SatLink VSAT User Guide
Publication no. 101557
Copyright © 2009 – STM Group, Inc.
Page 159 (160)
Appendix O. Accessing the Forward Link Signalling
When the receiver of the STM SatLink VSAT is switched on (using
dvb rx start), the VSAT 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 standardized in EN 301 790. The identifiers that the VSAT uses to find the DVB RCS SI
tables are embedded within standard DVB-S/DVB-S2 Forward Link signalling table sets that are
standardized in EN 300 468 and ISO/IEC 13818-1.
Table 10 lists the DVB-S/DVB-S2 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 10 List of DVB-S/DVB-S2 and DVB RCS specific tables that are used when accessing the network.
A rough outline of the procedure is as follows:
The STM SatLink VSAT 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 VSAT.
In the NIT, the VSAT 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 VSAT 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 VSAT finds the PID that identifies the PMT, which in
turn contains the PID value of the RMT. In the RMT, the VSAT 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 VSAT must retune to the new forward link. There the VSAT 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
VSAT will find the PID values of the PCR Insertion TS Packet, in addition to the other DVB RCS SI
tables.
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