Abstract:
There is disclosed a method of packet switched handover in a communications system having at least two modes of operation, the method comprising, at a terminal of the system, associating identifiers of each mode of operation, and responsive to a packet switched connection handover to a new mode, allocating the connection from an identifier of the existing mode to the associated identifier of the new mode.

Description:
BACKGROUND TO THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a technique for the handover of packet-switched data flows, particularly between systems supporting different radio access technologies and/or different modes of operation. 
         [0003]    2. Description of the Related Art 
         [0004]    The deployment of new radio technologies is typically, at least initially, in geographically limited areas. To meet user coverage needs, it is desirable to provide for a handover to an existing or alternative radio technology when a user moves out of an area supported by new but geographically limited radio technology. 
         [0005]    An example is the deployment of the UMTS radio access network (UTRAN), which offers limited geogpraphical coverage, at least initially, in comparison to the more established GSM EDGE radio access network (GERAN). It is proposed, in TSG GERAN, to provide for inter-radio access technology (inter-RAT) packet switched (PS) handover to address this issue. Specifically, it is proposed to provide for a handover between a GERAN A/Gb mode of operation and a UTRAN/CDMA2000 mode of operation. 
         [0006]    Within any given radio access technology, there may also be different operational modes. For example, within GERAN there is an A/Gb mode and an Iu mode. TSG GERAN further specifies an inter-mode packet switched (PS) handover between the A/Gb mode and the Iu mode. 
         [0007]    In GERAN A/Gb mode a base station subsystem packet flow context (BSS PFC), identified by a packet flow identifier (PFI), may be subject to packet switched (PS) handover. The mobile station (MS) to which this PFC is assigned is therefore also subject to handover. 
         [0008]    In GERAN Iu mode and UTRAN a radio access bearer (RAB) identified by a RAB identifier may be subject to relocation, and the user equipment (UE) to which the RAB identifier is assigned is also relocated. 
         [0009]    Hereafter, UTRAN mode and GERAN Iu mode are referred to as Iu mode, while A/Gb mode refers to GERAN A/Gb mode. 
         [0010]    There is a need to support inter-mode and inter-RAT PS handover and hence seamless interruption of data flows during handover. 
         [0011]    Packet switched handover in GERAN A/Gb mode is not yet defined. 3GPP TSG GERAN is currently specifying the packet switched handover in GERAN A/Gb mode. The signaling solution to supporting inter-mode and inter-RAT packet switched handover is presented in TS 43.129 (Stage 2 draft for PS handover in A/Gb mode). 
       SUMMARY OF THE INVENTION 
       [0012]    It is an aim of the invention to provide a mechanism to support inter-mode and/or inter-RAT packet switched handover. 
         [0013]    In one aspect the invention provides a method of packet switched handover in a communications system having at least two modes of operation, the method comprising, at a terminal of the system, associating identifiers of each mode of operation, and responsive to a packet switched connection handover to a new mode, allocating the connection from an identifier of the exisiting mode to the associated identifier of the new mode. 
         [0014]    Each identifier of a mode may be associated with a common identifier. Each common identifier may identify a packet data protocol context. The common identifiers may comprise network layer service access point identifiers. The identifiers of a first mode may identify packet flow contexts. The identifiers of the first mode may include packet flow identifiers. The first mode of operation may be a GERAN A/Gb mode. The identifiers of a second mode may identify radio access bearers. The identifiers of the second mode may include radio access bearer identifiers. The second mode of operation may be an Iu mode. The Iu mode of operation may be either a GERAN Iu mode of operation or a UTRAN mode of operation. 
         [0015]    In a further aspect the invention provides a method of packet switched handover in a communications system having first mode of operation being a GERAN A/Gb mode of operation and a second mode of operation being a UTRAN mode of operation or a GERAN Iu mode of operation, the method comprising, at a terminal of the system, the step of associating a plurality of packet data protocol contexts with both of a plurality of packet flow contexts and a plurality of radio access bearers. 
         [0016]    The step of associating may include mapping identifiers of the packet data protocol contexts to identifiers of the packet flow contexts and identifiers of the radio access bearers. 
         [0017]    The identifiers may be network layer service access point identifiers, packet flow identifiers, and radio access bearer identifiers. 
         [0018]    The association between the plurality of network layer service access point identifiers and the plurality of radio access bearer identifiers may comprise a mapping. 
         [0019]    The association between the plurality of network layer service access point identifiers and the plurality of packet flow identifiers may comprise an intermediate association between the network layer service access point identifiers aand service access point identifiers. 
         [0020]    There may be a mapping between the service access point identifiers and the packet flow identifiers. 
         [0021]    The invention also provides in another aspect a terminal for connection in a communication system in at least two modes of operation, wherein there is provided means for handing over at least one established connection between modes, the terminal comprising means for mapping a common identifier to an identifier of a first mode, and means for mapping the common identifier to an identifier of a second mode. 
         [0022]    The terminal may further include means, responsive to a handover between modes, for controlling the mapping. The at least one established connection may be a packet switched connection. 
         [0023]    There may be provided a set of common identifiers each associated with an established connection; a set of first mode identifiers each for association with an established connection; and a set of second mode identifiers each for association with an established connection. 
         [0024]    There may be provided a mapping means for mapping the common identifiers to either the first mode identifiers or the second mode identifiers in accordance with a correct mode of operation. 
         [0025]    The terminal may further include input means for receiving notification of a correct mode of operation. The notification may be a handover notification. 
         [0026]    In a further aspect the invention provides a mobile communication system comprising a network having at least two modes of operation, and at least one mobile terminal for connection in said network, the network being adapted to provide for handover of packet switched connections on transfer between operating modes, the mobile terminal further being adapted to map a common identifier for an established connection to an identifier for each respective mode of operation, wherein on handover an established connection is transferred from an identifier of one mode to an identifier of a further mode in accordance with said mapping. 
         [0027]    The modes of operation may include modes associated with different radio access technologies, the handover being responsive to a switch between radio access technologies within the network. The radio access technologies may include GERAN and UTRAN. 
         [0028]    The modes of operation may include different modes within a radio access technology, the handover being responsive to a switch between modes within a radio access technology. The modes may include a GERAN A/Gb mode and a GERAN Iu mode. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0029]    The present invention is now described with regard to particular examples with reference to the accompanying drawings in which: 
           [0030]      FIG. 1  illustrates the mapping of identifiers between modes in accordance with a preferred embodiment of the invention; 
           [0031]      FIG. 2  illustrates the signaling and steps carried out in a packet switched handover from a GERAN Iu mode or UTRAN mode to a GERAN A/Gb mode in an embodiment; and 
           [0032]      FIG. 3  illustrates the signaling and steps carried out in a packet switched handover from a GERAN A/Gb mode to a GERAN Iu mode or UTRAN mode in an embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]    The invention is described herein by way of example with reference to particular example embodiments, in order to clearly illustrate the concepts of the invention, which are not limited to the detail of the described embodiments. 
         [0034]    Reference is first made to  FIG. 1 , which illustrates the relationship of network layer service access point identifiers, service access point identifiers, and packet flow identifiers of a GERAN A/Gb mode cell, and a RAB Id of an Iu mode cell, in the context of a mobile station or user equipment in accordance with a preferred embodiment of the invention. 
         [0035]    Referring to  FIG. 1 , the mobile station or user equipment is generally indicated by reference numeral  100 . A block  102  denotes the functional elements utilized when connected in a GERAN A/Gb mode cell. A block  104  denotes the functional elements utilized when connected in an Iu mode cell. 
         [0036]    The block  102  includes a subnetwork dependent convergence protocol (SNDCP) functional block  110  and a service access point identifier (SAPI) functional block  108 . The SAPI functional block  108  is associated with a number of service access point identifiers  110   1 ,  110   2 ,  110   3 ,  110   4 . The SAPI functional block  108  is also associated with packet flow identifier (PFI) blocks  106   1 ,  106   2 , which identify packet flow contexts. 
         [0037]    The block  104  includes a radio access bearer (PAB) functional block  112 . The RAB functional block  112  is associated with a number of RAB identifiers, denoted PAB Ids, and referred to by reference numerals  114   1 ,  114   2 ,  114   3 ,  114   n . 
         [0038]    The mobile station or user equipment  100  further includes a network layer services access point identifiers (NSAPIs) functional block  116 . The NSAPI functional block  116  includes a number of network layer services access point identifiers  118   1 ,  118   2 ,  118   3 ,  114   n . 
         [0039]    A plurality of packet data protocols PDP 1 , PDP 2 , PDP 3  are denoted by blocks  120   1 , 120   2 , 120   3 . The packet data protocol (PDP) blocks represent session established between the mobile station or user equipment  100  and a network with which connections are established. 
         [0040]    The operation of a user equipment or mobile station such as MS/UE  100  of  FIG. 1  in different modes is known in the art. The general principles of the handover between modes in accordance with preferred embodiments of the invention is now descriebd further. 
         [0041]    In a GERAN A/Gb mode, the operation of which is supported by the functional block  102  in  FIG. 1 , a subnetwork dependent convergence protocol (SNDCP) of the SNDCP functional block  110  performs multiplexing of network protocol data units (N-PDUs) from one or several network layer service access point identifiers (NSAPIs)  118  onto a logical link connection (LLC) service access point identifier (SAPI)  110 . Each of the service access point identifiers is associated with a logical link connection, and may thus be considered to represent a logical link connection. 
         [0042]    NSAPIs that are multiplexed onto the same SAPI (or logical link connection) may, for example, use the same radio priority level, quality of service (QoS) traffic handling priority, and traffic class. In a case where BSS packet flow contexts are created (which are identified by PFIs  106 ) all NSAPIs that are multiplexed onto the same LLC SAPI may, for example, share the same BSS packet flow context, as defined by TS23.060. 
         [0043]    There are preferably four SAPI values defined for user data. Default values for SAPIs  3 ,  5 ,  9 , and  11  have been chosen to correspond with the four GPRS quality of service delay classes, although there is no fixed relationship between SAPI and delay class. These four values correspond, in a preferred embodiment, to the four SAPIs  110 . The LLC layer parameters for any SAPI can be negotiated to support any QoS profile. One SAPI is preferably related to one PFI per mobile station or user equipment, and there can be no more than one SAPI utilizing the same PFI per mobile station or user equipment for the same QoS class. There can be several NSAPIs  118  utilizing the same SAPI  110 , and thus the same PFI  106  for each mobile station or user equipment. In a GERAN A/Gb mode, there is thus not necessarily a one-to-one mapping between the NSAPIs and the SAPIs. 
         [0044]    In an Iu mode, which is supported by the functional block  104  in  FIG. 1  there is a one-to-one mapping between the NSAPIs and RAB identifiers. 
         [0045]    In the mobile station or user equipment, the NSAPI functional block  116  identifies the packet data protocol service access point (PDP-SAP). In the serving GPRS support node (SGSN) and the gateway GPRS support node (GGSN), the NSAPI identifies the PDP context associated with a PDP address. 
         [0046]    Within a BSS context the BSS packet flow contexts are identified by a packet flow identifier (PFI), which is assigned by the SGSN. A BSS packet flow context is shared by one or more activated PDP contexts of the same mobile station or user equipment with identical or similar negotiated QoS profiles. 
         [0047]    Thus for the same NSAPI, in GERAN A/Gb mode there is an associated PFI identifying the BSS PFC on the Gb interface and in Iu mode there is an associated RAB Id identifying the RAB on the Iu interface. Both the BSS PFC and RAE have the same QoS traffic class. 
         [0048]    In order to support inter-mode and inter-RAT packet switched handover, and seamless transfer of data flows during the handover, there is a need to define the relation/mapping between NSAPIs, PFIs used in GERAN A/Gb mode cell and NSAPIs, RAB Ids used in an Iu mode cell as well as a mechanism to perform this mapping during packet switched handover. 
         [0049]    In a preferred embodiment, the invention provides a mapping between:
   1. the BSS PFC identified by a PFI and used by a PDP Context identified by a NSAPI in the GERAN A/Gb mode cell; and   2. the RAB identified by a RAB Id to be used by the same PDP Context identified by the same NSAPI in the target Iu mode cell; during inter-mode/inter-RAT packet switched handover from/to GERAN A/Gb mode.   
 
         [0052]    This mapping is preferably done implicitly by the mobile station or user equipment. Note that for the purposes of this description UE (user equipment) is used when the mobile is under control of a UTRAN, and MS (mobile station) is used when the mobile is under control of a GERAN (A/Gb mode or Iu mode). The implicit mapping is done provided that the MS/UE is a node that has knowledge of the identifiers used on both RATs, i.e. GERAN A/Gb mode or GERAN Iu mode/UTRAN as depicted in  FIG. 1 . 
         [0053]    As depicted in  FIG. 1  the MS has to associate the same BSS PFC utilized in GERAN A/Gb mode cell with a RAB utilized in the Iu mode cell. This is achieved through a relation with the NSAPI, which as illustrated by the NSAPI functional block  116  in  FIG. 1  is the common identifier in both systems, and this relation may be used when applicable. 
         [0054]    For example, as depicted in  FIG. 1 :
   1. For PDP Context  1  the mapping relation is:   
 
         [0000]      NSAPI  1 −SAPI  3 −PFIL−RABId  1 →RAB Id  1  is related to PFI  1 .   2. For PDP Context  2  the mapping relation is:     
         [0000]      NSAPI  2 −SAPI  5 −PFI 2 −RABId  2 →RAB Id  2  is related to PFI  2 .   3. For PDP Context  3  the mapping relation is:     
         [0000]      NSAPI  3 −SAPI  5 −PFI 2 −RABId  3 →RAB Id  3  is related to PFI  2 . 
         [0058]    For the PDP Context  2  and PDP Context  3  an aggregation is achieved in the GERAN A/Gb mode due to the same QoS traffic class. However aggregation is not supported in the Iu side and therefore both RAB  2  and RAB  3  from the Iu side are associated to the same BSS PFC on the Gb side in this example. 
         [0059]    The network nodes do not need to know the associations between the PDP Context identified by NSAPIs, BSS PFC identified by PFI and RABs identified by PAB Id as this relation will only be needed and executed by the MS/UE  100 . However in order to enable the MS/UE  100  to perform this mapping relation there is a need for the MS/UE  100  to receive the relevant information from the network. The information needed by the MS/UE  100  depends on the radio access technology of the target cell. 
         [0060]    For example, where the target is an Iu mode cell, the MS receives from the target-RNC the target cell container with the radio related parameters for the allocated resources for RABs associated with the NSAPIs. The MS/UE receives from the source-BSS a list of PFIs for the BSS PFC associated with the same NSAPIs for which the resources are allocated in the target cell, i.e. RABs in the target RNC. It is the ‘old’ SGSN that is able to send the list of accepted PFIs in a PS Handover Command to a source-BSS based on the accepted NSAPIs. 
         [0061]    By way of further example, where the target is an A/Gb mode cell the MS/UE receives from the newSGSN the associated PFI for each NSAPI. The MS/UE receives from the targetBSS the radio related parameters for each of the PFIs for the BSS PFC associated with the NSAPIs for which the resources are allocated in the target GERAN A/Gb mode cell. 
         [0062]    An example of the detailed solution representing the mapping as well as the node functionalities and the mechanism for sending of the information needed to perform the mapping for both cases from/to GERAN A/Gb mode is given below with reference to  FIGS. 2 and 3 . 
         [0063]    In the first example, with reference to  FIG. 2 , there is illustrated the packet switched handover from GERAN A/Gb mode to GERAN Iu mode/UTRAN. The Figure illustrates signaling between various entities and the operation of those entities, the entities being a mobile station  150 , a source BSS  152 , a target RNC  154 , a source 2G SGSN  156 , and a target 3G SGSN  158 . The mobile station  150  may be adapted to operate also as a user equipment. 
         [0064]    The entities shown in  FIG. 2  have various responsibilities during the packet switched handover. 
         [0065]    For the purposes of describing an example, as illustrated in box  202  it is assumed that initially the mobile station has three active PDP contexts. These active PDP contexts may be identified by respective packet flow identifiers PFI 1 ,PFI 2 ,PFI 3 . 
         [0066]    The source BSS  152 , as illustrated by box  203 , makes the necessary decisions to perform A/Gb PS handover, in accordance with techniques known in the art. The source BSS  152 , as illustrated by box  204 , has, for each mobile station, three active BSS packet flow controls denoted PFC 1 ,PFC 2 ,PFC 3 , each respectively associated with the packet flow identifiers PFI 1 ,PFI 2 ,PFI 3 . 
         [0067]    The source BSS  152  initiates packet switched handover from the source BSS  152  to the  2 G SGSN  156  for all the active BSS PFCs. This is achieved by the transmission of a “PS Handover Required” signal  302  from the source BSS  152  to the source 2G SGSN  156 . This signal includes the packet flow identifiers PFI 1 ,PFI 2 ,PFI 3 . 
         [0068]    The 2G SGSN  156 , as illustrated by box  206 , sends the multimedia (MM) and packet data protocol (PDP) contexts per mobile station in a “Forward Relocation Request” message  304 . NSAPIs and QoS profiles are part of the PDP context. The message  304  is received by the target 3G SGSN  158 . 
         [0069]    The 3G SGSN  158  for the indicated NSAPIs, based on its local policies, assigns radio access bearer identifiers (RAB Ids) as illustrated by box  208 . The RAB Ids are created for NS API 1 , NS API 2 , and NS API 3 . 
         [0070]    The 3G SGSN  158  sends the RABs to be setup in a “Relocation Request” message  306  to the target RNC  154 . As illustrated in box  209 , the RABs-to-be- setup information contains information such as the RAB Id, the RAB parameters, the transport layer address, and the Iu transport association. The RAB Id information element contains the NS API value, and the RAB parameters information element gives the QoS profile. 
         [0071]    The target RNC  154 , as illustrated by block  210 , reserves the RNC resources and prepares the target cell to source cell container containing the RAB information for the RABs to be setup. 
         [0072]    The information relating to the RABs to be setup is sent in a “Relocation Request ACK” message  308  to the 3G SGSN  158 . 
         [0073]    The 3G SGSN  158  sends accepted NSAPIs together with the radio related containers to the 2G SGSN  156  using a “Forward Relocation Response” message  310 . As illustrated by box  212  the target 3G SGSN sends a forward relocation response indicating the NS APIs accepted only, and the target cell containers contain RABs setup. The target cell radio related containers have the RABs setup information. 
         [0074]    The 2G SGSN  156 , based on the received and accepted NSAPIs, sends a “PS Handover Command” message  312  to the source BSS  152  as illustrated by box  214 . As illustrated by box  216 , the source BSS  152  processes the container and creates the handover command structure for the PFIs indicated in the PS Handover Command message. 
         [0075]    The source BSS  152  further then sends a “PS Handover Command” message  314  to the mobile station  150 . 
         [0076]    As illustrated by box  218 , the MS  150  then processes the radio related containers, where the RABs to be setup are indicated, based on receipt of the PFIs established in the target cell. The MS  150  also receives the accepted PFIs for the NSAPIs for which the RABs are relocated/established in the target cell. The MS, provided that there is one-to-one mapping between the RAB Id and the NSAPI, then performs the mapping between the BSS PFC identified by the PFIs used by this NSAPI in the GERAN A/Gb mode cell, and the RAB identified by the RAB Id to be used by this NSAPI in the target cell. 
         [0077]    The NS API and the RAD Id are identical. In the target cell there is a switch to the RAD Id. 
         [0078]    In the second example, with reference to  FIG. 3 , there is illustrated the packet switched handover from GERAN Iu mode/UTRAN to GERAN A/Gb mode. The Figure illustrates signaling between various entities and the operation of those entities, the entities being a user equipment  160 , a source RNC  162 , a target BSS  164 , a source 3G SGSN  166 , and a target 2G SGSN  168 . The user equipment  160  may be adapted to operate also as a mobile station. 
         [0079]    The entities shown in  FIG. 3  have various responsibilities during the packet switched handover. 
         [0080]    It is assumed initially, as illustrated by box  302 , that the user equipment  160  has three active PDP contexts, identified by appropriate NSAPIs. As is known in the art, and is illustrated by box  303 , the source RNC  162  makes a decision to perfom A/Gb PS handover. At this point, as illustrated by box  304 , the source RNC  162  has three active radio access bearers identified by respective radio access bearer identifiers, RAB Ids. 
         [0081]    The source RNC  162  sends a “Relocation Required” message  402  to the source 3G SGSN  166  for all the RABs for the active PDP contexts identified by the NSAPIs. 
         [0082]    The 3G SGSN  166 , as illustrated by box  306 , sends the multimedia (MM) and PDP contexts per user equipment or mobile station in a “Forward Relocation Request” message  404 . The NSAPIs and the QoS profiles are part of the PDP context, and thus forwarded in the message  404 . 
         [0083]    The 2G SGSN  168 , as illustrated by box  308 , creates BSS PFCs for the indicated NSAPIs based on its local policies, assigns PFIs for each, and sends the PFCs to be setup, i.e. a list of PFIs, inside a “PS Handover Request” message  406  to the target BSS  164 . 
         [0084]    The target BSS  164 , as illustrated bu box  310 , reserves the resources and prepares the target cell to source cell container containing the PFIs information. 
         [0085]    The information related to the PFCs to be setup is then sent in a “PS Handover Request Ack” message  408  to the 2G SGSN  168 . The message  408  includes the PFC setup list. 
         [0086]    The 2G SGSN  168  then sends a “Forward Relocation Response” message  410  indicating the NSAPIs accepted and the related PFIs. The message  410 , as denoted by box  312 , provides the information to be sent transparently to the user equipment or mobile stationrelated to the NSAPI/SAPI/PFI. 
         [0087]    The 3G SGSN  166 , as illustrated by box  314 , indicates to the source RNC  162  which RABs are relocated in the target cell based on the accepted NSAPIs. It also forwards transparently the PFIs related to these NSAPIs to the source RNC  162  by a “Relocation Command” message  412 . 
         [0088]    The source RNC  162  processes the information received, as illustrated by box  316 , and then sends a “Handover Command” message  414  to the user equipment  160 . The processing by the source RNC  162  includes processing the container and creating the handover command based on the information received in the target RNC to source RNC containers and transparent information from the target RNC. 
         [0089]    The user equipment  160  receives the PFIs related to the NSAPI/SAPI established in the target cell from the containers and process the containers, as illustrated by box  318 . The user equipment also receives the accepted RABs from the source RNC  162 , and provided that there is one-to-one mapping between a RAB Id and a NSAPI, performs the mapping between the BSS PFC identified by PFIs to be used by this NSAPI in the GERAN A/Gb mode target cell. 
         [0090]    In the target cell the NSAPI and the RAB Id are identical. The target cell switches to the SAPI/PFI. 
         [0091]    The invention is described herein by way of reference to particular preferable embodiments. The invention is not, however, limited to the implementation details of these embodiments, and is more generally applicable. The scope of protection afforded by the invention is defined by the appended claims.