Technical analysis and engineering reference.
Even on high-capacity 100 Gbps laser links, transmitting a 9,000-byte jumbo frame takes approximately 720 nanoseconds. If an urgent vehicle collision-avoidance ping or missile tracking alert arrives at the MAC layer just as a jumbo frame starts serialization, the critical frame must wait in the buffer, adding unacceptable latency variance.
Frame Preemption splits the MAC layer into express and preemptible traffic paths: - When an express frame arrives, the transmitter aborts the current preemptible frame, attaches a cyclic redundancy check (CRC) fragment trailer, and sends the express packet immediately. - Once the express frame finishes, the remaining fragment of the preemptible frame is transmitted with a continuation preamble. - The receiver's MAC reassembles the fragments transparently before forwarding to higher layer software.
Hardware testing on optical transceivers demonstrates that frame preemption reduces worst-case express frame latency from over 800 nanoseconds down to less than 120 nanoseconds, providing rock-solid determinism across multi-hop orbital topologies.