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82

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

The following definitions apply:

First flag, Last flag: these flags are used to identify particular packets which form a succession of packets. The flags are assigned as follows:

 

 

Table 24b

 

 

 

First

Last

The packet is

flag

flag

 

0

0

an intermediate packet

0

1

the last packet of a data unit

1

0

the first packet of a data unit

1

1

the one and only packet of a data unit

Packet Id: this 2-bit field indicates the Packet Id of this packet.

Padded Packet Indicator: this 1-bit flag indicates whether the data field carries padding or not, as follows:

0:no padding is present: all data bytes in the data field are useful;

1:padding is present: the first byte gives the number of useful data bytes in the data field.

Continuity index: this 3-bit field shall increment by one modulo-8 for each packet with this packet Id.

6.6.1.2Data field

The data field contains the useful data intended for a particular service.

If the Padded Packet Indicator (PPI) field of the header is 0, then all bytes of the data field are useful bytes.

If the PPI is 1 then the first byte indicates the number of useful bytes that follow, and the data field is completed with padding bytes of value 0x00.

Packets with no useful data are permitted if no packet data is available to fill the logical frame. The PPI shall be set to 1 and the first byte of the data field shall be set to 0 to indicate no useful data. The first and last flags shall be set to 1. The continuity index shall be incremented for these empty packets. If less than 4 sub-streams are used within the data stream then an unused packet id shall be used. Empty packets using a packet id of <p> shall not be inserted during the transmission of a DRM data unit using the same packet id <p>.

6.6.2Asynchronous streams

Asynchronous streams can be used to transport byte-oriented information. Both single packets and data units can be used to transport asynchronous streams.

Applications that use the single packet transport mechanism shall be able to deal with missing data packets. The first and last flags indicate intermediate packets.

Applications that use the data unit transport mechanism can carry a collection of bytes that are related in a data unit and then make use of the error handling of data units for synchronization purposes.

6.6.3Files

The file may be carried in a data unit.

Applications that use this transport mechanism shall provide a mechanism to identify each object.

The first and last flags are used to indicate the series of packets that make up the data unit. The continuity index is used to determine whether any intermediate packets have been lost.

ETSI

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