Polling a primary workstation polls another at a

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Polling – a primary workstation polls another at a predetermined time to determine if it has data to transmit. Primary must give permission to others to transmit. Token passing n Token Ring and FDDI and ARCnet n Cannot transmit without the token n Each station can hold token for maximum predetermined amount of time LAN Transmission Methods: refer to the way packets are sent on the network n Unicast – from single source to single destination n Multicast - source copied and sent to multiple destinations n Broadcast - source copied and sent to all nodes on the network LAN Topologies Five common topologies : defines the manner in which the network devices are organized to facilitate communications. Bus n All transmissions travel full length of the cable and received by all other stations. n Single point of failure in the cable. n If one of the links between any of the computers is broken, the network is down. n Primarily Ethernet. n These networks were originally designed to work with more sporadic traffic. Ring n Unidirectional transmission links form closed loop. n Token Ring and FDDI. n Similar to the Star topology, however there’s a device called a Multistation Access Unit (MAU). n MAU works the same as a hub, but with Token Ring networks instead of Ethernet networks. n These networks were originally designed to serve large, bandwidth-consuming applications. Star
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n Nodes connected to a central LAN or a junction box called a hub or a concentrator at the center of the network. n Ads: reliability n Ring and Bus often use Star as physical connection. Tree – branches can have multiple nodes. Mesh – all nodes connected to every other node. LAN Media Access Methods (Physical and Data Link Layers): control the use of a network. Ethernet – 802.3 n Ethernet – uses CSMA/CD – Designed for sporadic traffic n Ethernet defines a bus topology with three different cabling standards n Thinnet – 10Base2 – coax with segments up to 185 meters. n Thicknet – 10BaseS – coax with segments up to 500 meters. n UTP – Unshielded Twisted Pair – all devices connected to a hub or switch 10BaseT 10 Mbps, 100BaseT 100 Mbps and 1000BaseT 1 GBps ARCnet – 802.5 n Early LAN technologies n Uses token passing in a Star topology on coax cable. Token Ring n Second to Ethernet n All end stations connected to a Multistation Access Unit (MSAU) n One station is designated as the Active Monitor n If a transmitting station fails, the Active monitor will remove the token and generate a new one. Fiber Distributed Data Interface – FDDI n Dual token ring LAN at 100 MBps on Fiber n Dual counter rotating rings only one active at a time n Operates over long distances with minimal interference n Predictable delays, deterministic n Permits several tokens to be present at a time n Expensive and requires expertise n Copper Distributed Data Interface (CDDI) – can be used with UTP cable but subject to interference and length issues associated with Copper.
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