Wide Area NetworksLearning ObjectivesLAN and WANWide Area Networks basicsSlide 5Slide 6Slide 7Types of SubnetsCircuit Switching SubnetReserved Capacity (Circuit Switching)Reserved CapacityPacket Switching SubnetDatagram Packet Switching SubnetDatagram Packet Switching SubnetsVirtual-Circuit Packet Switching SubnetsRouting decisionsSlide 17Slide 18Slide 19Summary QuestionsSlide 21Bridge versus RouterWide Area NetworksSchool of BusinessEastern Illinois University © Abdou Illia, Spring 2007(Week 11, Thursday 3/22/2007)2Learning ObjectivesDistinguish between LAN and WANDistinguish between –Circuit Switching Networks–Datagram Packet Switching Networks –Virtual Packet Switching NetworksUnderstand routing decisions3LAN and WANLAN = a communication network that interconnects networking devices within a small geographic area using broadcast system.WAN = a communication network that interconnects networks and networking devices within a wide geographic area using Point-to-Point system.A Point-to-Point system:–Many connections between individual pairs of stations–A packet may have to visit one or more intermediate stations–Multiple routes are possible; so routing decisions have to be madeQ: What are the main differences between a LAN and a WAN?4Wide Area Networks basicsWANs follows a mesh topologyOnly neighbor devices are connected to each otherTo transmit across the mesh, data has to be passed along a route from node to nodeSubnetSubnetSubnetSubnetLAN5Wide Area Networks basicsA sta tion is a device that interfaces a user to a networkA sta tion could be:–a computer (for Data networks)–a telephone (For Voice networks)6Wide Area Networks basicsData is transferred from node to node through the network A Node is a transfer point for passing data through the networkA Node is often a computer, a router, or a telephone switchQ: What is the difference between a station and a node?7Wide Area Networks basicsThe subn et is the underlying physical connection of nodes and communication lines that transfer data from one location to another.A Subnet is a collection of nodes and different types of transmission mediaQ: How does the subnet differ from the network?8Types of SubnetsBased on the way data is transferred from one end of the subnet to the other:–Circuit Switching Subnet–Packet Switching Subnet9Circuit Switching SubnetTraditionally used for Voice networksA subnet in which a dedicated circuit is established between sender and receiver and all data passes over this circuit.10Reserved Capacity (Circuit Switching)–Circuit capacity is reserved during duration of each communication–At each switch–On each trunk lineCircuitReservedCapacityReservedCapacity11Reserved CapacityNothing like congestion on the InternetReserved Circuit Capacity is Expensive–Pay for it whether you use it or not–Good for voice, because conversations are fairly constant–Bad for data, because most data transmission is bur sty; e.g., in World Wide Web, download, then stare at screen for a long time until next downloadQ: What are the main characteristics of Circuit Switching networks?12Packet Switching SubnetUsually used for Data networksA subnet in which all data messages are transmitted using fixed-sized packages, called packets.Two types of Packet Switching Subnets:–Datagram Packet Switching Subnets–Virtual-Circuit Packet Switching Subnets13Datagram Packet Switching SubnetIn all types of Packet Switching Subnets, large messages are broken into small pieces called packet s–Packets are short (averaging a few hundred bytes) because most nodes (routers) handle short messages more efficientlyMultiplexing onTrunk LinePacket SwitchingMultiplexing–Packets from many conversations are mixed (mul tiplex ed) over each trunk lineMessagePackets14Datagram Packet Switching SubnetsAs each packet arrives at a node a routing decision is made:–Which route the packet will follow next ?This dynamic routing decision allows flexibility should the network experience congestion or failureBut, a node has to examine each individual packet and determine the next pathRouter AB?D?C?BCDPacket15Virtual-Circuit Packet Switching SubnetsAmount of data broken into n packetsA virtual circuit (temporary path through the network) is determinedNote: The virtual circuit is not dedicated (not reserved)All n packets transmitted through the virtual circuitWhen transfer completed, virtual circuit dissolvedQ:16Routing decisionsMany possible routes exist for forwarding a packet.How does a router decide which line to transmit on?17Routing decisionsA subnet can be viewed as weighted network graphA weight is associated to each lineWeight can be:–Cost of using the transmission line–Time delay for transmitting data–Size of the queue18Routing decisionsDifferent algorithms (or techniques) for selecting a route through a networkCommon algorithms/techniques:–Dijkstra’s least cost algorithm–Flooding techniqueDijkstra’s least cost algorithm–Calculate the costs for using each route for a given node–Determine the route that minimize the sum of the costs –Calculation performed on a periodic basis or when changes happened (connection or node failure for example)19Routing decisionsFlooding Routing–When a packet arrives at a node, the node sends a copy of the packet out every link except the link the packet arrived on–Traffic grows very quickly when every node floods the packet–To limit uncontrolled growth, each packet has a hop count. Every time a packet hops, its hop count is incremented. When a packet’s hop count equals a global hop limit, the packet is discarded20Summary QuestionsHow does the subnet differ from the network?Answer: The network include: the subnet(s), the stations, the OS & other application software, and the other networking devices & transmission medium needed to connect the stations to the subnetWhat is the difference between a station and a node? Answer: A station is the device that interfaces a user to the network. A node is a transfer point for passing data through the network. A node can be a computer, a router, or a telephone switch. What are the main characteristics of Circuit Switching networks? Answer: In Circuit Switching networks: (1) a dedicated circuit is established between sender and receiver, (2) circuit capacity is reserved during the duration
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