Comm. & net. concepts

Behind the need to communicate,
there is a need to share.
Behind the need to share, there is the
need to be understood.
– Leo Rosten
Communicate and
Share with Networks…

Network Goals :
Resource Sharing
Reliability
Cost Factor
Communication Medium
Application of Networks :
1.Sharing – Easy and flexible. 3 types of sharing :
Peripherals – Expensive, Each peripheral connected to main frame.
Sharing in a multi-user system – Controlled access
Traditional time sharing – Central control
2.Access to remote database
3. Communication facilities

The Interspace :
 Client/server software which allows multiple users to
communicate online with real time audio, video and text chat in
dynamic 3D environments.
 Vision of what Internet will become.
Terminology of Networks :
Nodes(Workstations) - Computers in a network.
Server – A computer that facilitates data sharing.
Types of servers :
1.Non-dedicated – Workstation that can double up as server.
2.Dedicated – Computer reserved for server’s job.
Network Interface Unit (NIU) – Interpreter that helps establish
communication between server and workstations.

1.Circuit Switching :
Physical connection is established first b/w two
computers.
End-to-end path setup is needed to send any data.
2.Message Switching :
Data or message is sent to the switching office first.
The office sends this data to another office through a free
link.
Also known as store and forward.
3.Packet Switching :
Tight upper limit on block size.
Packets of fixed size are stored in main memory.
This improves performance Throughput improved.

Data Channel : Medium used to carry information from one point to another.
Baud : Unit of measurement for information carrying capacity of a channel.
Bits Per Second (bps) : Speed of data transfer.
Bandwidth : Difference between highest and lowest frequencies of a transmission channel.
Directly proportional to amount of data transmitted or received per unit time.
Higher bandwidth channels – broadband and lower ones – narrowband.
Data Transfer Rates : Amount of data transferred per second by a channel or a computing or
storage device.

• Come in pairs, twisted
around each other.
• Types – Shielded and
unshielded.
• Advantages :
• Disadvantages :
• S
• Solid wire core
surrounded by one or
more foil or wire.
• Used for television
signals.
• Types – Thicknet, Thinnet
• Advantages :
• Disadvantages :
• Thin strands of glass or
glass like material.
• Light sources – LEDs
or LDs.
• Advantages :
• Disadvantages :
o Simple, flexible
o Low weight
o Easy connection
o Inexpensive
o High attenuation –
Unsuitable for long
distances
o Low bandwidth
o Can be used as basis for
shared cable network.
o Higher bandwidths – upto
400 mbps
o Expensive
o Not compatible with
twisted pair cables
o Immune to electrical,
magnetic interference.
o Highly sustainable for harsh
industrial areas.
o Guarantees secure
transmission.
o Connection loss
o Difficult to solder.
o Fragile – Special care
(GUIDED)
TWISTE
D PAIR
COAXIAL OPTICAL
FIBRE

• Parabolic antennas
mounted on towers.
• Higher tower – greater
range
• Line-of-sight transmission
• Advantages :
• Disadvantages :
• S
• Sine waves are used to
transmit information.
• Transmitter and receiver
use antennas to radiate
and capture the radio
signal.
• Advantages :
• Disadvantages :
• Uses the synchronous
satellite to relay the radio
signal.
• Security provided by
coding and decoding
equipment.
• Advantages :
• Disadvantages :
o Cheap
o Ease of communication
over difficult terrain
o Insecure
o Susceptible to rain, storm,
etc.
o Limited bandwidth
o Mobility
o Ease of communication
over difficult terrain
o Insecure
o Susceptible to weather
effects
o Large area cover
o Heavy usage of
intercontinental traffic –
commercial attractive
o Overcrowding of
available bandwidths
o High investment cost
(UNGUIDED
)
MICRO
WAVE
RADIO
WAVE
SATELLI
TE

COMPUTER NETWORK – Computers linked by means of communication system.
4 TYPES OF NETWORKS : (Based on geographical spread)
LAN WAN MAN PAN

Local Area Network(LAN):
Confined to a localized area.
Purpose: Resource sharing.
Most LANs use cables to connect network
interface cards.
Example : Network within office/building.
Metropolitan Area Network(MAN):
Spread over a city.
Purpose: Sharing hardware and software resources
among users.
Examples: Cable TV networks over a city

Wide Area Network(WAN):
Across Countries.
Can also be a big group of LANs.
Purpose:
Connected through public networks/leased lines/satellites.
Example : The Internet-The Largest WAN.
Fast and efficient exchange of information
cost , speed
Personal Area Network(PAN):
Interconnection of IT devices within range of an individual.
Purpose : Transferring files from one device
to another.
Can be connected without wires.
Example : Laptop with printer (or) mobile with laptop.

DIFFERENCES B/W LOCAL AND WIDE AREA
NETWORK

Factors which decide the best suited topology:
Cost – Minimum cost by minimizing distances.
Flexibility – Network should allow easy reconfiguration.
Removing old nodes and adding new ones.
Reliability – Allowing detection of fault location
and providing means to isolate it.
TOPOLOGY – Pattern of interconnection of nodes.
Let us now see about different network topologies…

1.Point To Point Link :
Each station receives exactly from one transmitter and each
transmitter transmits to exactly one receiver.
Transmitting and receiving operations can occur over
separate/same wires.
2.Tree Topology :
Central root branching and sub-branching to the
network extremities.
Best suited for applications which have a hierarchial
flow of data control.
3.Graph Topology :
Arbitrary Linkage – A link may or may not connect two or more
nodes multiple links can also exist .
Connected Graph – Path established in two nodes via one or
more links.

 Single-path connection from all
nodes to a central node.
 Used in most info networks – data
processing, voice comm.
 Advantages :
 Disadvantages :
o Ease of service
o One device per connection
o Centralized control
o Simple access protocols
o Long cable length
o Difficult expansion
o Dependence on central node
 Various nodes attached to single
length of transmission media.
 Host at one end communicates with
several terminals.
 Advantages :
 Disadvantages :
o Short cable length
o Resilent architecture
o Easy extension
o Difficult fault detection and
isolation
o Repeater configuration –
necessary during extension
o Intelligent nodes needed
 Each node connects to only two
neighbours.
 Data travels in one direction only.
 Advantages :
 Disadvantages :
o Short cable length
o No wiring closet space needed
o Suitable for optical fibres
o Node failure Network failure
o Difficult fault diagnosis
o Very difficult fault isolation
4.STAR
TOPOLOGY
5.BUS/LINEAR
TOPOLOGY
6.RING/CIRCULA
R TOPOLOGY

7.Mesh Topology :
Each node is connected to more than one node to
provide an alternate route.
Excellent for long distance networks .
Ideal for distributed networks.
Back up, re-routing, pass through capabilities.
8.Fully Connected Topology :
Link exists b/w each host.

1.RJ 45(Registered Jack-45):
 Used to connect computers on LANs, especially ethernets.
Many devices play important roles in the smooth functioning of networks.
Let us discuss them…
2.Ethernet Card :
 Contains connections for co-axial or twisted pair cables.
3.Hub :
 Hardware device to connect several computers.
 Contains multiple independent, but connected network modules.
 Types : Active and Passive
 Functioning :
• Forwards data packets over one port from one workstation to all other ports.
• All users in a hub or stack of hubs are in the same segment, sharing the hub’s
bandwidth and data-carrying capacity.

4.Modem :
 A computer peripheral that allows us to connect and communicate
with other computers over telephone lines.
 Does modulation – changes digital data to analog data and
demodulation – analog to digital data.
 Types- internal and external
 Working of a modem (Explained through diagram)
DTE
TXD
RXD
RTS
CTS
CD
DTR
DSR
1
3
4
6
2
5
7
DCE
Telephone
lines
Handshaking
Signal
SIMILAR
DTE
DCE
Micro controlled MODEM MODEM
terminal 1.TXD: Transmit
2.RXD:Receive
3.RTS: Request to send
4.CTS: Clear to send
5.CD : Carrier detect
6.DTR: Data Terminal
ready
7.DSR: Data set ready
Data Communication
Equipment
Data Terminal
Equipment

5.SWITCH :
 Used to segment networks into different
sub-networks called SUBNETS/LAN SEGMENTS.
 Prevents traffic overloading in a network.
 Functioning :
To insulate transmission from other parts , the switch
establishes a temporary connection b/w the source
and destination.
Connection is terminated once the conversation is over.

6.REPEATER :
 Amplifies and restores signals for long distance transmission.
 Types:
AMPLIFIER – Amplifies all incoming signals over network.
SIGNAL REPEATER - Collects and retransmits the inbound
packet as if it were starting from source station.
7.BRIDGE :
 Establishes an intelligent connection b/w two local networks.
 Improves performances on both sides of the bridge.
 Checks the passage of a packet by examining its physical address.

8.ROUTER :
 Used to separate different segments in a network Better
performance and reliability.
 Routers and bridges differ by protocols .
 If destination is unknown, traffic is sent to another
destination-known router.
 Functioning:
Routers make sure that packets travel in the most efficient
paths by using a network road map – ROUTING TABLE.
If a link b/w two routers fails, the sending router can
determine an alternate route.

9.GATEWAY :
 Device that connects dissimilar networks.
 Expands functionality of routers by performing data translation
and protocol conversion.
 It is a node on a network that serves as an entrance to another.
10. WiFi CARD :
 Internal and external LAN adapter with a wireless radio and
antenna.
 Benefit – Allows to set up workstation or home office without
considering the proximity or availability of hard line network access.

GENERAL NETWORK DESIGN PROCESS :
 3 MAIN ELEMENTS :
Environment given – Location of hosts, servers, terminals, etc.
Performance constraints – Network reliability, traffic throughput,
host/client speeds.
Internetworking variables – Network topology, line capacities
and packet flow assignments.
MAIN GOAL MINIMISING COST WITHOUT COMPROMISING ON AVAILABILITY
REQUIREMENTS.

LAN HARDWARE
The following hardware technologies can be applied to LAN design :
 Using Repeaters :
Repeaters – basic unit to connect separate segments.
Basic rule – 5-4-3 rule.
 Using Bridges :
Bridges – Operate in the data link layer of the OSI model.
Bridges implement Spanning-Tree Protocol to build loop
free topology.

 Using Hubs :
Hubs can be used when more than two computers
need to be networked.
 Using Switches :
Switch – Gives each LAN segment a dedicated
bandwidth.
 Using Routers :
Routers filter network traffic based on an IP address.

For a small LAN
• Clients computers with NICs
• Hub
• Cabling
• Networking OS
• Server
For connecting offices &
departments
• Hubs
• Cabling
• Switch
• Networking OS
• Servers
• Router for shared Internet
access(opt.)
For connecting dispersed
office sites
• Hubs
• Cabling
• Switches
• Routers at each location for
WAN connections.
• Access server for dialup access
• WAN service (ISDN/leased line,
etc.)
NETWORK COMPONENT CHECKLISTS FOR DIFFERENT TYPES OF
NETWORKS

Twisted Pair Coaxial Fibre Optics
No high speed data
transmission
Short range transmission
Television signal
distribution
Long distance
telephone transmission
Short distance
computer links
Greater data capacity
Lower attenuation
Secure transmission
DIFFERENT TYPES OF GUIDED MEDIA WHEN TO USE WHICH ???...

Radio Wave Microwave Satellite
DIFFERENT TYPES OF UNGUIDED MEDIA WHEN TO USE WHICH ???...
Long distances
Signals need to
penetrate walls/buildings
Omni-directional
transmission
Long distance
telephone service
Minimize expenditure
Straight line
transmission
Transmission over very
large area
Long distance television
distribution

PROTOCOL – Rules that are applicable for a
network.
 Usually, multiple protocols will be in use
simultaneously.
 Most protocols support multi-tasking.
 One operation may involve several protocols.
SOME BASIC PROTOCOLS
Let us look at some most common protocols…

1.HTTP(Hypertext Transfer Protocol) :
It is a set of rules for transferring hypertext on WWW.
HTTP is a generic protocol used for communication between
user agents and gateways to Internet Protocols.
The HTTP consist of two items: The set of requests from
browsers to servers and The set of responses going back to the
other way.
2.FTP(File Transfer Protocol) :
It is a standard for the exchange of files across internet.
It is a potent and popular way to share information over the
internet.
FTP works as a client/ server process.

3.TCP/IP(Transmission Control Protocol/Internet Protocol) :
Layered set of protocols
It is responsible for making sure that the commands get through
to the other end.
It keeps tracks of what it sent and retransmits anything that did
not get through.
4.SLIP/PPP(Serial Line IP/Point-to-Point Protocol) :
SLIP is used for delivering IP packets over dial up lines.
SLIP has been largely supplanted by PPP.
PPP is used for transmission of IP packets over serial lines.
PPP is a layered protocol and it supports both synchronized
and unsynchronized lines.

WIRELESS COMMUNICATION – Data communication without landlines.
MOBILE COMPUTING – Computing device is not only continuously connected to
base or central network.
WIRELESS/MOBILE COMPUTING
TECHNOLOGIES :
1.GSM(Global System for Mobile) :
Leading digital cellular system.
GSM introduced SIM cards to connect to specific
service providers.
Works by dividing a radio frequency into time slots.
A single frequency can support multiple and
simultaneous data channels.

2.CDMA(Code-Division Multiple Access) :
Uses spread spectrum technique.
Data is sent in small pieces over a number of discrete
frequencies.
Signal is spread over by a unique spreading code.
3.WLL(Wireless in Local Loop) :
Connects subscribers to the PSTN(Public Switched
Telephone Network) using radio signals.
Do not suffer from weather damage.
Service features and quality can be provided.
Support high quality data transmission and signals.
4.GPRS(General Packet Radio Service) :
Radio transmission of data by small packets between
the mobile devices and the internet.
High speed – 56 k bits/second to 114 k bits/second.

5.Generation Networks :
1G : First analog cellular system designed for voice calls.
Popular 1G networks - Nordic Mobile Telephone(NMT) , Advanced Mobile
Phone System (AMPS).
2G : First digital cellular system. Offers better sound quality and capacity
and services such as paging faxes and text messages.
Popular 2G networks – GSM, CDMAOne, D-AMPS.
3G : Newer cellular networks. It is a broadband , packet based
transmission and delivers a speed up to 2Mbps.
Popular 3G networks - UMTS FDD and TDD.
4G : Offers downlink rates , low latency and efficient spectrum use.
Convergence of wired and wireless network.
4G – MAGIC- Mobile Multimedia, Anywhere, Global Mobility Solutions
Over, Integrated Wireless and Customized Services.

6.SMS(Short Message Service) :
Transmission of short text messages.
Message is received by SMSC(Short Message Service Centre).
SMSC sends a SMS request to HLR.
7.Chat :
Online textual talk.
Communication over the internet.
Enables participants to respond quickly.
Most common chat protocol - IRC
8.Video Conferencing :
Video phone conversation among multiple participants.
Communicate by simultaneous two way video and audio
transmission.
Most common video conferencing protocols – H.323 and SIP

9.Voice over Internet Protocol :
Enables voice communication over the internet.
Voice is efficiently compressed into data packets and is transmitted over
the networks.
Data networks like LAN uses the Packet Switched Technology.
Common protocol for packet-witched networks - Internet Protocol(IP).
10.Connecting Wirelessly to Internet :
Wi-Fi
• Connects to Internet without a direct line from PC
to ISP.
• Need : i)A broadband Internet , ii) A wireless
router and iii)A PC with net card/external wireless
adapter.
• Range : 30 – 100 m
WiMax
• Can provide wireless broadband access.
• Need : WiMax Base Station
• Range : 5 – 15 km

1.WWW(World Wide Web) :
This is a set of protocols that allows us to access any document
on the net based on URLs.
One can set up a server and construct hypertext documents with
links on them.
Graphic-intensive nature makes internet more popular and easily
reachable.
Attributes :
 User friendly
 Multimedia documents – Users can create, link or display web pages.
 Hypertext and hyperlinks – By incorporating images, videos and audios, net
surfing seems easier.
 Interactive
 Frames – More than one independently controllable section.

2.Telnet :
Character-based terminal window on another system.
Used by people who have logins on remote systems.
Widely used to connect to thousands of catalogs at libraries around
the world.
3.Web Browser and Web Server :
Web Browser – WWW client, navigates though WWW and displays
web pages.
Web Server – WWW server, responds to user’s requests.
4.Web Sites, Web Addresses and Web Pages :
Web Site – Location on a net server.
Web Address – Each web site has a unique URL.
Web Page – Documents residing on web sites.

5. URL and Domain Names :
General structure of a URL: type://address/path
type : specifies the type of the server
address: address of the server
path : location of the file on the server
Domain Name – Character-based Internet address.
Example:
http://www.sports123.com/about/reachus
type address domain path
indicator
6.Web Hosting :
Means of hosting web-server application on a system through
which electronic content on the Internet is available to any web-
browser client.
Types:
• Free – Hosting web pages for no cost.
• Virtual/Shared – Fully independent to one’s own web audience.
• Dedicated – A company rents entire web server from a hosting one.
• Co-location – Only physical needs managed by host.

7.Web 2.0 : - Added features and apps.
Revolutionized info-sharing, user-oriented design,
interoperability on Internet
Interactive platform – blogs, forums, social sites, etc.
8.HTML(Hypertext Markup Language) :
Used to design the layout of a document and specify
hyperlinks.
Provides layout commands – TAGS – Lets the user control
the presentation of information on a web page.
9.XML(eXtensible Markup Language) :
For documents containing structured information.
Provides facility to define tags and the structural
relationships b/w them.
Semantics of an XML document – Defined by applications
or by stylesheets.

10.DHTML(Dynamic HTML) :
Refers to Web content that changes each time it is viewed.
Same URL can result in a different page depending on the
following parameters :
Geographic location of the reader
Time of day
Previous pages viewed by the reader
Profile of the reader
11.Web Scripting :
Process of creating and embedding scripts in a web page.
Scripts are purposely written list of commands that are
embedded in a web page.
Two types of scripts :
Client-Side Scripts – Supports interaction within a webpage.
Server-Side Scripts – Supports execution at the server end.

Problems under Network Security:
Physical Security Holes – Hackers guess the password and
gain access to the network systems.
Software Security Holes – ‘Privileged’ software are
compromised into doing undesired things.
Inconsistent Usage Holes – Assembling a combination of
hardware and software.
Protection Methods :
Authorization : Confirms the service requestors credentials.
Performs by asking the user legal login ID.
Authentication/password protection : Ensures that each entity
involved in using a web service. It accepts the credentials from the
entity.
Encrypted Smart Cards: It is a hand held smart card that can
generate a token that a system can recognize.
Biometric System: Most secure level of authorization.
Involves finger prints.

Firewall : A system designed to prevent unauthorized
access to or from a private network. Implemented in both
hardware and software.
Types of Firewall Techniques:
 Packet Filter.
 Application Gateway.
 Proxy Sever.
 Circuit Level Gateway.
Cookies :
Messages given to a web browser by server.
Identify users and prepare customized web pages.
Do not act maliciously on systems.
They are just text files and can be deleted.
Cookies have 6 Parameters – Name , Value, Expiration, Date,
Path of the cookie is valid, Domain of the cookie, Need for a secure
connection.

Cyber Crime :
It is defined as unlawful act where in the computer is either a
tool or a target or both.
Classification Of Cyber Crimes:
 Tampering With Computer Source Documents
 Hacking
 Publishing of Information, which is obscene in electronic form
 Child Pornography
 Accessing Protected System
 Breach of Confidentiality and Privacy.
Intellectual Property :
 Product of the intellect that has commercial value, including
copyrighted property.
 Encourages fair-trading Socio-economic development

COMPUTER VIRUS – Malicious program that requires a host and is
designed to make a system sick.
3 types of viruses :
 File infectors – attach themselves to a program file.
 Boot sector viruses – install themselves on the beginning tracks
of a hard drive.
 Macro viruses – infect data files.
Spread :
 Move by attaching themselves to files/boot records.
 Found in various downloads and e-mails.

Damages :
 Can destroy FAT and lead to corruption of an entire file system.
 Can create bad sectors on the disk Parts of programs and files
destroyed.
 Can decrease space on hard disks by duplicating files.
 Can cause a loss of integrity by altering data in files.
 Can cause the system to hang.
Trojan Horses :
 Code hidden in a program that looks safe to run but has
hidden side effects.
Worms :
 A program designed to replicate Eats disk space.
 Self-contained, no host.
 Activated by creating process. Network worm can spread
across communication links.

Spam :
 Refers to electronic junk mail or junk newsgroup postings.
 Ways to avoid spam :
Create a filter that seperates the mails you suspect as spam.
Register with true personal information to sign up for accounts on the
internet.
Virus Prevention :
Never use a ‘foreign’ disk or CD without virus-scan.
Always scan downloaded files.
Never boot your PC from a floppy unless you ensure it is virus free.
 Use licensed software.
 Password protect your PC.
 Install and use antivirus software.
 Make regular backups.

We discussed…
The need for networking.
Evolution of Networking – ARPANET NSFnet Internet Interspace
Switching Techniques – Circuit, Packet and Message
Some data communication terminologies
Transmission Media – Guided and Unguided
Types of Networks – LAN, MAN, WAN, and PAN
Various Network Topologies
Major Network Devices
LAN Design – LAN hardware, Checklists for network components, Proper usage of
transmission media
Communication Protocols
Wireless/Mobile Computing – Different technologies
Internetworking Terms and Concepts
Network Security Concepts – Problems, Solutions, Cyber Crime, Intellectual Property
Viruses – Types, Prevention

Presented by :
Aravind
Ashwin
Kanthinathan
Sankheetha
Subiksha

Comm. & net. concepts

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