What are ECM, Emm, AU, and EMU?

ECM is called entitlement control message, which means "control information related to the conditional view (CA ".

EMU stands for emulator. It refers to a simulator. In the satellite receiving field, it refers to an environment where hardware or software is used to simulate conditional receiving authentication.

Emm: Entitlement Management message. Its Chinese meaning is "authorization management information", which is commonly referred to as "management information related to changes to the video card content ".

Emm contains sub-commands and data information required for the video card to change data. To defend against cracking, the information is encrypted in a complicated way.

AU auto update: automatically upgrades authorization information

Hops link count

The CA has a conditional receiving system. Common CAS include nagravision in Switzerland, NDS in the UK, Canal + and viacess in France, workcrypt and irdeto in the Netherlands, and Tsinghua Tongfang and fortune computing in China.

The caid has a conditional receiving system identifier. Generally, it is the code of the encryption system vendor.

Emmg emm generator, which generates user-specific information (also known as e information ). It grants users the permission to watch what programs, which is an important part of the user's viewing right management. To prevent EMM information from being broken

Some important EMM files must be encrypted before they can be used.

Ppua

CW control wold control word

PID Group Identifier

EPG Electronic Program Schedule

Key secret key

Procotol communication protocol

A group of channels that are frequently switched back and forth by zap

Frequency repeater downstream frequency

FEC forward correction Ratio

In dreambox, bouquets refers to a set of programs defined by users, such as sports channels and movie channels.

Pol polarisation LNB Polarization Mode

A protocol for satcodx satellite data information, which contains almost all information such as satellite longitude and repeater data, and can communicate with the receiver to automatically update the information.

Symbolrate Bit Rate

In the satellite field, Service generally refers to the channel or channel provider.

ID of the TID Forwarder
Sid channel sequence number
The PID channel contains various data IDs, including the following:

Vid video ID
Aud audio ID
PMT program ing table
PCR
Caid encryption systemCode4 bytes
ECM
Emm
6 bytes of PRV encryption system code
Text information appended to TTX
AC3 AC # Digital Audio ID

The packet length of the transmission stream is fixed to 188 bytes, including the TS header, the adaptive domain, and the net load data. The ts header consists of Synchronization Byte, flag bit, indicator bit, PID, and other timing information such as error correction. PID is used to distinguish different streams from specific program information (PSI ). There are five different PSI types: Program Association Table (PAT), program ing table (PMT), network information table (NIT), and conditional receiving table (CAT ), digital Storage media commands and controls (DSM-CC ).

Word TV is different from traditional analog TV programs. Each channel of traditional TV corresponds to a program and you only need to adjust it to the appropriate frequency to see the program. In digital TV signals, one channel of code streams corresponds to multiple programs, and multiplexing technology can be used. A physical channel can only provide a single transmission stream containing multiple programs. To watch a program, you must extract the compressed package of the program from the transmission stream before decoding. So how to select a program to play from a large number of transmission streams becomes very complicated. In the transport stream of MPEG-2, program specific information (PSI) specifies how different components of different programs and programs can be reused into a unified code stream. Based on PSI, a code stream can be provided to help you select programs. The service information SI (service information) in DVB is further extended by adding some useful information to users, marking the program type, service providers, and program relationships. Correctly Understand the PSI of MPEG-2 and the structure of DVB Si, and its application in program organization and selection, can correctly understand the position of service information in DVB decoding. It can also help us reuse the number of bytes.
1, PSI in MPEG-2 TS
PSI information mainly includes the following tables:
PAT (Program Association table): Program Group table. The PID of this table is a fixed 0x0000. Its main function is to point out the ID of the transmission stream, and the PID of the map table and network information table of the program streams corresponding to this transmission stream.
PMT (Program Map Table): Program ing table. The PID of this table is provided by Pat. This table can be used to obtain information contained in a program. For example, which streams constitute the program and the types of these streams (video, audio, and data ), specify the PID corresponding to each stream in the program and the PID corresponding to the PCR of the program.
Nit (network information table): network information table. The PID of this table is provided by Pat. NIT is mainly used to identify multiple transmission streams. Nit provides information related to multi-channel transmission streams, physical networks, and network transmission, such as the frequency information for tuning and encoding methods. Modulation method and other parameter information.
CAT (Conditional Access Table): Conditional Access Table, PID-0x0001.
In addition to the preceding tables, the MPEG-2 also provides private fields to expand the MPEG-2.

2. Si in DVB
The psi of the Mpeg-2 provides a lot of related contents and their relationship information, so that the receiver can correctly decompose the multi-channel transmission stream. However, this information is still insufficient in actual use. Therefore, Si is used in DVB to further expand the PSI information.
In addition to the information in PSI, DVB also defines some other tables.
The main functions of SI include:
A. Automatic channel tuning can be performed based on nit, Pat, PMT, and other information;
B. More convenient selection and positioning of programs;
C. Implementing the electronic program guide EPG (Electronic Program Guide.
The information in PSI is basically related to the current code stream, that is, all the content involved is related to part of the information in the current code stream. Unlike PSI, SI information can include services and events that are not in the current code stream, allowing you to select more services and learn more about other services.
DVB requires that the specified PID must be used for the transmission packet carrying SI information. The specified PID is as follows:
Table type PID Value
Pat 0x0000
Cat 0x0001
Tsdt 0x0002
Reserved 0x0003 to 0x000f
Nit, St 0x0010
SDT, bat, St 0x0011
EIT, St 0x0012
RST, st0 x 0013
TDT, TOT, st0 x 0014
Network synchroniztion 0x0015
Reserved for future use 0x0016 to 0x001b
Inband signaling 0x001c
Measurement 0x001d
Dit 0x001e
Sit 0x001f
In this table, we can see that the same PID can correspond to different tables. to distinguish such tables, we need to further find tableid for identification. The tableid table is as follows:
Value description
0x00 program_association_section
0x01 conditional_access_section
0x02 program_map_section
0x03 transport_stream_description_section
0x04 to 0x3f Reserved
Network_information_section-actual_network 0x40
Network_information_section-other_network 0x41
0x42 Service_description_section-actual_transport_stream
0x43 to 0x45 reserved for future use
0x46 Service_description_section-other_transport_stream
0x47 to 0x49 reserved for future use
0x4a bouquet_association_section
0x4b to 0x4d reserved for future use
0x4e Event_information_section-actual_transport_stream, P/F
0x4f Event_information_section-other_transport_stream, P/F
0x50 to 0x5f Event_information_section-actual_transport_stream, schedule
0x60 to 0x6f Event_information_section-other_transport_stream, schedule
0x70 time_data_section
0x71 running_status_section
0x72 stuffing_section
0x73 time_offset_section
0x74 to 0x7d reserved for future use
0x7e discontinuity_information_section
0x7f selection_information_section
0x80 to 0xfe user defined
0xff Reserved
With these two IDs, we can find any table we want in the code stream.
Si mainly includes the following information tables:
Nit (network information table): NIT is mainly used to identify multiple transmission streams.
Provides information related to multi-channel transmission streams, physical networks, and network transmission, such as the frequency information used for tuning
And encoding method. Modulation method and other parameter information. Set IRD (Integrated aggreger according to this information
You can switch between multiple transmission streams.
SDT (service description table): used to describe the names of programs in the system.
Donor, whether there is relevant time description table and other information. This table can describe the current transmission stream or
Other transmission streams, which are differentiated by tableid.
EIT (event information table): a further description of a program. It provides
The name, start time, length, and running status of the event.
TDT (time and data table): This table provides the current time information, which is used to decode the IRD.
Update clock
BAT (bouquet Association table): This table provides a collection of similar programs. These programs
This table can be used to conveniently browse related programs or certain types of programs.
And select.
RST (running status table): This table provides the running status of a specific event, which can be used on time.
Automatically switch to the specified event
Tot (Time Offset Table): This table provides the relationship between local time and TDT.
In combination.
Tsdt (transport stream description table): identified by pid0x0002, which provides
Some parameters.
ST (stuffing table): This table indicates that its content is invalid, only as the padding byte.

So how can we use the SI information table in DVB?

Getting started with DVB Si (II) -- using Ben for DVB Si

1. Network Information table (NIT)
The network information table provides a set of transmission streams and corresponding tuning information. NIT is enabled in IRD (Integrated Receiver decoder) Program And the tuning information can be stored in the same memory. NIT can also be used to indicate changes in tuning information. Nit complies with the following requirements:
A. The current transmission system must contain nit.
B. The current transmission system is valid only when nit contains available transport system descriptors. This specifies the conditions for nit to contain valid information. In some broadcast transmission system boundaries, nit IN ts is also allowed to describe the early networks in broadcast channels. IRD has to select a different mechanism to obtain the corresponding tuning information of the current transmission system. For example, if a satellite IRD receives a satellite transport system descriptor from the current transmission system, this descriptor is considered valid, if a cable IRD receives a cable transport system descriptor of the current transmission system, but if the cable IRD receives a satellite transport system descriptor of the current transmission system, this descriptor is invalid for This IRD.
C. If the current transmission system has a valid nit in the Si bit stream, the NIT should list all ts in the current transmission system.
D. The Si stream should contain at least eight ts packets every 10 seconds to transmit nit or empty packets. This rule simplifies the NIT reset (replacement) in the broadcast transmission boundary ). This reset mechanism makes it possible to use low-cost devices for local frequency control.
Si uses two flags to describe the transmission system. They are network_id and original_network_id respectively. The latter is used as the unique identifier of a service in a TS, even if the Ts is transferred to another transmission system. A ts can be uniquely identified by path: original_network_id/transport_stream_id. A service can be uniquely identified by path: original_network_id/transport_stream_id/service_id. Obviously, network_id is not in this path. In addition, each original_network_id has a different service_id. When a service (within the same TS) is transferred to another transmission system, only network_id is changed, and original_network_id is not affected.
The following example shows two services (a and B) that come from two different transmission systems and happen to have the same service_id and transport_stream_id, they are transmitted to a new transmission system.
In this example, the two services are arranged in different ts in the new network. If the two services are placed in the same ts, the service ID must be modified because one service_id in the same ts cannot be assigned to multiple services, in addition, a TS can only correspond to one original_network_id.
2. BAT information
Bat provides a set of services that provide a basis for IRD to demonstrate effective services to users. Bat transmission is optional. The following rules improve the consistency of Si bit streams and simplify IRD work.
The SI bit stream should list all services of the collection in each bat subtable.
Note: A service can belong to multiple bouquet. This rule allows ird to get a service through different ts.
If IRD provides the service information in bouquet to users, services listed in bouquet will be guaranteed. Otherwise, some services will be lost. One bouquet can combine services in multiple ts transmitted from different networks. If all services in BAT are listed in SDT, IRD access to all service information in bouquet will become easy. Similarly, if the NIT information gives the capacity of all services in ts, IRD access to the service will become easier.
3. SDT Information
SDT is used to list the service names and other parameters in ts. Each TS has an independent SDT sub-table. To improve service collection, the following rules are defined:
Forcibly transfer the SDT of the current ts.
The SI bit streams listed by SDT include at least all services in ts.
In addition:
When SDT in the current ts (for example, table_id = 0x46) describes other ts, all services of this TS should be listed.
We strongly recommend service_id. Once a service_id is assigned to a specific service in a network, this service_id will not change, so that IRD can implement functions such as the list of favorite channels.

Getting started with DVB Si (III)
4. EIT Information
The event info table is used to transmit information about current, future, or even further future events. Each service has its own independent EIT sub-table.
4.1 EIT present/following information (eit p/F)
The following rules simplify the acquisition of eit p/F information. The SI specification specifies that the maximum part of an EIT segment is 4096 bytes.
Each service in the SI stream has two sections to describe EIT present/following, section_number 0x00 to describe the current event, and section_number 0x01 to describe the next event. These constraints are not applicable to services referenced by NVOD. These services may have multiple event descriptions in each segment, and there may be more segments in EIT present/following. We recommend that you sort Event Description event_id in ascending order.
In a section, Si can use a maximum of 4096 bytes to describe a single event.
The following rules apply to the current event:
A. There is only one current event at a time.
B. When a current event exists, the event should be described in section0 of EIT present/following.
C. running_status in the current event should be given. See the following table:

E. There is a following event at most at the same time.
F. If the following event exists, the event should be in Section1 of EIT present/following.
G. If the following event does not exist, an EIT present/following with a blank Section1 is transmitted.
H. The running_status of the following event should be given, as shown in the following table:

The event duration is the same as the EIT duration. The event must be set to "not running" or "Pausing ". The start time of an event is the same as that of EIT start_time. It should be the start time of the entire event, rather than the time after recovery from pause.
Note: the start time and duration of an event may be smaller than the start time of the following event. In other words, an interval is allowed between events. In this case, the following event is considered as an event after the interval. This event should be included in Section1 of EIT present/following.
Note: the start time and duration are both scheduled. Some broadcast service providers may update this information. Others prefer to keep the start time unchanged. For example, to avoid misunderstanding of the event "8:01:23 news", change the start time in the message from 8:00:00.
4.2 EIT schedule information
1) EIT schedule Structure
Follow the following rules:
A. EIT/schedule allocates 16 table_id, 0x50-0x5f to the current ts, and 0x60-0x6f to other ts. These IDS are arranged in chronological order;
B. The 256 sections in the subtable are divided into 32 segments, each of which has one segment ). Segment #1, from section0 to 7, segment #2, from section8 to 15, and so on;
C. Each segment contains information about events that have started in three hours;
D. Arrange event information in a specific segment by time;
E. If a segment has n sections, and n <8, this information must be placed in the first n sections of the segment, it also explicitly specifies the position of the last section: S0 + N-1 (S0 is the first section in the segment). This value is in the segment_last_section_number of EIT. For example, if the second paragraph contains only two sections, segment_last_section_number contains 8 + 2-1 = 9;
F. If a segment contains a section, segment_last_section_number of the segment should have a value of S0 + 7;
G. A completely empty segment is represented by an empty segment (excluding any loop over events). The vsegment_last_section_number value of the segment is S0 + 0;
H. The event schedule in the segment follows the time t0.
T0 is the "last midnight" of the Universal Time Coordinated (UTC ".
For example, the UTC-6's five o'clock P.M. is the UTC-0's eleven o'clock P.M., that is, 23 hours from "last midnight. So for UTC-6, t0 is the day before six o'clock P.M;
I, table_id 0x50 (0x60 for other TS), including from midnight (UTC time) to "today" 02:59:59 (UTC time) (three hours) event information. Section 1st contains event information from 03:00:00 to 05:59:59 (UTC time), and so on. This means that the first sub-table contains information about the four days before the "Today" UTC midnight time;
J. last_section_number indicates the end position of the sub-table;
K and last_table_id indicate the end position of the entire EIT/schedule structure;
L. segments related to past events can be replaced by empty segments. See G rules;
In the event definition contained in M and EIT/schedule, running_status should be set to "defined", that is, 0x00;
N. the EIT/schedule table is not applicable to services involved in NVOD because these services have events with an undefined start time;
2) EIT Encryption
The EIT schedule table can be encrypted. To associate with conditional access, a service_id (= MPEG-2 program_number) must be assigned to describe the encrypted EIT schedule tables, which is in PSI. As defined in PMT, service_id is regarded as a variety of TV programs composed of a private stream (the EIT is identified in the Program Map Table (PMT) Section for this service_id as a programme
Consisting of one private stream), PMT contains one or more ca_descriptor to verify the relevant ca code stream. For this purpose, the service_id value 0xffff is retained in the DVB application.

At present, international digital high definition television transmission systems are mainly used in modulation technology: four-phase shift keying (PSK), multi-level orthogonal Amplitude Modulation (MQAM), multi-level residual side band modulation (mvsb) orthogonal Frequency Division Multiplexing modulation (OFDM ). MQAM Modulation is used in cable TV. QAM modulation is a digital amplitude modulation method that saves the frequency band (the spectrum utilization rate of 16QAM is 4 (bit/s)/Hz, and the spectrum utilization rate of 64QAM is 6 (bit/s) /Hz), with a high signal-to-noise ratio. The QAM modulation method is often used in medium and high-speed modulation of 2400bit/s and is widely used in downlink transmission of cable TV and ground Broadcast Transmission of HDTV.

2.2 disturbing Technology

The anti-disturbing technology is used to encrypt and decrypt digital programs. The basic principle is to use the encryption and control method of character transmission, and the client uses the IC card for decryption. In the mpeg transmission stream, there are two data streams related to the control word transmission: Authorization Control Information (ecms) and authorization management information (EMMS), which are composed of the Business key (SK) the encrypted control word is transmitted in ecms, including program source, time, content classification, program price, and other program information. The business keys that control word encryption are transmitted in authorization management, and the Business keys must be encrypted by the user's personal distribution key (PDK) before transmission, emms also includes address and user authorization information, such as the programs or time periods that users can watch and the video fees paid by users. The user's personal distribution key (PDK) is stored in the user's smart card. On the user side, the set-top box obtains the PID values of EMM and ECM Based on the cadescriptor In the PMT and CAT tables, filters ecms and Emms from the TS stream, and sends them to smartcard through the smartcard interface. Smart card first reads the user's personal distribution key (PDK), decrypts EMM with PDK, retrieves SK, decrypts ECM with SK, and retrieves CW, and send the CW to the disturbing engine through the smart card interface. The disturbing engine can use the CW interface to interpret the disturbing transmission stream. The anti-disturbing technology is divided into the same-password and multi-password technologies.

Same-Password Technology applies two or more conditional receiving (CA) systems to the same network platform. for cable TV stations, it is a choice of technology and a competitive environment.

Multi-key technology requires the set-top box to adopt CI technology, so that the same set-top box can receive encrypted programs from different CAS. From the user's point of view, there is no restriction on which CA's set-top box to purchase, and the possibility of selecting its ca service is also available.

2.3 reuse and demultiplexing technology

The entire reuse process can be described as two different levels of reuse.

· Program layer multiplexing: video streams, audio streams, and data stream multiplexing form a program transmission bit stream.

· System layer multiplexing: The transfer bit multiplexing of multiple programs is used as system bit streams.

Through these two levels of reuse generated are standard MPEG-2 ts code streams.

The demultiplexing unit consists of a dedicated processor, which is responsible for parsing the TS stream and the packet basic code stream (PES) of the MPEG-2, restoring the code stream required by the audio and video decoder, and marking the transmission error. The transfer system uses a transport stream grouping method defined by the MPEG-2 with a fixed length of 188 bytes that identifies video, audio, or data information through the group ID (PID) in the grouping header. A transfer stream contains one or more programs. Each program is composed of one or more reusable basic streams. When a single program is transmitted over and over again, the PID information of the transmission code stream of the program, the identifier used for transmission in the code stream (such as audio and video), and the relationship between these code streams, etc, it is represented by the program ing table (PMT. The PID Number of the code stream that contains PMT is provided by the Program Association Table (PAT) carried by the system-level control code stream defined by PID = 0 when the program system is reused. Both PMT and pat are part of the program-specific information (PSI) that contains program and system information. Demultiplexing uses the program Association Table (PAT) with PID = 0 to identify the PID of the bit stream carrying the required program ing table (PMT), and then from the program ing table (PMT) obtain the PID Number that constitutes the basic code stream of the program, and receive the transfer code stream of the program by setting the filter in the demultiplexing. The basic stream of audio and video is transmitted in the form of group basic streams (PES) in the transport layer, perform PES unpack compression audio, video stream data delivery audio, and video decoding unit processing on the selected program.