Ethernet frame size constraints (payload)

Question

Designers of ethernet have maintained the MTU as 1500 bytes(for payload),i wish to know what is the reason for that? Because IP datagram size (allowed is much more than 1500 bytes) then why ethernet designers chose frame size smaller than IP datagram size?? Also I understand that there is a minimum 46 bytes constraint on payload? why is it so?

Answer 1

The Ethernet maximum frame size was defined as a trade-off between cost (back then high-speed RAM for buffering was expensive) and performance (smaller frames mean more overhead and less efficiency).

The Ethernet minimum frame size was defined by the necessity of reliably detecting and propagating collisions in a 10BASE5 CSMA/CD network. The signal needs to travel the longest distance between two nodes (500 m at .77c) where a potential collision may be detected and the jamming signal needs to travel all the way back to the sender before that has finished the transmission. It was determined that 512 bits were required.

Note that Ethernet existed before TCP/IP and long before IP even became popular. IP is just one of the many protocols Ethernet can carry.