What Is NIT Or Network Information Table For Digital Headend

Network Information Table

Introduction

When the things comes in terms of Digital Video Broadcasting or Digital Headend then PSI SI Tables plays very important role in it. PSI is abbreviated for Program Specific Information.

From digital headend we multiplex the services and PSI SI information is also added in signal. We scramble services only not PSI SI tables. These tables makes easy to understand for STB to de-multiplex the services. Thus PSI provides the information about the services in it. NIT comes under SI Tables.

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What Is NIT

NIT stands for Network Information Table. NIT carries the information about the TS (Transport Stream) and the characteristics of Network. In other words NIT contains information of Digital Video Broadcasting. There are two IDs. First is Original_Network_Id and second is Transport_Stream_Id. These two IDs define the Unique Transport Stream. This is done by the ETS application area.

Each network is defined with unique network_id. Threw this network_id different networks are identified.

There is a non volatile memory available in the IRDs. The NIT is stored in this non volatile memory. NIT is stored in this memory to reduce navigating time between one channel to other.

There are two types of NIT

NIT Actual

NIT Others

We can also transmit the NIT of other network on our actual network. table_id value is responsible for to differentiate the NIT Actual and NIT Others. NIT contains Linkage Descriptor. The PID value for NIT is 0x0010.

There are different sections of NIT in which NIT is segmented. These sections are called Network_Information_Sections. These sections are transmitted in Transport Stream Packets. They are having PID value of 0x0010.

NIT Actual contains the table_id value of 0x40. While NIT Others contains the table_id value of 0x41. Network Information Sections are shown below in image,

Network Information Table sections

Above mentioned syntax are described below,

section_syntax_indicator

It is set to 1. It is 1 bit field as shown above in the table.

section_length

maximum section_length is of 1024 bytes. It should not exceed the 1021 bytes.

network_id

It is used to identify to the delivery system.

current_next_indicator

there are two position for this indicator is zero and one. If it is set to zero then it means sub_table is not applicable while for 1 indicates that sub_table is applicable.

section_number

first section is denoted by 0x00 while for next section the value will increase by 1 only.

version_number

whenever information is changed then its value increased by 1. Till 31 it incremented by 1 after that it goes 0. This information is carried in sub_tables.

transport_stream_loop_length

it defines the length of transport stream loop.

last_section_number

As its name indicate that it is used to define the number of the last section for sub_table.

network_descriptors_length

It defines the length of network descriptor. This length is in bytes.

original_network_id

It is used to define the network id for the actual network.

transport_stream_id

It is unique for each transport stream.

transport_descriptors_length

It is used to define the total length of the Transport Stream Descriptor. This length is in bytes.

CRC_32

It is used to contain the CRC value. It contains the CRC value for the register which gives zero output value.

table_id

table_id is shown below,

table value for nit

Conclusion Of Network Information Table

As discussed above PSI SI Tables are send from digital headend with Transport Stream packets. At the receiving end the STB de-multiplex and reads the information about the services. Thus Tables play an important role in Digital Video Broadcasting.

Network Information Table contains all the information about the services and delivery parameters. NIT let the STB know about the Network ID and other tuning parameters. Thus it contains all the information about the network so it is called as Network Information Table.

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