1.
2.
3.
4.
5.
Sharing of peripheral devices : printers,scanners etc can
be connected in a n/w.
Sharing of programs and data : less expensive to work
with a same software by many employees
Better communications : email
Security of information : files can be backed up or
duplicated on a device ,shared by others.
Access to database : users can enter in to many public or
privately owned databases.
1.
2.
If there comes a problem it ‘ll affect the entire network.
Efficiency is depend upon the system manager.
Distribution of s/w with its source code, its original
instructions.
We can make improvements.
Eg: linux, GNU
Controlled by FSF (Free s/w Foundation)
Network of n/w s
Communication passible through : TCP/IP
Transmission Control Protocol/Internet Protocol
Client Server architecture
Activities on the internet ?????
BSNL,MTNL,almost all the communication providers are
ISP’s.
It is a client server s/w that permits multiple users to
communicate online with real time audio,video and text chat
in dynamic 3D environment.
Reference to switching techniques
Three useful methods to establish communication link
between a sender and a receiver.
They are
1. Circuit switching
2. Message switching
3. Packet switching
A dedicated physical path is established between source and
destination.
Used in telephone conversation
Once this connection is established we can send messages .
Three phases : circuit establishment , data transfer and circuit
disconnection
1.
2.
3.
4.
Simple and require no special facilities
Suitable for long continuous transmission
Once connection is established data is transmitted with no
delay
Full capacity of circuit is available for the users.
1.
2.
3.
Before data transfer , time required to establish a
circuit
It is fully dedicated to the connected path, affect the
n/w
Uneconomical for computers
Message : logical unit of information and can be of any length.
First append the destination address to the message.
We have tow methods
1. Store and forward : source to intermediate node ,inspect
for errors , transmitted to other node which is available and
finally reach the destination.
Path taken by the node is dynamic.
2. Broadcast method: message is broadcast over a common
medium known as broadcast channel.
All nodes cheek the dest address attached to it .finally reach the
dest.
This method require that all nodes are connected to the n/w
simultaneously.
Advantages :
1. Unlike circuit switching , no physical connection required
b/n src and dest
2. Uses the channels effectively because channels are used only
when messages are transmitted.
Disadvantages
1. Each node must have sufficient storage to buffer messages.
2. In store and forward time delay will be there
3. Too slow for interactive real time applications
It routes message data on packet basis.
Message is divided into fixed sized packets. Each packet is
transmitted independently ,either store and forward or
broadcast.
All packets are re-assembled into original message at
destination node.
Packet : contains src & dest addr,ctrl info,mesg no,ackno and
error checking bytes etc.
Advantages :
1. Unlike messages, packets are of small and fixed size, storage
req is minimal
2. Routing is done on packet basis transmission is very fast
3. Suitable for computers , used in internet
Disadvantages :
1. Reassembling is needed
2. Time taken can’t be predicted
Communication is the process of transferring messages from one
point to another.
We have three modes of data transfer
1. Simplex : unidirectional flow of data
2. Half duplex : one direction transmission at a time with
acknowledgement
3. Full duplex : simultaneous transmission in both direction
Channel :
path which helps in data transmission
Baud :
number of signal changes per second.
1 baud = 1 signal change per sec = 1 bit per sec
Bandwidth :
is the range or band or frequencies that a
transmission medium can carry in a given period of time.
Expressed in hertz (Hz) or cycles per sec
The amount of data transferred per second.
It is measured in bps(bits per second)
It carries signals over a communication path.
Two ways
1. Wired (telephone wire)
2. Wireless
Wired communication
1.
2.
3.
Twisted-pair wire
Coaxial cable
Fiber-optic cable
The telephone line.
It consists of two strands of insulated copper wire , twisted
around each other.
It is relatively slow. Does not protect well against electrical
interference.
Advantages :
1. It is simple
2. Physically flexible
3. Low weight
4. Inexpensive
Disadvantages:
1.
2.
Repeaters are needed for long transmission
Unsuitable for broadband, as it has low bandwidth
frequencies
Cable network (cable tv).
It consists of insulated copper wire wrapped in a solid metal
shield and then in an external plastic cover.
Better than twisted as it resist noise.
Faster transmission is possible.
Advantages :
1. Data transmission is far better than twisted pair
2. Used in cable n/w
3. Can be used for broadband transmission
Disadvantages :
1.
2.
Expensive as compared to the previous
Not compatible with twisted pair
Consists of hundreds of thin strands of glass or plastic that
transmit pulsating beams of light rather than electricity.
Not affected by random electromagnetic interference in the
environment.
Advantages :
1. Much lower error rate
2. Lighter and more durable
3. Transmission is more secure
4. Used for broadband transmission
Disadvantages :
1.
2.
3.
Installation problem
Expensive
Connection losses are common
1.
2.
3.
4.
Infrared transmission
Broadcast radio
Microwave radio
Communication satellites
Sends data using IR waves at a low frequency
Advantages :
1. Used by TV remote control units
2. Very secure
Disadvantages :
1. Unobstructed view must be there in b/n sender and
receiver
2. Confined to short range
Tuning FM station
Requires a transmitter and a receiver (transceiver)
Advantages :
1.
2.
3.
Provides mobility
Cheaper than …
Ease of communication
Disadvantages :
1. Insecure
2. Affected by weather
Super high frequency radio waves
Used in satellite communication system
Advantages :
1. Cheaper than …
2. Communicate over oceans
Disadvantages :
1. Insecure
2. Strength may be reduced
3. Affected by weather
4. High cost of design ,imple ,maintenance
These are microwave relay stations in orbit around the earth.
Ground to satellite : up linking
Satellite to ground : down linking
Satellites occupy one of three zones
1. GEO : Geostationary Earth Orbit : high orbit
2. MEO : Medium Earth Orbit : 5000-10000 miles up
3. LEO : Low Earth Orbit : 200-1000 miles up
Advantages :
1.
2.
3.
Covers a large area
Best for global coverage
Commercially attractive
Disadvantages :
1.
2.
Technological limitations
High investment cost
1.
Modem (modemo)
Converts digital data in to analog and vice-versa for
transmission.
Modem modulates outgoing digital signals to analog signal
for twisted pair and demodulates the incoming analog signal
and converts it to a digital signal.
ISDN :Integrated Services Digital Network.
DSL : Digital Subscriber Line
Registered Jack-45 : Standard type of connector for n/w
cables.
Eight pins : For various configuration
RJ -11 :Used in telephone cables
One kind of n/w adapter.
Supports for high speed network connections via cables.
Also known as Network Interface Card (NIC)
Device that joins multiple computers together within one Local
Area Network(LAN)
It uses layer2 (Data link Layer ) of OSI model
Switch is generally more intelligent than hub.
Capable of inspecting data packets , determining the source
and destination of each packet and forward it.
Offers better performance than hub.
Hardware that acts as a bridge between two n/w s so that data
can be transferred b/n number of computers.
It is a n/w point that acts as an entrance to another n/w.
Associated with router and switch ???
Eg is a LAN connected to internet or other wide area n/w.
Topology:
The logical layout or shape of a n/w is called a topology
We have
1. Bus topology
2. Ring topology
3. Star topology
4. Tree topology
Like a bus system. (Bus & road)
All communication devices are connected to a common
channel(road).
All nodes are connected to a single wire , the bus which has
two end points.
Info can be passed to another device through this bus
Advantages :
1. Organized as client server or peer to peer n/w
2. Simple and needs short cable length than ring
3. Simple to install , older technology
4. Easy to expand
Disadvantages :
1.
2.
3.
4.
Extra s/w needed to avoid collision
If a connection is broken , entire n/w may stop working
Slow
Complex protocols are used
All communication devices are connected in a continuous loop
There are no end points
Messages are passed around the ring until they reach the
destination
Advantages
1.
2.
3.
4.
5.
Shorter cable length is needed as compared to star
Each node is connected to other by using a single connection
Messages flow in one direction , no scope for collision
Fast and efficient
Suitable to set up high speed n/w
Disadvantages :
1.
2.
3.
If one system stop working entire n/w may stop
Difficult to diagnose the fault
Difficult to add remove or reconfigure new node
All computers and other communication devices are directly
connected to a central server.
Messages are routed through the central hub to their
destinations
Hub monitors the traffic
Advantages :
1.
2.
3.
4.
5.
6.
Easy to install, hub prevents collision
It needs one connection per node
Easy management of n/w
Easy to detect faults
Uses simple communication protocols
Most popular used for LANs
Disadvantages :
1.
2.
3.
Needs large quantity of cable
Hub offers limited number of connection
Working of n/w depends upon working of hub
Suitable for n/w having hierarchical flow of data.
Means data travels level by level
Advantages :
1.
2.
3.
4.
5.
Can share devices like printer
Workstations do not need their own hard disk or CD ROM
drives
Save their work centrally on the n/w file server
Communicate with each other
One copy of application packages are needed.
Disadvantages :
1.
2.
3.
Special security measures are needed to prevent
unauthorized access
Need to be maintained by a skilled technician
If server develops error all users are affected.
Spans a large physical distance.
Internet is the largest WAN spanning the earth
Collection of LANs
Router connects LANs to WAN
Not owned by one organization
Used in ATMs
Covers the area larger than LAN but smaller than WAN
Interconnection of n/w s in a city
1.
TCP/IP
Topology:
The logical layout or shape of a n/w is called a topology
We have
1. Bus topology
2. Ring topology
3. Star topology
4. Tree topology
Like a bus system. (Bus & road)
All communication devices are connected to a common
channel(road).
All nodes are connected to a single wire , the bus which has
two end points.
Info can be passed to another device through this bus
Advantages :
1. Organized as client server or peer to peer n/w
2. Simple and needs short cable length than ring
3. Simple to install , older technology
4. Easy to expand
Disadvantages :
1.
2.
3.
4.
Extra s/w needed to avoid collision
If a connection is broken , entire n/w may stop working
Slow
Complex protocols are used
All communication devices are connected in a continuous loop
There are no end points
Messages are passed around the ring until they reach the
destination
Advantages
1.
2.
3.
4.
5.
Shorter cable length is needed as compared to star
Each node is connected to other by using a single connection
Messages flow in one direction , no scope for collision
Fast and efficient
Suitable to set up high speed n/w
Disadvantages :
1.
2.
3.
If one system stop working entire n/w may stop
Difficult to diagnose the fault
Difficult to add remove or reconfigure new node
All computers and other communication devices are directly
connected to a central server.
Messages are routed through the central hub to their
destinations
Hub monitors the traffic
Advantages :
1.
2.
3.
4.
5.
6.
Easy to install, hub prevents collision
It needs one connection per node
Easy management of n/w
Easy to detect faults
Uses simple communication protocols
Most popular used for LANs
Disadvantages :
1.
2.
3.
Needs large quantity of cable
Hub offers limited number of connection
Working of n/w depends upon working of hub
Suitable for n/w having hierarchical flow of data.
Means data travels level by level
Advantages :
1.
2.
3.
4.
5.
Can share devices like printer
Workstations do not need their own hard disk or CD ROM
drives
Save their work centrally on the n/w file server
Communicate with each other
One copy of application packages are needed.
Disadvantages :
1.
2.
3.
Special security measures are needed to prevent
unauthorized access
Need to be maintained by a skilled technician
If server develops error all users are affected.
Spans a large physical distance.
Internet is the largest WAN spanning the earth
Collection of LANs
Router connects LANs to WAN
Not owned by one organization
Used in ATMs
Covers the area larger than LAN but smaller than WAN
Interconnection of n/w s in a city
Allows to transfer files between two computers on the internet.
Simple n/w protocol based on internet protocol
To transfer files using FTP we use a program called the client
Client initiates a connection to a remote computer running FTP
server.
After the establishment of the connection-send files
Client require username and password
It supports two modes : plain data and binary data
Communication b/n two computers using a serial interface, ie
PC connected by phone line to server.
ISP provide you with a PPP connection., so that provider’s
server can respond to request and pass it to internet.
Uses IP , member of TCP/IP
Full duplex protocol, can be used on TP, FO, satellites
Transmitting voice, video and data in local or wide areas.
Signals through air and space using radio waves.
Frequency band is allocated for transmission.
Higher the frequency higher the band width and data carrying
capacity.
Data rates ? Devices ?? Mobile ???






Digital mobile telephone system
Uses Time Division Multiple Access (TDMA)
Most widely used of TDMA, GSM and CDMA (wireless
telephone technologies)
GSM digitalizes and compresses data
Operates b/n 900 to 1800 MHz frequency band.
Global access

Digital cellular technology that uses spread spectrum
technique

Unlike GSM it does not assign a specific frequency to users

Better capacity for voice and data communication
Common platform on which 3G are built





Non voice value added service that allows mobile for
sending and receiving data over an IP
Wireless access to data n/w like internet
Run internet applications using mobile phones
It supports
◦ IP
◦ PPP
◦ X.25 connections
Communication system that connects subscribers to the Public
Switched Telephone Network (PSTN) using radio frequency
signals
When underground cable n/w is not available but radio
coverage is available.

1G :
First generation wireless analog technology
standard used in mobile

2G :
TDMA

3G :
Fast data transmission speed , greater n/w capacity
and more advanced n/w services like global roaming
It uses digital protocols such as GSM,CDMA and
◦ Internet, mobile TV, video calls MMS are possible
Exchange of computer stored messages.
Usually encoded in ASCII text.
Uses TCP/IP
Protocol for sending email
:
SMTP
Protocol for receiving email
:
POP3
Advantages : Speed , reliable,paperless,cheaper , user friendly.
Disadvantages : emotionless , misuse …
1.
SMTP (Simple Mail Transfer Protocol)
Used to send mail.
Used by the Mail Transfer Agent (MTA) to deliver the email
Post Office Protoco3.
Standardized way for users to access mail boxes and download
messages to their computers
Video conferencing :
H.320
Voice over Internet Protocol
Phone calls over broadband connection.
Based on digital n/w
Wireless Fidelity
Used to connect machines in a LAN
Technically known as 802.11 protocol
Variations : 802.11a, 802.11b………
Worldwide Interoperability for Microwave Access
Called Broadband Wireless Access.
Intended for wireless MAN’s
Viruses :
s/w programs that are designed to spread from one
computer to another and to interfere with computer operation.
1.
Corrupt or delete data
2. Worms :
Like virus, designed to copy itself from one
computer to another automatically.
Replicate to a great volume.
3. Trojan horse :
Virus that affects the security and cause damage
4. Spams :
Many copies of the same message.
Antivirus s/w:
Program attempt to identify , neutralize or eliminate malicious
s/w
Cookies :
Little pieces of data such as login name, password and
preferences left on hard disk by some websites
It acts as a barrier between internet and your computer
and blocks threats including viruses
It provides legal recognition for transactions carried out
by means of electronic data interchange.
Cyber law : describes the legal issues related to use of
communication technology
Cyber crimes ?????
IPR issue : related to patents , copyright , trademark etc
Unauthorized use of computer and n/w resources.
Practice of modifying computer h/w and s/w to accomplish a
goal , can lead to constructive development
Crackers
:
hackers who steal information , change or
break security codes , to gain unauthorized access to n/w or
computer.
Destructive in nature
HTML (HyperText Markup Language)
Computer language for web creation.
Easy to learn, powerful , directed by
W3C :World Wide Web Consortium
HyperText : special text called hyperlinks
Markup
:
HTML tags
Language for documents containing structured information
Designed to carry data not to display data
Tags are not predefined
W3C recommendation
Hyper Text Transfer Protocol
Used to transfer files on the web.
Uses TCP/IP
Word sequences users enter in the address bar.
DNS : Domain Name System
Eg:
edu :
com :
educational institution
commercial organization
Uniform Resource Locator :
Global address of documents and other resources
Unique number which is assigned to the computer when
connect to internet.
External IP address :
Internal IP address :
user side
ISP
Related collection of WWW files.
s/w application which enables a user to display and
interact with data located on a web page at a web site on
WWW.
Computer that delivers web pages
Web hosting :
internet.
process of posting web pages to the
1. Client side scripting :
computer programs that are executed client side.
Eg: JavaScript, VB script
Run at the server
Eg : ASP,PHP,JSP
Associated with interactive info sharing ,inter oparability,user
centered design.
Social n/w sites,video sharing sites , blogs etc…
OSS (open Source S/w) : computer s/w for which source
code Is available under a copy right license.
Permits to change and improve the s/w and to redistribute it .
Open source definition :
free distribution,source code,derived works,distribution
of license etc
s/w that is available for use at no cost or for an optional fee.
Fully functional for unlimited time for no cost.
s/w that is copyrighted but can be distributed free of
charge .
Will have a trial period
Restrictions on use, private modification, copying or
republishing.
FLOSS
FOSS:
:
Free Libre Open Source S/w
Free Open Source S/w
Eg : apache , Firefox, open office etc.
Free S/W Foundation
OSI
:
Open Source Initiative
Process of combining two or more sorted arrays into
another array which is also sorted.
We have two techniques
Concatenate two arrays and then sort using any sorting
algorithm
Merge sort : Sorting while merging. Using this efficiency
increases
A , B be two arrays of size M and N respectively having
elements in ascending order. We merge these two to C
of size M+N ,ascending order. I ,J, K and R denotes
array indices.
I =1 ,J = 1, K = 1
2.
Repeat while (( I <= M & (J <= N))
{
If (A [I]<= B [J]) Then
{
C [K] = A [I]
I =I+1
}
else
{
C [K] = B [J]
J =J+1
}
K =K+1
}
3. If (I > M)
Then
{
Repeat for R = J ,J+1,…….,N
C[K]=B[R]
K=K+1
else
{
Repeat for R = I,I+1,….,M
{
C [K]= A [R]
K=K+1
}
4. End
1.
{
}
}
}
Here we Starts….