EP1310128A1

EP1310128A1 - Communication system and method for limiting the number of interrogation requests to an information register

Info

Publication number: EP1310128A1
Application number: EP00953164A
Authority: EP
Inventors: Serge Haumont
Original assignee: Nokia Oyj
Current assignee: Nokia Oyj
Priority date: 2000-08-09
Filing date: 2000-08-09
Publication date: 2003-05-14
Also published as: AU2000265708A1; WO2002013566A1

Abstract

The invention provides a communication method and system for handling interrogations in a communication network to which a plurality of subscribers are attachable and which comprises one or more subscriber information registers storing subscriber information including location information related to the subscribers. One or more support nodes provide access to the subscriber information register when information on one or more subscribers is necessary for handling calls directed to these subscribers. The network can generate interrogation access requests for accessing the subscriber information register. In order to avoid a breakdown or significant reduction of the operation of the register caused by a too high number of quasi-simultaneous requests, a limiting means is provided which limits the number or amount of network-generated interrogation access requests. The limiting means may be implemented in a support node of a network, such as a GGSN or an Interworking GSN which is implemented as an independent support node, or as a part of an SGSN.

Description

COMMUNICATION SYSTEM AND METHOD FOR LIMITING THE NUMBER OF INTERROGATION REQUESTS TO AN INFORMATION REGISTER

FIELD OF THE INVENTION

The present invention relates to a communication method and system having at least one communication network to which a plurality of subscribers are attachable. The system comprises at least one subscriber information register such as a home location register (HLR) storing information related to the subscribers. The subscriber information register is accessed when information on one or more subscribers is needed for handling calls and the like.

BACKGROUND OF THE INVENTION

It is customary to provide one or more location registers in telecommunication systems for mobile communication such as GSM (Global System for Mobile Telecommunications) , GPRS (General Packet Radio Service) , or UMTS (Universal Mobile Telecommunications System) networks. The location registers may be used as home location registers (HLRs) for permanent storage of subscriber information such as IMSI (International Mobile Subscriber Identity) , Visitor Location Registers (VLRs) providing access to the subscriber equipment, MSCs (Mobile Switching Centers) for transmitting data to the user equipment, and the like. When communication is established to a subscriber from an external network, for instance, the location register will be accessed for retrieving information necessary for properly routing packet data for the subscriber.

One of the procedures to be performed between a user equipment such as a mobile station (MS) and the network for enabling the routing of packet data to and from a host external or internal to the network, is a so-called "PDP context activation", in particular in a packet switched network such as a GPRS network. When performing a PDP Context Activation procedure, several information elements such as requested QoS (Quality of Service) , PDP address and the like are transmitted between the user equipment (MS) and a support node handling the communication with the user equipment. Such a "PDP context activation" procedure is a standardised procedure and is e.g. described in the publication ETSI (European Telecommunications Standards Institute) EN 301 344 Vβ.3.2 (1999-07), pages 59 ff. and will therefore not be explained in further detail. For further information, it is referred to the cited document.

Such a "PDP context activation" procedure may be initiated by a mobile station intending to activate packet data address after attach to the network, for instance, or may be requested by the network (called "network-requested context activation" (NRCA) procedure, see for instance the above mentioned EN 301 344, section 9.2.2.2). Such a network-request PDP context activation procedure allows e.g. a GGSN (Gateway GPRS support node) to initiate the activation of a PDP context. When receiving a PDP (Packet Data Protocol) PDU (Protocol Data Unit), the GGSN may check if a PDP context has been established for that PDP address. If no PDP context has previously been established, the GGSN may try to deliver the PDP PDU by initiating a network- requested PDP context activation procedure. The GGSN may send a message to the home location register HLR requesting routeing information for GPRS (IMSI) .

When the HLR determines that the request can be served, it returns a message to the GGSN indicating routeing information. When the HLR determines that the request cannot be served (e.g. the IMSI is unknown in HLR) , the HLR will send back a negative response indicating the reason for rejection. When the message flow to and from the home location register should be very high, there is a danger of crash of the home location register, or at least a probability of significant delay of message transmission.

Regarding the above-mentioned network-requested PDP context activation procedures, the traffic to and from the home location register may be very high when a large amount of NRCA (Network-requested PDP context activation) procedures followed by accesses to the home location register are initiated within a very small time interval. For instance, a company such as a gas utility company may send e.g. at the end of a month, reading requests to a large amount of reading devices installed in user environments and capable of communicating with the network using GPRS, UMTS or other type of packet-switched networks. In such a case, a large number such as several hundreds of thousands NRCA requests may be started within a very short time, leading to problems of the HLR in serving any other customers during this time. The network performance may therefore be adversely affected for some time.

SUMMARY OF THE INVENTION

The present invention aims at providing a solution for the above-stated problem and teaches a method and system for avoiding a system crash or performance reduction caused by a large number of network-requested accesses to the subscriber information register such as the home location register.

The invention provides a communication system such as a telecommunication system, having at least one communication network to which a plurality of subscribers are attachable, comprising at least one subscriber information register storing subscriber information which may include location information related to the subscribers, and at least one support node for accessing the subscriber information register when information on one or more subscribers is necessary for handling calls directed to these subscribers. The system comprises a limiting means for limiting the number or amount of network-generated interrogation access requests for accessing the subscriber information register.

The subscriber information register may be a home location register or any other type of register to be accessed when performing interrogation access requests.

The limiting means is preferably limiting the number of network-generated interrogation accesses per unit time, or the maximum number of TCAP transactions allowed per unit time.

In a preferred embodiment, the limiting means is part of a support node of a network such as a GGSN. The GGSN may be an Interworking GGSN which is implemented as an independent support node, or as part of an SGSN.

The limiting means can be represented by a parameter set in an entity performing an interrogation of the subscriber information register. This parameter set may be configurable or may be adjusted dynamically.

The invention furthermore provides a telecommunication method for handling interrogations in at least one communication network to which a plurality of subscribers are attachable and which comprises at least one subscriber information register storing subscriber information, and at least one support node for accessing the subscriber information register when information on one or more subscribers is necessary for handling calls directed to these subscribers, wherein interrogation access requests for accessing the subscriber information register are generated by the network, and wherein the number or amount of network-generated interrogation access requests is limiting by a limiting means. The subscriber information register is preferably adapted to detect an imminent or actual overload condition, and to send, when detecting such an overload condition, a command to the limiting means for limiting the interrogation accesses. The limiting means responds to such a command by blocking or at least limiting any further interrogation access to the subscriber information register for a certain time.

The invention is particularly relevant for an UMTS or GPRS network implementing NRCA procedures but is also applicable with regard to other types of networks such as GSM having registers which are to be accessed when initiating or performing connections.

According to the invention, the amount of interrogations of the subscriber information register is limited so that an overload of the register may be avoided. The system will therefore normally have enough resources available for serving other customers or requests. For instance, the amount of interrogations of the HLR in case of a burst of NRCA requests will be limited. In practice, this limit may be set by using a new parameter such as "maximum NRCA signalling amount" which limits the number of HLR interrogations. This parameter may be the "number of interrogations per seconds", or "maximum number of TCAP (Transaction Capabilities Application Part) transactions" (TCAP is used below MAP (Mobile Application Part) ) . This parameter may be set to a value which allows the home location register to continue to serve other GSM/UMTS/GPRS network operations even during a burst (very high number of requests during a short time interval) of NRCA. This parameter may be set in the entity performing the MAP interrogation which may be a GGSN or an Interworking GGSN which may be independent node, or can be implemented in a SGSN.

Therefore, there is no longer a risk of a too large number of NRCA requests or other requests to bring a network out of operation or to reduce its performance below an unacceptable level .

Although a certain slowing-down in handling a burst of NRCA requests may result, this effect will normally not be a severe problem as it only requests a longer time interval for transmitting all NRCA requests.

In the above description, NRCA is mainly used for explaining the problem and solution underlying the present invention.

However, the invention is not restricted to NRCA requests but is applicable to all network-requested accesses to the subscriber information register such as a home location register.

Furthermore, the invention provides a network element as defined in the network element claims.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 shows a schematic representation of one embodiment of the present invention;

Fig. 2 illustrates the process steps of a method according to an embodiment of the invention;

Fig. 3 illustrates a MAP-based signalling between a support node and a home location register HLR;

Fig. 4 illustrates a GTP and MAP-based GSN-HLR signalling; and

Fig. 5 illustrates the process steps of another embodiment of the invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

Fig. 1 shows an embodiment of a communication system in accordance with the invention which is implemented as a telecommunication system and comprises a network 1. The network 1 preferably is a packet-switched network such as a GPRS (General Packet Radio Service) or UMTS (Universal Mobile Telecommunications System) network, and comprises a plurality of user equipments such as mobile stations (MS) 2 which are able to communication with other network entities such as user equipments arranged in the same or another network. Forrouting packet data, the user equipment 2 of the packet data source or destination is supported by a support node 3 which here is a SGSN (Serving GPRS support node). The SGSN communicates, i.e. exchanges user traffic data and signalling, with a further support node 4 which may be a GGSN (Gateway GPRS support node) .

The GGSN 4 and/or the SGSN 3 can be adapted to communicate directly with a home location register (HLR) 7 storing location information and other information about subscribers, visitors and the like such as a party using the user equipment 2. In the present embodiment, the support nodes 4 and/or 3 are adapted to communicate with the HLR 7 via a support node 5 (GSN, i.e. GPRS support node) . In a practical implementation of the network 1, one or more support nodes 4 and/or support nodes 3 will be provided. All these support nodes 4 and/or 3 may be adapted to access the support node 5 or a similar node when requiring or sending information from or to the home location register 7. Hence, the support node 5 handles all traffic and signalling from all or at least some of the support nodes 4, 3.

For limiting the maximum number of accesses to the home location register 7, in particular with regard to network- requested PDP context activation procedures (NRCA) , the support node 5 comprises a limiting means 6 which may be implemented as hardware or software solution.

In the present example, the subscriber information register storing information on one or more subscribers necessary for routing packets directed to subscribers, is implemented as a home location register. It may also have different structure and/or information contents. The invention is applicable with regard to all subscriber information registers which have to be accessed when receiving requests such as network-requested procedures .

The limiting means 6 is limiting the number of accesses to the subscriber information register 7 per unit time (for instance per second) , and may be adapted to count the number of specific types of request such as network-requested PDP context activation procedures. When the number of a specific type of requests such as network-requested PDP context activation procedures exceeds a maximum number of requests allowable per unit time (set as a limit value in the limiting means 6), the limiting means 6 is limiting the maximum number of requests of this specific type to the subscriber information register 7 so as to avoid any overload of the latter. Such an overload could lead to a crash of the subscriber information register 7 and thus of the whole network.

The limiting means 6 are limiting the number of network- generated interrogation accesses per unit time. For achieving this function, the limiting means may contain, or be implemented as, a counter counting the number of network- generated interrogation accesses per unit time. For instance, the counter may count the number of network-generated interrogation accesses per each second, the count value being incremented with each network-generated interrogation access, and being decremented with a fixed rate. The fixed rate will be calculated based on the average time duration of an access to the subscriber information register 7 including receipt of the requested information from the register 7. If, for instance, one thousand interrogation accesses to the register 7 may be allowed within a unit time such as one second, without any danger of overload of the register 7 caused by these interrogation accesses, and the additional accesses performed by other functions of the network requiring access to the register 7, the counter will be decremented with a rate corresponding to one thousand interrogation accesses per unit time. Each time an interrogation access to the register 7 is requested, the count value of the counter of means 6 will be increased by one. When the count number reaches the maximum number, i.e the set limit value, the limiting means 6 or another a control means of the GSN 5 will detect this situation, and will block any further interrogation access of this type to the register 7, so that no further network- requested interrogation access will be performed until the count value has again decreased below the maximum number. All network-requested interrogation accesses not being immediately performed may either be stored and carried-out as soon as the counter value has decreased below the maximum number, or may simply be rejected, i.e deleted. In the latter case, the node generating the network-requested access requests may be adapted to again try, one or several times, to access the register 7 (via means 5, 6) to a later time such as after expiry of a unit time .

In an alternative embodiment, the limiting means may determine a very short time gap in which only one access request is allowed. For instance, if hundred access requests per second are allowed, the time gap can be adjusted into ten milliseconds.

The amount of HLR interrogations is therefore limited, especially when experiencing a burst of NRCA requests. In a practical embodiment, a new parameter such as "maximum NRCA signalling amount" is set in the support node 5, for instance in the limiting means 6, limiting the number of HLR interrogations per unit time. This parameter may represent the "number of interrogations per seconds"; or "maximum number of TCAP (Transaction Capabilities Application Part) transactions". The parameter is preferably set to a value which allows the subscriber information register to continue serving other network operations, for instance of the GSM and/or UMTS network, even during a burst (high number of simultaneous or quasi/simultaneous requests) of NRCA requests. The parameter is set in the entity performing the MAP interrogation, here the support node 5. The entity can also be a GGSN 4 or an interworking GGSN (this function may be independent or implemented in a SGSN) .

Fig. 2 illustrates an embodiment of a method according to the invention for limiting the maximum number of interrogation accesses per unit time. As mentioned above, the network- requested PDP context activation procedure is standardised and e.g. described in EN301 344 V6.3.2 (1999-07) of ETSI (European Telecommunications Standards Institute), see page 61 ff., section 9.2.2.2. The network-requested PDP context activation procedure allows the GGSN to initiate the activation of a PDP (Packet Data Protocol) context. When receiving a PDP PDU (Protocol Data Unit), the GGSN checks if a PDP context is established for that PDP address. If no PDP context has been previously established, the GGSN may try to deliver the PDP PDU by initiating the network-requested PDP context activation procedure .

The criteria used by the GGSN to determine whether trying to deliver the PDP PDU to the MS may be based on subscription information. To support network-requested PDP context activation the GGSN has to have static PDP information about the PDP address. To determine whether network-requested PDP context activation is supported for a PDP address, the GGSN checks if there is static PDP information for that PDP address. Once these checks have been performed, the GGSN may initiate the network-requested PDP context activation procedure.

A successful network-requested PDP context activation procedure is illustrated in Fig. 2. Each step will be explained below.

1.) When receiving a PDP PDU, the GSN 5 determines if a network-requested PDP context activation procedure has to be initiated. The GSN 5 may store subsequent PDUs received for the same PDP address.

2.) In accordance with the invention, the GSN 5 has a function (illustrated by means 6 in Fig. 1) to limit the maximum number of network-requested interrogation processes (NRCA) to the register 7 per unit time, and limits the maximum number of simultaneous or quasi-simultaneous interrogation processes such as NRCA requests to avoid an overload of register 7.

3.) When the maximum number of interrogation accesses per unit time is not reached, the GSN 5 may send a "Send routing information for GPRS (IMSI)" message to the HLR 7.

4.) When the HLR determines that the request can be served, it returns, in step 4.), a "Send routing information for GPRS Ack (IMSI, SGSN address, mobile station not reachable reason MNRR) " message to the GSN 5. The "mobile station not reachable reason" parameter is included if a respective flag is set in the HLR 7. If the HLR 7 determines that the request cannot be served (e.g., IMSI unknown in HLR), the HLR will send a message of step 4.) specifying the reason for the negative response.

5.) If the SGSN address is present and either "mobile station not reachable reason" is not present, or the "mobile station not reachable reason" indicates "no paging response", the GSN 5 will send a PDU notification request (IMSI, PDP type, PDP address) message to the SGSN 3 indicated by the HLR 7. Otherwise, the GSN 5 will set the "mobile station not reachable" flag for that MS 2.

6.) The SGSN 3 returns a PDU notification response (cause) message to the GSN 5 in order to acknowledge that it will request the MS 2 to activate the PDP context indicated with PDP address.

7.) The SGSN 3 sends a "Request PDP context activation (TI, PDP type PDP address)" message to request the MS 2 to activate the indicated ^'PDP context.

8.) The PDP context is activated with the PDP context activation procedure in the known manner.

Fig. 3 schematically illustrates the signalling between a gateway support node GGSN 4 incorporating the limiting means 6, and the HLR 7. The signalling path shown in Fig. 3 allows the GGSN 4 to exchange signalling information with the HLR 7 using a SS7 (signalling system 7) interface (not shown) installed in the GGSN 4. The MAP (Mobile Application Part) protocol is used between the GGSN 4 and the HLR 7. Apart from the limiting means 6, the signalling plane shown in Fig. 3 is standardised and is e.g. shown in European Standard EN 301 344 V6.3.2 (1999-07) of ETSI (European Telecommunications Standards Institute) , section 5.6.2.7.1, page 25, Fig. 10). TCAP means Transaction Capabilities Application Part. SCCP stands for Signalling Connection Control Part. MTP2 and MTP3 are abbreviations of message transfer part layer 2 and 3, respectively. LI stands for layer 1. Because of standardisation of the signalling exchange, this section will not be described in further detail. According to Fig. 3, the limiting means 6 is implemented in the GGSN 4. Therefore, no intermediate support node 5 as in Fig. 1, is necessary. The GGSN is able to communicate directly with the HLR 7. Therefore, the limiting means 6 is implemented in support node 4. The function and structure of the limiting means 6 is identical or similar to the above-described structure and functioning of the limiting means 6.

When several gateway support nodes 4 are provided in the network 1 which are able to communicate with the HLR 7, each gateway support node 4 is equipped with a limiting means 6. In such a case, the maximum number of allowable HLR interrogations (in particular NRCA request) per unit time set in the limiting means 6 is fixed to a value below the totally acceptable maximum number of HLR interrogations per unit time. For instance, the maximum number set in each limiting means 6 may be calculated by dividing the totally acceptable maximum number of HLR interrogations by the number of gateway support nodes 4, or a fraction of this number of gateway support nodes. This reduction of the maximum number set in each gateway support node is providing a protection in case several or even all gateway support nodes should simultaneously access the HLR 7 with similar interrogation requests.

Fig. 4 shows a further embodiment, wherein the limiting means 6 is implemented in a support node 5 having internal interworking function. This interworking function provides protocol conversion in particular in a case where no SS7 interface is installed in the gateway support node 4. In such a case, any GSN 5 having an SS7 interface installed in the same PLMN

(public land mobile network) as the GGSN 4 can be used as a GTP-to-MAP protocol converter to allow signalling between the GGSN 4 and the HLR 7. Fig. 4 shows the GTP and MAP-based GGSN- HLR signalling, wherein the interworking function provides the interworking between the different protocol types GTP (GPRS tunnelling protocol) and MAP for the signalling between GGSN 4 and HLR 7.

In the embodiment shown in Fig. 4, the limiting means 6 is incorporated in the GSN 5 which provides the advantage of installing only one limiting means 6 in the network 1. Each GGSN 4 (or, if having the capability) , each SGSN 3 has to communicate with the GSN 5 for access to the HLR 7. The limiting means 6 can therefore be set to the maximum number of allowable network-requested interrogations to HLR 7 per unit time, without necessity of providing any safety margin by reducing the total number of allowable interrogations - as necessary in the case of Fig. 3 (several GGSNs 4 equipped with limiting means 6) so as to avoid an overload when all GGSN 4 should simultaneously try to access the HLR 7.

The maximum value set in limiting means of Fig. 4 is the absolute maximum value of allowable HLR interrogations occurring per unit time even when several GGSNs 4 should try to simultaneously access the HLR via the GSN 5.

Fig. 5 shows a further embodiment which is partly similar to the embodiment shown in Fig. 2 as regards steps 1.) and 3.) to 8.). In the embodiment of Fig. 5, the HLR 7 is equipped with an overload detection means or function which is represented by the numeral 9. An overload here is a too high number of simultaneous or quasi-simultaneous access requests of any type, or of a certain type such as NRCAs .

When the HLR 7 is detecting an overload (block 9) , it sends a message to the GSN 5 for limiting the number of network- requested accesses to the HLR, or blocking for a certain time any further such requests, as indicated in step 2.) of Fig. 5. The sending of the message is triggered by the overload condition in the HLR 7, and leads to a rejection or a delay of subsequent network-requested accesses to the HLR 7, so as to avoid any overload reducing the HLR function for dealing with other requests of other network entities.

In an alternative embodiment, there may be several HLRs served by one interworking GSN or equivalent node. If the HLR in this kind of an embodiment detects an overload condition, it defines separate limits for each interworking GSN. The total of the limits correspond to the overall amount of access requests desired by the HLR. The limits for each interworking GSN can be calculated based on the share of access requests from the respective interworking GSNs. The share can be calculated from a behaviour observed during a longer period. Of course, there may be defined upper limits per interworking GSN in order to avoid one interworking GSN to steal all capacity. Alternatively, the share of the limits i.e. ratios between the interworking GSN specific limits can be manually defined into the HLR configuration data.

The GSN 5 of Fig. 5 can either be the GGSN 4 as shown in Fig. 3, or any interworking GSN 5, as shown in Fig. 4.

In each case, the number of HLR inquiries for network-requested interrogations such as NRCAs from a given GSN node is limited to a maximum number of requests per time interval e.g. per second.

Although the invention has been described above mainly referring to a GPRS system, it may equally be applied to any other packet-switched network, such as UMTS, or to any mobile network.

Claims

1. Communication system having at least one communication network to which a plurality of subscribers are attachable, comprising at least one subscriber information register storing subscriber information, and at least one support node for accessing the subscriber information register when information on one or more subscribers is necessary for data communication directed to these subscribers, wherein interrogation access requests for accessing the subscriber information register can be generated by the network, comprising a limiting means for limiting the number or amount of network-generated interrogation access requests.

2. Communication system according to claim 1, wherein the subscriber information register is a home location register.

3. Communication system according to claim 1 or 2, wherein the limiting means is limiting the number of network-generated interrogation accesses per unit time.

4. Communication system according to claim 1 or 2 or 3, wherein the limiting means is limiting the number of network-generated interrogations generated for a specific procedure.

5. Communication system according to any one of the preceding claims, wherein the limiting means is adapted to limit the number of Network-Requested PDP Context Activation (NRCA) procedures .

6. Communication system according to any one of the preceding claims, wherein the limiting means is limiting the maximum number of TCAP transactions allowed per unit time.

7. Communication system according to any one of the preceding claims, wherein the limiting means is part of a support node of a network.

8. Communication system according to any one of the preceding claims, wherein all interrogation access requests are sent to the subscriber information register from a single support node of a network wherein the limiting means is part of said support node .

9. Communication system according to claim 7 or 8, wherein the support node is a GSN (GPRS Support Node) .

10. Communication system according to claim 7, 8, or 9, wherein the support node is a GGSN.

11. Communication system according to claim 7, 8, 9, or 10, wherein the support node is an Interworking GSN which is implemented as an independent support node, or as part of an SGSN.

12. Communication system according to any one of the preceding claims, wherein the limiting means is represented by a parameter set in an entity performing an interrogation of the subscriber information register.

13. Communication system according to any one of the preceding claims, wherein the subscriber information register is adapted to send a message to the limiting means or to a support node connectable to, or containing the limiting means, the message indicating an overload or maximum acceptable load condition of the subscriber information register.

14. Communication method for handling interrogations in at least one communication network to which a plurality of subscribers are attachable and which comprises at least one subscriber information register storing subscriber information, and at least one support node for accessing the subscriber information register when information on one or more subscribers is necessary for data communication directed to these subscribers, wherein interrogation access requests for accessing the subscriber information register are generated by the network, and wherein the number or amount of network- generated interrogation access requests is limiting by a limiting means.

15. Communication method according to claim 14, wherein the subscriber information register is a home location register.

16. Communication method according to claim 14 or 15, wherein the limiting means is limiting the number of network-generated interrogation accesses per unit time.

17. Communication method according to any one of claims 14 to 16, wherein the limiting device is limiting the number of network-generated interrogations generated for a specific procedure .

18. Communication method according to any one of claims 14 to 17, wherein the limiting device is limiting the number of network-requested PDP Context Activation (NRCA) procedures.

19. Communication method according to any one of claims 14 to 18, wherein the limiting means is limiting the maximum number of TCAP transactions allowed per unit time.

20. Communication method according to any one of claims 14 to

19, wherein the limiting means is implemented in a support node of a network.

21. Communication method according to any one of claims 14 to

20, wherein all interrogation access requests are sent to the subscriber information register from a single support node of a network wherein the limiting means is part of said support node.

22. Communication method according to claim 20 or 21, wherein the support node is a GGSN.

23. Communication method according to claim 20, 21, or 22, wherein the support node is an Interworking GSN which is implemented as an independent support node, or as a part of an SGSN.

24. Communication method according to any one of claims 14 to 23, wherein the limiting means is represented by a parameter set m an entity performing an interrogation of the subscriber information register.

25. Communication method according to any one of claims 14 to 24, wherein the interrogation access requests are caused by network-requested PDP Context Activation requests (NRCA) .

26. Communication method according to any one of claims 14 to 25, wherein the subscriber information register is adapted to detect an imminent or actual overload condition, and is sending, when detecting such an overload condition, a command to the limiting means for limiting the interrogation accesses, the limiting means responding thereto by blocking or at least limiting any further interrogation access to the subscriber information register for a certain time.

27. Communication method according to any one of the preceding claims 14 to 26, wherein the subscriber information register, when detecting an overload or maximum acceptable load condition, sends a message to the limiting means or to a support node connectable to, or containing the limiting means, the message indicating the overload or maximum acceptable load condition of the subscriber information register.

28. Network element, preferably for a communication system as defined m any one of claims 1 to 13, or for use in a method as defined in any one of claims 14 to 27, comprising a limiting means for limiting the number or amount of network-generated interrogation access requests for accessing a subscriber information register.

29. Network element according to claim 28, wherein the limiting means is limiting the number of network-generated interrogation accesses per unit time, or the number of network-generated interrogations generated for a specific procedure.

30. Network element according to claim 28 or 29, wherein the limiting means is adapted to limit the number of Network- Requested PDP Context Activation (NRCA) procedures.

31. Network element according to any one of claims 28 to 30, wherein the limiting means is limiting the maximum number of TCAP transactions allowed per unit time.

32. Network element according to any one of claims 28 to 31, wherein the network element is a support node of the network.

33. Network element according to claim 32, wherein the support node is a GSN (GPRS Support Node) .

34. Network element according to claim 32 or 33, wherein the support node is a GGSN.

35. Network element according to claim 32, 33, or 34, wherein the support node is an Interworking GSN which is implemented as an independent support node, or as part of an SGSN.