Abstract:
The present invention relates to a method and system for performing a multicast transmission in a cellular network, wherein an identification information, which indicates terminal devices and/or areas in which authorized terminal devices are assumed to be located, is transmitted from a core network ( 100 ) to a radio access network of the cellular network by using a control information transmission protocol. Then, a signalling connection of a control and user data transmission protocol is establishing based on said identification information and used for transmitting multicast related data and corresponding control information between the core network ( 100 ) and the radio access network. Thereby, already defined protocol layers can be used for implementing multicast transmission, while modifications are minimized.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a method, system and network element for providing a multicast transmission from a core network to a radio access network, e.g. to a Universal Mobile Telecommunications System Terrestrial Radio Access Network (UTRAN).  
         BACKGROUND OF THE INVENTION  
         [0002]    In the 3GPP (3 rd  Generation Partnership Project) specification TS 23.041, a CBS (Cell Broadcast Service) is defined, which is similar to the Teletex service offered on television, in that like Teletex, it permits a number of unacknowledged general CBS messages to be broadcast to all receivers within a particular region. CBS messages are broadcast to defined geographical areas known as cell broadcast areas. These areas may comprise of one or more cells, or may comprise the entire cellular network. Individual CBS messages will be assigned their own geographical coverage areas by a mutual agreement between the information provider and the network operator. CBS messages may originate from a number of Cell Broadcast Entities (CBEs), which are connected to a Cell Broadcast Centre (CBC). CBS messages are then sent from the CBC to the cells, in accordance with the CBS&#39;s coverage requirements.  
           [0003]    The work to standardize multicast transmission as a new service has been started in 3GPP. The aim is to enhance the current capabilities not only in UTRAN but also in core networks, so as to provide a service using common network resources and being provided only to a restricted group of people in a cell. These requirements are not yet fulfilled in the above described cell broadcast concept.  
           [0004]    Basically the standardisation of the multicast type of service means that the new service concept should be capable of transmitting data simultaneously to a group of people, who previously indicated their interest to receive data belonging to a multicast service. Thus, when the multicast related data is transmitted from the core network to the UTRAN, this data is not addressed to only one user equipment (UE), but to a group of UEs which may even be located in different cells.  
           [0005]    However, the known CBS is designed for transmission of cell broadcast messages, which in practice means that all UEs, which are in the cell, are allowed to received the transmitted data. Therefore, the functionality of the CBC doesn&#39;t provide any solution e.g. how different UEs in a multicast group can be identified and how the evaluation between the cells (e.g. the number of UEs in the cell, the load of the cell etc.) and between the different sessions (e.g. delay requirements for the transmission, priority of the session etc) can be taken care of.  
         SUMMARY OF THE INVENTION  
         [0006]    It is therefore an object of the present invention to provide a multicast transmission function from a core network to a radio access network.  
           [0007]    This object is achieved by a method of performing a multicast transmission in a cellular network, said method comprising the steps of:  
           [0008]    transmitting an identification information, which indicates terminal devices and/or areas in which authorized terminal devices are assumed to be located, from a core network to a radio access network of said cellular network by using a control information transmission protocol;  
           [0009]    establishing based on said identification information a signalling connection of a control and user data transmission protocol; and  
           [0010]    using said established signalling connection for transmitting multicast related data and corresponding control information between said core network and said radio access network.  
           [0011]    Furthermore the above object is achieved by a system for performing a multicast transmission in a cellular network, said system comprising:  
           [0012]    a core network node for transmitting an identification information, which indicates terminal devices and/or areas in which authorized terminal devices are assumed to be located, to a radio access network of said cellular network by using a control information transmission protocol; and  
           [0013]    a radio access network node for receiving said identification information and for establishing based on said identification information a signalling connection of a control and user data transmission protocol;  
           [0014]    wherein said established signalling connection is used for transmitting multicast related data and corresponding control information between said core network node and said radio access network node.  
           [0015]    Additionally, the above object is achieved by a network node for providing a multicast transmission in a cellular network, said network node being adapted to transmit an identification information, which indicates terminal devices and/or areas in which authorized terminal devices are assumed to be located, to a radio access network of said cellular network by using a control information transmission protocol.  
           [0016]    In addition thereto, the above object is achieved by a network node for providing a multicast transmission in a cellular network, said network node being adapted to receive an identification information, which indicates terminal devices and/or areas in which authorized terminal devices are assumed to be located, and to establish based on said identification information a signalling connection of a control and user data transmission protocol, wherein said established signalling connection is used for transmitting multicast related data and corresponding control information.  
           [0017]    Accordingly, by using the control information transmission protocol for transmitting the identification information required for establishing the signalling connection, already defined protocol layer can also be used for multicast related data transmission. Therefore, no new protocol layer is required.  
           [0018]    The signalling connection may be established by creating a virtual context for a multicast session at the radio access network. The virtual context may be coupled to several subscriber identities or/and multicast area identities. The virtual context may have the signalling connection as a single signalling connection. Thus, one signalling connection is related to several terminal devices or/and multicast area IDs.  
           [0019]    In particular, the control information transmission protocol may be the RANAP protocol and the signalling connection may be an Iu interface connection.  
           [0020]    The identification information may be transmitted by using a paging message. Alternatively, the identification information may be transmitted by a multicast calling procedure provided between the radio access network and the core network.  
           [0021]    Furthermore, a multicast radio access bearer assignment procedure may be used to establish the signalling connection. This multicast radio access bearer assignment procedure may comprise a radio access bearer assignment request message containing an information which indicates terminal devices or predetermined areas to which the multicast transmission is directed.  
           [0022]    The signalling connection may be established when a new multicast session is created, and released after said multicast session is terminated, or it may be established when the first multicast session is created, and then used for other multicast sessions. Then, different interface resources may be reserved based on quality requirements of data types transmitted through the signalling connection, or one pipe may be reserved for all kinds of data types transmitted through the signalling connection.  
           [0023]    A multicast support mode is provided in the Iu User Part protocol layer to transmit the multicast related data and the corresponding control information. In this case, the control information may be divided into multicast data related control information and other connection related data. The multicast related control information may be transmitted using an inband signalling.  
           [0024]    As an alternative, a multicast service mode may be provided in the SABP of a cell broadcast centre to transmit the multicast related data and the corresponding control information. Then, control and data frames may be transmitted between the cell broadcast centre and an enhanced BMC (Broadcast/Multicast Control) protocol layer at an RNC of the radio access network. Alternatively, the control and data frames are transmitted between the cell broadcast centre and a multicast related protocol layer at the RNC. Furthermore, the control and data frames may be divided into data frames, data related control frames and management control frames.  
           [0025]    As a further alternative, a multicast area broadcast protocol layer may be provided on the IuBC-interface of the cell broadcast centre to transmit the multicast related data and the corresponding control information.  
           [0026]    As a still further alternative, a predetermined field may be added to data packets of the SABP of the cell broadcast centre to separate the multicast related data and the corresponding control information from the cell broadcast related data.  
           [0027]    Hence, multicast related data can be separated from cell broadcast related data to thereby avoid radical modifications of the conventional cell broadcast concept.  
           [0028]    Further advantageous developments are defined in the dependent claims.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]    In the following, the present invention will be described in greater detail based on preferred embodiments with reference to the accompanying drawings, in which:  
         [0030]    [0030]FIG. 1 shows a schematic block diagram indicating a network architecture in which the present invention can be applied;  
         [0031]    [0031]FIG. 2 shows an operating and signaling diagram indicating a multicasting procedure according to a first preferred embodiment; and  
         [0032]    [0032]FIG. 3 shows a schematic block diagram of an architecture of a cell broadcast service used in a second preferred embodiment. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]    The preferred embodiments will now be described on the basis of a network architecture comprising a UTRAN  90  and a core network (CN)  100 , as shown in FIG. 1.  
         [0034]    According to FIG. 1, a first and a second UE  11 ,  12  are connected via the Uu radio interface to respective first and second node Bs  21 ,  22  of the UTRAN  90 . The node Bs  21 ,  22  participate in the radio resource management and have the same function as the more generic base station. Furthermore, the UTRAN  90  comprises at least one Radio Network Controller (RNC)  30  connected to the node Bs  21 ,  22  via the lub interface and responsible for the control of the radio resources in its domain, i.e. the node Bs  21 ,  22  connected to it. The RNC  30  is the service access point for all services the UTRAN  90  provides to the CN  100 .  
         [0035]    The CN  100  comprises a Mobile Switching Centre/Visitor Location Register (MSC/VLR)  40  which is a switch (MSC) and database (VLR) that serves an UE in its current location for circuit switched (CS) services. The MSC function is used to switch the CS transactions, and the VLR function holds a copy of the visiting user&#39;s service profile, as well as information on the UE&#39;s location within the serving system. The part of the network which is accessed via the MSC/VLR  40  is often referred to as CS domain. The MSC/VLR  40  is connected to a Gateway MSC (GMSC)  50  which is a switch at the point where the CN  100  is connected to external CS networks  110 , e.g. Public Switched Telephone Networks (PSTNs), Integrated Services Digital Networks (ISDNs) or Public Land Mobile Networks (PLMNs). All incoming and outgoing CS connections go through the GMSC  50 .  
         [0036]    Furthermore, the CN  100  comprises a Serving GPRS (General Packet Radio Services) Support Node (SGSN)  60  having a function similar to the MSC/VLR  40  but typically used for packet switched (PS) services. The part of the network accessed via the SGSN  60  is often referred to as PS domain. The SGSN  60  is connected to a Gateway GPRS Support Node (GGSN)  70  having a functionality similar to the GMSC  50  but in relation to the PS services. The GGSN  70  is thus a switch at the point where the CN  100  is connected to external PS networks  120 , e.g. the Internet.  
         [0037]    The MSC/VLR  40  and the SGSN  60  are connected to the RNC  30  via the Iu-interface which thus connects the UTRAN  90  to the CN  100 . the Iu-interface is an open interface which handles switching, routing and service control.  
         [0038]    To achieve a multicast transmission function between the CN  100  and the UTRAN  90  via the Iu-interface, different characteristics of the multicast related data transmission needs to be taken into account not only upon the active data transmission, but also upon reservation and configuration the required resources from Iu-interface. For these different phases the current 3GPP specifications define signaling protocols such as RANAP (Radio Access Network Application Part) and IuUP (Iu Interface User Plane Protocol). The RANAP is a signalling protocol in the Iu-interface that contains all control information specified for the Radio Network Layer used for UTRAN-related issues. The IuUP also belongs to the Radio Network Layer and has been defined to be as much as possible independent of the CN domain that it is used for. The purpose of the IuUP is to carry user data related to Radio Access Bearers (RABs) over the Iu-interface. Each RAB has its own instance of the protocol. The protocol performs either a fully transparent operation, or framing for user data segments and some basic control signalling to be used for initialisation and online control. Based on these cases, the IuUP has two modes, i.e. a transparent mode for fully transparent operation and a support mode for predefined SDU (Service Data Unit) sizes corresponding to framed user data segments. Only upon the support mode, control procedures are specified.  
         [0039]    Thus, the Iu UP is the only protocol in the above group, which is capable of transmitting not only control information but also user plane data (i.e. in this case multicast related data) and therefore it is the candidate for the user plane data transmission and the transmission of connection related control information over the Iu-interface. RANAP can be used for transmission of control information and therefore they are not directly available for multicast data transmission. The RANAP messages can be used to configure and reserve resources from the Iu-interface for the multicast sessions.  
         [0040]    In the following, the first preferred embodiment is described with reference to the operating and signalling diagram shown in FIG. 2.  
         [0041]    To get the full benefit of multicasting in the UTRAN  90 , the same transport resource should be used, i.e. only one user plane transport resource should be reserved over the Iu-interface for a certain multicasting session to be received by several UEs. Currently, in the Iu-interface it is possible to reserve transport/RAB resources only for a particular UE by RANAP. Hence, it is not possible to make an RAB/transport reservation in the Iu-interface, which is related to more than one UE which may be identified in RANAP by an Iu signalling connection identifier.  
         [0042]    To achieve a reservation of RAB/transport resources for more than one UE, the following new concepts and procedures in RANAP are introduced. Thereby, several UEs may receive the same multicast session transmission. These new concepts and procedures are:  
         [0043]    Multicast UE concept with identifier for “virtual UE/area”;  
         [0044]    Multicast paging response message;  
         [0045]    Multicast RNC calling procedure; and  
         [0046]    Multicast RAB assignment procedure.  
         [0047]    In the multicast UE/area concept, a virtual UE and/or area context is created for a certain multicast session (containing one or several RABs). I.e., no particular International Mobile Subscriber Identity (IMSI) is coupled to this UE/area context, instead there could be several IMSIs (i.e. IMSIs of the Ues) which are related to this particular multicast session group. This virtual UE/area context then has just one Iu signalling connection over the Iu-interface. With such a multicast UE/area concept, the existing RAB assignment procedure in RANAP can be used to reserve resources over the Iu-interface. Alternatively, the virtual UE/area context could consists of a list of multicast area Ids, instead of IMSIs. The SGSN  60  may generate or derive this area list e.g. based on information which it could fetch from the HLR, VLR etc.  
         [0048]    Thus, three options are given for the content of the virtual UE/area context:  
         [0049]    1) group of IMSIs, corresponding to particular UE associated with a particular multicast group;  
         [0050]    2) group of multicast area IDs associated with particular multicast services; and  
         [0051]    3) a combination of the above, meaning that only specific UEs can receive in specific areas certain multicast sessions. (This option is related to location services).  
         [0052]    Thus, in summary, the virtual UE/area context created for a certain multicast session could be coupled to several IMSIs or/and multicast area IDs.  
         [0053]    As can be gathered from FIG. 2, a paging message which may be a currently defined message to which all the IMSIs of the UEs included in the desired multicast group related to this virtual UE/area and the identifier (e.g. virtual IMSI) for this virtual UE/area may have been added is generated at a network node (e.g. the SGSN  60 ) of the CN  100  and transmitted in step  1  from the CN  100  to the RNC  30  using RANAP. A virtual UE/area context can then be established in the RNC  30  in step  2  after it has received the paging message from the CN  100 . The paging message may also include a routing and/or service area information indicating the area to which the multicast session should be transmitted. The RNC  30  can then reply to the CN  100  with Initial UE message without any NAS PDU (Non Access Stratum Packet Data Unit) (step  3 .a) or, alternatively, with the new multicast paging response message, which would be a new RANAP message (step  3 .b).  
         [0054]    As an alternative procedure, the new multicast RNC calling procedure can be used to indicate to the RNC  30  e.g. by multicast RNC calling/response messages that a multicast session is planned/requested to be established to the UEs identified by IMSIs and/or virtual IMSI and/or these routing/service areas in the multicast RNC calling message. This multicast calling procedure is provided only between the CN  100  and the UTRAN  90 , and the aim is to reserve required resources for the session from the Iu-interface. Thus, this alternative multicast RNC calling procedure may replace the above steps  1  to  3 .a/ 3 .b.  
         [0055]    Then, the new multicast RAB assignment procedure is used to establish RABs for the multicast session over the Iu-interface via RANAP. In addition to existing information, a (multicast) RAB assignment request message, which is transmitted from the CN  100  to the RNC  30  in step  4 , may contain information indicating which UEs (identified by IMSIs)—if not included in the paging message of step  1 —should be able to receive the multicast transmission or to which routing/location/service areas the multicast transmission is directed. Optionally, an additional information element (IE) may be added to indicate that this RAB is used for a multicast transmission. Based on this information, the RNC  30  can then establish the needed radio and transport resources in the UTRAN  90  to support the requested multicast session (step  5 ). Thereafter, the RNC  30  responds to the CN  100  by transmitting an RAB assignment response message (step  6 ).  
         [0056]    If paging procedures are used before RABs for multicast are requested, the connection oriented SCCP mode may be used for the RANAP messages. With the new multicast RAB assignment procedure including the IMSI and/or location/routing/service areas, the connectionless mode of SCCP for RANAP messages can be used as well.  
         [0057]    Finally, in step  7 , a multicast session is performed using a IuUP protocol signaling via the established Iu signaling connection. As regards the timing of the configuration of the Iu-interface for the multicast session, the Iu signaling connection to be used to transfer control messages between the RNC  30  and the CN  100  can either be established when the RNC  30  is configured (i.e. it exists as long as the RNC  30  is configured) in case a new multicast session (virtual UE/area) is created and released after the multicast session (virtual UE/area) is terminated, or it can be established when the first multicast session in the RNC  30  is established and can then be used for other multicast session as well, i.e. the control messages for a certain session are multiplexed to the same Iu signaling connection. E.g., the virtual UE/area identifier can be used identify different multicast sessions.  
         [0058]    Upon RNC configuration or when first multicast session in the RNC  30  is established, the reserved resources can be served based on Quality of Service (QoS) requirements, i.e. video and text files are using different Iu-interface resources. As an alternative, it is possible to reserve only one “pipe”, which is capable of transmitting all kinds of data types.  
         [0059]    When a new multicast session (virtual UE/area) is created and released, the resources are reserved based on data type demands and therefore each multicast session will have Iu resources of their own.  
         [0060]    In order to send the multicast related data and the corresponding control information between the CN  100  and the UTRAN  90  the IuUP protocol is used for this purpose in the first preferred embodiment. However, because the current IuUP concept doesn&#39;t support transmission of such data, which is not addressed to any particular UE, some modifications to the current concept are required. Therefore, a new mode is introduced to the Iu UP protocol layer. This new mode is named as a “Multicast Support” (MuS) mode, which is meant to provide not only multicast related data transmission over the Iu-interface but also transmission of corresponding control information between the UTRAN  90  and e.g. the SGSN  60  of the CN  100 . The MuS mode multicast data transmission may occur only in the downlink direction from the CN  100  to the UTRAN  90 , whereas transmission of control information may be bi-directional.  
         [0061]    In the MuS mode, the transmitted control information can be divided into two categories:  
         [0062]    1) directly multicast data related control information  
         [0063]    2) other connection related data transmission.  
         [0064]    The first category contains such information, which is always transmitted along with the corresponding multicast data as an inband signaling, i.e. information is included into the header of a multicast SDU. This information may contain information such as session identification, information about the start and the end of the session, the order of the SDUs, multicast group information, scheduling related information (e.g. in which cell data must be sent, how many times, priority etc).  
         [0065]    The second category contains such information, which is needed to take care of the successful data transmission between the SGSN  60  and the UTRAN  90 . This kind of information could consists of e.g. flow control information, information for transmission management like reset requests, deletion requests, transmission related parameter updating etc.  
         [0066]    The main difference in this case compared to the currently defined modes for IuUP (i.e. transparent mode, support mode for predefined SDU size) is that in this MuS mode data is not addressed to any single UE, but is always belonging to the multicast session, i.e. several UEs in the cell.  
         [0067]    [0067]FIG. 3 shows schematic block diagram of an architecture of a cell broadcast service used in the second preferred embodiment. The basic network structure comprises a cell broadcast center (CBC)  150  which is part of the CN  100  and connected to a routing node e.g. an SGSN (not shown) via the Bc reference point. Thus, the CBC  150  can reach every RNC  30  via the user plane of the Iu interface. On the logical interface between the CBC  150  and the RNC  30 , a mandatory protocol IuBC is defined. Based on this architecture and the current requirements for cell broadcast, other core network elements like MSC, VLR (Visitor Location Register), HLR (Home Location Register) etc are not involved in the service delivery.  
         [0068]    If the IuBC interface is used for multicast transmission, both control information and user plane information must be sent by using the same transmission protocol of the IuBC-interface, i.e. the Service Area Broadcast Protocol (SABP) specified between the CBC  150  and the RNC  30 , to fulfil the CBC-RNC communication requirements over the IuBC reference point. The SABP consists of elementary procedures (EPs) which are units of interaction between the CN  100  (i.e. CBC  150 ) and the RNC  30 . The EPs are defined separately and are intended to be used to build up complete sequences in a flexible manner. Currently, the CBC  150  and the SABP are designed for transmission of the cell broadcast messages, which in practice means that all UEs, which are in the cell, are allowed to received the transmitted data.  
         [0069]    In order to support multicast data transmission through the IuBC-interface, the concept in the SABP can be divided between two modes, a cell broadcast service mode (CBS) and a Multicast Service (MuS) mode. The CBS mode consists of such transactions and control and data frames, which are already now defined for the cell broadcast services. In this case data is transmitted between the CBC  150  (at the CN side) and a BMC (at the RNC side).  
         [0070]    The new MuS mode is taken into use when data is to be transmitted to a group of UEs under the CBC  150 . In this mode, the control and/or data frames could be transmitted either between the CBC  150  and an “enhanced BMC” or between the CBC  150  and a new multicast related protocol layer at the RNC side. The available frames of this mode can be divided into three groups:  
         [0071]    1) data frames  
         [0072]    2) data related control frames  
         [0073]    3) management control frames.  
         [0074]    The data frames consist not only of user plane data, but also of such control information, which is required to schedule, cipher etc. data properly at the UTRAN side.  
         [0075]    Furthermore, the data related control frames consist of information, which is required to control data transmission from the CBC  150  and to control data transmission between different sessions. It also may be used to change the used configuration at the UTRAN side and to provide e.g. such transactions like deletion/reset of outdated data from the UTRAN  90  (this data can be either control or user plane data).  
         [0076]    Finally, the management control frames are used to same purpose that what e.g. RANAP is used on the Iu-interface. However also in this case some modifications are require, as described in the first preferred embodiment.  
         [0077]    If no new mode is to be introduced, a new protocol layer could be introduced on the IuBC-interface. This new protocol layer may be called Multicast Area Broadcast Protocol (MABP). The MABP protocol layer could be terminated at the CN side in the CBC  150  or a MMC (Multicast/broadcast Multimedia Centre), if a new network device is provided at the CN side, and at the RNC  30  either in the “enhanced BMC” or in a new multicast related protocol layer. Also in this case, the idea is to separate the multicast related frames from the cell broadcast related frames in order to avoid radical modifications to the cell broadcast concept.  
         [0078]    Another alternative is to use the SABP protocol on the IuBC-interface and to modify the currently used CBC PDU frame structure in such a way that multicast related frames could be separated from the cell broadcast related frames. This can be done by including into each frame e.g. a new field which indicates whether the corresponding frame is containing multicast related data (i.e. control or user plane data), cell broadcast related data or whether this frame is valid to both of these service types. In this way, it is possible to use for the multicast related data transmission also those frames which are already defined for the cell broadcast transmission and which are also suitable for the multicast services. This method also allows an identification of those new multicast service control frames which are not currently needed for cell broadcast services.  
         [0079]    Despite of which of the above three method is used on the IuBC-interface to organise and support the multicast data transmission, the configuration and the timing to configure the signaling connection through the Iu-BC interface could follow the same principles as defined in the first preferred embodiment.  
         [0080]    It is noted that the present invention is not restricted to the specific network nodes, signalling protocols and network types described in the preferred embodiments described above. In particular, the multicast transmission concept can be used on any interface structure between a radio access network node and a core network node. The preferred embodiments may thus vary within the scope of the attached claims.