Abstract:
A mobile radio communication system having a mobile radio communication network and a mobile radio subscriber appliance, wherein a unit in the network layer of the core network of the mobile radio communication network is configured to transmit to the mobile radio subscriber appliance a first message, based on an occurrence of a predetermined event, with a request for a statement which describes at least one radio characteristic of the mobile radio subscriber appliance.

Description:
RELATED APPLICATION 
     This Application is a Continuation Application of U.S. application Ser. No. 11/346,997 entitled “Mobile Radio Communication System.” The priority of the U.S. application Ser. No. 11/346,997 is hereby claimed. 
    
    
     BACKGROUND 
     In the course of further development of mobile radio communication systems, work is currently being undertaken to replace the mobile radio communication systems based on the GSM (Global System for Mobile Communications) standard with the more powerful mobile radio communication systems based on the UMTS (Universal Mobile Telecommunication System) standard. 
     Since the network coverage achieved using UMTS mobile radio networks, that is to say mobile radio communication systems based on the UMTS standard, is not yet as far advanced as the network coverage achieved using the existing GSM mobile radio networks, that is to say mobile radio communication systems based on the GSM standard, it is possible to use UMTS mobile radio networks only in particular geographical areas for communication services, while other geographical areas have only GSM mobile radio networks available. Accordingly, the situation may arise in which a user of a mobile radio subscriber appliance is using a GSM mobile radio network to use a communication service and moves into the domain of a UMTS radio cell, that is to say into a geographical area in which a UMTS mobile radio network can be used, and, because the reception quality of the UMTS mobile radio network is higher there than the reception quality of the GSM mobile radio network, for example, or because a higher data rate can be achieved in the communication service when using the UMTS mobile radio network, the user now wishes to use the communication service using the UMTS mobile radio network, or because the user wishes to use a communication service which is provided only by means of the UMTS mobile radio network. 
     A change of mobile radio network used to provide a communication service or to provide a communication link is called inter-system handover of the communication service or of the communication link. In the described case of a change from a GSM mobile radio network to a UMTS mobile radio network, this is specifically inter-system handover from a GERAN (GSM EDGE Radio Access Network; EDGE: Enhanced Data Rates For GSM Evolution) to a UTRAN (Universal Terrestrial Radio Access Network). 
     When a communication service is provided using a packet-switched communication link, for example when the communication service involves allowing a user to transmit data between the user&#39;s mobile radio subscriber appliance in the Internet, handover is referred to as packet-switched handover for the communication service or the communication link. 
     In the case of inter-system handover for a packet-switched communication link, that is to say packet-switched inter-system handover, from a GERAN to a UTRAN, it is necessary for the UTRAN, that is to say the radio access network of the UMTS mobile radio network, to have some information specific to the mobile radio subscriber appliance in order to be able to perform the inter-system handover. 
     This information is defined in the RRC (Radio Resource Control) container INTER RAT HANDOVER INFO, which contains the RAC (Routing Area Code) for the mobile radio subscriber appliance and the parameter START PS, an input parameter which is stored on the USIM (Universal Subscriber Identity Module) for the encryption algorithm used in the PS (packet-switched) domain, see 3GPP TS 25.331; 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Radio Resource Control (RRC); Protocol Specification (Release 5). 
     This information, which is subsequently called the required information, needs to be available in the UTRAN, that is to say in an RNC (Radio Network Controller) for the UTRAN, no later than when a GERAN node, that is to say a BSC (Base Station Controller) for the GERAN, requests the inter-system handover. 
     Among the required information, particularly the UTRAN capabilities (parameters specifying the extent to which the mobile radio subscriber appliance is UMTS-compatible) specific to the mobile radio subscriber appliance represent a significant volume of data (compared with the other signaling data). 
     In the course of the development for performing packet-switched inter-system handover, carried out as part of the 3GPP (Third Generation Partnership Project) standardization work, no solution has currently been provided for the problem of transmitting the required information. There are currently two proposals: 
     1. The mobile radio subscriber appliance transmits the required information as part of the GMM (GPRS Mobility Management; GPRS: General Packet Radio Service) registration request messages, that is to say using an Attach Request message or a Routing Area Update Request message, to the SGSN (Serving GPS Support Node) associated with the mobile radio subscriber appliance in the core network of the GSM mobile radio network. The SGSN stores the information and forwards it to the GERAN. 
     A drawback of this procedure is that the mobile radio subscriber appliance has no information about whether the GSM mobile network supports packet-switched inter-system handover to a UMTS mobile radio network, and the information is therefore always transmitted and forwarded, even if the GSM mobile radio network does not support packet-switched inter-system handover to a UMTS mobile radio network. In addition, this means that the information is repeatedly transmitted to the SGSN unnecessarily when the location within the SGSN&#39;s territory changes. 
     2. The GERAN node, that is to say the BSC associated with the mobile radio subscriber appliance in the GERAN, uses the RLC/MAC signaling radio link to request the required information from the mobile radio subscriber appliance immediately before the packet-switched inter-system handover to the UMTS mobile radio network is carried out. 
     The mobile radio subscriber appliance transmits the required information to the GERAN node using the RLC/MAC signaling radio link. 
     A drawback of this procedure is that the conventional RLC/MAC protocol allows only small volumes of data to be transmitted (25 octets per message), which is not sufficient for transmitting the required information. Extending the RLC/MAC protocol so that the mobile radio subscriber appliance can transmit specific information is involved and complex. In addition, the request for the required information immediately before the inter-system handover (a just-in-time request) increases the probability that the inter-system handover will fail or that errors will occur, since a significant delay can arise. In addition, this procedure requires the information to be transmitted using the radio interface upon each inter-system handover, which results in significant signaling involvement. 
     WO 02/01895 A1 discloses a method in which the information about the compression algorithms supported by a mobile radio subscriber appliance is transmitted to an RNC (Radio Network Controller) when a radio bearer is set up. 
     EP 1494494 A2 discloses a method for handover of a terminal to a UTRAN in which a mobile terminal transmits information to the UTRAN which relates to handover of circuit-switched communication links, and transmits no information relating to handover by packet-switched communication links. 
     SUMMARY OF THE INVENTION 
     The invention is based on the problem of providing a method, which is improved over the prior art, for transmitting a mobile radio subscriber appliance&#39;s specific information required for inter-system handover. 
     The problem is solved by a mobile radio communication system, a method for operation of a mobile radio communication system, a core network network-layer unit and a method for operation of a core network network-layer unit. 
     The invention provides a mobile radio communication system having a mobile radio communication network and a mobile radio subscriber appliance, where the mobile radio communication network has a radio access network and a core network. A unit in the network layer of the core network is configured to transmit to the mobile radio subscriber appliance a first message, based on an occurrence of a predetermined event, with a request for a statement which describes at least one radio characteristic of the mobile radio subscriber appliance, and the mobile radio subscriber appliance is configured to transmit to the unit a second message with the statement which describes the at least one radio characteristic of the mobile radio subscriber appliance. 
     The invention also provides a method for operating a mobile radio communication system having a mobile radio communication network and a mobile radio subscriber appliance, where the mobile radio communication network has a radio access network and a core network, and where the method involves a unit in the network layer of the core network transmitting to the mobile radio subscriber appliance a first message, based on an occurrence of a predetermined event, with a request for a statement which describes at least one radio characteristic of the mobile radio subscriber appliance, and the mobile radio subscriber appliance transmitting to the unit a second message with the statement which describes the at least one radio characteristic of the mobile radio subscriber appliance. 
     The invention also provides a core network network-layer unit in a mobile radio communication network which has a core network and a radio access network, which unit is configured to transmit to the mobile radio subscriber appliance a first message, based on an occurrence of a predetermined event, with a request for a statement which describes at least one radio characteristic of a mobile radio subscriber appliance, and to receive a second message, sent by the mobile radio subscriber appliance, with the statement which describes the at least one radio characteristic of the mobile radio subscriber appliance. 
     The invention also provides a method for operating a core network network-layer unit in a mobile radio communication network which has a core network and a radio access network, where the method involves the core network network-layer unit transmitting to the mobile radio subscriber appliance a first message, based on an occurrence of a predetermined event, with a request for a statement which describes at least one radio characteristic of a mobile radio subscriber appliance, and receiving a second message, sent by the mobile radio subscriber appliance, with the statement which describes the at least one radio characteristic of the mobile radio subscriber appliance. 
     Clearly, the request for the statement which describes at least one radio characteristic of the mobile radio subscriber appliance is made by a unit which is part of a higher layer of the communication layer model used than the unit used for this on the basis of the prior art, namely the network layer. In contrast to the prior art, particularly the request for the statement which describes at least one radio characteristic of the mobile radio subscriber appliance is not made by a unit in the radio access network but rather by a unit in the core network. In addition, the request is made only when a predetermined event occurs, for example when the mobile radio subscriber appliance registers in the core network or when it is established that the mobile radio subscriber appliance has moved into a geographical area in which a UMTS mobile radio network is available. 
     However, the statement which describes at least one radio characteristic of the mobile radio subscriber appliance does not need to be requested and transmitted whenever the predetermined event occurs, for example whenever the mobile radio subscriber appliance registers in the core network, but rather only when the unit in the network layer which is associated with the mobile radio subscriber appliance changes. 
     If the mobile radio communication network is a GSM mobile radio communication network, for example, that is to say is a mobile radio communication network based on the GSM (Global EDGE System for Mobile Communications) standard, and if the unit in the network layer is an SGSN (Serving GPRS Support Node; GPRS: General Packet Radio Service) then the statement is requested and transmitted again only when the SGSN associated with the mobile radio subscriber appliance has changed (inter-SGSN change). 
     In this case, particularly the statement which describes at least one radio characteristic of the mobile radio subscriber appliance is not requested by the GERAN (GSN EDGE Radio Access Network; EDGE: Enhanced Data Rates for GSM Evolution) of the GSM radio communication network, but rather by the core network of the GSM mobile radio communication network. 
     In addition, the unit in the network layer requests a statement which describes at least one radio characteristic of the mobile radio subscriber appliance only when this is necessary, for example when (in the case of a GSM mobile radio communication network) the GSM mobile radio communication network supports inter-system handover to a UMTS mobile radio communication network. 
     Since the SGSN associated with the mobile radio subscriber appliance changes relatively rarely, the radio characteristics of the mobile radio subscriber appliance are requested and transmitted only relatively rarely, in comparison with the procedure in which the statement which describes at least one radio characteristic of the mobile radio subscriber appliance is requested and stored by the GERAN. 
     The result of what has been said is that using the invention the signaling involvement for the statement which describes at least one radio characteristic of the mobile radio subscriber appliance is low in comparison with the prior art, which means that significant advantages are obtained for the operator of the mobile radio communication network—in particular the network operator can save costs by using the invention. 
     By way of example, the statement which describes at least one radio characteristic of the mobile radio subscriber appliance is the radio characteristic itself or an index specifying a radio characteristic, for example including an index specifying the type of mobile radio subscriber appliance, so that the index can be used to ascertain the radio characteristic or the radio characteristics of the mobile radio subscriber appliance. 
     The further refinements of the invention which are described in connection with the mobile radio communication system apply mutatis mutandis also to the method for operation of a mobile radio communication system, to the core network network-layer unit and to the method for operation of a core network network-layer unit. 
     It is preferred for the predetermined event to be the registration of the mobile radio subscriber appliance in the core network. 
     By way of example, the predetermined event is the initiation of a GPRS Attach procedure by the mobile radio subscriber appliance or the initiation of a Registration Area Update procedure by the mobile radio subscriber appliance. 
     The statement which describes at least one radio characteristic of the mobile radio subscriber appliance can thus be transmitted as part of a registration procedure, so that no additional messages need to be transmitted and the signaling involvement remains low. 
     It is also preferred for the unit in the network layer also to be configured to store the statement which describes at least one radio characteristic of the mobile radio subscriber appliance. 
     It is also preferred for the mobile radio communication system to have a further mobile radio network having a further radio access network and having a further core network, and for the unit in the network layer also to be configured to transmit to a further unit in the network layer of the further core network the statement which describes at least one radio characteristic of the mobile radio subscriber appliance upon inter-system handover of the mobile radio subscriber appliance from the mobile radio network to the further mobile radio network. 
     Clearly, the statement which describes at least one radio characteristic of the mobile radio subscriber appliance is transmitted, in the event of inter-system handover, from the unit in the network layer (of the core network of the mobile radio network from which the inter-system handover takes place, for example from the SGSN of a GSM mobile radio network) to the unit in the network layer of the core network of the mobile radio network to which the inter-system handover takes place (for example to an SGSN in a UMTS mobile radio network). 
     Preferably, the further unit in the network layer is configured to transmit to the further radio access network the statement which describes at least one radio characteristic of the mobile radio subscriber appliance. 
     Preferably, the further mobile radio communication network is designed on the basis of the UMTS (Universal Mobile Telecommunication System) standard. 
     Preferably, the mobile radio communication network is also designed on the basis of the GSM standard. 
     Clearly, the invention is preferably used for inter-system handover from a GSM mobile radio network to a UMTS mobile radio network. 
     It is also preferred for the unit in the network layer to be an SGSN. 
     Preferably, the predetermined event is activation of the mobile radio subscriber appliance at the SGSN. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The use of the same reference number in different instances in the description and the figures may indicate similar or identical items. 
         FIG. 1  shows a communication system based on an exemplary embodiment of the invention. 
         FIG. 2  shows a message flowchart based on an exemplary embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a communication system  100  based on an exemplary embodiment of the invention. 
     The communication system  100  has a GSM (Global System for Mobile Communications) mobile radio network  101  and a UMTS (Universal Mobile Telecommunication System) mobile radio network  102 . 
     A mobile radio subscriber appliance  103  is both GSM compatible and UMTS compatible. That is to say that the mobile radio subscriber appliance  103  can set up radio communication links to the GSM mobile radio network  101  and can set up radio communication links to the UMTS mobile radio network  102 . 
     When a radio communication link has been set up between the mobile radio subscriber appliance  103  and the GSM mobile radio network, it is provided by the GSM mobile radio network using a BTS (Base Transceiver Station)  104 , a base station in the GSM mobile radio network  101 . The BTS  104  is coupled to a BSC (Base Station Controller)  105  and is managed by it. The BTS  104  and the BSC  105  are part of the GERAN (GSM Edge Radio Access Network; EDGE: Enhanced Data Rate for GSM Evolution)  106  of the GSM mobile radio network  101 . The GERAN  106  is the radio access network of the GSM mobile radio network  101 . 
     So that the GSM mobile radio network  101  is able to provide, in particular, packet-switched communication links and packet-switched communication services, for example data transfers to and from the Internet  108 , the BSC  105  is coupled to a first SGSN (Serving GPRS Support Node)  107 . The first SGSN  107  is coupled to a first GGSN (Gateway GPRS Support Node)  109 , which is coupled to the Internet  108  and has the functionality of a gateway. 
     The first SGSN  107  and the first GGSN  109  are part of the core network  110  of the GSM mobile radio network  101 . 
     When a radio communication link has been set up between the mobile radio subscriber appliance  103  and the UMTS mobile radio network  102 , it is provided by means of a NodeB  111 , a UMTS base station. The NodeB  111  is managed by an RNC (Radio Network Controller)  112 . So that the UMTS mobile radio network  102  is able to provide packet-switched communication links and packet-switched communication services, for example data transfers to and from the Internet  108 , the RNC  112  is coupled to a second SGSN  113 . The second SGSN  113  is coupled to a second GGSN  114 , which in similar fashion to the first GGSN  109  has the functionality of a gateway and is coupled to the Internet  108 . 
     The NodeB  111  and the RNC  112  are part of the UTRAN (Universal Terrestrial Radio Access Network)  115  in the UMTS mobile radio network  102 . The UTRAN  115  is the radio access network of the UMTS mobile radio network  102 . 
     The second SGSN  113  and the second GGSN  114  are part of the core network  116  of the UMTS mobile radio network  102 . 
     The first SGSN  107  and the second SGSN  113  are coupled to one another. In one embodiment, the first SGSN  107  and the second SGSN  113  are one and the same SGSN (shared SGSN). 
     When a packet-switched communication link has been set up from the mobile radio subscriber appliance  103  to the Internet  108 , for example, using a radio communication link to the GSM mobile radio network  101 , it is possible, if the mobile radio subscriber appliance  103  is in the domain of the UMTS mobile radio network  102 , to clear down the radio communication link to the GSM mobile radio network  101 , and the packet-switched communication link can be extended to the UMTS mobile radio network  102  using a radio communication link which has just been set up. That is to say that it is possible to perform inter-system handover of the packet-switched communication link from the GSM mobile radio network  101  to the UMTS mobile radio network  102 , or in other words inter-system handover of the packet-switched communication link from the GERAN  106  to the UTRAN  115 . 
     To be able to perform such inter-system handover, however, it is necessary for the RNC  112  to have information specific to the mobile radio subscriber appliance  103 . By way of example, as in 3GPP TS 25.331; 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Radio Resource Control (RRC); Protocol Specification (Release 5), section 10.3.3.42, this information is: 
     
       
         
               
               
               
               
             
           
               
                   
               
               
                 Information  
                   
                   
                   
               
               
                 Element/Group  
                   
                 Type and 
                 Semantics 
               
               
                 name 
                 Need 
                 reference 
                 description 
               
               
                   
               
             
             
               
                 Access stratum 
                 MP 
                 Enumerated 
                 Indicates the release  
               
               
                 release indicator 
                   
                 (R99) 
                 of the UE according  
               
               
                   
                   
                   
                 to [35]. The IE also  
               
               
                   
                   
                   
                 indicates the release  
               
               
                   
                   
                   
                 of the RRC transfer  
               
               
                   
                   
                   
                 syntaxsupported by  
               
               
                   
                   
                   
                 the UE 
               
               
                   
                 CV-not_rr 
                 Enumerated  
                 13 spare values are  
               
               
                   
                 c_conn ection 
                 (REL-4, REL-5 
                 needed. 
               
               
                   
                 SetupC  
                 REL-6) 
                   
               
               
                   
                 complete 
                   
                   
               
               
                 DL capability with 
                 OP 
                 Enumerated  
                   
               
               
                 simultaneous HS- 
                   
                 (32 kbps)  
                   
               
               
                 DSCH configuration 
                   
                 64 kbps,  
                   
               
               
                   
                   
                 128 kbps,  
                   
               
               
                   
                   
                 384 kbps) 
                   
               
               
                 PDCP capability 
                 MP 
                 PDCP capability 
                   
               
               
                   
                   
                 10.3.3.24 
                   
               
               
                 RLC capability 
                 MP 
                 RLC capability 
                   
               
               
                   
                   
                 10.3.3.34 
                   
               
               
                 Transport channel 
                 MP 
                 Transport  
                   
               
               
                 capability 
                   
                 channel  
                   
               
               
                   
                   
                 capability 
                   
               
               
                   
                   
                 10.3.3.40 
                   
               
               
                 RF capability FDD 
                 OP 
                 RF capability 
                   
               
               
                   
                   
                 FDD 10.3.3.33 
                   
               
               
                 RF capability TDD 
                 OP 
                 RF capability 
                 One “TDD RF  
               
               
                   
                   
                 TDD 10.3.3.33b 
                 capability” entity 
               
               
                   
                   
                   
                 shall be included  
               
               
                   
                   
                   
                 for every Chip rate  
               
               
                   
                   
                   
                 capability supported 
               
               
                 Physical channel 
                 MP 
                 Physical 
                   
               
               
                 capability 
                   
                 channel 
                   
               
               
                   
                   
                 capability 
                   
               
               
                   
                   
                 10.3.3.25 
                   
               
               
                 UE multi-mode/ 
                 MP 
                 UE multi- 
                   
               
               
                 multi- 
                   
                 mode/multi- 
                   
               
               
                 RAT capability 
                   
                 RAT capability 
                   
               
               
                   
                   
                 10.3.3.41 
                   
               
               
                 Securing capability 
                 MP 
                 Security 
                   
               
               
                   
                   
                 capability 
                   
               
               
                   
                   
                 10.3.3.37 
                   
               
               
                 UE positioning 
                 MP 
                 UE positioning 
                   
               
               
                 capability 
                   
                 capability 
                   
               
               
                   
                   
                 10.3.3.45 
                   
               
               
                 Measurement 
                 CH- 
                 Measurement 
                   
               
               
                 capability 
                 fdd_re q_sup 
                 capability 
                   
               
               
                   
                   
                 10.3.3.21 
               
               
                   
               
             
          
         
       
     
     This information is subsequently called the required information (for inter-system handover). 
     In the case of the exemplary embodiment explained below, the information specific to the mobile radio subscriber appliance  201  which the RNC  205  needs to know for inter-system handover between the GERAN  106  and UTRAN  115  is transmitted as part of a GPRS Attach to the first SGSN  203  and is forwarded from there to the RNC  205 . 
       FIG. 2  shows a message flowchart  200  based on an exemplary embodiment of the invention. 
     The message flow shown takes place between a mobile radio subscriber appliance  201 , a BSC  202 , a first SGSN  203 , a second SGSN  204  and an RNC  205 , which are arranged and in form explained with reference to  FIG. 1 . 
     It is assumed that a first radio communication link has been set up from the mobile radio subscriber appliance  201  to the GSM mobile radio network  101 . 
     In step  206 , the mobile radio subscriber appliance  201  transmits an Attach Request message  220  to the first SGSN  203 , which message contains the request for a GPRS Attach for the mobile radio subscriber appliance  201 , that is to say registration of the mobile radio subscriber appliance  201  at the first SGSN  203 . 
     The Attach Request message  220  is a conventional Attach Request message for requesting a GPRS Attach and is in form described in 3GPP TS 24.008 V6.7.0; 3rd Generation Partnership Project; Technical Specification Group Core Network; Mobile radio interface Layer 3 specification; Core network protocols; Stage 3 (Release 6), for example. 
     It is assumed that the GPRS Attach for the mobile radio subscriber appliance  201  is successful at the first SGSN  203 . 
     The first SGSN  203  decides whether to request the required information from the mobile radio subscriber appliance  201 . By way of example, the first SGSN  203  can decide to request the required information from the mobile radio subscriber appliance  201  if the GSM mobile radio network  101  supports packet-switched inter-system handover, that is to say inter-system handover of a packet-switched communication link or of a packet-switched communication service to the UMTS mobile radio network. If the GSM mobile radio network  101  does not support packet-switched inter-system handover to the UMTS mobile radio network  102 , then the first SGSN  107  will decide not to request the required information from the mobile radio subscriber appliance  201 . In this example, however, it is assumed that the GSM mobile radio network  101  does support packet-switched inter-system handover to the UMTS mobile radio network  102 . 
     The first SGSN  203  may also decide, by way of example, to request the required information from the mobile radio subscriber appliance  201  if the mobile radio subscriber appliance  201  is in a geographical area in which both the GSM mobile radio network  101  and the UMTS mobile radio network  102  can be used using the mobile radio subscriber appliance  103 . 
     In this example, it is assumed that the first SGSN  203  decides to request the required information from the mobile radio subscriber appliance  201 . 
     In step  207 , the first SGSN  203  transmits an Attach Accept message  221  to the mobile radio subscriber appliance  201 . The first SGSN  203  uses the Attach Accept message  221  to acknowledge to the mobile radio subscriber appliance  201  that the GPRS Attach for the mobile radio subscriber appliance  201  has been successful. In addition, the Attach Accept message  221  contains the request to the mobile radio subscriber appliance  201  for transmission of the required information to the first SGSN  203 . 
     By way of example, the Attach Accept message  221  is in form explained in 3GPP TS 24.008 V6.7.0; 3rd Generation Partnership Project; Technical Specification Group Core Network; Mobile radio interface Layer 3 specification; Core network protocols; Stage 3 (Release 6), but additionally has the specification that the mobile radio subscriber appliance  201  needs to transmit the required information to the first SGSN  203 . 
     To this end, the Attach Accept message  221  may contain, by way of example, an information element (IE) which is in form shown in table 1. 
     
       
         
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 8 
                 7 
                 6 
                 5 
                 4 
                 3 
                 2 
                 1 
                   
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Requested MS 
                 UE- 
                 0 
                 0 
                 0 
                 octet 1 
               
             
          
           
               
                 Information IEI 
                 RAC 
                 Spare 
                   
               
               
                   
               
             
          
         
       
     
     In this context, the value 0 of the parameter UE-RAC indicates that the required information is not being requested, and the value 1 of the parameter UE-RAC indicates that the required information is being requested. 
     In step  208 , the mobile radio subscriber appliance  201  transmits to the first SGSN  203  an Attach Complete message  222 , which is in similar form to the Attach Complete message described in 3GPP TS 24.008 V6.7.0; 3rd Generation Partnership Project; Technical Specification Group Core Network; Mobile radio interface Layer 3 specification; Core network protocols; Stage 3 (Release 6), but additionally has an inter-RAT information container containing the required information. 
     In this embodiment, the inter-RAT information container is an information element of type 4 based on GPP with a minimum length of 3 octets. The limitation of the maximum length is given by the maximum number of octets in an L3 message based on 3 GPP, see 3GPP TS 44.006; 3rd Generation Partnership Project; Technical Specification Group GSM EDGE Radio Access Network; Mobile Station—Base Station System (MS—BSS) interface; Data Link (DL) layer specification (Release 5). The inter-RAT information container is in form shown in table 2. 
     
       
         
               
               
               
               
               
               
               
               
               
             
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 8 
                 7 
                 6 
                 5 
                 4 
                 3 
                 2 
                 1 
                   
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Inter-RAT information container IEI 
                 octet 1 
               
               
                 Length of the inter-RAT information 
                 octet 2 
               
               
                 container 
                   
               
               
                 Inter-RAT information container&#39;s value 
                 oct 3-n 
               
               
                 portion 
               
               
                   
               
             
          
         
       
     
     The “value portion” (see line 3 of table 2) of the inter-RAT information container is the inter-RAT Handover info as defined in 3GPP TS 25.331; 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Radio Resource Control (RRC); Protocol Specification (Release 5). 
     The inter-RAT information container contains the required information. The inter-RAT information container may also contain security information, for example a START PS value, that is to say an input parameter for the encryption method used, which parameter is intended to be used after inter-system handover. The inter-RAT information container may also contain further information, for example prescribed configuration information. 
     The first SGSN  203  stores the required information transmitted to it. 
     It is assumed that following the successful GPRS Attach from the mobile radio subscriber appliance  201  to the Internet  108  a packet-switched communication link is set up. When setting up the communication link, the SGSN  203  transmits the required information to the BSC  202  in step  209 . 
     It is also assumed that the mobile radio subscriber appliance  201  is in the domain of a UMTS radio cell of the UMTS mobile radio network  102  in step  210 , for example the user of the mobile radio subscriber appliance  201  has taken the mobile radio subscriber appliance  201  into a UMTS radio cell of the UMTS mobile radio network  102 . The mobile radio subscriber appliance  201  performs radio measurements and measures the reception quality of the UMTS mobile radio network  102  and of the GSM mobile radio network  101  and notifies the BSC  202  of the measurement results. 
     In step  211 , the BSC  202  takes into account the required information in deciding that the packet-switched communication link which was set up at the first SGSN  203  after the GPRS Attach for the mobile radio subscriber appliance  201  now needs to be extended using the UMTS mobile radio network  102 , that is to say that a new packet-switched communication link to the Internet  108  needs to be provided using the UMTS mobile radio network  102 , and the packet-switched communication link using the GSM mobile radio network needs to be cleared down. 
     It is thus necessary to perform inter-system handover of the packet-switched communication link from the GSM mobile radio network  101  to the UMTS mobile radio network  102 . 
     By way of example, a decision is made that the packet-switched communication link to the Internet  108  now needs to be provided using the UMTS mobile radio network  102 , since in this way a higher data transmission rate is possible than when using the GSM mobile radio network  101 . The movement of the mobile radio subscriber appliance  103  may also mean that the reception quality of the GSM mobile radio network  101  has become so poor that the measurement results of the radio measurements are taken as a basis for deciding that inter-system handover to the UMTS mobile radio network  102  needs to be performed. In addition, it is possible that the user of the mobile radio subscriber appliance  201  wishes to use a communication service which can be provided only using the UMTS mobile radio network  102 . 
     On the basis of the decision that inter-system handover needs to be performed, the BSC  202  sends a first handover request message  223  to the SGSN  203 , which is used to request inter-system handover of the existing packet-switched communication link from the GSM mobile radio network  101  to the UMTS mobile radio network  102 . 
     In step  212 , the SGSN  203  sends a second handover request message  224  to the RNC  205 , which is used to ask the RNC  205  to make the necessary preparations for the inter-system handover. 
     In particular, a second radio communication link needs to be set up from the mobile radio subscriber appliance  201  to the UMTS mobile radio network  102 , so that the packet-switched communication link can in the future be provided by means of the second SGSN  113  and the UMTS mobile radio network  102 . 
     It is assumed that a decision is made that the second radio communication link needs to be cleared down using the NodeB  111  (for example because the mobile radio subscriber appliance has moved into the domain of the NodeB  111 ). 
     The second handover request message  224  contains the required information, which is transmitted to the RNC  205  in this way. 
     In step  213 , the second RNC  205  takes into account the required information in reserving radio resources for the second radio communication link and acknowledges the second handover request message  224  using a first acknowledgement message  225 . 
     In step  214 , the first SGSN  203  sends a first Handover Command message  226  to the BSC  202 . The BSC  202 , for its part, transmits a second Handover Command message  227  to the mobile radio subscriber appliance  201  in step  215 . 
     In step  216 , the mobile radio subscriber appliance transmits a Handover Complete message  228  to the RNC  205  in order to acknowledge that it is now using the second radio communication link for the data transmission. 
     In the embodiment described, the required information is requested by the first SGSN  203  as part of the GPRS Attach for the mobile radio subscriber appliance  201  (Attach Accept message  221 ), and the required information is also transmitted to the first SGSN  203  as part of the GPRS Attach (Attach Complete message  222 ). 
     In another embodiment, the required information is requested and transmitted as part of a Routing Area Update. In a similar fashion to the Attach Request message  220 , the mobile radio subscriber appliance  201  transmits a Routing Area Update Request message as part of a Routing Area Update procedure. This is described in 3GPP TS 24.008 V6.7.0; 3rd Generation Partnership Project; Technical Specification Group Core Network; Mobile radio interface Layer 3 specification; Core network protocols; Stage 3 (Release 6). The first SGSN  203  responds to the Routing Area Update Request message with a Routing Area Update Accept message, which is essentially in a form as in 3GPP TS 24.008 V6.7.0; 3rd Generation Partnership Project; Technical Specification Group Core Network; Mobile radio interface Layer 3 specification; Core network protocols; Stage 3 (Release 6), but in this embodiment contains the request to the mobile radio subscriber appliance  201  to transmit the required information to the first SGSN  203 . 
     The mobile radio subscriber appliance  201  then responds with a Routing Area Update Complete message, which is in the form described in 3GPP TS 24.008 V6.7.0; 3rd Generation Partnership Project; Technical Specification Group Core Network; Mobile radio interface Layer 3 specification; Core network protocols; Stage 3 (Release 6) but additionally contains the required information. 
     In other embodiments, a hybrid form of the procedures described above is used for requesting and transmitting the required information. By way of example, the first SGSN  203  requests transmission of the required information from the mobile radio subscriber appliance using a Routing Area Accept message, and the mobile radio subscriber appliance  201  transmits the required information as part of a GPRS Attach using a Routing Area Update Complete message. 
     In addition to the required information being requested and transmitted as part of a registration signaling procedure such as a Routing Area Update and a GPRS Attach, the required information may also be requested and transmitted as part of a different procedure. By way of example, one embodiment defines a new GMM (GPRS Mobility Management) procedure in comparison with the prior art, which procedure involves the required information being requested by the first SGSN  203  and being transmitted from the mobile radio subscriber appliance  201  to the first SGSN  203 . 
     This new GMM procedure is carried out when a predetermined event occurs or when a predetermined criterion has been met. An example of a predetermined event of this type is when the mobile radio subscriber appliance  201  moves into a geographical area in which both the GSM mobile radio network  101  and the UMTS mobile radio network  102  are available, that is to say that radio communication links can be set up both to the GSM mobile radio network  101  and to the UMTS mobile radio network  102 . 
     In one embodiment, the mobile radio subscriber appliance receives signaling determining whether the GSM mobile radio network  101  supports inter-system handover to the UMTS mobile radio network  102 . 
     By way of example, this is done using an Information Request message containing an information element (IE), for example, which is in the form shown in table 1. The mobile radio subscriber appliance then transmits in an Information Provision message which has an inter-RAT information container containing the required information. 
     In this embodiment, the inter-RAT information container is an information element of type 4 based on GPP with a minimum length of 3 octets. The limitation of the maximum length is given by the maximum number of octets in an L3 message based on 3 GPP, see 3GPP TS 44.006; 3rd Generation Partnership Project; Technical Specification Group GSM EDGE Radio Access Network; Mobile Station—Base Station System (MS—BSS) interface; Data Link (DL) layer specification (Release 5). The inter-RAT information container is in the form shown in table 2.