1.introduction to computer networks


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1.introduction to computer networks

  1. 1. Computer Communication & Networks Introduction to Networking Made by: Sidra !
  2. 2. What is a Network?A network consists of 2 or more computersconnected together, and they can communicateand share resources
  3. 3. Why Networking?• Sharing information — i.e. data communication • Do you prefer these? • Or this?
  4. 4. • Sharing hardware or software • E.g. print document• Centralize administration and support • E.g. Internet-based, so everyone can access the same administrative or support application from their PCs
  5. 5. How many kinds of Networks?• Depending on one’s perspective, we can classify networks in different ways • Based on transmission media: Wired (UTP, coaxial cables, fiber- optic cables) and Wireless • Based on network size: LAN and WAN (and MAN) • Based on management method: Peer-to-peer and Client/Server • Based on topology (connectivity): Bus, Star, Ring …
  6. 6. LAN - Local Area Network• Local Area Network (LAN) • Small network, short distance • A room, a floor, a building • Limited by no. of computers and distance covered • Usually one kind of technology throughout the LAN • Serve a department within an organization • Examples: • Network inside the Student Computer Room • Network inside your home
  7. 7. WAN – Wide Area Network • A network that uses long-range telecommunication links to connect 2 or more LANs/computers housed in different places far apart. • Towns, states, countries • Examples: • Network of our Campus • Internet Your home USA WAN Campus
  8. 8. MAN - Metropolitan Area Network  Larger than a LAN and smaller than a WAN - example: campus-wide network - multi-access network  Technologies:  coaxial cable  microwave
  9. 9. Network Management MethodPeer to Peer Network• Peer-to-peer network is also called workgroup• No hierarchy among computers all are equal• No administrator responsible for the network Peer-to-peer
  10. 10. Network Management Method• Advantages of peer-to-peer networks: • Low cost • Simple to configure • User has full accessibility of the computer• Disadvantages of peer-to-peer networks: • May have duplication in resources • Difficult to uphold security policy • Difficult to handle uneven loading• Where peer-to-peer network is appropriate: • 10 or less users • No specialized services required • Security is not an issue • Only limited growth in the foreseeable future
  11. 11. Network Management MethodClients and Servers • Network Clients (Workstation) • Computers that request network resources or services • Network Servers • Computers that manage and provide network resources and services to clients • Usually have more processing power, memory and hard disk space than clients • Run Network Operating System that can manage not only data, but also users, groups, security, and applications on the network • Servers often have a more stringent requirement on its performance and reliability
  12. 12. Network Management Method• Advantages of client/server networks • Facilitate resource sharing – centrally administrate and control • Facilitate system backup and improve fault tolerance • Enhance security – only administrator can have access to Server • Support more users – difficult to achieve with peer-to-peer networks• Disadvantages of client/server networks • High cost for Servers • Need expert to configure the network • Introduce a single point of failure to the system
  13. 13. Topology ― 3 basic types• Bus Topology • Simple and low-cost • A single cable called a trunk (backbone, segment) • Only one computer can send messages at a time • Passive topology - computer only listen for, not regenerate data
  14. 14. Topology ― 3 basic types Advantages of a bus topology:  uses less cable compared to other physical topologies like star  works well for small networks  does not need a central device, such as a hub, switch, or router Disadvantages of a bus topology:  slower access to the network and less bandwidth due to the sharing of the same cable by all devices  challenging to identify and isolate problems  break at any point in the bus cable can disable the entire bus network
  15. 15. Topology ― 3 basic typesStar Topology • Each computer has a cable connected to a single point • More cabling, hence higher cost • All signals transmission through the hub; if down, entire network down • Depending on the intelligence of hub, two or more computers may send message at the same time Hub
  16. 16. Topology ― 3 basic types Advantages of a Star Topology:  upgradeable, flexible, and reliable  easy to design and install  diagnosing problems relatively easy  allows for more throughput than any other topology Disadvantages of a Star Topology:  requires a lot of cable to connect computers .  expensive to build because of the additional cost of cables and devices
  17. 17. Topology ― 3 basic types• Ring Topology • Every computer serves as Ack T T a repeater to boost signals T • Typical way to send data: T dat T dat • Token passing a a • only the computer who gets the token can send T data T T Ack • Disadvantages T Ack dat • Difficult to add computers a • More expensive T • If one computer fails, whole network fails T Ack
  18. 18. Network Devices: Repeaters  A repeater receives the signal, regenerates it, and passes it on.  Repeaters are used mainly at the edges of networks to extend the wire so more workstations can be added.
  19. 19. Network Devices: Hubs  Using a hub changes the network topology from a linear bus, where each device plugs directly into the wire, to a star.  Hubs come in three basic types:  Passive  Active  Intelligent
  20. 20. Network Devices: Bridges  Bridges operate at the data link layer of the OSI model.  The function of the bridge is to make intelligent decisions about whether or not to pass signals on to the next segment of a network.  When a bridge sees a frame on the network, it looks at the destination MAC address and compares it.
  21. 21. Network Devices: Switches  Switches learn certain information about the data packets that they receive from computers on the network.  They use this information to build forwarding tables to determine the destination of data sent by one computer to another on the network.  They help segment a network and reduce network traffic congestion.
  22. 22. Network Devices: Routers  Routers operate at the Network layer of the OSI model.  They are slower than bridges and switches but make "smart" decisions on how to route packets.  Routers are capable of segmenting the network.