Introduction to Ethernet

Introduction

Ethernet was designed in the 1970s at the Palo Alto Research Center. The first prototype used a coaxial cable as the shared medium and 3 Mbps of bandwidth.

First Official Ethernet Specification

Ethernet was improved during the late 1970s and in the 1980s, Digital Equipment, Intel and Xerox published the first official Ethernet specification.

Important Parameters

This specification defines several important parameters for Ethernet networks.

1. The first decision was to standardize the commercial Ethernet at 10 Mbps.

2. The second decision was the duration of the slot time. In Ethernet, a long slot time enables networks to span a long distance but forces the host to use a larger minimum frame size. The compromise was a slot time of $51.2$ microseconds, which corresponds to a minimum frame size of $64$ bytes.

3. The third decision was the frame format. The experimental 3 Mbps Ethernet network built at Xerox used short frames containing $8$ bit source and destination address fields. Up to $554$ bytes of payload using $8$ bit addresses was suitable for an experimental network, but it was clearly too small for commercial deployments. Hence, they came up with $48$ bit source and destination address fields and up to $1500$ bytes of payload.