Proximity-1

Defined by CCSDS 211.2-B-3 for short-range inter-spacecraft links. Proximity-1 frames include a Physical Layer Control Word (PLCW) that carries physical-layer status (e.g. signal quality, link mode) within the frame itself, enabling the two spacecraft to coordinate link parameters without a separate control channel. An optional segment header supports segmentation at the data link layer for time-critical data.