Abstract:
The disclosure relates to a technique for transporting content data to a plurality of mobile clients in a network. Among others, a method embodiment for controlling bearer selection by the mobile client in the network having a plurality of access areas is presented. Each access area provides for a transmission of the content data at least one of a point-to-multipoint-type bearer (PTM-type bearer) and a point-to-point-type bearer (PTP-type bearer). The method comprises the step of receiving information regarding a local bearer topology (LBT). The LBT comprises at least two neighboring access areas including an access area of the mobile client. The LBT information indicates for each access area of the LBT an availability or unavailability of at least one bearer of at least one bearer type. The method further comprises the step of performing bearer selection based on the LBT information.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure generally relates to a technique for transporting content data such as video data, audio data, multimedia data or text data to a plurality of mobile clients in a network. In particular, the disclosure is directed to an efficient usage of different transport mechanisms in a hybrid network. 
       BACKGROUND 
       [0002]    Content services such as mobile TV, multimedia channels, audio programs and newsticker services can be provided by mobile broadcast technologies. Existing broadcast technologies include the so-called Multimedia Broadcast/Multicast Service (MBMS) standard. The MBMS standard enhances cellular networks that are based on the Global System for Mobile communications (GSM), the Universal Mobile Telecommunication System (UMTS), or a combined GSM-UMTS-network architecture. Other broadcast technologies include Digital Video Broadcasting to Handheld receivers (DVB-H) and Digital Multimedia Broadcasting (DMB), which provide a digital data stream over individual frequency bands for each broadcasting program. 
         [0003]    Broadcasting refers to transmitting content data to all terminals or user equipments in a network, collectively referred to as clients, or to a specified group of clients. The latter is also referred to as multicasting. Throughout this document, a broadcast transmission is to be understood as a generic term for a one-to-many (or point-to-multipoint, PTM) transmission, encompassing also a multicast transmission. A geo-graphical area covered by the broadcast transmission of a certain content service is referred to as a broadcast area or PTM area. 
         [0004]    While broadcasting distributes content data from a sender to a plurality of clients, the counterpart is a point-to-point (PTP) transmission, which is also referred to as unicasting. With unicast transmission, content data is transferred from a sender to a single destination. By example, unicast transmissions are realizable by the High-Speed Downlink Packet Access (HSDPA) standard defined for UMTS-based networks. Independent of the underlying transmission technology, the provision of certain content data is collectively referred to as a content service herein. 
         [0005]    The simultaneous distribution of identical content to a plurality of clients using a broadcast transmission is significantly more resource-efficient than individual unicast transmissions. The general idea of a broadcast transport mechanism is to propagate the content in a network only once, creating copies only when links to the multiple destinations split. The broadcast transmission saves considerable resources in both a Core Network (CN) and a Radio Access Network (RAN), the latter connecting the clients with the CN. Standardized implementations of RANs include GSM EDGE RAN (GERAN) and UMTS Terrestrial RAN (UTRAN). 
         [0006]    The unicast transmission of content requires resources depending on the number of clients. In broadcast transmissions, on the other hand, it is not the number of clients but the number of content services that determines the required resources. Consequently, for mass content services, particularly content services with high bandwidth demands such as mobile TV, broadcast transmission is generally preferred over unicast transmission. 
         [0007]    While mobile users expect the content service to be comprehensive in spatial coverage, it is not reasonable to provide comprehensive service coverage based entirely on mobile broadcast technologies. In sparely populated areas, such as rural areas with infrequent service requests, unicast transmission is more efficient because of its flexible resource allocation. Allocating a unicast transmission requires a registration of the client at the sender or at a service center node of the hybrid network, such as the Broadcast-Multicast Service Centre (BM-SC) of the MBMS technology. 
         [0008]    Broadcast content reception, on the other hand, in many cases does not require a registration of the client, which may result in limitations of conventional techniques. By example, file delivery by Push-Broadcast Services (PBS) subdivides the transmission into separate transmission sessions. A broadcast bearer of the PBS is therefore idle between the transmission sessions. A non-registered client leaving the broadcast area of the PBS cannot be alerted by the hybrid network, because the hybrid network is unaware of the broadcast content reception of the client in the absence of a registration. Conversely, the client is also not able to detect the leaving of the broadcast area, because the client cannot differentiate from pure listening whether it is inside the broadcast area and the broadcast bearer is idle or if it is outside of the broadcast area. This causes a client having left the broadcast area to miss all following transmission sessions of the PBS, even though the client outside the broadcast area might still have the possibility of switching to the unicast bearer. Thus, the conventional technique suffers, especially for mobile clients and small broadcast areas, from a high risk of missing transmission sessions. 
         [0009]    A possible solution to control a safe broadcast content reception of all transmission sessions would be to enforce a registration of all clients receiving the PBS at the beginning of the PBS and to require for each transmission session a report to follow in case of successful reception. However, the broadcast transmission regularly addresses a large number of clients. Checking all reception reports for each transmission session would cause a long delay and a large amount of signaling data. 
       SUMMARY 
       [0010]    Accordingly, a technique is needed which allows for an optimized usage of transport mechanisms for content services provided by a hybrid network. 
         [0011]    This need is satisfied according to a first aspect by a method of controlling bearer selection by a mobile client in a network having a plurality of access areas, each access area providing for a transmission of content data at least one of a point-to-multipoint-type bearer (PTM-type bearer) and a point-to-point-type bearer (PTP-type bearer). The method comprises the step of receiving information regarding a local bearer topology (LBT) comprising at least two neighboring access areas including an access area of the mobile client, wherein the information regarding the LBT (LBT information) indicates for each access area of the LBT an availability or unavailability of at least one bearer of at least one bearer type. The method further comprises the step of performing bearer selection based on the LBT information. 
         [0012]    The LBT information can comprise an availability list indicating one or more access areas (for example by access area identifiers) and for each listed access area at least one available bearer or bearer type. The LBT information can also provide information regarding “blank spots” in a coverage area of the network or in a coverage area of a specific bearer type. Additionally, or as an alternative, the LBT information can thus comprise an unavailability list indicating one or more access areas (for example by access area identifiers) and for each listed access area at least one unavailable bearer or bearer type. The indicated unavailability of a bearer type can prevent the mobile client from repeatedly trying to access the unavailable bearer or bearer type, which reduces power consumption of the mobile client. 
         [0013]    The indication of at least one bearer of at least one bearer type can furthermore encompass the indication of at least two different PTM-type bearers or at least two different PTP-type bearers. For example, the LPT information can indicate for some or all access areas of the LBT the availability or unavailability of two PTM-type bearers, such as DVB-H and MBMS bearers. This LBT information can induce a mobile client within a specific access area to perform PTM-to-PTM switching. 
         [0014]    The method may be performed for content services (such as PBS) subdividing a content transmission into separate transmission sessions. For example, when a mobile client is switched on during an idle period of the content transmission, the mobile client can select, based on the received LBT information, a bearer indicated as available in the (current) access area of the mobile client and safely receive the following transmission sessions on the selected bearer. 
         [0015]    Based on the LBT information, the mobile client can move within a geographic region covered by the LBT and select a preferred bearer without further need of additional signaling, thereby saving network resources. Moreover, with the received LBT information, the mobile client can autonomously select the bearer available in the (current) access area of the mobile client even during idle periods of the transmission. 
         [0016]    The reception of the LBT information and the bearer selection can depend on a change of the access area of the mobile client. At least one of the method steps can be repeated after or triggered by the change of the access area by the mobile client. In case the mobile client receives content data in a first access area of the mobile client while moving to a second access area, the mobile client can thus repeat the step of performing bearer selection. As an advantage, this allows the mobile client to seamlessly switch to another bearer type. For example, if the first access area provides a PTM-type bearer and the second access area only provides a PTP-type bearer, the mobile client can switch, based on the LBT information, from the PTM-type bearer to the PTP-type bearer as a result of the repeated bearer selection, and vice versa. 
         [0017]    As another example, the first access area of the mobile client may only provide a FTP-type bearer, while the second access area of the mobile client provides a PTM-type bearer and a PTP-type bearer. In this case, the mobile client moving from the first to the second access area can select a preferred bearer based on the LBT information. For example, the mobile client can select the PTM-type bearer whenever indicated as available in the LBT information. In such a way, resources of the network are used more efficiently. 
         [0018]    The method can furthermore comprise the step of sending an LBT request for the LBT information to a node of the network. For example, when the mobile client does not receive any content data, there is no need for LBT information, and the mobile client may refrain from sending an LBT request. On the other hand, when the mobile client is switched on, it can send an LBT request and receive LBT information for performing bearer selection. Accordingly, network traffic caused by the LBT information can be adapted to an actual need of the mobile client, which further minimizes the network traffic. 
         [0019]    The LBT request can furthermore include a service identifier regarding a content service provided by the network, and a bearer indicated as available in the requested LBT information can provide content data of the identified content service. This allows to tailor the LBT information to those content services which are of particular interest to the mobile client. For example, the access area of the mobile client can provide for a PTM-type bearer and a PTP-type bearer in general, while the content service of interest can be provided via PTP transmission. In this case, the LBT information is tailored to the content service by indicating (only) the PTP-type bearer as available. 
         [0020]    The LBT information can furthermore indicate for at least one access area of the LBT if it is a border access area of the LBT. In other words, the LBT may comprise one or more border access areas. The LBT may also comprise one or more access areas that are not border access areas. In one implementation, the LBT is generated such that the current access area of the mobile client is not a border access area. 
         [0021]    According to an exemplary first definition, a border access area of the LBT is an access area of the LBT which is not surrounded by one or more other access areas of the LBT. According to a second definition, the border access area of the LBT can be any access area of the LBT which is partially or completely within a predefined border distance to a border line of the LBT. According to a third definition, the border access area can be any access area of the LBT which is partially or completely in a predefined spot area within the LBT. According to a fourth definition, the border access area may have at least one neighboring access area that is not included in the LBT. 
         [0022]    The mobile client can, for example, compare the (current) access area of the mobile client with those access areas of the LBT indicated as border access area of the LBT. This allows the mobile client to request new LBT information for a newly defined LBT in which the border access area is no longer a border access area (but, e.g., fully surrounded by access areas also included in the new LBT) or switch to any conventional content reception technique sufficiently ahead in time before leaving the LBT. 
         [0023]    A border access area of the LBT can be indicated in the LBT information by an access area identifier without position information of the border access area, which reduces the amount of signaling data. Furthermore, the mobile client does not have to perform a topological analysis of the received LBT information to identify border access areas, which reduces required computational power of the mobile client. However, the method may alternatively include the step (performed by the mobile client) of performing such a topological analysis to determine border access areas itself (e.g., in cases in which the border access areas are not expressly indicated in the LBT information). 
         [0024]    Sending the LBT request and/or the LBT information can be triggered when the mobile client is located in or enters a border access area. This allows the mobile client to update its LBT information prior to leaving the area covered by the previous LBT. Based on the updated LBT information, the mobile client can seamlessly continue performing bearer selection in spite of a limited size covered by the LBT. Changing the size of the LBT allows adapting a frequency of the LBT updates. 
         [0025]    The network can provide a plurality of content services, wherein each content service provides content data. For example, the content service can provide the content data to a plurality of mobile clients. The method can furthermore comprise the step of sending a service request for service information to a node of the network, wherein the service information indicates at least one content service provided at present or in future in the access area of the mobile client. Additionally, the service information can indicate for each indicated content service which bearer or bearer type to select. Still further, the method can comprise the step of receiving from the node of the network the requested service information indicating for each of indicated content service which bearer or bearer type to select. Based on the received service information, the mobile client can display to a user of the mobile client which services are actually available in the access area of the mobile client. The service information can also include starting times of the at least one content service provided. 
         [0026]    The method can further comprise the step of sending service subscription information regarding an indicated content service to the node in the network. This allows, also in the case of content reception via the PTM-type bearer, the network to automatically update the LBT information of the subscribed mobile client. Additionally, the LBT information can be tailored to the content service (i.e., generated based on the availability of the content service in the LBT). 
         [0027]    The need is satisfied according to a further aspect by a method of controlling bearer selection by a mobile client in a network having a plurality of access areas, each access area providing for a transmission of content data at least one of a point-to-multipoint-type bearer (PTM-type bearer) and a point-to-point-type bearer (PTP-type bearer). The method comprises the step of determining information regarding a local bearer topology (LBT) comprising at least two neighboring access areas including an access area of the mobile client, wherein the LBT information indicates for each access area of the LBT an availability or unavailability of at least one bearer of at least one bearer type. The method further comprises the step of sending the LBT information to the mobile client. 
         [0028]    In case the network cannot provide a certain or any bearer or bearer type within a certain access area, the LBT information covering this access area can indicate the unavailability of this bearer or bearer type. The indication can also encompass the indication of at least two different PTM-type bearers or at least two different PTP-type bearers. 
         [0029]    Based on the LBT information provided by the network to the mobile client, the mobile client can autonomously select a preferred bearer or bearer type while moving in the area covered by the LBT without further need of additional signaling. The network can further apply the LBT information as an instrument of balancing a content traffic load over different bearer types. 
         [0030]    The method may also comprise the step of receiving an LBT request for the LBT information from the mobile client. Receipt of an LBT request for the LBT information can beneficially reduce the frequency of sending the LBT information to the mobile client. For example, the network can trigger the steps of determining LBT information and sending the LBT information by the reception of an LBT request. 
         [0031]    The LBT information can, furthermore, indicate for at least one access area of the LBT if it is a border access area of the LBT. This allows the mobile client to detect the border of the area covered by the LBT. The step of sending the LBT information can be triggered when the mobile client is located in or enters a border access area of a current or previous LBT. For example, the network can track the access area of the mobile client and trigger at least one of the steps of determining and sending new LBT information to the mobile client in case the tracked access area of the mobile client is a border access area of the previous LBT. Accordingly, the mobile client can automatically receive updates of the LBT information. 
         [0032]    The network can provide a plurality of content services, wherein each content service provides content data. The method can furthermore comprise the steps of receiving a service request for the service information from the mobile client, wherein the service information indicates at least one content service provided at present or in future in the access area of the mobile client on the selected bearer type or bearer out of the plurality of content services provided by the network. Still further, the method can comprise the step of sending to the mobile client the requested service information indicating for each indicated content service which bearer or bearer type to select. The service information can also include starting times of the indicated content service. 
         [0033]    The content services indicated in the service information can furthermore depend on the mobile client requesting the service information. For example, the service information can select the at least one content service according to an interest profile assigned to the mobile client or a user of the mobile client. 
         [0034]    The method can furthermore comprise the step of receiving service subscription information regarding a content service from the mobile client. The network may automatically provide at least one of LBT information and service information to the subscribed mobile client. Furthermore, the network can analyze subscription information for a plurality of mobile clients regarding the at least one content service in order to select an efficient bearer type for providing the content service. 
         [0035]    The network can determine the LBT information by generating the LBT information based on a PTM area definition (which may be retrieved from a first database of the network). Generating the LBT information can furthermore be based on an access area status (which may be retrieved from the first database or from a second database of the network). For example, the network can retrieve a current status regarding the availability or unavailability of a certain bearer or bearer type in a certain access area. 
         [0036]    The shape of the LBT can take into account client mobility information. The mobility information may include at least one of the access area of the mobile client, a location of the mobile client, a location history of the mobile client, a movement direction of the mobile client, and a movement speed of the mobile client. For example, the location history or the movement direction can indicate a linear or almost linear motion of the client along a road, in which case the shape of the LBT can be elongated in the direction of motion. Furthermore, the network can match the client mobility information with a road map stored in the network, so that a location of the mobile client matching a road causes the shape of the LBT to be elongated along the road. An adapted shape of the LBT avoids irrelevant signaling information. 
         [0037]    Alternatively or in addition, the LBT information can be retrieved from a third database in the network depending on the client mobility information. For example, the network can store specific LBT information for different locations or access areas or groups of access areas. This can speed-up the step of determining LBT information and reduce computational requirements for the node of the network. 
         [0038]    The LBT information can comprise at least one of a first list for indicating PTM bearer access areas, a second list for indicating PTP bearer access areas, and a third list for indicating border access areas of the LBT. The first list and the second list for indicating different bearer types can, furthermore, indicate different PTM bearer types or different PTP bearer types. Moreover, the first list and the second list can indicate the availability or the unavailability of the indicated bearer or bearer type in the access area. An access area can be indicated in one of the lists by an access area identifier. Alternatively or in addition, access areas can be indicated by position information. The indication by access area identifiers is beneficial to reduce an amount of signaling data. The indication of position information is beneficial to improve a spatial resolution of the bearer selection. 
         [0039]    The need is also satisfied according to a still further aspect by a computer program product. The computer program product comprises program code portions for performing one or more of the steps of one or more of the method aspects described herein when the computer program product is executed on one or more computing devices. The computer program product may be stored on a computer-readable recording medium such as a permanent or re-writeable memory, a CD-ROM, or a DVD. The computer program product may also be provided for download via one or more computer networks, such as the Internet, a cellular telecommunications network or a wireless or wired Local Area Network (LAN). 
         [0040]    The need is also satisfied according to another aspect by a bearer selector for a mobile client connected to a network having a plurality of access areas, each access area providing for a transmission of content data at least one of a point-to-multipoint-type bearer (PTM-type bearer) and a point-to-point-type bearer (PTP-type bearer). The bearer selector comprises a receiver and a processor. The receiver is adapted to receive information regarding a local bearer topology (LBT) comprising at least two neighboring access areas including an access area of the mobile client, wherein the LBT information indicates for each access area of the LBT availability or unavailability of at least one bearer of at least one bearer type. The processor is adapted to perform bearer selection based on the LBT information. 
         [0041]    The need is also satisfied according to another aspect by a bearer topology generator for a node of a network having a plurality of access areas, each access area providing for a transmission of content data at least one of a point-to-multipoint-type bearer (PTM-type bearer) and a point-to-point-type bearer (PTP-type bearer). The bearer topology generator comprises a processor and a sender. The processor is adapted to determine information regarding a local bearer topology (LBT) comprising at least two neighboring access areas including an access area of the mobile client, wherein the LBT information indicates for each access area of the LBT an availability or unavailability of at least one bearer of at least one bearer type. The sender is adapted to send the LBT information to the mobile client. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0042]    In the following, the invention will further be described with reference to exemplary embodiments illustrated in the figures, in which: 
           [0043]      FIG. 1  is a schematic overview of a PTP-enabled network in which the technique presented herein can be practiced; 
           [0044]      FIG. 2  is a schematic overview of a PTM-enabled network in which the technique presented herein can be practiced; 
           [0045]      FIG. 3  illustrates functional components of a system comprising a bearer selector embodiment and a bearer topology generator embodiment; 
           [0046]      FIG. 4  shows an example of a local bearer topology; and 
           [0047]      FIG. 5  is a signaling diagram illustrating a method embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0048]    In the following description, for purposes of explanation and not limitation, specific details are set forth, such as specific network systems including particular network nodes, communication standards etc., in order to provide a thorough understanding of the technique presented herein. It will be apparent to one skilled in the art that this technique may be practiced in other embodiments that depart from these specific details. For example, the skilled artisan will appreciate that the technique may be practiced in connection with wireless communication networks different from the UMTS network implementing MBMS services as discussed below. The technique may also be practiced in wireline communication systems, for example, in IP networks. Basically, the disclosure may be practiced within any PTP/PTM-enabled data transmission system in which some kind of data content is provided to one or more mobile clients. 
         [0049]    Those skilled in the art will further appreciate that the steps and functions explained herein below may be implemented using individual hardware circuitry, using software functioning in conjunction with a programmed microprocessor or a general purpose computer, using an Application Specific Integrated Circuit (ASIC), or using one or more Digital Signal Processors (DSPs). It will also be appreciated that while the technique is described as a method, it may also be embodied in a computer processor and a memory coupled to the processor, wherein the memory is encoded with one or more programs that perform the method disclosed herein when executed by the processor. 
         [0050]      FIG. 1  schematically illustrates an UMTS network  100  as an embodiment of a (third generation) PTP-enabled network. A content provider  110  provides content data to a Broadcast-Multicast Service center (not shown) attached to or included in a core network  120  of the UMTS network  100 . The core network  120  is divided in circuit switched (not shown) and packet switched domains. Packet switched elements of the core network  120  comprise a Serving GPRS Support Node (SGSN)  122  and a Gateway GPRS Support Node (GGSN)  124 . 
         [0051]    The UMTS network  100  further comprises a radio access network  130 . The radio access network  130  comprises a Radio Network Controller (RNC, not shown) and several base transceiver stations (or NodeBs)  132  connected to the RNC. Each NodeB  132  covers one or more cell areas  134  in which one or more mobile clients  136  are attached to the NodeB  132 . 
         [0052]      FIG. 1  illustrates by arrows the PTP transmission of content data (corresponding to a certain content service) from the content provider  110  through the core network  120  to individual mobile clients  136  of the radio access network  130  via multiple PTP-type transport bearers. As shown in  FIG. 1 , there is one PTP connection between the content provider  110  and each mobile client  136 . 
         [0053]    As opposed to the many individual PTP transmissions of identical content data shown in  FIG. 1 , a PTM transmission based on the MBMS standard in a PTM-enabled UMTS network  100  is shown by arrows for the analogous setup in  FIG. 2 . Like reference numbers refer to like components. The content provider  110  provides a single stream of content data entering the core network  120  at a GGSN  124 , where it is split up to one or more SGSN  122  and further distributed to several NodeBs  132 . The content data is provided by each NodeB  132  to a plurality of mobile clients  136  in a PTM transmission via a single PRM-type transport bearer. 
         [0054]    The following discussion of exemplary embodiments uses the example of a hybrid network supporting both PTP and PTM delivery technologies as illustrated in  FIGS. 1 and 2 . The MBMS standard and the DVB-H standard are examples of PTM delivery technologies used in addition to PTP bearers, which are preferably interactive bearers. 
         [0055]    Each content service distributed via the hybrid network  100  has a service identifier and distributed within one or more PTM areas. Each PTM area has a PTM area identifier. In the case of the MBMS standard, the PTM area is referred to as a MBMS service area (MSA), and the PTM area identifier is referred to as a MBMS service area identifier (MSAI). 
         [0056]    Each PTM area comprises one or more access areas. Each access area is identified by an access area identifier. In the case of a cellular network, such as the UMTS-based hybrid network illustrated in  FIGS. 1 and 2 , each cell area  134  is an example of an access area, but each cell area may also be divided in multiple separate access areas. In the following, the term “access area” is used as a collective term for a cell area, a location area, a routing area, or a tracking area. The concept of the disclosure applies analogously to all these and other spatial segmentations of the hybrid network  100 . In the present embodiments, the access area segmentation defines the geographical granularity in which bearer availability (and unavailability) information is defined and provided to the mobile clients  136 . 
         [0057]      FIG. 3  shows a system  300  comprising an embodiment of a mobile client  136  and an embodiment of a network node  140  that may be components of the UMTS network  100  of  FIGS. 1 and 2 . The node  140  is connected to the mobile client  136  via a core network  120  and a radio access network  130 . Via this connection, Local Bearer Topology (LBT) information  150  is transmitted to the mobile client  136 . 
         [0058]    The mobile client  136  comprises a bearer selector  160  connected to a receiver  162  and a processor  164 . The mobile client  136  further comprises a receiver application  170  that is executed by the processor  164  and consumes content data. The receiver application  170  may, for example, be a mobile TV application. In the mobile client  136 , the bearer selector  160  is functionally arranged between the receiver  162  and the receiver application  170 . Accordingly, the bearer selector  160  acts as a middleware agent during the reception of content services. 
         [0059]    On the stationary network side, the network node  140  comprises a Broadcast/Multicast Service Center (BM-SC)  180  and a bearer topology generator (BTG)  190 . The BM-SC  180  may serve as an entry point for content providers such as the content provider  110  shown in  FIGS. 1 and 2  (i.e., for third party content providers). Furthermore, the BM-SC  180  is adapted to provide service announcements regarding a content service. 
         [0060]    The receiver  162  of the mobile client  136  is adapted to receive the service announcements from the node  140 . The mobile client  136  is furthermore adapted to send a PTP registration for a PTP reception. The BM-SC  180  is adapted to receive and analyze the PTP registration from the mobile client  136 . 
         [0061]    The BTG  190  of the node  140  is adapted to generate the LBT information  150 . In the present embodiment, the BTG  190  comprises a database  192  providing a mapping from PTM areas to one or more access areas of each PTM area. In the MBMS context, this mapping includes a mapping from the MBMS Service Area Identifiers (MSAI) to cell area identifiers. Furthermore, the database  192  stores information regarding operation and maintenance of components in the radio access network  130  in a status register. Alternatively, the mapping and the status register can be stored in different databases. Further alternatively or in addition, status information regarding operation and maintenance of components in the radio access network  130  can be directly requested by the BTG  190  via an operation and maintenance interface  194  from the radio access network  130 . 
         [0062]    The node  140  shown in  FIG. 3  has the BTG  190  co-located with the BM-SC  180  outside the core network  120  to facilitate information exchange between these components. In an alternative embodiment, the BTG  190  is located in the core network  120 , in particular in the SGSN  122  or in a Mobility Management Entity (MME, not shown). In a still further embodiment, the BTG  190  is entirely implemented in the radio access network  130 . 
         [0063]    With reference to  FIG. 4 , an exemplary LBT  400  as defined or generated by the BTG  190  is shown in more detail. In generating the LBT  400 , the BTG  190  may take into account the network status information retrievable from the database  192  or via the interface  194 , and the PTM area defined for a specific content service and stored in the database  192 . Information regarding the LBT  400 , such as the LBT information  150  shown in  FIG. 3 , comprises one or more lists of access area identifiers. Generally speaking, these lists indicate access areas in a direct neighborhood around a current location or access area of a mobile client  136  and furthermore indicate for each listed access area at least one bearer type (and/or bearer identifier) provided by the hybrid network  100  in the specific area. 
         [0064]    In a first embodiment, the LBT information  150  representative of the LBT  400  comprises a first list including access areas of the LBT  400  that provide a PTM-type bearer inside respective PTM areas  134   a.  A second list includes access area identifiers of access areas outside the PTM access areas  134   b,  that provide only PTP-type bearers. A third list of access areas of the LBT  400  indicates border access areas  134   c.  The border access areas  134   c  of the LBT  400  describe a closed “ring” around a central set of access areas covered by the LBT  400 . The border access areas  134   c  may be included in or may be excluded from any one or both of the first list and second list. In the case of including the border access areas, an alternative embodiment of the LBT information  150  comprises an additional attribute (in the first and/or second list) indicating the border access areas. 
         [0065]    The embodiment of the LBT  400  shown in  FIG. 4  uses an inside/outside PTM characteristic as a hybrid criteria of the hybrid network  100 . In another embodiment of the LBT  400 , the LBT information  150  includes an alternative second list of access areas in the LBT  400  indicating whether the corresponding access area provides a PTM-type bearer (independent of the parallel provision of a PTM-type bearer). The latter embodiment of the LBT  400  is an example for a PTM/PTP characteristic describing the hybrid criteria of the hybrid network  100 . In a still further embodiment of the LBT  400 , a fourth list of access areas in the LBT  400  includes access areas providing a DVB-H PTM-type bearer (instead of or in addition to the aforementioned MBMS PTM-type bearer). In still another embodiment of the LBT  400 , additional lists are provided indicating an unavailability of the entire hybrid network  100  or of a specific type of bearer in the access areas belonging to the LBT  400 . 
         [0066]    The LBT information  150  (and LBT  400 ) is either generated individually for the mobile client  136  (or for each request of the mobile client  136 ) or the LBT information  150  and LBT  400  can be default parameters. In the case of an individualized LBT  400 , the shape of the LBT  400  optionally depends on a mobility of the mobile client  136 . The client mobility can be derived from a movement history or movement prediction (direction and speed of the mobile client). Depending on the location of the mobile client, the LBT  400  can be individually shaped as a circle for residential areas or more elliptically in case of road or tracks. The mobile client  136  is able to identify and/or monitor a current access area  134   d  of the mobile client  136 , which is identified by an area identifier (particularly by a cell identifier). Adapting the shape of the LBT  400  depending on the client mobility reduces the number of update requests for LBT information  150  of the mobile client moving along a motorway. 
         [0067]    As regards the mobile client  136 , the main task of the bearer selector  160  is to evaluate the LBT information  150  in order to retrieve information for the current access area  134   d.  The bearer selector  160  selects a preferred or an appropriate bearer or bearer type for the reception of a content service depending on the received LBT information  150  and sends requests for new LBT information  150  if the current access area  134   d  is or becomes a border access area  134   c.  The request for LBT information  150  may include the current access area identifier, particularly the current cell identifier or other location information. Optionally, the request for LBT information  150  further includes the movement history or the movement prediction. 
         [0068]    As regards the receiver application  170  in the mobile client  136 , the functionality of a conventional Electronic Program Guide (EPG) or Electronic Service Guide (ESG) can be enhanced as follows. In existing solutions for mobile TV services, the mobile client  136  receives the EPG, which informs the mobile client  136  that a particular content service is or will be provided via a specific PTM bearer for a PTM transmission. The conventional EPG works fine for streaming content services, such as “nationwide” mobile TV services, which are continuously provided at the times announced by the EPG. However, the conventional technique fails for regionally adapted content services, since the information provided by the EPG is independent of the current location of the mobile client  136 . 
         [0069]    The enhanced ESG is adapted to the current access area  134   d  of the mobile client  136  and indicates for a certain content service the bearer or bearer type providing this content service. As a result, a list of available content services can be generated and displayed by the receiver application  170  to a user of the mobile client  136 . For example, in a rural access area where PTM-type coverage is not efficient, mobile TV services are indicated as available on a PTP-type bearer. Content services which are regionally adapted are included in this list according to the current location of the mobile client  136 . Accordingly, content services which are not offered in the current access area of the mobile client  136  may be removed from the enhanced ESG. 
         [0070]    Another advantage arising from the LBT  400  as well as the enhanced ESG is the reduction of power consumption and start-up time. A conventional mobile client  136  cannot detect if the access area  134 , to which the mobile client  136  is currently connected provides a PTM bearer. Thus, the conventional mobile client  136  loops a continuous bearer monitoring which consumes battery power in vane while resting in an access area that provides no PTM bearers. This problem arises in particular for conventional hybrid mobile TV clients, which are required to check on the PTM-type bearer whether the content service is provided in order to detect an opportunity of switching to the preferred PTM transmission. For example, a conventional mobile TV client  136  residing in a rural access area where PTM-type bearers are permanently unavailable (for example, a client with a “home zone” in the rural access area) unnecessarily wastes battery and start-up time checking the broadcast bearer. This problem is solved by the LBT  400  and/or the enhanced ESG, which provides the correct bearer type. The enhanced ESG beneficially combines with the LBT  400  since the mobile client  136  may request an ESG update triggered by the bearer selector  160  when the received LBT information  150  indicates a change in the bearer type. 
         [0071]    As regards the node  140  in the hybrid network  100 , the BTG  190  maintains the database  192 , or has (in a limited embodiment of the BTG  190 ) at least access to the database  192 . The database  192  furthermore includes geographical data of the access areas  134  for adapting the shape of the LBT  400  and indicating border access areas. 
         [0072]    An overview of method steps in a signaling interaction between a mobile client  136  and a node  140  of the hybrid network  100  is shown in  FIG. 5 . As already shown for the system embodiment  300  in  FIG. 3 , the node  140  comprises a BM-SC  180  and a BTG  190 . The node  140  is connected by Core Network (CN)  120  and Radio Access Network (RAN)  130  with the mobile client  136  comprising a bearer selector  160  and a receiver application  170 . 
         [0073]    The BM-SC  180  registers a new service with the BTG  190  providing a service identifier (ID) and a MBMS Service Area (MSA) in step signaling  501 . The latter information is stored by the BTG  190  in the database  192 . In signaling step  502 , the BM-SC  180  publicly announces the content service providing, amongst other information, the service identifier. The service recently registered with the BTG  190  causes the BTG  190  to request cell identifiers corresponding to the MSA Identifier (MSA-ID) of the recently registered content service as shown in signaling step  503 . In response, the radio access network  130  provides to the BTG  190  in signaling step  504  the requested cell information corresponding to the MSA, including its status information. The provided cell identifiers and provided cell locations are stored by the BTG  190  in the database  192 . Based on such information, the BTG  190  (gradually) generates a complete network topology (that forms the basis for generating LBTs) in step  505 . 
         [0074]    The reception of a content service is initiated by a user  195  of the mobile client  136  as shown in step  506 . The user  195  interacting with the receiver application  170  (and, optionally, an ESG or EPG) determines the content service to be requested. The corresponding service identifier is handed over from the receiver application  170  to the bearer selector  160  in step  507 . The bearer selector  160  determines the current access area  134   d  of the mobile client  136  (particularly the cell identifier) and optionally the movement history or movement prediction of the mobile client  136 . The bearer selector  160  sends a request for LBT information including the current cell identifier and the service identifier and the optional mobility information as shown in signaling step  508  to the node  140 . 
         [0075]    The request is received by the BM-SC  180  (managing at least a subset of the multi-media services provided by the hybrid network  100 ), which resolves the service identifier using a MSA identifier list and forwards the information in signaling step  509  to the BTG  190 . In step  510 , the BTG  190  determines the requested LBT information. 
         [0076]    In case of a default LBT information (i.e., of default LBTs), the LBT information  150  is retrieved from a database (not shown) depending on the access area  134   d  (in particular depending on the cell identifier received with the LBT request in step  508 ). In case of individually generated LBT information (i.e., of client-individual LBTs), the BTG  190  generates the LBT information depending on the client location and/or mobility information. 
         [0077]    In case the LBT request includes mobility information (e.g., a mobility prediction), the BTG  190  adapts the shape of the LBT  400  to be elongated along a predicted trace. In case the mobility information includes the movement history, the BTG  190  calculates an expected future location of the mobile client  136  based on the movement history. For example, if the mobile client  136  rarely moves according to the movement history, the shape of the LBT  400  is set to a small circle area around the location of the mobile client  136 . In case of the absence of the optional movement information, the shape of the LBT is set to a default shape. Optionally, the BTG  190  compares the received cell identifier with location context information to adapt the shape of the LBT  400  according to the location context information. The location context information may be indicative of specific geographical or infrastructure features of the current location of the mobile client  136 . For example, if the corresponding cell covers a motorway, the shape of the LBT is elongated in the direction of the motorway. 
         [0078]    The BTG  190  requests those access areas (particularly, those cell areas) of the MSA corresponding to the service identifier from the database  192  within the LBT  400  as determined before. Based on those access areas, the BTG  190  generates a first list for the LBT information  150  indicating the availability of the content service via the PTM-type bearer. Then, the BTG  190  requests all other access areas (particularly cell areas) from the database  192  within the LBT. For these access areas, the BTG  190  generates a second list indicating the availability of the content service via the PTP-type bearer. Finally, based on the geographical information in the database  322  for the access areas in the LBT, the BTG  190  identifies border access areas of the LBT. Based on the these border access areas, the BTG  190  generates a third list. 
         [0079]    In step  511 , the BTG hands the LBT information  150  comprising the three lists to the BM-SC  180 , from where it is sent via the CN  120  and RAN  130  to the mobile client  136 . In the mobile client  136 , the LBT information  150  is passed to the bearer selector  160  in step  512 . The bearer selector  160  continuously monitors the identifier of the current access area of the mobile client  136  as shown in step  513 . Monitoring the current access area identifier by the bearer selector  160  can be combined with the conventional Mobility Management (MM) procedures. From the received LBT information  150  (i.e., from the one or more lists), the bearer selector  160  determines which bearer type is currently available. In case of a change in the availability of the current bearer or if a movement prediction indicates a future change of the currently available bearer, the bearer selector  160  performs bearer selection in step  514  by signaling the change to the receiver application  170  in step  515 . In case the bearer selector  160  finds the current cell indicated as a border cell of the LBT, the bearer selector  160  requests new LBT information repeating signaling step  508 . 
         [0080]    As has become apparent from the above embodiments, the technique presented herein provides various advantages. First of all, the technique can be integrated with already existing and wide spread technologies as shown with reference to  FIGS. 1 to 3 . In any case, the mobile client  136  gets informed regarding the local bearer topology  400 . This is in particular beneficial to receive all transmission sessions of a hybrid Push Broadcast Service. Based on the bearer selection, the mobile client receives seamlessly and undelayed content data of the content service. The mobile client may furthermore be informed regarding regionally available bearer types which combines beneficially with the enhanced ESG indicating regional content services. 
         [0081]    The amount of signaling data is minimized as the mobile client  136  can move autonomously in the area covered by the LBT. There is, furthermore, no need for evaluating reception reports for the typically very large group of mobile clients  136  receiving a mass content service. The amount of signaling data is reduced in total, and the frequency of updates for LBT information are adapted to the client mobility. 
         [0082]    Eventually, the energy consumption of the mobile client is reduced, since reception of PTM bearers can be disabled if the unavailability of the PTM-type bearer is indicated for the current access area in the LBT information. 
         [0083]    In the foregoing, the principles, preferred embodiments and various modes of implementing the techniques disclosed herein have exemplarily been described. However, the present invention should not be construed as being limited to the particular principles, embodiments and modes discussed above. Rather, it will be appreciated that variations and modifications may be made by a person skilled in the art without departing from the scope of the present invention as defined in the following claims.