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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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