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Networks

Networks. U2M3 Topology. Objectives. Describe different topologies State to pros and cons of each type of topology Distinguish between the physical layout and the logical operation of a network topology. Network Topology. A Network Topology

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Networks

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  1. Networks U2M3 Topology

  2. Objectives • Describe different topologies • State to pros and cons of each type of topology • Distinguish between the physical layout and the logical operation of a network topology

  3. Network Topology • A Network Topology • refers to the layout of the computers and devices in a communication network. • physical layout – the way nodes are connected.

  4. Criteria used to assess Network Topologies • Basic cost: How expensive is it to link the various nodes? • Communication Cost: How long does it take to send a message from node A to node B? • Reliability: If a link or site in the system fails, can the remaining nodes still communicate with each other?

  5. Network Topologies • Star • Bus • Ring • Mesh • Hybrid

  6. Star Topology • A star network consists of one central node (switch or hub) to which all other nodes are connected • All signals pass through the central node • HUB - Logical bus • signal is broadcast • Multi-station Access Unit • (MSAU) MAU Physical star– Logical ring • Switch – logical star • signal is routed only to the intended node

  7. Star Topology Features Pros • If one of the computers fails or it cable is broken the others are unaffected. • Easy to add a new node • Easy to Troubleshoot • Switch – more secure Cons • If the central node fails, the whole network goes down • Single point of failure • Higher cost - More cable and switch

  8. BUS TOPOLOGY • The bus is the physical cable that connects the computers and other devices • a straight line • HUB –Physical star Logical bus • Message is broadcast

  9. BUS TOPOLOGY Features • Pros • inexpensive no special devices needed • Cons • Not secure – message broadcast • One open connection cause the network to fail • Difficult to troubleshoot • Slows down as number of nodes increase • Increase collsions

  10. Ring Topology • A ring network is one in which each node connects to exactly two other nodes, forming a single continuous pathway for signals through each node - a ring. • Data travels from node to node, with each node along the way handling every packet.

  11. Token ring (802.5) • A small packet, called a token, is passed around the ring to each computer in turn. • If a computer has information to send, • Waits for the token • it modifies the token, • adds address information and the data, and sends it down the ring. • When a packet is received by the intended destination computer, • it returns a message to the sender indicating its arrival. • Multi-station Access Unit • (MSAU) MAU Physical star– Logical Ring

  12. Ring Topology Features • Pros • Low cost • All nodes will get service • No collisions • Cons • may be disrupted by the failure of a single link. • Low security • Slows down as more nodes are added

  13. Hybrid Topology • These networks are some combination of two or more different standard topologies (bus, star, ring) • the resulting network does not exhibit features of any standard topology • Example • ISP (TSTT/FLOW) roll out bus networks and each home is a node on the ISP’s bus • within each house star networks are used to distribute network access among home computers. • Two examples for Hybrid network • star-bus network • Star-ring network

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