Computer networking class 12

 Computer network : An interconnected
collection of autonomous computers and other
devices that are connected in various ways in
order to communicate and share resources.
Usually, the connections between computers in a
network are made using physical wires or cables
However, some connections are wireless, using radio
waves or infrared signals.
Autonomous computers means , independent computers,
no computer on the network can control another.
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 Network Goals
1. Resource Sharing: to make data and peripherals
available to anyone irrespective of location of
resources and the user.
2. Reliability: If any file is unavailable due to system
failure or hardware crash, making copies of a file
help us to work smoother.
3. Cost factor: Aim to have one PC per user , with data
shared on one shared file server.
4.Communication medium: helps the officers working
far apart to prepare reports . The changes at end
can be noticed immediately at the other and hence
speeds up the communication.

 Applications of Network
1.Sharing :
 Peripherals
 Data & Information
 Control or Access(Distributed control)
2. Access to remote database
3. Communication Facilities

1.Nodes(Workstations)
 Computes that are attached to the network
 A computer becomes a workstation or a node as
soon as it is attached to a network.
2. Server
 All shareable stuff(like data, software) is
stored in the server.
 A network can have more than one server
 All users of the network identify the users by
the server by the unique name.

Server
Non-
dedicated
server
Dedicated
server

Non-dedicated server(For small networks)
 Not completely dedicated to the cause of
serving.
 Recourse sharing in among workstations on
smaller scale
 One computer works as a workstation a swell
as a server, it is slower and require more
memory.
 The networks using such a sever are called
PEER-TO-PEER networks.
Dedicated Servers (For Bigger networks)
 There is a computer reserved for server's job
and its only job is to help workstations access
data, software and hardware resources.
 MASTER-SLAVE networks

3. Network Interface Unit(NIU)
A stand alone computer can carry out its tasks
with its own Resources. But as soon as it
becomes a workstation, its need an interface
to establish a connection with the network,
because without this , workstations will not
be able to share resources.
• NIC is a device that is attached to each
workstation and the server.
 Each NIC attached to the workstation has a
unique number to identify , which is known
as node address.
 Different manufacturers have different names
for NIC : TAP(Terminal Access Point) ,
NIC(Network Interface Card)

 NIC manufacturers assigns a unique physical address
to each NIC card, which is known as MAC (Media
Access Control)
 It’s a 6 –byte address with each byte separated by a
colon.
Manufacturer id
 Eg: 10: b5:03: 63: 2E: FC
card number
 So MAC address is the number assigned to the
network card of your computer
 The first three bytes are manufacturer id(assigned to
the manufacturer by an IEEE)
 The last three bytes are card number(assigned by the
manufacturer)

IP Address
 All computers in a network follow some set of rules for communicating with
one another, these are of rules are called protocols.
 Most commonly used networking protocol is TCP/IP. Internet follows TCP/IP.
 A network that follows TCP/IP protocol is called TCP/IP network.
 Each network device needs to have a unique address on the network, called IP
address.
 IP address is a series containing four numbers separated by dots or periods.
 IP address is written decimal form, computers convert them into binary form.
Eg: 192.0.2.1 to 0001011100100001
 How a computer gets it,s IP address?
 Whenever a computer becomes a part of a network , it is assigned its IP
address.
Or
 When you get connected to your ISP,


Domain Name or URL
 Websites on internet also have unique IP
address.
 URL is the domain name of the web site.
www.amazon.com
A domain name has three main parts:
a. www
b. name describing the website's purpose
c. TLD(Top Level Domain) eg: .com, .net,.ca

 It is the process of finding corresponding IP
address from a domain name.
How does it work?
Step1 :Enter domain name in the browser
Step2: Browser sends a command to the OS to
provide IP address
Step3: OS finds IP address either by:
a) referring the HOSTS file(text file of
the main computer)
b) or by DNS server , which has the
directory of IP address

Network Topologies :
 The way in which computers are connected,
the structure, layout etc.
The factors to be considered while choosing the
topology are:
1) Cost : should be cost effective
2) Flexibility : topology should allow easy
configuration of the network
3) Reliability : to find the location of faults.

Point-to-Point Link
Transmit Receive
Transmit
Receive

 It has a central node to Which all other nodes
are connected by a single path.
Twisted pair cable is used
Eg: 10 Base-T Ethernet network
The leading number
(10 in 10BASE-T) refers to the transmission
speed in Mbit/s.
BASE denotes that baseband transmission is
used.
The T designates twisted pair cable, where the
pair of wires for each signal is twisted
together to reduce electromagnetic
interference and crosstalk between pairs.

 Advantages:
1. Ease of Access
2. One device per connection
3. Centralized control or problem diagnosis
4. Simple Access protocol
Disadvantages:
1. Long cable length
2. Difficult to expand
3. Central node dependency

•Data is transmitted in
small packets
•Each packet has some
data and destination
address
•The destination device
identifies the address
and receives the data.

Advantages
Short cable length
Resilient Architecture
Easy to extend
Disadvantages
Fault diagnosis is difficult
Fault isolation is difficult
Repeater configuration
Odes must be intelligent

 Each node is connected to two neighbouring
nodes
 Data travels one direction only

Advantages:
 Short cable length
 No extra wiring space required
 Suitable for optical fibres(very high speed
transmission)
Disadvantages:
 Node failure causes network failure
 Difficult to diagnose fault
 Network reconfiguration is difficult

 Central server is
branching and sub
branching.
 when the packets
reaches at the end of
medium, it is absorbed
by the terminator
 Suited for application
which have a
hierarchical flow
Terminator

 A link may or may not
connect two or more
nodes
 There may be multiple
links

MESH TOPOLOGY
 For long distance
 Communication is
possible between any
two nodes.
 Used in large
internetworking

 Each workstation is
connected to other
workstations.
 There is a link between
all workstations in a
network.

On the basis of the size of network,
complexity and geographical spread,
networks are classified as
1.LAN
2. MAN
3. WAN
4. PAN

• For small network(For local area)
• One computer is designed as File server
LAN
Wired/ Wireless LAN
Technologies used for wireless LAN
1. WiFi
2. Access Point- Device that connects wireless
devices together
3. Hotspot- Area covered by wireless access point

 A large computer network on the large
geographical area that include several
buildings or even the entire city .
 The geographical area of the MAN is larger
than LAN, but smaller than WAN.

 A Personal area network (PAN) is a
computer network that is used for data
transmission between different personal
devices (computers, telephones, digital
devices, etc.) and for connecting to the higher
level network and Internet.
 PAN can be wired or wireless
 Wired PAN can be established through USB
cables.
 Wireless PAN uses wireless technologies such
as Bluetooth or infrared technologies.

LAN WAN
1. Diameter is not more than a
kilometer
2. A total data rate of several
mbps
3. Complete ownership by a singe
organization
4. Very low error rates
Span entire country
Data rate less than 1 mbps
Owned by multiple organization
Comparatively higher error rates

 Internet stand for Interconnected Network
 WAN
 Internet access is provided through Internet
Service Computer, run by ISP
History
 An agency named ARPANET started a small
network in 1969 .
 In 1972 , development of FTP with 37
operating computers
 NCP/IP(Network Control Program)
 NCP/IP TCP/IP

 In1986, NSFNet(National Science Foundation
Network), backbone of internet.
 In1990,HTML, HTML, Web pages, Gateways
 In 1994, browsers Mosaic , Netscape
Navigator.

 WWW
 E-Mail
 Online Messaging
 Newsgroup(newsnet)
 Real-Time streaming
RSS(Really Simple Syndication)
http://rss.cnn.com/rss/edition.rss
http://rss.cnn.com/rss/edition_europe.rss
Telephony
 Internet Backup
 FTP
 Telnet

 Connecting cables or connecting media
 The cables that connects two or more
workstations.
Transmission Media
Guided media Un guided media
(wired technologies) (air, water etc)
Twisted pair, Coaxial, Microwave Radio
wave,
Optical fibers Satellite

1. Twisted Pair Cables
 Two identical wires wrapped together in
a double helix.
 Different categories of Twisted pair cable
exist, but the common features of all
cables are
1. Wires in come in pairs
2. Pairs of wires are twisted around each
other
Most commonly used twisted pair cable is
CAT5 or CAT5,it is also called Ethernet
Cable.
 Twisting of wires reduces crosstalk

Most commonly used cables used for point-to-
point connections.
Structure:
1. Many pairs of twisted wires in the center
2. Shield : To give protection against “Cross-talk”
3. PVC Jacket: To provide protection against wear
and tear.

Crosstalk is any phenomenon by
which a signal transmitted on one
circuit or channel of a transmission
system creates an undesired effect
in another circuit or channel.
Crosstalk is usually caused by
undesired capacitive, inductive, or
conductive coupling from one
circuit or channel to another.

Advantages
 Easy to install and
maintain
 Physically flexible
 Relatively inexpensive
 It has a low weight
Disadvantages
 “Repeaters” are needed
for transmission of
signal over long
distances.
 Low Bandwidth
capabilities
 Supports only data rate
of 1 Mbps to 10 Mbps.

The coaxial cables have high electrical
properties and is suitable for high-speed
communication
Structure:
1. Inner Core: Carries the signal
2. Insulator
3. Wire Mesh
4. Outer Shield: For protection and
grounding

Advantages
 Better Data
Transmission
characteristics
 Offer higher Bandwidth
 Several Channels can be
transmitted
simultaneously
Disadvantages
 More Expensive
 Not compatible with
Twisted Pair Cables

 Optical Fibers consists of glass like material
,which can carry light from a source at one end
of the fiber to a detector at other end.
 The light sources used are LEDs and LDs
The data to be transmitted is modulated into
light beam using FDM techniques. The signals
can be picked up at the receiving end and
demodulated.
The three parts of optical fibers are:
1. The core
2. The cladding
3. Protective coating

 These signals are used to transmit data
without the use of cables, used for
long distance communication
 Consists of transmitter, receiver and
atmosphere.

Radio waves are a wireless mode of
communication.
They operate on different
frequencies allocated to them by the
government, thus preventing overlap
of signals. They operate in a 10 mile
radius.

Radio Waves work by making use
of sine wave frequencies. They
have three hardware
components.:-
1.Transmitter
2.Receiver
3.Antennas
1

A continuous wave or continuous
waveform is an electromagnetic
wave of constant amplitude and
frequency. Information is carried
in the varying duration of the on
and off periods of the signal, for
example by Morse code in early
radio. In early wireless telegraphy
radio transmission, CW waves
were also known as "undamped
waves".

In electronics and telecommunications a transmitter
or radio transmitter is an electronic device which
produces radio waves with an antenna. The
transmitter itself generates a radio frequency
alternating current, which is applied to the antenna.
When excited by this alternating current, the antenna
radiates radio waves.

In radio communications, a radio receiver is an electronic
device that receives radio waves and converts the information
carried by them to a usable form. The antenna intercepts
radio waves and converts them to tiny alternating currents
which are applied to the receiver, and the receiver extracts
the desired information. The receiver uses electronic filters to
separate the desired radio frequency signal from all the other
signals.

An antenna is a device used for transmissions in AM
or FM frequencies, designed with the aim of
emitting and / or receiving electromagnetic waves
towards the free space. A transmitting antenna
transforms electrical energy into electromagnetic
waves, and a receiver performs the inverse function.

Advantages
1.It is
geographically
independent.
2.No cables are
required.
3.No land
acquisition
needed.
Disadvantages
1. It has no network
security.
2.Weather has adverse
effects on it.

Earlier data transfer used to be carried out with cables.
But as the demand for higher data rates, lower energy
consumption , better data security grew, the need to
exchange data in a wireless media also began to
take place. Using a wireless medium also means
there is no need for maintenance work.
 INFRARED DATA TRANSMISSION
 This uses infrared light to send data.
 Transfer speed is 2400 bps-4 mbps.
 The infrared light transmits data through air
 It is a secure transmission
 Use in everyday life- TV remotes, automotive garage
doors,etc.
 It supports max. 2 devices.
 Distance for transmission is 10-30 metres.
 It is developed for point-to-point transmission.
 The main application is short range and one-to-one
data exchange.

Some disadvantages of infrared data
transmission are:
 It can be used for short distance
applications only.
 Devices can not move around while
transmission is in process.
 It requires both – transmitter and
receiver in line of sight.

LASER DATA TRANSMISSION :
 Requires direct line of line
 Unidirectional
 Much higher speed.

3. Bluetooth technology :
 It is a wireless technology standard for
exchanging data over short distances
and building PAN’s.
 Typically max. range is 10 metres.
 It requires low cost transceiver chip in
each device (i.e pre-built)
 Useful for transferring data between two
or more devices, in low bandwidth
situations.
 Bluetooth exists in many products-
wireless speakers, smartphones, tablets,
laptops, smartwatches , smart TV’s
modems etc.

APPLICATIONS:
 Communication between phones and car
stereo system
 Wireless control with iOS, android tablets
with portable speakers.
 Working by radio waves instead of wired or
cables.
 SOME DISADVANTAGES OF BLUETOOTH :
○ Slow data – due to less energy consumption.
○ Poor security
○ Battery drain – bcz it tries to connect to more
and more devices that is why is it
recommended to switch off your bluettoth
when not in use.

 It is a computer peripheral that allows you to
connect and communicate with other
computers via telephone lines.
 There are two types of modems:
 Internal: the modems that are fixed within the
computer.
 External modems: modems that are
connected externally to a computer as other
peripherals are connected.

 As ordinary telephone lines cannot carry
digital information , a modem converts the
digital information into analog data which
is transmitted through telephone cables. At
the receiving end, the analog data is
converted back into digital data.
 This process of transformation of signals is
called modulation and demodulation ,and
this is how Modem received its name.

 A network hub is a device that allows multiple
computers to communicate with each other over a
network. It has several Ethernet ports that are
used to connect two or more network devices
together. Each computer or device connected to
the hub can communicate with any other device
connected to one of the hub's Ethernet ports.

 Passive Hubs
 One of the types of a network hub is the so-called passive hub.
It's a pass-through that does not do anything more than just
broadcast signals it receives through its input port, then sends it
out through the output port. It does not do anything to
regenerate or process the signals because it only functions as a
connector of different wires in a topology.
 Active Hubs
 An active hub works more than just a connector but also
regenerates the data bits to ensure the signals are strong.
Another name for an active hub is a multiport repeater. It
provides an active participation in the network aside from acting
as an interface. It participates in the data communication, such
as storing signals received through the input ports, before
forwarding them. It can monitor the data it is forwarding and
sometimes help improve signals before forwarding them to
other connections. Such a feature makes troubleshooting of
network problems easier.

 When a packet arrives at one port from a source ,it is
copied to the other ports so that all segments of LAN
can see all packet and hub forwards the segments to
all connected devices , only expected
destination accept this segment and other device
discard this segment.
 As more users are added ,they compute for the
available bandwidth and the data transfer speed
reduces.
 Example: a hotel with just a single telephone line ,if a
user calls someone else ,all the other users will have
to attend a call and check whether it is meant for
them or not. And until their conversation ends ,no
one will be able to use the line.

 Switch is a device used to segment networks
into different sub networks called subnets or LAN
segments. Segmenting prevents traffic overloading
in a network.
 Switch is responsible for transforming data in
a specific way and forwarding packets
between LAN segments
 Establishes a temporary connection between
the source and destination and terminates
the connection once conversation is done

 It is a device that amplifies a signal being
transmitted on the network
 Used in long network lines
 It ensures that the data packets reach their
destination
TWO TYPES
1. Amplifiers- amplifies all the incoming
signals
2. Signal repeaters- Collects the inbound
packets and retransmit.

 A device which connects dissimilar networks
 It’s a node on the network that serves as an
entrance to another network.
 Expands the functionality of routers by
performing data translation and protocol
conversion.

• A device used to connect two separate Ethernet
networks into one extended Ethernet.
• A bridge is a device that connects and passes packets
between two network segments that use the same
communications protocol. Bridges operate at the data link
layer (layer 2) of the OSI reference model. A bridge will
filter, forward or flood an incoming frame based on the
MAC address of that frame.

 A router is a networking device that forwards data packets
between computer networks. Routers perform the traffic
directing functions on the Internet.
 A data packet is typically forwarded from one router to
another router through the networks that constitute an
internetwork until it reaches its destination node by
identifying the IP address.

 Intrusion Problems
1. Snooping
2. Eavesdropping
 Denial of Service(Dos) attacks
1. Denial of Access to information
2. Denial of Access to Application
3. Denial of Access to Systems
4. Denial of Access to communications

 SMS
 Voice Mail
 Email
 Chat
 Videoconferencing

 Active protection
a) Authorization
b) Authentication
c) Firewall
d) Intrusion deletion
Preventive measures
a) Implement security policies
b) Use proper file access permissions when
sharing files in internet.

Introduction to GSM
GSM[Global System For Mobile Communications] is a
standard for digital cell phones. Earlier it was established
in Europe in the mid of 1980s for providing voice
communication . The penetration of GSM has enabled
development and better utilisation of technology . this
innovation continued in developing the technology for
data, networking and M2M [machine to
machine]communication beyond voice. GSM has evolved
from 1G[1st generation communication ] in 1990s
to 5G[5th generation] in the year 2017. now it has become
the international standard in Europe,Australia and much of
Asia and Africa.

GSM is a standard developed by the European Telecommunications Standards
Institute (ETSI) to describe the protocols for second-generation digital
cellular networks used by mobile devices such as tablets, first deployed in
Finland in December 1991.[2] As of 2014, it has become the global standard
for mobile communications – with over 90% market share, operating in over
193 countries and territories.[3]
2G networks developed as a replacement for first generation (1G) analog
cellular networks, and the GSM standard originally described as a digital,
circuit-switched network optimized for full duplex voice telephony. This
expanded over time to include data communications, first by circuit-switched
transport, then by packet data transport via GPRS (General Packet Radio
Services) and EDGE (Enhanced Data rates for GSM Evolution, or EGPRS).
Subsequently, the 3GPP developed third-generation (3G) UMTS standards,
followed by fourth-generation (4G) LTE Advanced standards, which do not
form part of the ETSI GSM standard.
"GSM" is a trademark owned by the GSM Association. It may also refer to the
(initially) most common voice codec used, Full Rate.

The main feature of GSM is to
provide network for
communication of data . In
covered areas, cell phone
users can buy one phone that
will work anywhere where the
standard is suppported.To
connect to these users the
GSM allots a SIM[subscriber
identification module] card.Its
a small chip which provide
rooms to the data, contacts
and others details . it is the
main profile of the user.

Now, the question arises how does this GSM provide
network to its users . the answer is simple through
"towers". A tower or a cell site is a cellular enabled
mobile device site. it contains all the equipments such
as base stations which radiates or transmits radio
signal[RF] for mobile communications. the base station
is intern connected to the main switching stations via
microwave/optical fibre . the main switching
station[MSS] is the heart of the entire GSM/cellular
network which provides connectivity between the
users.

the radio signals transmitted provides the
network coverage which could be seen in the mobile
phones . each BTS tower provides coverage to a
limited distance around the cellsite(360) to enable
a coverage, it is divided into three sectors called
Alpha, Beta and Gama having120 degree each . each
sector is called as a cell in a complete covered area
will have a cell structure as shown in the following
diagram.

so till now we have learnt how the network coverage
is provided across. now we wil be learning how these
signals are sent back and as what it is sent. so these
radio signals are now sent as network coverage
.these coverages sent helps the people to
communicate with each other. these conversation
signals are sent back through the process of
TDMA(time division multiple access) . time division
multiple access is a process in which a milli second is
given to each user. the division of time to the users
is again combined together and sent back to the
tower. do note one thing that in a tower only eight
users can access a single tower at a period of time

Baseband Encoding &
Interleaving
Walsh code
Walsh code
Decode & De
-interleaving
Baseband
data
FREQUENCY

RADIO
COMMUNICATION
TECHNOLOGIES
MILITARY (During WW2)
GLOBAL POSITIONING
SYSTEM (GPS)

 Wireless Local Loop(WLL) is a system of
communication similar to conventional
telephone system, designed to serve homes,
offices, local areas etc.
 It is a system that connects subscribers to the
Public Switched Telephone Network(PSTN)
using radio signals as a substitute for other
media.

 Deploys many multichannel transmit/receive base
stations (tranceivers) that are within the line of site of
intended customers.
 Each customer is equipped with a mini station with
low power to which the telephone or PBX(private
branch exchange)
 Two cables and a telephone connector are the only
outlets.
WLL UNIT
Radio tranceiver
WLL interface
One cable- connects to
antenna
Phone receptacle(socket)-
connects to common
telephone set

User1
Base
station 1
Switchin
g centre
Base
station 2
User 2
User1 transmits signals
that are received by the
base station located within
the range of the User1.
Then the base station
further sends the signal to
the main switching centre.
The switching centre which
is like a database figures
out the user to which the
signals have to be sent.
The signals are sent to the
base station located in the
vicinity of user2 and then
to User2. Thus a wireless
connection is established.

 Follows CDMA(code division multiple access)
 Spread spectrum technique- data is
transferred in small bits over a number of
discrete frequencies.
 Each user’s signal is spread over the entire
bandwidth by unique spreading code.
 At the receiver’s end, the unique code is used
to recover the signal.
 Transmission occurs over a terrestrial
microwave platform.

•Ability to connect with users in remote areas without need
of laying new cables
•No fear of communication disruption as there are no cables
used that could be vulnerable to damage
•More bandwidth, higher quality, more speed
•No need of satellite feeds or local phone service. Offers
advanced customer service features, signaling services etc.

 WLL can operate on GSM Handsets/mobile
units as well as GSM Subscriber Units.
 A good WLL system should satisfy the
following:-
1.Good voice quality
2.No disruption in communication
3.User should be able to connect fax,
modem etc and the system should be
connectable to the Public Call Office.

1. Cyber law- IT Act and IT Amendment Act ,
2008
2. Firewall- To prevent unauthorized access to
or from a private network
3. Hackers and Crackers- Individuals who are
expert in subjects, who gain unauthorized
access to computer systems for the purpose
of stealing and corrupting data.
4. Cookies

Alltheinformationthatisenteredintothewebbrowserisstoredintheformofa COOKIE(Itisatext
file).Thiscookieisstoredinthewebserverandisusedbythewebbrowsertoenhancetheexperienceof
theuserwiththewebpage.
Cookiesareharmlessandcannotcauseanyharmtothecomputer.
Theyarejusttextfilesthatstorealltheinformationtheuserenters.Iftheuserentersanypersonal
informationinthecookiesthentheycanbeaccessedbyathirdparty.
Topreventthis,thereisafeatureinwebbrowsersthatcanpreventscookies
Tobemade.

A system that prevents unauthorized
access to or from and private networks
All the messages that enter or leave
through the firewall are checked by the
firewall .
Any message that does not meet the
security criteria are blocked by the firewall

Hackers are simply computer enthusiast, that is ,
these are the people that just like to learn computer
programming and new languages and is an expert
in these subjects(s).
This term can be taken as complimentary or
derogatory. Nowadays the meaning of the word is
considered to be as people that hack into system
and destroy data or steal it.
But that is the term that defines a Cracker

 Different ways to access your computer
remotely are :
1. Remote Desktop software
2. Remote File Access
3. Accessing/storing documents via cloud

Computer networking class 12

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Computer networking class 12