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Chapter 1 ’Overview’ — System Applications
24 Amethyst III DTV Smart Switch
User Manual
SFN Stream Redundancy
Figure 1-13. System overview: DVB-T/T2 SFN stream redundancy (ASI only)
For SFN systems in DVB-T/T2, it is imperative that the terrestrial
transmitters broadcast:
 The same signal
 On the same cell
 At the same frequency
 At the same time
To do so in DVB-T, Amethyst III uses the signaling information present in
the transport stream, namely the Megaframe Initialization Packets (MIP),
which are generated by the SFN adapters in the head-end.
When redunding 1+1 SFN adapters, it is necessary to preserve the MIP
positioning when switching from one piece of equipment to another.
Amethyst III is able to realign two streams originating from two
Thomson Video Networks NetProcessor SFN adapters by using the PID
of the MIP (PID=21).
To do so in DVB-T2, Amethyst III realigns the T2-MI streams present in
the transport stream. The T2-MI streams host DVB-T2 frames data and
various parameters (signaling, transmission and synchronization).
When redunding 1+1 T2 gateways, it is necessary to preserve the T2-MI
structure and timestamp. Amethyst III is able to realign two streams
originating from two Thomson Video Networks NetProcessor T2
gateways.
In both DVB-T/T2 architectures, Amethyst III guarantees the broadcasting
continuity, as the terrestrial transmitters detect no discontinuity when
switching from a piece equipment to another. Service outage caused by
the modulators resynchronization (up to 30 seconds) is avoided.