User Manual

24
- Smart Switching
The modulator input interface includes an advanced management feature, called Smart Switching, that allows
an automatic switching from the primary to the secondary MPEG-TS input in case of errors on the Transport
Stream packets. The Smart Switching feature can be enabled or disabled.
The Smart Switching is based on a counter and a threshold: erroneous packets counter (Err Counter) and
erroneous packets threshold (Err Threshold). The input processing section of the modulator counts consecutive
erroneous packets and compare them with the Err Threshold: if the Err Counter goes over the Err Threshold,
the switching to the other input takes place. From now on, the modulator compare the Err Counter of the new
input with the Err Threshold.
Errors detected by the modulator that increase Err Counter are the stream synchronization error (TS_sync_loss
and Sync_byte_error as described in ETSI TR 101 290) and RS decoding failure (only for 204-bytes MPEG
packets on ASI inputs).
Together with Smart Switching feature, it's also possible to enable the Auto Switch Back feature in order to
configure a priority input that is active when it is valid. This sub-feature is based on another counter and
another threshold: valid packets counter (Ok Counter) and valid packets threshold (Ok Threshold). When
the Auto Switch Back feature is enabled, the currently active input is assumed as the priority input. After a
Smart Switching to the secondary input (as described above), the priority input is selected again if its Ok
Counter goes over the Ok Threshold.
In this way it's possible to configure a histeresis that avoid false switching with noisy inputs.
The OK Threshold and Err Threshold can be freely changed to finely adjust the switching histeresis (default
values for OK Threshold is 5, for Err Threshold is 80000).
- Reed Solomon FEC
If the ASI incoming inputs (note: only for ASI input mode) include the Reed Solomon codes (204 bytes
packets), the module performs the error correction thanks to the 16 RS bytes.
- Bit rate adaptation
When operating in ASI input mode, the input management unit can perform an automatic bit-rate adaptation,
if required. When this mode of operation is activated, the unit automatically removes and/or inserts null packets
in order to adapt the incoming ASI bit-rate to the exact bit-rate defined by the ATSC recommendation. PCR
restamping is then executed in real time.
- Squelch
The RF output signal can be muted if one of the following conditions occurs:
- a hardware problem is present (for example, the amplifier temperature is too high, the modulator does not
communicate with the controller and so on);