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6.1 | |
Ethernet Fundamentals | |
| 6.1.1 | |
Introduction to Ethernet |
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Most of the traffic on the Internet
originates and ends with Ethernet connections. From its beginning in
the 1970s, Ethernet has evolved to meet the increasing demand for high
speed LANs. When a new media was produced,
such as optical fiber, 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 is carrying data at 10 Gbps.
The success of Ethernet is due to the following factors:
With the introduction of Gigabit Ethernet, what started as a LAN technology now extends out to distances that make Ethernet a metropolitan-area network (MAN) and wide-area network (WAN) standard. The original idea for Ethernet grew out
of the problem of allowing two or more hosts to use the same medium
and prevent the signals from interfering with each other. 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. 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 developed using the Ethernet standard were sold during the early 1980s. Ethernet transmitted at up to 10 Mbps over thick coaxial cable up to a distance of two kilometers. This type of coaxial cable was referred to as thicknet and was about the width of a small finger. In 1985, the Institute of Electrical and Electronics Engineers (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)/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 network interface card (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 personal computers (PCs) of the 1980s. By the early 1990s PCs became much faster, file sizes increased, and data flow bottlenecks were occurring. 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 per second (Gbps, 1 billion bits per second) 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 without changing the underlying Ethernet technology. The original Ethernet standard has been amended a number of times in order to manage new transmission media and higher transmission rates. These amendments provide standards for the emerging technologies and maintain compatibility between Ethernet variations.
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This work later formed the basis for the Ethernet access
method known as CSMA/CD.
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