Ethernet

Ethernet is a technology that connects computers over a local area network (LAN), which is a network that encompasses a relatively small area such as a room or building. Ethernet is different from the Internet in that it connects computers to form a local network, while the Internet connects networks on a global scale. First developed in the 1970s, Ethernet has evolved to become the most common method used to create a LAN. It works by allowing computers to recognize and regulate the flow of information over a connection. Ethernet is a wired technology that uses cables to connect computers and other network devices. Modern Ethernet is capable of reaching speeds of up to 10 gigabits per second (gbps). The protocol for the technology was given the designation IEEE 802.3 by the Institute of Electrical and Electronics Engineers, a professional organization that develops standards for various technologies. A protocol is a standardized set of rules that allows different devices to be able to communicate with each other.

Background

The roots of modern computer networks can be traced back to the 1960s and a joint project between scientists and the United States military. They developed a system that linked together computers over a network called the ARPANET, a name taken from the United States Advanced Research Projects Agency (ARPA). The system used a method of transmitting information called packet switching, which broke down data into smaller blocks before sending it to its destination where it was reconstructed into its original form.

In the early 1970s, most computers were large mainframe devices that took up entire rooms. In an attempt to make computers smaller and more easily accessible, engineers at the Xerox research labs at Palo Alto, California, created the first computer workstation that featured an operating system and a graphical user interface—features that would become commonplace on later personal computers. They also invented the first high-speed laser printers. In 1972, Xerox engineer Bob Metcalfe was seeking to develop a way for the computer and printer to communicate with each other at the local level. He was inspired by earlier work at the University of Hawaii that managed the transfer of radio communication over a common channel. Metcalfe's method detected potential "collisions" between packets of information over the network and regulated the flow of data between devices. At first, he named this system the Alto Aloha Network, a combination of the Hawaii project and the work done at the Palo Alto facility. He later renamed it Ethernet, after the mythical element that the ancients once believed made up the heavens.

The first Ethernet system was activated in 1973 and featured a speed of 3 megabits per second (mbps). A bit is the smallest amount of information that can be used by a computer. A megabit is the equivalent of one million bits. When Metcalfe left Xerox in 1979, he convinced the company to allow Ethernet to be used as the industry standard technology for local connections. Four years later, it was approved by the IEEE Standards Association under the designation IEEE 802.3.

Overview

Ethernet is used to create a local area network by connecting computers and devices such as printers and routers. A router is a device that sorts, or routes, data from the LAN to other networks. To be able to connect via Ethernet, the computer or device must have an Ethernet adapter or a network card—a card integrated into the product's hardware with ports, or sockets, that accommodate Ethernet cables. These cables are usually similar to wires used for landline phone systems. They consist of eight twisted pairs of wires inside and are slightly thicker than a phone wire. Some modern Ethernet connections use fiber-optic cables that replace the wires with thin strands of glass as a medium for transmitting data. The cables running from each device are connected to a common hub, or gateway, which acts as a switching station to manage the traffic over the network.

There are several types of modern Ethernets, but the most common supports data transfer rates of 10 mbps. Some fast Ethernet connections can support data speeds of up to 1 gbps—1 billion bits per second. Although introduced in 2002, 10 Gbps or 10GE Ethernet, which is capable of sending up to 10 billion bits per second, is not widely available. It is used primarily for high-speed storage networks and metropolitan area and wide area networks. Devices on an Ethernet connection use a common communication line. Each computer, printer, or other attached hardware has its own distinct Ethernet address. When data is sent out over an Ethernet connection, it is transmitted in the form of frames, short chunks of information that can be no more than 1518 bytes long. A byte is a unit of digital information, usually consisting of eight bits.

Each frame contains a header that includes both the source address of the sender and the destination address of the recipient device. Since data sent over the Ethernet is received by all network devices, each one reviews the addresses in the frame to see if it was intended for them and decides whether to accept or discard it. Like a traffic cop at a busy intersection, Ethernet systems manage the flow of data by watching out for collisions between frames. A device that is ready to send information first checks the main network connection to see if it is in use by another machine. If it is free, the device sends the frame on its way, where it is checked by the other devices and accepted by the proper recipient. If two frames are using the network at the same time, a control function called carrier-sense multiple access with collision detection (CSMA/CD) institutes a slight delay in transmitting one of the frames. It allows the other frame to proceed before sending the delayed frame on its way.

Most Ethernet cables and devices are compatible with both older and newer systems, although the Ethernet hub, or switch, will automatically adjust to the highest common speed between sender and receiver. This means that devices capable of 100 mbps of data transmission will be limited to 10 mbps if the Ethernet cable is only able to handle the lower amount. Since Ethernet relies on wired technology, it has been replaced in some areas with wireless networks. These networks, however, are prone to more interference and are less secure than wired networks. As a result, Ethernet technology remains the standard used by most businesses and organizations for their local area networks.

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