by Gulshan K Maheshwari(QAU)

1. Computer Networks
BY:
GULSHAN KUMAR MAHESHWARI
QAU_ISLAMABAD

2. What is data transmission
 Data transmission is the process of sending digital or
analog data over a communication medium to one or
more computing, network, communication or
electronic devices.

3. Forms of data transmission
 Analog Data Transmission:
 Analog signal is a continuous electrical signal in the form of
wave. wave is known as carrier wave.
 Telephone is most commonly used media for analog
transmission.
 Light sound, radio and microwave are also examples of
analog signals.

4.  Digital signal is a sequence of voltage represented in binary form. Data
transmit in the form of pulses ON and OFF
 It provides high transmission.
 on speed,

5. Comparison
Analog
 Analog signal transmitted
without regard to content
 May be analog or digital data
 Attenuated over distance
 Use amplifiers to boost signal
 Also amplifies noise
Digital
 Concerned with content
 Integrity endangered by
noise, attenuation etc.
 Repeaters used
 Repeater receives signal
 Extracts bit pattern
 Retransmits
 Attenuation is overcome
 Noise is not amplified

6. Types of data transmission
Asynchronous
 Transmission of data is generally
without the use of an external clock
signal, where data can be transmitted
intermittently rather than in a steady
stream.
 Any timing required to recover data
from the communication symbols is
encoded within the symbols.
 The most significant aspect is that data
is not transmitted at regular intervals,
thus making possible variable bit rate.
 And that the transmitter and receiver
clock generators do not have to be
exactly synchronized all the time.
Synchronous
 In Synchronous the transmission of
data is sent in a continuous stream
at a constant rate.
 Synchronous communication
requires that the clocks in the
transmitting and receiving devices
are synchronized running at the
same rate.
 so the receiver can sample the
signal at the same time intervals
used by the transmitter. No start or
stop bits are required.
 For this reason synchronous
communication permits more
information to be passed over a
circuit per unit time

7. What is network
 Computer network is defined as the interconnection of two or more
computers. It is done to enable the computers to communicate and share
available resources.
 APPLICATIONS:
 Sharing of resources such as printers
 Sharing of expensive software's and database
 Communication from one computer to another computer
 Exchange of data and information among users via network
 Sharing of information over geographically wide areas.

8. Communication Links
 Used to build a network
 Vary in physical characteristics, error rate and transmission speed
 In early days, data transmitted through switched, dial-up telephone
lines. The term ‘switched, dial-up’ means that when you dial a telephone
number, a circuit is temporarily between the caller and callee. This circuit
last for the duration of the call and when you hang up is terminated.

9. Computer networks
A computer network is a set of computer systems connected by
telecommunication links for the purpose of sharing information and resources.
 A node can be a computer or some other device, such as a printer. Every node has
a unique network address, sometimes called a Data Link Control (DLC) address or
Media Access Control (MAC) address.
 A network host is a computer or other device connected to a computer network.
A network host may offer information resources, services, and applications to
users or other nodes on the network. A network host is a network node that is
assigned a network address.
 In networking terminology, the computers that are connected to a computer
network are sometimes referred to as end systems. They are labeled end systems
because they sit at the edge of the network. The end user always interacts with the
end systems. End systems are the devices that provide information or services.

10. Advantages of Computer
Networks
 SHARING RESOURCES
 Types of resources are:
 Hardware: A network allows users to share many hardware devices such as
printers , modems, fax machines, CD ROM, players, etc.
 Software: sharing software resources reduces the cost of software installation,
saves space on hard disk.
 OTHER BENEFITS OF COMPUTER NETWORK
 Increased speed o Reduced cost
 Improved security
 Centralized software managements
 Electronic mail
 Flexible access

11. Disadvantages of Computer Networks
 High cost of installation
 Requires time for administration
 Failure of server
 Cable faults

12. Communication devices/ Network
devices
 Communication devices: used to carry message from one place to
another.
 1: Modem: modem stand for modulator / demodulator.
 It is commonly used communication device. Sending and receiving
computers both must have modems.
 Modulation: digital analog
 when modem receive data from computer in digital form and converts
into analog, this process is called modulation.
 Demodulation: Analog Digital
 when modem receive data from computer in analog form and converts
into digital, this process is called demodulation.

13. Communication devices
 Types of Modem
 External : Attached to the system unit as an external device through
telephone line. It requires external Power supply. move from one
computer to another easily.
 Internal: It is a circuit board that is inserted on the motherboard.
Cannot be moved from one computer to another easily.
 Wireless: it transmit the data through Air instead of cables. It also
known as Radio frequency modem.
 Satellite: it send and receive data using satellite technology.

14. Communication devices
(cOnt.)
 2: Hub: Hub provides a central point for cables in a network. It share all
messages to every connected computer but only the intended recipient
computer takes the message.it is also called Concentrator or multi access
unit.
3: Switch/ Bridge: it is more intelligent than hub. It sends messages only to
the intended computer. Each network segment connected to switch must
have same type of devices.

15. Communication devices
(cOnt.)
4: Router: it is more intelligent because it use algorithms to find out the
best path to transfer. It connects multiple computers or other routers
together. It connects multiple networks using similar or different
protocols. They can connect networks of different countries.
4: Gateways: it can connect two or more networks with different types of
protocols. It is also intelligent because converts data according to the
protocol.

16. Communication channels/ Transmission Media:
1. Physical transmission Media: it is also called BOUNDED MEDIA.
Communication devices directly connected with each other by using some
physical media.
i. Twisted pair: Twisted pair cables are quite literally a pair of insulated wires
that are twisted together to help
reduce noise from outside sources.
ii. Coaxial cable:
Coaxial cables are high-frequency transmission cables made up of a single
solid-copper core.
This type of cable is commonly used to deliver
TV signals (its higher bandwidth makes
it more suitable for video applications) and
to connect computers in a network.

17. Communication channels/
Transmission Media:
iii. Fiber Optic: Fiber is the newest form of transmission cable
technology. Instead of transferring data over copper wires, these
cables contain optical fibers that transmit data via light, rather than
pulses of electricity.
Each optical fiber is individually coated with plastic layers and
contained in a protective tube, making it extremely resistant to
external interference.

18. Communication channels/ Transmission
Media:
2: Wireless transmission Media: it is also called UNBOUNDED MEDIA.
Communication devices directly connected through air or space using broadcast
signals like radio signals, microwave signals and infrared.
i: Microwave transmission refers to the technology of transmitting information or
energy by the use of radio waves whose wavelengths are conveniently measured in
small numbers of centimeter; these are called microwaves.
Electromagnetic waves having frequencies between 1 and 300 GHz are called micro
waves. Micro waves are unidirectional.
 ii: Radio Waves: Electromagnetic waves ranging in frequencies between 3 KHz
and 1 GHz are normally called radio waves.
 Radio waves are omnidirectional. When an antenna transmits radio waves, they
are propagated in all directions.

19. Network Topologies
 Topology:
 The physical layout or arrangement of connected devices in
a network is called topology.
 Types: there are five types
1. Bus
2. Ring
3. Star
4. Tree
5. Mesh

20. BUS TOPOLOGY
 All computers and devices connected to central
cable or bus.
 Consists of a main run of cable with a terminator at
each end.
 Popular on LANs because they are inexpensive and
easy to install.
 It only support small no of computers.
 If one node fail doesn't effect the rest of network

21. RING TOPOLOGY
 Cable forms closed ring or loop, with all
computers and devices arranged along ring.
 Data travels from device to device around entire
ring, in one direction.
 Primarily is used for LANs, but also is used in
WANs
 Every computer has equal access.
 If one node fail it effects the network

22. STAR TOPOLOGY
 All devices connect to a central device, called hub.
 All data transferred from one computer to another passes through hub.
 If central hub is fail, the entire network break down .
 If one node fail doesn't effect the rest of network
 It requires large length of cables

23. Tree
TOPOLOGY
 It has a root node and all other nodes are connected to it forming a
hierarchy. It is also called hierarchical topology.
 Used in Wide Area Network
 Extension of bus and star topologies
 Expansion of nodes is possible and easy
 Easily managed and maintained
 Error detection is easily done
 Costly
 If more nodes are added maintenance is difficult
 Central hub fails, network fails

24. Mesh
TOPOLOGY
 It is a point-to-point connection to other nodes or devices. All the
network nodes are connected to each other.
 Fully connected
 Not flexible
 Installation and configuration is difficult
 Bulk wiring is required
 Cabling cost is more
 It is robust
 Provides security and privacy

25. Types of Computer Networks
LAN (connects hardware devices such as
computers, printers, and storage devices that
are all in close proximity.)
WAN (connects devices that are not in close
proximity but rather are across town, across the
country, or across the ocean.)
MAN (Connect devices that are across town,
across the country, or across the ocean)

26. Local Area Networks
 Local area network (LAN)
 Connects hardware devices that are in close proximity
 The owner of the devices is also the owner of the
means of communications
 Common wired LAN topologies
Bus
Ring
Star
26

27. Local Area Networks (continued)
 Ethernet
 Most widely used LAN technology
 Uses the bus topology
 Two ways to construct an Ethernet LAN
 Shared cable
 Hubs: The most widely used technology
27

28. Typical Structure of a Wide Area Network
28

29. ETHERNET LAN IMPLEMENTED USING
SHARED CABLES
29

30. AN ETHERNET LAN IMPLEMENTED USING A HUB
30

31. Local Area Networks (cont..)
 Client server: A computer network in which one centralized,
powerful computer (called the server) is a hub to which many less
powerful personal computers or workstations (called clients) are
connected. The clients run programs and access data that are stored
on the server.
 Client server LAN is a network in which one or more computer works
as servers other as client.
31

32. Local Area Networks (cont..)
 Peer to Peer: A network of personal computers, each
of which acts as both client and sever, so that each can
exchange files and email directly with every other
computer on the network.
 Peer to peer LAN is simple and inexpensicomputers.ve.
It normally connect less than ten
32

33. Wide Area Networks
 Wide area networks (WANs)
 A wide area network (WAN) is a telecommunications network or
computer network that extends over a large geographical distance.
 Connect devices that are across town, across the country, or across the
ocean
 Users must purchase telecommunications services from an external
provider
 Dedicated point-to-point lines
 Most use a store-and-forward, packet-switched technology to deliver
messages
33

34. MAN (metropolitan area network)
 A metropolitan area network (MAN) is a computer network that interconnects users with
computer resources in a geographic area or region larger than that covered by even a large
local area network (LAN) but smaller than the area covered by a wide area network (WAN)