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COMPUTER NETWORK A computer network is an interconnection of various computer systems located at different places Two or more computers are linked together with a ... – PowerPoint PPT presentation

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  • A computer network is an interconnection of
    various computer systems located at different
  • Two or more computers are linked together with a
    medium and data communication devices for the
    purpose of communicating data and sharing
  • The computer that provides resources to other
    computers on a network is known as server.
  • Individual computers in the network, which access
    shared network resources, are known as nodes.

Local Area Network (LAN)
  • Networks used to interconnect computers in a
    single room, rooms within a building or buildings
    on one site are called Local Area Network (LAN).
  • LAN transmits data with a speed of several
    megabits per second
  • The transmission medium is normally coaxial
  • LAN links computers, in the same area for the
    purpose of sharing information.
  • Usually LAN links computers within a limited
    geographical area because they must be connected
    by a cable, which is quite expensive.
  • People working in LAN get more capabilities in
    data processing, work processing and other
    information exchange compared to stand-alone

Characteristics of LAN
  • every computer has the potential to communicate
    with any other computers of the network
  • high degree of connection between computers
  • easy physical connection of computers in a
  • inexpensive medium of data transmission
  • high data transmission rate

Use of LAN
  1. File transfers and Access
  2. Word and text processing
  3. Electronic message handling
  4. Remote database access
  5. Personal computing
  6. Digital voice transmission and storage

Wide Area Network
  • The term Wide Area Network (WAN) is used to
    describe a computer network spanning a regional,
    national or global area.
  • For example, for a large company the head
    quarters might be at Cairo and regional branches
    at Mansoura, Tanta , and Aswan.
  • the transmission medium used are normally
    telephone lines, microwaves and satellite links

The characteristics of WAN
  • Communication Facility For a big company
    spanning over the country the employees can save
    long distance phone calls and it overcomes the
    time lag in overseas communications.
  • Computer conferencing is another use of WAN where
    users communicate with each other through their
    computer system.

  • Remote Data Entry is possible in WAN. It means
    sitting at any location you can enter data,
    update data and query other information of any
    computer attached to the WAN
  • Centralized Information This means if the
    organization is spread over many cities, they
    keep their important business data in a single
    place. WAN permits collection of this data from
    different sites and save at a single site
  • Ethernet Ethernet developed by Xerox Corporation
    is a famous example of WAN

Difference between LAN and WAN
  1. LAN is restricted to limited geographical area of
    few kilometers. But WAN covers great distance and
    operate nationwide or even worldwide.
  2. In LAN, the computer terminals and peripheral
    devices are connected with wires and coaxial
    cables. In WAN there is no physical connection.
    Communication is done through telephone lines and
    satellite links.
  3. Cost of data transmission in LAN is less because
    the transmission medium is owned by a single
    organization. In case of WAN the cost of data
    transmission is very high because the
    transmission medium used are hired, either
    telephone lines or satellite links.
  4. The speed of data transmission is much higher in
    LAN than in WAN. Few data transmission errors
    occur in LAN compared to WAN.

  • In star topology a number of workstations are
    directly linked to a central node as the next
  • Any communication between stations on a star LAN
    must pass through the central node.
  • The central node controls all the activities of
    the nodes.
  • The advantages of the star topology are
  • It offers flexibility of adding or deleting of
    workstations from the network.
  • Breakdown of one station does not affect entire
  • The major disadvantage of star topology is that
    failure of the central node disables
    communication throughout the whole network

Star topolgy
Bus Topology
  • In bus topology all workstations are connected to
    a single communication line called bus.
  • There is no central node as in star topology.
  • Transmission from any station travels the length
    of the bus in both directions and can be received
    by all workstations.
  • The advantage of the bus topology is that
  • It is quite easy to set up.
  • If one station of the topology fails it does not
    affect the entire system.
  • The disadvantage of bus topology is that any
    break in the bus is difficult to identify.

Bus Topology
Ring Topology
  • In ring topology each station is attached nearby
    stations on a point to point basis so that the
    entire system is in the form of a ring.
  • In this topology data is transmitted in one
    direction only.
  • Thus the data packets circulate along the ring in
    either clockwise or anti-clockwise direction.
  • The advantage of this topology is that any
    signal transmitted on the network passes through
    all the LAN stations.
  • The disadvantage of ring network is that the
    breakdown of any one station on the ring can
    disable the entire system.

  • Ring Topology

  • The Internet is a network of networks
  • Computer users on the Internet can contact one
    another anywhere in the world
  • In Internet a huge resource of information is
    accessible to people across the world
  • Information in every field starting from
    education, science, health, medicine, history,
    and geography to business, news, etc. can be
    retrieved through Internet
  • You can also download programs and software
    packages from anywhere in the world

Origin of Internet
  • In 1969 Department of Defense (DOD) of USA
    started a network called ARPANET (Advanced
    Research Projects Administration Network )
  • Around 1970, NSFNET (National Science Foundation
    Network) was created. With the advancement of
    modern communication facilities,
  • By 1990 many computers were looking up to NSFNET
    giving birth to Internet

Internet functions
  • Internet is not a governmental organization.
  • The ultimate authority of the Internet is the
    Internet Society.
  • This is a voluntary membership organization whose
    purpose is to promote global information
  • Internet has more than one million computers
    attached to it.

  • E-mail stands for electronic mail.
  • This is one of the most widely used features of
  • In electronic mail the data are transmitted
    through Internet and therefore within minutes the
    message reaches the destination may it be
    anywhere in the world.
  • Therefore the mailing system is excessively fast
    and is being used widely for mail transfer

Features of E-mail
  • One-to-one or one-to-many communications
  • Instant communications
  • Physical presence of recipient is not required
  • Most inexpensive mail service, 24-hours a day and
    seven days a week
  • Encourages informal communication

Components of an E-mail Address
  • As in the case of normal mail system, e-mail is
    also based upon the concept of a recipient
  • The email address provides all of the information
    required to get a message to the recipient from
    anywhere in the world. Consider the e-mail ID

  • In the example above, "john" is the local part,
    which is the name of a mailbox on the destination
    computer, where finally the mail will be
  • Hotmail is the mail server where the mailbox
    "john" exists,
  • .com is the type of organization on net
  • .edu     Educational institutions
  • .gov     Government site

File Transfer Protocol (FTP)
  • File Transfer Protocol, is an Internet utility
    software used to upload and download files.
  • It gives access to directories or folders on
    remote computers and allows software, data and
    text files to be transferred between different
    kinds of computers.
  • FTP works on the basis of same principle as that
    of Client/Server.

  • FTP "Client" is a program running on the your
    computer that enables you to talk to, and get
    stuff from, remote computers.
  • The FTP client takes FTP commands and sends them
    as requests for information from the remote
    computer or known as FTP servers.
  • To access remote FTP server it is required but
    not necessary to have an account in the FTP
  • When the FTP client gets connected

The objectives of FTP
  • The basic objectives of FTP are
  • to give flexibility and promote sharing of
    computer programs, files and data
  • to transfer data reliably and more efficiently
    over network
  • to encourage implicit or indirect use of remote
    computers using Internet
  • to shield a user from variations in file storage
    systems among hosts

Telnet (Remote Computing)
  • Telnet or remote computing is telecommunication
    utility software, which uses available
    telecommunication facility and allows you to
    become a user on a remote computer.
  • Once you gain access to the remote computer, you
    can use it for the intended purpose.
  • The TELNET works in a very step by step
    procedure. The commands typed on the client
    computer are sent to the local Internet Service
    Provider (ISP), and then from the ISP to the
    remote computer that you have gained access.
  • Most of the ISP provides facility to TELNET into
    your own account from another city and check your
    e-mail while you are traveling or away.

  • WWW is the short form for the World Wide Web. It
    is also commonly known as The Web.
  • The WWW is hypertext based information retrieval
  • One can easily surf the Web by jumping from one
    document to another using the links in those
  • These documents can be in many formats, such as
    text, graphics, animation, sound and latest is
    video. They may also be a combination of all
  • All the information on Internet are presented to
    the user as a document or more popularly known as
    Web Page.
  • All these Web Pages are link to each other or
    even to section within a Web Page. And these
    links are known as Hyper Links.

The Web browser
  • The tool used to view these Web Pages on Internet
    is known as Internet browser or simply browser.
  • It is a software program specifically developed
    to extract information on user request from the
    Internet and present them as a Web Page to the
  • The most popular are Internet Explorer from
    Microsoft and Netscape from Netscape Inc