ITC Specification of Digital Cable Television Transmissions in the United Kingdom. July 2002

Transcription

1 Transmissions in the United Kingdom July 2002 Note: This document will be subject to revisions as the standards referred to are updated and revised. Independent Television Commission 33 Foley Street London W1W 7TL

2 Transmissions in the United Kingdom CONTENTS 1 INTRODUCTION REFERENCE SYSTEM MODULATION AND CHANNEL CODING SOURCE CODING OF VIDEO SIGNALS SOURCE CODING OF AUDIO SIGNALS MULTIPLEXING OF SIGNALS Program Specific Information Service Information Allocation of SI codes Multiplexing of Data Broadcast Services SCRAMBLING REFERENCES TERMS AND DEFINITIONS...9 Page 3

3 1 Introduction This document specifies the system generally used to provide a fully digital service under an ITC Local Delivery Service Licence. This document describes a reference system for digital cable television transmissions intended for general reception which will allow for maximum commonality between digital television transmission systems. This reference system specifies only the minimum necessary to ensure commonality whilst recognising the need for operators to retain flexibility in all other aspects concerning the implementation and operation of the services. It supersedes the ITC Community Digital Standard for Digital Cable Television [1]. 2 Reference System Features and recommendations are optional but where used shall conform to the provisions of the relevant ETSI standard or associated guideline. 2.1 Modulation and Channel Coding EN [2] specifies the modulation and channel coding of the services. Transmissions are broadcast in an 8 MHz channel. 2.2 Source Coding of Video Signals Video encoding conforms to ISO/IEC [3] and observes the implementation guidelines contained in TR [4]. Table 1 shows the parameters for video streams carried as part of a Digital Television Service. Table 1: Mandatory Video Parameters Parameter Value MPEG-2 Profile Main MPEG-2 Level Main Frame Rate 25 Hz Aspect Ratio 4:3 or 16:9 2.3 Source Coding of Audio Signals Audio encoding conforms to ISO/IEC [5] and observes the Implementation Guidelines contained in TR [4]. 2.4 Multiplexing of Signals The multiplexing of baseband signals and associated data conforms to ISO/IEC [6] and observes the Implementation Guidelines contained in TR [4]. Page 4

4 In summary this requires that all of the individual components of a service are combined into a single MPEG-2 compatible Transport Stream subject to the constraints outlined in the Implementation Guidelines on the use of MPEG-2 Systems TR [4] Program Specific Information All Transport Streams provide the tables and descriptors of Program Specific Information (PSI) required by ISO/IEC [6], TR [4], EN [7] and TR [8]. These and anynydditional optional items are used in the manner required by these specifications and guidelines. In summary each Transport Stream carries the following PSI tables PAT, PMT & NIT. Transport Streams carrying scrambled services also carry a CAT. The PIDs of all of the Transport Stream packets relating to the transmission of licensed services intended for General Reception in each Transport Stream are one of the PIDs defined by ISO/IEC [6] or EN [7] and are listed in the CAT, PAT or PMT as described above Service Information All Transport Streams provide the tables and descriptors of Service Information (SI) required by EN [7] and TR [8] and the additional requirements below Network Information Table (NIT) Each Transport Stream shall carries, where reasonably practicable, NITs describing ALL of the Transport Streams on the Delivery System regardless of whether they are part of the same Network Service Description Table (SDT) Subject to the qualification set out in the paragraph below, each Transport Stream carries, where reasonably practicable, SDTs describing the services in ALL of the Transport Streams originating from a specific Emitting Point regardless of whether they are part of the same Network. If the SDTs as described above are being provided on a different Transport Stream originating from the same Emitting Point then, providing that all other Transport Streams provide an active linkage_descriptor with linkage type 0x04 to that Transport Stream, each Transport Stream carries only SDTs describing the services carried on the Actual Transport Stream. A service_descriptor is provided for each service described. All of the service_descriptor carried in each SDT carry Meaningful names in respect of services which are intended for identification by and display to viewers. Page 5

5 Event Information Table (EIT) Each Transport Stream carries EIT present and following information for all events carried on both the Actual and ALL other transport streams originating from a specific Emitting Point. This does not apply to those services which do not normally make use of a schedule, for instance music only services. Each EIT carries a short event name with a Meaningful name. It is recommended that the maximum length of this name should not exceed 64 characters in length. It is recommended that the transition between the present and following event should normally be accurate to within 10 seconds of the event transition in the Digital Television Service Time Offset Table (TOT) Each Transport Stream carries TOTs with a time offset descriptor time offset descriptor for at least the United Kingdom (country code GBR ). The values of current time offset and next time offset shall reflect the legal requirements in the UK at the time of broadcast Time and Date Table (TDT) Each Transport Stream carries a Time and Date Table Allocation of SI codes SI codes are detailed laid down in Table 2 below: Table 2: Service Information Codes SI Code Status Network_id Codes as listed in [9] Service_id To be agreed with individual service licensees for services broadcast Bouquet_id Codes as listed in [9] CA_system_id Licensees to use only codes listed in [9] Country Code Codes as published in ISO 3166 [10] and ETR 162 [9]. Private_data_specifier Codes as listed in [9] Multiplexing of Data Broadcast Services Any stream of transport packets carrying Data Broadcast Services intended to be identified by and displayed to viewers conforms with the general requirement to use any of the methods described in EN [11]. The data transmission is referenced in the SI tables as described by EN [11] and EN [7] and observes the guidelines in TR [13] and TR [8]. Page 6

6 2.5 Scrambling Where scrambling is required, the Common Scrambling Algorithm defined in ETR 289 [12] would normally be used unless there are reasonable grounds that this would compromise security. The specification and licensing rights to the Common Scrambling Algorithm and the Common Descrambling Algorithm are distributed separately under arrangements with the European Telecommunications Standards Institute which acts as Custodian for the companies which have developed the Common Scrambling Algorithm. For further information regarding the distribution and licensing of the specifications licensees should consult DVB Common Scrambling Algorithm - Distribution Agreements DVB A011 [15] or should contact: The European Telecommunications Standards Institute as Custodian attention Mr Pierre de Courcel Route des Lucioles F Sophia Antipolis CEDEX France Page 7

7 3 References [1] ITC Community Digital Standard for Digital Cable Television, Issue 1.1, March [2] ETSI EN , Digital broadcasting systems for television, sound and data services; Framing structure, channel coding and modulation for cable systems. [3] ISO/IEC , Information Technology - Generic Coding of Moving Pictures and Associated Audio - Video. [4] ETSI TR , Digital Video Broadcasting (DVB); Implementation guidelines for the use of MPEG-2 systems, video and audio in satellite, cable and terrestrial broadcasting applications. [5] ISO/IEC , Information Technology - Generic Coding of Moving Pictures and Associated Audio - Audio. [6] ISO/IEC , Information Technology - Generic Coding of Moving Pictures and Associated Audio - Systems. [7] ETSI EN , Digital Video Broadcasting (DVB); Specification for Service Information (SI) in DVB systems. [8] ETSI TR , Digital Video Broadcasting (DVB); Guidelines on implementation and usage of Service Information (SI). [9] ETSI ETR 162, Digital broadcasting systems for television, sound and data services; Allocation of Service Information (SI) codes for Digital Video Broadcasting (DVB) systems, October [10] ISO 3166, Codes for the representation of names of countries. [11] ETSI EN , Digital Video Broadcasting (DVB); DVB specification for data broadcasting, August [12] ETSI ETR 289, Digital Video Broadcasting (DVB); Common Scrambling (CS) system description, October [13] ETSI TR , Digital Video Broadcasting (DVB); Guidelines for the implementation and usage of the DVB data broadcasting specification. [14] ETSI ETS , Digital Video Broadcasting (DVB); Subtitling systems. [15] DVB A011 rev. 1, DVB Common Scrambling Algorithm - Distribution Agreements, June Page 8

8 4 Terms and Definitions Digital Television Service Delivery System Network Emitting Point General Reception Meaningful Data Broadcast Services Any television service licensed by the ITC and broadcast in a digital format The physical means of delivering Digital Television Services to the home. This includes a digital cable system, a digital terrestrial system and a digital satellite system and a digital microwave delivery system. A Network is the collection of transport streams from a single Emitting Point none of whose components are subsequently altered. More than one reference may be made to the same physical location. Each network from such an emitting point shall be identified by a unique network_id. An Emitting Point is a reference to the physical location of a transmitter which broadcasts a Transport Stream. This may be a terrestrial transmitting site, a cable head end or a satellite or series of satellites operated by a single organisation (e.g. SES, Eutelsat) at a fixed orbital position. A service which is being broadcast for General Reception should be available to any person in the territory (such as the UK) providing they posses an appropriate receiver and have paid any subscription or other fees if such fees are chargeable for that service. A Meaningful name, as used for service and event information tables, should allow a viewer to determine easily the identity of the service or event being broadcast. This name would normally be linked to the name or brand under which the service is currently being marketed. Data services which are intended for General Reception. Page 9