March 22, 2019
Parallel processing of virtual channels
A new feature to process multiple VC at the same time is available in CCS5 daily builds.Typically, a satellite might download two types of telemetry in parallel on different VC, for example:
- VC0 – live telemetry containing the status of the satellite now;
- VC7 – recorded telemetry, recorded and stored onboard before the ground contact, e.g. during the preceding orbit, and then downlinked on VC7 at the same time as VC0.
The TM packets in VC7 were recorded, so they are from a different time context. Therefore, they should not be processed at the same time as current housekeeping, otherwise it would lead to jumping OBT, firing of delta limits and so on.
To avoid processing both streams in parallel, we would normally set the CCS to process only the TM parameters in VC0 (the live HK) while downloading and archiving packets in VC7 (recorded HK) using an appropriate VC mask.
To analyse the TM parameters on VC7, or to perform general monitoring on it, we can wait for the current contact with the satellite to end, switch session, and then replay VC7 with a different VC mask. However, this would rely on waiting for the contact to end, which may not be acceptable.
This new feature allows the TM packets on VC7 to be processed immediately in a separate session with the same name, with an added suffix specific to the VC. Note that the packets on VC7 in this example are stored in both the original archive and the new one. The syntax is as follows:
CCSSEQ::replayVC ?rate=100? ?session=current?
Of course, this additional processing places somewhat more load on the server host, both for the parallel processing, and for the saving of TM parameters to the archive. Your CCS host needs sufficient processing capacity to do this.
Please refer to the CCS User Manual vol.4 for the full description of this feature.