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Introduction to Computer Networks

Learn about the difference between networks and internets, logical and physical addresses, protocols, layering, and various network models. Explore the applications of networks, different network categories, network topologies, network operating software, and network hardware and physical media.

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Introduction to Computer Networks

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  1. Introduction to Computer Networks Chapter 2 INTRODUCTION TO COMPUTER NETWORKS

  2. Learning outcomes • The difference between networks and internets • The difference between logical and physical addresses • What is a protocol in the context of computer networking • How protocols are used on remote computers to communicate easily • Explain the concept of layering • OSI , • TCP/IP and • hybrid models

  3. Reading • Joe Casad, Teach Yourself TCP/IP, Chs 1-2 • William Buchana, Mastering the Internet, Ch. 3 • Neil Briscoe, Understanding the 7-layer OSI model, July 2000. • http://pcnetworkadvisor.com • Julian Moss, Understanding TCP/IP (first part September 1997) • http://pcnetworkadvisor.com

  4. What is a network? A network consists of two or more computers • connected by network media • .i.e cables, telephone lines, radio waves • share the same resources such as database, printer • Exchange files • Exchange electronic message between each others • Email

  5. Example of a simple network

  6. How are they linked? • Computers on a network may be linked through: • cables, • telephone lines, • radio waves, satellites or • wireless technologies

  7. An example of a network Router Hub Bridge Segment Node Hub Internet

  8. Introduction to Computer Networks Applications of Networks • Resource Sharing • Hardware (computing resources, disks, printers) • Software (application software) • Information Sharing • Easy accessibility from anywhere (files, databases) • Search Capability (WWW) • Communication • Email • Message broadcast • Remote computing • Distributed processing (GRID Computing)

  9. Categories of networks

  10. Local Area Network • A LAN is a network that is used for communicating among computer devices, usually within an office building or home • LAN’s enable the sharing of resources such as files or hardware devices that may be needed by multiple users • Is limited in size, typically spanning a few hundred meters, and no more than a mile • Is very fast, with speeds from 10 Mbps to 10 Gbps • Requires very little wiring, typically a single cable connecting to each device • Has lower cost compared to MAN’s or WAN’s

  11. LAN

  12. LAN (Continued)

  13. Metropolitan-Area Networks (MAN) • MAN is designed extended over an entire city. • May be wholly owned and operated by a private company, or it may be a service provided by a public company, such as a local telephone company.

  14. Wide-Area Networks (WAN) • Provides long-distance transmission of data, voice, image, and video information over large geographic areas

  15. WAN (Continued) • WANs connect larger areas, such as whole states, or even the world. • Transoceanic cables and satellites are used to connect WANs

  16. Topology • The physical topology of a network refers to the configuration of cables, computers and other peripherals. • The main types of network topologies are: • Linear Bus • Star • Ring • Tree or Hybrid

  17. Linear Bus topology • A linear bus topology consists of a main run of cable with a terminator at each end. All servers workstations and peripherals are connected to the linear cable

  18. Star topology • A star network is designed with each node (file server, workstation, peripheral) connected directly to a central network hub or server

  19. Ring topology • A ring network is one where all workstations and other devices are connected in a continuous loop. There is no central server

  20. Tree or hybrid topology • A tree or hybrid topology combines characteristics of linear bus and star and/or ring topologies. • It consists of groups of star-configured workstations connected to a linear bus backbone cable

  21. Network Operating Software • Network operating systems co-ordinate the activities of multiple computers across a network • The two major types of network OS are: • Peer-to-peer • Client/server

  22. Peer to peer network OS • In peer to peer network OS, there is no file server or central management source; all computers are considered equal • Peer to peer networks are design primarily for small to medium LANS • AppleShare and Windows for Workgroups are examples of programs that can function as peer to peer

  23. Client/Server network OS • Client/server network OS centralise functions and applications in one or more dedicated file servers. • The file server provides access to resources and provides security • Novel Netware and Windows NT Server are examples of client/server network operating systems

  24. Network Hardware and Physical Media • Network hardware includes: • Computers • Peripherals • Interface cards and • Other equipment needed to perform data processing and communications within the network

  25. File servers • A very fast computer with a large amount of RAM and storage space along with a fast network interface card • The network operating system software resides on this computer

  26. Workstations • All computers connected to the file server on a network are called workstations

  27. Network interface cards • The network interface card (NIC) provides the physical connection between the network and the computer workstation. • Most NICs are internal with the card fitting into an expansion slot in the computer. • Three common network interface connections are Ethernet cards, Local Talk connectors and Token Ring cards

  28. Ethernet cards • The most common Network Interface Cards are Ethernet cards • They contain connections for either coaxial or twisted pair cables, or both Co-axial cable Twisted pair cable

  29. Concentrators / Hubs • A concentrator is a device that provides a central connection point for cables from workstations, servers and peripherals • Hubs are multi-slot concentrators

  30. Switches • hubs provide an easy way to scale up and shorten the distance that the packets must travel to get from one node to another • they do not break up the actual network into discrete segments. That is where switches come in.

  31. Switches (continued) • A vital difference between a hub and a switch is • all the nodes connected to a hub share the bandwidth among themselves. • while a device connected to a switch port has the full bandwidth all to itself. • Think of a switch as a ‘clever’ hub

  32. Repeaters • A signal loses strength as it passes along a cable, so it is often necessary to boost the signal with a device called a repeater • A repeater might be a separate device, or might be part of a concentrator

  33. Bridges • A bridge is a device that allows you to segment a large network into two smaller, more efficient networks

  34. An example of a network with a bridge Router Hub Bridge Segment Node Hub Internet

  35. Routers • A router translates information from one network to another • The router directs traffic to prevent “head-on” collisions • If you have a LAN that you want to connect to the Internet, you will need a router to serve as the translator between information on your LAN and the Internet

  36. Routers (continued)

  37. Physical Media • Physical media provide the connections between network devices that make networking possible • There are four main types of physical media in widespread use today: • Coaxial Cable • Twisted Pair • Fiber Optic Cable • Wireless Media

  38. LAN Technologies Ethernet • Physical Media :- • 10 Base5 - Thick Co-axial Cable with Bus Topology • 10 Base2 - Thin Co-axial Cable with Bus Topology • 10 BaseT - UTP Cat 3/5 with Tree Topology • 10 BaseFL - Multimode/Singlemode Fiber with Tree Topology • Maximum Segment Length • 10 Base5 - 500 m with at most 4 repeaters (Use Bridge to extend the network) • 10 Base2 - 185 m with at most 4 repeaters (Use Bridge to extend the network) • 10 BaseT - 100 m with at most 4 hubs (Use Switch to extend the network)

  39. Thick Coaxial Cable • Used in the first Ethernet networks • Type RG-11 / 10Base5 • Usually orange/black • Thickness of a small garden hose • Very expensive and heavy cable • Two strands along the axis • Conductor down the center • Insulator surrounds conductor • Shielded mesh serves as outside

  40. Thin Coaxial Cable • Alternative to Thick Ethernet Cable • Type RG-58 / 10Base2 / “Cheapnet” • Usually black • Thickness of a pencil • More flexible than thick Ethernet • Reduced the cost of the cabling • Flexible

  41. Coaxial cable connectors • The most common type of connector used with coaxial cables is the BNC connector

  42. Twisted Pair Cable • Phone Systems • Twisted Pair Cable consists of two copper wires, usually twisted around each other to cancel out any noise in the circuit • Two main type of Twisted Pair Cabling • Shielded Twisted Pair (STP) • Unshielded Twisted Pair (UTP)

  43. RJ-45 Shielded Twisted Pair (STP) • STP is the original media used for token ring networks • STP can be used for high-speed networks, such as FDDI or ATM, where shielding is important.

  44. Unshielded Twisted Pair (UTP) • UTP has four pairs of wires inside the jacket • Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs

  45. UTP (Continued) • Most commonly used twisted pair cable • Uses common telephone wire • UTP was standardized by the IEEE 802.3 committee in October of 1990 • UTP for LANs is now classified as: • Category 3 - used for LANs up to 10 Mbps • Category 4 - used for LANs up to 16 Mbps • Category 5 - used for LANs up to 100 Mbps

  46. Fiber Optic Cable • Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials • It transmits light rather than electronic signals • It is the standard for connecting networks between buildings, due to its immunity to the effects of moisture and light

  47. Fiber Optic (continued) • Fiber optic cable has the ability to transmit signals over much longer distances than coaxial or twisted pair • It can also carry information at vastly greater speeds • Fiber optic cable is more difficult to install than other cabling

  48. Wireless LANS • Wireless networks use high frequency radio signals to communicate between the workstations and the fileserver or hubs. • Disadvantages of wireless networks are: • they are expensive (relatively), • provide poor security, • are susceptible to interference and • are slower than cabled networks

  49. PROTOCOL = SET OF RULES ABOUT COMMUNICATIONS BETWEEN NETWORKS! Introduction network Protocol • A protocol is a set of rules that governs the communications between computers on a network • These rules include guidelines that regulate: • the method of access, • types of cabling and • speed of size data transfer

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