Streaming/ATAC 3.0

[ATAC 3.0] Signalling message mode for payload

김뿡한 2017. 10. 18. 17:07

9.3.4 Signalling message mode

9.3.4.1 General

The signalling message mode of MMTP is defined for the delivery of signalling messages.

Signalling messages may be encoded in one of different formats, such as binary format or XML format. 

It is therefore important to enable quick access and filtering of signalling messages at the transport layer and thus to avoid parsing the signalling message itself for filtering purposes.

Signalling messages may also be large in size, exceeding the MTU size. 

Other signalling messages may be much smaller than the MTU. 

The signalling message payload format provides fragmentation and aggregation functionality to support efficient packetization.


9.3.4.2 MMTP payload header for signalling message mode

9.3.4.3 Semantics

The semantic of each field are as follows.

Fragmentation Indicator (f_i: 2 bits) – contains information about fragmentation of a signalling message in the MMTP payload. The valid values of this field are shown in Table 18.


                                                                   Table 18 — Value of fragmentation indicator

 Value

 Decription

 00

 Payload contains one or more complete signalling message.

 01

 Payload contains the first fragment of a signalling message.

 02

 Payload contains a fragment of a signalling message that is neither the first nor the last fragment.

 11

 Payload contains the last fragment of a signalling message.



aggregation_flag (A: 1 bit) – when set to “1” indicates that more than 1 signalling message is present in the payload, i.e. multiple signalling messages are aggregated.

fragmentation counter (frag_count: 8 bits) – this field specifies the number of payload containing fragments of the same signalling message following the current fragment. This field shall be “0” if aggregation_flag is set to “1”.

RES (4 bits) – this field contains bits that are reserved for future use and shall be set to 0.

H (1 bit) – this flag indicates if an additional 16 bit is used to indicate the signalling message length

MSG_length (16+16*H bits) – this field indicates the length of the signalling message following this field. When aggregation_flag is set to “0”, this field shall not be present. When aggregation_flag is set to “1”, this field shall appear as many times as the number of the signalling messages aggregated in the payload and preceding each aggregated signalling message.