The Development of the Ethernet Multiple Access Protocol

Introduction

Ethernet is an affiliation of computer networking technologies for local area networks (LANS) based on transfer of frames. It contains LAN products covered by IEEE 802.3 standard that explains what is commonly known as the CSMA/CD protocol. Currently, Ethernet is the most popular LAN technology with an approximated use of close to 85 percent of the LAN – connected PCs and workstations (ideafider.com). In addition, it is the most broadly installed LAN with at least 50 million computers connected. The main reason for invention of LAN was to establish something that could provide linking to as many computers as possible in a building and at very fast speed.

The development of Ethernet multiple access protocol

In the late 19760s, an American engineer and computer scientist called Norm Abramson developed a network, ALOHANET when director for Aloha Systems. ALOHANET was a digital radio network aimed at transmitting autonomous packets of information wirelessly. In ALOHANET Protocol, a station could transmit a packet including the destination IP address. Once sent, the transmitting station waited for an acknowledgement (ACK) from the receiver. To get the destination, all stations kept listening to the channel and on arrival of packet; reading of the destination address was done. If a match was found, the CRC was verified for correctness and if correct a short ACK was sent to transmitter. If no matches, then no ACK hence packet is resent. The major drawback was the occurrences of collisions, when two or more stations tried to transmit simultaneously, which in turn reduced ALOHA systems’ efficiency to about 18%. Slotted ALOHA provided synchronization by dividing stations’ transmit time into windows, which increased the efficiency to about 36%.

The invention first Ethernet dated back to 1973 by Robert Metcalfe at Palo Alto Research Center of Xerox Corporation (PARC). A personal workstation was established with a Graphical User Interface (GUI with no means of networking them with their laser printers. Metcalfe referred to this network as Alto ALOHA, but changed it in 1973 to Ethernet 3Mbps, shared coaxial cable and CSMA/CD protocol. Ether means network passed bits to each workstation (Metcalfe, 1996).

In 1980 Metcalfe facilitated a consortium by Digital Equipment Corporation (DEC), Intel and Xerox to assent on a common Ethernet standard DIX 10Mbps Ethernet. In 1982, the IEEE, Institute of Electrical and Electronics Engineers adopted IEEE802.3 standard, based on DIX Ethernet. Poor performance of ALOHA prompted the establishment of Carrier Sense Multiple Access with Collision Detection (CSMA/CD) that led to Multiple Access Control (MAC) protocol that minimized collisions with 80% efficiency. Here, CSMA influenced a station ready to transmit to listen to the channel for any transmission in progress, if idle, transmit then and wait for ACK, if busy wait. Upon arrival, receiving station checks CRC for correctness then sends ACK. If no ACK received by transmitter, time out, and restart process. CD enables the sending of jamming signals to inform other stations on collision occurrence.

Growth of Ethernet

Gigabit Ethernet development eliminated network size limits associated with shared media, bandwidth and half-duplex to achieve reliable and high speed services (Metcalfe, 1996). This saw inclusion of long- haul (40km +) optical transceiver for building MANs and WAN option with 10 Gigabit Ethernet transmission across existing SDH/SONET infrastructures (Spurgeon, 2000).

References

Metcalfe R. M., Packet communication. Annabooks/RTC books. San Jose: Califonia.1996.

Spurgeon C.E., Ethernet: The Definitive Guide. O’Reilly and Associates, Inc. Sebastopol: CA. 2000.

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