Abstract:
A communication system supports multicall capabilities. Described herein are methods and techniques for exchanging the multicall capabilities of different entities, e.g., RNCs, MSCs, and terminals, such that the handling of call requests is efficient and backwardly compatible. Multicall capabilities of different entities is forwarded to a limit calculation device. The limit calculation device determines a bearer limit for a set of entities, which limit it transmitted back to at least some of the entities which forwarded their capability information. The bearer limit is used to selectively setup subsequent calls.

Description:
RELATED APPLICATION  
       [0001]    This application is related to, and claims priority from, U.S. Provisional Patent Application Ser. No. 60/174,908, entitled “Exchange of Multicall Capabilities between UE and CN in UMTS”, filed on Jan. 10, 2000, the disclosure of which is incorporated here by reference. 
     
    
     
       BACKGROUND  
         [0002]    The present invention relates to handling and signaling associated with multicall capability in radiocommunication systems.  
           [0003]    Radiocommunication standards and systems continue to evolve at a fast pace in recent years. The so-called third generation networks are among the latest developments in this sector, one example of which is referred to as the Universal Mobile Telecommunication Systems (UMTS). These third generation networks enable subscribers to set up a variety of different user services, e.g., multimedia services, speech calls, data calls, fax calls, short messages, etc. Among other capabilities, third generation systems allow a subscriber to set up more than one call simultaneously, providing an individual radio bearer for each of the calls. This feature is called “Multicall” in UMTS specifications.  
           [0004]    The Multicall feature enables a subscriber in a UMTS system to have, for instance, a speech connection while sending a fax, browsing the Internet, or performing data transmissions of any kind. Furthermore, the feature provides the capability to increase the bandwidth for a certain type of connection beyond the limit given by a single bearer. This is done by performing an inverse multiplexing scheme to aggregate the bandwidth of several calls. For readers interested in more detail regarding the multicall feature in general, an exemplary explanation can be found in the 3GPP specification 3G TS 22.135 Version 3.0.0, published October 1999, the disclosure of which is incorporated here by reference.  
           [0005]    The Multicall feature interacts with other features specified in the UMTS standard, e.g., the supplementary services referred to as Call Waiting and Call Hold. The Call Waiting service permits a mobile subscriber to be notified of an incoming call while no other bearer is available to support the incoming call and the mobile subscriber is already engaged in at least one active or held call. Upon notification, the subscriber can either accept, reject, or ignore the incoming call.  
           [0006]    The Call Hold service allows a served mobile subscriber, who is provisioned with this Supplementary Service, to interrupt communication on an existing active call and then subsequently, if desired, re-establish communication. The radio bearer remains assigned to the mobile subscriber after the communication is interrupted to allow the origination or possible termination of other calls. Consider the following interactions between the Multicall, Call Waiting and Call Hold features.  
           [0007]    For a Multicall subscriber, the Call Waiting service is invoked when all bearers available for a certain subscriber are in use and an incoming call is received by the serving network entity or if a speech call is offered and another speech call is already ongoing for that subscriber. The serving network entity can, for example, be a Mobile services Switching Centre/Visitor Location Register (MSC/VLR) that performs the call control and requests the establishment of a call bearer for the subscriber. The number of available bearers depends on the maximum limit of bearers as defined in the Multicall subscription, the capabilities of the serving network entity, and the capabilities of the terminal.  
           [0008]    For a Multicall subscriber, the Call Hold service is implicitly invoked when all bearers available for a certain subscriber are in use, one of the established calls is a speech call, and the subscriber wants to set up or accept a new call. This procedure is well known to those skilled in the art, for example as described in the 3GPP specification TS 22.030 Version 3.0.1, published October 1999, the disclosure of which is also incorporated here by reference. When this occurs, the speech call is put on hold, and the new call will use the bearer formerly used by the speech call. The number of available bearers in this context depends on the maximum limit of bearers as defined by limits set by the operator, limits set by the user, the capabilities of the serving network entities, and the capabilities of the terminal. In addition to the MSC/VLR mentioned above, the capabilities of the serving network in connection with the number of bearers available may also be limited by other nodes, e.g, the Radio Network Controller (RNC).  
           [0009]    However, currently no mechanism exists to detect the actual limit for the number of bearers available to a Multicall subscriber. This shortcoming prevents backward compatible service behavior for second generation networks, e.g., GSM networks. The actual limit is the lowest number of bearers supported by the terminal, the network, the operator setting and the user setting. The number of bearers supported by the terminal, the network, the operator setting and the user setting may differ. This can cause a number of problems in the handling of calls made by GSM and/or UMTS equipment, particularly in hybrid GSM/UMTS equipment.  
           [0010]    For example, if the maximum number of bearers supported by the terminal is higher than the maximum number of bearers supported by the serving network entity, the following problems can occur. Consider that, for a particular call incoming to the terminal, the serving network entity detects that the maximum number of bearers allowed by the multicall subscription of the called subscriber is already used. The serving network entity will then invoke the Call Waiting service. The call is then offered as a waiting call to the terminal. However, since the maximum number of bearers from the terminal point of view is not yet reached, it may request the serving network entity to allocate a new bearer for the waiting call, which bearer is not available.  
           [0011]    Likewise, for calls which are to be setup from the terminal, this imbalance between the number of bearers available for the terminal versus the number of bearers available for the serving network entity can cause difficulties. Since the terminal perceives that at least one radio bearer is available for it to set up an outgoing call, the terminal does not implicitly invoke the Call Hold service for its ongoing Speech call prior to attempting call setup. In response to the call setup signalling, the network will detect that there is no bearer available. Since the speech call is not on hold, the serving network entity cannot re-use the bearer allocated for the speech call for the new call. The serving network entity will then reject the call set-up.  
           [0012]    Problems may also occur for the reverse discrepancy, i.e., in the case that the maximum number of bearers supported by the terminal is lower than the number of bearers that can be offered by the network. When the serving network entity tries to set up a call to a terminal that is using all of its available bearers, it may not invoke the Call Waiting feature since, from the serving network entity&#39;s perspective, there is an available radio bearer to set up the call. Instead, the terminal may reject the call and the waiting call will not be offered to the subscriber.  
           [0013]    Accordingly, it would be desirable to provide systems and methods for handling the exchange of multicall capabilities in a manner which permitted Call Waiting and Call Hold to be performed in a manner that supports backward compatibility with second generation devices and handles potential imbalances between the number of bearers available for setting up calls between different nodes of radiocommunication systems.  
         SUMMARY  
         [0014]    These and other drawbacks, problems and limitations of conventional radiocommunication systems are overcome according to the present invention.  
           [0015]    It is object of the invention to provide a mechanism for the exchange of information regarding multicall capabilities.  
           [0016]    It is a further object of the invention to provide a mechanism to determine the actual limit on the number of bearers available between a particular device and the network at a given time.  
           [0017]    It is another object to use the actual limit on the number of bearers in order to ensure that the service interactions as seen by the user are backward compatible with second generation systems.  
           [0018]    The involved system entities include the terminal, the serving network entity and the entity handling the radio resources.  
           [0019]    This limit information can take a number of forms and vary according to exemplary embodiments of the present invention. For example, limit information associated with an involved system entity can be, for example, either at least one informational parameter available at the system entity regarding factors limiting the number of available bearers or an informational parameter available at the system entities regarding a most limiting factor.  
           [0020]    The bearer limiting factors associated with terminal devices are, for example, introduced by the manufacturer of the terminal, and may include limitations introduced by the involved protocols, bandwidth restrictions on the involved interfaces, user settings, operator settings, etc.  
           [0021]    The bearer limiting factors in the radio access network entity are, for example, introduced by the manufacturer of the radio access network entity, and may include limitations introduced by the involved protocols, bandwidth restrictions on the involved interfaces, operator settings, etc.  
           [0022]    The limiting factors in the serving network entity are for example introduced by the manufacturer of the serving network entity, are limitations introduced by the involved protocols, bandwidth restrictions on the involved interfaces, user settings, operator settings, etc. User settings can for example be related to the active calls (never offer a further call when a call to or from a certain destination is in progress), the maximum number of bearers allowed by the user, the services in progress, etc. Operator settings can for example be related to a specific subscriber, a group of subscribers, a specific network entity, a group of network entities, and the terminal.  
           [0023]    According to one exemplary embodiment of the present invention the involved entities provide a limit calculation unit with their bearer limit information. This limit calculation unit determines the actual limit on the number of available bearers for a given set of entities at a given time. This actual limit can then be returned to the involved entities and used to invoke multicall capabilities in a manner which prevents the afore-described problems.  
           [0024]    According to one exemplary embodiment, the limit calculation unit is located in the serving network entity. The terminal and the radio access network entity inform the limit calculation unit in the serving network entity of their bearer limit information. As the limit information of the radio access network entity is not subject to frequent change, it can be mirrored in a RNC limits storage unit. This RNC limits storage unit can be located at the serving network entity and holds the limit information about all of the radio access network entities which are frequently or permanently in contact with a particular serving network entity MSC/VLR. Alternatively, the RNC limits storage unit can be placed as a stand-alone network entity that holds the limit information of all radio network entities. Furthermore, a combined approach of the before mentioned distributed or centralized schemes could be applied. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    These and other objects, features and advantages of the present invention will become more apparent upon reading from the following detailed description, taken in conjunction with the accompanying drawings, wherein:  
         [0026]    [0026]FIG. 1 is a block diagram which depicts signalling between an RNC and MSC/VLR for informing the MSC/VLR of the RNC&#39;s bearer capabilities according to an exemplary embodiment of the present invention;  
         [0027]    [0027]FIG. 2 is a block diagram which depicts signalling associated with the exchange of bearer information between user equipment and an MSC/VLR according to an exemplary embodiment of the present invention;  
         [0028]    [0028]FIG. 3 is a block diagram of selected functional units within user equipment according to an exemplary embodiment of the present invention;  
         [0029]    [0029]FIG. 4 is a flowchart depicting user equipment processing of a user call request according to an exemplary embodiment of the present invention;  
         [0030]    [0030]FIG. 5 is a block diagram of selected functional units within an MSC/VLR according to an exemplary embodiment of the present invention;  
         [0031]    [0031]FIG. 6 is a flowchart depicting MSC/VLR processing of an incoming call request according to an exemplary embodiment of the present invention;  
         [0032]    [0032]FIG. 7 is a block diagram which depcits signalling associated with changes to bearer capabilities associated with user equipment according to another exemplary embodiment of the present invention;  
         [0033]    [0033]FIG. 8 is a block diagram which depicts signalling associated with changes to bearer capabilities associated with network equipment according to another exemplary embodiment of the present invention and  
         [0034]    [0034]FIG. 9 is a signaling/block diagram which depicts bearer capability signalling associated with relocation of user equipment according to still another exemplary embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0035]    The various features of the invention will now be described with reference to the figures, in which like parts are identified with the same reference characters. In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular circuits, circuit components, techniques, etc. in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known methods, devices, and circuits are omitted so as not to obscure the description of the present invention.  
         [0036]    Operation in accordance with GSM communication systems is described in, for example, European Telecommunication Standard Institute (ETSI) documents ETS 300 573, ETS 300 574 and ETS 300 578, which are hereby incorporated by reference. Therefore, the operation of the GSM system is only described herein to the extent necessary for understanding the present invention. Similar standards related documents are also available for UMTS. Although, the present invention is described in terms of exemplary embodiments in a UMTS/GSM system, those skilled in the art will appreciate that the present invention may be applicable to other digital communication systems.  
         [0037]    Referring now to FIG. 1, as mentioned above, exemplary embodiments of the present invention contemplate the exchange of radio bearer limit information as a first part of a mechanism for handling multicall features in radiocommunication systems where entities may (or may not) be capable of handling multiple bearers simultaneously, the number of which may differ as between interacting entities. Therein, in a first step  101 , the radio access network entity (RNC)  102  sends a RanMcCapabilities message to a radio network storage entity (RSU)  104  that includes the limit information available regarding the number of bearers which can be supported, e.g., per terminal, at the RNC  102 . This action is triggered, when, for example, a software update, hardware update, a start or restart, or a change of operator settings takes place at the RNC  102 . The radio network entity storage unit RSU  104  stores the received limit information for later usage as described below. As mentioned above, the RSU  104  can be physically located within MSC/VLR  106  or remotely therefrom but, in any case, has some mechanism for transferring information to the entity wherein bearer limit decisions are made.  
         [0038]    [0038]FIG. 2 depicts part of an exemplary UMTS network including a terminal (UE)  206 , a serving network entity (MSC/VLR  208 ) and a limit calculation unit (LCU  210 ) that is located, for example, in the MSC/VLR  208 . The LCU  210  is, in this example, collocated together with the RSU  104 . For the purposes of this portion of the discussion, consider that the RSU  104  has already received the limit information of the RNC  102  which is currently serving the UE  206 .  
         [0039]    In a first step  201 , the terminal UE  206  performs a location updating request towards serving network entity MSC/VLR  208 . This occurs, for example, during the initial local registration process, also known as IMSI (International Mobile Subscriber Identity) Attach, as well as for any subsequent location updating. In a next step  202 , the terminal UE  206  sends a UeMcCapabilities message to the limit calculation unit LCU  210 . This message includes the bearer limit information of the terminal UE  206 . For the case where the terminal performs a location updating that involves change of serving network entity and for the case of an initial location registration, a Home Location Register (HLR, not shown) will provide the limit information as defined by the multicall subscription data. The serving network storage unit (MSU)  212  will store the limit information received from the Home Location Register. Therefore, for the other cases of locating updating, the limit information provided by Home Location Request is present in radio network entity storage unit RSU  104 . Those skilled in the art will appreciate that the transmission of limit information from the UE  206  to the LCU  210  can occur during processes other than location updating, which is described here as one example. In general, limit information can be exchanged at any time before the interaction between Multicall and Call Hold or Multicall and Call Waiting should take place as described in the Background section above.  
         [0040]    The limit calculation unit LCU  210  then calculates the actual limit, i.e., the largest number of bearers of any of the three involved entities, taking into account the limit information of the serving network entity MSC/VLR, the limit information of the involved radio access network entity stored in the serving network storage unit MSU and the limit information provided by the UE.  
         [0041]    In a next step  203 , the limit calculation unit LCU  210  returns the actual limit to the terminal UE  206  in a NwMcCapabilities message. The terminal UE  206  stores the actual bearer limit in the terminal storage unit USU  214 . Furthermore, the actual limit is stored in a serving network entity storage unit MSU  212 . In step  204 , the serving network entity MSC/VLR  208  confirms the positive outcome of the location updating procedure by sending a Location Update Accept message to the terminal UE  206 .  
         [0042]    According to another exemplary embodiment of the present invention, the limit information of the terminal UE  206  can be transmitted in the Location Updating Request message itself, e.g., in an extension of an MS Classmark 2 Information Element. The MS Classmark 2 Information Element in the Location Updating Request message is well known to those person skilled in the art from the 3GPP TS 24.008 specification, section 10.5.1.6, version 3.2.1, released January 2000, the disclosure of which is incorporated here by reference. The UeMcCapabilities message depicted in FIG. 2 can, in this exemplary embodiment, then be omitted. The actual limit can also be returned as a parameter in the Location Update Accept message, in which case the NwMcCapabilities message depicted in FIG. 2 can be omitted as well.  
         [0043]    As shown in FIG. 3, a terminal UE  206  according to exemplary embodiments of the present invention comprises a terminal storage unit USU  214 , a terminal counter UCTR  304 , and a terminal control unit UCU  306 . The terminal storage unit USU  214  stores the actual limit calculated by the limit calculation unit LCU  210 . Alternatively, the UE  206  may instead calculate the actual limit itself given its knowledge of the UE&#39;s limits as well as limit information for the network side that is transmitted thereto. Regardless of where the actual limit is calculated, the terminal counter UCTR  304  counts the number of bearers established for the subscriber and the type of the respective calls. The terminal control unit UCU  306  determines whether the Call Hold service should be implicitly invoked at a user request for call set-up, or whether the user request for call set-up involves the request for a bearer allocation. For this purpose, the terminal control unit UCU  306  processes the information provided by the terminal storage unit USU  214  and the information provided by the terminal counter UCTR  304 . The processing by UCU  306  starts, for example, when the user requests a call set-up as depicted in the flowchart of FIG. 4.  
         [0044]    Therein, the UE processing starts with the user call request  400 . In decision step  401  it is determined whether a bearer is available for the call request. A bearer is available if the number of bearers as counted by terminal counter UCTR  304  is lower than the actual limit as stored in the terminal storage unit USU  214 . If the result of decision step  401  is that a further bearer is available, then the flow moves to decision step  402  where a check is performed as to whether the requested call is a speech call.  
         [0045]    If the result of decision step  402  is that the requested call is not a speech call, e.g., it is for a data connection, then the flow moves to action  405  wherein a new bearer is requested and the terminal counter UCTR  304  is incremented. If, on the other hand, the result of decision step  402  is that the requested call is a speech call, then in decision step  403  it is determined whether another speech call is already in progress. If the result of decision step  403  is that a speech call is already in progress, then in action  404  the in progress speech call is implicitly put on hold. If the result of decision step  403  is that no speech call is in progress, then in action  405  a new bearer is requested and the terminal counter UCTR  306  is incremented.  
         [0046]    If the result of decision step  401  is that no further bearer is available, i.e., if the number of bearers as counted by terminal counter UCTR  304  is equal to the actual limit as stored in the terminal storage unit USU  214 , then in decision step  406  it is determined whether a speech call is in progress. If the result of decision step  406  is that a call of type speech is in progress, then in action  404  the speech call in progress is put implicitly on hold. If, on the other hand, the result of decision  406  is that no speech call is in progress, then in action  407  the call request is denied. The decisions made in steps  402 ,  403  and  406  can be influenced by user settings, e.g., conference calling, preferred numbers, etc.  
         [0047]    Referring now to FIG. 5, therein a serving network entity MSC/VLR  106 ,  208  according to an exemplary embodiment of the present invention includes a serving network entity storage unit MSU  212 , a serving network entity counter MCTR  502 , and a serving network entity control unit MCU  504 . The serving network entity storage unit MSU  212  stores the actual limit as calculated by the limit calculation unit LCU  210 . The serving network entity counter MCTR  502  counts the number of bearers established for the subscriber. The serving network entity control unit MCU  504  determines whether the Call Waiting service should be invoked when an incoming call is received for the user, or whether the incoming call may involve the request for a bearer allocation. For this purpose, the serving network entity control unit MCU  504  processes the information provided by the serving network entity storage unit MSU  212  and the information provided by the a serving network entity counter MCTR  502 . The processing starts, for example, when an incoming call is received for the user at the MSC/VLR  106 ,  208  as depicted in the flowchart of FIG. 6.  
         [0048]    Therein, the processing starts with the incoming call at step  600 . In decision step  601 , it is determined whether a bearer is available for the call request. A bearer is available if the number of bearers as counted by serving mobile entity counter MCTR  502  is lower than the actual limit as stored in the serving mobile entity storage unit MSU  212 . If the result of decision  601  is that a bearer is available, then, in decision step  602 , the check is performed to determine whether the requested call is a speech call. If the result of decision step  602  is that the requested call is not a speech call, then in, action  605 , the incoming call set up is performed towards the terminal UE  206 . If the terminal UE  206  requests allocation of a new bearer for the call, a new bearer is allocated and the serving network entity counter MCTR  502  is incremented.  
         [0049]    If the result of decision  602  is that the requested call is a speech call, then, in decision step  603  it is determined whether a speech call is in progress. If the result of decision step  603  is that a speech call is in progress, then, in decision step  606 , it is further determined whether Call Waiting can be invoked for the subscriber.  
         [0050]    If the result of decision step  606  is that Call Waiting can be invoked for the subscriber, then in action  604  the incoming call set-up is performed towards the terminal UE  206 , indicating that it is a waiting call. Otherwise, if the result of decision step  606  is that Call Waiting can not be invoked for the subscriber, then in action  607  the incoming call set-up is denied.  
         [0051]    If the result of decision step  603  is that no speech call is in progress, then, in action  605 , the incoming call set up is performed towards the terminal UE  206 . If the terminal UE  206  requests allocation of a new bearer for the call, a new bearer is allocated and the serving network entity counter MCTR  502  is incremented.  
         [0052]    Returning to decision step  601 , if the decision there is, instead, that no further bearer is available, then in decision  606  the check is performed whether Call Waiting can be invoked for the subscriber. If the result of decision step  606  is that Call Waiting can be invoked for the subscriber, then in action  604  the incoming call set-up is performed towards the terminal UE  206 , indicating that it is a waiting call. Otherwise, if the result of decision step  606  is that Call Waiting can not be invoked for the subscriber, then in action  607  the incoming call set-up is denied. The decision steps  601  and  606  can be influenced by user settings and the decision step  601  can be influenced by operator settings, e.g., prioritizing calls (such as prioritizing a voice call over a data call).  
         [0053]    When a bearer limiting factor in the terminal changes, the terminal UE  206  informs the serving network entity MSC/VLR  106 ,  208  as depicted in FIG. 7. Therein, in a first step  701 , the terminal UE 206  sends a UeMcCapabilities message to the limit calculation unit LCU  210 . This message includes the current (new) limit information of the terminal UE  206 . The limit calculation unit LCU  210  calculates the new actual limit taking into account the actual limit information stored in the serving network entity storage unit MSU  212 . The new actual limit is then stored in the serving network entity storage unit MSU  212 . In a next step  702 , the limit calculation unit LCU  210  returns the new actual limit to the terminal UE  206  in a NwMcCapabilities message. The terminal  206  stores the actual limit in the terminal storage unit USU  214 .  
         [0054]    When a limiting factor in the serving network entity changes the serving network entity MSC/VLR  106 ,  208  informs the terminal UE  206  as depicted in FIG. 8. Therein, in a first step, the limit calculation unit LCU  210  calculates the new actual limit taking into account the actual limit information as stored in the serving network entity storage unit MSU  212 . The new actual limit is then stored in a serving network entity storage unit MSU  212 . In a next step  802 , the limit calculation unit LCU  210  returns the actual limit to the terminal UE  206  in a NwMcCapabilities message. The terminal stores the actual limit in the terminal storage unit USU  214 .  
         [0055]    When a Relocation procedure takes place, i.e., a handoff which involves switching RNCs, the new RNC&#39;s bearer limiting factors may not be known to the serving network entity MSC/VLR  106 ,  208 . The limiting factors of the new radio access network entity RNC are then sent to the serving network entity MSC/VLR  106 ,  208  as depicted in FIG. 9. Therein, at step  901 , the current radio access network entity RNC1 ( 900 ) requests a relocation procedure from the serving network entity MSC/VLR  106 ,  208  by sending a Relocation Required message. This message includes the information that the relocation is to be performed towards radio access network entity RNC2 ( 908 ).  
         [0056]    In a next step  902 , the serving network entity MSC/VLR  106 ,  208 , confirms the request of the radio access network entity RNC1 ( 900 ). Then, at step  903 , the serving network entity MSC/VLR  106 ,  208  requests the relocation from RNC2  908  by sending the Relocation Request message. At step  904 , the radio access network entity RNC2  908  sends its own bearer limit information in a RanMcCapabilities message to the radio network entity storage unit RSU  104 .  
         [0057]    Then, at step  905 , the radio access network entity RNC2  908  ends the relocation procedure by sending the Relocation Request Ack message to the serving network entity MSC/VLR  106 ,  208 . The limit calculation unit LCU  210  calculates (step  906 ) the new actual limit taking into account the new limit information in the radio network entity storage unit RSU  104 , the actual limit stored in the serving network storage unit MSU and the limit associated with the UE. The new actual limit is stored in the serving network storage unit MSU  212 . The limit calculation unit LCU  210  returns the actual limit to the terminal UE  206  in a NwMcCapabilities message. The terminal stores the actual limit in the terminal storage unit USU  214 .  
         [0058]    The functions described herein may, as will be apparent to those skilled in the art, be performed, at least in part, by way of software implemented on a computer-readable medium, to perform the afore-described techniques. The computer-readable medium may reside, for example, in any of the entities described herein and may also be found on portable computer-readable medium for the purpose of loading such software onto these entities.  
         [0059]    Although the invention has been described in detail with reference only to a few exemplary embodiments, those skilled in the art will appreciate that various modifications can be made without departing from the invention. For example, the above-mentioned counters, i.e., the terminal counter UCTR and the serving network entity counter MCTR, may not be explicitly implemented as counters, but can also be derived from other data already available at the terminal UE and, respectively, the serving network entity MSC/VLR.  
         [0060]    The terminal control unit UCU and the serving network entity control unit MCU and the limit calculation unit LCU can be implemented for example as integrated circuits or software modules. The limit calculation unit LCU may be implemented in any of the involved system entities or may be implemented as a stand-alone unit. Furthermore, each of the involved system entities may host a limit calculation unit LCU of its own for local computation of the actual limit. In such a case, instead of the actual limit, the limiting information is exchanged between the involved system entities.  
         [0061]    The exchange of limit information may be initiated by one of the system entities by requiring the limit information from the other involved system entities. Alternatively, one of the system entities may initiate the exchange of limit information by sending its limit information to at least one of the involved system entities. Accordingly, the invention is defined only by the following claims which are intended to embrace all equivalents thereof.