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1. UNIT 4
Basics of Data Communication
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2. COMMUNICATION:
 refers to the transfer of data from a transmitter (sender or source)
to a receiver across a distance.
 It has the following basic element:
 Sender - a device to send data/ information.
 Channel - a communication over which data/ information is sent.
 Receiver - a device to receive the sent data/ information.
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3. The data transfer can be
 sound,
 image
 videos,
 text or
 a combination of all multimedia
SENDER RECEIVER
CHANNEL
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4. TYPES OF DATA TRANSMITTER SIGNALS
 Data transmitter by two types of signals.
 Analog signals &
 Digital signals.
 Analog signals (continuous wave)
 is a continuous electrical signal in the form of wave.
 The wave is called carrier wave.
 The older forms of communication technology were design to
work with an analog signal.
 Sound is an example of analog signal.
 Two characteristics of analog carrier waves are frequency and
amplitude. 4

5. …
 Frequency: - is the number of times a wave repeats during a
specific time
 Amplitude: - is the height of a wave with in a given period of
time.
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6. DIGITAL SIGNALS:
 are discrete/discontinuous on & off electrical signal.
 Example a digital watch
 Digital signals are better that is faster, more accurate,
easier to reduce & cleanup noise & errors.
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7. DATA FLOW MODES
 When two machines or computer is in communication, data can
flow 3 these modes.
 These are:
 Simplex transmission
 Half-duplex transmission
 Full-duplex transmission
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8. SIMPLEX TRANSMISSION
 Data can travel in only one direction.
 The transmitting line has a transmitter on one end and a
receiver on the other end.
 It is like a one way street.
 Example:- a radio & television broadcasting.
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9. HALF-DUPLEX TRANSMISSION
 Data travels in both directions but only one way at a time.
 Device A acting as transmitter and device B acting as a receiver.
 Then A&B simultaneously switch roles and B sends and A
receives.
 Example is a talk-back radio.
A
B
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10. FULL-DUPLEX TRANSMISSION
 Data is transmitted back and forth at the same time.
 It is equivalent to two simplex lines one in each
direction.
 Example:- telephone networks
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11. DATA TRANSMISSION WAYS
 Data Transmission refers to the amount of data transmitted
across a channel with in a specific period of time.
 Data transmitted in two ways:
 Serially and
 In Parallel.
 Serial data transmission- bits are transmitted sequentially, one
after another.
 It use two methods for transmitting data
Asynchronous transmission &
synchronous transmission
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12. ASYNCHRONOUS TRANSMISSION
 Asynchronous transmission:- data is sent one byte (one
character) at a time.
 Each string of bits making up the byte is bracketed or marked
off with special control bit called “start” and “stop” .
 And sometimes this type of mode is called start-stop
transmission.
 This method, used with most microcomputer.
 Synchronous transmission:- sends data in blocks.
 Start & stop bit patterns are transmitted at the beginning and
end of the blocks. 12

13. PARALLEL DATA TRANSMISSION
 Bits are transmitted simultaneously.
 Parallel line send more information than serial lines do, but
they are efficient up to 3 meters.
 Example data transmit from computer CPU to printer.
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14. COMPUTER NETWORKS
 Network:- is a system of interconnected computers, telephones,
or other communication devices that can communicate with one
another and share resources.
 Resources can include hardware, software & shared data.
 Computer Network: - refers to the system of two or more
interconnected computers to share data, device, peripherals and
remote computer databases.
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15. ADVANTAGES OF NETWORKING
 Sharing information
 Sharing Hardware Resources
 Sharing Software Resources
 Communication
 Protecting Information
 Can all access the same data…
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16. THE DISADVANTAGES NETWORKING
 Cost of set-up (network cards, cables, connectors)
 Danger of hacking
 Maintenance & supervision cost
 If network breaks down it can cause many problems
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17. TYPES OF COMPUTER NETWORKING
 Depending on their geographical coverage networks generally
categorized in to the following type:
 Local Area Networks (LAN): is a private owned network
 The range is usually with in one office, one building, or a college
campus.
 Metropolitan Area Network (MAN): covering a size of city or sub
city.
 Wide Area Network (WAN): covering a size of a state or a
country.
 WANs are a collection of LANs.
 The largest WAN is the internet.
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18. NETWORK RESOURCE ACCESS MODEL
 There are two main ways to operate a network .
 Peer-to peer networks
 The main features of peer-to peer networks:
 All the computers on the network are considered equal (peers).
 All computers are able to share each others resources
 They are only suitable for small networks with less users.
 All the users need to have some basic knowledge of networks in
order to use them.
 As more users are added to the network, the whole network slows
down considerable. 18

19. CLIENT-SERVER NETWORKS
 The main features of client-server networks:
 There is one computer, called the server, which is usually
(but not always) more powerful than the rest
 It is used to store all the data and programs needed by the
network.
 The server controls the network.
 More popular choice of large organizations.
 They are simple to run.
 The network is totally dependent on the server.
 If the server breaks down, then the network can’t function.19

20. COMPUTER NETWORK TOPOLOGIES
 The topology:- It shows the geometric arrangement of
computers in a network.
 Topologies can be physical and logical.
 The physical topology describes what the overall configuration
look like where every node on the network likes physically.
 The logical topology describes how information travels along
the network.
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21. MAJOR TYPES TOPOLOGIES
 Bus topology
 Star topology
 Ring topology
 Tree topology
 Hybrid topology
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22. BUS TOPOLOGY
 Some times called a line topology
 All the terminals are connected to a single cable, which is
often called the backbone.
 Signals are normally passed in either direction along the
backbone.
 At each end of the cable these are terminators.
 A collision might occur when a number of terminals
transmit their messages simultaneously.
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23. ADVANTAGE & DISADVANTAGE
 Advantage
 Easy to implement
 Uses a small amount of Cable
 Disadvantage
 Limits on cable length & number of computers
 Difficult to find network faults
 A fault on the backbone stops whole network
 As the number of computers increase, the speed of the
network slows down. 23

24. STAR TOPOLOGY
 All the devices on the network are connected to a
central node called a hub.
 A hub is a device that provides a meeting location for
all the cables.
 The network does not stop work if one node is down
in the network.
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25. ADVANTAGE & DISADVANTAGE
 Advantage
 Easy to add new device (Workstation)
 Centralized control
 Failure of a computer doesn’t affect the network
 disadvantage
 require greater amount of cabling and a hub, so these is a
higher cost
 Hub failure downs all devices(Workstations) connected to
that hub is stop working. 25

26. RING TOPOLOGY
 The entire terminal is connected in a circle.
 Data passes around the network in one direction.
 These are no collision in a ring topology.
 It stops dead if one terminal is removed from the network.
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27. ADVANTAGE & DISADVANTAGE
 Advantage
 Simple design, require less Cable than bus or star
 Data can sent over large distances (as computer act
repeaters)
 Disadvantage
 the more terminals, the slower the network becomes.
 data security may be compromised
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28. TREE TOPOLOGY
 A tree topology can be thought of as being a “star of stars”
network.
 Each device is connected to its own central terminal of host in
the same manner as in a star topology.
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29. MESH TOPOLOGY
 Each device is connected to every other device on
the network.
 It very expensive to install & maintain.
 The advantage you get from it is high fault tolerance.
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30. HYBRID TOPOLOGY
 A hybrid topology is the mix of the other topologies.
 This topology might be very expensive.
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