DVB数据广播实施指南中文版：ETSI TR 101202 V1.2.1

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本文档是关于"数字视频广播 (DVB) 数据广播实施指南"的技术报告，由欧洲广播联盟 (EBU) 和 ETSI（欧洲电信标准研究所）联合发布，具体参考了 RTR/JTC-DVB-142。这份ETSITR101202V1.2.1版本于2003年1月推出，标题清晰地表明它针对的是DSMCC（数字卫星多载波广播控制）的广播协议规范，特别适用于中文环境。 DSMCC是数字电视广播中的一个重要组成部分，它定义了一套标准，用于在数字卫星广播系统中进行高效的多路复用和管理数据广播服务。这份规范详细阐述了如何通过广播方式传输数据，确保了数据的安全性和服务质量，对于电视、广播和多媒体服务的提供者以及接收设备制造商具有重要意义。关键词涵盖了"广播"、"数据"、"数字"、"DVB"（Digital Video Broadcasting）、"电视"和"视频"等核心概念。该文档提供了关于DSMCC协议的具体实现指导，包括但不限于编码技术、传输模式、错误检测与纠正策略、频道配置、用户认证和计费等方面的要求。它强调了版本管理和更新流程，指出所有用户在使用时需注意，可能存在不同电子版本间的细微差异，但PDF格式的印刷版本存放在ETSISecretariat的特定网络驱动器上是官方的参考版本。用户在下载或引用这份文档时，必须了解其可能需要修订或更新，因此应定期检查最新的版本以获取最准确的信息。此外，如果发现任何内容上的争议，应当以ETSISecretariat发布的PDF打印版本为准。这份"ETSITR101202V1.2.1 DSMCC广播协议规范中文版"为DVB系统的数据广播实践者提供了一个全面且权威的参考框架，对于理解并遵循DSMCC标准，优化数字电视服务的广播质量和效率至关重要。

ETSI

TSI TR 101 202 V1.2.1 (2003

On the layer of MPEG-2 Transport Stream data are transmitted within packets with a fixed length of 188 bytes

(184 bytes payload), therefore datagrams of higher layers must be fragmented at the transmission side and be

re-assembled at the reception. For fragmentation of the datagrams there are three possible ways (see also figure 4.1):

• Private mechanisms based on the Data Pipe.

• MPEG-2 Packetized Elementary Streams (PES).

• MPEG-2 Sections.

MPEG-2 PES provides a mechanism to transmit datagrams of variable size with a maximum length of 64 kbytes.

Additionally it provides the facility to synchronize different data streams accurately (as used in MPEG for

synchronization of Video and Audio), therefore it was chosen by DVB for the transmission of synchronous and

synchronized but also asynchronous data streams (see EN 301 192 [1], clauses 5 and 6).

MPEG-2 Sections can be used to transmit datagrams of variable size with a maximum length of 4 kbytes. The

transmission is asynchronous. MPEG-2 Sections are built in a way that MPEG-2 demultiplexers available on the market

can filter out single sections in hardware which may reduce the required software processing power of the receiver. This

is the main reason why the MPEG-2 Sections have been chosen as the mechanism for the transmission of encapsulated

protocols and data carousels.

For data broadcasting services in the DVB framework the data_broadcast_id_descriptor (EN 300 468 [6]) can be

present in the PMT, i.e. use of this descriptor is optional.

4.3 Data Pipe

The Data Pipe is an asynchronous transportation mechanism for data. The data are inserted directly in the payload of

MPEG-2 Transport packets.

There is no mechanism for fragmentation and reassembly of datagrams defined. This - if required - is part of the

application definition. For instance, the payload_unit_start_indicator could be used to signal the start of a datagram in a

packet while the transport_priority field could signal the end of a datagram.

The continuity_counter shall be used as defined by MPEG (ISO/IEC 13818-1 [2], clause 2.4.3).

4.3.1 Usage of the adaptation field

The main use of the Adaptation Field is stuffing. However, it is possible to use it for other purposes, e.g. the

transmission of PCR.

4.4 Asynchronous/Synchronized/Synchronous Data Streaming

4.4.1 Usage of the adaptation field

According to ISO/IEC 13818-1 [2], clause 2.4.3 a PES packet always has to start at the first payload byte of an

MPEG-2 Transport Packet. This means that for PES packets which are not aligned with the MPEG-2 Transport Packet

there is stuffing necessary. Since MPEG only allows stuffing bytes at the end of the packet for sections and not for PES

(see ISO/IEC 13818-1 [2], clause 2.4.3.3) stuffing can only be achieved by using Adaptation fields. This is no real

constraint for the performance of a decoder since most demultiplexer implementations provide the automatic extraction

of Adaptation Fields and therefore no additional processing power is required.

An Adaptation Field that is only used for stuffing can be created by setting all adaptation field flags

(discontinuity_indicator, random_access_indicator, elementary_stream_priority_indicator, PCR_flag, OPCR_flag,

splicing_point_flag, transport_private_data_flag, adaptation_field_extension_flag) to "0" and inserting the number of

required stuffing bytes.

The elementary_stream_priority_indicator and the adaptation_field_extension_flag shall be set to zero, since the

affiliated features have no meaning for Data Streaming.

ETSI

TSI TR 101 202 V1.2.1 (2003

4.4.2 Asynchronous Data Streaming

Asynchronous Data Streaming is used in the case that the PES mechanism is of advantage for applications that need the

asynchronous transmission of datagrams.

Since no synchronization is necessary for this kind of transmission the stream_id "private_stream_2" (see

ISO/IEC 13818-1 [2]) has been chosen which implicitly excludes the usage of the PES packet header fields. Therefore

the PES_packet_length field is immediately followed by the datagram.

The definition of the datagram format is part of the private implementation ant therefore not subject of the DVB

specification.

4.4.3 Synchronous/Synchronized Data Streaming

In order to meet the requirements of the Synchronous and Synchronized Data Streaming an additional header, specific

to this DVB application profile has been defined (see EN 301 192 [1], table 1).

The field stream_id shall be set to "private_stream_1", allowing for the usage of the PES header fields, especially the

PTS. Usage of the time stamps requires the definition of Access Units. Since this is application dependant it has not

been defined within the DVB data broadcasting specification.

The first byte of this header (which is from MPEG-2 PES point of view the first payload byte) contains the

data_identifier. It is defined in accordance with the specifications for embedding of EBU-data (EN 300 472 [7]) and

DVB-subtitling (EN 300 743 [8]) and indicates the type of Data Streaming (synchronous /synchronized).

A combination of Synchronized and Synchronous Data Streaming in the same PES packet is not allowed. However,

both types of streaming data can be carried as part of a same program in separate PID's.

The field sub_stream_id may be used for private definition.

The two flags PTS_extension_flag and output_data_rate_flag indicate the existence of an output data rate field and of a

field for PTS extension. The usage of these fields is explained below.

The PES_data_packet_header_length indicates the length of the header and allows the addition of private bytes in the

header.

The DTS field in PES header is of no use while the PTS shall be coded in the same way as defined by MPEG in

ETS 300 802 [3].

4.4.4 Synchronous Data Streaming

Synchronous data streaming may be used if the output data rate at the receiver side needs to be very accurate. The

receiver clock is synchronized by the PCR. The 9 bit PTS_extension is needed to position data access units (a bit, a byte

or few bytes depending on how one defines access units) very accurately over a large range of data rates (kbit/s to

Mbit/s). The 9 bits extends the accuracy of the PTS clock from 11 µs to the same accuracy as a 27 MHz clock (37 ns).

Precise positioning of the data is required if multiple data decoders receiving the same data services (and knowing the

latency through the process) have to output the data at the same time in an aligned way, or if it is required to maintain

synchronization in the data output stream following a temporary loss of signal.

The field output_data_rate is used in order to specify the output data rate for the synchronous data stream. With the

28 bit accuracy (instead of the 400 bit/s resolution of 22 bit ES_rate in PES header) it is possible to implement PLL

(with clock down conversion) with a ratio of data output rate to 27 MHz (±30 ppm) covering a wide range of data rates.

The output_data_rate field conveys the bit rate of the regenerated signal for a synchronous data stream. The encoding of

the bit rate of the data stream into the output_data_rate field depends on the application. Applications which require bit

rates which are a multiple of 1 bit per second may encode the data streams bit rate into the output_data_rate field

directly with the units of output_data_rate as bits/second. Applications which require a continuous range of bit rates to

be regenerated within the 30 ppm tolerance specified by MPEG for the 27 MHz system_clock_frequency may encode

the bit rate of the data stream into the output_data_rate field as:

• output_data_rate = bit rate x M/system_clock_frequency;

ETSI

TSI TR 101 202 V1.2.1 (2003

where M is chosen to be a number sufficiently large to express the range of bit rates required for the application with

the desired bit rate accuracy. The practical range of bit rates for synchronous data streaming with a

system_clock_frequency of 27 MHz is 1 bit/s to 27 Mbit/s.

Note that the decoder model described in clause 12 of EN 301 192 [1] is not necessarily applicable if the output data

rate field is used.

ES_rate in the PES header can be used without the output_data_rate field in the PES data_packet for applications where

the 400 bit/s accuracy of ES_rate is adequate (e.g. T1 and E1). If both ES_rate and output_data_rate are present in an

encoded stream, the decoder can use either of the rates.

The recommended buffer size for synchronous data streaming is 4 800 byte. This gives sufficient capacity for a typical

maximum multiplexing jitter of 4 ms and a bit rate up to 9 Mbit/s.

4.4.5 Synchronized Data Streaming

Synchronized Data Streaming is used when the data stream shall be synchronized with another MPEG-2 PES stream.

4.5 Multiprotocol encapsulation

4.5.1 Overview

The multiprotocol encapsulation provides a mechanism for transporting data network protocols on top of the MPEG-2

Transport Streams in DVB networks. It has been optimized for carriage of the Internet Protocol (IP) (RFC 791 [5]), but

can be used for transportation of any other network protocol by using the LLC/SNAP encapsulation. It covers unicast

(datagrams targeted to a single receiver), multicast (datagrams targeted to a group of receivers) and broadcast

(datagrams targeted to all receivers). 48-bit MAC addresses are used for addressing receivers. However, DVB does not

specify how the MAC addresses are allocated to the receivers.

Due to the broadcast nature of DVB networks, security of the data is very important. The encapsulation allows secure

transmission of data by supporting encryption of the packets and dynamically changing MAC addresses.

4.5.2 Data transport

The datagrams are transported in datagram_sections which are compliant to the DSMCC_section format for private

data. The section format provides an efficient format for mapping the datagrams to the MPEG-2 Transport Stream

packets and support filtering of datagrams based on the MAC address using existing hardware or software

demultiplexers.

The section format permits fragmenting datagrams into multiple sections. If the length of the datagram is less or equal

than 4 080 bytes (including the possible LLC/SNAP header), the datagram shall be sent in one section. In case of IP and

the LLC/SNAP header being omitted, the MTU shall be set to 4 080 bytes or less, so that the datagrams will never be

fragmented. In case of IP and the LLC/SNAP header being present the MTU shall be set to 4 074 or less.

The MAC address has been divided into 6 bytes that are located in two groups. The reason for this is that the bytes 5

and 6 are in place of the table_id_extension field of the DSMCC_section while bytes 1, 2, 3 and 4 are in the payload

area of the DSMCC_section.

48-bit MAC address byte:

table

....

section

length

MAC

address

reserved

last

section

umber

MAC

address

MAC

address

MAC

address

MAC

address

MAC

address

....

section :

MSB

LSB

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