The Ethernet Essay -- essays research papers

Bob Metcalfe of the Xerox Corporation developed the first experimental Ethernet system in late 1972. The goal of the Ethernet was to interconnect the Xerox Alto Aloha Network. The experimental Ethernet was used to link Altos workstations, servers, and laser printers. Data transmission of the Ethernet was 2.94 Mbps. In 1973, Metcalfe changed the name to "Ethernet," to make it clear that the system could support any computer, and not just Altos, and to point out that his new network mechanisms had evolved well beyond the Aloha system. He chose to base the name on the word "ether" as a way of describing an essential feature of the system. The physical medium (cable) carries bits to all stations, much the same way that the old "luminiferous ether" was once thought to propagate electromagnetic waves through space. The Ethernet is a LAN (Local Area Network) technology that uses a shared bus topology, and Carrier Sense Multiple Access/Collision Detection access. It consists of a single, long cable, named the bus, to which computers, or sometimes referred to as workstations, are attached. Ethernet signals are transmitted serially, one bit at a time, over the bus and are received by every attached station. Data in the Ethernet is transmitted in the form of a frame, or packet. The frame consists of a set of bits organized into several fields. These fields include address fields, a variable size data field that carries from 46 to 1,500 bytes of data, and an error checking field that checks the integrity of the bits in the frame to make sure that the frame has arrived intact. The first two fields in the frame carry 48-bit addresses, called the destination and source addresses. The Destination Address contains the physical address of the station to which the frame is being sent. Any signal sent across the shared network reaches all attached workstations. However, communication doesn’t usually involve all workstations. To allow direct communication between stations the addressing scheme is used. Each workstation is assigned a unique numeric value, called a physical address or media access control address (MAC address). Although sharing allows all workstations to receive a copy of a frame, the hardware of each workstation checks the address of each incoming frame to determine whether it should accept the frame. The Source Address contains... ... its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the "root" of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub ports) alone. In a mesh topology each computer is connected to every other computer by separate cabling. This allows for superior redundancy and reliability, as well as ease of troubleshooting. This type of topology is expensive and difficult to install because of the amount of cabling required. The original Ethernet operated at 10 Mbps, a later version Fast Ethernet operates at 100 Mbps and the newest version Gigabit Ethernet operates at 1 Gbps. The Ethernet is the most popular physical layer LAN technology in use today. It is popular because it strikes a good balance between speed, cost and ease of installation. These benefits combined with wide acceptance in the computer marketplace and the ability to support virtually all-popular network protocols, make the Ethernet an ideal networking technology for most computer users today.