Ethernetwas the first commercially available local area network system and remain,without a doubt, the most popular local area network system today. The wiredversion of Ethernet is based primarilyon the star-wired bus topology and uses the CSMA/CD medium access protocol.
Because Ethernet is so popular and has been around the longest, it has evolvedinto a number of different forms. To avoid mass mayhem, the IEEE created a setof individual standards specifically for Ethernet or CSMA/CD local area networks, all under thecategory of 802.3.let’s examine the different 802.3 protocol in alittle moredetail.
For your reference, the 802.3 standars to be discussed are summarizedin table 1.1 Table 1.1Theoriginal 802.3 standard include 10Base5, 10Base2, 1Base5, and 10BaseT. The 10Base5standard was one of the first Ethernet standards approved.
The term “Base” isan abbreviation for baseband signals using a Manchester encoding. Recall thebaseband signals are digital signals. Because there is no multiplexing of digitalsignals on any baseband LAN’s there is onlt one channel of information on thenetwork.
The 10 of 10Base5 represent a 10-Mbps transmission speed, and the 5represents 500-meter maximum cable segment length.(Note that these standard,like those associated with conducted media, are based on the Metric system;where applicable, the English equivalent will be provided.) 10Base(nicknamedCheapernet) was designed to allow for aless-expensive network by using less-expensive components . The 10Base2 networkcan transmit 10-Mbps digital signals over coaxial cable, but only for a maximum of 200 meters (the value 2in 10Base2). 1Base5 was a system designed for twisted pair writing,but with only a 1-Mbps data transfer rare for 500 meter. Perhaps the mostpopular Ethernet system ( and the most popular local area network systemoverall) is 10BaseT.
A 10BaseT system transmit 10-Mbps baseband (digital)signals over twisted pair maximum of 100 meters per segment length. Since each mode on a10 Base-T network has its own cable connecting it to a central hub,it is farless likely that any node can cause the entire network to fail. The hub alsohas a “partitioning” function built into it which allows it to detect a problemon any of its ports.If a problem is found,the node is disconenected from therest of the network. This isolates thr problem until the node can betroubleshot and repaired.
Because of the partitioning function built in to thehubs and the star-wired topology, it is generally easy to troubleshoot a10BaseT network.in a worst-case scenario,one can be trounleshoot by simpledisconnecting nodes from the hub one at a time until the network recovers. Usually,thehub will give an indication as to which node is causing a problem,allowing the technician totroubleshoot that node as opposed to speding many hours finding where theproblem is.Token-Ring Lan Technology was developed by IBM in the middle1980s a fast and reliable alternative toEternet.Token ring technology uses a different concept,known as token passing,for allowing network adapters to transmit data on the media.Token Ring uses aStar Ring topology, a hybrid topology, looking physically like a Star Topologybut logically wired as a Ring Topology. Token Ring operates in RingTopology, in a logical Ring, where the central device which is used to connectthe network devices (Servers, Workstation, Printers, Scanners and etc.
) hosts an internal ring,where acess to the networkmedia for a network device is given only by the possession of a token that ispassed from device to device in the ring. The central device which is used toconnect the network device is called as a Multistation Acess Unit,or MAU.Token-ring is more sophisticated than Ethernet , and it includes a number ofbuilt-in diagnosis and correction mechanism that can help troubleshoot shootnetwork problems and Token-Ring networks does not produce the collisions thatcan take place in the Ethernet Network.The main difference of Ethernet andToken Ring is that, Ethernet uses Star Topology and Token Ring uses logicalRing topology. When a Token-Ring network starts up, the devices take partin a negotiation to decide who willbecome the “Active Monitor”. In Token-Ring network ,”Active Monitor ” is amachine with the highest MAC address andall other machines are ‘standby Monitors’. The job of the Active Monithor is tomake sure that none of the machines are causing problems on the network, and tore-establish the ring after a break or an error has occurred.
A computer thatpasses the token to the next computer on the logical ring would be called thenearest active upstream neighbor (NAUN). The computer receiving the token isthe nearest active downstream neighbor (NADN). Once a computer takes possessionof the token and transmits data, it then creates a new token and passes it tiits NADN.Early Token-Ring network has 4Mbps speed and later 16Mbps and 100Mbps speedToken-Ring networks were also available.Token Ring networks were replaced byEthernet family Technologies due to the advantages of Ethernet technologies. Thesedays, it is extremely difficult to find a business network operating using Token Ring technology . Token Ring networks are deterministic in nature.
In English,this means that the nodes may only transmit at certain, well defined times. Thiseliminates incidents of two or more nodes transmitting at the same time andcorrupting each other,s transmission (collisions). The elimination of collisions results in a networkwhere data almost always gets to its destination on the first attempt, greatlyreducing retransmissions which waste bandwidth at the same wire speed.