Abstract:
This invention relates to a communications network, comprising a first network controller, a second network controller and a proxy function, said proxy function being arranged when control of user equipment is to change from said first network controller to said second network controller to cause said first network controller to release resources associated with said first controller.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method for communications network.  
       BACKGROUND OF THE INVENTION  
       [0002]     The coverage area of a cellular radio communication system, such as GSM (Global System for Mobile Communications) and UMTS (Universal Mobile Telecommunication System), is made up of individual cells. A cell can be defined as a specific geographical area where radio access is supplied by a base station (BS) associated with the cell. The base station thus provides radio access to all mobile stations located within the cell.  
         [0003]     Several cells may be grouped together and the respective base stations associated with respective ones of the cells in the group are controlled by a radio network controller (RNC). An RNC can therefore control communications with a mobile station located within one of its associated cells. In a Universal Mobile Telecommunication System (UMTS) network, the RNCs are connected to gateway elements, such as a mobile switching centre (MSC) and a serving GPRS (General Packet Radio Service) support node (SGSN). The MSC and SGSN are part of the core network (CN), and provide circuit switched and packet switched services. Specifically, the MSC can be used to provide circuit switched services and can be connected to circuit switched networks, such as a public switched telephone network (PSTN). The SGSN can provide packet switched services and can be connected to a gateway GPRS support node (GGSN). The GGSN can be connected to packet switched networks, such as the Internet or another UMTS network.  
         [0004]     When the mobile station moves from one cell to a new cell, the base station associated with the new cell may be controlled by a different RNC, the target RNC, to that of the original cell, the source RNC. Two situations can arise.  
         [0005]     In the first situation, control of the MS is retained by the source RNC, and traffic is routed from the target RNC to the source RNC using the inter-RNC interface (lur interface). The connection to the source RNC is therefore maintained, and control of communications is also maintained by the source RNC. This procedure is commonly referred to as anchoring.  
         [0006]     In the second situation, control of the MS by the source RNC is released and control of communications is transferred completely to the target RNC associated with the cell where the MS has moved to. The target RNC thus becomes the new source RNC after communication has been transferred. This procedure is referred to as serving radio network subsystem (SNRS) relocation.  
         [0007]     Entities in the core network are involved in SRNS relocation. In particular, information relating to relocation is transmitted to and received from the core network to effect SRNS relocation. However, this is not always desirable as the core network, or the network operator of the core network, may not necessarily support SRNS relocation. This may be the case even if SRNS relocation is preferable for the RNCs that would be involved.  
         [0008]     If a there is a cluster of RNCs, relocation may be required because the UE controlling function is CPU and memory intensive and it is necessary to balance the load between different RNCs. The core network should not be involved in this case because the relocation is only due to UTRAN (UMTS terrestrial radio access network) internal capacity reasons and there are no mobility issues involved.  
         [0009]     Furthermore, if there is more than one RNC that can be used to control communications, SRNS relocation may help distribute communications resources, such as bandwidth, more effectively and increase the overall internal capacity of the network. However, it has previously not been feasible to involve the core network in SRNS relocation for capacity reasons.  
         [0010]     This is because this may dramatically increase the number of relocations and if the core network is involved, this may burden the SGSN or MSC too much. Additionally it is undesirable to involve the core network in UTRAN internal capacity issues.  
         [0011]     In short, current SRNS relocation procedures do not include the possibility of relocation without the involvement of the CN.  
       SUMMARY OF THE INVENTION  
       [0012]     It is the aim of embodiments of the present invention to address one or more of the above discussed problems.  
         [0013]     According to one aspect of the present invention, there is provided a communications network, comprising a first network controller, a second network controller and a proxy function, said proxy function being arranged when control of user equipment is to change from said first network controller to said second network controller to cause said first network controller to release resources associated with said first controller.  
         [0014]     According to a second aspect of the present invention, there is provided a method of changing from a first network controller associated with a user equipment to a second network controller, the method comprising the steps of determining that control of the user equipment by the first network controller is to be changed to the second network controller; and using a proxy function to cause said first network controller to release resources associated with said first controller.  
         [0015]     According to a third aspect of the present invention; there is provided a proxy function in a communications network comprising a first network controller and a second network controller, said proxy function being arranged when control of user equipment is to change from said first network controller to said second network controller to cause said first network controller to release resources associated with said first controller. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     For a better understanding of the present invention, reference will now be made, by way of example only, to the accompanying drawings, in which:  
         [0017]      FIG. 1  illustrates a schematic diagram of a cellular communication system;  
         [0018]      FIG. 2  illustrates a communication system of the prior art;  
         [0019]      FIG. 3  illustrates a message flow diagram in an example of a relocation procedure;  
         [0020]      FIG. 4  illustrates a communication system in an example of the present invention; and  
         [0021]      FIG. 5  illustrates a signalling flow in an embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]     The present invention is described herein with reference to particular examples. The invention is not, however, limited to such examples. In particular, the invention is described by way of reference to an exemplary UMTS network. However it should be appreciated that embodiments of the present invention may be used with any other suitable communications network.  
         [0023]     Reference is first made to  FIG. 1 , in which 3 cells  100 ,  102  and  104  of a typical cellular GSM/UMTS network are shown. Each cell  100 ,  102  and  104  is served by a respective base transceiver station (BTS)  106 ,  108  and  110 . Each BTS is arranged to transmit signals to and receive signals from user equipment (UE)  112  located in the cell associated with the BTS. Examples of UEs include mobile stations, personal digital assistants (PDAs), computers and other suitably configured devices. Each UE  112  can move from one cell to another cell.  
         [0024]     The operation of the exemplary network in  FIG. 1  is now described in more detail with reference to  FIG. 2  which is known.  
         [0025]      FIG. 2  illustrates a UMTS network  200 . The network  200  comprises various network elements including UE  202 , BTS 1   204  and BTS 2   206 . BTS 1   204  and BTS 2   206  are each associated with a respective cell. The UE  202  communicates with BTS 1   204  over the Uu interface  220  when located within the cell associated with BTS 1 . The UE  202  can also communicate with BTS 2   206  over the Uu interface  222  when located within the cell associated with BTS 2   206 . Further, BTS 1   204  is connected to radio network controller  1  (RNC 1 )  208  via lub interface  224 , and BTS 2   206  is connected to radio network controller  2  (RNC 2 )  210  via lub interface  226 . More than one BTS can be connected to each RNC, although only one is illustrated here for clarity.  
         [0026]     RNC 1   208  and RNC 2   210  can communicate with each other directly via lur interface  228 . RNC 1   208  and RNC 2   210  can also communicate with a mobile switching centre (MSC)  212  and a serving GPRS support node (SGSN)  214 . The MSC  212  and the SGSN  214  form part of the core network (CN). Other entities not illustrated in  FIG. 2 , such as a home location register, may also be found in the CN.  
         [0027]     Communication between RNC 1   208  and MSC  212  is via the lu-cs interface  230 . Communication between RNC 2   210  and MSC  212  is via the lu-cs interface  234 . The MSC  212  provides support for circuit switched services and can be connected to circuit switched networks, such as a public land mobile network (PLMN)  216 . The MSC  212  can also be connected to other circuit switched networks not illustrated such as a public switched telephone network (PSTN).  
         [0028]     Communication between RNC 1   208  and SGSN  214  is via the lu-ps interface  232 . Communication between RNC 2   210  and SGSN  214  is via the lu-ps interface  236 .  
         [0029]     The SGSN  214  provides support packet switched services and can be connected to a gateway GPRS support node (GGSN)  218  and onto the Internet  219  or other packet data network. The GGSN  218  can also or alternatively be connected to other packet switched networks not illustrated such as another UMTS network.  
         [0030]     In  FIG. 2 , the UE  202  is initially in a cell supported by BTS 1   204 . Communications between the UE  202  and BTS 1   204  is over the Uu interface  220 , illustrated by the solid line. UE  202  may move into a new cell supported by BTS 2   206 , in which case, UE  202  may begin communications with BTS 2   206  over Uu interface  222 , illustrated by the dashed line. In a procedure referred to as serving radio network subsystem (SRNS) relocation, control of communications passes from RNC 1   208 , which controls BTS 1   204 , to RNC 2210 , which controls BTS 2   206 . RNC 1   208  is often referred to as the source RNC and RNC 2   210  as the target RNC during SRNS relocation.  
         [0031]     Once all control has been passed from the source RNC to the target RNC, the target RNC becomes the new source RNC until a further SRNS relocation procedure is carried out.  
         [0032]     Entities in the core network, such as the MSC  212  and the SGSN  214 , are used in the SRNS relocation procedure.  FIG. 3  illustrates a message flow diagram of a relocation procedure of the prior art involving the core network.  
         [0033]     In the core network, a MSC and a SGSN are used. The MSC is involved if the user has CS radio bearers and the SGSN if the user has PS bearers. Both will be involved in the case where there are both CS and PS radio bearers. The MSC and/or SGSN are involved because the termination point of the lu connection will change if the RNC changes.  
         [0034]     The message flow in  FIG. 3  is between the network elements of the UE  300 , the target RNC  302 , the core network (CN)  304  and a source RNC  306 .  
         [0035]     In step  310 , the source RNC  306  makes a decision to start relocation to the target RNC  302 . This may be triggered by the UE  300  moving into a cell controlled by the target RNC and may be further dependent on parameters such as signal strength.  
         [0036]     Once relocation is started, the source RNC  306  transmits a radio access network application part (RANAP) relocation required message, step  312 , to the CN  304 . The CN  304  then transmits a RANAP relocation request message to the target RNC  302  in step  314 .  
         [0037]     If the target RNC  302  is able to support relocation, it transmits a RANAP relocation request acknowledgement message back to the CN  304  in step  316 . The CN  304  then transmits a RANAP relocation command to the source RNC  306  in step  318 , which informs the source RNC  306  that relocation can continue.  
         [0038]     The source RNC  306  then transmits a radio network subsystem application part (RNSAP) relocation commit message to the target RNC in step  320 . This message is transmitted directly between the source RNC  306  and the target RNC  302  via an lur interface. The commit message is a notification to a target RNC that the source RNC has received the relocation command message and the control can be switched from the source RNC to the target RNC. After the SRNC has sent the commit message, the relocation cannot be cancelled. The commit message includes all direct transfer messages that have been received in the SRNC after relocation was started. In the case of lossless relocation, there will be PDCP and GTP sequence numbers but this in practice may be rare occurrence.  
         [0039]     The target RNC  302  then transmits a RANAP relocation detect message to th CN  304  instep  322  to confirm to the CN  304  that the target RNC has received the RNSAP message from step  320 . Furthermore, the target RNC  302  also transmits a radio resource control (RRC) message to the UE  300  in step  324 . The RRC message is transmitted via the BTS serving the UE in the target cell. The RRC message contains UTRAN (UMTS terrestrial radio access network) mobility information required for the relocation.  
         [0040]     In step  326 , the UE  300  transmits a RRC UTRAN mobility information confirm message to the target RNC  302 . In turn, the target RNC transmits a RANAP relocation complete message in step  328  to the CN  304 .  
         [0041]     The CN  304  then transmits a RANAP lu release command message to the source RNC  306  in step  330 , instructing the source RNC  306  to release control of communications between the source RNC  306  and the UE  300 . The source RNC  306  confirms release by transmitting a RANAP lu release complete message instep  332 . SRNS relocation is now complete.  
         [0042]     It should be appreciated that the UE involved in the SRNC relocation is not a handover as such as the UE already has a connection to the TRNC—the drift link. The UE is involved about the change of the controlling RNC with the message sent in step  324 . When the UE receives this message it will do the following:  
         [0043]     1. change U-RNTI—this needs to be done because the U-RNTI is RNC specific and the RNC has changed.  
         [0044]     2. reset the RLC sequence numbers—new RLC entities are created in the TRNC so the sequence numbering must start from 0.  
         [0045]     3. reset ciphering counters,  
         [0046]     When the target RNC sends a the relocation detect message, the CN startst to transmit data to the new RNC and when the target RNC sends the relocation complete message the CN shall release the source RNC. After this the relocation is successfully over.  
         [0047]     An example of the present invention will now be described with reference to  FIG. 4 .  
         [0048]      FIG. 4  illustrates a GMS/UMTS network  400  embodying the present invention. The network  400  comprises various network elements including UE  402 , BTS 1   404  and BTS 2   406 . BTS 1   404  and BTS 2   406  are each associated with a respective cell. The UE  402  communicates with BTS 1   404  over the Uu interface  420  when located within the cell associated with BTS 1   404 . The UE  402  can also communicate with BTS 2   406  over the Uu interface  422  when located within the cell associated with BTS 2   406 . Further, BTS 1   404  is connected to RNC 1   408  via lub interface  424 , and BTS 2   406  is connected to RNC 2   410  via lub interface  426 . More than one BTS can be connected to each RNC, although only one is illustrated here for clarity.  
         [0049]     RNC 1   408  and RNC 2   410  can communicate with each other directly via lur interface  428 . RNC 1   408  and RNC 2   410  can also communicate with a mobile switching centre (MSC)  412  and a serving GPRS support node (SGSN)  414 . The MSC  412  and the SGSN  414  form part of the core network (CN). Other entities not illustrated in  FIG. 4 , such as a home location register, may also be found in the CN.  
         [0050]     Communication between RNC 1   408  and MSC  412  may be via a lu-cs interface (not illustrated). Communication between RNC 2   410  and MSC  412  may also be via a lu-cs interface (not illustrated). The MSC  412  provides support for circuit switched services and can be connected to circuit switched networks, such as a public land mobile network (PLMN)  416 . The MSC  412  can also be connected to other circuit switched networks not illustrated such as a public switched telephone network (PSTN).  
         [0051]     Communication between RNC 1   408  and SGSN  414  may be via the lu-ps interface (not illustrated). Communication between RNC 2   410  and SGSN  414  may be via the lu-ps interface  36  (not illustrated). The SGSN  214  provides support packet switched services and can be connected to a gateway GPRS support node (GGSN)  218  and onto the Internet  219 . The GGSN  218  can also be connected to other packet switched networks not illustrated such as another UMTS network.  
         [0052]     In  FIG. 4 , the UE  402  is initially in a cell supported by BTS 1   404 . Communications between the UE  402  and BTS 1   404  is over the Uu interface  420 , illustrated by the solid line. UE  402  may move into a new cell supported by BTS 2   406 , in which case, UE  402  may begin communications with BTS 2   406  over Uu interface  422 , illustrated by the dashed line. In SRNS relocation, control of communications passes from RNC 1   408 , which controls BTS 1   404 , to RNC 2   410 , which controls BTS 2   406 . During SRNS relocation, RNC 1   408  is often referred to as the source RNC and RNC 2   410  as the target RNC. Once control of communications has been passed from the source RNC to the target RNC, the target RNC becomes the new source RNC until a further SRNS relocation.  
         [0053]     In an example of the present invention, the core network, such as the MSC  412  and the SGSN  414 , are not used in the SRNS relocation procedure, unlike the procedure illustrated in  FIG. 2 . Instead, a core network proxy is provided. This may be a separate core network proxy  430  or may be provided as part of one or more RNCs.  
         [0054]     Thus, a dummy core network process can be introduced, which emulates the functionality of the existing core network. This may be implemented in the source RNC or the target RNC, and the messages sent between the source RNC and the target RNC may be transmitted via a modified interface. Alternatively a separate CN proxy is introduced which is able to receive messages from and send messages to the RNCs.  
         [0055]     Thus either of the RNCs works as a CN proxy or there is a separate proxy server  430 . More particularly, the RNCs or proxy server are arranged to emulate the functionality of the MSC and/or SGSN which would be provided in RNC relocation.  
         [0056]     Reference is now made to  FIG. 5  which shows the signalling in an embodiment of the invention which uses a core network proxy function. As mentioned, the core network proxy can be a separate entity or part of the target RNC or source RNC.  
         [0057]     In step S 1 , the source RNC sends a RNSAP message relocation prepare to the target RNC  408 . This is so that new control resources for the user equipment are created at the target RNC. The required information about the old context is sent in this message.  
         [0058]     In step S 2 , the target RNC  408  replies to the source RNC  410  with the RNSAP message relocation prepare confirm. This message confirms to the SRNC that the TRNC has created the control resources.  
         [0059]     In step S 3 , the SRNC may now start to forward data to the target RNC. This is coordinated with the CN proxy  430 . It should be appreciated that this step is optional and in some embodiments of the invention may be omitted.  
         [0060]     In step S 4 , the SRNC sends a RNSAP: relocation commit message to the target RNC. This confirms that the control can be switched from the SRNC to the target RNC. For the avoidance of confusion, the target RNC is now acting as a source RNC but will for the purposes of clarity continue to be referred to as the TRNC.  
         [0061]     In step S 5 , the target RNC  408  sends an internal relocation detect message to the CN proxy  450 . This confirms to the CN proxy  430  that the target RNC has received the relocation commit message. The proxy will delete the old internal lu connection to the old SRNC.  
         [0062]     In step S 6 , the SRNC sends a RRC UTRAN mobility information message to the UE. This is as in step  324  of  FIG. 2 .  
         [0063]     In step S 7 , the UE replies to the TRNC with a RRC message—UTRAN mobility information confirm. This is as in step  326  of  FIG. 2 .  
         [0064]     In step S 8 , the TRNC  408  sends a internal relocation complete message to the CN proxy  430 .  
         [0065]     In step S 9 , the CN proxy sends an internal IU release request to the SRNC. This requests that the SRNC delete the old resources.  
         [0066]     In step S 10 , the source RNC sends to the CN proxy  430  an internal IU release complete message confirming that the SRNC has successfully completed the deletion of old resources.  
         [0067]     In embodiments of the invention relay RANAP is used because the lu interface signalling cannot be reallocated. The lu user plane will be switched with means of ATM re-routing. Thus after relocation, the proxy entity is able to pass the data received to/from the IU to the new source RNC, ie to the TRNC.  
         [0068]     In some embodiments of the invention, the introduction of the emulated CN proxy may be advantageous when introducing clustered RNCs because the modifications to the existing implementations may be minimal.  
         [0069]     The above described arrangement results in several advantages over prior art arrangements.  
         [0070]     Firstly, user equipment can be relocated between RNCs without the need for the involvement or support of the CN. This is important as not all CN operators currently support SRNS relocation, which is considered as an important mobility issue.  
         [0071]     Furthermore, SRNS relocation may be performed for capacity reasons within a cluster of RNCs, which can be done quickly as there is no need for CN to be involved. This also saves on CN resources.  
         [0072]     It should be appreciated that the transmission costs between the proxy and the RNC are not considered to be an issue because the cluster is designed to have efficient internal transmission medias.  
         [0073]     It is also noted herein that while the above describes exemplifying embodiments of the invention, there are several variations and modifications which may be made to the described embodiments without departing from the scope of the present invention as defined in the appended claims. One skilled in the art will recognise modifications to the described embodiments.