lec introduction to networking

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  • 1. 1Introduction to Networking and Local-Area Networks 2008 The McGraw-Hill Companies

2. 2 Topics Covered Network Fundamentals LAN Hardware Ethernet LANs Token-Ring LAN 2008 The McGraw-Hill Companies 3. 3 12-1: Network Fundamentals A network is a communication system with two ormore stations that can communicate with one another. When it is desired to have each computercommunicate with two or more additional computers,the interconnections can become complex. The number of links L required between N PCs(nodes) is determined by using the formula L = N(N1) / 2 The number of links or cables increases in proportion to the number of nodes involved 2008 The McGraw-Hill Companies 4. 4 Network Fundamentals Each computer or user in a network is referred to as a node. The interconnection between the nodes is referred to as the communication link.A network of four PCs. 2008 The McGraw-Hill Companies 5. 5Network FundamentalsTypes of Networks There are four basic types of networks: Wide-area networks (WANs), Metropolitan-area networks (MANs) Local-area networks (LANs) Personal-area networks (PANs) 2008 The McGraw-Hill Companies 6. 6Network FundamentalsWide-Area Networks (WANs) A WAN covers a significant geographical area. Local telephone systems are WANs, as are the manylong-distance telephone systems linked together acrossthe country and to WANs in other countries. The nationwide and worldwide fiber-optic networks setup since the mid-1990s to carry Internet traffic are alsoWANs. Known as the Internet core or backbone, these high-speed interconnections are configured as either directpoint-to-point links or large rings with multiple accesspoints 2008 The McGraw-Hill Companies 7. 7Network FundamentalsMetropolitan-Area Networks (MANs) MANs are smaller than WANs and generally cover acity, town, or village. Cable TV systems are MANs. Other types of MANs, or metro networks as they aretypically called, carry computer data. MANs are usually fiber-optic rings encircling a city thatprovide local access to users. Businesses,governments, schools, hospitals, and others connecttheir internal LANs to them. 2008 The McGraw-Hill Companies 8. 8Network FundamentalsLocal-Area Networks (LANs) A LAN is the smallest type of network in general use. A LAN consists primarily of personal computersinterconnected within an office or building. LANs can have as few as three to five users, althoughmost systems connect to several thousand users. 2008 The McGraw-Hill Companies 9. 9Network FundamentalsPersonal-Area Networks (PANs). A PAN is a short-range wireless network that is set upautomatically between two or more devices such aslaptop computers, personal digital assistants (PDAs),peripheral devices, or cell phones. The distance between the devices is very short, nomore than about 10 m and usually much less. PANs are referred to as ad hoc networks that are set upfor a specific single purpose, such as the transfer ofdata between the devices as required by someapplication. 2008 The McGraw-Hill Companies 10. 10 Network FundamentalsStorage-Area Networks (SANs) SANs are an outgrowth of the massive data storagerequirements developed over the years These networks usually attach to a LAN or Internetserver and store and protect huge data files. The SAN also provides network users access tomassive data files stored in mass memory units, calledredundant arrays of independent disks (RAIDs). RAIDs use many hard drives interconnected to thenetwork and may be located anywhere since accesscan be via the Internet or a fiber-optic WAN or MAN. 2008 The McGraw-Hill Companies 11. 11 Network FundamentalsNetwork Topologies The topology of a network describes the basiccommunication paths between, and methods used toconnect, the nodes on a network. The three most common topologies used in LANs arestar, ring, and bus. 2008 The McGraw-Hill Companies 12. 12Network FundamentalsStar Topology A basic star configurationconsists of a centralcontroller node and multipleindividual stationsconnected to it. The central or controllingPC, often referred to as theserver, is typically largerand faster than the otherPCs and contains a largehard drive where shareddata and programs arestored. 2008 The McGraw-Hill Companies 13. 13Network FundamentalsStar Topology A star-type LAN is extremely simple andstraightforward. New nodes can be quickly and easily added to thesystem, and the failure of one node does not disable theentire system. If the server node goes down, the network is disabledbut individual PCs will continue to operateindependently. Star networks generally require more cable tha othernetwork topologies 2008 The McGraw-Hill Companies 14. 14Network FundamentalsRing Topology In a ring configuration,the server or maincontrol computer and allthe computers are simplylinked together in asingle closed loop. Usually, data istransferred around thering in only one direction,passing through eachnode. 2008 The McGraw-Hill Companies 15. 15 The ring topology is easily implemented and low incost. The downside of a ring network is that a failure in asingle node generally causes the entire network to godown. It is also difficult to diagnose problems on a ring. 2008 The McGraw-Hill Companies 16. 16 Network FundamentalsBus Topology A bus is a common cable towhich all of the nodes areattached. The bus is bidirectional in thatsignals can be transmitted ineither directions between anytwo nodes. Only one node can transmit ata given time. 2008 The McGraw-Hill Companies 17. 17 A signal to be transmitted can be destined for a single node, ortransmitted or broadcast to all nodes simultaneously. The bus is faster than other topologies, wiring is simple, and the buscan be easily expanded 2008 The McGraw-Hill Companies 18. 18Network FundamentalsMesh Topology A mesh network is onein which each node isconnected to all othernodes. In a full mesh, everynode can talk directly toany other node. There are major costsand complications as thenumber of nodesincreases 2008 The McGraw-Hill Companies 19. 19Network FundamentalsOther Topologies. The daisy chain topology isa ring that has been broken. The tree topology is a busdesign in which each nodehas multiple interconnectionsto other nodes through a starinterconnection. 2008 The McGraw-Hill Companies 20. 20Network FundamentalsClient-Server and Peer-to-Peer LANs Most LANs conform to one of two generalconfigurations: client-server or peer-to-peer. In the client-server type, one of the computers in thenetwork, the server, essentially runs the LAN anddetermines how the system operates. The server manages printing operations of a centralprinter and controls access to a very large hard drive orbank of hard drives containing databases, files, andother information that the clientsthe other computerson the networkcan access. The server also provides Internet access. 2008 The McGraw-Hill Companies 21. 21 Network Fundamentals In a peer-to-peer system, any PC can serve as eitherclient or server; any PC can have access to any otherPCs files and connected peripherals. Peer-to-peer LANs are smaller and less expensive thanthe client-server variety, and provide a simple way toprovide network communication. Disadvantages include: Lower performance (lower-speed transmission capability). Manageability and security problems (any user mayaccess any other users files). 2008 The McGraw-Hill Companies 22. 22LAN Hardware All LANs are a combination of hardware and software. The primary hardware devices are the computers,cables, and connectors. Additional hardware includes: Network interface cards (NICs) Repeaters Hubs and concentrators Bridges Routers Gateways 2008 The McGraw-Hill Companies 23. 23 LAN HardwareCablesMost LANs use some type of copper wire cable to carry data from one computer to another via baseband transmission. The three basic cable types are:1. Coaxial cable2. Twisted pair3. Fiber-optic cable 2008 The McGraw-Hill Companies 24. 24 LAN Hardware: Coaxial cable. 2008 The McGraw-Hill Companies 25. 25 LAN HardwareTypes of twisted-pair cable. (a) Twisted-pair unshielded (UTP) cable. (b) Multipleshielded twisted-pair (STP) cable. 2008 The McGraw-Hill Companies 26. 26 12-2: LAN HardwareTwisted-Pair Cable The most widely used UTP is category 5 (CAT5). It cancarry baseband data at rates up to 100 Mbps at a rangeup to 100 m. Twisted-pair cable specifications also includeattenuation and near-end cross talk figures. Attenuation means the amount by which the cableattenuates the signal. The longer the cable, the greaterthe amount of loss in the cable and the smaller theoutput. 2008 The McGraw-Hill Companies 27. 27LAN HardwareTwisted-Pair Cable Cross talk refers to the signaltransferred from one twisted pairin a cable to another by way ofcapacitive and inductive coupling.Near-end cross talk is the signalappearing at the input to thereceiving end of the cable. Many newer office buildings areconstructed with special verticalchannels or chambers, calledplenums, through which cablesare run between floors or acrossceilings. Cable used this way, calledplenum cable, must be made offireproof material that will not emittoxic fumes if it catches fire. 2008 The McGraw-Hill Companies 28. 28 LAN HardwareFiber-optic cable. 2008 The McGraw-Hill Companies 29. 29LAN HardwareCoaxial Cable ConnectorsCoaxial cables in networks use two types of connectors:1. N connectors are widely used in RF applications2. BNC (Bayonet Neill-Concelman )connectors are commonly used for attaching test leads to measuring instruments such as oscilloscopes. 2008 The McGraw-Hill Companies 30. 30 LAN HardwareConnectors: Coaxial Cable Connectors BNC T connectors are used to interconnect two cablesto the network hardware. The barrel connector provides a convenient way toconnect two coaxial cables. A terminator is a special connector containing aresistor whose value is equal to the characteristicimpedance of the coaxial cable (typically 50). 2008 The Mc