compression

Overview ¶

Example: Compressing data before you downlink it

A downlink is the scarcest thing a mission has. Two CCSDS standards shrink what goes over it, and they solve completely different problems:

LDC (CCSDS 121.0), pkg/ldc
  Science data. Decorrelate neighbouring samples, then entropy code the
  residuals. Lossless, integer arithmetic throughout.

RHC (CCSDS 124.0), pkg/rhc
  Housekeeping. Most bits are the same as the last packet, so send only
  the ones that changed. Built for a lossy link, with a caveat.

Both produce ordinary octets, so they sit above the packet layer and know nothing about frames.