When the progenitors of Ethernet at Xerox PARC created their first (3Mb/s) version in the late 1970s, they focused their efforts on connectivity, and paid little attention to network latency or throughput. Network nodes back then were humans at workstations and laser printers, and nobody cared if packets interfered with one another in transit, and had to be retransmitted many times before reaching their destinations. Mixing long and short packets on the network resulted in long delays for short packets, as they waited for longer packets to go by, in much the same way as autos at a railroad crossing wait for a train to pass before they can get to the other side.
Fast forward to today, when Ethernet speeds have accelerated significantly. The higher speeds greatly enhance capacity, but do little to manage latency or optimize bandwidth. It’s still OK to drop and retransmit packets in heavily loaded situations. Realizing that this would limit the utility of Ethernet in applications that require precise and deterministic timing, the IEEE 802 committee that oversees Ethernet specifications created a new set of sub-standards collectively referred to as “Time Sensitive Networking (TSN),” that allow various classes of network traffic to share a common link.