Abstract:
A system for sending a data packet from a first communication network ( 255 ) to a second communication network ( 270 ) is disclosed in which the second communication network ( 270 ) is directly unreachable by the first communication network ( 255 ). The system comprises a transmitting device for transmitting the data packet to the first communication network; a receiving device for accepting the data packet from the second communication network and generating a data packet response; and a relay ( 260 ) for acceptance of the data packet from the first communication network ( 255 ), passing the data package to the second communication network ( 270 ) and for acceptance of the generated data package response and passing the generated data packet response to the first communication network ( 255 ). Furthermore a Method for sending the data packet from the first communication network ( 255 ) into the second communication network ( 270 ) is taught which has the following steps: the data packet from the first communication network ( 255 ) is passed into the second communication network ( 270 ), a response signal is awaited; and the response signal is forwarded back into the first communication network ( 255 ).

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates in particular to a system and a method for sending a data packet from a first communication network to a second communication network, in particular mobile communications networks. 
       BACKGROUND TO THE INVENTION 
       [0002]    Packet transmission services have continuously gained in importance in mobile communications. Such services include the SMS (Short Message Service), first introduced in the GSM (Global System for Mobile Communications) protocol, and TCP/IP (Transmission Control Protocol/Internet Protocol) services. More details of these services are described in the book by M.-B. Pautet: The GSM system for mobile communications, published by the authors, ISBN 2-9507190-0-7, 1992; and in M. Rahnema: Overview of the GSM system and protocol architecture, IEEE Communications Magazine, vol. 31 (April 1992) no. 4, pp. 92-100. 
         [0003]    In mobile communications, one example of a packet transmission service which has had tremendous economic success is the SMS used both in GSM and in GPRS (General Packet Radio Service) mobile communications networks. Principles of the SMS are described in G. Brasche, B. Walke: Concepts, services, and protocols of the new GSM phase 2+ general packet radio service. IEEE Communications Magazine, vol. 35 (August 1997) no. 8, pp. 94-104. 
         [0004]    As is pointed out in J.-H. Park: Wireless internet access for mobile subscribers based on the GPRS/UMTS network, IEEE Communications Magazine, vol. 40 (April 2002) no. 4, pp. 38-49, a sustained high Quality of Service (QoS) level is mandatory and insisted upon by the senders of the messages. In order to enable the deployment of the packet transmission services like SMS in professional environments, it is necessary to define and maintain a pre-determined level of reliability for the packet transmission services and also to define and maintain attributes relating to precedence of packet transmission services as well as for the delay of the packet transmission service. 
         [0005]    Further problems in the delivery of packets arise when the originating mobile station and the destination mobile station are subscribed to different network operators of different mobile communications networks in the absence of roaming agreements between these network operators. 
         [0006]    Roaming agreements for packet transmission services between network operators are established all around the world. However, in some areas SMS roaming can sometimes be difficult. Quite often, small network operators are faced with numerous problems in establishing roaming agreements with larger network operators. Voice telephone calls between different mobile communications networks into foreign countries can be routed through the ISUP (ISDN User Part) using fixed telephone networks; however the provision of SMS services requires roaming agreements between the network operators. That is the reason for scenarios in which customers are able to phone mobile terminals in foreign countries, but are unable to use packet transmission services to the same mobile terminal. Presently, there are long waiting lists for small network operators who want to establish roaming agreements with the major network operators. The major network operators are often unwilling to establish these roaming agreements because an unwieldy number of roaming agreements. As a result there are restrictions in the service accessibility for packet transmissions, such as SMS services. 
         [0007]    Together with the SMS service in the GSM protocol, there are other packet switched services which have sprung up in the last years and are having similar compatibility problems like the SMS services. An example is found in North America in which the IS41 and IS95 protocols are used in TDMA (Time Division Multiple Access) and CDMA (Code Division Multiple Access) networks (e.g. CdmaOne, Cdma2000). 
         [0008]    Even providers of the popular Instant Messaging (IM) Services (e.g. ICQ, MSN Messenger, AIM or IRC) are beginning to connect their IM networks, in order to get over the obstacles of communication restricting incompatibility. Currently there are many different protocols used by the different IM providers. Some of the most important protocols are Jabber, an accepted internet standard, and SIP (Session Initiation Protocol), which is created by the IETF (Internet Engineering Task Force) and popular for its packet switched telephoning use (“voice over IP”). 
         [0009]    The above-mentioned services use central Mapping Servers, which provide status and routing information to the different devices, Mobile Stations (MS), etc (collectively called service clients). To be reachable, the service client notifies the central Mapping Server about its status and location, when it is turned on or changes its address. When the service client, that wants to initialize a connection with a target device, has the needed routing information from the Mapping Server, the service client is able to connect to the target device directly through the network, without further detour over the central Mapping Server or another server. 
         [0010]    In order to forward signals into a destination network subsystem which is not directly reachable (e.g. due to missing roaming agreements), a signal relay system is used, which is described later in more detail. 
         [0011]    In case of a GSM network, a Home Location Register (HLR) provides the functionality of the aforementioned Mapping Server. The stored information about a mobile station (service client), are the IMSI (International Mobile Subscriber Identity) of the mobile station and its last known status or address, if the mobile station is reachable. This address is the global title (GT) of the Mobile Switching Center (MSC) which is connected with a base station having a radio link to the mobile station. The GT of the MSC (the MSC-GT) is routing information to that MSC and therefore routing information to the mobile stations which are located in the NSS (network and switching subsystem) of that MSC. 
         [0012]    SMS are typically first send to a SMS Center (SMSC) which is responsible for the delivery of the SMS to the called party. The SMSC uses several MAP primitives of the SS7 protocol to transmit short messages. The “send routing information” request is used to query a HLR for routing information to a subscriber (the mobile station). The “forward short message” service request is used to forward the short message to the MSC which is connected to the called party subscriber and to the called party subscriber. The “report SM delivery status” service request is used to set the “message waiting data flag” in the HLR after a unsuccessfully delivery attempt. The three service requests are explained in more detail later. 
         [0013]    Every service request delivers a status report. The interpretation of these status reports at the SMS Center facilitates the generation of various error codes, including the acknowledgement of the successful delivery of the SMS. In order to enable a high Quality of Service (QoS) level and to keep the control of the SMS, it is important for the SMSC or a message originating Operator, to retrieve all signal acknowledgements, even if a signal relay system is used to forward signals into a destination network subsystem which is not directly reachable. 
         [0014]    It is possible for a service subscriber to change its subscription and thus its home network from a first network operator OP 1  to a second network operator OP 2 . The service subscriber is generally able to keep his old logical address (ISDN number) when changing—this is known as porting the called party number. In case of mobile networks the called party address is the MSISDN (Mobile Station Integrated Services Digital Network). Usually the Mapping Server of the mobile station, which was ported from the first network operator OP 1  to the second network operator OP 2 , is located in the second network OP 2 . 
         [0015]    Suppose now that a sender wishes to send an SMS to the service subscriber of the ported mobile number. The sender is subscribed to a message originating operator (OP). This message originating operator has roaming agreements with the first network operator OP 1  which is the number range holder of the MSISDN global title of the ported mobile station. As long as the message originating operator also has a roaming agreement with the new home operator (second network operator) OP 2  of the service subscriber, no problems occur: In order to retrieve routing information to the destination subscriber (here: the ported mobile number), the message originating operator (OP) will send a querying MAP service request to the number range holder of the called party address, the MSISDN of the destination subscriber. This number range holder is the first network operator OP 1 . If, as usual, the mapping server or Home Location Register (HLR), which is responsible for the ported destination subscriber, is located in the second network OP 2 , a Signaling Relay Function for support of Mobile Number Portability (MNP-SRF) of OP 1  will forward the querying MAP service request to OP 2 . The mapping server (HLR) of OP 2 , responsible for the ported destination subscriber will answer the query with an acknowledging signal which is sent to the message originating operator (OP). If, however, the message originating operator OP has no agreement with the first network operator (number range holder) OP 1 , no communication between the message originating operator OP and the first network operator OP 1  is possible. On the other hand, if the message originating operator OP has an agreement with the first network operator OP 1 , but no agreement with the second network operator OP 2  (and now home network of the service subscriber), the acknowledging answer from the mapping server (HLR) of OP 2  will not reach the origination operator (OP) due to the absence of roaming agreements between OP and OP 2 . The message originating operator OP does not get any answer as to the sent MAP service request and may only guess the reason. 
         [0016]    Several patents and patent applications are known which address the problem of improving the service between mobile communications networks. 
         [0017]    US patent application 2005-0124302 (Yoon et al.) teaches a method to improve the service within wireless systems which collaborate. The HLR information is periodically updated and synchronized through interfacing between the wireless network systems. 
         [0018]    The U.S. Pat. No. 6,832,089 (Nilcom) teaches a method which addresses the problem of number portability or incomplete number plans within the same country. A computer with SS7 connections is used as an SMSC relay to relay the short messages sent by an operator OP to a subscriber of a network OP 1  visiting a second network OP 2 , OP 2  having no roaming agreement with the network OP. The SMS is sent with the global title GT of the visited MSC to a companion SMSC in a network which does have a roaming agreement with network OP 2 . The computer is capable of interrogating all the HLRs of the country in which the number portability is operated. A database is built in a cache memory of the computer for all the mobile subscribers of the country in which the portability is operated so that the computer will know which HLR to interrogate, without searching, once the HLR has been found a first time. 
         [0019]    The U.S. Pat. No. 6,512,926 teaches a dynamic routing system for transmission of SMS. A numbering plan contains the numbers of the short message transmission centers (SMSC) and the possible interconnections between the different SMSCs and the switching centers (MSC) of the networks of the called mobile telephone. A numbering plan manager defines from the number of the called party the relay transmission center or centers (SMSC) in order to reach the switching centre (MSC) visited by the intended recipient of the short message (SMS). 
         [0020]    Various approaches to improve the delivery of SMS between different network providers have been suggested in the prior art. However, none of the known approaches teaches a method which allows the generation of reliable Quality of Service data. Currently, there is no practical way to determine the receipt of packet transmissions between several different network operators which have no roaming agreements. These operators can be possibly located in different countries. 
       SUMMARY OF THE INVENTION 
       [0021]    It is therefore an object of the invention to ensure reliable packet transmission services between different communications networks. 
         [0022]    It is furthermore an object of the invention to improve packet transmission services between different communication networks which provide number portability. 
         [0023]    It is another object of the invention to provide a method which allows the determination of Quality of Service for packet transmission services, such as Short Message Service, exchanged between communications networks without roaming agreement. 
         [0024]    It is a further object of the invention to enable maintaining a high level of Quality of Service for a SMS-Center. 
         [0025]    These and other objects of the invention are solved by a system for sending a data packet from a first communication network to a second communication network, the second communication network being directly unreachable by the first communication network, whereby the system comprises a transmitting device for transmitting the data packet to the first communication network; a receiving device for accepting the data packet from the second communication network and generating a data packet response; and a relay for acceptance of the data packet from the first communication network, passing the data package to the second communication network and for acceptance of the generated data package response and passing the generated data packet response to the first communication network. 
         [0026]    Any system in which the transmitting device, which sends the data package (such as an SMS or a MMS), is in a first communication network and the receiving device is in a second communication network and the second communication network is directly unreachable for the first communication network needs to provide some means of transferring the data package from the first communication network to the second communication network. The receipt of a response of the receiving device which acknowledges the receipt of the data package is advantageous as it enables a reliable packet transmission service to be provided compared to an uncertain situation when no received response is provided. 
         [0027]    The communication network is a mobile communication network such as GSM, CDMA or UMTS network, or an instant messaging network, such as Jabber, AIM, ICQ, MSN or IRC. 
         [0028]    The system of the invention further allows the measurement of quality of service parameters for the delivery of data packages. An operator of a packet transmission service on the side of the first communication network needs to know whether the packet transmission has been received by the receiving device. Only then the operator can assess the quality of service of its packet transmission service to the second communication network which is the prerequisite of improving the quality of service in the transmission of data packages. 
         [0029]    The invention further provides a relay which comprises a first module for the reception of a data packet from a first communication network and for transmission of a first response to the first communication network and a second module for the transmission of a data packet to a second network and for reception of a second response from the second communication network. The first module and the second module can be implemented as a single system. 
         [0030]    The relay provides the facility to forward information bi-directionally between a first communication network and a second communication network which is directly unreachable. It is advantageous not only to transfer information from the first communication network to the second communication network which would be sufficient to send a data package to a designated recipient. The additional transfer of the response, e.g. the acknowledgement of receipt of the data packet, in the opposite direction from the second communication network to the first communication network enables the use of the packet transmission for messages. 
         [0031]    The invention further provides a method for sending a data packet from a first communication network into a second communication network which is directly unreachable for the first communication network. The method comprises the steps of passing the data packet from the first communication network into the second communication network; awaiting a response signal; and forwarding the response signal back into the first communication network. 
         [0032]    It is advantageous to receive the response signal from the second communication network to the sent data packet from the first communication network even when the second communication network is directly unreachable for the first communications network. The response signal allows the measurement of the quality of service provided by the data packets. As discussed above, the response signal also allows the use of the packet transmission for services which require a proof of delivery or even for time critical services. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0033]      FIG. 1  shows a system for messaging with a central mapping server. 
           [0034]      FIG. 2  shows the system of  FIG. 1  for handling of SMS in GSM. 
           [0035]      FIG. 3  shows a system for number portability. 
           [0036]      FIG. 4  shows a system for signal forwarding by a transparent relay. 
           [0037]      FIG. 5  shows a system for message forwarding by a transparent relay. 
           [0038]      FIG. 6  shows a multi operator relay system. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0039]      FIG. 1  shows schematically a system for messaging. The system has a central mapping server  100 . Packet transmission services, such as SMS, ICQ, MSN Messenger, XMPP, use the central mapping server  100  which provides status and routing information to service clients, such as mobile stations, which are shown as a first service client  110  and a second service client  120  on  FIG. 1 . To be reachable the first service client  110 , notifies the central mapping server  100  about its status and location, when it is turned on or changes the address. This is shown as a notification signal  11 . In case of the GSM protocol, this is done by sending a location update to the HLR  140  (not shown in the overview  FIG. 1 ). The notification signal  11  contains the global title of the MSC (the MSC-GT) of the network and switching subsystem (NSS) in which the first client  110  roams. To contact another device, for example the first client  110 , within the same mobile communications network, the second client  120  needs the address/number of the first client  110 . In the GSM protocol this is the MSISDN (i.e. the telephone number). The MSISDN of the first client  110  comprises routing information to the mapping server  100  of the first client  110 . Hence, a query  12 , containing the MSISDN as the called party address of the first client, can be answered by the mapping server  100  with the status and logical location of the first client  110  within the mobile communications network. When the second client  120 , that wants to initialize the connection, has obtained the needed routing information from the mapping server  100 , the second client  120  is able to connect to the first client  110 , directly through the mobile communications network, without further detour over a central server. This is shown as messaging signal  13 . 
         [0040]      FIG. 2  shows how an SMS is sent in a GSM network as an example. Let us suppose that a destination mobile station  130  is roaming in a visitor network and switching subsystem. To be reachable, the destination mobile station  130  notifies the HLR  140  of its home NSS (network and switching subsystem)  150  about its location, when it is turned on or changes the NSS. This is done by a location update procedure. The location update request, containing identification data about the destination mobile station  130 , is transmitted by signal  21  to a MSC VLR (Visitor Location Register)  160  of the network and switching subsystem (NSS) in which the destination mobile station  130  is located. The MSC VLR  160  informs the HLR  140  via signal  22 . The transmitted routing information (the global title of the mobile switching center, i.e. MSC-GT, and VLR) is stored into the HLR  140  for the destination mobile station  130  and can be used to route signals to the destination mobile station  130 . 
         [0041]    Suppose now that an SMS is originated by an originating mobile station  170  and is to be sent to the destination mobile station  130 . The SMS is sent to the SMSC (SMS-Center)  180  which is responsible for the home NSS of the message originating MS  170  (signals  23  and  24  in  FIG. 2 ). Then the SMSC  180  queries the routing information (the MSC-GT) for the destination mobile station  130  from the HLR  140  (signal  25  in  FIG. 2 ). Having obtained the routing information, the SMSC  180  forwards the SMS to the destination MS  130  (signals  26  and  27  in  FIG. 2 ). 
         [0042]    For the SMS center  180  in a GSM network, several primitives out of the MAP of the SS7 protocol are used to transmit short messages, namely: 
         [0000]    MAP-SEND-ROUTING-INFO-FOR-SM (srism) 
         [0043]    This service request is used between a gateway MSC (Mobile Switching Center) and the HLR  140  (Home Location Register) to retrieve the routing information needed for routing the short message to a servicing MSC of the destination mobile station  130 . This request for routing information from the SMS Gateway MSC contains the MSISDN (Mobile Subscriber ISDN) of the subscriber (i.e. destination mobile station  130 ), while the result contains the ISDN number (routing address) of the Servicing MSC (i.e. MSC  160  of the visitor NSS). This address is used to forward the short message in a forward SM process. 
         [0000]    MAP-FORWARD-SHORT-MESSAGE (fwsm) 
         [0044]    This service request is used to forward mobile originated or mobile terminated short messages between the SMS Gateway MSC, which has a connection to the SMS center  180 , and the Servicing MSCs. 
         [0000]    MAP-REPORT-SM-DELIVERY-STATUS (rsds) 
         [0045]    This service request is used between the Gateway MSC and the HLR  140 . When the transmission of a short message from the SMS center  180  to the mobile station—such as the destination mobile station  130 —is unsuccessful, e.g. because the subscriber was absent, the MSC, e.g. the MSC  160  of the visitor NSS, returns a negative response to the Gateway MSC and the Gateway MSC sends a ReportSM-Delivery Status to the HLR  140  to allow for a delayed delivery of the short message. MAP-REPORT-SM-DELIVERY-STATUS is used to set the Message Waiting Data flag into the HLR  140  or to inform the HLR  140  of successful SM transfer after polling. 
         [0046]    MAP-ALERT-SERVICECENTER (asc) (only for incoming message from an HLR  140  to a SMS-C  180 ). This service request informs the SMS-Center  180  that the mobile station  130  has become available again for message reception after a prior unsuccessful delivery attempt from the SMS-Center  180 ) 
         [0047]    Every one of the service requests delivers a status report. The interpretation of these status reports at the SMS center  180  facilitates the generation of various error codes, including the acknowledgement of the successful delivery of the SMS. The mapping of error codes to their verbose description has not been standardized. Table I shows a conceivable mapping of error code numbers to verbose descriptions. Since the error code descriptions are not yet standardized other error codes descriptions are conceivable. 
         [0048]    In order to enable a high QoS level and to keep the control of a SMS, it is important for the SMSC  180  or the message originating operator, to retrieve all signal acknowledgments, even if a signal relay system is used to forward signals into a destination network and switching subsystem, which is not directly reachable. The signal relay system has to be transparent to provide this functionality. 
         [0000]    
       
         
               
             
               
               
             
               
               
             
           
               
                 TABLE I 
               
             
             
               
                   
               
               
                 ERROR CODES FOR MAP SERVICE REQUESTS IN AN 
               
               
                 SMS CENTER 
               
             
          
           
               
                 Error code 
                 Verbose description 
               
               
                   
               
             
          
           
               
                 0 
                 Successful SMS Without Errors 
               
               
                 1 
                 TC-INVOKE Timeout 
               
               
                 2 
                 Unknown MSISDN 
               
               
                 3 
                 Absent Subscriber Short Message 
               
               
                 4 
                 Short Message Delivery Failure: 
               
               
                   
                 SIM (Subscriber Identity Module)/Mobile Terminal Memory 
               
               
                   
                 Exceeded 
               
               
                   
               
             
          
         
       
     
         [0049]      FIG. 3  shows the situation of a first operator  190 , which could be a mobile communications network operator or a SMSC operator, which communicates with a called subscriber  200  within a signalling network  210 . A hub  220  in  FIG. 3  denotes an access point which is used by the first operator  190  in order to connect to the signalling network  210  and to exchange signals with the signalling network  210 . The hub  220  routes signals, coming from the first operator  190 , into the signalling network  210  and returns signals to the first operator  190  if the signals are addressed to the first operator  190 . In the case of SMS signals in a GSM network, for instance, the hub  220  would be the Gateway MSC (GMSC), the signalling network  210  is the SS7 network of GSM and the called subscriber  200  could be a Mobile Station (MS). 
         [0050]    When the called subscriber  200  wants to change from a first network provider  230  to a second network provider  240 , the called subscriber  200  generally is able to keep his old called party address (MSISDN), as explained above. The first network provider  230  and the second network provider  240  can also be network operators or they could be “virtual providers” utilising networks established by network operators (MVNO&#39;s). The first network provider  230  of the called subscriber  200  and the new home network provider, the second network provider  240  to which the called subscriber  200  moves, have usually no contract to share their mapping server  100  (HLR  140 ). The MSISDN is adopted by the new home network provider  240  and gets an entry, providing status and routing information, in a corresponding register of the mapping server  100  (HLR  140 ) of the second network provider  240  which is the new home network provider. 
         [0051]    Suppose now a message is to be sent to by the first operator  190  to the called subscriber  200 . In order to retrieve routing information a querying signal, containing the called party address of the called subscriber is sent from the first operator  190 , therefore called querying message originating first operator, to the mapping server  100  (HRL  140 ). The querying signal has to be sent before the first operator  190  is able to build up a connection or send a message to the called subscriber  200 . The called party address (ISDN, MSISDN) is interpreted by the hub  220 , to which the querying signal is sent, as routing information to the network provider to which the number range of the called party address is assigned. This is often no longer the home network provider of the called subscriber  200 , if the called subscriber  200  has changed the network provider. In other words, the called party address is within the number range assigned to the original home network provider (the first network provider  230 ) and the called subscriber  200  has moved to the second network provider  240  as new home network provider. A Signalling Relay Function for support of Mobile Number Portability (MNP-SRF) of the original home network provider (the first network provider  230 ) forwards the querying signal to the new home network provider (the second network provider  240 ) of the called subscriber  200 . The mapping server  100  (HLR  140 ) of the new home network provider answers the querying signal and returns a response signal back to the querying message originating operator (i.e. the first operator  190 ). 
         [0052]    It is also conceivable, that the original home network provider, the first network provider  230 , and the new home network provider, the second network provider  240 , collaborate and share their mapping server  100  (HLR  140 ) and the ported called subscriber  200  remains the responsibility of its old mapping server  100  (HLR  140 ) of the first network provider  230 . In this case, the querying signalling, querying for the routing information for the called subscriber  200  does not have to be forwarded by the MNP-SRF. 
         [0053]    In the following example we consider the common case that the mapping server  100  (HLR  140 ) of the called subscriber  200 , e.g. a mobile station, which was ported from the first network provider  230  to the second network provider  240 , is located in the network of the second network provider  240 . The querying signals, sent to the first network provider  230  (as the number range holder of the called party address of the destination subscriber  200 ) are forwarded by the MNP-SRF of the first network provider  230  to the new home network provider, the second network provider  240 . 
         [0054]    As explained above, as long as the message originating first operator  190  has roaming agreements with the number range holder (i.e. the first network provider  230 ) as well as with the new home network first operator, the second network provider  240 , of the called subscriber  200 , no problems occur. If the message originating first operator  190  has no agreement with the number range holder (the first network provider  230 ), no communication between the message originating provider  190  and the number range holder (first network provider  230 ) is guaranteed. On the other hand, if the message originating first operator  190  has an agreement with the number range holder (the first network provider  230 ), but no agreement with the new home network provider (the second network provider  240 ) the querying signal will be forwarded to the new home network provider, but the response of the target mapping server  100  (HLR  140 ), respectively, will not reach the message originating first operator because of the absence of a roaming agreement between the new home network provider in which the mapping server  100  (HLR  140 ) is located and the message originating first operator. In this case, the message originating first operator  190  does not get any response to the querying signal. A routing failure occurs or the signal times out without any acknowledgement and the message originating first operator  190  could merely be able to guess the reason. 
         [0055]    A message originating first operator  190 , that has no roaming agreement for sending messages to a particular destination mobile communications network could order a service from another second operator, which can interact with the particular destination mobile communications network. However, if the message originating operator wants to control and manage the messages, a transparent signal relay is required. 
         [0056]      FIG. 4  illustrates a transparent signal relay  260  and its interactions. The transparent signal relay  260  is designed to translate and control all of the signals between the message originating network  255  and the destination network  270 . 
         [0057]    Suppose that the message originating network  255  wants to send a signal into the destination network  270  and the destination network  270  does not accept its signals or direct transmission is not provided. This problem can be solved by sending a signal  41  to the transparent signal relay  260  instead. The transparent signal relay  260  then forwards the content of the signal  41  into the destination network  270  (signal  42 ), waits for a response signal  43  and forwards the response signal  43  back to the message originating network  255  as signal  44 . Due to the forwarding of the acknowledging responses of the transmitted signals, the transparent relay system  260  is transparent for the message originating network  255 . In case of SMS messages for instance, this is important for billing and prepaid applications as well. 
         [0058]      FIG. 5  shows that the message originating operator  190  first has to query the mapping server  100  (HLR  140 ) for the routing information to the service access point, i.e. the subscriber hub  300 , of the called subscriber  200  to send a message or build a connection to the called subscriber  200 . In this context, the hub  300  is the access point to the destination network operator  275  for the called subscriber  200 . A servicing MSC could be such a hub  300  for instance. 
         [0059]    To forward the routing information to the destination network operator  275 , which is unreachable for the message originating operator  190 , the transparent signal relay  260  provides a virtual mapping server  280 . The query signal  51  for the routing information to the called subscriber  200  is sent to the virtual mapping server  280 . The query signal  51  contains at least, but not only the MSISDN of the called address party  200  and the address (global title) of the originating operator  190 . The transparent signal relay  260  replaces the source address, i.e. the global title of the message originating operator  190  by the global title of the transparent relay  260  and transmits the query signal  52  to the mapping server  100  (HLR  140 ) of the destination network operator  275 . The response signal  53  of the mapping server  100  (HLR  140 ) is sent back to the virtual mapping server  280  of the transparent signal relay  260 . The transparent signal relay  260  replaces the returned routing information of the response signal  52  by its own global title, i.e. the global title of the transparent signal relay  260 , and forwards the routing information with the response signal  54  to the message originating operator  190 . The replaced routing information is temporarily stored into a memory of the virtual mapping server  280  of the transparent signal relay  260 , in order to associate following signals from the message originating operator  190  to the called subscriber  200  with its previous queried location. 
         [0060]    Next, the message originating operator  190  sends one or more content signals  55 , containing e.g. messages, commands or requests for the called subscriber  200 , to a relay switching center  290 . The content signals  55  contain, along with the raw data (PDU), some signalling overhead, in particular the address (global title) of the originating operator  190 , the called party address of the called subscriber  200  and global title of the transparent relay  260 . The relay switching center  290  replaces the global title of the transparent relay  260  by the previously saved routing information to the subscriber hub  300 , which is temporary associated with the called party address of subscriber  200 . The relay switching center  290  then forwards the content of all signals  55  as signals  56  to the mobile communication network  275  in which the called subscriber  200  is located. All acknowledge and/or response signals  57  are sent back to the relay switching center  290 . The relay switching center  290  replaces the global title of the subscriber hub  300 , where the called subscriber  200  is located by its own global title, i.e. the global title of the transparent relay  260 , and forwards the content of the acknowledge and/or response signals  58  as signals  58  to the message originating operator  190 . 
         [0061]    The called subscriber  200  could be a destination mobile station  130 , if we consider SMS in GSM as an application example for the transparent signal relay  260 . The mapping server  100 , containing status and routing information about the destination mobile station  130  would be the HLR  140  which is responsible for the destination mobile station  130 . The subscriber hub  300  of the mobile station  130  is the servicing MSC of the NSS in which the mobile station  130 , is located. The query signal  51  and signal  52  for the routing information is done by a srism service request, while an fwsm service request is used for sending a message to the destination mobile station  130 , i.e. for the signal  55  and signal  56 . 
         [0062]    Apart from the transmission of SMS messages, other applications are also conceivable for the transparent signal relay  260 , e.g. the IS41 or IS95 protocols, which are used in other mobile applications. These protocols also use mapping servers  100  which provide routing information to the subscribers. The corresponding mobile networks (e.g. TDMA, CdmaOne, Cdma2000), comprise several network and switching subsystems, which are connected by roaming agreements. Furthermore, networks of Instant Messaging providers and their mapping servers  100  can also be connected by one or more of the transparent signal relays  260 . 
         [0063]    The obstacles occurring with the number portability problems require more sophisticated relay systems as shown in  FIG. 6 . In such a relay system there are several operators having different roaming agreements, if no single operator is available to provide roaming agreements to all operators involved in the communication, i.e. to and between the message originating operator  190 , a number range holder  370  of the global title of the called subscriber  200  and to the destination network operator  275  of the called subscriber  200 . Similar to the aforementioned examples, the transparent relay  260  can be applied to different standards and protocols. In the following the short message service (SMS) in a GSM network just acts as an example. 
         [0064]    The transparent signal relay  260  of the invention may connect several network operators, e.g. a first relay operator  310 , a second relay operator  320 , and a third relay operator  330 . Each of the different network operators of the transparent signal relay  260  uses a servicing MSC to transmit and receive SS7 signals for SMS messages. Generally the different network operators of the transparent signal relay  260  have different roaming agreements and possibilities to interact with other network operators and mobile network providers. 
         [0065]    Suppose that a subscriber of the message originating operator  190  wishes to send an SMS to the destination subscriber, mobile station  130 . The called party address (MSISDN) of mobile station  130  is in the number range of the number range holder  370  which has been the (first) provider of the mobile station  130 , before it was ported to another (second) provider. This second provider is now the subscriber network operator  275 , i.e. the network provider of mobile station  130 . The new HLR (mapping server) which is now responsible for the mobile station  130  is the destination network HLR  380  of the subscriber network operator  275 . However, the global title of the MSISDN (telephone number) from mobile station  130  is routing information to the number range holder  370 . 
         [0066]    The message originating operator  190  sends a srism service request  61  to a first virtual HLR  340  of the transparent signal relay  260 . The first virtual HLR  340  forwards the srism service request  61  as signal  62  to a second virtual HLR  350  of a second service MSC  360  inside the transparent signal relay  260 . The second virtual HLR  350  can interact with the number range holder  370  of the global title of the destination mobile station  130 . Signalling transmission inside the transparent signal relay  260  system can be done using IP connections or an internal signalling system such as SS7. The second virtual HLR  350 , which interacts with the number range holder  370 , changes the MSC-GT of the signal  62 , before forwarding the signal  62  as signal  63  to the number range holder  370 . The MNP-SRF of the number range holder forwards the signal as signal  64  to the subscriber network operator  275 . 
         [0067]    As previously explained the network operator which is the number range holder  370  does not have to be the network operator for the called subscriber  200  of the message. If not, the srism service request  63  is forwarded as signal  64  by the MNP-SRF  390  to the correct destination network HLR  380  of the destination network operator  275 . The destination network operator  275  may not necessarily be able to interact with the second relay operator  320  of the transparent signal relay  260 . As a result, the second relay operator  320  would have to change the MSC-GT of the calling party (the own global title) of the srism service request  63  to a global title, which is not necessarily one of the global titles of the second service MSC  360 , but is a global title of a third MSC  400 . The third MSC  400  belongs to a third relay operator  330  which is also part of the transparent signal relay  260  and has a roaming agreement with the destination network operator  275 . The destination network HLR  380  of the destination network operator  275  will return the response of the srism service request, the signal  65 , to the third relay operator  330 . 
         [0068]    The second relay operator  320  is not able to replace the calling party address in the srism service request with the global title of the third MSC  400  as it does not know that the number range holder  370  of the called subscriber&#39;s  200  MSISDN is not the destination network operator  275 . If, furthermore, the destination network operator  275  has no roaming agreement with the second relay operator  320 , the response (signal  65 ) of the destination network HLR  380  will not reach the second relay operator  320 . As a result, the requesting srism service request  63  would time out, so the second relay operator  320  has to guess which one of the relay operators within the transparent signal relay  260  has a roaming agreement with the destination network operator  275 . This can be done by querying the required routing information with several srism service requests with global titles of several other relay operators  330  within the transparent signal relay  260 . As each relay operator  330  will have different roaming agreements, it is likely that at least one of the queries for the required routing information will be successful. 
         [0069]    Using the relay internal connection, the finally retrieved signal  65 , now containing the routing information and the path to the NSS of the subscriber network operator  275  where the destination mobile station  130  for the message is located, is sent as signal  66  to the second virtual HLR of the transparent signal relay  260 , and further as signal  67  to the first virtual HLR. The first virtual HLR  340  from the first relay operator  310 , which interacts with the message originating operator  190 , stores this routing/path information into a temporary memory and replaces the global title of the NSS MSC where the destination subscriber  130  is located in signal  67  by its own global title, i.e. the global title of the first service MSC  410 , and returns the response of the srism service request as signal  68  to the message originating operator  190 . Once signal  68  is received, the message originating operator  190  sends an fwsm service request  69 , containing the message for the destination mobile station  130  to the first service MSC  410  of the transparent signal relay  260 . Using the internally provided connections, the message is forwarded as signal  70  to the third service MSC  400 , which can interact with the destination network operator  275 . The third relay operator  330  replaces the global title of the calling party in the message by its own (i.e. the third service MSC&#39;s  400 ) global title and sends the message as signal  71  into the network and switching subsystem where the destination mobile station  130  is located. The signal acknowledgement returns as signal  72  to the third service MSC  400  and is forwarded as signal  73  to the first service MSC  410 , which then interacts with the message originating operator  190  by the signal  74 . 
         [0070]    To route the signal responses back to the message originating operator  190 , it is necessary to store the global title of the message originating operator  190 , when it is replaced by a global title of a MSC within the transparent relay system  260 . The global title of the message originating operator  190  may be replaced two times: first by the global title of MSC  360  when the srism is send to the number range holder  390  and second by the global title of MSC  400  when the fwsm is sent to the subscriber network OP  275 . It is not replaced by the global title of MSC  410 . 
         [0071]    The rsds service request can be routed in the same manner as the srism service request. Alternatively, the second virtual HLR  350  can select a specific third relay operator  330  as a destination the response to the rsds service request, by associating the MSISDN of signal  62  with the sender of signal  66  in a temporary memory after receiving the response to the srism service request. 
         [0072]    In order to adapt the multi operator relay system for other standards and protocols, the HLRs  350  can be replaced by other types of mapping servers (e.g. DNS systems, ENUM) and the MSCs  360 , 400  by other types of access points or hubs, where the destination subscriber (which has not to be mobile) are connected to the network. 
       LIST OF REFERENCE NUMBERS 
       [0000]    
       
           11  Notification 
           12  Query 
           13  Messaging 
           21  Notification about location of MSC VLR 
           22  Notification about location of HLR 
           23  Sending of SMS by Originating MS to MSC VLR 
           24  Sending of SMS by MSC VLR to SMSC 
           25  Query of SMSC for routing information from HLR 
           26  Sending SMS from SMSC to MSC VLR 
           27  Forwarding of SMS form MSC VLR to destination MS 
           41  Signal from message originating network 
           42  Forwarded signal from transparent signal relay to destination network 
           43  Response signal from destination network to transparent signal system 
           44  Forwarding response signal from transparent signal system to message originating network 
           51  Query signal from message originating operator to virtual mapping server 
           52  Query signal from virtual mapping server to mapping server of destination network operator 
           53  Response signal from mapping server of destination network operator to virtual mapping server 
           54  Response signal from virtual mapping server to message originating operator 
           55  content signal from message originating operator to relay switching center 
           56  content signal from relay switching center to subscriber hub 
           57  Acknowledge and/or response signal from subscriber hub to relay switching center 
           58  Acknowledge and/or response signal from relay switching center to message originating operator 
           61  Srism service request from message originating operator to first virtual HLR 
           62  Srism service request from first virtual HLR to second virtual HLR 
           63  Srism service request from second virtual HLR to MNP-SRF of number range holder 
           64  Srism service request from MNP-SRF of number range holder to destination network HLR 
           65  Response to srism service request from destination network HLR to third relay operator 
           66  Forwarding of response to srism service request from third service MSC to the second virtual HLR of the transparent signal relay 
           67  Forwarding of response to srism service request from second virtual HLR to the first virtual HLR 
           68  Forwarding of response to srism service request from HLR of the first service MSC of the transparent signal relay to the message originating operator 
           69  Fwsm service request of message originating operator to first service MSC 
           70  Forwarding of fwsm service request of message originating operator from first service MSC to third service MSC 
           71  Forwarding of fwsm service request of message originating operator from third service MSC to destination network operator MSC 
           72  Acknowledgement signal from destination network MSC to third service MSC 
           73  Forwarding of acknowledgement signal of destination network MSC from third service MSC to first service MSC 
           74  Forwarding of acknowledgement signal of destination network MSC from first service MSC to message originating operator 
           100  Mapping server 
           110  Client  1   
           120  Client  2   
           130  Destination MS  130   
           140  HLR 
           150  Home NSS 
           160  MSC VLR 
           165  MSC VLR 
           170  Origination MS 
           180  SMSC 
           190  First operator/message origination operator 
           200  Called subscriber 
           210  Signalling network 
           220  Hub 
           230  First provider 
           240  Second provider 
           250  MNP-SRF 
           255  Message originating network 
           260  Transparent signal relay 
           270  Destination network 
           275  Destination network operator 
           280  Virtual mapping server 
           290  Relay switching center 
           300  Subscriber hub 
           310  First relay operator 
           320  Second relay operator 
           330  Third relay operator 
           340  First virtual HLR 
           350  Second virtual HLR 
           360  Second service MSC 
           370  Number range holder 
           380  Destination network HLR 
           390  number range holder MNP-SRF 
           400  third service MSC 
           410  First service MSC