This paper examines the Ethernet protocol as a foundational technology for local area network (LAN) communication. It covers the protocol's core functions in governing data transmission speed, access methods, cable types, and network topologies, with particular focus on frame structure and its seven constituent fields. The paper also explains Ethernet's implementation of the bottom two OSI layers, the role of Manchester encoding for signal synchronization, various Ethernet device types from 10Base5 through gigabit standards, the MAC sublayer's data encapsulation and error detection functions, and the CSMA/CD access mechanism that prevents transmission collisions. The analysis demonstrates why Ethernet has remained the dominant LAN standard since its 1973 introduction by Xerox, controlling approximately 85% of the world's LAN-connected devices.
The Ethernet protocol is a set of rules that administer the infrastructure so computers can communicate over a network. The rules act as guidelines that control the speed of the data transferred, access method, types of cables used, and physical topologies. Most Ethernet systems use Carrier Sense Multiple Access with Collision Detection (CSMA/CD) to control access to the network and frames for combining data into data packets, which is defined by the IEEE 802.3 standard. The Ethernet protocol allows for linear bus, star, or tree topologies. The data can be transmitted over coaxial, twisted pair, wireless access points, or fiber optic cable at speeds of 10 Mbps, 100 Mbps, or 1 Gbps.
The Frame Structure allows the Ethernet network to send information as discrete messages known as frames. The frame structure consists of seven different fields.
The Preamble, which consists of seven bytes, is a binary code that informs the receiving side that a frame is coming and synchronizes the frame reception between the two stations. The Start of Frame Delimiter, which is a one-byte code, is used to indicate the beginning of a frame. The Destination Address, which consists of six bytes, is the address of the station that will receive the frame. The addresses used in 802.3 use 48-bit addresses where the first bit identifies whether the address is an individual or group address, and the second bit identifies whether the address is globally or locally administered.
The Source Address, which consists of six bytes, is used to identify the sending station. The Length field consists of two bytes and identifies the value of the data in the Ethernet frame. The value can range from 0 to 1500. The Data field contains the actual information being sent. If the data field is less than 46 bytes, the pad field will compensate and extend the data field to 46 bytes. The Checksum, which consists of 4 bytes, is used to check for frames that may have been damaged during transmission.
Ethernet devices use only the bottom two layers of the OSI protocol model, with the physical layer as the first level. For encoding the signals, Ethernet uses Manchester encoding, which is a form of data communication line code where each bit of data is signified by at least one voltage level transition. This makes synchronization of a data stream possible so that the sending and receiving stations can remain synchronized together.
Ethernet devices are usually connected to PCs through network interface cards that plug into the motherboard. Because Ethernet devices implement only the bottom two layers of the OSI protocol stack, they are typically implemented as network interface cards integrated into or connected to the host device's motherboard. The different network interface cards are identified by a three-part product name that is based on physical layer attributes.
There are many different types of Ethernet standards. The earliest types were the 10Base5, known as thick Ethernet, and 10Base2, known as thin Ethernet, both of which used coaxial cable and worked at the speed of 10 Mbps. The 10BaseT uses twisted pair wiring instead of coaxial cable and uses an Ethernet hub to connect to the network. The 100BaseT, which is known as Fast Ethernet, has three different wiring schemes and works at speeds of 100 Mbps. The 1000BaseT, which is known as Gigabit Ethernet, has four different media types it can operate with and works at speeds of 1000 Mbps.
The main challenge with increasing the speed of Ethernet is that an increase in speed results in a decrease in network size because of collision detection constraints. To maintain compatibility with Ethernet, the carrier event is extended, which allows Ethernet to send and receive larger amounts of information at higher speeds.
The Ethernet Media Access Control (MAC) sublayer is part of the second layer of the OSI protocol. The MAC sublayer is used for data encapsulation, which includes assembling the frame before transmission and detecting errors after reception. It is also used for media access control, which initiates frame transmission and recovers the frame when the transmission fails.
Carrier Sense Multiple Access with Collision Detection (CSMA/CD) is an access method used by Ethernet. CSMA/CD is a system in which each computer receives a signal through verifying that the line is clear before transmitting. If another node is occupying the line, the computer will delay until the line is clear.
There are times when two computers on a network will simultaneously try to transmit; this will cause a data collision, causing both computers to withdraw their transmission. When this occurs, both computers will wait a random amount of time and then attempt to transmit again. Although collisions are very common in CSMA/CD networks, they have very little effect on the overall transmission speed of the network because of the efficiency of the backoff mechanism.
"Historical dominance and competitive advantages in LAN technology"
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