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Overview

The radio transmits a continuous stream of symbols with no inherent boundaries. Framing inserts known marker patterns into the bitstream so the receiver can locate the start of each coded block and begin decoding at the correct position. Without framing, the receiver would have no way to align itself to the incoming data. CCSDS uses different framing for the TM (downlink) and TC (uplink) directions.

  • ASM / CADU — TM direction frame synchronization (131.0-B-5)
  • CLTU — TC direction command link transmission units (231.0-B-4)