Patent Publication Number: US-8125945-B2

Title: Datacast services

Description:
TECHNICAL FIELD 
     This invention relates to a mobile terminal and to a method of operating a mobile terminal. The invention relates also to datacasting apparatus and to a method of datacasting. 
     BACKGROUND 
     Much has been written about the incorporation of digital broadcasting receivers into mobile handheld terminals, such as mobile telephones, personal digital assistants (PDAs), laptop computers and the like. 
     A system has been proposed in which data services are transmitted on a time-sliced, or time-multiplexed, basis allowing plural services to be transmitted at a given channel frequency. This has advantages for mobile terminals since their receivers only need to be powered and they only need to buffer, decode and process received data when data relating to the service of interest is being broadcast, and can be switched off at other times. This would normally result in a receiver being switched on for a relatively short period at regular intervals. 
     The present invention aims to provide a mechanism whereby the power consumption of data broadcast receivers can be further reduced. 
     SUMMARY 
     A first aspect of the invention provides a receiver terminal suitable for operating in a system in which plural service components of a service are datacast sequentially within a burst, the terminal being arranged to detect which of the service components are required to be received, and to enable a receiver in the terminal to receive signals at one or more times in a burst period corresponding to the required service components, and to disable the receiver for substantially the remainder of the burst period. 
     Typically, the terminal will arranged to enable and disable the receiver on the basis of received timing information identifying the timing of transmission of service components, although it may instead be able to derive timing information from the service components themselves. 
     In one embodiment the terminal is arranged to detect which of the service components are required to be received on the basis of a comparison of receiver capability information and received service component data type information. Here, the terminal can be arranged to source the service component data type information on the basis of a received service component identifier. 
     In another embodiment the terminal is arranged to detect which of the service components are required to be received on the basis of a comparison of receiver to classification information and received service component classification information. The service component classification information can relate merely to a level, e.g. high, medium or low capability, or may be more specific as to receiver requirements, for example requiring more than a specified amount of ROM or RAM or specific display or decoding characteristics. Regardless of what the service component classification information relates to, the terminal can be arranged to source the received service component classification information on the basis of a received service component identifier. 
     Sourcing any of the above mentioned information on the basis of a received service component identifier allows for simple datacasting, and allows complexity to be built into the receiver terminal only if it is required, with receiver terminals not arranged as above being able easily to ignore the received service component identifier. 
     The receiver classification information might be determined by a setting of the terminal. In this case, the classification setting can be automatically adjustable in dependence on one or more terminal parameters. The setting may alternatively or additionally be adjustable manually. In any case, adjustment of the receiver classification setting may be upwards or downwards. 
     In one embodiment the terminal is arranged to notify characteristics of the terminal to a remote station. In any case, the terminal may be arranged to notify a service being consumed to a or the remote station. 
     The receiver terminal might be a mobile, handheld terminal, but this is not critical to the invention, although mobile terminals clearly have certain advantages. 
     According to a second aspect of the invention, there is provided a method of operating a mobile terminal in a system in which plural components of a service are datacast sequentially within a burst, the method comprising: detecting which of the service components are required to be received; and allowing signals to be received and processed at one or more times in a burst period corresponding to the required components, and disallowing signal reception and processing for substantially the remainder of the time in the burst period. 
     According to a third aspect of the invention, there is provided datacast apparatus comprising: a sequencer arranged to organise service components relating to a service sequentially in a burst, different service components within a burst including content data of different data types; a metadata handler arranged to organise, separately from the content data, metadata dependent on the data type of each service component; a timing data handler arranged to organise timing data from which a receiver terminal can determine the times of datacast of the service components within a burst; and a datacaster arranged to datacast the service components, the metadata and the timing data. 
     The metadata can identify a class of receiver, or alternatively the metadata can identify the data type of the corresponding service component, for example. 
     Whether or not the metadata identifies such a class or data type, the metadata can identify the corresponding service component. This can allow a receiver terminal to determine the data type or classification using another data source, for example a webpage of a datacast operator if this is required. The data type or classification information may instead be sourced from another suitable information source. 
     The metadata can be datacast as part of the corresponding service component, for example as part of a header thereof. This is advantageous since it does not require receiver terminals to receive data transmitted on other bearers. However, in some embodiments the metadata can instead be datacast on a different bearer to the service components. 
     In any case, the metadata may be datacast as part of a PSI/SI table, or it may take any other suitable form. 
     In one embodiment the sequencer may be constructed to arrange the service components relating to a service in an order dependent on a perceived priority. In this case, service components having a higher priority can be grouped together, and services having a lower priority can be arranged before and/or after the service components having a higher priority. Alternatively or additionally, service components can be arranged in an ascending or descending priority order. 
     The datacasting apparatus might be arranged to use received data identifying the characteristics of one or more receivers associated with a service to determine the priority of the service components relating to that service. 
     A fourth aspect of the invention provides a method of datacasting, comprising: datacasting service components relating to a service sequentially within a burst the service components including content data of different data types; datacasting, separately from the content data, metadata dependent on the data type of each service component; and datacasting data from which a receiver terminal can determine the times of datacast of the service components within a burst. 
     The term ‘datacasting’ will be understood to mean the broadcasting or multicasting of data, and the term ‘datacast’ will be interpreted accordingly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, of which: 
         FIG. 1  is a schematic illustration of the components of a data broadcasting station according to certain aspects of the invention; 
         FIG. 2  is a diagram schematically illustrating a signal provided by the  FIG. 1  station; and 
         FIGS. 3 and 4  are schematic drawings of mobile receivers according to certain aspects of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , datacast apparatus  10  is illustrated in schematic form. The datacast apparatus  10  in this example is configured to provide data suitable for broadcast or multicast over a DVB-T (terrestrial digital video broadcasting or DVB-H (hand held DVB) link. However, the datacast apparatus  10  may alternatively relate to any other kind of datacasting system. The datacast apparatus  10  includes generally an input  11  over which service component files are received from one or more service operators, an encapsulation and multiplexing device  12  and a broadcast transmitter  13 . In the illustrated example the broadcast transmitter  13  is shown as forming part of the same apparatus, i.e., is at the same physical location, as the encapsulation and multiplexing system  12 , but in other embodiments the components  12  and  13  may be located within separate hardware devices, which may be local to each other or remote from each other. The datacasting apparatus  10  further includes a timing data subsystem  14 , which is connected to be in bi-directional communication with the encapsulation and multiplexing system  12 . The datacast transmitter  13  receives data from the encapsulation and multiplexing system  12  and modulates it onto a radio frequency carrier before transmission in accordance with the relevant DVB standards. 
     Put simply, the datacasting apparatus  10  is arranged to receive service component files relating to plural services, to arrange service components relating to a given service sequentially in a data stream, to provide each of the service components with an appropriate header if one is not already present, to multiplex the different services together, to provide the services and service components with appropriate timing data, and datacast the resulting data for reception by receiver terminals within the range of the transmitter station  13 . There are a number of ways of achieving this, some of which are described in more detail below. 
     A signal datacast by the  FIG. 1  apparatus is illustrated in  FIG. 2 . Here, the horizontal axis is linear and represents the progression of time. In respect of a first service (marked ‘service  1 ’) first to fourth service components  20  to  23  are transmitted sequentially. The service components  20  to  23  have transmission periods of various lengths in this example, although this is not critical. The first service component  20  begins transmitting at a time T(c,t) and the fourth component  23  begins transmission at time T(c+3,t), with the second and third service components  21  and  22  having transmission start times at T(c+1,t) and T(c+2,t) respectively. Each of the service components  20  to  23  includes a content payload and a header. The header sections for the service components  20  to  23  are illustrated at  25  to  28  respectively, and the payload sections are indicated at  29  to  32  respectively. In this example, the first service component  20  comprises video data, the second service component  21  comprises audio data, the third service component  22  comprises auxiliary data and the fourth service component  23  comprises data constituting an enhanced video layer. 
     In respect of a second service (marked as ‘Service  2 ’), first to fourth service components  34  to  37  are illustrated. Although not shown, each of the service components  34  to  37  also has a header section and a content payload section. Here, the first and second service components  34  and  35  are video and audio data service components respectively, the third service component  36  contains JPEG image data and the fourth service component  37  comprises a part of an executable program file. 
     Following the first to fourth service components  34  to  37  of the second service, there may be service components in respect of one or more further services (not shown) before a time T(c,t+1) at which a first service component  38  is transmitted in respect of a second burst and in connection with the first service. The interval between the time T(c,t) at which the first service component of the first service of the first burst is begun to be transmitted at the corresponding time T (c,t+1) in the next burst is known as the burst period. In IPDC (Internet Protocol datacasting) for DVB-T or DVB-H, the burst period is substantially constant, although this may not be the case for other datacasting systems. 
     Furthermore, the transmission length of the service components  20  to  23  of the first service may be the same for each of the burst. However, the transmission duration of the service components can be varied between bursts if this is required. 
     In this embodiment, the headers  25  to  28  each include metadata which describes the type of data in the corresponding payload content section  29  to  32  of the service component  20  to  23 . Also datacast is timing data which identifies the start time of each of the service components  20  to  23  and  34  to  37  forming part of the IPDC services. This timing data may be transmitted in any suitable way, for example in the header or in the payload of the service components, or separately to the service components, for example as part of the PSI/SI data table associated with the IPDC transmissions. The timing data can be included in a header at any level in the system, for example a burst header, a packet header or the illustrated service component header. This timing data may take any suitable form. For example, it might identify in absolute terms the start time of the transmission of a service component in one burst and identify the inter-burst interval, allowing the start times of the corresponding service components in successive bursts to be unambiguously calculated. Alternatively, the start time of the transmission data corresponding to the service components may be stated relevant to any time which is known to the transmitter station  13  and which can be identified by a receiver station. The exact way in which the start times of the transmissions of the service components elements is calculated by a receiver station is not critical to the invention so is not described in detail here. 
     The timing data is used along with the metadata included in the headers  25  to  28  by a receiving terminal in order to switch on its receiver only at times in a burst period when required service components are incident, and to disable the receiver for substantially the remainder of the burst period, as will now be described with reference to  FIG. 3 . 
     A terminal  39  is shown schematically in the form of a combined mobile telephone handset and DVB-T receiver. Since the terminal  39  includes a receiver it can be termed a receiver terminal. 
     In one embodiment, the receiver terminal  39  includes first and second antennas  40 ,  41 , which are connected to a DVB-T receiver  42  and a mobile telephone transceiver  43  respectively. The receiver  42  and the transceiver  43  each include RF signal processing circuits (not shown) for amplifying and demodulating received signals and one or more processors (not shown) for channel decoding and demultiplexing. 
     The receiver terminal  39  also includes a controller  44 , a user interface  45 , one or more memories  46 , a coder/decoder (codec)  49 , a speaker  50  with a corresponding amplifier  51  and a microphone  52  with a corresponding pre-amplifier  53 . The receiver  42  and the transceiver  43  operate under control of the controller  44 . 
     The user interface  45  includes a display  53  and a keypad  55 . The display  53  is adapted for displaying images and video by, for instance being larger and/or having greater resolution than a display of a conventional mobile telephone and being capable of presenting colour images. The receiver terminal  39  also includes a power source in the form of e.g. a rechargeable battery  56 , to provide DC power. 
     The controller  44  manages operation of the receiver terminal  39  under the direction of software (not shown) stored in one of the memories  46 . The controller  44  provides output signals for the display  53  and receives and processes inputs from the keypad  55 . 
     In another embodiment, the receiver terminal  39  is modified by providing a single receiver adapted to receive signals from the DVB-T network and mobile telephone networks and a transmitter adapted to transmit signals on the mobile telephone network (not shown). In a further embodiment, a single transceiver is provided for both communication over both networks. 
     The controller  44  is arranged to extract the metadata identifying the service components data type from the header  25  to  28 , and to isolate the timing data, which is discussed above. The controller  44  uses knowledge of the capabilities and configuration of the mobile terminal  39  to determine which of the services components  20  to  23  are required to be received. This may be carried out in any suitable manner. For example, the controller  44 , knowing that the resolution of the display  53  is not sufficient for high definition video presentation to be noticeably better than normal video presentation, may determine that the enhanced video layer service component  23  is not required. In this example, the controller  44  also uses to knowledge that the receiver terminal  39  is not provided with software enabling the provision of multi-language subtitles, to make a determination that the third service component  22  carrying multi-language subtitles is not required to be received. The controller  44  in this instance decides that the first and second service components  20  and  21  are required to be received, because the mobile terminal  39  has the capability to utilise the video and audio data from the content payloads  29  and  30 . 
     Following determination of which service components are required to be received, the controller  44  controls the DVB-T receiver  42  to be switched on to receive data between the times T(c,t) and T(c+2,t) and also during the corresponding points in time in successive burst periods. The controller  44  controls the DVB-T receiver to be switched off for other times in the burst periods and accordingly also does not perform data buffering or processing. In this way, the DVB-T receiver  42  is switched on only when data relating to the required service components are incident on the antenna  40 , and is disabled at all other times. This means that power from the rechargeable battery  56  is used to receive and process the required service components  20 ,  21  and is not used to receive and process the service components  22  and  23  which are not required. 
     In an alternative embodiment, the receiver terminal  39  is provided in a form of a personal digital assistant (PDA), and will now be described, again with reference to  FIG. 3 . The PDA  39  has all of the components of the mobile terminal of  FIG. 3 , although here the keypad  55  may be provided instead by way of a touch screen and stylus input, and the display  53  has considerably larger dimensions than the corresponding display of the mobile telephone. 
     On receiving the signal shown in  FIG. 2 , the PDA  39  determines that the first and second service components  20  and  21  are required to be received, as with the mobile telephone embodiment described above. However, the PDA  39  determines also that the display  53  is sufficient for it to be worthwhile to utilise the payload content  32  of the enhanced video layer service component  23 . The controller  44  determines that the PDA  39  does not have the software to utilise effectively the auxiliary data payload content  31  of the third service component  22 . 
     Using this determination of which of the service components are required to be received, the controller  44  controls the DVB-T receiver  42  to receive the first, second and fourth service components  20 ,  21  and  23  for each of the burst periods of the  FIG. 2  signal. In this way, the DVB-T receiver  42  may be switched off when the third service component  22  is incident on the antenna  40 , and power from the battery  56  is not unnecessarily spent receiving and processing the data forming part of the third service component  22 . However, if the transmission duration of the third service component  22  is short, it might be convenient to keep the receiver switched on. 
     If the PDA  39  is not required to operate as a mobile telephone, the transceiver  43  and the antenna  41  may be omitted, along with, the microphone  52  and the amplifier  53 . The loudspeaker  50  may also be omitted if the PDA is provided with a headphone jack instead, although this embodiment is not illustrated. 
     An alternative embodiment is illustrated in  FIG. 4 . Referring to this Figure, a laptop computer  59  is illustrated comprising generally a microprocessor  60 , which is connected to each of a display  61 , which could be a TFT display or any other type, one or more speakers  63 , a keyboard  64 , RAM  65 , ROM  66  and a hard drive  67 . The laptop computer  59  is mostly conventional, except that it is provided with a DVB-T or DVB-H receiver  68 , which receives DVB datacast transmissions through an antenna  69 . Also, the ROM  66  is provided with a program allowing the microprocessor  60  to effect suitable control of the DVB-T receiver  68  and to present audiovisual data using the display  61  and the speaker  63  under control of a user interface, which includes the keyboard  64  and the display  61 . 
     In this embodiment, the microprocessor  60  operates similarly to the controller  44  of  FIG. 3 . In particular, the microprocessor  60  determines from the metadata included in the headers  25  to  28  and from its capabilities and configuration that each of the first to fourth service components  20  to  23  contains data which is required to be received and utilised by the laptop computer  60 . Accordingly, the microprocessor  60  controls the DVB-T receiver  68  to receive and process signals received between the times T(c,t) and T(d,t) and between the corresponding times in successive burst periods. The microprocessor  60  is therefore provided with the payload contents data  29  to  32  from each of the first to fourth service components  20  to  23 , and is able to utilise this in providing an output at the display  61  and the speaker(s)  63 . 
     The mobile telephone or PDA  39  and the laptop computer  59  can determine what service components are required to be received on the basis of software and/or hardware capabilities. For instance, if a service component contains content payload data which is an MPEG4 file, MPEG4 decoding software is required in the mobile terminal  39 ,  59  in order to utilise the data. Accordingly, if the mobile terminal  39 ,  59  does not have MPEG4 decoding software, then the corresponding service component will be deemed to be not required and thus the receiver  42 ,  68  will be controlled by the controller  44 ,  60  not to be switched on during the transmission of that service component. Similarly, MP3 decoding software is required to decode MP3 files, and JPEG decoding software is required to decode JPEG files. 
     If a service component comprises part of a data file, the corresponding header of that service component then preferably includes metadata identifying the total size of the file. In this way, the receiver terminal  39 ,  59  can determine whether or not it has sufficient memory to store the entire file (which is transmitted over a series of bursts), and is arranged to receive service components relating to that data file only if sufficient memory is present. Such a situation may occur when the file is an executable programme file, for example, a game, or a document file such as a PDF file or a spreadsheet or a word processor file. In the event that the file is an executable programme, it is likely that a certain amount of RAM will be required to execute the program. In this case, the amount of RAM required to execute the program is included in the metadata as well as the size of the file, so that the receiver can determine whether or not it has the capabilities to execute the program. 
     In an alternative embodiment, the metadata does not identify directly the data type of the corresponding payload content data. Instead, the metadata may identify a class of receiver terminal which is required to consume the data. In a simple example, there may be three classes of receiver terminal capabilities, namely a limited receiver, a medium receiver and a high-end receiver. In this example, each receiver  39 ,  59  can be fed with data identifying the class to which it belongs. In order to be classified as a medium level receiver, a receiver must contain all of the software and hardware capabilities required to utilise the data which is classified by the IPDC operator into the medium class. Corresponding requirements apply to the high-end and limited receiver classes. On decoding the class information from the header of a received service component, the receiver terminal  39 ,  59  can compare this to the receiver classification in order to arrive at a determination as to whether the corresponding service component is required to be received and processed or not. If the receiver is classified as a limited receiver, it is arranged only to receive service components for which the header identifies that a limited receiver class is suitable. A medium class receiver is arranged to receive and process service components for medium and limited class receivers, and so on. 
     The receiver capabilities required to meet one of the classifications may be made available to the mobile terminal  39 ,  59  in any suitable manner. For example, the classification may be pre-programmed into the receiver terminal  39 ,  59  before sale. Alternatively, or in addition, the information could be datacast along with the transmitted content, or be datacast on another channel. Alternatively, this information could be available on a webpage operated by the operator of the datacasting apparatus  10 . The information may be retrievable from another source in any suitable way, for example as an SMS or MMS reply to an MMS or SMS request to a telephone number designated by the operator. The exact mode of informing the mobile receiver  39 ,  59  of its classification or the requirements needed to be met to have a classification is not important to the invention. 
     If required, the classification of the receiver terminal may be made available to a user. This information may be available through a menu option, or alternatively it could be presented on the display  53 ,  61  when the receiver classification has been determined by the controller  44 ,  60 . In one embodiment the classification of the mobile terminal  39 ,  59  can be changed. The classification may be changed by a user through the user interface provided on the receiver  39 ,  59 . Alternatively, or in addition, the classification may be changed by the controller  44 ,  60 . If, for example, it is determined that the remaining power resources of the mobile terminal  39 ,  59  are low, the controller  44 ,  60  may automatically downgrade the classification of the mobile terminal. Downgrading the classification in this way results in fewer service components being deemed relevant, and thus fewer service components are received and processed. This results in reduced power consumption, thereby increasing the amount of time before the power remaining is insufficient to allow the mobile receiver terminal  39 ,  59  to remain switched on. 
     The classification of the receiver terminal  39 ,  59  may be changed also if, for example, the amount of available ROM or RAM falls below a threshold, which results in the receiver terminal  39 ,  59  falling into a lower classification than previously experienced. 
     Similarly, in another embodiment the receiver terminal  39 ,  59  is operable to allow the classification to be upgraded. The classification may be upgraded if a hardware or software upgrade allows the receiver terminal  39 ,  59  to meet the requirements of a higher classification. Also, the PDA  39  may include many of the hardware and software capabilities which are required to be classified as a high-end receiver but be missing one or more essential capabilities so cannot be classified as a high-end receiver. However, this does not mean that the PDA  39  is unable to receive and consume the content of all service components which are classified as being usable by high-end receivers, merely that such cannot be guaranteed. Accordingly, allowing a user to upgrade manually the classification of a receiver terminal  39 ,  59  may mean that the user can be presented with content which the PDA  39  is able to consume but which is classified to a higher classification than that to which the PDA is entitled. Of course, if any received and processed service components contain data which the PDA  39  is not equipped to consume, then the PDA  39  will not be able to consume that data. In this case, the PDA  39  may inform the user of this, or alternatively this may be transparent to the user. 
     Furthermore, if the classification of the receiver terminal  39 ,  59  is above the most basic classification, the user may be provided with an option to select the desired classification. Allowing the classification to be selected by the user in this way is advantageous since it allows the user to influence the rate of power consumption, allowing him or her to choose between rich content and extended battery life. If the user has the option of selecting between three or more classification options, then this may allow the user to select between extremes of extended battery life and richness of content, and also one or more compromises. 
     Instead of, or as well as, the broadcast data including information which identifies a classification of receiver which is required to consume the content of the service component or data indicating the type of data within the service component, each service component may include a component identifier. Such an identifier needs to uniquely identify the service component from other service components which are not provided with classification information or data type metadata. A receiver terminal  39 ,  59  can use the component identifier to determine from an operator&#39;s web page, or from any other suitable information source, either the data type or the classification of receiver required to consume the corresponding service component. 
     The datacasting apparatus  10  is arranged to select an order for the service components within a timeslot relating to a service dependent on the actual or assumed characteristics of the receiver terminals which are receiving the service, as will now be described with reference to  FIG. 1 . Connected to receive the service component files from the input  11  and in parallel to the encapsulation and multiplexing system  12  is a component analyser  15 . The component analyser  15  examines the data forming part of each of the service components received at the input  11  and determines therefrom the data type thereof. This may occur in any suitable manner. At one extreme, the component analyser  15  may apply the received data to plural software emulators, each emulating a different data consumption program, until one of the software emulators is found to produce usable content as its output. By determining which emulator has a satisfactory output, it can be determined what data type the corresponding service component is. At the other extreme, the component analyser  15  may simply read data forming part of the service component files or attached to the service component files which identifies in unambiguous terms the type of data in the corresponding service component. Any other scheme may be used instead. 
     If the service component files received at the input  11  of the datacasting apparatus  10  do not indicate the data type to which the service components relate, then the component analyser  15  is arranged to provide metadata indicating the data type of the service components. This metadata is used by the encapsulation and multiplexing system  12  to provide a header for each of the service components which identifies the data type of the corresponding service component. Of course, this is only carried out if it is required to provide the datacast service components  20  to  23  with data particularly identifying the data type of the corresponding service component, which is not true in all embodiments. 
     A component classifier  16  is connected to receive data from the component analyser  15 . The component classifier  16  is arranged to determine on the basis of the metadata produced by the component analyser  15  what class of receiver terminal is required to consume the content of the corresponding service component. This information along with the metadata identifying the service component data type is passed from the component classifier  16  to a receiver configuration classifying and analysing module  18 . 
     A receiver configurations database  17  is connected to receive configuration information from all of the receiver terminals which are consuming a service datacast by the datacasting apparatus  10  and which choose to notify their configurations to the apparatus. The database  17  is divided into a number of sections (not shown), one section for each of the services which are handled by the datacasting apparatus  10 . The exact form of the receiver configuration data is not critical to the invention. In one example, it comprises information identifying the hardware and software capabilities of the receiver and an identification of the type of service (or services) which the corresponding receiver terminal is consuming. The level of detail provided concerning the hardware and software capabilities determines the amount of analysis processing which is required to be performed by the datacasting apparatus  10 . The amount of detail also determines the quantity of data which needs to be transmitted from the receiver terminal  39 ,  59  to the datacasting apparatus  10 . This is particularly important if the communication channel used is a mobile telephone network. GPRS is seen as a particularly convenient channel for the communication of this information, although it may be communicated instead by SMS, MMS or using any other suitable communication channel. To minimise the amount of data communicated, the receiver configuration data can be stored permanently in the database  17 , and notification then is made by receiver terminals as to their identity and the service(s) that they are consuming. Changes in receiver configuration may also be notified. 
     The receiver configuration classifying and analysing module  18  uses data provided by the component classifier  16  and the receiver configurations database  17  to determine the most appropriate order for the service components. This is carried out for each of the services. The exact algorithm used to determine the most appropriate service component order is not critical to the invention. The resulting order is passed to the encapsulation and multiplexing system  12 , which arranges the service components in the appropriate order. 
     If data type information is required to be provided in the datacast and this information is not provided with the service component files received at the input  11 , it is provided by the component classifier  16  directly to the encapsulation and multiplexing system  12 , where type data is included appropriately in the transport streams fed to the datacast transmitter  13 . 
     The receiver terminals  39 ,  59  may be arranged to notify their configurations and/or services which they are consuming to the datacasting apparatus  10  in any suitable manner. For example, this may be triggered by the inclusion in a datacast signal of an instruction to notify, or it may be performed periodically or on any other suitable basis The notification of receiver characteristics and service consumption data may be transparent to the user. However, if notification incurs a cost to the user, for example, through utilisation of a chargeable mobile telephone channel, then the receiver terminal  39 ,  59  may require acknowledgement from the user before providing notification of receiver characteristics to the datacasting apparatus  10 . 
     The receiver terminals  39 ,  59  may also subscribe to services or bundles of services using a mobile telephone network (not shown), for example, using WAP or SMS or MMS or any other suitable scheme. 
     It is not essential that the datacasting apparatus  10  has knowledge of the characteristics and capabilities of the receiver terminals which are consuming services. In the absence of this information, the apparatus  10  can estimate the likelihood of each service component being usable by the relevant receiver terminals. This can occur in any suitable manner. 
     The datacasting apparatus  10  preferably is arranged to organise the service components relating to a service in an order such that service elements which are consumable by fewer receiver terminals  39 ,  59  are positioned at the beginning or the end of the sequence, but not at both ends. This is advantageous since it maximises the probability that a receiver will be needed to be switched on and switched off only once during each burst period. In particular, a basic receiver may be able to consume only the first and second service components  20  and  21  relating to the first service shown in  FIG. 2 . Since these service components  20  and  21  are adjacent, the basic receiver terminal need only to switch on its receiver once during a burst period. The inclusion of the third service component  22  which is considered in this instance to be more likely to be consumable than the fourth service component  23 , is placed adjacent to the second service component  21 . 
     Thus, a medium classification receiver terminal, such as the PDA  39 , described with reference to  FIG. 3 , can receive the first to third service components  20  to  22  and no other service components by switching on and switching off once within the burst interval. The fourth service component  23 , which is deemed to be the least likely to be consumable by a receiver terminal  39 ,  59  is included at the periphery of the group of service components  20  to  23 . 
     It will be appreciated that the service components which are most likely to be consumable by a receiver terminal are not in all embodiments of the invention included in the beginning of the sequence, since it is equally feasible that the order of the service components  20  to  23  could be reversed. In this case, a basic receiver would be switched on later than the switch-on time of a higher-end receiver, although the receivers would be switched off at the end of the same service component. Another alternative would be to include the service components which are most likely to be consumed in the middle of the timeslot allocated to a given service and to arrange the services less likely to be consumable by a receiver terminal before and after those more popular service components. This embodiment is particularly advantageous where there are service components which do not necessarily relate to different receiver classifications but which require different software and/or hardware for their consumption. 
     The service components within a service are ordered by the encapsulating multiplexing system  12  according to any of the above described schemes. It will be appreciated that the encapsulation and multiplexing system  12  also includes either data identifying the classification of each of the service components or alternatively the data type of the service components, as well as metadata identifying the transmission times of the service components, in the transport streams sent to the datacast transmitter  13 . The timing data is provided by the timing data subsystem  14 . This subsystem  14  receives from the encapsulation and multiplexing system  12  information identifying the sizes of the data files constituting the content payloads of the service components and information identifying the ordering of the service components within a time slot relating to a service, and calculates the timing data therefor. Data is passed in both directions between the metadata and timing data subsystem  14  and the encapsulation and multiplexing system  12 . The resulting transport streams are passed from the encapsulation and multiplexing system  12  to the data transmitter  13 . 
     The ordering of the service components within a timeslot relating to a given service may be dependent also on the size of the service component, i.e., dependent on the amount of data included in each of the service components. In particular, larger service components may receive a higher priority such that they are more likely to be transmitted earlier in a timeslot than later in a timeslot. However, it is preferred that the data type of the service components is taken into account as well as the size of the components in determining the order of transmission within a burst. 
     To maximise the ease of reception by a receiver terminal  39 ,  59 , the order of the service components preferably is the same within the consecutive bursts. However, the order of the service components may vary between bursts in some circumstances. 
     Another example of a service component which may be usable by some receivers but not all receivers occurs when forward error correction (FEC) is used. For example, the data comprising the video and audio service components  20  and  21  of the first service shown in  FIG. 2  may be subjected to MPE-FEC (multiprotocol encapsulation-FEC), and the resulting parity data provided as the fourth service components  23  in place of the enhanced video layer service component shown. Here, a special decoder, such as a Reed-Solomon decoder is required in the receiver terminals  39 ,  59  in order for error correction to be properly carried out. Accordingly, the FEC parity data service component  23  is usable by some but not all of the receiver terminals  39 ,  59  receiving and decoding this service. FEC decoding capability may be required for a receiver terminal  39 ,  59  to be classified as a high-end receiver, although it will be appreciated that this is not essential. 
     The above described embodiments are not intended to be limiting to the scope of protection conferred. For example, although the embodiments relate to a DVB-T broadcast/datacast network, the invention is not limited to such. The invention instead may be implemented using ISDB-T (Integrated Services Digital Broadcasting Terrestrial) or the US ATSC (Advanced Television Systems Committee) system, or any other kind of broadcast data system. 
     Also, although four service components are shown for each service, this is just an example, and any number of service components may be used instead. Different services may also have different numbers of service components. 
     In some embodiments described above, the relative order of the transmission of the service components and the timing data is included in the header of the service components, so can be considered to be inband with the signalling of the bearer. However, this information could be provided out of band, for example, by the inclusion of appropriate information in a PSI/SI table or any other suitable way. In this instance, it is not necessary to provide headers in the manner described above, although it is necessary instead to ensure that the appropriate information is made available to the receiver terminals requiring a service. Alternatively, the relative order of the service components could be transmitted in the header(s) and the timing data transmitted separately, or vice versa.