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ETSI ES 201 980 V4.1.2 (2017-04)

Code 0x1F (hex) may be inserted to indicate a preferred word break. This code may be used to display long words comprehensibly.

Cyclic Redundancy Check (CRC): this 16-bit CRC shall be calculated on the header and the body. It shall use the generator polynomial G16(x) = x16 + x12 + x5 + 1.

6.6Packet mode

6.6.0Introduction

Data services generally consist of either streams of information, in either synchronous or asynchronous form, or files of information. A generalized packet delivery system allows the delivery of asynchronous streams and files for various services in the same data stream and allows the bit rate of the (synchronous) data stream to be shared on a frame-by-frame basis between the various services. The data stream may be provided with additional error control by the addition of forward error correction. Services can be carried by a series of single packets or as a series of data units. A data unit is a series of packets that are considered as one entity with regard to error handling - one received errored packet within a data unit causes the whole data unit to be rejected. This mechanism can be used to transfer files and also to allow simpler synchronization of asynchronous streams. The carriage of data applications is described in ETSI

TS 101 968 [8].

The size of a packet mode data logical frame shall be a multiple of the packet size. The maximum length of a data unit is 8 215 bytes.

6.6.1Packet structure

6.6.1.0Introduction

The packet is made up as follows:

header

8 bits.

data field

n bytes.

CRC

16 bits.

The header contains information to describe the packet.

The data field contains the data intended for a particular service. The length of the data field is indicated by use of data entity 5, see clause 6.4.3.6.

Cyclic Redundancy Check (CRC): this 16-bit CRC shall be calculated on the header and the data field. It shall use the generator polynomial G16 (x) = x16 + x12 + x5 + 1 (see annex D).

6.6.1.1Header

The header consists of the following fields:

first flag

1 bit.

last flag

1 bit.

packet Id

2 bits.

Padded Packet Indicator (PPI)

1 bit.

Continuity Index (CI)

3 bits.

ETSI

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