duplex

Overview ¶

Example: A full-duplex link, with the CLCW riding home

The downlink example sends telemetry. The uplink example sends commands. Neither is a whole link, because the two are joined: FOP-1 on the ground will not send past its sliding window until a CLCW comes back saying what the spacecraft accepted, and that CLCW travels in the Operational Control Field of a telemetry frame.

So this example closes the loop:

Ground                                       Spacecraft
  commands ──► FOP-1 ──► CLTU ──────────────► FARM-1 ──► commands
                                                 │
                                                 ▼
  FOP-1 ◄──── CLCW ◄──── OCF of a TM frame ◄── CLCW generated
     │
     └─ the window moves, so more commands can go

The whole point is the third arrow. Without it the ground sends its window's worth of commands and then stops, and nothing is wrong with the link.