Nera SatLink 1000, Руководство пользователя

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Nera SatLink Terminal User Guide – Revision P
117
Appendix O. Accessing the Forward Link signalling
When the receiver of the Nera SatLink terminal is switched on (using
dvb rx start
), the terminal
carries out a Forward Link acquisition procedure to obtain the DVB RCS system information necessary to
perform log-on to the network. The DVB RCS system information is transmitted in specific DVB RCS SI
tables that are standardised in EN 301 790. The identifiers that the terminal uses to find the DVB RCS SI
tables are embedded within standard DVB-S Forward Link signalling table sets that are standardised in
EN 300 468 and ISO/IEC 13818-1.
Table 14
lists the DVB-S tables and the DVB RCS SI tables that are
relevant for accessing the DVB RCS network.
DVB-S SI tables DVB RCS SI tables
Table name Abbrev PID Table name Abbrev PID
Network Information Table NIT 0x0010 RCS Map Table RMT assigned
Program Association Table PAT 0x0000 PCR Insertion TS Packet PCR assigned
Program Map Table PMT assigned Satellite Position Table SPT assigned
Superframe Composition Table SCT assigned
Frame Composition Table FCT assigned
Timeslot Composition Table TCT assigned
Terminal Information Message TIM assigned
Terminal Burst Time Plan TBTP assigned
Correction Message Table CMT assigned
Table 14 List of DVB-S and DVB RCS specific tables that are used when accessing the network.
A rough outline of the procedure is as follows:
The Nera SatLink Terminal tunes to the transport stream of the forward link that it has pre-configured as
”start-up” forward link. There it reads the NIT. The NIT PID value is hard-coded in the SatLink terminal.
In the NIT, the terminal finds tuning parameters for accessing the satellite and forward link transport
stream containing the RMT. If the RMT is on a different satellite or transponder than the ”start-up”
forward link, the terminal will re-tune to the forward link carrying the RMT. The RCST then reads the
PAT and PMT on the same forward link as the RMT. In the PAT, the terminal finds the PID that
identifies the PMT, which in turn contains the PID value of the RMT. In the RMT, the terminal uses its
pre-configured population ID to find and thereafter extract tuning parameters for accessing the correct
Forward Link Signalling service (i.e. parameters defining forward and return link satellite(s), NCC, and
Superframe_ID for initial log-on). If the forward link for DVB RCS services defined in the RMT is
different from its current forward link, the terminal must retune to the new forward link. There the
terminal will access the PAT of the new forward link and extract the PID that identifies the PMT that is
relevant for its forward signalling. In the PMT, the terminal will find the PID values of the PCR Insertion
TS Packet, in addition to the other DVB RCS SI tables.