Module Three

Carrier sense multiple access csma n foundation of

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Carrier Sense Multiple Access (CSMA) n Foundation of Ethernet Protocol. n Workstation continuously monitors the line waiting until it thinks it is free. n If the workstation doesn’t receive an acknowledgement from the destination to which it sent the packet, it assumes a collision has occurred and it resends the packet. n Persistent Carrier Sense - Unless receives acknowledgement it will resend. n Nonpersistent Carrier Sense – waits random amount of time and resends. CSMA/CA - Carrier Sense Multiple Access Collision Avoidance – Workstations connected to two coax cables, one to send and one to receive data. CSMA/CD - Carrier Sense Multiple Access Collision Detection Ethernet If the host detects another signal while transmitting it will send a jam signal causing all nodes to stop sending data. Nodes wait to resend. Designed to avoid collisions. 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
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Carrier Sense Multiple Access CSMA n Foundation of Ethernet...

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