COMMAND RANGING & TELEMETRY UNIT CORTEX
Is.Rev.
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Page 100
3.3.12.3.
Telemetry Data Flows
Three types of data flow can be selected:
3.3.12.3.1.Single Frame / Block Transmission
In this mode, the channel number and the number of buffered TM blocks/frames are only checked on reception
of the first telemetry request. In the subsequent requests they are ignored. The socket must be closed and then
re-open to modify the request.
3.3.12.3.2.Permanent Flow
In this mode, only the first request is checked and processed. Subsequent requests are ignored. The socket
must be closed and then re-
open to modify the request. When the telemetry chain unlocks (loss of signal, …),
data transmission is stopped.
3.3.12.3.3.Permanent Flow and Dummy TM
As per the « permanent flow ». When the telemetry chain unlocks, dummy frames or blocks are transmitted until
telemetry re-acquisition. The dummy frames/blocks transmission rate is derived from the programmed telemetry
bit rate plus 100ms delay on each frame/block (example: if the frame duration is 1 second, then dummy frames
will be transmitted at the rate of one frame every 1.1 second to the Telemetry Clients). Dummy frames or blocks
indicate that the telemetry chain is unlocked (this information is also available to Monitoring Clients) and that the
loss of telemetry is not due to a LAN failure.
The use of dummy frames transmission is highly recommended when the telemetry receiver is likely to stay
unlocked for a significant amount of time (15 minutes or more), such as before AOS in a LEO application. Using
dummy frames transmission insures that data transmission activity is maintained on the TM port and avoids the
TM port from being scheduled to a low priority by the operating system, resulting in possible loss of data at AOS.
Important
: It should be noted that whatever the type of data flow on the Telemetry port (permanent flow or
permanent flow with dummy TM or single frame/block transmission), dummy frames or blocks are automatically
generated and stored in the telemetry circular buffer as soon as the telemetry chain is unlocked, and the amount
of buffered telemetry data specified in the telemetry request includes dummy frames or blocks.
3.3.13.
Telemetry Data Decommutation
Telemetry decommutation is normally carried out by the Control Center.
However, the MCS software allows up to thirty-two 32-bit telemetry words to be decommutated, transcoded and
displayed in real-time at the Graphical User Interface (telemetry « Quick Look »).
Refer to the MCS User’s
Manual.
