Proximity-1 Space Link Protocol is a short haul delivery communications protocol designed to establish a two-way communications link between a lander and an orbiter, negotiate data rate and communications mode, and reliably deliver data during short orbiter-to-surface contacts.
Developed by Consultative Committee for Space Data Systems and documented in a number of CCSDS Recommendations Proximity-1 is implemented on Mars Exploration Rovers, Mars Odyssey, Mars Reconnaissance Orbiter, Mars Express as well as on Phoenix Mars Lander.
The frequency band used by this protocol is in the 400 MHz band so as to reduce complexity of the ground craft, using these frequencies:
However, using this protocol over the standard CCSDS frequency bands is perfectly acceptable if the UHF allocation is not usable.