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Mgt 301 - Critical Analysis of Ethernet: How Used and Why Businesses Need It

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Critical Analysis of Ethernet: How used and why businesses need it

MGT 301

Ethernet: How used and why businesses need it


Networks are increasingly important in the business use of computers as well as for the applications and data that networks can deliver. If a single computer with standard desktop software, such as, word processing, spreadsheets, and databases, can make anyone more productive, then connecting multiple computers on a network brings individuals and data together to improve communications, bolster productivity, and open up opportunities for collaboration and the exchange of information.

The most elementary of all networks consists of two computers, each connected to the other using some kind of wire or cable to permit information exchange. Regardless of how many computers may be interlinked, or what kinds of connections may be used, all networking derives from the basic premise.

The primary motivation for networking arises from a need for businesses to share data within their organization, quickly and efficiently. PC's alone are a valuable business tool, but without a network, PC's are isolated and can neither share data with other computers nor access network-attached devices such as printers, scanners, and fax machines.

Because data sharing permits messages, documents, and other files to circulate among users, it can also improve human communication. Although no company installs a network simply to support electronic mail (e-mail), e-mail remains the most popular networked application in most organizations because it makes communication between individuals easy and efficient.

Invention of Ethernet?

A gentlemen by the name of Bob Metcalfe realized that he could improve on a system called the Aloha System which arbitrated access to a shared communications channel. He developed a new system that included a mechanism that detects when a collision occurs (collision detect). The system also includes \"listen before talk,\" in which stations listen for activity (carrier sense) before transmitting, and supports access to a shared channel by multiple stations (multiple access). Put all these components together, and you can see why the Ethernet channel access protocol is called Carrier Sense Multiple Access with Collision Detect (CSMA/CD). Metcalfe also developed a much more sophisticated backoff algorithm, which, in combination with the CSMA/CD protocol, allows the Ethernet system to function all the way up to 100 percent load.

In late 1972, Metcalfe and his Xerox PARC colleagues developed the first experimental Ethernet system to interconnect the Xerox Alto. The Alto was a personal workstation with a graphical user interface, and experimental Ethernet was used to link Altos to one another, and to servers and laser printers. The signal clock for the experimental Ethernet interfaces was derived from the Alto\'s system clock, which resulted in a data transmission rate on the experimental Ethernet of 2.94 Mbps.

Metcalfe\'s first experimental net was called the \"Alto Aloha Network.\" 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. Physicists Michelson and Morley disproved the existence of the ether in 1887, but Metcalfe decided that it was a good name for his new network system that carried signals to all computers. Thus, Ethernet was born.

The Ethernet System

The Ethernet system consists of three basic elements: 1. the physical medium used to carry Ethernet signals between computers, 2. a set of medium access control rules embedded in each Ethernet interface that allow multiple computers to fairly arbitrate access to the shared Ethernet channel, and 3. an Ethernet frame that consists of a standardized set of bits used to carry data over the system. The analysis of this system describe the configuration rules for the first element, the physical media segments. The second and third elements; the set of medium access control rules in Ethernet, and the Ethernet frame, are followed and analyzed as well.

Operation of Ethernet

Each Ethernet-equipped computer, also known as a station, operates independently of all other stations on the network: there is no central controller. All stations attached to an Ethernet are connected to a shared signaling system, also called the medium. Ethernet signals are transmitted serially, one bit at a time, over the shared signal channel to every attached station. To send data a station first listens to the channel, and when the channel is idle, the station transmits its data in the form of an Ethernet frame, or packet.

After each frame transmission, all stations on the network must contend equally for the next frame transmission opportunity. This ensures that access to the network channel is fair, and that no single station can lock out the other stations. Access to the shared channel is determined by the medium access control (MAC) mechanism embedded in the Ethernet interface located in each station. The medium access control mechanism is based on a system called Carrier Sense Multiple Access with Collision Detection (CSMA/CD).

The CSMA/CD Protocol

The CSMA/CD protocol functions somewhat like a dinner party in a dark room. Everyone around the table must listen for a period of quiet before speaking (Carrier Sense). Once a space occurs everyone has an equal chance to say something (Multiple Access). If two people start talking at the same instant they detect that fact, and quit speaking (Collision Detection.)

To translate this into Ethernet terms, each interface must wait until there is no signal on the channel, then it can begin transmitting. If some other interface is transmitting, there will be a signal on the channel, which is called carrier. All other interfaces must wait until carrier ceases before trying to transmit, and this process is called Carrier Sense.

All Ethernet interfaces are



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