Abstract:
A datacast operator&#39;s main page ( 36 ) is transmitted to receivers. The datacast operator&#39;s main page ( 36 ) may include links to services and include information specific to the datacast operator and the network area it serves.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to datacasting, particularly, though not exclusively to internet protocol datacasting.  
       BACKGROUND ART  
       [0002]     In Internet Protocol datacasting (IPDC), IP data is transmitted to mobile and fixed receivers using a digital video broadcasting (DVB) network. IPDC can be used to deliver data services, such as a news or software updates, at rates over 11 Mbits −1 .  
         [0003]     It is possible for more than one datacast operator to provide datacast services in the same area using one or more broadcast networks. Furthermore, a user having a mobile receiver can move from one area to another, each area being served by different datacast operators. Where a user moves into a new area, it is likely they will have no prior knowledge of available services or information regarding datacast service operators.  
         [0004]     In either case, but particularly in the case of a user having a mobile receiver, it is desirable that datacast operators are easily identifiable and that information about the services they provide is readily available.  
       SUMMARY OF THE INVENTION  
       [0005]     According to a first aspect of the present invention there is provided a method of datacasting, the method comprising providing electronic service guide (ESG) data relating to one or more services and providing supplementary data selectively provided by a datacast operator.  
         [0006]     The method may comprise providing a main page including at least some of said supplementary data. The method may comprise providing a data file including information for locating said main page. The data file may include information for locating at least one service main page.  
         [0007]     According to a second aspect of the present invention there is provided a computer program including instructions which when executed by a data processing apparatus causes said apparatus to perform the method.  
         [0008]     According to a third aspect of the present invention there is provided a system for datacasting comprising providing electronic service guide (ESG) data relating to one or more services and providing supplementary data selectively provided by a datacast service operator.  
         [0009]     According to a fourth aspect of the present invention there is provided apparatus for datacasting comprising means for providing electronic service guide (ESG) data relating to one or more services and means for providing supplementary data selectively provided by a datacast service operator.  
         [0010]     According to a fifth aspect of the present invention there is provided a method of operating a terminal for receiving datacast services, the method comprising receiving electronic service guide (ESG) data relating to one or more services and receiving supplementary data provided by a datacast operator.  
         [0011]     The method may comprise receiving at least some of said supplementary data in preference to receiving said ESG data. The method may comprise using said supplementary data to locate said ESG data. The method may comprise receiving a main page including at least some of said supplementary data. The method may comprise providing a data file including information for locating said main page. The data file may include information for locating at least one service main page. The method may further comprise receiving datacast data via a first network, receiving data from a second, different network and displaying at least some of said datacast data and at least some of said data. The method may comprise displaying a list of services and selecting one or more services. The method may comprise intermittently switching on a receiver to receive a time-sliced burst of data and switching off said receiver.  
         [0012]     According to a sixth aspect of the present invention there is provided a computer program including instructions which when executed by a data processing apparatus causes said apparatus to perform the method.  
         [0013]     According to a seventh aspect of the present invention there is provided a system for operating a terminal for receiving datacast services, the system comprising receiving electronic service guide (ESG) data relating to one or more services and receiving supplementary data provided by a datacast operator.  
         [0014]     According to an eighth aspect of the present invention there is provided a terminal for receiving datacast services comprising means for receiving electronic service guide (ESG) data relating to one or more services and means for receiving supplementary data provided by a datacast operator.  
         [0015]     The terminal may comprise means for receiving datacast transmissions and means for communicating with public land mobile network. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which:  
         [0017]      FIG. 1  is a schematic diagram of an exemplary communications system;  
         [0018]      FIG. 2  is a more detailed schematic diagram of aspects of the system shown in  FIG. 1 ;  
         [0019]      FIG. 3  is block diagram of an embodiment of a datacast service system according to the present invention;  
         [0020]      FIG. 4  is a schematic diagram of a main page carousel including a datacast operator main page in accordance with one embodiment of the present invention;  
         [0021]      FIG. 5  is a schematic diagram of a hierarchy file carousel in accordance with one embodiment of the present invention;  
         [0022]      FIG. 6  is a schematic diagram of ESG data including service description;  
         [0023]      FIG. 7  is a schematic diagram of a hierarchy file in accordance with one embodiment of the present invention;  
         [0024]      FIG. 8  illustrates a main page directory structure in accordance with one embodiment of the present invention;  
         [0025]      FIG. 9  illustrates a protocol stack used for transmission of data in the datacast service system shown in  FIG. 3 ;  
         [0026]      FIG. 10  illustrates a transport stream output from the datacast service system shown in  FIG. 3 ;  
         [0027]      FIG. 11  illustrates an example of a network interface table and an IP/MAC Notification table;  
         [0028]      FIG. 12  is a flow diagram of a process performed by datacast service system shown in  FIG. 3  in one embodiment of the invention;  
         [0029]      FIG. 13  is a schematic diagram of a mobile terminal in one embodiment of the invention;  
         [0030]      FIG. 14  is a flow diagram of a first process performed by the mobile communications device shown in  FIG. 13  in one embodiment of the invention;  
         [0031]      FIG. 15  is a flow diagram of a second process performed by the mobile communications device shown in  FIG. 13  in one embodiment of the invention;  
         [0032]      FIG. 16  shows an old hierarchy file and a new hierarchy file;  
         [0033]      FIG. 17  illustrates a first view of datacast operator main page in accordance with one embodiment of the present invention;  
         [0034]      FIG. 18  illustrates a second view of datacast operator main page in accordance with one embodiment of the present invention;  
         [0035]      FIG. 19  illustrates a viewer; and  
         [0036]      FIG. 20  is a flow diagram of a third process performed by the mobile communications device shown in  FIG. 13  in one embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0037]     Communications System  1   
         [0038]     Referring to  FIG. 1 , a communications system  1  for delivering content to a mobile terminal  2  is shown. The communications system  1  includes sources  3   1 ,  3   2 ,  3   3 ,  3   4  of content, for example in the form of video, audio and data files, and content servers  4   1 ,  4   2  for retrieving content and, optionally, re-formatting, storing, aggregating and/or scheduling the content. The content servers  4   1 ,  4   2  may be controlled by respective entities  5   1 ,  5   2  referred to as “content providers”. However, the content servers  4   1 ,  4   2  may be controlled by the same entity.  
         [0039]     The communications system  1  further includes a datacast service system  6 . The datacast service system  6  receives content from the content servers  4   1 ,  4   2  via a network  7 , such as the Internet, and performs a number of functions including receiving content, providing service sets and service bundles, arranging service sets data in carousels, generating service information (SI) data, encapsulating and multiplexing data. In one embodiment of the invention a service set can be used for combining same kind of services of one service or content provider together. One service may belong to a number of service sets. In another embodiment of the invention a number of services are bundled into a service bundle, which may be a sellable entity. The datacast service system  6  may also re-format, store, aggregate and/or schedule content  
         [0040]     The communications system  1  also includes a broadcast network  8 , for example in the form of a terrestrial digital video broadcasting (DVB-T) network, for providing a transmission channel from the datacast service system  6  to the mobile terminal  2 . Other broadcast networks may be used including other types of DVB networks, such as a cable DVB network or satellite DVB network, a Digital Audio Broadcasting (DAB) network or an Advance Television System Committee ATSC) network or a terrestrial Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) network.  
         [0041]     The datacast service system  6  and broadcast network  8  are controlled by an entity  9  referred to as a “datacast operator”. However, the broadcast network  8  may also be used for other purposes, such as transmission of digital television, and may be controlled by another, different operator (not shown). Under those circumstances, the datacast operator  9  controls the datacast service system  6  but not the broadcast network  8 .  
         [0042]     A public land mobile network (PLMN)  10 , for example in the form of a GSM system, may provide a return channel from the mobile terminal  2  to the Internet  7 .  
         [0043]     Other PLMN networks may be used, such as other types of second-generation (2G) network such as digital advanced mobile phone system (D-AMPS) network or Personal Digital Communication System (PDC) network, a “two-and-a-half” generation network, such as General Packet Radio Service (GPRS) network and enhanced data rates for GSM evolution (EDGE), or a third-generation network (3G), such as Universal Mobile Telephone System (UMTS) network based on wideband code division multiple access (W-CDMA), or a time division synchronous code division multiple access (TD-SCDMA) network.  
         [0044]     A local area network (LAN)  11 , for example using IEEE 802.11x, may also be provided for obtaining data from local sources (not shown) or from the Internet  7 . Other LANs or personal area networks (PANs) may be used such as Bluetooth™.  
         [0045]     Referring to  FIG. 2 , first and second geographical regions  12 ,  13  are shown. One or both of the regions  12 ,  13  may be a country, a part of a country, city or town or a district of a city or town. For example, the first region  12  may be a city, while the second region  13  may be a countryside surrounding the city.  
         [0046]     The first region  12  is served by the first datacast service system  6  via the broadcast network  8 . The broadcast network  8  comprises a core network  14  and one or more transmitters  15   1 ,  15   2 ,  15   3  which transmit in respective cells  16   1 ,  16   2 ,  16   3 . Gap filler transmitters (not shown) may also be provided. It will be appreciated that alternative configurations of the broadcast network  8  may be used. For example, the core network need not be provided.  
         [0047]     The broadcast network  8  is in this example arranged to transmit as a single frequency network (SFN) using 16 Quadrature Amplitude Modulation (QAM) at frequency lying in the range 470 to 862 MHz.  
         [0048]     The first region  12  is also served by PLMN  10  ( FIG. 1 ) in a conventional manner. The second region  13 is served by second datacast service system  17  via another broadcast network  18  comprising a core network  19  and one or more transmitters  20   1 . Alternative configurations may be used as with the first datacast service system.  
         [0049]     A user is initially located in the second region  13  and moves to the first region  12 , taking their mobile terminal  2  with them. In the first region  12 , the mobile terminal  2  receives a signal  21  transmitted from a transmitter  15   3  carrying a number of services.  
         [0050]     As explained earlier, it is desirable that the datacast service system  6  is easily identifiable and that information about services is readily available. Therefore, the datacast service system  6  provides its own information service which supplements an electronic service guide (ESG). The information service is specific to the area served by the datacast service system  6 . Thus, when the mobile terminal  2  moves to the first region  12 , local information can be provided quickly.  
         [0051]     Datacast Service System  6   
         [0052]     Referring to  FIG. 3 , a schematic diagram of an embodiment of a datacast service system  6  according to the present invention is shown.  
         [0053]     In this embodiment of the invention, the datacast service system  6  comprises an interface  22  for receiving service data  23  and, optionally, relevant electronic service guide (ESG) data  24 , both in the form of IP data, from content servers  4   1 ,  4   2  ( FIG. 1 ) and storage  25  for optionally storing at least part of the service data  23  and ESG data  24 . The system  6  also comprises a controller  26 , memory  27  storing a computer program  28  for controlling the datacast system  6  shown in  FIG. 3 , a service information (SI) table generator  29 , a carousel generator  30 , a multiprotocol encapsulation (MPE) encapsulator  31  and a multiplexer  32 .  
         [0054]     The controller  26  includes an ESG data generator  33  for generating ESG data  34 , which together with ESG data  24 , is used for describing the scheduling and timing of content. The controller  26  also includes a main page generator  35  for producing a main page  36  for the datacast operator, herein referred to as the “DCO main page”. The controller  26  also includes a hierarchy page generator  37  for generating a hierarchy page  38  which will be described in more detail later. The controller  26  may provide main pages  39   1 ,  39   2 ,  39   3  for a number of services. The service main pages  39   1 ,  39   2 ,  39   3  may be provided by the content servers  4   1 ,  4   2  ( FIG. 1 ). However, the controller  26  may modify the service main pages  39   1 ,  39   2 ,  39   3  or generate the service main pages  39   1 ,  39   2 ,  39   3  from the service data  22 .  
         [0055]     The DCO main page  36  is selectively provided by the datacast operator  9  ( FIG. 3 ) and may include data for identifying the datacast operator, data for advertising and/or data for informing the user, for example announcing new, upcoming or updated services, informing the user of popular services or providing recommendations.  
         [0056]     The carousel generator  30  receives data relating to the services such as service data.  22  and ESG data  24 ,  34 . It may generate a number of carousels  40 ,  41 ,  42 ,  43 ,  44  including an alert carousel  40  for notifying the mobile terminal  2  ( FIG. 1 ) e.g. of changes in service, a security association carousel  41  for encryption keys for encrypted content, a session announcement carousel  42  for announcing sessions, a main page carousel  43  for providing main pages for the datacast operator and the services and a hierarchy carousel  44  for providing data relating to the hierarchy of available services. Carousels  40 ,  41 ,  42 ,  43 ,  44  repeatedly transmit data usually in a cyclically manner.  
         [0057]     Referring to  FIG. 4 , the main page carousel  43  may comprise the DCO main page  36  in the form of one or more files  47   1 ,  47   2 ,  47   3  and service main pages  39   1 ,  39   2 ,  39   3  each in the form of one or more files  48   11 ,  48   12 ,  48   13 ,  48   21 ,  48   22 ,  48   23 ,  48   31 ,  48   32 ,  48   33 . The number of files  47   1 ,  47   2 ,  47   3  comprised in the DCO main page  36  need not be the same as the number of files  48   11 ,  48   12 ,  48   13 ,  48   21 ,  48   22 ,  48   23 ,  48   31 ,  48   32 ,  48   33  comprised in any other service main page  39   1 ,  39   2 ,  39   3 . Furthermore, the number of files  48   11 ,  48   12 ,  48   13  comprised in any service main page, for example the first service main page  39   1 , need not be the same as the number of files  48   21 ,  48   22 ,  48   23  comprised in another service main page, for instance the second service main page  39   2 .  
         [0058]     The files  47   1 ,  47   2 ,  47   3 ,  48   11 ,  48   12 ,  48   13 ,  48   21 ,  48   22 ,  48   23 ,  48   31 ,  48   32 ,  48   33  are in one embodiment of the invention in the form of hypertext mark-up language (HTML) protocol files. However, other file formats may be used, such as extensible mark-up language (XML) or session description protocol (SDP). Reference is made to “Session Description Protocol” by M. Handley &amp; V. Jacobson, RFC 2327, IETF, April 1998.  
         [0059]     Referring to  FIG. 5 , a hierarchy file carousel  44  comprises a hierarchy file  38  in the form of one or more sub-files  49   1 ,  49   2 ,  49   3 . In one embodiment of the invention the hierarchy file  38  need not be configured or transmitted in the form of a carousel  38 .  
         [0060]     Referring to  FIG. 6 , the ESG data  24 ,  34  includes service description data  50  in one embodiment of the invention.  
         [0061]     Referring to  FIG. 7 , the hierarchy file  38  comprises sets  51   1 ,  51   2 ,  51   3 ,  51   4 ,  51   5  of carousel information. Each carousel  40 ,  41 ,  42 ,  43 ,  44  ( FIG. 3 ) has a respective set  51   1 ,  51   2 ,  51   3 ,  51   4 ,  51   5  of carousel information comprising an identifier  52   1 ,  52   2 ,  52   3 ,  52   4 ,  52   5  for identifying the carousel type, a list  53   1 ,  53   2 ,  53   3 ,  53   4 ,  53   5  of IP addresses and port numbers for sets of pages within a carousel, an optional list  54   1 ,  54   2 ,  54   3 ,  54   4 ,  54   5  of times for indicating when carousel information will expire and optional list  55   1 ,  55   2 ,  55   3 ,  55   4 ,  55   5  of times for indicating frequency of updates.  
         [0062]     The session, main page and hierarchy carousels  42 ,  43 ,  44  include respective lists  54   2 ,  54   4 ,  54   5  of expiry times. The main page and hierarchy carousels  43 ,  44  may include respective lists  55   4 ,  55   5  of update times.  
         [0063]     Thus, the main page carousel  43  ( FIG. 3 ) has a set  51   4  of carousel information including an identifier  52   4  for indicating that the carousel is the main page carousel, a list  53   4  of IP addresses and port numbers for the DCO main page  36  ( FIG. 4 ) and the service main pages  39   1 ,  39   2 ,  39   3  ( FIG. 4 ), a list  54   4  of expiry times and a list  55   4  of update intervals.  
         [0064]     The IP addresses in lists  53   1 ,  53   2 ,  53   3 ,  53   4 ,  53   5  conform in one embodiment of the invention to IPv6 protocols and reference is made to “Internet Protocol, Version 6 (IPv6) Specification”, by S. Deering and R. Hindern, RFC 2460, IETF, December 1998 and other related IPv6 RFCs. However, other IP protocols may be used.  
         [0065]     The expiry times in lists  54   1 ,  54   2 ,  54   3 ,  54   4 ,  54   3  conform in one embodiment of the invention to Network Time Protocol (NTP) and reference is made to “Network Time Protocol (version 3) Specification, Implementation” by D. Mills, RFC 1305, IETF, March 1992. However, other times may be used. The expiry times in lists  54   1 ,  54   2 ,  54   3 ,  54   4 ,  54   5  may differ from one another.  
         [0066]     The update intervals  55   1 ,  55   2 ,  55   3 ,  55   4 ,  55   5  may be expressed in seconds. However, other units of time such as milliseconds may be used in various embodiments of the invention.  
         [0067]     Referring to  FIG. 8 , an exemplary directory structure  56  of the main pages  36 ,  39   1 ,  39   2 ,  39   3  is shown. In this example the DCO main page  36  includes the service main pages  39   1 ,  39   2 ,  39   3 .  
         [0068]     As will be explained in more detail later, in one embodiment of the invention the IP address of the hierarchy file  38  is signalled through SI, in particular through the NIT  45  ( FIG. 3 ) and the INT  46  ( FIG. 3 ).  
         [0069]     Referring to  FIG. 9 , in one embodiment of the invention the datacast service system  6  transmits data in accordance with a number of transport protocols and a protocol stack  57  is shown.  
         [0070]     In one embodiment of the invention in the network layer (layer 3), IPv6 protocols  58  are used and reference is made to “Internet Protocol, Version 6 (IPv6) Specification” ibid. IP security (IPsec) is not necessarily used when transmitting main page files  47   1 ,  47   2 ,  47   3 ,  48   11 ,  48   12 ,  48   13 ,  48   21 ,  48   22 ,  48   23 ,  48   31 ,  48   32 ,  48   33 .  
         [0071]     Further in one embodiment of the invention in the transport layer (layer 4), Usergram Data Protocol (UDP)  59  is used and reference is made to “User Datagram Protocol”, by J. Postel, RFC 768, IETF, August 1980.  
         [0072]     In one embodiment of the invention Real-time Transport Protocol (RTP)  60   1  may be used to transport files. However, Asynchronous Layered Coding (ALC) protocol  60   2  may be used in other embodiments of the invention. Reference is made to “A Transport Protocol for Real-Time Applications” by H. Schulzrinne et al., RFC 1889, IETF, January 1996 and “Asynchronous Layered Coding Protocol” by M. Luby et al., RFC 3450, IETF, December 2002.  
         [0073]     On the RTP/ALC layer  60 , a filecast payload format may be used which specifies, in detail, the use of RTP/ALC protocols.  
         [0074]     A number of different file formats may be used. For example, XML  62   1  may be used for hierarchy files  49   1 ,  49   2 ,  49   3  ( FIG. 5 ), security association files (not shown) and session announcement files (not shown). SDP  62   2  may be used for technical session information that is not directly shown to the user. In various embodiments of the invention HTML  62   3  may be used for main page files  47   1 ,  47   2 ,  47   3 ,  48   11 ,  48   12 ,  48   13 ,  48   21 ,  48   22 ,  48   23 ,  48   31 ,  48   32 ,  48   33 .  
         [0075]     If more than one language is supported, then the main pages can be sent in files for different languages. The language used is indicated e.g. using language codes. Reference is made to “Tags for the Identification of Languages” by H. Alvestrand, RFC 1766, IETF, March 1995.  
         [0076]     Referring again to  FIG. 3 , an MPE encapsulator  31  encapsulates data, such as data from carousels  40 ,  41 ,  42 ,  43 ,  44 , into sections (not shown) compliant with DSM-CC section format for private data as specified Section 7 “Multiprotocol Encapsulation” in “Digital Video Broadcasting (DVB); DVB specification for data broadcasting”, ETSI EN 301 192, V1.3.1 (2003).  
         [0077]     Data for a given service may be time-sliced.  
         [0078]     However, some data may not be so encapsulated. For example, the NIT  45  may be segmented into network information sections, for example as specified in Section 5 “Service Information (SI) tables” in “Digital Video Broadcasting (DVB); Specification for Service Information (SI) in DVB systems”, ETSI EN 300 468, V1.5.1 (2003).  
         [0079]     Referring also to  FIG. 10 , the multiplexer  32  places the sections (not shown) into MPEG-2 transport stream (TS) packets  63 , according to International Organisation for Standards/International Electrotechnical Commission (ISO/IEC) Standard 13818-1 “Information technology—Generic coding of moving pictures and associated audio information: Systems” and outputs a transport stream  64 . The transport stream  64  is provided to the broadcast network  8  ( FIG. 1 ) in which it may be multiplexed with other streams (not shown), then modulated and broadcast.  
         [0080]     As mentioned earlier, the IP address of the hierarchy file  38  may be signalled through SI, in particular through the NIT  45  ( FIG. 3 ) and the INT  46  ( FIG. 3 ).  
         [0081]     Referring to an example illustrated in  FIG. 11 , the NIT  45  includes first and second descriptor loops  65 ,  66  in which a plurality of descriptors (not shown) for, inter alia, specifying data values and identifying other parts of the transport stream, may be inserted.  
         [0082]     A linkage descriptor  67  can be used to point to other parts of the transport stream and thus obtain further data or access a service. To identify itself as such, the linkage descriptor  67  includes a descriptor tag  68  containing a predetermined value, e.g. 0×0B. The linkage descriptor  67  also includes a transport stream id  69  and an original network id  70  to identify uniquely a transport stream, in this case carrying the INT  46 .  
         [0083]     The transport stream  54  ( FIG. 10 ) may carry a plurality of sets of IP streams, a set of IP streams being known as an “IP platform”. Each IP platform can be identified by a platform id  71  and a platform name  72  which describes the platform and can be used by the mobile terminal  2  to select a platform.  
         [0084]     Reference is made to Section 7.4 “Network (SI) signalling” in “Digital Video Broadcasting (DVB); DVB specification for data broadcasting”, ETSI EN 301 192 ibid. and in Section 6.2.17 “Linkage descriptor” in “Digital Video Broadcasting (DVB); Specification for Service Information (SI) in DVB systems” ETSI EN 300 468 ibid.  
         [0085]     To identify itself as such, the INT  46  includes a table id  73  containing a predetermined value, such as 0×4C. The INT  46  includes a platform id  74  and may include one or more target IP address descriptors  75 , each including a target IP address  76 . The IP address on which the hierarchy file  38  ( FIG. 6 ) is transmitted is specified in target IP address  70 .  
         [0086]     Referring to  FIG. 12 , a process performed by the datacast service system  6  in one embodiment of the invention is shown in the form of a flow diagram.  
         [0087]     Referring also to  FIG. 3 , in one exemplary embodiment of the invention the DCO main page generator  35  generates a DCO main page  36  and the hierarchy page generator  37  generates a hierarchy page  38  (step S 1 ). This may be done periodically, for example every 10 or 100 seconds. Additionally or alternatively, the DCO main page generator  35  may generate a DCO main page  36  when any one of a number of predefined events occurs, such as a change in service, or any one of a number of predefined conditions, such as when a number of consumers exceeds a given number, are satisfied. Additionally or alternatively, the DCO main page generator  35  may generate a DCO main page  36  as-and-when directed to do so by the DCO operator  9 .  
         [0088]     The controller  26  also may provide service main pages  39   1 ,  39   2 ,  39   3  (step S 2 ). The carousel generator  30  receives the DCO main page  32  ( FIG. 4 ), the service main pages  33   1 ,  33   2 ,  33   3  and the hierarchy page  38  and generates the main page carousel  43  and the hierarchy file carousel  44  (step S 3 ).  
         [0089]     Generation of the main page carousel  43  and the hierarchy file carousel  44  includes assigning respective IP addresses and port numbers to the DCO main page  36  ( FIG. 4 ) and the service main pages  39   1 ,  39   2 ,  39   3  ( FIG. 4 ), and to the hierarchy file  38  ( FIG. 6 ).  
         [0090]     The IP address and port numbers assigned to the DCO main page  36  ( FIG. 4 ) and the service main pages  39   1 ,  39   2 ,  39   3  ( FIG. 4 ), as well as IP address and port numbers assigned to other carousels, are included in the hierarchy file  38  ( FIG. 6 ). The IP address and port number assigned to the hierarchy file  38  ( FIG. 6 ) are supplied to the table generator  29  for inclusion in the INT  46 .  
         [0091]     The carousels  40 ,  41 ,  42 ,  43 ,  44  are local, i.e. specific to the network area. In other words, each network area has its own hierarchy, main page, security association, session announcement and alert carousels. Thus, the hierarchy file  38  ( FIG. 6 ) has a different IP address in each network area.  
         [0092]     The IP addresses may be assigned on an ad-hoc basis. Alternatively, the IP addresses may be pre-assigned.  
         [0093]     The NIT  45  and INT  46  are prepared and cyclically transmitted (step S 4 ). The main page and hierarchy file carousels  43 ,  44  are transmitted (step S 5 ).  
         [0094]     Mobile Terminal  2   
         [0095]     Referring to  FIG. 13 , the mobile terminal  2  in one embodiment of the invention is in the form of a mobile telephone handset with a multimedia capability.  
         [0096]     The mobile terminal  2  includes first and second antennae  77   1 ,  77   2 , a receiver  78 , and a transceiver  78   2 . In this example, the first antenna  77 , and receiver  78 , are used to receive signals from the broadcast network  8  ( FIG. 1 ). The second antenna  77   2  and transceiver  78   2  are used to transmit and receive signals to and from the PLMN  10  ( FIG. 1 ). The receiver and transceiver  78   1 ,  78   2  each include respective r.f. signal processing circuits (not shown) for amplifying and demodulating received signals and respective processors (not shown) for channel decoding and demultiplexing.  
         [0097]     The mobile terminal  2  also includes a controller  79 , a user interface  80 , memory  81 , storage  82  a smart card reader  83 , smart card  84  received in the smart card reader  83 , a coder/decoder (codec)  85 , a speaker  86  with corresponding amplifier  87  and a microphone  88  with a corresponding pre-amplifier  89 .  
         [0098]     The user interface  80  comprises a display  90  and a keypad  91 . The display  90  is adapted for displaying images and video by, for instance, being larger and/or having greater resolution than a display of conventional mobile telephone and being capable of colour images. The mobile terminal  2  also includes a battery  92 .  
         [0099]     A transceiver  93  may optionally be provided for transmitting and receiving signals to and from the LAN  11  ( FIG. 1 ). The transceiver  93  may be a wireless card compliant to IEEE 802.11x or Bluetooth™ specifications.  
         [0100]     The controller  79  manages operation of the mobile terminal  2  under the direction of computer software  94  stored in memory  81 . For example, the controller  79  provides an output for the display  90  and receives inputs from the keypad  91 .  
         [0101]     The mobile terminal  2  may be modified by providing a single receiver adapted to receive signals from the broadcast network  8  ( FIG. 1 ) and the PLMN  10  ( FIG. 1 ) and a transmitter adapted to transmit signals to the PLMN  10  ( FIG. 1 ). Alternatively, a single transceiver for both communications networks  8 ,  10  may be provided.  
         [0102]     When the mobile terminal  2  is switched on and/or if the mobile terminal  2  moves from one region  13  ( FIG. 13 ) to another region  12  ( FIG. 2 ) served by different datacast operators  6 ,  17  ( FIG. 2 ) or served by the same datacast operator and having at least partly different services available, then the mobile terminal  2  may not have up-to-date—or even any—electronic service guide (ESG) information.  
         [0103]     The mobile terminal  2  acquires ESG data  24 ,  25  ( FIG. 3 ), which includes NIT  45 , INT  46 , main pages  47   1 ,  47   2 ,  47   3 ,  48   11 ,  48   12 ,  48   13 ,  48   21 ,  48   22 ,  48   23 ,  48   31 ,  48   32 ,  48   33  ( FIG. 4 ) and service description data  50  ( FIG. 6 ) using information included in the hierarchy file  38  ( FIG. 5 ) and the DCO main page  36  ( FIG. 3 ). More detailed information may also be acquired, on request, using information included in the ESG data  24 ,  25  ( FIG. 3 ).  
         [0104]     Referring to  FIGS. 13 and 14  illustrating one embodiment of the invention, a process performed by the mobile terminal  2 , for example when it is switched or moves from one region  13  ( FIG. 13 ) to another region  12  ( FIG. 2 ), is shown in the form of a flow diagram.  
         [0105]     The controller  79  instructs the receiver  78   1  to locate a network, in this case the broadcast network  8  ( FIG. 1 ) (step S 6 ). This may be achieved by scanning a part of the radio frequency spectrum until signal  21  ( FIG. 2 ) is found. Alternatively, the controller  79  may select one or one or more pre-defined or user inputted network frequencies. Then again, the user may instruct the controller  79  to find a given network.  
         [0106]     In this exemplary embodiment of the invention the controller  79  locates, downloads, parses and stores the NIT  45 , then locates, downloads, parses and stores the INT  46  (step S 7 ). The controller  79  obtains the IP address and port number of the hierarchy file  38  (step S 8 ). This may comprise determining whether any IP address within the hierarchy file  38  falls within a predefined ESG IP address range and returning any address which falls within that range. The controller  79  joins the address, downloads, parses and stores the hierarchy file  38  in storage  82  (step S 9 ).  
         [0107]     From the hierarchy file  38 , the controller  79  can obtain respective IP addresses and port numbers for the carousels  40 ,  41 ,  42 ,  43 ,  44 .  
         [0108]     In particular, the controller  79  may obtain the IP address and port number for the main pages  36 ,  39   1 ,  39   2 ,  39   3  (step S 10 ),may join the addresses and download one or more of the main pages  36 ,  39   1 ,  39   2 ,  39   3  (step S 11 ). Furthermore, the controller  79  can obtain the IP address and port number for session announcement carousel  42  (step S 12 ), join the address and download the session description data  50  (step S 13 ). The session description data  50  may include universal resource locators (URLs) for obtaining further, more detailed information (not shown). At the request of the user, the controller  79  may retrieve more detailed information (not shown) via the PLMN  10  ( FIG. 1 ) or LAN  11  ( FIG. 1 ).  
         [0109]     Referring to  FIGS. 13, 15  and  16 , a process performed by the mobile terminal  2  in one embodiment of the invention, for example once it obtained ESG information, is shown in the form of a flow diagram.  
         [0110]     The controller  79  may only listen to announcements, such as hierarchy file  38 , when it is time for an update.  
         [0111]     Based upon the expiry time  54   5  ( FIG. 7 ), the controller  79  determines whether it is time to update the hierarchy file  38  (step S 15 ). If it is time for an update, the controller  79  downloads a new hierarchy file  38 ′ (step S 16 ). The currently stored hierarchy file  38  and the new hierarchy file  38 ′ each have values  95 ,  95 ′ indicating when they were last modified.  
         [0112]     The controller  79  compares the modification time  95 ′ of the new hierarchy file  38 ′ with the modification time  95  of the currently-stored hierarchy file  38  (step S 17 ). If the modification time  95 ′ of the new hierarchy file  38 ′ is later than the modification time  95  of the currently-stored hierarchy file  38 , in other words the new hierarchy file  38 ′ is indeed newer than the currently-stored hierarchy file  38 , then the new hierarchy file  38 ′ is stored in storage  82  (step S 18 ). If not, the expiry time  54   5  ( FIG. 7 ) is simply updated (step S 19 ).  
         [0113]     The controller  79  may also check expiry times  54   4  for the main page carousel  43 . However, the update interval  55   4  ( FIG. 7 ) for the main page carousel  43  may be shorter than the update interval  55   5  ( FIG. 7 ) for the hierarchy file carousel  44 . Therefore, the controller  79  may calculate expected expiry times for the main page carousel  43  using the update interval  55   4 , thereby avoiding the need to check the hierarchy file  38 .  
         [0114]     Referring to  FIG. 17 , a first view of a DCO main page display  96  as displayed by the mobile terminal  2  in display  90  is shown in one embodiment of the invention.  
         [0115]     The DCO main page display  96  is the first page which is presented to the user when the datacast service system  6  ( FIG. 1 ) is accessed and can be used to view the ESG. The DCO main page display  96  can be quickly presented because the DCO main page  36  ( FIG. 3 ) is used as a default starting point and presents the most relevant information to the user.  
         [0116]     The DCO main page display  96  may include a number of fields including an operator identity field  97 , terminal status area  98 , an active area  99 , selection buttons  100 , time/date field  101  and further soft key selection buttons  102 .  
         [0117]     The operator identify field  97  may include the name of the datacast operator  9  ( FIG. 1 ) and a logo. The terminal status area  98  may include information such as network connection status, battery level and incoming call alert. The information may be presented in the form of icons, animated icons or text.  
         [0118]     Some of the fields may display data and information which has been received from the datacast service system  6  ( FIG. 1 ). Some of the fields may display data and information which has been stored in the storage  82  ( FIG. 13 ) and which originates from the datacast service system  6  ( FIG. 1 ), the user, the terminal  2 , another source, for example via PLMN  10  ( FIG. 1 ) or a combination of these.  
         [0119]     The selection buttons  100  may include a button  100   1  for presenting a viewing history, a button  100   2  for displaying programs which are currently running, a button  100   3  for displaying available channels and a button  100   4  for switching to a viewer  105  ( FIG. 19 ) which fills substantially all or most of the display  90 .  
         [0120]     The DCO main page display  96  is updated to reflect changes in ESG, service popularity etc. It can also be used for informing users of upcoming events, changes in services or service availability. The DCO main page display  96  may also be used for advertising purposes, such as displaying trailers.  
         [0121]     In  FIG. 17 , the active area  99  shows a list  103  of available channels.  
         [0122]     Referring to  FIG. 18 , a second view of the DCO main page display  96  is shown in which the active area  99  shows a list  104  of programs currently running. The selection buttons  100  may include a button  100   5  for entering an options menu, a button  100   6  for reverting back to the first view shown in  FIG. 17  and a button  100   7  for obtaining further details.  
         [0123]     Referring to  FIG. 19 , a viewer  105  is shown. The viewer  105  includes an active area  106  and a button  107  for reverting to the DCO main page display  96 .  
         [0124]     As mentioned earlier, the mobile terminal  2  can be used not only to obtain and render content obtained from the broadcast network  8  ( FIG. 1 ), but also content and/or data obtained from the PLMN  10  ( FIG. 1 ).  
         [0125]     Referring to  FIG. 20 , a process performed by the mobile terminal  2  in one embodiment of the invention is shown in the form of a flow diagram.  
         [0126]     Referring also to  FIGS. 1, 3  and  13 , the controller  79  retrieves at least a part of the service data  23  from the datacast service system  6  via the broadcast network  8  (step S 20 ). Additionally, the controller  79  retrieves data (not shown) from a source (not shown) via the PLMN  10  (step S 21 ). The processor  79  displays service data  23  in the display  90 , for example in the DCO main page display  96  (step S 22 ) and also displays data obtained from the PLMN  10  in the display  90 .  
         [0127]     It will be appreciated that many modifications may be made to the embodiments hereinbefore described. For example, the mobile terminal  2  may take the form of a personal digital assistant (PDA). Furthermore, a fixed or semi-fixed terminal may be used, for example in the form of a set-top box or personal computer.