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Digital Video Broadcasting (DVB); Guidelines on implementation and usage of Service Information (SI) DVB Document A005 October 2010 3 Contents Intellectual Property Rights ................................................................................................................................ 6   Foreword............................................................................................................................................................. 6   1 Scope ........................................................................................................................................................ 7   2 References ................................................................................................................................................ 7   2.1 Normative references ......................................................................................................................................... 7   2.2 Informative references ....................................................................................................................................... 8   3 Definitions and abbreviations................................................................................................................... 9   3.1 Definitions ......................................................................................................................................................... 9   3.2 Abbreviations ................................................................................................................................................... 10   4 Rules of operation .................................................................................................................................. 12   4.1 Service Information (SI) table information ...................................................................................................... 12   4.1.1 Network Information Table (NIT) information .......................................................................................... 13   4.1.2 Bouquet Association Table (BAT) information ......................................................................................... 14   4.1.3 Service Description Table (SDT) information ........................................................................................... 14   4.1.4 Event Information Table (EIT) information ............................................................................................... 14   4.1.4.1 EIT Present/Following information ...................................................................................................... 15   4.1.4.2 EIT Schedule information .................................................................................................................... 16   4.1.4.2.1 EIT Schedule structure .................................................................................................................... 16   4.1.4.2.2 EIT scrambling ............................................................................................................................... 17   4.1.5 Time and Date Table (TDT)....................................................................................................................... 17   4.1.6 Time Offset Table (TOT) ........................................................................................................................... 17   4.1.7 Running Status Table (RST) ...................................................................................................................... 17   4.1.8 Stuffing Table (ST) .................................................................................................................................... 18   4.1.9 Transport Stream Description Table (TSDT) ............................................................................................. 18   4.1.9.1 Digital Satellite News Gathering (DSNG)............................................................................................ 18   4.1.10 Table update mechanism ............................................................................................................................ 18   4.1.11 Table segmentation .................................................................................................................................... 19   4.1.11.1 Generic segmentation rules .................................................................................................................. 19   4.1.11.1.1 General rules ................................................................................................................................... 19   4.1.11.1.2 NIT and BAT .................................................................................................................................. 19   4.1.11.1.3 SDT and EIT ................................................................................................................................... 19   4.1.11.2 Segmentation rules for DVB-H and DVB-SH systems ........................................................................ 20   4.1.11.2.1 General rules ................................................................................................................................... 20   4.1.11.2.2 NIT and BAT for DVB-SH and DVB-H ........................................................................................ 20   4.1.11.2.3 SDT for DVB-SH and DVB-H ....................................................................................................... 21   4.2 SI descriptor allocation and usage ................................................................................................................... 21   4.2.1 Descriptors of the Network Information Table (NIT) ................................................................................ 21   4.2.1.1 First descriptor loop .............................................................................................................................. 22   4.2.1.1.1 Linkage descriptor .......................................................................................................................... 22   4.2.1.1.2 Multilingual network name descriptor ............................................................................................ 22   4.2.1.1.3 Network name descriptor ................................................................................................................ 22   4.2.1.1.4 Cell list descriptor ........................................................................................................................... 22   4.2.1.1.5 Network change notify descriptor ................................................................................................... 23   4.2.1.2 Second descriptor loop ......................................................................................................................... 23   4.2.1.2.1 Delivery system descriptors ............................................................................................................ 23   4.2.1.2.2 Service list descriptor ...................................................................................................................... 23   4.2.1.2.3 Frequency list descriptor ................................................................................................................. 23   4.2.1.2.4 Cell frequency link descriptor ......................................................................................................... 23   4.2.2 Descriptors of the Bouquet Association Table (BAT) ............................................................................... 23   4.2.2.1 First descriptor loop .............................................................................................................................. 24   4.2.2.1.1 Bouquet name descriptor ................................................................................................................ 24   4.2.2.1.2 CA identifier descriptor .................................................................................................................. 24   4.2.2.1.3 Country availability descriptor ........................................................................................................ 24   4.2.2.1.4 Linkage descriptor .......................................................................................................................... 24   4.2.2.1.5 Multilingual bouquet name descriptor ............................................................................................ 25   DVB BlueBook A005 4 4.2.2.2 Second descriptor loop ......................................................................................................................... 25   4.2.2.2.1 Service list descriptor ...................................................................................................................... 25   4.2.3 Descriptors of the Service Description Table (SDT).................................................................................. 25   4.2.3.1 Announcement support descriptor ........................................................................................................ 25   4.2.3.2 Bouquet name descriptor ...................................................................................................................... 25   4.2.3.3 CA identifier descriptor ........................................................................................................................ 25   4.2.3.4 Component descriptor........................................................................................................................... 26   4.2.3.5 Country availability descriptor ............................................................................................................. 26   4.2.3.6 Data_broadcast_descriptor ................................................................................................................... 26   4.2.3.7 Linkage descriptor ................................................................................................................................ 26   4.2.3.8 Mosaic descriptor ................................................................................................................................. 27   4.2.3.9 Multilingual service name descriptor ................................................................................................... 27   4.2.3.10 NVOD reference descriptor .................................................................................................................. 27   4.2.3.11 Service descriptor ................................................................................................................................. 27   4.2.3.12 Service availability descriptor .............................................................................................................. 27   4.2.3.12.1 Network Implementation Considerations ....................................................................................... 28   4.2.3.12.2 IRD implementation considerations ................................................................................................ 28   4.2.3.13 Telephone descriptor ............................................................................................................................ 28   4.2.3.14 Time shifted service descriptor ............................................................................................................. 29   4.2.4 Descriptors of the Event Information Table (EIT) ..................................................................................... 29   4.2.4.1 CA identifier descriptor ........................................................................................................................ 29   4.2.4.2 Component descriptor........................................................................................................................... 30   4.2.4.3 Content descriptor ................................................................................................................................ 30   4.2.4.4 Data_broadcast_descriptor ................................................................................................................... 30   4.2.4.5 Extended event descriptor .................................................................................................................... 30   4.2.4.6 Linkage descriptor ................................................................................................................................ 30   4.2.4.7 Multilingual component descriptor....................................................................................................... 31   4.2.4.8 Parental rating descriptor ...................................................................................................................... 31   4.2.4.9 PDC descriptor ..................................................................................................................................... 31   4.2.4.10 Short event descriptor ........................................................................................................................... 32   4.2.4.11 Telephone descriptor ............................................................................................................................ 32   4.2.4.12 Time shifted event descriptor ............................................................................................................... 32   4.2.5 Descriptors of the Time Offset Table (TOT) ............................................................................................. 32   4.2.5.1 Local time offset descriptor .................................................................................................................. 32   4.2.6 Descriptors of the Program Map Table (PMT) .......................................................................................... 33   4.2.6.1 AC-3 descriptor .................................................................................................................................... 33   4.2.6.2 Adaptation field data descriptor............................................................................................................ 33   4.2.6.3 Ancillary data descriptor ...................................................................................................................... 33   4.2.6.4 Data broadcast id descriptor ................................................................................................................. 33   4.2.6.5 Mosaic descriptor ................................................................................................................................. 33   4.2.6.6 Service move descriptor ....................................................................................................................... 33   4.2.6.7 Stream identifier descriptor .................................................................................................................. 34   4.2.6.8 Subtitling descriptor ............................................................................................................................. 34   4.2.6.9 Teletext descriptor ................................................................................................................................ 34   4.2.6.10 VBI data descriptor............................................................................................................................... 34   4.2.6.11 VBI teletext descriptor.......................................................................................................................... 34   4.2.7 Other descriptors ........................................................................................................................................ 34   4.2.7.1 Private data specifier descriptor............................................................................................................ 34   4.2.7.2 Stuffing descriptor ................................................................................................................................ 35   4.2.7.3 Data_broadcast_descriptor ................................................................................................................... 35   4.2.7.4 Transport_stream_descriptor ................................................................................................................ 35   4.2.7.5 Target_region and target_region_name descriptors .............................................................................. 35   4.2.7.5.1 General Description ........................................................................................................................ 35   4.2.7.5.2 Region selection by the IRD ........................................................................................................... 36   4.2.8 ISO/IEC 13818-1 descriptors ..................................................................................................................... 36   4.2.9 Unknown descriptors.................................................................................................................................. 37   4.3 Program Specific Information (PSI) and DVB SI operational interaction states ............................................. 37   4.4 Minimum repetition rates ................................................................................................................................. 37   4.4.1 Satellite and cable delivery systems ........................................................................................................... 37   4.4.2 Terrestrial delivery systems ....................................................................................................................... 38   4.5 Terrestrial systems ........................................................................................................................................... 38   4.5.1 Terms used within terrestrial systems ........................................................................................................ 38   DVB BlueBook A005 5 4.5.2 The use of alternative frequencies for multiplexes ..................................................................................... 40   4.5.3 Regional or local services .......................................................................................................................... 41   4.5.4 Hand-over ................................................................................................................................................... 43   4.5.4.1 General description of the requirements ............................................................................................... 43   4.5.4.2 Hand-over by means of the frequency_list_descriptor ......................................................................... 43   4.5.4.3 The occurrence of tuning failures ......................................................................................................... 44   4.5.4.4 Hand-over methods with a reduced risk of tuning failures ................................................................... 45   4.5.4.4.1 Local SI insertion ............................................................................................................................ 46   4.5.4.4.2 Cell identification............................................................................................................................ 46   4.5.4.4.3 Performance enhancement with GPS data ...................................................................................... 46   4.5.4.4.4 Two front-end solution ................................................................................................................... 46   4.5.4.5 Performance considerations .................................................................................................................. 47   4.5.4.6 Receiver guidelines .............................................................................................................................. 47   4.5.4.6.1 Hand-over by means of the frequency_list_descriptor.................................................................... 47   4.5.4.6.2 Hand-over by means of cell identification ...................................................................................... 48   4.5.4.6.3 Hand-over by means of cell description and GPS position ............................................................. 48   4.5.4.6.4 Hand-over with two-front-end solutions ......................................................................................... 49   4.5.4.7 Additional linkage modes ..................................................................................................................... 49   4.5.4.8 Additional remarks ............................................................................................................................... 50   4.6 Text string formatting ...................................................................................................................................... 50   4.6.1 Use of control codes in names .................................................................................................................... 50   4.6.2 Use of control codes in text ........................................................................................................................ 51   4.6.3 Use of UTF-8 ............................................................................................................................................. 51   5 Applications ........................................................................................................................................... 51   5.1 NVOD services ................................................................................................................................................ 51   5.2 Mosaic services ................................................................................................................................................ 53   5.2.1 General considerations ............................................................................................................................... 53   5.2.2 Relationship between mosaic service and SI/PSI Tables ........................................................................... 54   5.3 Transitions at broadcast delivery media boundaries ........................................................................................ 55   5.3.1 Seamless transitions ................................................................................................................................... 55   5.3.2 Non-seamless transitions without re-multiplexing ..................................................................................... 56   5.3.3 Transitions with re-multiplexing ................................................................................................................ 56   5.4 Announcements ............................................................................................................................................... 57   6 Storage media ......................................................................................................................................... 57   6.1 Program Association Table (PAT) ................................................................................................................... 57   6.2 Program Map Table (PMT) ............................................................................................................................. 57   6.3 SI tables (NIT, SDT, EIT, BAT, RST, TDT, TOT) ......................................................................................... 57   6.4 Selection Information Table (SIT) ................................................................................................................... 58   6.5 Discontinuity Information Table (DIT) ........................................................................................................... 58   History .............................................................................................................................................................. 59   DVB BlueBook A005 6 Intellectual Property Rights IPRs essential or potentially essential to the present document may have been declared to ETSI. The information pertaining to these essential IPRs, if any, is publicly available for E TSI members and non-members, and can be found in ETSI SR 000 314: " Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in respect of ETSI standards" , which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web server (http://webapp.etsi.org/IPR/home.asp). Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web server) which are, or may be, or may become, essential to the present document. Foreword This Technical Specification (TS) has been produced by Joint Technical Committee (JTC) Broadcast of the European Broadcasting Union (EBU), Comité Européen de Normalisation ELECtrotechnique (CENELEC) and the European Telecommunications Standards Institute (ETSI). NOTE: The EBU/ETSI JTC Broadcast was established in 1990 to co-ordinate the drafting of standards in the specific field of broadcasting and related fields. Since 1995 the JTC Broadcast became a tripartite body by including in the Memorandum of Understanding also CENELEC, which is responsible for the standardization of radio and television receivers. The EBU is a professional association of broadcasting organizations whose work includes the co-ordination of its members' activities in the technical, legal, programme-making and programme-exchange domains. The EBU has active members in about 60 countries in the European broadcasting area; its headquarters is in Geneva. European Broadcasting Union CH-1218 GRAND SACONNEX (Geneva) Switzerland Tel: +41 22 717 21 11 Fax: +41 22 717 24 81 The Digital Video Broadcasting Project (DVB) is an industry-led consortium of broadcasters, manufacturers, network operators, software developers, regulatory bodies, content owners and others committed to designing global standards for the delivery of digital television and data services. DVB fosters market driven solutions that meet the needs and economic circumstances of broadcast industry stakeholders and consumers. DVB standards cover all aspects of digital television from transmission through interfacing, conditional access and interactivity for digital video, audio and data. The consortium came together in 1993 to provide global standardisation, interoperability and future proof specifications. DVB BlueBook A005 7 1 Scope The present document provides implementation guidelines for the use and implementation of the DVB Service Information (SI) coding in a DVB digital TV environment including satellite- cable- and terrestrial networks. The guidelines are intended to be highly recommended rules for the usage of the DVB SI syntax specified in EN 300 468 [[1]. As such, they facilitate the efficient and reliable implementation of basic user-interaction functions in Integrated Receiver-Decoders (IRD). The rules apply to broadcasters, network operators as well as manufacturers. The rules are specified in the form of constraints on the DVB SI streams or in terms of intended interpretation by IRDs. The specification of these functions in no way prohibits IRD manufacturers from including additional features, and should not be interpreted as stipulating any form of upper limit to the performance. The guidelines do not cover features related to user-interface details or advanced Electronic Program Guides (EPG). Such issues are left to the marketplace. NOTE: It is highly recommended that the IRD should be designed to allow for future compatible extensions to the DVB SI syntax. All the fields "reserved" (for ISO), "reserved_future_use" (for ETSI), and "user defined" in the EN 300 468 [1] should be ignored by IRDs designed not to make use of them. The "reserved" and "reserved_future_use" fields may be specified in the future by the respective bodies, whereas the "user defined" fields will not be standardized. The present document uses the terminology defined in EN 300 468 [1] and should be read in conjunction with that EN. 2 References References are either specific (identified by date of publication and/or edition number or version number) or non-specific. For a specific reference, subsequent revisions do not apply. Non-specific referencemay be made only to a complete document or a part thereof and only in the following cases: - if it is accepted that it will be possible to use all future changes of the referenced document for the purposes of the referring document; - for informative references. Referenced documents which are not found to be publicly available in the expected location might be found at http://docbox.etsi.org/Reference. NOTE: While any hyperlinks included in this clause were valid at the time of publication ETSI cannot guarantee their long term validity. DVB BlueBook A005 8 2.1 Normative references The following referenced documents are indispensable for the application of the present document. For dated references, only the edition cited applies. For non-specific references, the latest edition of the referenced document (including any amendments) applies. Not applicable. 2.2 Informative references The following referenced documents are not essential to the use of the present document but they assist the user with regard to a particular subject area.For non-specific references, the latest version of the referenced document (including any amendments) applies. [1] ETSI EN 300 468: "Digital Video Broadcasting (DVB); Specification for Service Information (SI) in DVB systems". [2] ISO/IEC 13818-1: "Information technology - Generic coding of moving pictures and associated audio information: Systems". [3] ETSI EN 300 472: "Digital Video Broadcasting (DVB); Specification for conveying ITU-R System B Teletext in DVB bitstreams". [4] ETSI TS101 162: " Digital Video Broadcasting (DVB); Allocation of identifiers and codes for Digital Video Broadcasting (DVB) systems". [5] ETSI EN 301 192: "Digital Video Broadcasting (DVB); DVB specification for data broadcasting". [6] ETSI TS 101 202: "Digital Video Broadcasting (DVB); Implementation guidelines for Data Broadcasting". [7] ITU-R Recommendation BS.1196-1: "Audio coding for digital terrestrial television broadcasting". NOTE 1: Available athttp://www.itu.int/rec/recommendation.asp?type=items&lang=e&parent=R-REC- BS.1196-1-200104-I. NOTE 2: Annex 2 "Digital Audio Compression (AC-3) Standard (ATSC Standard)", contains additional information on the AC-3 audio encoding algorithm and decoding requirements, relevant to the present document. Appendix 1 to Annex 2 of this Recommendation should be disregarded as it is not applicable to the present document. [8] ETSI EN 300 744: "Digital Video Broadcasting (DVB); Framing structure, channel coding and modulation for digital terrestrial television". [9] ETSI TR 101 154: "Digital Video Broadcasting (DVB); Implementation guidelines for the use of MPEG-2 Systems, Video and Audio in satellite, cable and terrestrial broadcasting applications". [10] ETSI EN 301 775: "Digital Video Broadcasting (DVB); Specification for the carriage of Vertical Blanking Information (VBI) data in DVB bitstreams". [11] ETSI EN 301 210: "Digital Video Broadcasting (DVB); Framing structure, channel coding and modulation for Digital Satellite News Gathering (DSNG) and other contribution applications by satellite". DVB BlueBook A005 9 [12] ETSI EN 300 231: "Television systems; Specification of the domestic video Programme Delivery Control system (PDC)". [13] ISO/IEC 13818-3: "Information technology - Generic coding of moving pictures and associated audio information - Part 3: Audio". [14] ISO/IEC 11172-3: "Information technology - Coding of moving pictures and associated audio for digital storage media at up to about 1,5 Mbit/s - Part 3: Audio". [15] ETSI EN 300 743: "Digital Video Broadcasting (DVB); Subtitling systems". [16] ETSI EN 300 401: "Radio Broadcasting Systems; Digital Audio Broadcasting (DAB) to mobile, portable and fixed receivers". [17] ETSI TS 102 006: "Digital Video Broadcasting (DVB); Specification for System Software Update in DVB Systems". [18] ISO/IEC 13818-2: "Information technology - Generic coding of moving pictures and associated audio information: Video". [19] ETSI TS 102 201: " Digital Video Broadcasting (DVB); Interfaces for DVB Integrated Receiver Decoder (DVB-IRD) [20] Digital Video Broadcasting (DVB); Interaction channel through Public Switched Telecommunications Network (PSTN) / Integrated Services Digital Networks (ISDN) [21] Digital Video Broadcasting (DVB); Interaction channel through the Digital Enhanced Cordless Telecommunications (DECT) 3 Definitions and abbreviations 3.1 Definitions For the purposes of the present document, the following terms and definitions apply: A C-3: refers to the coding of audio using the Dolby AC-3 method (ITU-R Recommendation BS.1196-1 [7]) NOTE: The Service Information requirements for AC-3 streams carried in DVB systems is described in annex E of EN 300 468 [[1]. The carriage of AC-3 elementary streams as private data within MPEG systems is described in annex C of TR 101 154 [9]. bouquet: collection of services marketed as a single entity broadcaster (SE R V I C E Provider): organization which assembles a sequence of events or programmes to be delivered to the viewer based upon a schedule cell: geographical area that is covered with DVB signals delivering one or more particular transport or other DVB streams throughout the area by means of one or more transmitters DVB BlueBook A005 10 NOTE: The cell may in addition contain repeaters. Two neighbouring cells may be intersecting, or fully overlapping. The cell_id that is used to uniquely identify a cell is unique within each original_network_id. For hand-over purposes it is more convenient if the transport streams associated with the cell cover exactly the same area, or only one transport stream per cell is used. component (E L E M E N T A R Y Stream): one or more entities which together make up an event EXAMPLE: Video, audio, Teletext. Conditional A ccess (C A) system: system to control subscriber access to services, programmes and events EXAMPLE: Videoguard, Eurocrypt. delivery system: physical medium by which one or more multiplexes are transmitted EXAMPLE: Satellite system, wide-band coaxial cable, fibre optics, terrestrial channel of one emitting point. emitting site: collection of transmitters and/or repeaters gathered on one geographic plant event: grouping of elementary broadcast data streams with a defined start and end time belonging to a common service EXAMPLE: First half of a football match, News Flash, first part of an entertainment show. gap filler: type of repeater which allows to receive a DVB-T signal and to re-transmit it on the same frequency. Local SI insertion: local SI insertion means that individual SI is inserted for each cell or network. NOTE: Consequently, one or more cells may correspond to one network. M PE G-2:Refers to the standard ISO/IEC 13818. NOTE: Systems coding is defined in part 1 [2]. Video coding is defined in part 2 [18]. Audio coding is defined in part 3 [13]. M ulti F requency Networ k (M F N) mode: geographical area is operated in MFN mode if the frequencies used to broadcast a specific transport stream differ from one emitting site to another multiplex: stream of all the digital data carrying one or more services within a single physical channel networ k : collection of MPEG-2 TS multiplexes transmitted on a single delivery system EXAMPLE: All digital channels on a specific cable system. NOTE: A network is identified by its network_id. It might be composed of one or more emitting sites. programme: concatenation of one or more events under the control of a broadcaster EXAMPLE: News show, entertainment show. DVB BlueBook A005 11 repeater: equipment which allows to receive a DVB-T signal and to re-transmit it. It does not allow to change the TPS bits and thus the cell_id section: syntactic structure used for mapping all service information into ISO/IEC 13818-1 [2] NOTE: Transport Stream (TS) packets. service: sequence of programmes under the control of a broadcaster which can be broadcast as part of a schedule Service Information (SI): digital data describing the delivery system, content and scheduling/timing of broadcast data streams, etc. NOTE: It includes MPEG-2 Program Specific Information (PSI) together with independently defined extensions. service insertion point: emitting site at which a transport stream is compiled in order to broadcast it within one network NOTE: The compilation includes the insertion of signalling data. Single F requency Networ k (SF N) mode: geographical area is operated in SFN mode if the frequencies used to broadcast a specific transport stream does not differ from one emitting site to another subcell: geographical area that is part of the cell's coverage area and that is covered with DVB signals by means of a transposer NOTE: In conjunction with the cell_id the cell_id_extension is used to uniquely identify a subcell. sub-table: comprised of a number of sections with the same value of table_id, table_id_extension and version_number NOTE: The table_id_extension field is equivalent to the fourth and fifth byte of a section when the section_syntax_indicator is set to a value of "1". table: comprised of a number of sections with the same value of table_id transmitter: equipment, that allows to modulate a baseband transport stream and to broadcast it on one frequency, is called transmitter T ransport Stream (TS): data structure defined in ISO/IEC 13818-1 [2] NOTE: It is the basis of the DVB standards. transposer: type of repeater which allows to receive a DVB signal and to re-transmit it on a different frequency 3.2 Abbreviations For the purposes of the present document, the following abbreviations apply: AC-3 dolby AC-3 audio coding ASCII American Standard Code for Information Interchange ATSC Advanced Television Systems Committee of the USA BAT Bouquet Association Table CA Conditional Access DVB BlueBook A005 12 CR Carriage Return character DAB Digital Audio Broadcasting DIT Discontinuity Information Table DSNG Digital Satellite News Gathering DVB Digital Video Broadcasting DVD Digital Versatile Disc EIT Event Information Table EPG Electronic Program Guide ES Elementary Stream GPS Global Positioning System IRD Integrated Receiver-Decoder LF Line Feed Character MFN Multi-Frequency Network MJD Modified Julian Date MPEG Moving Pictures Expert Group NIT Network Information Table NVOD Near Video On Demand PAT Program Association Table PDC Programme Delivery Control PID Packet IDentifier PIL Programme Identification Label PMT Program Map Table PSI Program Specific Information QAM Quadrature Amplitude Modulation QPSK Quadrature Phase Shift Keying RST Running Status Table SDT Service Description Table SFN Single Frequency Network SHY Soft HYphen SI Service Information SIT Selection Information Table SMATV Satellite Master Antenna TeleVision ST Stuffing Table TDT Time and Date Table TOT Time Offset Table TPS Transmission Parameter Signalling TS Transport Stream TSDT Transport Stream Description Table UCS Universal Character Set UTC Universal Time Coordinated UTF UCS Transformation Format VBI Vertical Blanking Interval VPS Video Programme System WSS Wide Screen Signalling DVB-H DVB-SH DVB BlueBook A005 13 4 Rules of operation This clause contains some recommendations on the usage of the Digital Video Broadcasting (DVB) Service Information (SI) syntax. 4.1 Service Information (SI) table information Figure 1: SI table information 4.1.1 Network Information Table (NIT) information The Network Information Table (NIT) provides a grouping of Transport Streams (TSs) and the relevant tuning information. The NIT could be used during set-up procedures of the IRD and the relevant tuning information may be stored in non-volatile memory. The NIT also could be used to signal changes of tuning information. The following rules apply to the NIT: a) transmission of the NIT is mandatory for the actual delivery system; b) the NIT describing the actual delivery system is valid if and only if it contains applicable delivery system descriptors for the actual delivery system. At some transitions of broadcast delivery system boundaries, the NIT carried in a TS is allowed to be invalid, and to describe an earlier network in the broadcast chain. In this case,a different mechanism has to be selected by the IRD to obtain the relevant tuning information for the actual delivery system. More information is provided in clause 5.3; c) if a valid NIT for the actual delivery system is present in the SI bit stream then it shall list all TSs of the actual delivery system; DVB BlueBook A005 14 d) the SI stream shall have at least 8 TS packets per 10 s carrying NIT data or NULL packets. This rule simplifies the replacement of the NIT at broadcast delivery system boundaries. With the simple replacement mechanism, local frequency control is possible with relatively low cost equipment. The SI uses two labels related to the concept of a delivery system, namely the network_id and the original_network_id. The latter is intended to support the unique identification of a service, contained in a TS, even if that TS has been transferred to another delivery system than the delivery system where it originated. A TS can be uniquely referenced through the path original_network_id/transport_stream_id. Each service_id shall be unique within each original_network_id. Therefore the combination of service_id and original_network_id uniquely identifies a service. A service may be transmitted in multiple TS. Each unique instance of a service can be uniquely referenced through the path original_network_id/transport_stream_id/service_id (see EN 300 468 [1]). The network_id, thus, is not part of this path. When a TS containing a service is transferred to another delivery system, only the network_id changes, whereas the original_network_id remains unaffected. By way of example, consider the following, where two services (A and B), which originate in two different delivery systems and happen to have the same service_ids and transport_stream_ids, are transferred to a new delivery system.In thisexample, the two services are located on different TSs (X and Y) in the new network. If the two services were being combined onto the same TS, then it would be necessary to modify the identification of the services, since the same service_id value cannot be assigned to more than one service within a TS, and only one original_network_id can be associated with a TS (see clause 5.3 for further discussion on transitions at broadcast delivery media boundaries). Figure 2: Transfer to a new delivery system 4.1.2 Bouquet Association Table (BAT) information The BAT provides a grouping of services which serves as one basis on which an IRD presents the available services to a user. Transmission of the BAT is optional. The following rule improves the consistency in the SI bit streams and simplifies the processing in the IRDs. DVB BlueBook A005 15 The SI bit stream shall list in each BAT sub-table all the services belonging to that bouquet. NOTE: One service may belong to more than one bouquet. This rule creates consistency across the different TSs which are accessible to the IRD. If it is intended for the IRD to present service information to the user grouped in bouquets, then it would be beneficial to ensure that every service is listed in one or more bouquets, or some services will be omitted from this method of presentation. A bouquet may group together services from more than one TS, which could even be carried in different networks. The IRD's access to information on all the services of a bouquet would be facilitated if all the services referred to in the BAT were listed in the Service Description Table (SDT). Similarly, the IRD's access to these services is facilitated if NIT information is given for all TSs in which services of the bouquet occupy capacity. 4.1.3 Service Description Table (SDT) information The SDT is used to list the names and other parameters of the services within TSs. For each TS a separate SDT sub-table exists. The following rules apply in order to improve the acquisition of services: the transmission of the SDT for the actual TS is mandatory; the SI bit stream shouldlist in the SDT of a particular TS all the services of that TS. In addition: any SDT for another TS than the actual one (i.e. with table_id = 0x46) shouldlist all the services of that TS; it is strongly recommended that service_ids, once assigned to a specific service within a network, remain unchanged in order to enable IRDs to implement features like favourite channel lists, etc. 4.1.4 Event Information Table (EIT) information The Event Information Table (EIT) is used to transmit information about present, following and further future events. For each service a separate EIT sub-table exists. 4.1.4.1 EIT Present/Following information The following rule simplifies the acquisition of the EIT Present/Following information. The SI specification states that an EIT section has a maximum size of 4 096 bytes. The SI bit stream shall have two sections per service of the actual TS,for an EIT Present/Following with the section_number 0x00 reserved for the description of the present event and section_number 0x01 for the following event. These constraints do not apply in the case of an NVOD reference service which may have more than one event description per section, and may have more than two sections in the EIT Present/Following. The SI bit stream shall have maximum of 4 096 bytes to describe a single event in a section. The organization of the EIT Present/Following is based on the concept of present and following events. Which event is the present one can be determined using the following scheme: a) at each instant in time, there is at most one present event; b) when there is a present event, this event shall be described in section 0 of the EIT Present/Following; DVB BlueBook A005 16 c) when there is no present event (e.g. in the case of a gap in the schedule) an empty section 0 of the EIT Present/Following shall be transmitted; d) the running_status field in the description of the present event shall be given the interpretation in table 1; Table 1: running_status of the present event undefined No information except the nominal status is provided. IRDs and recording devices shall treat the present event as running. running IRDs and recording devices shall treat the present event as running. not running IRDs and recording devices shall treat the present event as not running. In other words, this event is nominally the present one, but at this time has either not started or already ended. pausing IRDs and recording devices shall treat the present event as pausing. In other words, this event is nominally the present one and has already started, but at this time the material being broadcast is not a part of the event itself. The transmission of event material shall resume at a later time. starts in a few IRDs and recording devices shall prepare for the change of event status to "running" seconds in a few seconds. service off-air IRDs and recording devices shall treat the present event as being off-air. However the service may provide an interactive application to cover the off-air period. e) at each point in time, there shall be at most one following event; f) if a following event exists, it shall be described in section 1 of the EIT Present/Following; g) if no following event exists, an empty section 1 of the EIT Present/Following shall be transmitted; h) the running_status field in the definition of the following event shall be given the following interpretation. Table 2: running_status of the following event undefined No information except the nominal status is provided. IRDs and recording devices shall treat the following event as not running. running Not allowed. not running IRDs and recording devices shall treat the following event as not running. pausing This status is intended to indicate that the "following" event has been running at some time, but is now overlapped by another event. In such a case, during the whole time that the "following" event has status "pausing", one and the same overlapping event shall be encoded in section 0 of the EIT Present/Following. Furthermore, an event which has the status "pausing" shall acquire the status "running" at a later time, then replacing the overlapping event in section 0 of the EIT Present/Following. starts in a few IRDs and recording devices shall prepare for the status of the following event to seconds change to running within a few seconds. service off-air IRDs and recording devices shall treat the following event as being off-air. However the service may provide an interactive application to cover the off-air period. The duration of an event as encoded in the field duration of the EIT shall also include the duration of all times when the event has the status "not running" or "paused". The start time of an event as encoded in the field start_time of the EIT shall be the start time of the entire event, i.e. not the start time after the pause has finished. DVB BlueBook A005 17 NOTE 1: The start time of one event plus its duration may be smaller than the start time of the following event. In other words, gaps between events are allowed. In such a case, the following event is considered to be the event scheduled to begin after the gap. This event shall be encoded in section 1 of the EIT Present/Following. NOTE 2: The start time and duration are scheduled times. Some broadcasters may update this information if the schedule is running late, whereas others may prefer to keep the indicated start time unchanged, e.g. to avoid having an event called "The News at 8" from being indicated as starting at 8:01:23, instead of 8:00:00. 4.1.4.2 EIT Schedule information 4.1.4.2.1 EIT Schedule structure The EIT Schedule information is structured in such a way that it is easy to access the EIT data in a flexible manner. The EIT Schedule Tables shall obey the following rules: a) the EIT/Schedule is distributed over 16 table_ids, being 0x50 to 0x5F for the actual TS, and 0x60 to 0x6F for other TSs, which are ordered chronologically; b) the 256 sections under each sub-table are divided into 32 segments of 8 sections each. Segment #0, thus, comprises sections 0 to 7, segment #1 section 8 to 15, etc.; c) each segment contains information about events that start (see below) anywhere within a three-hour period; d) the information about separate events is ordered chronologically within segments; e) if only n < 8 sections of a segment are used, the information shall be placed in the first n sections of the segment. To signal that the last sections of the segment are not used, the value s0 + n - 1, where s0 is the first section number of the segment, shall be encoded in the field segment_last_section_number of the EIT header. As an example, if segment 2 contains only 2 sections, the field segment_last_section_number shall contain the value 8 + 2 - 1 = 9 in those two sections; f) segments that contain all their sections shall have the value s0 + 7 encoded in the field segment_last_section_number; g) entirely empty segments shall be represented by an empty section, (i.e. a section which does not contain any loop over events) with the value s0 + 0 encoded in the field segment_last_section_number; h) the placing of events in segments is done referring to a time t0. t0 is "last midnight" in Universal Time Coordinated (UTC) time. Suppose, for instance, that it is 5.00 PM in the time zone UTC-6. It is then 11.00 PM in the time zone UTC+0, which makes it 23 hours since "last midnight". Therefore, t0 is 6.00 PM the previous day in UTC-6; i) segment #0 of table_id 0x50 (0x60 for other TSs) shall contain information about events that start between midnight (UTC Time) and 02:59:59 (UTC Time) of "today". Segment #1 shall contain events that start between 03:00:00 and 05:59:59 UTC time, and so on. This means that the first sub-table (table_id 0x50, or 0x60 for other TSs) contains information about the first four days of schedule, starting today at midnight UTC time; DVB BlueBook A005 18 j) the field last_section_number is used to indicate the end of the sub-table. Empty segments that fall outside the section range indicated by last_section_number shall not be represented by empty sections; k) for all sections used in the delivery of EIT/Schedule information for a particular service the field last_table_id is used to indicate the last table_id used in the delivery of EIT schedule information for that service. Empty segments that fall outside the table_id range indicated by last_table_id shall not be represented by empty sections; l) segments that correspond to events in the past may be replaced by empty segments (see rule g); m) the running_status field of event definitions contained in the EIT/Schedule shall be set to either undefined (0x00) or service off air (0x05). The use of service off-air (0x05) indicates the event represents a period when the service is off-air; n) EIT/Schedule tables are not applicable to NVOD Reference Services, since these have events with undefined start times. 4.1.4.2.2 EIT scrambling The EIT Schedule Tables may be scrambled. In order to provide an association with the Conditional Access (CA) streams, it is necessary to allocate a service_id (= MPEG-2 program_number) which is used in the Program Specific Information (PSI) to describe scrambled EIT Schedule Tables. The EIT is identified in the Program Map Table (PMT) section for this service_id as a programme consisting of one private stream, and this PMT section includes one or more CA_descriptors to identify the associated CA streams. The service_id value 0xFFFF is reserved in DVB applications for this purpose. 4.1.5 Time and Date Table (TDT) The Time and Date Table (TDT) transmits the actual UTC-time coded as Modified Julian Date (MJD). It may be used to synchronize the internal clock of an IRD. The TDT shall be transmitted, andwith a repetition rate as defined in clause 4.4. The encoded time is intended to be valid when the section becomes valid according to figure 3. 4.1.6 Time Offset Table (TOT) The TOT transmits the actual UTC-time including also time offset information coded as MJD. It may be used to synchronize the internal clock of an IRD. Transmission of the TOT is optional, but if present it shall be transmitted with a repetition rate as defined in clause 4.4. The encoded time is intended to be valid when the section becomes valid according to figure 3. 4.1.7 Running Status Table (RST) Running status sections are used to rapidly update the running status of one or more events. Running status sections are sent out only once, at the time the status of an event changes, unlike other SI Tables which are normally repetitively transmitted. Thus there does not exist any update mechanism for RSTs. At the moment an RST is transmitted to update the running status of an event, it invalidates the running status of that event, transmitted previously by the EIT Present/Following. The following time the EIT is transmitted, it shall contain the updated running status bits. DVB BlueBook A005 19 The intended use of this optional mechanism is to enable IRDs or recording devices to implement highly accurate switching to the beginning of events by setting up a filter on Running Status Tables and waiting for the occurrence of the RST section containing the event. 4.1.8 Stuffing Table (ST) A stuffing section may occur in anywhere that a section belonging to an SI Table is allowed. Stuffing Tables may be used to replace or invalidate either sub-tables or complete SI Tables. In order to guarantee consistency, all sections of a sub-table shall be stuffed. It is not allowed to replace some sections of a sub-table by stuffing some sections while keeping others. 4.1.9 Transport Stream Description Table (TSDT) The transmission of the Transport Stream Description Table (TSDT) (ISO/IEC 13818-1 [2]) within DVB Transport Streams is optional but recommended. The decoding of the TSDT is optional. Decoders which are designed to support different MPEG based systems should be able to decode and interpret this table. If the TSDT is present, at least one transport_stream_descriptor shall be present at the beginning of the descriptor loop. The compatibility of a transport stream with different MPEG-based systems shall be indicated by the presence of more than one transport_stream_descriptor. If the Transport Stream is compatible with DVB, the following descriptors are allowed in the descriptor loop and shall appear after the transport_stream_descriptor: linkage_descriptor; private_data_specifier_descriptor followed by private descriptors; and private_data_indicator_descriptor (ISO/IEC 13818-1 [2]). 4.1.9.1 Digital Satellite News Gathering (DSNG) For DSNG transmissions the Transport Stream Description Table (TSDT) shall be present in the bitstream. The TSDT descriptor loop shall contain the transport_stream_descriptor with the ASCII codes for "DSNG" in the text field. At least one DSNG_descriptor shall be present in the TSDT. The semantics for the DSNG descriptor are defined in EN 301 210 [11]. In pure DSNG transmissions only the PAT, PMT and TSDT need to be present. If compatibility with consumer IRDs is required, at least all mandatory SI-tables and descriptors shall be present in the bitstream and the first TSDT descriptor shall contain "DVB" while the second contains "DSNG". 4.1.10 Table update mechanism The section syntax used in the DVB Service Information (SI) supports various signalling mechanisms for SI contents updates. The update of a section with the section_syntax_indicator flag set to 1, will be signalled by incrementing the version_number field. The update will be effective immediately following the last byte of the CRC_32 of the new version of the section, so the current_next_indicator shall always have the value of "1". Sections with current_next_indicator set to "0" are never transmitted. DVB BlueBook A005 20 NOTE: Due transmission errors or operational changes, the version number may not always increment by one. Due to this any change of the version number should be seen as an indication for an update to the table. T ransmission STj Vi STj Vi STj Vi+1 St j V i+1 S1 S2 S3 S4 S1 S2 S3 S4 S1 S2 S3 S4 S1 S2 S3 S4 V alidity Time Sub-table STj version Vi all sections valid STj Vi all sections still valid STj Vi+1 section S1 valid, rest of ST j not defined STj Vi+1 S1 + S 2 valid, rest of ST j not defined STj Vi+1 S1 + S 2 + S3 valid, rest of ST j not defined STj Vi+1 S4 becomes valid, whole of STj Vi+1 valid NOTE: Sections of a sub-table do not have to be transmitted in number order. Some IRD implementations may acquire data with improved efficiency if the sections of a sub-table are transmitted in numerical order. However, a broadcaster may not transmit the sections in order owing to random access considerations. NOTE: In transition phases, where STjVi+1 is not yet valid because not all sections have been received for Vi+1, and STj Viis already not defined, receivers may choose not to discard and continue to use some information from sections received for Vi until the whole of STj Vi+1 has become valid. This scheme may be particularly useful for sub-tables with long cycle times like for example the EIT Schedule. Figure 3: Timing of table updates and validity 4.1.11 Table segmentation The generic table segmentation rules in clause 4.1.11.1 are designed to ensure maximum compatibility with legacy receivers. DVB-H and DVB-SH systems table segmentation rules are described in clause 4.1.11.2. It should be noted that most SI tables can be conveyed in multiple sections and this shall be supported. In particular NIT, BAT and SDT tables are likely to increase from one to multiple sections as a platform grows over time. Equipment shall also support EIT schedule tables with multiple sections per segment. 4.1.11.1 Generic segmentation rules 4.1.11.1.1 General rules Use of private data specifier and private data indicator descriptors shall obey the rules in clause 4.2.7.1. 4.1.11.1.2 NIT and BAT All the first loop descriptors shall be conveyed in the one or more sections of the sub-table starting in the first section. No transport stream loops shall be started until the first loop descriptors have been completed. Therefore the initial sections shall have the transport_stream_loop_length set to zero if the first loop descriptors continue in the next section. DVB BlueBook A005 21 The network_descriptors_length and bouquet_descriptors_length fields shall be set according to the number of bytes of the loop contained in the section. The description of a particular transport stream in a BAT or NIT shall not be split across more than one section. Therefore the same pair of transport_stream_id and original_network_id shall not appear in the transport stream loop of more than one section of a particular sub-table. This limits the maximum size of a second descriptor loop to 1002 bytes. 4.1.11.1.3 SDT and EIT The description of a particular service in an SDT shall not be split across more than one section. Therefore the same service_id shall not appear in more than one section of a particular sub-table. Similarly for EIT the description of an event shall not be split across more than one section. Therefore an event_id shall not appear in more than one section of a particular sub-table. These constraints limit the size of the EIT or SDT descriptor loop to that which can fit within the maximum section size for the respective table. 4.1.11.2 Segmentation rules for DVB-H and DVB-SH systems 4.1.11.2.1 General rules Use of private data specifier and private data indicator descriptors shall obey the rules in clause 4.2.7.1. 4.1.11.2.2 NIT and BAT for DVB-SH and DVB-H All the network descriptors shall be conveyed in the one or more sections of the sub-table starting in the first section. No transport stream loops shall be started until the first loop descriptors have been completed. Therefore the initial sections shall have the transport_stream_loop_length set to zero if the network descriptors continue in the next section. The network_descriptors_length and bouquet_descriptors_length fields shall be set according to the number of bytes of the loop contained in the section. An instance of the transport stream loop for a particular transport stream in a BAT or NIT may be split across more than one section. Therefore the same pair of transport_stream_id and original_network_id may appear in the transport stream loop of more than one section of a particular sub-table. In this case, the following rules apply: a) The transport_stream_loop_length field in the current section shall be set according to the number of bytes of the loop contained in the section. b) The description of a transport stream shall be encoded in numerically sequential sections. c) No other description of a transport stream shall be encoded before the completion of the current transport stream description. Therefore, descriptors for the next transport stream shall not be encoded before the current transport stream has been fully described. The most efficient packing of the descriptors to reduce the number of sections is not mandated. EXAMPLE: The NIT is constituted of a single TS, and both the network descriptors loop and the description of the single transport stream span approximately 2.5 sections each, therefore the NIT is conveyed in 5 successive sections: Section 0: DVB BlueBook A005 22 - Content: beginning of network descriptors loop, of length 800 bytes; - Structure: network_descriptors_length = 800 bytes; transport_stream_loop_length = 0; Section 1: - Content: follow-up of network descriptors loop, of length 1 000 bytes; - Structure: network_descriptors_length = 1000; transport_stream_loop_length = 0; Section 2: - Content: remainder of network descriptors loop, of length 200 bytes; start of transport stream loop, of length 600 bytes; - Structure: network_descriptors_length = 200; transport_stream_loop_length = 600; transport_descriptors_length = 594; Section 3: - Content: Follow-up of transport_stream_loop, of size 1 000 bytes; - Structure: network_descriptors_length = 0; transport_stream_loop_length = 1 000; transport_descriptors_length = 994; Section 4: - Content: remainer of transport stream loop, of length 300 bytes; - Structure: network_descriptors_length = 0; DVB BlueBook A005 23 transport_stream_loop_length_= 300; transport_descriptors_length = 294. 4.1.11.2.3 SDT for DVB-SH and DVB-H The description of a particular service in an SDT may be split across more than one section. Therefore the same combination of service_id and original_network_id may appear in more than one section of a particular sub-table. If the description of a service is split across more than one section, the same rules as listed in clause 4.1.11.2.2 shall apply. 4.2 SI descriptor allocation and usage This clause specifies the location where descriptors can be expected in a SI bit stream, and identifies which descriptors may occur multiple times. Descriptors which contain fundamental SI data are identified as recommended to be decoded by the IRD. The interpretation of other descriptors by the IRD, including those not listed in this clause, is optional. 4.2.1 Descriptors of the Network Information Table (NIT) The NIT is organized as follows: /*  header  ....*/     for  i  =  0;;  i  <  N;;  i++  {  /*  1st  descriptor  loop  */     descriptor()   }   for  (  i  =  0;;  i  <  N;;  i++)  {     /*  loop  over  Transport  Streams  */     transport_stream_id     original_network_id     for  (  j  =  0;;  Ij  <  M;;  j++)  {  /*  2nd  descriptor  loop  */       descriptor()     }   }     /*  CRC  etc.  */     4.2.1.1 First descriptor loop 4.2.1.1.1 Linkage descriptor This descriptor is used to give a link to aservice or TS. If it appears in the firstloop of the NIT it links to a service that is attached to the network operator. It could for example point to the "Paris Cable Info channel" and to "Paris Cable Text". This descriptor is allowed more than once in the firstloop of the NIT.Transmission of this descriptor is optional. The meaning of the descriptor when it occurs in the first loop of the NITdepends on the value of the linkage_type. If the linkage_type is: a) 0x01, it refers to a service that contains information about the network. An example of the intended use is for the IRD to switch to the information service when the user requests additional information about the network; b) 0x02, it refers to an Electronic Program Guide (EPG) for the network. Note that the IRD can only make use of this type of linkage if it can decode the EPG service. The present document does not specify the contents of such a service; c) 0x04, it refers to a TS which carries comprehensive Service Information. The SI carried in the referenced TS includes at least all the SI information available on all other TSs of the network; DVB BlueBook A005 24 d) 0x08, it refers to a service in a terrestrial network to which the receiver might tune to if the actual service is no longer receivable under its service_id. Valid links for the actual service can be identified by the initial service id. The hand-over_type indicates whether the linkage_descriptor is used to link to an identical service in a neighbouring country, to a local variation of the service or an associated service; e) 0x09, it refers to a transport stream carrying a System Software Update service, see TS 102 006 [17]; f) 0x0A, it refers to a transport stream carrying a System Software Update BAT or NIT with detailed signalling information about System Software Update services, see TS 102 006 [17]. The meaning of other values of linkage_type is not defined in this context. Note that the linkage_type does not indicate the service_type of the referenced service. An example of the intended use of the linkage descriptor is that an IRD user interface could include a mechanism like "info about the network" which would make the IRD tune to the linked service after the user initiated the mechanism. 4.2.1.1.2 Multilingual network name descriptor This descriptor may be used to convey the name of the network in one or more languages. This descriptor is optional, but when present shall only be included once in the first descriptor loop of the NIT. 4.2.1.1.3 Network name descriptor This descriptor is used to transmit the name of a physical network, e.g. "ASTRA", "EUTELSAT", "MUNICH CABLE" etc. This descriptor shall be used exactly once in the first loop of any NIT sub-table. 4.2.1.1.4 Cell list descriptor This descriptor is only allowed in a Network Information Table (NIT) that describes a terrestrial network. It is used to list the cells of a network. TPS bits (EN 300 744 [8]) may be used to identify a cell.If this cell identification mechanism is usedto supporthand-over,this descriptor shall be present. Otherwise, the transmission of this descriptor is optional. If it is present, the cell list shall be complete.The descriptor is allowed more than once in the first loop of the NIT. The latitude and longitude indicate the south-western corner of the spherical rectangle that approximately describes the coverage area of the cell. They do not indicate the position of the transmitter. 4.2.1.1.5 Network change notify descriptor This descriptor allows broadcasters to signal network change events to receivers. A network change event is a single, clearly identifiable change in the network configuration, e.g. transmission parameters and/or available services, which may require action on the part of receivers. Inclusion of this descriptor is optional. If it is used, it is allowed more than once in the first loop o fthe NIT. Where the network_change_notify descriptor is used, the following rules shall apply: DVB BlueBook A005 25 a) each period of engineering works shall be signalled separately and the duration of each shall be kept to a minimum; b) network changes should be signalled at least one week in advance and continue to be signalled for at least one month afterwards; c) the descriptorshall signal at all times the current list of scheduled network change events; d) absence of the descriptor shall be used to indicatethat there are no scheduled network change events; e) broadcasters shouldmake sure that all network changes have been completed by the end of the signalled period since receivers may start scanning immediately after the end of the signalled period. Network changes may be confined to a part of the network, as indicated by the use of the cell_id field (used in DVB-T and DVB-T2 systems) or may apply to the whole network, as defined by the NIT. Different network change periods affecting the same part of the network shall not overlap. Receivers should not rely on a steady network stateduring the signalled change period. 4.2.1.2 Second descriptor loop 4.2.1.2.1 Delivery system descriptors The delivery system descriptors are defined in clause 6.2.13 of EN 300 468 [1] and in the delivery system descriptor sub-clause of clause 6.4of EN 300 468 [1]. The deliverysystemdescriptors are used to transmit the physical parameters for each DVB stream in the network. One (and only one) delivery system descriptor shall appear in each second loop of the NIT, except for DVB-T2 systems where more than one instance of the T2 delivery system descriptor may be present. IRDs shall be able to interpret the delivery system descriptor in order to tune to TSs quickly (see clauses 4.1.1 and 5.3.1). 4.2.1.2.2 Service list descriptor This descriptor is used to list the services and service types for each TS. The services are listed identified by service_id (= MPEG-2 program_number). The transport_stream_id and original_network_id, which are necessary to identify an instance of a DVB service uniquely, are given at the start of the second descriptor loop of the NIT. The service list descriptor is allowed only once in each second loop of the NIT. Transmission of this descriptor is optional. When present, it should list all services. NOTE: When a service is not listed in the service descriptor in the SDT, the service list descriptor can still be used to indicate the service type. 4.2.1.2.3 Frequency list descriptor This descriptor lists the additional frequencies used in transmission of a multiplex on other frequencies. The frequency_list descriptor is allowed only once in each second loop for which there is a delivery system descriptor. Inclusion of this descriptor is optional, but if it is present, then the list of frequencies shall be complete. DVB BlueBook A005 26 4.2.1.2.4 Cell frequency link descriptor This descriptor is only allowed in a Network Information Table (NIT) that describes a terrestrial network. It is used to provide links between a cell and the frequencies that are used in this cell for the transport stream described. TPS bits (EN 300 744 [8]) may be used to identify a cell. If this cell identification mechanism is usedto support hand-over,this descriptor shall be present. Otherwise, the transmission of this descriptor is optional. If it is present, the cell list shall be complete.The descriptor is allowed more than once in each second loop of the NIT. 4.2.2 Descriptors of the Bouquet Association Table (BAT) The BAT is organized as follows: /*  header  ....*/     for  i  =  0;;  i  <  N;;  i++  {  /*  1st  descriptor  loop  */     descriptor()   }   for  (  i  =  0;;  i  <  N;;  i++)  {     /*  loop  over  Transport  Streams  */     transport_stream_id     original_network_id     for  (  j  =  0;;  I  <  M;;  j++)  {  /*  2nd  descriptor  loop  */       descriptor()     }   }     /*  CRC  etc.  */     The BAT has the same structure as the NIT. The BAT gives a logical grouping of services into bouquets, which may group together services delivered by different networks. A TS may contain services from more than one bouquet within a network. Each BAT collects the services that are allocated to the specified bouquet. 4.2.2.1 First descriptor loop 4.2.2.1.1 Bouquet name descriptor This descriptor is used to transmit the name of the bouquet the following services are allocated to, e.g. "THE NEWS BOUQUET", "HEAVEN MOVIE CHANNELS" etc. This descriptor is allowed once in the first loop of each sub-table of the BAT. It is mandatory to be transmitted in the first loop of any BAT sub-table in the TS. 4.2.2.1.2 CA identifier descriptor Transmission of this descriptor is optional; it is allowed only once in the firstloop of the BAT. It identifies one or more CA systems which apply to the services in the BAT. 4.2.2.1.3 Country availability descriptor This descriptor is used to indicate whether a bouquet is available in a specific country. It has no meaning in the sense of CA. NOTE: IRDs can use this descriptor to only display bouquets that are available in order to avoid confusionof the viewer. This descriptor is allowed at most twice in the first loop of each BAT sub-table;at most once to indicate a list of countries in which the bouquet is intended to be available, and at most once to indicate those countries in which it is not intended to be available. If the descriptor is not present, the availability status of the bouquet is undefined. Transmission of this descriptor is optional. DVB BlueBook A005 27 4.2.2.1.4 Linkage descriptor This descriptor is used to give a link to aservice or TS. If it appears in the firstloop of the BAT, it links to a service that is attached to the bouquet provider. For example it could point to the "Heaven movie teasers" and to "Heaven text TV". The linkage_descriptor is allowed more than once in the firstloop of the BAT.Transmission of this descriptor is optional. The meaning of the descriptor when it occurs in the first loopof the BAT depends on the value of the linkage_type. If the linkage_type is: a) 0x01, the descriptor refers to a service that contains information about the bouquet. An example of the intended use is for the IRD to switch to the information service when the user requests additional information about the bouquet; b) 0x02, the descriptor refers to an Electronic Program Guide (EPG) for the bouquet; NOTE: The IRD can only make use of this type of linkage if it can decode the EPG service. The present document does not specify the contents of such a service. c) 0x04, it refers to a TS which carries comprehensive Service Information. The SI carried in the referenced TS includes at least all the SI information available on all other TSs which carry services of the bouquet; d) 0x09, it refers to a transport stream carrying a System Software Update service, see TS 102 006 [17]; e) 0x0A, it refers to a transport stream carrying a System Software Update BAT or NIT with detailed signalling information about System Software Update services, see TS 102 006 [17]. The meaning of other values of linkage_type is not defined in this context. Note that the linkage_type does not indicate the service_type of the referenced service. An example of the intended use of the linkage descriptor is that an IRD user interface could include a mechanism like "info about the bouquet" which would make the IRD tune to the linked service after the user initiated the mechanism. 4.2.2.1.5 Multilingual bouquet name descriptor This descriptor may be used to convey the name of the bouquet in one or more languages. This descriptor is optional, but when present shall only be included once in the first descriptor loop of the BAT. Transmission of this descriptor is optional. 4.2.2.2 Second descriptor loop 4.2.2.2.1 Service list descriptor This descriptor is used to list the services and service types for each TS that belong to the bouquet of this BAT sub-table. This descriptor is optional, but when present shall only be included once in the second descriptor loop of the BAT.It should be transmitted since it allows the IRD to find all services that belong to a specific bouquet. NOTE: This implies that the use of this descriptor in the BAT need not list all the servicesin this transport stream. DVB BlueBook A005 28 4.2.3 Descriptors of the Service Description Table (SDT) The SDT is organized as follows: table_id            /*  distinction  between  actual  &  foreign  MUXes  */   /*  header  ....*/     transport_stream_id   original_network_id   for  i  =  0;;  i  <  N;;  i++  {  /*  descriptor  loop  */     service_id     EIT_schedule_flag     EIT_present_following_flag     running_status     free_CA_mode     for  (  j  =  0;;  j  <  M;;  j++){        descriptor()     }   }   /*  CRC  etc.  */     The SDT has a loop for descriptors for each service described in the SDT. 4.2.3.1 Announcement support descriptor The announcement support descriptor informs about announcements supported by the service. It is an optional descriptor and allowed only once in each SDT service loop. 4.2.3.2 CA identifier descriptor If a service is generally CA-protected, this descriptor may be used to transmit data of the CA-system. The CA_identifier_descriptor is not involved in any CA control function, it is an indication for the user interface software in the IRD that a service is under conditional access, and which CA-system is used. Then the user interface software may decide whether this service is reachable or not. The aim of the transmission of this descriptor is to avoid frustration to users caused by services being displayed for selection that are not reachable. This descriptor is allowed only once in the SDT service loop. It is not allowed if there is a time_shifted_service_descriptor. Transmission of this descriptor is optional in the SDT. 4.2.3.3 Component descriptor This descriptor is used to specify streams that are part of a DVB service. When present in the SDT, this can be used by the IRD to control the presentation of the service to the viewer. When present in the SDT, the component_descriptor defines a default stream specification that is inherited by all events forming part of this service. NOTE 1: Any such default stream specification may be overriden on an event by event basis by the use of the component_descriptor in the EIT (see clause 4.2.4.2). Transmission of this descriptor is optional in the SDT. However, it is only allowed if there is no time_shifted_service descriptor. The descriptor may appear more than once in an SDT service loop since there may be more than one stream being specified. NOTE 2: This does not imply any mandatory requirements regarding which (if any) streams are specified within the SDT by use of a component_descriptor. DVB BlueBook A005 29 4.2.3.4 Country availability descriptor This descriptor is used to indicate whether a service is available in the specified country. It has no meaning in the sense of CA. NOTE: IRDs can use this descriptor to only display services that are available in order to avoid confusion of the viewer. This descriptor is allowed at most twice in each SDTservice loop, at most once to indicate a list of countries in which the service is intended to be available, and at most once to indicate those countries in which it is not intended to be available. If the descriptor is not present, the availability status of the service is undefined. It is not allowed if there is a time_shifted_service_descriptor.Transmission of this descriptor is optional. 4.2.3.5 Data_broadcast_descriptor See clause 4.2.7.3. 4.2.3.6 Linkage descriptor This descriptor is used to give a link to aservice. If it appears in the SDT serviceloop, it links to a service that is relatedto this service. Transmission of this descriptor is optional. More than one linkage descriptor is allowed in a loop. The meaning of the descriptor, when it occurs in the SDT service loop, depends on the value of the linkage_type. If the linkage_type is: a) 0x01, the descriptor refers to a service that contains information about this service. An example of the intended use is for the IRD to switch to the information service when the user requests additional information about this service; b) 0x02, the descriptor refers to an Electronic Program Guide (EPG) for this service; NOTE 1: The IRD can only make use of this type of linkage if it can decode the EPG service. The present document does not specify the contents of such a service. c) 0x03, the descriptor refers to a CA replacement service for this service. An example of the intended use is for the IRD to switch automatically to the replacement service if the CA system denies access to this service; d) 0x05, the descriptor refers to a replacement service for this service. An example of the intended use is for the IRD to switch automatically to this replacement service when the selected service has a running status of "not running"; NOTE 2: The linkage_type does not indicate the service_type of the referenced service. An example of the intended use of the linkage descriptor is that an IRD user interface could include a mechanism like "info about the service", which would make the IRD tune to the linked service after the user initiated the mechanism. e) 0x08, it refers to a service in a terrestrial network to which the receiver might tune to if the actual service is no longer receivable under its service_id. The hand-over_type indicates whether the linkage_descriptor is used to link to an identical service in a neighbouring country, to a local variation of the service or an associated service. DVB BlueBook A005 30 4.2.3.7 Mosaic descriptor This descriptor may be located in the SDT service loop, and/or the PMT. It is used to describe mosaic services is described in clause 5.2. It is not allowed if there is a time_shifted_service_descriptor. 4.2.3.8 Multilingual service name descriptor This descriptor may be used to convey the name of the service provider and service name in one or more languages. It is allowed only once in the SDT serviceloop. Inclusion of this descriptor is optional. 4.2.3.9 NVOD reference descriptor This descriptor lists the services which belong to a Near Video On Demand (NVOD) service. A description of the NVOD-mechanisms is given in clause 5.1. The NVOD_reference_descriptor is allowed only once in each SDT serviceloop. It is mandatory to be transmitted if the corresponding services are described using the time_shifted_service_descriptor. IRDs are recommended to make use of the NVOD_reference_descriptor in order to allow access to NVOD-services. 4.2.3.10 Service descriptor This descriptor contains the basic textual identifications of a service such as service name and provider name. It is mandatory to be transmitted unless a time_shifted_service_descriptor is present, in which case the service descriptor shall not beused. If the service descriptor is present, it shall only be allowed once in each SDT serviceloop. IRDs are recommended to make use of it in order to display the service names in the user interface. 4.2.3.11 Service availability descriptor This descriptor is used in the SDT to provide a link between a service in a terrestrial network and the network cells in which it is available or unavailable. Transmission of this descriptor is optional. The descriptor is allowed more than once in the SDT serviceloop. This descriptor may be used in terrestrial networks for local services which are not present on the whole network. In this case the association between the multiplex and the cell on which it is broadcast is made by the insertion of the cell_id in the TPS bits of the radiated multiplex. By extracting this information from the TPS bits, and using the descriptor in the SI, the receiver is able to build a service list containing only the relevant services available in the cells it is currently able to receive. The mechanism prevents the user from being presented services which are in fact not receivable at his/her current location. In a specific multiplex / cell_id combination, the components of all services indicated to be available in the SDT actual shallbe available in the multiplex, if the service is running. The services in the SDT actual, matching the cell_id in one of theservice availability descriptors,shalldescribe all services available in the multiplex. The SDT actual shoulddescribe all services occurring in all multiplexes of a network that match its transport_stream_id and its original_network_id. The SDT shall notcontain multiple instances of the DVB BlueBook A005 31 same combination of service_id and original_network_id in a subtable.However, for DVB-SH and DVB-H, the SDT sub-table sections may contain multiple instances of the same combination of service_id and original_network_id (see clause 4.1.11.2.3). NOTE: The cell_id can not be used to identify a service.The combination of service_id and original_network_idremains a unique identification of a service. It is not the intention to describe multiplexes that are only distinguished by service_availability separately in the NIT and BAT. Therefore, in the second loop of the NIT and BAT there shall be at most one association between original_network_id, transport_stream_id and the frequency_list_descriptor. The same shall apply for service_list_descriptor. NOTE: Both frequency_list_descriptor and service_list_descriptor remain optional when local service availability is used in a network. Mixed use of service_availability qualification of services in a network or even in a multiplex is possible. A service not linked to a particular service_availability_descriptor shall be considered available in all cells transmitting the multiplex. 4.2.3.11.1 Network Implementation Considerations By using the service_availability_descriptor, network operators can create one SI for multiple multiplexes in a network, yet still define specific subsets of these services to be valid for the different transmitters in a network (i.e. this creates one large "virtual" transport stream of which only the relevant parts are transmitted on each transmitter). A typical example purpose for this are local variations of one 'mother' service carried in a transport stream. The SI may for example be the same for a set ofmultiplexes, but each of these multiplexes may carry a different set of services and indicate (through the association between cell_id and service_availability descriptor) which of the services are actually carried in a specific instance of the multiplex. The only differentiation between these multiplexes is made in the receiver through the link with the cell_id. It is also clear that the PSI information of different multiplexes should be consistent (as normal) and should not contain PSI for services that are not available. I.e. the network operator may use a central SI generator but should (re)multiplex the multiplexes at the PSI and ES level. When defining terrestrial networks and local variations on these networks, the number of network cells and the association between the cells and the services have to be carefully defined in order to control the amount of SI information in the multiplex because the SDT and EIT carried in all multiplexes will grow as the common SI has to carry more service instances. The network operator should be aware that resolution of linkage_descriptor information and other references to transport streams only via transport_stream_id may no longer be uniquely possible by an IRD. So in case such a reference is made, the specific resolution to multiplex shall be arbitrary. Note that resolution to a service carried in a specific multiplex from the service_id should still be uniquely possible (if the multiplex(es) carrying it can be received by the IRD). 4.2.3.11.2 IRD implementation considerations The recommendations below should be followed to allow optimal functionality in networks deploying service_availability_descriptors: It is recommended to match SDT and EIT information (depending on the purpose of use) either with: - Cell_id of current multiplex (for deriving information on the currently tuned multiplex). DVB BlueBook A005 32 - Cell_ids of all receivable instances of a multiplex (for deriving information on all receivable services including cross-carriage information for multiplexes with the same transport_stream_id). - No matching on cell_id for generating the most abundantly available SI information. It is recommended to make all receivable multiplexes with the same transport_stream_id but with different cell_ids available to the user, and only when a service (not a transport stream) is available through multiple multiplexes to select a preferred multiplex based on e.g. reception quality. Any reference resolution from a transport_stream_id or a service_id (e.g. from a linkage_descriptor transport_stream_id/service_id pair) to a multiplex / frequency requires consideration to handle the potential multiplicity of the result. Note that in networks deploying the service_availability_descriptor, the unique identification of a transport stream by the tuple (transport_stream_id, original_network_id), can often be sensibly replaced by identification through the triplet (transport_stream_id, original_network_id, cell_id). 4.2.3.12 Service relocated descriptor This descriptor provides a mechanism which enables an IRD to track a service which has moved from one TS to another, or has changed service identifiers. If the service remains within the same original network, then the new_service_id should be the same as the previous service_id where possible (see clause 4.1.1). If a complete TS is moved, then this can be achieved by updating the NIT tuning information for the TS. In this case the original_network_id, transport_stream_id, and service_ids are unchanged, and the service_relocated_descriptor is not applicable. Transmission of this descriptor is optional, but if present it shall only occur only once in the SDT serviceloop. It is not allowed if there is a time_shifted_service_descriptor. The following rules are recommended to minimize the discontinuity: a) Before a service moves, the network change notify descriptor (see 4.2.1.1.5) should be used to give receivers advance notice of a change. b) During the change, the service should be available at the old and new locations, where possible. In this case, a service move descriptor (see 4.2.6.6) should be used to make c) After the change is completed, the service relocated descriptor should be present for some time to indicate the old location and assist receivers which have not acquired the service during the changeover period. 4.2.3.13 Telephone descriptor Transmission of this descriptor is optional, and it may occur more than once in the SDT serviceloop. It is not allowed if there is a time_shifted_service_descriptor. IRDs cannot make use of it without further information [19, 20, 21]. DVB BlueBook A005 33 4.2.3.14 Time shifted service descriptor This descriptor identifies a service as a time shifted copy of another service (clause 5.1). The time_shifted_service_descriptor is allowed only once in each SDT serviceloop. It is mandatory to be transmitted for services listed in an NVOD_reference_descriptor. If a time_shifted_service_descriptor is present in an SDT service loop, the following descriptors are not allowed in the same descriptor loop: multilingual_service_name_descriptor; CA_identifier_descriptor; country_availability_descriptor; mosaic_descriptor; telephone_descriptor; bouquet_name_descriptor; service_descriptor. IRDs are recommended to be able to interpret it in order to access NVOD-events. 4.2.4 Descriptors of the Event Information Table (EIT) An EIT-section is organized as follows: table_id          /*  classification  of  the  EI-­section  :  present  following  etc.  */   /*  header  ....*/     service_id   transport_stream_id   original_network_id   for  i  =  0;;  i  <  N;;  i++  {  /*  descriptor  loop  */     event_id     start_time     duration     running_status     free_CA_mode     for  (  j  =  0;;  j  <  M;;  j++){       descriptor()     }   }   /*  CRC  etc.  */     The EIT has a loop for descriptors for each event described in the EIT. 4.2.4.1 CA identifier descriptor If an event is CA-protected, this descriptor may be used to transmit data of the CA-system. The CA_identifier_descriptor is not involved in any CA control function, it is an indication for the user interface software in the IRD that the event is under conditional access and which CA-system is used. Then the user interface software may decide whether this service is reachable or not. The aim of the transmission of this descriptor is to avoid frustration to users caused by events being displayed for selection that are not reachable. This descriptor is allowed only once in the EIT event loop. It is not allowed if there is a time_shifted_event_descriptor. Transmission of this descriptor is optional in the EIT. DVB BlueBook A005 34 4.2.4.2 Component descriptor This descriptor is used to specify streams that are part of a DVB event. The descriptor may appear more than once in the EIT event loop since there may be more than one stream. If there is a time_shifted_event_descriptor, this descriptor is not allowed. Transmission of this descriptor in the EIT Present/Following for the actual TS is mandatory for all Elementary Streams except those: whose specification can be inherited from use of the component_descriptor in the relevant SDT; or which are present but are not used during the current event; or NOTE: A broadcaster may choose not to remove an Elementary Stream from the PMTduring events where this Elementary Stream is not used. The presence of the component descriptor in the EIT indicates whetherthe Elementary stream is in use during the event. which are only suitable for presentation by an accompanying (e.g. MHP) application; or which are coded according to the data broadcasting specification, for which the data broadcasting descriptor may be used. Transmission of this descriptoris optional for EIT schedule (actual & other) and for EITp/f other. It is useful to indicate which streams will be available for future events. The stream specification provided by an instance of this descriptor in EIT shall override any default stream specification for the same component (as identified by component_tag) defined in the SDT (see clause 4.2.3.4). 4.2.4.3 Content descriptor This descriptor is used to classify the content of the event. Only one content descriptor may appear in the EIT event loop.It is possible to transmit more than one classification term because there is a loop within the descriptor. If there is a time_shifted_event_descriptor, this descriptor is not allowed, since the content information can be provided in the EIT sub-table for the corresponding NVOD reference service. Transmission of this descriptor is optional. 4.2.4.4 Data_broadcast_descriptor See clause 4.2.7.3. DVB BlueBook A005 35 4.2.4.5 Extended event descriptor This descriptor is used to transmit a bigger amount of textual information for an event than is possible with the short_event_descriptor. The information in extended event descriptors supplements that given in a short event descriptor. A language code is transmitted in order to indicate in which language the text is written. More than one extended_event_descriptor is allowed in the EIT event loop, for transmitting more data than one descriptor cancontain (255 bytes excluding header), and for different languages. The last_descriptor field specifies the number of the last extended_event_descriptor for a specific language. If there is a time_shifted_event_descriptor, this descriptor is not allowed. Transmission of this descriptor is optional. 4.2.4.6 Linkage descriptor This descriptor is used to give a link to anevent or service. If it appears in The EIT eventloop, it links to an event or a service that is attached to this event. Transmission of this descriptor is optional. More than one linkage descriptor is allowed in an EIT event loop. The meaning of the descriptor, when it occurs in the EIT event loop, depends on the value of the linkage_type. If the linkage_type is: 0x01, the descriptor refers to a service that contains information about this event. An example of the intended use is for the IRD to switch to the information service when the user requests additional information about this event. If there is a time_shifted_event_descriptor, this linkage_type is not allowed. An example of the intended use of this linkage_type is that an IRD user interface could include a mechanism like "info about the event" which would make the IRD tune to the linked service after the user initiated the mechanism. 0x0D, the descriptor is used to link from the current event (assumed to be an SD event) to an HD version of the same content. They may be scheduled at the same or at different times. When the SD and HD events are scheduled to start at the same time, the event_simulcast field should be set to 1. In all other cases the field should be set to 0. In order for sequential HD simulcast events to be displayed by a receiver without channel change interruption, the service operator should cross-carry the EIT of the original service in the multiplex of the target service. This allows the receiver to always track the next event on the original service and detect a subsequent HD_simulcast_event link. Receivers are recommended to implement a user confirmation when switching back and forth to the HD simulcast event, and take into account the reception quality of the service carrying the HD event. In case of target_listed_flag = 0, the receiver should use the service identification (i.e. service_name) of the original service, when appropriate, while displaying the target service. The meaning of other values of linkage_type is not defined in this context. Note that the linkage_type does not indicate the service_type of the referenced service. 4.2.4.7 Multilingual component descriptor This descriptor may be used to convey text describing a component of an event in one or more languages. This descriptor is optional, but when present shall only be included once in the EIT DVB BlueBook A005 36 event loop for each component of an event. If there is a time_shifted_event_descriptor, then this descriptor is not allowed. 4.2.4.8 Parental rating descriptor This descriptor is used to give a rating of the programme based on age or other criteria that is used to prevent children from viewing unsuitable programmes. If there is a time_shifted_event_descriptor, this descriptor is not allowed, since the parental rating information can be provided in the EIT sub-table for the corresponding NVOD reference service. This descriptor is optional, but when present shall only be included once in the EIT event loop Country_codes relating to groups of countries may be used within the descriptor. If, as a result, there is more than one entry for a country in the descriptor, then the first entry in the descriptor which includes the country shall take precedence over any subsequent entry. For example, the following sequence of data within the descriptor would describe a parental rating of minimum age of 12 in all countries except UK, for which the minimum age is 18. EXAMPLE: country_code = UK rating = 0x0F country_code = all countries rating = 0x09 4.2.4.9 PDC descriptor The PDC_descriptor extends the DVB system with the functionalities of PDC (EN 300 231 [12]). The descriptor carries the Programme Identification Label (PIL) as defined in EN 300 231 [12]. This label has, in principle, the same function as the DVB event_id, but with the advantage of being available to the public implicitly by many media a long time in advance. The PIL contains date and time of the first published start time of a certain event. Within analogue systems the PIL is either broadcast in the teletext format or as a part of the VPS label in dataline 16. No change is made to the PIL once it has been made publicly available provided the transmission time remains within the validity time window (EN 300 231 [12]). No use shall be made of types of "service codes" (EN 300 231 [12]) which would imply dynamic changes during a running event. Their function shall only be covered by the RST. If a service supports the PDC function, a PDC descriptor shall appear once in all EIT present/following subtables for the actual TS of the service. 4.2.4.10 Short event descriptor This descriptor is used to transmit the name and a short text description for an event. A language code is transmitted in order to indicate in which language the title and the text are written. Transmission of this descriptor is mandatory, unless there is a time_shifted_event_descriptor, in which case the descriptor is not allowed. This descriptor is allowed more than once in the EIT event loop for different languages. Thus it is not allowed to have more than one short_event_descriptor with the same language code. 4.2.4.11 Telephone descriptor Transmission of this descriptor is optional, and it may occur more than once in the EIT event loop. IRDs cannot make use of it without further information [19, 20, 21]. DVB BlueBook A005 37 4.2.4.12 Time shifted event descriptor This descriptor is used to indicate that an event is the time-shifted copy of another event. If this descriptor is present only a PDC_descriptor, private_data_specifier_descriptors and private descriptors are allowed in the EIT event loop. Transmission of this descriptor is mandatory in case of NVOD. IRDs are recommended to decode this descriptor, without which access to the Service Information of NVOD events is not possible. 4.2.5 Descriptors of the Time Offset Table (TOT) The TOT is organized as follows: /*  header  ....*/     UTC_time   for  i  =  0;;  i  <  N;;  i++  {  /*  descriptor  loop  */     descriptor()   }   /*  CRC  etc.  */   4.2.5.1 Local time offset descriptor This descriptor may be used to indicate the local time offset and the automatic adjustment between summer and winter time by an IRD. Broadcasters should ensure that time_of_change is valid in that it should represent the time of the last daylight savings change or that of the next forthcoming daylight savings change.Time_of_change should be updated to carry a forthcoming daylight savings change with as much notice as possible. This should be at least equal to the time scope of any associated EIT schedule to ensure a correct presentation of the programme schedule to the user across the change. The data given in the descriptor will be constant for most of the time, but will be updated by the broadcaster to announce the transitions from summer time to winter time and vice versa in advance. In the TOT descriptor loop the local time offset descriptor may occur more than once. It is assumed that the same set of countries/country regions be included in the TOT at all times. Only one time_of_change should be signalled for each combination of country_code and country_region_id. If the time of the next change is unknown, or there is no next change (in the case of a region that does not use daylight saving) then the time_of_change field shall contain a valid value and the next_time_offset field shall convey the same value as the local_time_offset field. If a country uses more than one time zone, the country_region_id field identifies the different regions of the country with different time zones. Example data for the descriptor fields: country_code: x9yy (European Continent countries group) country_region_id 000000 local_time_offset_polarity 0 local_time_offset 0000000100000000 (Winter: 1 hour) 0000001000000000 (Summer: 2 hours) The descriptor may be applied in the following applications: display of the current local time on the IRD or TV screen; DVB BlueBook A005 38 display of the programme guide in local time; timer programming of the video recorder in local time. 4.2.6 Descriptors of the Program Map Table (PMT) The PMT is organized as follows: /*  header  ....*/   program_number   /*  service_id  */   PCR_PID   for  (i=0;;  i running or The service will broadcast again undefined 4.4 Minimum repetition rates 4.4.1 Satellite and cable delivery systems For satellite and cable delivery systems, where there will usually be sufficient bandwidth within a single delivery system to carry the SI, the following minimum repetition rates are specified: a) all sections of the NIT shall be transmitted at least every 10 s, including those for other delivery systems, if present; b) all sections of the BAT shall be transmitted at least every 10 s, if present; c) all sections of the SDT for the actual multiplex shall be transmitted at least every 2 s; d) all sections of the SDT for other TSs shall be transmitted at least every 10 s, if present; e) the TDT shall be transmitted at least every 30 s; f) the TOT (if present) shall be transmitted at least every 30 s; g) all sections of the EIT Present/Following Table for the actual multiplex shall be transmitted at least every 2 s; h) all sections of the EIT Present/Following Table for other TSs shall be transmitted at least every 10 s, if present; The repetition rates for further EIT tables will depend greatly on the number of services and the quantity of related SI information. The following transmission intervals should be followed if practicable but they may be increased as the use of EIT tables is increased. The times are the consequence of a compromise between the acceptable provision of data to a viewer and the use of multiplex bandwidth. a) all sections of the EIT Schedule Table for the first 8 days shouldbe transmitted at least every 10 s, including those for other TSs, if present; b) all sections of the EIT Schedule Table for further than 8 days ahead shouldbe transmitted at least every 30 s, including those for other TSs, if present; DVB BlueBook A005 45 4.4.2 Terrestrial delivery systems For terrestrial delivery systems bandwidth within a single transmitted TS is a valuable resource and in order to safeguard the bandwidth allocated to the primary services receivable from the actual multiplex, the following minimum repetition rates are specified in order to reflect the need to impose a limit on the amount of available bandwidth used for this purpose: a) all sections of the NIT shall be transmitted at least every 10 s; b) all sections of the BAT shall be transmitted at least every 10 s, if present; c) all sections of the SDT for the actual multiplex shall be transmitted at least every 2 s; d) all sections of the SDT for other TSs shall be transmitted at least every 10 s if present; e) the TDT shall be transmitted at least every 30 s; f) the TOT (if present) shall be transmitted at least every 30 s; g) all sections of the EIT Present/Following Table for the actual multiplex shall be transmitted at least every 2 s; h) all sections of the EIT Present/Following Tables for other TSs shall be transmitted at least every 20 s if present. The repetition rates for further EIT tables will depend greatly on the number of services and the quantity of related SI information. The following transmission intervals should be followed if practicable but they may be increased as the use of EIT tables is increased. The times are the consequence of a compromise between the acceptable provision of data to a viewer and the use of multiplex bandwidth. a) all sections of the EIT Schedule table for the first full day for the actual TS, shouldbe transmitted at least every 10 s, if present; b) all sections of the EIT Schedule table for the first full day for other TSs, shouldbe transmitted at least every 60 s, if present; c) all sections of the EIT Schedule table for the actual TS, shouldbe transmitted at least every 30 s, if present; d) all sections of the EIT Schedule table for other TSs, shouldbe transmitted at least every 300 s, if present; 4.5 Terrestrial systems The definition of the term "network" in terrestrial systems allows for different implementations. A terrestrial network may be based: exclusively on the MFN mode. In this case each cell of the network is operating in MFN mode for all transport streams of the network; exclusively on the SFN mode. In this case each cell of the network is operating in SFN mode for all transport streams of the network; on a mixture of the MFN and SFN mode. In this case some cells of the network may be operating in MFN mode and some others may be operating in SFN mode. It is also possible DVB BlueBook A005 46 for some transport streams from a cell to be broadcast in the MFN mode, whereas other transport streams from the same cell may be broadcast in the SFN mode. It is possibleto overlay networks, so that the receiver might receive transport streams from more than one network at the same time. Emitting sites may broadcast transport streams from different networks. A transport stream which belongs to one network is however not allowed to differ from one transmitter to another except for: a) different audio, video and data components due to regional variations; NOTE: The receiver might toggle between components with different content since the transmission of different local components is not signalled. b) SI -tables) which may be different. PSI and SI describing the transport stream itself (for instance all actual -tables) shall remain unchanged. 4.5.1 The use of alternative frequencies for multiplexes The NIT shall signal the use of possible alternative frequencies. One or more of the following three signalling methods maybe implemented. Each provides progressively more specific information to the IRD and may help providing faster methods to find usable frequencies.Receivers should check which of the signalling methods are being used. 1) Use the other_frequency_flag in the terrestrial_delivery_system descriptor to advise the IRD that the identical multiplex may be receivable on other centre frequencies. The IRD may, for example, try scanning for a more reliable signal. 2) Use the frequency_list_descriptor in order to provide a list of all the possible frequencies used in transmitting a particular multiplex within the network. This descriptor is in the second descriptor loop of the NIT and so it is specific to a single transport stream. The IRD may, for example, try to determine the best signal to use at the time 3) Use the cell_frequency_link_descriptorin order to provide the frequency used in a particular cell to transmit a particular multiplex within the network. This descriptor is in the second descriptor loop of the NIT. A mobile IRD may try to determine those of the alternative frequencies that are probably used at its actual position. Where the frequency_list_descriptor or the cell_frequency_link_descriptor are used, it is strongly recommended that the list for each transport stream reflects the same order of emitting sites. Thus, if there are two transport streams in a network each being emitted from the same three emitting sites, then the order in the frequency list descriptor should, for both transport streams, be: emitting_site_1; emitting_site_2; emitting_site_3. Where one of the emitting sites does not broadcast a particular transport stream the corresponding frequency in the list should be set to zero. DVB BlueBook A005 47 In many cases a receiver will receive all of the available transport streams from a single aerial position. These descriptors can be used to aid the receiver in finding a "best first guess" of the frequency. The IRD can then try first the alternative frequency for a second multiplex which is in the corresponding position within the list for the receivable frequency for the first multiplex. Table 4: Use of ordered alternative frequency lists station_1 station_2 station_3 frequency list for multiplex_A frequency_1, A frequency_2, A frequency_3, A frequency list for multiplex_B frequency_1, B frequency_2, B frequency _3, B Where a network covers a large geographical area, it is possible that different emitting sites may use the same frequency for different transport streams. It is therefore important to the viewer that the IRD ensures that the services provided are those which are requested. In some places, an IRD may be able to receive signals from more than one emitting site which carry different networks. If an IRD receives a signal from one emitting site, it would normally only have information about services from that site. The use of NIT other and SDT other is recommended to assist the IRD in finding the services from the other networks. Even though a NIT may indicate that a transport stream is available it does not guarantee that the stream can be received by the IRD. It is important that the IRD should ensure the availability of the service before offering the service to the viewer for selection. For optimization of the network coverage, operators can broadcast the same transport stream in a network on alternative frequencies using different modulation parameters. The modulation parameters in the terrestrial_delivery_system_descriptor apply to the frequency indicated in the terrestrial_delivery_ system_descriptor and may not always apply to alternative frequencies. When the IRD uses an alternative frequency to tune to a transport stream it should not rely on those modulation parameters indicated in the terrestrial_delivery_system_descriptor. Allocation of network_ids can be found in TS101 162 [4]. 4.5.2 Regional or local services The insertion of local services is an important feature of terrestrial TV systems (see figure 4). The aim is to have a principal service which, at some precise time, may be displaced in order to provide a regional or local service. There are several methods for achieving this. The simplest method is to broadcast multiplevariants of a principal service, each containing different local programming.Each instance will have different identifiers and indicates the variation of the content in theservice name. EXAMPLE: If the pr TV , the variation for the south-east might be called TV SE A better method would be to broadcast all variants of the service using the same service name, and use the target region descriptors[1] to allow receivers to present the appropriate service. Another way would be for aregional service tooccupy the same bandwidth as the principal service at the moment of the switch. This method allows for better use of bandwidth, but requires strict constraints on stream preparation and receiver behaviour to allow seamless switching. DVB BlueBook A005 48 Figure 4: Simple replacement of a principal service by a regional or local service At time B the principal service, service_id = 1, is displaced by a locally provided service, service_id = 2. This runs from time B to time C at which time the principal service, service_id = 1, is restored. Up to time A the service_id = 1 has a running_status set to "running" and service_id = 2 has a running_status set to "not running". The changes in the SI tables reflect the more precisely timed changes in the PSI tables and streams. During the period when service_id = 2 is not providing a service it is a null service. This can be achieved by simply providing a reference to the service in the SDT only. PAT and PMT data are not required at this time (see clause 4.3). It is not necessary to provide any video or audio packets and thus the overhead incurred by this null service is reduced to the bits involved in the SDT entry. The running-status permits the setting of an intermediate state "starts in a few seconds". The IRD may use this period to prepare for the change. At the time of the change the appropriate data, audio and video streams for service_id = 2 are introduced whilst those for service_id = 1 are simultaneously ceased. At the point of change service_id = 1 will become a null service. The process reverses when service_id = 2 terminates. It may be thought preferable for operational reasons to provide a number of still picture frames, either at black or using a viewable picture, in order to accommodate the effect of switching to a fresh video and audio stream. The path to the replacement service shall be indicated by the linkage_descriptor using the linkage_type "service replacement service". More complex service switching operations can be envisaged (see figure 5). These include switching from two services to a single higher bitrate service and from three services to two higher bitrate services. In either case the changes in the SI tables will reflect the more precisely timed changes in the PSI tables and streams. The IRD must decide what to do at the end of the service replacement. In many cases the IRD will be able to determine that the identity of the service to which it should return from the identity of the service from which it switched. The automatically determined choice may not necessarily be correct.Receivers are recommended to implement a user confirmation when switching. DVB BlueBook A005 49 Figure 5: More complex replacement of two main servicesby a premium wider bandwidth service 4.5.3 Hand-over 4.5.3.1 General description of the requirements A stationary or portable IRD can assume that a transport stream on a given frequency will be constantly available during its operation. In contrast, a mobile IRD will face the situation that the selected transport stream signal is no longer available on the tuned frequency if the IRD is moving out of the reception area. In order to continue the selected service, the mobile IRD then needs to automatically select and tune a different frequency carrying either exactly the same transport stream or a different transport stream containing the same service. If the IRD moved from one cell to another cell of the same network, the same set of transport streams will be available but they will be on different frequencies. The mobile IRD has to determine on which frequency the lost transport stream is transmitted in the entered cell. If the IRD moved from a cell belonging to one network into a cell of another network then the lost transport stream is not necessarily available. The IRD might want to find out if the service that had been selected before is available on some transport stream of the entered network or if there are alternative services to select. a) If the previously selected service is still available, the IRD needs to determine the transport stream that carries the service and the frequency of that transport stream in the entered network. b) If the service is not available, the IRD might try to select an alternative service (which could be a local variation of the original service or an associated service) before it prompts the user for a decision. Deploying this mechanism, co-operating networks might provide automatic hand-over between services of similar program type or services which provide additional information such as traffic announcements. Figure 6 shows the two general hand-over situations: hand-over from one cell to another cell of the same network (network II) and the hand-over between cells of different networks (from network I to network II). DVB BlueBook A005 50 Figure 6: Hand-over situations in DVB-T networks 4.5.3.2 Hand-over by means of the frequency_list_descriptor If a network consist of multiple cells, then for each transport stream the centre frequency used in one cell is given in the terrestrial_delivery_system_descriptor.To support mobile hand-over, the frequency_list_descriptor should be used to give the complete list of additional frequencies for a multiplex which is transmitted from multiple cells. Knowing all availablecentre frequencies, the IRD only needs to test those frequencies for a sufficient signal strength, decode the transport stream, and check for the same pair of original_network_id and transport_stream_id. When the mobile IRD crossesa network border, the previously acquired frequencies may no longerlead to the same transport stream. To support mobile hand-over across network boundaries, NIT subtables for the neighbouring networks should betransmitted.Ifthe transport stream is also carried in the neighbouring networks, then the IRD willbe able to find the sametransport stream again by testing the frequencies given in the NIT-other subtablesfor the same pair of original_network_id and transport_stream_id. If the sametransport stream is not transmitted in the newly entered network, the last possibility is to check the service_list_descriptor of each transport stream to find the service_id of the previously selected service and use that transport stream. Note that this method can only be deployed if the neighbouring networks are using unique, coordinated service_id values. The actual number of frequencies to be tested strongly depends on the network layout. If a network tries to reuse same frequencies for a transport stream in as many cells as possible, then the actual number of frequencies to be tested will be less then the number of cells. If all neighbouring networks that provide the same transport stream use coordinated frequencies, then again the number of different frequencies can be less then the number of neighbouring networks. DVB BlueBook A005 51 Figure 7: Hand-over at network borders by means of the frequency_list_descriptor and the service_list_descriptor 4.5.3.3 The occurrence of tuning failures Apart from a full frequency scan, the hand-over method described above isthe simplest that can be implemented on the basis of the terrestrial_delivery_system_descriptor and the frequency_list_descriptor in conjunction with the service_list_descriptor. The disadvantage of this solution is that tuning failures may occur that lead to a visible or audible service interruption. The occurrence of tuning failures isshownin figure 8. DVB BlueBook A005 52 Figure 8: The occurrence of tuning failures In network II the selected service (service X) is part of transport stream TS 1. At the current position of the receiver this transport stream is transmitted on frequency fN. Reaching a cell border the receiver will check the alternative frequencies given in the NIT actual and other sub-tables. In the NIT actual of network II the frequencies fA and fB are listed as alternative frequencies for transport stream TS 1. If the receiver moved to another cell of the same network (case a), the test on frequency fA would lead to a sufficient signal strength and the receiver starts to decode transport stream TS 2. Only after decoding TS2 the receiver can detect this tuning failure and switch to the next alternative frequency. If the receiver moved to a cell of network I (case b), the frequency fA will not carry a signal but testing fB again leads to sufficient signal strength and the receiver starts to wrongly decode transport stream TS 2 of network I. The risk of tuning failures is proportional to the number of alternative frequencies that are used to transmit a single transport stream in the different cells of a network. Note that a tuning failure in this context is the event where a receiver has decoded a transport stream that is different (by means of the original-network-id and transport-stream-id) from the transport stream that the receiver intended to decode. 4.5.3.4 Hand-over methods with a reduced risk of tuning failures The risk of tuning failures can be reduced if the number of alternative frequencies that need to be tested is minimized. Some different approaches are described below. Note that these mechanisms require unique service-id's across transport streams and networks if service hand-over between varying transport streams in co-ordinated networks shall be successful. DVB BlueBook A005 53 4.5.3.4.1 Local SI insertion One possibility is to make each cell a separate network (each network consists of only one cell) described by individual Service Information. The transport streams of the actual cell are then described with the NIT actual while all neighbouring cells are described by corresponding NIT other sub-tables. Hence, the frequency for a transport stream of the actual cell is given in the terrestrial_delivery_system_descriptor in the NIT actual and the alternative frequencies for the surrounding cells (networks) can be found in the terrestrial_delivery_system_descriptor of the corresponding transport stream in the NIT other sub-tables. The frequency_list_descriptor is not used. In this way, the receiver only needs to check the frequencies of the same transport stream in the surrounding cells and, by the geographical network layout the number of surrounding cells is typically limited to six or less. Depending on the geographical conditions, the number of actually different frequencies can be even less then the number of surrounding cells. Thus, the probability of tuning failures can be minimized by appropriate network planning and frequency reuse. 4.5.3.4.2 Cell identification In those cases where a local SI insertion is not possible the reduction of relevant alternative frequencies can be achieved if the receiver knows to which cell the current signal belongs, what the neighbouring cells are and which frequency is used in which cell. The following components provide this information: The cell_frequency_link_descriptor is similar to the frequency_list_descriptor but it also identifies the cells and the subcells for which the frequencies are valid. The cell_list_descriptor describes the coverage area of all the cells that belong to a network. The cell_idtransmitted in the TPS bits (EN 300 744 [8]). Using the cell_idenables the receiver to determine which cell has been entered and to reduce the number of frequencies to be tested to those for the current and neighbouring cells. 4.5.3.4.3 Performance enhancement with GPS data If the receiver knows its actual position, for example it might use position data from an additional GPS receiver, then it will be able to determine which cell will be entered before the actual network border has been reached. This calculation depends on the geographical dimensions of the actual and surrounding cells given with the cell_list_descriptor. Knowing the cell that will be entered, the frequency used in that cell can be determined beforehand by using the cell_frequency_link_descriptor. However, it might not always be possible to exactly determine the destination cell, for example if the position is at a juxtaposition of three cells. Nevertheless, the risk of tuning failures can be dramatically reduced, especially if leaving large SFN cells. 4.5.3.4.4 Two front-end solution The risk of tuning failures can completely be eliminated by means of a second front-end, provided that: a) a second demultiplexer is available; or b) cell_id, cell_list_descriptor and cell_frequency_link_descriptor are supported. DVB BlueBook A005 54 Furthermore, only a two front-end solution offers the possibility to make the duration of a successful hand-over shorter. 4.5.3.5 Performance considerations Figure 9 gives an overview of the hand-over mechanisms that have been described before. They are arranged according to the performance with respect to the risk of service interruption. The performance of all solutions can additionally be enhanced by means of a second front-end and a second demultiplexer. Figure 9: Performance analysis for the hand-over 4.5.3.6 Receiver guidelines for hand-over 4.5.3.6.1 Hand-over by means of the frequency_list_descriptor a) Prior knowledge: - The user has selected a certain service. The service_id, the transport_stream_id, and the original_network_id of this actual service can be derived from the SDT. b) Prior considerations: - The receiver has to collect all alternative frequencies from the frequency list descriptor, if present, by the following method: Use of the alternative frequencies used in the actual network. These frequencies can be found in the NIT-actual, namely in the loop that describes the transport stream with the same transport_stream_id and the same original_network_id. Both the terrestrial delivery system descriptor and the frequency list descriptor have to be taken into account. Use ofone or morealternative frequencies used in neighbouring networksfor the same transport_stream_id and the same original_network_id. These frequencies can be found in the NIT-other, if present. The receiver has to check all networks given in the NIT-other. If the sametransport stream (i.e. with the same DVB BlueBook A005 55 transport_stream_id and the same original_network_id) also exists in the neighbouring network, the alternative frequencies can be found in the same way as for the actual network. If the sametransport stream does not exist in the neighbouring network, the receiver should search for the same service with the same service_id and original_network_id in the service list descriptors of all transport streams listed in the second loop of the NIT-other. If successful, the frequencies of the matchingtransport streams are also valid alternatives. c) If the reception deteriorates below acceptable levels: - The receiver has to find a new frequency, that means, it has to tune to the alternative frequencies one by one until a frequency with acceptable reception has been found. The receiver has then to read the PAT and to check if the transport stream containing the service of interest is available. 4.5.3.6.2 Hand-over by means of cell identification a) Prior knowledge: - The user has selected a certain service. The service_id, the transport_stream_id, and the original_network_id of the actual service can be derived from the SDT. Furthermore, the receiver can determine the cell_id by means of the TPS bits. b) Prior considerations: - The receiver has to determine the neighbouring cells. For that purpose it has to compare the location of the actual cell with the location of other cells. Corresponding information is given in the cell_list_descriptor, if present. The receiver should check both, the cells of the actual network and, if the NIT-other is available, the cells of neighbouring networks. - Thereafter, the receiver has to determine the frequencies that are used in the neighbouring cells. o If a neighbouring cell is part of the actual network the receiver can directly read the cell_frequency_link_descriptor that may be present for the actual transport stream in the NIT-actual. o If a neighbouring cell is part of another network the receiver has to check first whether the transport stream of interest is available in this other network or not. If the transport stream is available, the receiver can read the cell_frequency_link_descriptor that may be present in the NIT-other for the transport stream with the same transport_stream_id and original_network_id. If the transport stream is not available, the receiver has to search for the same service in other transport streams. If a service with the same service_id and original_network_id can be found,the information in the cell_frequency_link_descriptor of the transport stream that carries the service can be used. If no service with matching identifers can be found, other meanscan be used to find suitable replacement services, for example linkage_descriptor information. DVB BlueBook A005 56 NOTE: When the receiver is searching within the cell_frequency_link_descriptor for those cell_ids that have been identified as cell_ids of neighbouring cells, it may have to examine thefrequenciesused in thesecells as well as further transposer frequencies that are used in subcells of thesecells. c) If the reception deteriorates below acceptable levels: - The receiver has to find a new frequency, that means, it has to tune to the alternative frequencies one by one until a frequency with acceptable reception is found. The receiver can then read the TPS data and check whether it contains the cell_id of interest or not. 4.5.3.6.3 Hand-over by means of cell description and GPS position For this method to be used, both, the cell_list_descriptor and the cell_frequency_link_descriptor have to be present. a) Prior knowledge: - The user has selected a certain service. The service_id,transport_stream_id, and the original_network_id of the actual service can be derived from the SDT. Furthermore, the receiver knows the frequency to which it is tuned and, by means of an additional GPS receiver, its position. b) Prior considerations: - The cell_list_descriptor, the cell_frequency_link_descriptor, andthe tuned frequency can be used to determine the actual and neighbouring cells or subcells. By also considering GPS information, this can be used to determine one or morecells the receiver will probably need to tune tonext. The frequency of these cells, and the frequencies used in the subcells of these cells, can be determined as explained for the previous method. c) If the reception deteriorates below acceptable levels: - The receiver has to tune to the alternative frequencies one by one until a frequency with acceptable receptionand the required service is found. 4.5.3.6.4 Hand-over with two-front-end solutions a) Prior knowledge: - Identical to one of the scenarios mentioned above (depending on the actual solution). b) Prior considerations: - Identical to one of the scenarios mentioned above (depending on the actual solution). c) If the reception deteriorates below acceptable levels: - While still presenting the service on the actual frequency the receiver might use the other front-end to tune to alternative frequencies in order to check the reception of these frequencies. In this way the number of alternative frequencies can be reduced to the relevant ones in advance. Furthermore, tuning failures can be avoided: If both, the cell_frequency_link_descriptor and the cell identification by means of the cell_id in the TPS bits is supported, the set of frequencies to examine can be DVB BlueBook A005 57 reduced to those with a matching cell_id. Note that cell_id is only unique within the scope of an original_network_id. If a second demultiplexer is available, the receiver is able to read the PAT transmitted on the alternative frequency. Note that the second demultiplexer can also be used to shorten the service interruption during the transition process form one frequency to another. 4.5.3.7 Additional linkage modes Most of the hand-over requirements can be fulfilled by means of the comparison methods that have been described so far. For some specific purposes which are not covered by the comparison methods above, the linkage_descriptor provides a linkage type for mobile hand-over that is sub- divided into three different hand-over types: 1) The service identifiers of a service that is offered in more than one country will probably differ from country to another. In order to support a hand-over even when crossing country boundaries the hand-over type "hand-over to an identical service in the neighbouring country" (hand-over_type 0x01) can be used. 2) If the neighbouring network does not provide exactly the same service but a local variation of the service, the hand-over type "hand-over to a local variation of the same service" (hand- over_type 0x02) can be used. 3) If the neighbouring network does not provide the actual service but there is an associated service available, the hand-over type "hand-over to an associated service" (hand-over_type 0x03) can be used. An associated service may be one that offers comparable content, e.g. traffic alerts. When this hand-over type is used, the receiver should avoid the hand-over as long as possible in order to minimize toggling between different content. The hand-over linkage for a particular service may occur in eitherthe SDT orthe NIT. 4.5.3.8 Additional remarks In order to support an optimum hand-over it is highly recommended that service providers uses only one service_id for one service even if DVB allows to allocate several service_ids for one service. In distinction from the DAB system [16] the DVB-T systems does not support the estimation of the position by the interpretation of signals from different transmitters or repeaters at well-known positions since the DVB-T systems does not allow the identification of a specific transmitter or repeater within a SFN. 4.6 Text string formatting Strings in SI may be transmitted using different encodings (EN 300 468 [1], Annex A). Therefore thecontrol characters described in this clause may appear in the decoded stream, but mayappear in an encoded form in the transmitted string. DVB BlueBook A005 58 4.6.1 Use of control codes in names Name fields are found in the descriptors shown in table 5. Table 5: Name fields bouquet_name_descriptor, bouquet name multilingual_bouquet_name_descriptor network_name_descriptor, network name multilingual_network_name_descriptor service_descriptor, service provider name multilingual_service_descriptor service name short_event_descriptor event name target_region_name_descriptor region name The following rules apply to the use of control codes in these name fields: a) It is expected that the range of name lengths transmitted might vary significantly. It is also expected that IRDs may have some limitations in the text length that can be displayed. Such limitations may depend on the method of display in use at the time. For example an IRD may be able to present the time-schedule of events in a graphical format, but only with a short label for each event. The following mechanism allows a short section of a name to be identified. This uses the emphasis control codes with the following interpretation in the name fields: - 0x86 short_name_on; - 0x87 short_name_off. These codes may only be used in pairs, and the short_name_off code should be preceded by the short_name_on code. Use of the codes to identify a short name in any name field is optional. EXAMPLE: The [0x86]Asterix[0x87] Digital Satellite TV Network (short name: Asterix). The [0x86]P[0x87]ay [0x86]M[0x87]ovie [0x86]C[0x87]hannel (short name: PMC). b) The use of the CR/LF code is not recommended in name fields. 4.6.2 Use of control codes in text Text fields are found in the descriptors shown in table 6. Table 6: Text fields short_event_descriptor: text extended_event_descriptor: item description component_descriptor, component description multi-lingual_component_descriptor data_broadcast_descriptor description of data broadcast service DVB BlueBook A005 59 The following rules apply to the use of control codes in these text fields: a) The "emphasis character on code" indicates that the IRD is recommended to emphasize the display of text which follows this code, e.g. by using bold or highlighted characters, and the "emphasis character off code" indicates when an IRD should revert to the normal character display. EXAMPLE: The winners are announced of the [0x86]£10million[0x87] draw. Is J.R. [0x86]really[0x87] dead ? b) The CR/LF code is used to indicate points in the text where the IRD is recommended to start on a new line, i.e. it indicates new paragraphs. The IRD is expected to perform automatic word-wrapping to suit its text display width. c) The use of the Soft-HYphen code (SHY in the character coding tables) is recommended to indicate possible hyphenation points in long words. 4.6.3 Use of UTF-8 By restricting the encoding to the Basic Multilingual Plane, the maximum length of any UTF-8 encoded character is three bytes. Those characters with an encoding of 0x007F or less map to the standard ASCII encoding within UTF-8, and hence are compatible with those ASCII encodings. The character set selection mechanism is preserved and UTF-8 encoding only need be signalled where strings require characters with encodings greater than 0x7F. 5 Applications The SI syntax is designed to work under a wide range of operation conditions. This clause describes some applications and explains how SI can be used in such an environment. 5.1 NVOD services The MPEG-2 specification provides the means of transmitting several video programmes simultaneously in a single TS, which allows for the possibility of a broadcaster to provide a Near Video On Demand (NVOD) service. This clause describes how such a service could be implemented and how it is described within the Service Information (SI). The concept of providing a NVOD service where several time shifted versions of the same programme are transmitted simultaneously is not a new one, but it was not until the advent of the DVB System that the system became a viable one. Figure 10 shows the concept using six time- shifted versions of a service. DVB BlueBook A005 60 This is the simplest form of such a service where all the programmes are identical on all of the channels (other forms could exist where for example the interstitial breaks could be different). Service 1 Prog1 Prog2 Prog3 Prog4 Prog5 Prog6 Prog7 Service 2 Prog1 Prog2 Prog3 Prog4 Prog5 Prog6 Prog7 Service 3 Prog1 Prog2 Prog3 Prog4 Prog5 Prog6 Prog7 Service 4 Prog1 Prog2 Prog3 Prog4 Prog5 Prog6 Prog7 Service 5 Prog1 Prog2 Prog3 Prog4 Prog5 Prog6 Prog7 Service 6 Prog1 Prog2 Prog3 Prog4 Prog5 Prog6 Prog7 Figure 10: Example of a NVOD service To describe such a NVOD service with conventional SI would require the repetition of six Event Information Tables (EIT). Instead the concept of a reference service is used. The reference service is a fictitious service and provides a means within the SI of associating the actual time shifted services (services 1 to 6). This reference service is allocated a reference_service_id which links a common description of the events within the service for all the services belonging to the NVOD service. The EIT of the reference service can always be found in the TS in which the NVOD services are located. Each time shifted service is given a full reference in terms of transport_stream_id, original_network_id, service_id and these services are listed in the NVOD_reference_descriptor. In addition, each time shifted service is described by a time_shifted_service_descriptor which points back to the reference description. This is shown in figure 11. DVB BlueBook A005 61 S e r v i c e DP e r s o c g r r i T a b l e T a b l e D e s c r i p t o r s N V O D _ r e f e r e n c e t i m e _ s h s i e f r t v e i d c _ t i m e _ s h s i e f r t v e i d c _ t i m e _ s h s i e f r t v e i d c _ t i m e _ s h s i e f r t v e i d c _ t i m e _ s h s i e f r t v e i d c _ t i m e _ s h s i e f r t v e i d c _ E v e n t I n f o r m T a b l e s e r v i c e E_ vi ed n t = T a b l e D e s c r i p t o r s s h o r t _ e s v e e r n v t i / c e c o m p o n D e n s t c r i p C A _ i d e tn it i m f ei _e sr c o n t e n t p a r e n t a l _ r a t i Figure 11: SI description of NVOD services Using this method reduces the amount of data by nearly five times. The start times in the EIT for the reference service are set to void values of all "1"s, the correct start times for each event being given in the EITs of the respective time shifted services. All the events of the NVOD reference service (i.e. all the events which are referenced from the associated EIT present/following and EIT schedule tables of the associated time-shifted services) shall be described in the EIT present/following table of the NVOD reference service. 5.2 Mosaic services 5.2.1 General considerations Mosaic services can be spread out over several TSs. A complete mosaic system can be organized in a tree structure. A mosaic component is a collection of different video images to form a coded MPEG-2 video stream. The merging of the video images is performed at the source level, in such a way that at the display each image will occupy a specific area of the screen. Each specific area is called a logical cell. Logical cells are composed of elementary cell(s). The mosaic screen is subdivided by a maximum of 8 8 elementary cells. Each elementary cell is numbered. A logical cell is a collection of elementary cells. Each logical cell is identified by a unique logical_cell_id. The mosaic descriptor identifies the elementary cells (see figure 12), groups different elementary cells to form logical cells (see figure 13), and establishes a link between the content of all or part of the logical cell and the corresponding information carried in the SDT or EIT or BAT. Thus there is DVB BlueBook A005 62 a close association between the mosaic descriptor and other SI Tables. The mosaic descriptor may be placed in either or both of the SDT and PMT sections for the mosaic service. Use in the SDT reduces the amount of interaction between the DVB SI and MPEG Tables. However, a single mosaic service containing multiple video components can only be described by having the mosaic descriptor appearing multiple times within the PMT section. Some logical cells may have no link to SI (see figure 12 and figure 13). 5.2.2 Relationship between mosaic service and SI/PSI Tables Algorithm to look for a mosaic service: a) check the SDT Tables (actual TS / other TSs); b) if a mosaic service exists: - go to the corresponding TS; - process the PAT and PMT; - display the mosaic service; - look after the content of the mosaic service: if you are interested by the content of one logical cell and if it is related to: - a bouquet: display the information of the corresponding BAT, go forward or cancel; - a service: display the information of the corresponding SDT, process the PAT and the PMT and display the selected service; - an event: display the information of the corresponding EIT, process the PAT and the PMT and display the selected event; - a mosaic service: display the information of the corresponding SDT, process the PAT, the PMT, display the selected mosaic service, and go to "- look after the content of the mosaic service". Figure 12: Example elementary cell organizations DVB BlueBook A005 63 0 1 2 3 VIDEO VIDEO VIDEO VIDEO Service  K     Bouquet  A     Bouquet  B     Service  L     4 7 VIDEO VIDEO     VIDEO Event  A     Event  C     link with 8 11 VIDEO a mosaic service VIDEO Event  B     Event  D     12 13 14 15 VIDEO VIDEO VIDEO VIDEO Service  M     Bouquet  J     Bouquet  F     Service  O     0 VIDEO 1 VIDEO 2 VIDEO 3 VIDEO Event K Event 1 Event B Event I service J Service A Service K Service J 7 VIDEO Bouquet Mosaic service on X 11 VIDEO Bouquet R the content of 15 VIDEO alpha network Mosaic Service L Figure 13: Examples of logical cell organization and content 5.3 Transitions at broadcast delivery media boundaries A very common broadcast delivery media infrastructure will be, that signals received from the a satellite are converted and rebroadcast on a cable network. Depending on the size of the network, various technical options exist to facilitate these transitions. 5.3.1 Seamless transitions A simple and low-cost solution is to remove the Quadrature Phase Shift Keying (QPSK) modulation from a satellite signal and replace it with a Quadrature Amplitude Modulation (QAM) suitable for the cable system or a modulation system suitable for (Satellite) Master Access TeleVision ((S)MATV). This mode is usually called a seamless transition. The major complication in this seamless mode is that the bit stream is left unchanged, which causes the NIT to be invalid for the actual delivery system to which the IRD is connected, for example a cable or SMATV system. Seamless transitions are supported by the SI System, with the proviso that it must be readily possible for the IRD to identify whether the NIT information is valid. The rules of operation specified in clause 4.1.1 permit invalid NIT data in the case that applicable delivery system descriptors are not given for the actual delivery system. DVB BlueBook A005 64 EXAMPLE: If a satellite IRD receives a satellite delivery system descriptor for the actual delivery system, then it is valid. If a cable IRD receives a cable delivery system descriptor for the actual delivery system, then it is valid. If a cable IRD receives a satellite delivery system descriptor for the actual delivery system, then it is assumed to be invalid for the cable IRD. The NIT is intended to simplify the set-up and installation procedure for the viewers, and to signal changes of tuning information. However, since it is impossible after a seamless transition of a broadcast delivery media boundary always to maintain valid information in the NIT, the IRD may require mechanisms in addition to reception of the NIT to obtain tuning data. The support of seamless network transitions is based on the definition of a unique identification mechanism for a TS. The transport_stream_id field, as specified in the MPEG-2 standard, allows 65 536 TSs to be uniquely identified. If transport_stream_id values are uniquely assigned to multiplex originators in Europe, this number is considered too small. Thus, the range of unique identifications of TSs has been extended in the DVB SI by a field called original_network_id of 16 bits. The concatenation of these 2 fields results in 4 294 967 296 unique identifiers for TSs. This gives sufficient room to allow for a unique identification of TSs without requiring a registration procedure. Given this unique identification of the TSs, it is then possible to build IRDs that do not require a correct NIT for correct installation purposes. In order to support seamless transitions of TSs for small cable systems and SMATV it is highly recommended that IRDs are able to initiate a frequency scan and store the unique TS identifiers with the sets of delivery system parameters. With this procedure the same information as carried in the NIT can be obtained. However, the presence of a NIT does provide certain advantages for installation set-up and network management purposes. In a seamless mode of operation, an IRD is able to detect the permitted instances of incorrect NIT data, even though no modifications to the bit stream have been made. In general, a network transition will occur between two different types of networks, e.g. from satellite to cable. In this case, the detection of an incorrect NIT is based on the value of the descriptor_tag in the NIT's delivery_system_descriptor. If the transition is between networks of the same type, the NIT should be replaced (see clause 5.3.2) by either a valid NIT or a NIT for another type of network. After the detection of an incorrect NIT, the IRD should be able to initialize itself correctly, e.g. by using a frequency scanning procedure. 5.3.2 Non-seamless transitions without re-multiplexing A slightly more complex option is to restore the TS packet bit stream and to perform some selective TS packet replacements in the TS. Such a packet replacement option does not require a re-timestamp operation and is of relatively low complexity. Some error handling operations need to be implemented in order to deal with the unrecoverable errors in the satellite signal and with lost TS packets. The NIT is carried in TS packets with a unique Packet IDentifier (PID) value which allow the replacement function to be based on simple PID filter logic. If a network transition is based on a TS packet replacement function, it is desirable that the new NIT information is stored and managed at the network boundary. This is the logical location, as each network operator will demand the control over the frequency allocation in his network. For this local control to be as simple as possible, a fixed PID value is selected for TS packets carrying NIT data. A certain minimum data rate for the transmission of NIT data is specified in clause 4.1.1 to allow the replacement function to meet the minimum repetition time for the replacement NIT. DVB BlueBook A005 65 5.3.3 Transitions with re-multiplexing The most complicated and expensive solution is to combine two or more TSs into a single one at the broadcast delivery media boundary. This re-multiplexing also involves the re-timing of the TS packets and the generation of a new SI data stream. The SI data in other TSs might in this case also be incorrect, which requires the checking and regeneration of the SI data in all TSs in the network. This option will only be feasible for very large networks. 5.4 Announcements DVB supports spoken announcements of several types. They can dynamically occur during any event, If a certain service supports such announcements, the corresponding SDT shall indicate this by means of a announcement_support_descriptor. This descriptor gives information about which types of announcements may occur and where the announcements will occur. This can either be in the audio stream which is currently decoded or in other audio streams on the same or on a different transport stream. The dynamic flags which trigger the real time announcement switching are encoded in the private data bytes of the adaptation field. The syntax of the announcement_switching_data_field is defined in EN 300 743 [15]. This data field is present only in those streams that carry announcements. Services that support announcements by means of giving a reference to announcement streams will not provide this announcement_switching_data_field in their streams. Thus, the demultiplexer has to monitor the adaptation field of the announcement stream if the support of announcements is realized by referencing an announcement stream. If a reference is made to an announcement stream in a different TS a copy of the announcement switching data field has to be embedded in the actual TS, namely in the audio stream of a service that uses the reference to an announcement stream in a different TS. The service and the stream that carries this duplicated trigger information is also indicated by the announcement_support_descriptor of the SDT. 6 Storage media A recording device can store a partial bitstream from the DVB TS. This partial bitstream does not carry any DVB SI data other than the Selection Information Table (SIT) described in EN 300 468 [1]. The SIT contains a summary of all SI information in the broadcast stream relevant for storage media. All relevant MPEG-2 PSI information should be coded to correctly describe the partial MPEG-2 TS. The presence of the SIT in a bitstream flags the bitstream as a partial bitstream coming from the digital interface. This allows the IRD to ignore the absence of any mandatory SI tables and only use information coded into the SIT. In addition to the SIT table, a second table, called Discontinuity Information Table (DIT), is defined in EN 300 468 [1]. This table is to be inserted at transition points at which SI/PSI information may be discontinuous. The IRD may use this information to recapture the SI/PSI information. Note that it is not necessary to signal normal changes to the SI/PSI information, for example an event transition, which are covered by the table version signalling mechanism. 6.1 Program Association Table (PAT) The PAT only lists selected services. In addition, the network_PID reference should take the value of the SIT_PID instead of the NIT_PID. The references to non-selected programs/services should be removed. The PAT should not violate the MPEG-2 Systems rules. DVB BlueBook A005 66 6.2 Program Map Table (PMT) The PMT should not violate the MPEG-2 Systems requirements. For selected services, the corresponding PMT section may remain unchanged only if all elementary streams referenced from it are selected and kept unchanged. In case any of the referenced elementary streams of the service is removed or changed, the PMT section should be modified to reflect this. For non selected services the obsolete PMT sections may remain in the stream only if they are in the same PID as a PMT section of any selected service. In all other cases they should be removed. 6.3 SI tables (NIT, SDT, EIT, BAT, RST, TDT, TOT) These tables should be removed after selection. 6.4 Selection Information Table (SIT) The SIT should be packetized in TS packets starting from the beginning of the payload, i.e. in a packet with payload_unit_start_indicator in the TS packet header set to "1" and with the pointer_field set to "0x00". Furthermore, it is recommended that the SIT is packetized in a single TS packet (if possible). The transmission_info_loop in SIT should contain the partial_transport_stream_descriptor. The following service loop should contain all the service_ids of the selected services. Each instance of service_loop may contain descriptors from the original EIT and SDT. 6.5 Discontinuity Information Table (DIT) At a transition, the bitstream may be discontinuous with respect to any of the SI information (including PAT and PMT). The DIT table shall be inserted at this transition point. Whenevera partial bitstream discontinuity occurs, two transport packets belonging to PID 0x001E shall be inserted directly at the transition point, with no other packets in between. The first one shall have 184 bytes of adaptation field stuffing with discontinuity_flag set to "1" (in order to ensure compliance to MPEG-2 continuity counting constraints for successions of transitions introduced at independent transmission/storage stages). The second of these transport packets shall contain the "DIT" and shall not have such a flag set to "1". DVB BlueBook A005 67 Annex A (informative): Bibliography ATSC Document A/56: "System Information for Digital Television", (http://www.atsc.org). DVB BlueBook A005 68 History Document history Edition 1 April 1996 Publication as ETR 211 Edition 2 August 1997 Publication as ETR 211 V1.4.1 July 2000 Publication as TR 101 211 V1.5.1 January 2003 Publication as TR 101 211 V1.6.1 May 2004 Publication as TR 101 211 V1.7.1 February 2006 Publication as TR 101 211 V1.8.1 August 2007 Publication as TR 101 211 V1.9.1 June 2009 Publication as TR 101 211 V1.10.1 October 2009 Pre-processed by the ETSI Secretariat editHelp!E-mail: mailto:edithelp@etsi.org DVB BlueBook A005