Thursday, 6 October 2011

Ethernet is the most popular LAN technology currently in use. Other popular LAN type include Token Ring , fast Ethernet , Distributed Data Interface ( FDDI) , Localtalk , Ethertalk , and Arcnet. Ethernet is popular due to it’s low cost , multitude of wiring types and market acceptance. 
The Ethernet standard is defined by the Institute for Electrical and Electronic Engineers (IEEE). The IEEE stander 802.3 defines the rules for configuring Ethernet as well as the protocol that allow the computers to communicate . 
Network protocols re standards that allow computers to communicate with each other . A protocol defines how the computers should identify each other on the network, the form that the data should take in transit , and how the information should be reconstructed once it reaches its final destination . Protocols also define how to handle damaged transmissions. IPX , TCP/IP, DECnet, Apple Talk , LAN SMB, DLC, and Net BEUI are examples of network protocols. 
Although each protocol is differenr, they all use the physical cabling in the same manner, which allows them to peachfully coexist. This concept known as “protocol independence” 
Media and Topologies. 
One of the most important parts of designing and installing a network is deciding on which cabling medium and wiring topology to use. There are four major types of media in use today: Thickwire, Thincoax, unshielded twisted pair(UTP), and fiber optic. Ethernet media are used in two basic topologies called “bus” and “star”. The topology defines how a node is connected to the network. 
A bus topology consists of nodes connected together by a single long cable. Each node “taps” into the bus and directly communicates with all other nodes on the bus. The major advantage of this topology is the easy expantion, by adding extra “taps” and the lack a hub. The major disadvantage is that any break in the cable will cause all nodes on the cable to loose connection to the network. 
A star topology links exactly two nodes together on the network a hub is used to collection point where many of the connections come together. The major advantage is any single break only disables one host. The major disadvantage is the added cost of a hub. 

Thickwire Ethernet. 

Thickwire or 10base5 Ethernet, was generally used to creat large “backbones”. A network backbone joins many smaller network segments into one large LAN. Thickwire made an execellant backbone because it can support many nodes in a bus topology and the segment can be quite long. It can be run from workgroup to workgroup where smaller networks can then be attached to the backbone. A thickwire segment can be up to 500 matters long and have as many as 100 nodes are connected to the cable by drilling into the media with a device known as “vampire tap”. Node must be spaced exactly2.5 meter apart to prevent signals from interfacing with one another. 
Thin Coax Ethernet.
Thin Coax, or 10BASE2 Ethernet offer the advantage of thicknet’s bus topology, with reduce cost and easier installation. Thin coaxil cable is thiner and more flexible then thickwire but it can support only 30 nodes per segment, and each node must be at least 1.5 meters apart. 
Twisted pair Ethernet. 
Unisheld twisted pair (UTP) which is very similar to telephone cable in both appearance and end connector appearance. It comes in a variety of grades, with level 1 being the lowest quality and level 5 being the best. 
A Unshielded Twisted Pair Ethernet network uses a star topology, with each node being connected directly to a hub. The major limitation of this cable is a maximum cable length of 100 meters, and that each node must have its won connection to the hub. 
Fiber Optic Ethernet. 
Fiber optic Ethernet is similar to twisted pair. Fiber optic cable can handle100 mbps transmission speeds, but is not affected by electrical emission or electro-magnatic interface. The major disadvantage is the higher cost of cable and equipment. 
Fast Ethernet. 
With the addition of large data steams such as real time video and audio , networks have begunto require high transmission speeds. The new Ethernet standered established to handle this requirement is called fast Ethernet.


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