Description of various PSI/SI tables in DVB-C

 

Abstract: combined with the psi/Si information table in a TS stream of DVB-C Cable Digital TV, this paper analyzes the PSI Information of MPEG-2 and the various tables in SI information of DVB, this gives you a clearer understanding of the functions and functions of each table.

Key words: Digital TV; TS stream; PSI information; SI information; Electronic Program Guide EPG

1. Introduction

In digital TV, all the video, audio, text, pictures and so on after digital processing into the data, and according to the MPEG-2 Standard packaging, forming a fixed length (188 bytes) and then the data packets are reused to form a transport code stream (TS ). Generally, a TS (transportstream transmission stream) stream composed of multiple programs and business multiplexing corresponds to an 8 MHz bandwidth channel.

In order to find the required code stream and identify different business information, you must add some pilot information to the TS stream. To this end, the PSI (programspecificinformation) is defined in the MPEG-2) information, which is used to find a specific program correctly from a TS stream carrying multiple programs.

The PSI table defined in the MPEG-2 standard is a description of a single TS stream. Because the system usually has multiple ts streams, in order to guide digital TV users to quickly find the services they need in ts streams, DVB expands the PSI of MPEG-2, nine more tables are added on the basis of four PSI tables to form Si (serviceinformation ). Si is a description of all ts streams in the system. It inserts the service information (SI) defined by the DVB standard in the TS transmission stream that complies with the MPEG-2 (13818-1 ), enable the set-top-box Integrated Receiver Decoder (IRD) to extract the list and broadcast parameters of the program broadcast by the program provider from the TS stream, it is displayed to digital TV users in an intuitive way, allowing users to conveniently receive and select digital TV programs.

The PSI table consists of a program Association Table (PAT), a condition receiving table (CAT), a program ing table (PMT), and a network information table (NIT, these tables are inserted into the TS stream through a multiplead and identified with a specific PID (package identifier. Si includes the business description table (SDT), event information table (EIT), time and date table (TDT), Time Offset Table (TOT), and Business Group Association Table (BAT) and running status table (RST), fill table (ST), select the information table (SIT), discontinuing information table (DIT) and other table information. The tables in Si do not need to be transmitted in actual use. Nit, SDT, EIT, and TDT must be transmitted, and other tables must be transferred as needed.

There are two types of identifiers in the TS Stream: Package identifiers and table identifiers. Different information tables with the same PID are differentiated by table identifiers tableids, which are found at the receiving end by querying these specific PIDs.

Each table has a specific PID value. The specific values are as follows:

This article analyzes the psi/Si information table based on a specific TS Stream configuration in Cable Digital TV. Figure 1 shows the psi/Si full table.

Figure 1psi/Si table

2. Analysis of PSI Information

To receive a specified program, the PSI table first obtains the PID value of the program ing table (PMT) from the program Association Table (PAT, find the program ing table (PMT) corresponding to the PID value from the TS stream, and obtain the PID value that constitutes the basic code stream of the program from the program ing table, based on the PID value, the corresponding BASIC video, audio, data, and other code streams are filtered out. After decoding, the codes are restored to the original signal and the transfer packets containing the remaining PID are deleted.

I. Pat table

To ensure that the TS stream can be normally received, there must be at least one complete and valid Pat in the stream. The program Association Table Pat includes all program ing tables in the TS stream, that is, the pmtpid and Transfer Stream ID of each program.

2. The Pat table package identifier PID is 0x0000, the table identifier (table_id) is 0x00, And the TS Stream ID (transport? _ Stream_id) is 0x000d, that is, 15th transmission streams, including the PMT information of 8 programs, 0x0061, 0x0062, 0x0063, 0x0064, 0x0065, 0x0066, 0x0067, and 0x0083 respectively.

Because PSI data integrity is very important, CRC verification code must be added in each PSI segment.

Figure 2pat table

Ii. PMT table

The program ing table (PMT) contains the basic code stream information of each program, that is, the video information, Audio Information, and ECM authorization control information of multiple CAS of the same password. As shown in figure 3, pmt_pid is 0x0063, table identifier (table_id) is 0x02, pcrpid is 0x1141, video PID is 0x1141, and audio (streamtype0x04) PID is 0x1142. Among them, the MPEG-2 digital TV 13818-2 video part of the standard sets the basic video stream type (streamtype) to 0x02,138 18-3 audio part of the standard sets the basic audio stream type (streamtype) to 0x04.

The PMT table needle also contains the CA system used for Program Encryption and ecm_pid to inform users of how to search for ECM. Ca_system_id uniquely identifies the CA system and is allocated to the user's smart card. The following table lists the three ca systems with the same password: ca_system_id: 0x491a, 0x602, 0x606, and ecmpid: 0x114a, 0x114b, and 0x114c. Because the disturbing parameters and encryption methods of each program are different, different ecmpids are assigned for different programs. Therefore, each basic stream of each stream has different ecmpids.

Figure 3 PMT table

Iii. Cat table

The cat table contains the ca_system_id that identifies the specific CA system and the index emm_pid used to obtain the authorization management information for users in the specific CA system, these two items can be used to obtain the EMM information of the user's CA system. The conditional receiving process of the user end starts from the ca_system_id in the read card and obtains the corresponding Emm. After ECM, the decryption and decryption work starts in the order of inverse to the sending end.

Cat table PID is 0x0001, table_id is 0x01, including three ca systems with the same password, ca_system_id is 0x491a, 0x602, 0x606, the corresponding emmpids are 0x49, 0x50, and 0x51. Because EMM information is transmitted through the TS stream and other program information, and in order to obtain the authorization information in a timely manner, emmpid is the same in each transmission stream.

Iv. Nit table

The nit table includes the physical transmission network information of all transmission streams in the digital TV network, including channel tuning parameters, frequency, and symbol rate of the program, this information allows the receiver to change the channel and tuning parameters with little or no delay according to the user's choice, and correctly decode ts.

In the NIT table, the PID is 0x0010, The table_id is 0x40, and the network ID (network_id) is 0x01, including 13 transmission streams. the IDs of transmission streams are 0x0001 ~ 0x000d: displays all program IDs in the current transmission stream 0x000d. And the transmission parameters of the current stream, including the center frequency (frequency) 379 MHz, the digital modulation method (modulator) 64QAM, And the symbol rate (symbolrate) 6.875 msymbol/s.

3. Si Information Analysis

PSI data only provides the information of a single ts, so that the digital TV set-top box can decode different program streams in a single ts, however, it cannot provide information about the business and program types, programs, and start time of multiple ts. Therefore, the DVB system extends the PSI, it provides various other forms with different types of information to form an SI. In practice, we organize the data provided by Si in an orderly manner to generate similar forms of Program Reports, which can be viewed in real time on the TV, which will greatly facilitate the use of users, this is the EPG guide for Electronic programs.

Common tables in Si are network information table (NIT table), business description table (SDT), event information table (EIT), Business Group Association Table (BAT), time and date table (TDT) time Offset Table (TOT ). The nit table is described in the PSI table above.

I. SDT table

Service description table (SDT): it contains the Business Information of the current transmission stream and other transmission streams, such as the ID of the current transmission stream, the program name contained in the current transmission stream, and the program type.

SDT table PID is 0x0011, table_id is 0x42, current transmission stream ID is 0x0d, program running status (running_status) is run, service type (servicetype) for the digital TV business, the service name (servicename) is colorful drama.

Ii. EIT table

Event info table (EIT): it contains data related to events or programs. EIT is the main table that generates EPG. Including the name, start time, time period, parent control level, and other information of the current program and the next program.

Section-number = 0 indicates the current broadcast event information and section-number = 1

It is the information of the next broadcast event, including the event start time, playback duration, eventname, parantelratingdescriptor, and so on.

Iii. Table TdT, TOT, and bat

Time and date table (TDT): it provides information related to the current time and date. because the information is updated frequently, you need to use a table separately. Time Offset Table (TOT): it provides information related to the current time, date, and Local Time Offset. Because of the frequent updates, you need to use a separate table.

Business Group Association Table (BAT): it provides information about the business group, the name of the business group, and the list of businesses in each business group. There are three groups of business groups: Movie, sports, and upgrade program, including the program ID of the group, the transmission stream ID of the specific program, and the program type. Using the bat table function, you can easily and quickly search for programs in different business groups based on the definition of the front-end.

4. Conclusion

By inserting psi/Si information in a digital TV, digital TV users can conveniently and quickly search for and query all Transmitted program names, program categories, weekly program content, and specific playback time, and book programs on digital TV receiving devices as you like, so as to implement the electronic program guide.