1、Rec. ITU-R BT.1207-1 1RECOMMENDATION ITU-R BT.1207-1DATA ACCESS METHODS FOR DIGITAL TERRESTRIALTELEVISION BROADCASTING(Question ITU-R 121/11)(1995-1997)Rec. ITU-R BT.1207-1The ITU Radiocommunication Assembly,consideringa) that many kinds of service signals, from high-speed video signals to low-speed
2、 data signals may be multi-plexed within a channel;b) that multiple programme services may be multiplexed within a channel;c) that special care should be taken in choosing methods to access particular signals;d) that in many cases, particularly in the case of data services, receivers may not be requ
3、ired to deal with all themultiplexed signals carried by the channel,recommends1 that digital terrestrial television broadcasting (DTTB) systems should use the data access methods as specifiedin the International Organization for Standardization/International Electrotechnical Commission Standard 1381
4、8-1(ISO/IEC Standard 13818-1). The outline of the specifications is shown in Annex 1.ANNEX 11 IntroductionIn DTTB, many kinds of television programmes, sound programmes, and data broadcasting programmes are broadcastover one channel. The indirect identification by the Program Specific Information (P
5、SI) of ISO/IEC Standard 13818-1should be used as the data access method which enables viewers/listeners to easily access the desired program.Furthermore, the ISO/IEC Standard 13818-1 specifications allow the system to extend the receivers functions forviewers/listeners, using private sections or pri
6、vate descriptors.2 Basic data access flow in the receiverA program is received based on the following four tables of PSI in ISO/IEC Standard 13818-1 specifications: Program Map Table (PMT), which transmits the relationship among the elementary streams which constitute theprogram, its attribute infor
7、mation, and the Packet Identifier (PID) of the packet in which the program is sent. Network Information Table (NIT), which transmits the information about the transmission channel in which theprogram is sent. Program Association Table (PAT), which indicates the PIDs in which PMT or NIT is transmitte
8、d. Conditional Access Table (CAT).When the desired program is designated, the elementary streams which construct each program are received according tosuch a flow diagram as shown in Fig. 1 using these tables.2 Rec. ITU-R BT.1207-11207-01. . . . . . . . . . . . . . . . . . . . . . . . .FIGURE 1An ex
9、ample of data access flow in the receiverTransport streamReceivePID = 0Program AssociationTable (PAT)PR # = 0 PID = NPR # = X PID = PXProgram # = XSelectReceivePID = NNetworkInformationTable (NIT)ReceivePID = 1ConditionalAccessTable (CAT)ReceivePID = PXProgram MapTable (PMT)ReceivePID = PCReceivePID
10、 = PVReceivePID = PAProgramclock(PCR)Video PESpacketAudio PESpacketTimingregenerationVideodecodingAudiodecodingVideodisplayAudiodisplayPES : packetized elementary bit streamPCR: program clock referencePR # = X video PID = PVaudio PID = PAclock PID = PCFIGURE 1/BT.1207.D01 = 3 CMRec. ITU-R BT.1207-1
11、33 Outline of the PSI of the Moving Pictures Expert Group (MPEG) specifications andthe extensions for broadcasting applicationsFunctions of each field in the PSI of the ISO/IEC Standard 13818-1 specifications and the extensions and newdefinitions of descriptors for broadcasting applications are as f
12、ollows. NIT indicates the service, transport ID, channelfrequency, etc., in general, but it is not specified in ISO/IEC Standard 13818-1. Specifications for NIT standards andmore extensions for broadcasting applications are defined and recommended in Recommendation ITU-R BT.1300.3.1 Program Associat
13、ion Table (PAT)The structure of the program association section which is used for the transmission of PAT is shown in Fig. 2.1207-0216 13 16 133388 1 12 16 5 1 8 3212 2table_idsection_syntax_indicatorsection_lengthtransport_stream_idversion_numbercurrent_next_indicatorsection_numberlast_section_numb
14、erCRC_32program_number 0network_PIDprogram_number iprogram_map_PID_i. . . . . . . .FIGURE 2Structure of the program association sectionNo. ofbytesNo. of bytes“0”NloopFIGURE 2/BT.1207.D02 = 3 CMtable_id: it identifies the content of a Transport Stream PSI section, and it is set to 0 for PAT.section_s
15、yntax_indicator: it is set to 0 for PAT.section_length: it specifies the number of bytes of the section including the CRC.transport_stream_id: it can be used as a label to identify this Transport Stream from any other multiplex within anetwork, and its value is defined by the user.version_number: it
16、 indicates the version number of the whole PAT.current_next_indicator: it indicates whether the PAT sent is currently applicable or next applicable.section_number: it gives the number of this section in the PAT.last_section_number: it gives the number of the last section of the complete PAT.program_
17、number: it specifies the program to which the program_map_PID is applicable. If this is set to 0then the following PID reference is the network PID. The program_number is used as adesignation for a broadcast channel, which is called program channel (program channelmeans a time series of broadcast pr
18、ogrammes and a plural number of program channels aretransmitted in a physical channel for the case of the multichannel system).network_PID: it specifies the PID of Transport Stream Packets (TSPs) which send the networkinformation table.program_map_PID: it specifies the PID of TSPs which send the PMT
19、 applicable for the program as specifiedby the program_number.CRC: it checks the error in the entire program association section.4 Rec. ITU-R BT.1207-13.2 Program Map Table (PMT)The structure of the program map section which is used for the transmission of PMT is shown in Fig. 3.1207-038 1 12 16 2 1
20、 8 81523134table_idsection_syntax_indicatorsection_lengthprogram_numberversion_numbercurrent_next_indicatorsection_numberlast_section_numberPCR_PID8131234stream_typeelementary_PIDES_info_length32program_info_lengthCRC_32FIGURE 3Structure of the program map sectionNo. ofbytesNo. ofbytes“0”Nloopdescri
21、ptorsNloopdescriptorsNloopFIGURE 3/BT.1207.D01 = 3 CMtable_id: it is set to 2 for the program map section.section_syntax_indicator: it is set to 1.section_length: it is the same as PAT.program_number: it specifies the program to which the program_map_PID is applicable.version_number: it is the same
22、as PAT.current_next_indicator: it is the same as PAT.section_number: it is always set to 0.last_section_number: it is always set to 0.PCR_PID: it indicates the PID of the TSP which contain the PCR valid for the program specified bythe program_number.program_info_length: it specifies the number of by
23、tes of the descriptors immediately following this field.stream_type: it specifies the type of elementary stream or payload carried within the packets with thePID whose value is specified by the elementary_PID. The values are specified by a table;for example, 2 is for MPEG-2 video and 4 is for MPEG-2
24、 audio.elementary_PID: it specifies the PID of TSP which carry the associated elementary stream or payload.ES_info_length: it specifies the number of bytes of the descriptors of the associated elementary streamimmediately following the field.CRC_32: it checks the error in the entire program map section.
