Chapter_2, advanced usage of data communication
- 1. 08/15/2025 PREPARED BY DAWIT M. 1 Chapter Two Introduction to Computer Networks Computer Science 2nd Year Prepared By Mr. Dawit M.
- 2. OUTLINE † Computer Network and its Applications † Network Criteria † Computer Network Types † Computer Network Topologies † Computer Network Components † Computer Network Models
- 3. Introduction Personal computers are powerful tools that can process and manipulate large amounts of data quickly, but they do not allow users to share that data efficiently. Before networks, users needed either to print out documents or copy document files to a disk for others. Copying files onto floppy disks and giving them to others to copy onto their computers was sometimes referred to as the "sneakernet." 1. Computer Network and its Applications
- 4. Networks is a set of devices (nodes) connected by communication links to convey information from the point of origin to point of destination. A node can be a computer, printer, or any other device capable of sending and/or receiving data. 1.1 What is Network and Computer Network?
- 5. Cont’d... Computer Networking Old paradigm/Traditional: A single powerful computer serving all the needs of an organization Sneaker-net -- Method of sharing data by copying it to a disk and carrying it from computer to computer Needs Time, effort.
- 6. New Paradigm: A computer network is a collection of computers and devices connected together via connecting devices and transmission media A large number of autonomous computers that are internetworked in order to exchange information using some transmission media. The computers can be geographically located anywhere (no geographical barrier)
- 7. A network must be able to meet a certain number of criteria. The most important of these are performance, reliability, and security. Performance: Performance can be measured in transit time and response time. Transit time: amount of time required for a message to travel from one device to another. Response time: is the elapsed time between an inquiry and a response. Reliability: The time it takes a link to recover from a failure, and the network's robustness in a catastrophe. Security: Network security issues include: i) Protecting data from unauthorized access, & from damage and ii) Development, and implementing policies and procedures. E.g, FW, ACL, VPN,… Network Criteria
- 8. To share information using the network i. E-mail ii. FTP etc… To Share Resources i. Printer ii. Scanner on LAN Flexible Working Environment i. Work on remote offices from home ii. Video Conferencing
- 9. A) Geographical span/Area coverage (Size) : i. Personal Area Network iii. Metropolitan Area Network ii. Local Area Network iv. Wide Area Network B) Network architecture or way of file sharing: iii. Peer to Peer Network iv. Client Server Based Network C) The connection: v. Point to point connection vi. Multipoint connection Classification of Computer Network Computer network can be classified based on:
- 10. A) Computer network based on GSA 1. Personal Area Network (PAN) A PAN, is smallest network which is very personal to a user. PAN has connectivity range up to 10 meters. This may include Bluetooth enabled devices or infra-red enabled devices. Example: wireless computer keyboard and mouse, Bluetooth enabled headphones, wireless printers and TV remotes.
- 11. 2. Local Area Network (LAN): LAN is a computer network spanned inside a building and operated under single administrative system. It covers an organization's, offices, schools, college/universities etc. In LAN, resources like Printers, File Servers, Scanners is easy sharable among computers. It uses cheap cable media like UTP. It is mostly used in bus, star and ring topology. Early LANs had data rates in the 4 to 16 megabits per second (Mbps) range. Today, however, speeds are normally 100 or 1000 Mbps. The first LANs were limited to a range (from a central point to the most distant computer) of 185 meters and no more than 30 computers.
- 12. Layer 2 devices like switches, bridges. Layer 1 devices like hub, repeaters are used
- 13. 3. Metropolitan Area Network (MAN) It covers large geographical areas than LAN such as cities, districts, Regions etc. Backbone of MAN is high-capacity and high-speed fiber optics. Metro Ethernet is a service which is provided by ISPs. This service enables its users to expand their Local Area Networks.
- 14. 4. Wide Area Network (WAN) A WAN covers a large geographic area such as across states, or countries. Uses fiber optic cables & satellite (wireless Technology), Telephone line etc.. Telecommunication and internet network are example of WAN. Layer 3 devices: routers, layer 3 switches are used
- 15. 1. Peer to Peer Network Each device can act both as client or as servers, where each device can request and provide services. There is no fixed division into clients and servers (all computers are equal). This can support up to 10 computers Security is not an issue. Example: Families sharing photos, movies etc. B) Computer network based on Architecture
- 16. Cont’d… Advantages: Less expensive. Server is costy, cost of conf. Easy to administer. B/c there is small number of devices Used for small business and home users (up to 10 computers). Disadvantages: Not very secure. Hard to back up.
- 17. 2. client Server Based Network There is a division between clients and servers. There will be a dedicated server which provide service to requests from network clients quickly and to ensure the security of files and directories. It is more complex to install, configure. Security is often the primary reason for choosing a server-based approach to networking.
- 18. Cont’d… Backups can be scheduled several times a day or once a week depending on the importance and value of the data. A server-based network can support thousands of users. Advantages: Very secure Better performance Centralized backups Disadvantages: Expensive administration.
- 19. Cont’d… i) Point-to-point ii) Multipoint. 1. Point to point A point-to-point connection provides a dedicated link between two devices. E.g, a connection between the remote control and TV. C) Computer network based on connection:
- 20. 2. Multipoint A multipoint connection is one in which more than two specific devices share a single link. In a multipoint environment, the capacity of the channel is shared If several devices can use the link simultaneously, it is a spatially shared connection. If users must take turns, it is a timeshared connection.
- 21. Computer Network Topologies The term topology refers to the way in which a network is laid out physically. A Network Topology is the arrangement with which network devices are connected to each other. Topology can be: i. Physical Topology ii. Logical Topology Physical Topology is the way computers are connected together physically. It is the physical look of the network.
- 22. Cont’d… There Four Physical Topology 1. Bus Topology: In bus topology all devices share single communication line or cable. One long cable acts as a backbone to link all the devices in a network Nodes are connected to the bus cable by drop lines and taps A drop line is a connection running between the device and the main cable. A tap is a connector that either splices (extend) into the main cable or punctures (small hole) that protect the cable from a contact with the metallic core.
- 23. Cont’d… Both ends of the shared channel have line terminator which is used to removes the data from the line. Advantage: Ease of installation and use less cabling than mesh and star topology. Disadvantage: Fault or break in the bus cable stops all transmission for the connected nodes, and it is difficult to reconnection and fault isolation.
- 24. 2. Star Topology In a star topology, each device has a dedicated point-to-point link only to a central controller, usually called a hub. The controller act as an exchange. Unlike a mesh, the devices are not directly linked to one another. Each device needs only one link and one I/O port to connect it to any number of others. The whole network topology depends on the central unit is hub. Star topology mostly used in LAN.
- 25. Cont’d… Advantages It is easy to install and reconfigure. Uses less cabling than mesh: less expensive than mesh topology. Robustness: If one link fails, only that link is affected. All other links remain active. Disadvantages Use more cable than bus and ring topology. If the hub fail the whole system is fail.
- 26. 3. Ring Topology Each device has a point-to-point connection with only the two devices on either side of it. Each device in the ring incorporates a repeater. When a device receives a signal intended for another device, its repeater regenerates the bits and passes. Advantage: Easy to install and reconfigure. Disadvantage Failure of any host results in failure of the whole ring.
- 27. 4. Mesh Topology In mesh topology, every device has a point-to-point link/connection to every other device. Each device is connected to n-1 devices. For n devices, n(n-1)/2 link is needed Every device on the network must have n – 1 input/output ports to be connected to the other n - 1 stations. Advantage: Point-to-point links make fault identification and fault isolation easy. Disadvantage: It require much amount of cable (expensive), Difficult to install and reconfigure.
- 28. 2. Logical Topology Logical topology is concerned with the movement of data i.e. how the data moves from one computer to another. a) Ring Logical Topology Ring logical topology functions by passing data from one node to next. The data follows in a ring rotates over the ring. b) Bus Logical Topology The sending node broadcasts the data to the entire network. The data is sent to common line to where every node is connected. c) Star Logical Topology The movement of data is through central device
- 29. i. Servers - computers that provide shared resources for network users. ii. Clients - computers that access shared resources provided by servers. iii. Media - the wires that make the physical connections. iv. Shared data - files provided to clients by servers across the network. v. Shared peripherals - additional hardware resources provided by servers. Computer Network Components
- 30. 08/15/2025 30 • T H E E N D Data Communication and Computer Networks By Prepared By Dawit M.