein the platform comprises means for assigning a default number for numbers not in the number portability database.

10. A number portability platform comprising means for performing the signalling relay 10 operations of a method as claimed in any preceding claim.

11. A computer program product comprising software code for performing a method as claimed in any of claims 1 to 9 when executing on a digital computer.