Introduction to Ethernet

Introduction to Ethernet
6.1.1 This page provides an introduction to Ethernet. Most of the traffic on the Internet originates and ends with Ethernet connections. Since it began in the 1970s, Ethernet has evolved to meet the increased demand for high-speed LANs. When optical fiber media was introduced, Ethernet adapted to take advantage of the superior bandwidth and low error rate that fiber offers. Now the same protocol that transported data at 3 Mbps in 1973 can carry data at 10 Gbps.


The success of Ethernet is due to the following factors:

• Simplicity and ease of maintenance
• Ability to incorporate new technologies
• Reliability
• Low cost of installation and upgrade

The introduction of Gigabit Ethernet has extended the original LAN technology to distances that make Ethernet a MAN and WAN standard.

The original idea for Ethernet was to allow two or more hosts to use the same medium with no interference between the signals. This problem of multiple user access to a shared medium was studied in the early 1970s at the University of Hawaii. A system called Alohanet was developed to allow various stations on the Hawaiian Islands structured access to the shared radio frequency band in the atmosphere. This work later formed the basis for the Ethernet access method known as CSMA/CD.

The first LAN in the world was the original version of Ethernet. Robert Metcalfe and his coworkers at Xerox designed it more than thirty years ago. The first Ethernet standard was published in 1980 by a consortium of Digital Equipment Company, Intel, and Xerox (DIX). Metcalfe wanted Ethernet to be a shared standard from which everyone could benefit, so it was released as an open standard. The first products that were developed from the Ethernet standard were sold in the early 1980s. Ethernet transmitted at up to 10 Mbps over thick coaxial cable up to a distance of 2 kilometers (km). This type of coaxial cable was referred to as thicknet and was about the width of a small finger.

In 1985, the IEEE standards committee for Local and Metropolitan Networks published standards for LANs. These standards start with the number 802. The standard for Ethernet is 802.3. The IEEE wanted to make sure that its standards were compatible with the International Standards Organization (ISO) and OSI model. To do this, the IEEE 802.3 standard had to address the needs of Layer 1 and the lower portion of Layer 2 of the OSI model. As a result, some small modifications to the original Ethernet standard were made in 802.3.

The differences between the two standards were so minor that any Ethernet NIC can transmit and receive both Ethernet and 802.3 frames. Essentially, Ethernet and IEEE 802.3 are the same standards.

The 10-Mbps bandwidth of Ethernet was more than enough for the slow PCs of the 1980s. By the early 1990s PCs became much faster, file sizes increased, and data flow bottlenecks occurred. Most were caused by the low availability of bandwidth. In 1995, IEEE announced a standard for a 100-Mbps Ethernet. This was followed by standards for Gigabit Ethernet in 1998 and 1999.

All the standards are essentially compatible with the original Ethernet standard. An Ethernet frame could leave an older coax 10-Mbps NIC in a PC, be placed onto a 10-Gbps Ethernet fiber link, and end up at a 100-Mbps NIC. As long as the packet stays on Ethernet networks it is not changed. For this reason Ethernet is considered very scalable. The bandwidth of the network could be increased many times while the Ethernet technology remains the same.

The original Ethernet standard has been amended many times to manage new media and higher transmission rates. These amendments provide standards for new technologies and maintain compatibility between Ethernet variations.

The next page explains the naming rules for the Ethernet family of networks.