The foundation of Ethernet topology was first established in 1970, with a program called Alohanet.
Alohanet required all stations to follow a protocol in which an unacknowledged transmission required re-transmitting after a short period of waiting. The techniques for using a shared medium in this way were later applied to wired technology in the form of Ethernet.
Ethernet was designed to accommodate multiple computers tha were interconnected on a shared bus topology.
The first version of this was incorporated a media access method known as Carrier Sense Multiple Access with Collision Detection (CSMA/CD) that managed the problems that result when multiple devices attempt to communicate over a shared physical medium.
Ethernet operates across two layer of the OSI model. The model provides a reference to which the Ethernet can be related but it is actually implemented in the lower half of the Data Link Layer, which is known as the Media Access Control (MAC) sublayer, and the Physical Layer only.
Ethernet at Layer 1 involves signals, bit streams that travel on the media, physical components that put signals on the media, and various topologies. It performs a key role in the communication that take place between devices, but each of it's functions has a limitations.Ethernet stations communicate by sending each other data packets: blocks of data individually sent and delivered. As with other IEEE 802 LANs, each Ethernet station is given a 48-bit Mac Address. The MAC addresses are used to specify both the destination and the source of each data packet. Ethernet establishes link level connections, which can be defined using both the destination and sources addresses. On reception of a transmission, the receiver uses the destination address to determine whether the transmission is relevant to the station or should be ignored. Network interfaces normally do not accept packets addressed to other Ethernet stations
The success of Ethernet is due to the following:
- Simplicity and ease of maintenance
- Ability to incorporate new technologies
- Reliability
- Low cost of installation and upgrade
In an overview Of Ethernet Physical Layer; "Ethernet is covered by the IEEE 802.3 standards in which four data rates are currently defined for operation over optical fiber and twisted-pair cables:
- 10 Mbps - 10 Base- T Ethernet
- 100 Mbps - Fast Ethernet
- 1000 Mbps - Gigabit Ethernet
- 10 Gbps - 10 Gigabit Ethernet
The principal 10 Mbps implementation of Ethernet include:
- 10 Base5 -using a thicknet coaxial cable
- 10 Base2 -using a thinnet coaxial cable
- 10 Base-T - using Cat3 / Cat5 unshielded twisted-pair cable
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