a navigation - satellite receiver uses a reference station accessible over a network to store nav data subframes for pattern matching at a network client . alternatively , the pattern matching is performed by the server when per - byte communication costs are high . the stored nav data repeats ephemeris data every thirty seconds , and full almanac data every 12 . 5 minutes . this permits the client to instantly recognize where in the nav data sequence its own received signals are , and it need not actually wait to receive the preambles in the tlm words . several precious seconds are therefore saved in producing a rapid time - to - first - fix .