Ethernet : IEEE 802.3 Local Area Network (LAN) Protocols : Ethernet protocols refer to the family of local-area network (LAN) technology covered by the IEEE 802.3. It is working examplc of the more general carrier sense multiple access with collision detect (CSMA/CD). In the Ethernet Computer Network standard, there are two modes of operation: half-duplex and full-duplex modes. In the half duplex mode, data are transmitted using the popular Carrier-SenseMultiple Access/Collision Detection (CSMA/CD) protocol on as hared medium.
The main disadvantages of the half-duplex are the efficiency and distance limitation, in which the link distance islimited by the minimum MAC frame size. This restriction reducesthe efficiency drastically for high-rate transmission. Therefore, thecarrier extension technique is used to ensure the minimum framesize of 512 bytes in Gigabit Ethernet to achieve a reasonable linkdistance.Four data rates are currently defined for operation over opticalfiber and twisted-pair cables :
- 10 Mbps - 10Base-T Ethernet (IEEE 802.3)
- 100 Mbps - Fast Ethernet (IEEE 802.3u)
- 1000 Mbps - Gigabit Ethernet (IEEE 802.3z)
- 10-Gigabit - 10 Gbps Ethernet (IEEE 802.3ae).
The Ethernet is a multi-access network, meaning that a set of nodes send and receive frames over a shared link you can, therefore, think of an Ethernet or being like a bus that has multiple stations plugged into it. The "carrier sense" in CSMA/CD means that all the nodes can distinguish between an idle and a busy link and "collision detect" means that a node listens as it transmits and can therefore detect when a frame it is transmitting has collided with a frame transmitted by another node.
The Ethernet has its root in an early packet radio network, called ALOHA, like, the ALOHA, the problem faced by the Ethernet is how to mediate access to a shared medium fairly and efficiently. In ALOHA, the medium was the atmosphere, while in Ethernet the medium is coax cable.
In the earliest days, 10-Mbps Ethernet war used, but now it has been extended to include a 100-Mbps version called Fast Ethernet and a 1000-Mbps version called Gigabit Ethernet.
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.
As with all IEEE 802 protocols, the ISO data link layer is divided into two IEEE 802 sub-layers, the Media Access Control (MAC) sub-layer and the MAC-client sub-layer. The IEEE 802.3 physical layer corresponds to the ISO physical layer.
Each Ethernet-equipped computer 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. 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. 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).
As each Ethernet frame is sent onto the shared signal channel, all Ethernet interfaces look at the destination address. If the destination address of the frame matches with the interface address, the frame will be read entirely and be delivered to the networking software running on that computer. All other network interfaces will stop reading the frame when they discover that the destination address does not match their own address.