COMPUTER LECTURES

Home Introduction Hardware Software Database Management Networking Web Development Programming Computer Terms

NETWORKING

A network is a group of computers and devices interconnected by communications channels that facilitate communications among users and allows users to share resources.
OR
A network is a group of computers and other devices (such as printers, servers) that are connected by some type of transmission media, usually wireless or wired with the purpose of sharing resources and information.
OR
A network is a group of computers that conneted together in a way that allows information to be exhanged between the computers .

    Why do we need networking?
  1. Facilitating communications: Using a network, people can communicate efficiently and easily via email, instant messaging, chat rooms, telephone, video telephone calls, and video conferencing.
  2. Sharing hardware: In a networked environment, each computer on a network may access and use hardware resources on the network, such as printing a document on a shared network printer.
  3. Sharing files, data, and information: In a network environment, authorized user may access data and information stored on other computers on the network.
  4. Sharing software: Users connected to a network may run application programs on remote computers.
  5. Information preservation.
  6. Security.

    Advantages of using a computer network
  1. Connectivity and Communication:
    Networks connect computers and the users of those computers. Once connected, it is possible for network users to communicate with each other using technologies such as electronic mail. This makes the transmission of business (or non-business) information easier, more efficient and less expensive than it would be without the network.
  2. Data Sharing:
    One of the most important uses of networking is to allow the sharing of data. Before networking was common, an accounting employee who wanted to prepare a report for her manager would have to produce it on his PC, put it on a floppy disk, and then walk it over to the manager, who would transfer the data to her PC's hard disk.
  3. Hardware Sharing:
    Networks facilitate the sharing of hardware devices. For example, instead of giving each of 10 employees in a department an expensive color printer, one printer can be placed on the network for everyone to share.
  4. Internet Access:
    The Internet is itself an enormous network, so whenever you access the Internet, you are using a network. The significance of the Internet on modern society is hard to exaggerate, especially for those of us in technical fields.
  5. Internet Access Sharing:
    Small computer networks allow multiple users to share a single Internet connection. Special hardware devices allow the bandwidth of the connection to be easily allocated to various individuals as they need it, and permit an organization to purchase one high-speed connection instead of many slower ones
  6. Data Security and Management:
    In a business environment, a network allows the administrators to much better manage the company's critical data on a centralized shared servers. This makes it easy for everyone to find the data, makes it possible for the administrators to ensure that the data is regularly backed up, and also allows for the implementation of security measures to control who can read or change various pieces of critical information.
  7. Entertainment:
    Networks facilitate many types of games and entertainment. The Internet itself offers many sources of entertainment, of course. In addition, many multi-player games exist that operate over a local area network. Many home networks are set up for this reason, and gaming across wide area networks (including the Internet) has also become quite popular.
  8. Performance Enhancement and Balancing:
    Under some circumstances, a network can be used to enhance the overall performance of some applications by distributing the computation tasks to various computers on the network.

    Disadvantages of using a computer network
  1. Sever fault stop application being available
  2. Network faults can cause lose of data
  3. Network faults could lead to lose of resources
  4. User work depend upon network
  5. System open to hackers
  6. Decision tend to become centralized
  7. Could degrade in performances

NETWORK TPYES
Network can be classified into following types :-
  1. Local-area networks (LAN)
  2. Wide Area Network (WAN)
  3. Metropolitan Area Network (MAN)
  4. Storage Area Network

  1. Local-area network (LAN)
    It connects many computers in a relatively small geographical area such as a home, an office, a building, or a campus
    The general shape or layout of a LAN is called its topology.
    All LANs require the networked computers to share the communications channel that connects them.

  2. Wide Area Network (WAN)
    A WAN is usually segmented into multiple LANs that make up a WAN.
    These lines are called point-to-point because they connect only two devices, one on each side of the line.
    They are called serial lines because the bits of information are transmitted one after another in a series.
    Connections across WAN lines may be temporary or permanent and WANs normally operate at lower speeds than LANs.

  3. Metropolitan Area Network (MAN)
    A network spanning a physical area larger than a LAN but smaller than a WAN, such as a city. A MAN is typically owned an operated by a single entity such as a government body or large corporation.

  4. Storage Area Network

NETWORK TOPOLOGY
Computer networks may be classified according to the network topology upon which the network is based. A network topology defines the layout of the network.
Topology shows how devices on the network are interconnected.
Network topology is the layout pattern of interconnections of the various elements (links, nodes, etc.) of a computer network. Devices on the network are termed nodes.
    Network topologies may be either : -
  1. physical topology
  2. logical topology

  1. Physical topology
    Physical topology means the physical design of a network including the devices, location and cable installation.
    Physical topology shows the physical topology of a network, which refers to the actual physical layout of the devices and media.
  2. Logical topology
    Logical topology refers to how data is actually transferred in a network as opposed to its physical design.
    Logical topology refers to the paths (data) that signals travel from one point on the network to another.
    These two terminologies can be confusing, because the word "logical" in this instance has nothing to do with the way the network appears to be functioning.

    Common network topologies are :-
  1. Bus network
  2. Star network
  3. Ring network
  4. Mesh network
  5. Hybrid topology

  1. Bus Topology
    A bus network topology is a network architecture in which a set of clients are connected via a shared communications line, called a bus. It is also called the backbone.
    Commonly referred to as a linear bus, all the devices on a bus topology are connected by one single cable, which proceeds from one computer to the next. This topology is rarely used and would only be suitable for a home office or small business with only a few hosts.
    1. Advantages of a bus topology
    2. Easy to implement and extend.
    3. Easy to install.
    4. Well-suited for temporary or small networks not requiring high speeds (quick setup), resulting in faster networks.
    5. Cheaper than other topologies.
    6. Cost effective; only a single cable is used.
    7. Easy identification of cable faults.
    8. Reduced weight due to fewer wires.
    9. The thin net cabling it uses is quite inexpensive.
    10. It uses less cable compared to other physical topologies like star or extended star
    11. It works well for small networks
    12. It does not need a central device, such as a hub, switch, or router

      Disadvantages of a bus topology
    1. Limited cable length and number of stations.
    2. If there is a problem with the cable, the entire network breaks down.
    3. Maintenance costs may be higher in the long run.
    4. Performance degrades as additional computers are added or on heavy traffic (shared bandwidth).
    5. Proper termination is required (loop must be in closed path).
    6. Significant Capacitive Load (each bus transaction must be able to stretch to most distant link).
    7. It works best with limited number of nodes.
    8. Slower data transfer rate than other topologies.
    9. Only one packet can remain on the bus during one clock pulse.
    10. It results in slower access to the network and less bandwidth due to the sharing of the same cable by all devices
    11. It is challenging to identify and isolate problems
    12. A break at any point in the bus cable can disable the entire bus network
    13. It needs terminators

  2. Star Topology
    The star topology is the most commonly used architecture in Ethernet LANs and resembles spokes in a bicycle wheel.
    A star topology generally costs more to implement than the bus topology because more cable is used and a central device is needed, such as a hub, switch, or router.
    In a star topology, each network host is connected to a central hub.
    In contrast to the bus topology, the star topology connects each node to the hub with a point-to-point connection.
    All traffic that traverses the network passes through the central hub. The hub acts as a signal booster or repeater.
    The star topology is considered the easiest topology to design and implement.
    Data on a star network passes through the hub, switch, or concentrator before continuing to its destination.
    1. Advantages of a Star Topology
    2. It is upgradeable, flexible, and reliable
    3. It is easy to design and install
      This topology makes diagnosing problems relatively easy since the problem is localized to one computer or device
    4. This topology allows for more throughput than any other topology

      Disadvantages of a Star Topology
    1. It requires a lot of cable to connect computers since a cable is required between each device and the central location.
    2. It is more expensive to build because of the additional cost of cables and devices like hubs and switches that are needed to run between the central device and each computer

  3. Ring Topology
    A ring topology is a network topology in which each node connects to exactly two other nodes, forming a single continuous pathway for signals through each node - a ring. Data travels from node to node, with each node along the way handling every packet.
    Each machine or computer has a unique address that is used for identification purposes.
    The signal passes through each machine or computer connected to the ring in one direction.
    Ring topologies typically utilize a token passing scheme, used to control access to the network. By utilizing this scheme, only one machine can transmit on the network at a time.
    The machines or computers connected to the ring act as signal boosters or repeaters which strengthen the signals that traverse the network.

      Advantages of a Ring Topology
    1. Very orderly network where every device has access to the token and the opportunity to transmit
    2. Performs better than a bus topology under heavy network load
    3. Does not require network server to manage the connectivity between the computers

      Disadvantages of a Ring Topology
    1. One malfunctioning workstation or bad port in the Multi-station Access Unit (MAU) can create problems for the entire network
    2. Moves, adds and changes of devices can affect the network
    3. Network adapter cards and MAU's are much more expensive than Ethernet cards and hubs
    4. Much slower than an Ethernet network under normal load

  4. Mesh Topology
    The mesh topology connects all devices (nodes) to each other for redundancy and fault tolerance.
    It is used in wide-area networks (WANs) to interconnect LANs and for critical networks.
    1. Advantages of a Mesh topology
    2. Provides redundant paths between devices
    3. The network can be expanded without disruption to current users.
    4. Mesh networks are self-healing: the network can still operate when one node breaks down or a connection goes bad.
    5. The network may typically be very reliable, as there is often more than one path between a source and a destination in the network.

      Disadvantages of a Mesh Topology
    1. Requires more cable than the other LAN topologies.
    2. Complicated implementation.
    3. The cabling costs associated with the mesh topology can be high
    4. Troubleshooting a failed cable can be tricky.
    5. The mesh topology is expensive and difficult to implement.

  5. Hybrid Topology
    The hybrid topology combines more than one type of topology.
    When a bus line joins two hubs of different topologies, the configuration is called a star bus.
    The bus line is used to transfer the data between the star topologies.