Communication and Networking
3.1
Introduction
COMPUTER
NETWORK:
A system in which two or more computer is
interconnected with each other is called Computer Network. The main purpose of
computer networking is to share resources such as files, printers, scanners etc
within a networks domain.
The
connection method between two computers can be wired such as twisted pair,
co-axial cable, optical fiber or wireless such as microwave, satellite,
Bluetooth etc.
Advantages of computer Network
i.
Cheap due to resource share
ii.
Fast and real time communication
iii.
Access to more resource through
internet.
iv.
Long distance communication/remote
connection.
v.
Increase storage capacity.
Disadvantages of computer network
i.
Security issue
ii.
Computer virus
iii.
High installation cost.
iv.
Dependency server can lead to network
failure.
3.2
Analog and digital signal:
Signal
is
the electromagnetic representation of data.
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Analog
Signal
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Digital
signal
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1. The
analog signal is continuously varying electromagnetic waves called sine wave.
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1. The
digital signal is a sequence of discrete voltage pulses and called square
waves.
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2. Diagram
time
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2. Diagram
time
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3. It
is suitable for long distance communication through bounded media.
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3. It
is not suitable for long distance communication through bound media.
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4. Demodulator
converts analog signal into digital signal.
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4. Modulator
converts digital signal into analog signal.
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3.3
Direction of Communication Flow:
a)
Simplex:
In a simplex mode the communication
is unidirectional as on one way street. Only one of the two devices on a link
can transmit, other can only receive. The simplex mode can use the entire
capacity on the channel to send data in one directional. Eg: Radio, Keyboard
etc.
b)
Half
duplex:
In this mode each station can
transmit and receive but not at the same time. When one device is sending the
other can only receive and vice-versa. The half duplex mode is like a one lane
road with traffic allowed in both direction. In this mode the entire capacity
of a channel is taken over by whichever of the two devices is transmitting at a
time. The half duplex mode is used in cases where there is no need of
communication in both directions at the same time. Example: Walkie-talkie
c)
Full
Duplex:
In this mode can transmit and
receive data simultaneously. The full duplex mode is like two way street with
traffic flowing in both direction at the same time. In full duplex signals
going in one direction share the capacity of link with signals going in the
other direction. This sharing can occur in two ways either the link must
contain two physically separate transmission path. One for sending and another
for receiving or the capacity of channel are divided between signals travelling
in both directions. An example of full duplex communication is telephone
network, mobile network etc.
3.4
Types of Network/Network Architecture
·
The theoretical concept behind the
design of a computer network is called network architecture. In computer
network two or more computers are linked together with a medium and data
communication devices for the purpose of communicating data and sharing
resources.
·
The computer that provides resources to
other computers on a network is called server.
·
In the network the individual computers,
which access shared network resources are known as workstations or nodes.
3.4.1 Network Based on servers:
Based on how the
computers in a network are configured and how they access information network
are classified into two types: peer to peer and client-server.
a)
Peer to Peer network:
- The technique of data
transmission from node to fashion in which each node behaves like as server or
host temporarily is called peer to peer architecture.
- There is no client or
good and powerful server.
- In the peer network
the network users simply share disk space and other resources.
b) Client server architecture:
- The network in which
the all workstations or nodes are connected with main server.
- The data sent by any
computer, at first reaches to server, and then passed to each workstation.
- The server behaves
like as distribution station.
- All the clients are
busy at the time distribution by server.
- The star topology is
the suitable example of client server architecture.
3.4.2 Network Based on Geographical
Area:
According to it the network is of 3 types.
1)
Local Area Network (LAN):
- LAN refers to a combination of computer hardware
and transmission media that is relatively small.
- LAN is typically comprised of only one
transmission media type such as coaxial cable or twisted pair cable but never
both.
- Examples of LAN: Two computers connected together
in an office or two building connected together by a high speed wire etc.
- LAN is characterized by comparatively high only
one kind of cable, which generally is limited to 5 KM or less.
2)
Metropolitan Area Network (MAN):
- MAN is a network that
is larger than a LAN.
- It is called
metropolitan since it normally covers the area of city (a few tens to about 100
KM).
- Different hardware
and transmission media are often used in MAN because they don’t require
complete access to location between the network sites.
- The main important
characteristic of MAN is their diversity (range).
- Two most important
components of MANs are security and standardization is necessary to ensure
reliable data communication.
3) Wide Area Network (WAN):
- A WAN includes all
networks larger than a MAN.
- WANs are
characterized by the slowest data communication rates and the largest distance.
- The connections in
WANs are done by the device called global WANs.
- An enterprise WAN
connects an entire organization, including all LANs at various sites.
- Global WANs also span
the world, but they don’t have to connect LANs within a single organization.
Internet is an example of global WAN.
- Private WANs
(Internet) are also available.
3.5
LAN Topology
- A network topology is the arrangement of
computers, cables and other components on a network. There are 5 basic
topologies:
a)
Bus Topology
- Cable or bus is
terminated at either end.
- Data is transmitted
to all network adapters through that cable.
Advantages:
-
It is simple, reliable, easy to use and
easy to understand.
-
The bus requires the least amount of
cable to connect the nodes; therefore, it is less expensive.
-
It is easy to extend a bus.
Disadvantages:
-
Heavy network traffic can slow a bus
considerably.
-
It is difficult to trouble shoot a bus.
-
Each BNC barrel connector weakens the
electrical signal.
b)
Ring Topology:
-
Each
computer is connected to the next computer with the last one connected to the
first.
-
It provides equal access for all
computers on the network.
-
A ring network usually needs more
cabling then a bus network.
Advantages:
-
Every computer is given equal access.
Disadvantages:
-
Failure of one computer on the ring can
affect the entire network.
-
Difficult to trouble shoot.
-
More cable is needed.
c)
Star Topology:
-
The
computers are connected by a device called hub in a central located computer.
-
Stars are used in concentrated networks.
Advantages:
-
It is easy to modify and add new
computers to a star network without disturbing the rest of the network.
-
The center the star is a good place to
diagnose network problems.
-
Single computer failures don’t necessarily
bring down the whole star network.
Disadvantages:
-
If the central hub failure, the whole
network stops.
-
It cost more to cable in star topology.
d)
Mesh Topology
- The node is linked to each other through
intermediate nodes with redundant paths.
- The Internet is an example of a large mesh
topology.
Advantages:
-
Fault tolerance.
-
Communication channel is guaranteed.
-
Easy to troubleshoot.
Disadvantages:
-
Difficult to install and reconfigure.
-
Cost of maintaining redundant lines.
e)
Tree Topology:
- Each device is connected to it own port or hub
just like a star topology.
Advantages:
- easy to extend.
- Easy to add new nodes.
- Allows the network to isolate and prioritize
communication from different computers.
Disadvantage:
-
If the main root or hub fails to operate
then the entire networks fail to operate.
3.6
Transmission Media:
A
path for a data communication between source and destination is called
Transmission Media. It is of two types:
a)
Guided Transmission Media
b)
Unguided Transmission Media
a) Guided Transmission Media:
The
electromagnetic waves or electrical signals are guided along the physical path.
For examples: C0-axaial cable, twisted pair cable, optical fiber etc.
For
guided transmission the bandwidth depends on distance and medium.
Mainly
three guided media are used.
1.
Twisted pair cable
2.
Co-axial Cable
3.
Optical Fiber
1. Twisted Pair Cable:
Physical
description:
-
It consists of two conductors (insulated
Cu-wire) twisted together spirally.
-
One of the wire is used to carry signal
whereas the other wire is used as ground or reference.
-
Generally twisted length 5 to 15 cm.
Thickness/diameter=0.4 to 0.9 cm.
Application:
1. Telephone
Network
2. Communication
within building
There
are two types of twisted pair cable and these are:
i) Unshielded Twisted Pair (UTP)
-
It provides reduced interference.
-
It provides better work performance.
-
The metallic shield is grounded at both ends.
ii) Shielded Twisted Pair (STP)
-
Used for cheaper network.
-
Used for small distance transmission.
-
Subjected to noise and electromagnetic signals interference.
2.
Co-axial Cable:
-
Co-axial cable is made of two conductors that share a common axis.
-
The center of the cable is copper wire encased in insulating plastic form.
-
The foam is surrounded by the second conductor.
-
They are used in communication network.
-
Each co-axial cable can provide more than 5000 links.
-
There are two types of co-axial cable. They are: thin net and thick net.
3. Optical Fiber:
-
Optical fiber cable is made of glass materials. The cable works on the
principle of total internal reflection.
-
There are three parts in an fiber. The inner part is called core. The core is
surrounded by cladding and cladding by jacket.
Some advantages of optical fiber:
-It
has a much greater bandwidth than metal cables.
-It
is much thin and light.
-Data
can be transmitted digitally.
-But
the cables are expensive.
b) Unguided Transmission Media:
It
provides a means for transmitting electromagnetic waves but don’t guide them.
For example: Propagation through air, satellite, wireless media, microwave etc.
In
this case, bandwidth signals is more important than medium itself.
1. Satellite:
-
A communication satellite is a microwave relay station, linking two or more
ground based on microwave transmitter or receiver known as earth station or
ground station.
-
Satellite receives transmission on one frequency band (uplink), amplifies or
repeats the signals and transmits it on another frequency called downlinks.
2. Wireless Media:
-Wireless
media are used when it is impossible to install cables.
Many
wireless devices that access the WAP (Wireless Application Protocol) Example:
Bluetooth, microwave, artificial satellite etc.
3. Microwaves:
-
Microwaves are radio waves that provide high speed signal transmission.
-A
microwave station is an earth-based reflective dish that contains the antenna,
transceivers and other equipment necessary for microwave communications.
-Current
users of microwave transmission include cable TV providers, telephone
companies, Hospital etc.
3.7 Networking connecting device
1. Modem (Modulation-Demodulation)
-
Modem is a device that allows a computer to transmit information over a
telephone line.
-
Modem translates between the digital signals the computer uses and analog
signals that the telephone uses.
-
The modem modulates the digital data onto a carrier signal on the telephone
line while transmitting.
-
When receiving, the modem demodulates the carrier signal to digital data.
-
The maximum bit rate of PSTN (Public Switched Telephone Network). Example: FAX
(Facsimile).
2. NIC (Network Interface Card)
-It
is also called network adaptor.
-
It is a circuit board or card that is installed in computer so that it can be
connected to a network.
-PC
will contain the NIC such as Ethernet.
-Network
interface card provides a dedicated, full-time connection to a network.
3. Switch
-A
bridge is a device that passes data packets between multiple network segments
that use the communications protocol.
-Switches
are similar to bridge but often a more direct network connection between the
source and destination computers.
4. Hubs
-Hubs
are connectively devices that connect computers in a star topology.
-Hubs
contain multiple ports for connecting to network components.
-Use
of hub has become very common networking as its cost is lower and easier to
install.
5. Router
-A
router is a device that acts like a bridge or switch but provides more
functionality.
-Routes
enable all users in a network to share a single connection to the internet or a
WAN.
6. Gate Way
-
A Gate Way is a device that enables communication between different network
architecture.
-
A Gate Way takes the data from one network and repackages it , so that each
network can understand the other network’s data.
-
A Gate Way is like an interpreter.
7. Repeater
-
A repeater is a physical layer device used to interconnect the media segments
of an expanded network.
-
A repeater receives signals and retransmits them at their original strength and
definition.
8. Bluetooth
-A
proposed radio frequency (RF) specification that many portable devices will
uses for short-range wireless communication is called Bluetooth.
-
To use Bluetooth device must include a transceiver chip and be within a
specified range (about 10 meters).
-For
example: Laptops computers, Cellular Telephones etc
9. IR (Infrared)
-
Infrared is a type of electromagnetic wave of large wavelength and small
frequencies than visible lights.
-Routine
controls and IRDA (Infrared Data Association) uses infrared emitting nodes to
emit infrared radiation.
-
It is used in TV, Printers, and Wireless LAN etc.
10. Wi-Fi
-
Wi-Fi is a trademark of the Wi-Fi Alliance that manufactures may use to brand
certified products that belongs to a class of Wireless LAN devices.
-
A Wi-Fi enabled device such as a PC, Video-game Console, mobile Phone, MP3
Player can connect to the internet when within a range of a wireless network
connected to the internet.
3.8 OSI (Open System
Interconnection) Reference Model
-ISO
certified origination for standard model for a network communication, called
the OSI Reference Model in 1982 AD.
-The
OSI Model divides network communication into 7 layers.
-The
7 layers of OSI Reference Model can be divided into 2 categories. They are:
Upper Layer and Lower Layer
-
Upper Layers of the OSI Model deal with application issues and generally are
implemented only in software.
-
Lower Layer of the OSI Model handle data transport issue.
Layer
|
Protocols
|
Application Layer
|
FTP,
TFTP, Telnet, HTTP
|
Presentation Layer
|
SMTP,NFS
|
Session Layer
|
Telnet,
SNMP
|
Transport
Layer
|
TCP,UDP
|
Network Layer
|
IP
|
Data
Link Layer
|
ARP,RARP,RIP
|
Physical Layer
|
Ethernet,
Token Ring
|
Figure: 7 Layers of the OSI Reference Model
3.9
Communication Protocol
-
A set of rules which is used by computers to communicate with each other across
the network is called Protocol.
-
Protocol specifies the format of message and the rules for exchanging the
message.
Some
of the popular protocols are defined below:
a)
TCP/IP
-
The main task of IP is the best effort
delivery of the packets.
-
The function of TCP is the reliable,
ordered delivery of stream of stream of bytes from a program on one computer to
another computer.
b)
SMTP
( Simple Mail Transfer Protocol)
-
It is an application layer protocol for
sending email using underlying TCP transport layer protocol in TCP/IP network.
-
STMP is a complete text based protocol.
-
STMP is extended to send other types of
information such as text, picture, videos and other multimedia, program and
data files using an internet standard called (Multimedia Internet Mail
Extension).
c)
POP
(Post Office Protocol)
-
It is an application layer protocol to
receive the email from a remote mail server using TCP as a transport layer of
serves.
d)
FTP
(File Transfer Protocol)
-
It is an application layer protocol to
exchange files between computers on a TCP/IP network.
-
FTP uses the TCP of the transport layer
to transfer the files.
-
FTP is reliable and secure file transfer
protocol.
e)
HTTP
(Hyper Text Transfer Protocol)
-
HTTP is one of the popular application
layer protocols which specify the rules for interlinks documents called
Hypertext Documents.
-
The hypertext documents are placed in
special host computer called server and a server, usually called internet
browser.
f)
Telnet
(Terminal Network)
-
It is an application layer protocol that
provides interactive text based interference to access the command shell of the
remote computer through virtual terminal connection.
-
Telnet protocol uses the transport layer
facilities through the TCP protocol.
UNIT - 3 [HOMEWORK QUESTIONS]
1.
What is networking? List out the
advantages and disadvantages of Networking?
2.
Explain any two transmission media with
appropriate diagrams.
3.
Describe the types of Network
Topologies with their clear diagrams.
4.
Define computer Network. Explain in
about LAN and WAN.
5.
Write short notes on:
a)
Coaxial cable b) satellite
6.
What are the types of LAN topology?
Explain with diagram.
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