1. The document discusses various methods of connecting to the internet including through online services, dumb terminals, direct connections, and digital subscriber lines. 2. It also covers how different internet technologies work such as email, usenet newsgroups, internet relay chat, and internet telephony. These technologies transmit information using protocols like TCP/IP by breaking communications into packets. 3. Additional topics include how satellite, cable modems, network computers, and palmtop devices can provide internet access as well as issues around internet spam and security.

1. D.Seethalakshmi MCA.,M.Phil.,
Assistant Professor
Bon Secours College for Women
Thanjavur
*Working Principles of
Internet

2. *Connecting to the
Internet
*Connecting your computer
*Connecting to the Internet from online services
*How ISDN works
*The Internet/Television connection
*How Network Computers(NCs) Work
*How the Digital Subscriber line (DSL) works
*How satellite and palmtop connections work

3. *Connecting your
Computer
*Dumb Terminal
*A terminal that is connected to a mainframe or
other kind of computer
*Eg
*Library or universities
*Internet access than dumb terminals provide

4. *Terminal Emulation
*A personal computer can connect via modem to
a large computer
*The computer works like a dumb terminal,
except it is connected via a phone line instead
of direct connection
*This kind of internet account is sometimes
called a shell account

5. Direct Connection
LANs or large computers such as mainframes can be
directly connected to the internet.
SLIP
Serial Line Internet Protocol
Full Internet connection over telephone lines
PPP(Point to Point Protocol)
Like tSLIP, via modem
it resends any damaged packets

6. ISDN line
Special digital telephone lines
speed 64 kbps to 128 kbps
cost more than normal phone lines
ASDL (Assymentic Digital Subscriber Line)
Provide Very High speed connection
Cable Modem
Cable TV system using coaxial cable
Faster than conventional medem 10 to 20 times

7. Network Computer
low cost network computer
Web TV
Using set top box through television
Online Services
No special setup is equired
Dial up connections

8. *Connecting to the
Internet from other
services
Compu serve or America online
Own s/w – easy to access internet
Dial directly to get resources
Firewall
It is a Security system of accepting or
blocking packets as they are transmitted across
a network.

9. *How Works ISDN
Integrated Services Digital Network

11. *The Internet/Television
Connection
*How Cable Modem Works
*Coaxial Cable – Broad Band
*2 connections
*Normal set top box access TV
*Next Wire is for Broadband modem
*It carries signal simultaneously

13. *How WebTV works
*Use Internet and watch TV same time
*Set top box capability to accept add-ons
*Screens use RGB colors
*Convert signal from RGB to NSTC
*Web tv box connects to web tv network
*Simple remote unit control webtv

15. *How Network
Computers Work
*Low cost computers with little or no local storage
*No CD – ROM Drives or Pheripherals
*EG ATM Machine
*Silicon chip, card reader,NC
*Get PIN for Authorization
*NC used for email, games or word processor

16. *How the DSL works
Digital Subscriber line
ASDL – it doesn’t need any special wires
Send and receive as all digital data
It enables talk on telephone and use internet
simultaneously
Divides phone line into 3 channels
 Receiving Data
 Sending Data
 Talking over the phone

18. *How Satellite &
Palmtop Work
Satellite connection – DirecPC Satellite
Much higher speed than normal modems
Webserver send information to satellite ground
stataion (NOC)
Network operations center send info to satellite
above earth at 400 kilobits per second

19. *Palmtop Computers
Browse on web

20. *Palm device – proxiweb s/w
*ISP – modem
*Proxy Server
*Webserver

21. *Communicating on
the Internet
*How Email Works
*Email spam & Blocking
*How Usenet newsgroup work
*How internet chat and Instant Messaging work
*Making phone calls on the Internet

22. *How Email Works
*Anatomy of a Mail Message
*ASCII code
*Attach pictures, sounds, videos and other files
*Automatically doing Encode and decode
*E-mail address must be In a format
*Otherwise message not sent

23. *Email is Delivered
the Internet
*Send packets using TCP/IP protocol
*Routers look address and send the mail correct
path to reach destination
*All packets are received address then
recombined to read receiver
*Subscribe to receive mails (Mail Reflector)

24. *How Email Software
Works
*Compose
*Send
*Inbox
*Trash
*Create group mailing
*Add Signature
*Create own folder
*Spam

25. *How Email is sent between
networks

26. *LDAP
*Lightweight Directory Acess Protocol

27. *How Email
Encryption works
Avoid Snoopers & Hackers
Public (Encrypt)& Private (Decrypt)Key
Encryption Progam PGP
Copy of private key have sender
Receiver uses the private key to decrypt the
email
Some softwares decrypted automatically
Internet won’t understand, it see only
random characters

28. *Email Spam & Blocking
 Spam – unsolicited email sent to you
 Spam is sent out bulk of emails
 To get bulk of email address from company
servers
 Spammers hide their email address
The mail have from, sender and reply
The mail come from someone not spammer
Doing this sometimes called SPAMOUFLAGE

29. *How Email Spam is
Blocked
*Filter out mail from certain addresses
*This feature is spam filter or spam blocker
*ISP’s and online service can block spammers
*Routing table find spammer email address
*But Spammers change therir email address
often
*So Routing table also can’t fine spammer email
address perfectly

30. *How Usenet
Newsgroups work
*It is a global bulletin board & discussion area
*Newsgroups can be found on many host
computers across internet.
*2 Newsgroups
*Moderated
*Unmoderated

31. *Moderated
Newsgroup
*A human moderator receives and reads all the
messages for the newsgroup.
*The moderator then decides which messages
are should be post.
*The messages to be posted are put on a
newsgroup server.
*Other messages are discarded.

32. *Unmoderated
Newsgroups
 All messages are put directly on the server.
 Newsgroups and all their messages are stored
on a Usenet server.
 Usenet server communicate with one another,
so that all messages posted on one server are
duplicated on other servers.
 Although there are many usenet servers, not
all servers carry all newsgroups.
 Each site decides which newsgroups to carry.

33. *Pictures, Multimedia files & exe programs can be posted in
newsgroups for others see & use.
*A common encoding scheme used on newsgroups is called
uuencode.
*Newsgroup reader software lets read messages and respond
to newsgroups.
*New messages will automatically be delivered to when you
check the server.
*You will also be able to cancel your subscription

35. *Hierarchy of Usenet
Newsgroups
*1000’s of newsgroup .
*Divided into hierarchies of topics to make it
easier to find particular newsgroup you want to
participate.
*Not all sites carry all newsgroups.
*System administrator decide which newsgroup
carry at their site.

36. *The major topic comes first, followed by subtopic.
*Subtopic can be further subdivided…
*Rec.arts.books
*New newsgroups are created and old one are being
eliminated.
*Newsgroup client software give a complete up-to-date list.

38. *How IRC Works
 Internet Relay Chat
 It is a way for people all over the world to
“chat” with one another by using keyboards.
 It runs on a client/server model.
 Make a internet connection & then start your
client software.
 IRC servers are located all over the world.

40. *Choose a specific channel to join & choose a username.
*After joining channel able to see the conservation.
*The messages sent from your server to other servers.
*Under spanning tree server structure the messages takes
shortest route to reach destination.
*People read & respond messages.

41. *How Instant
Messaging Works

42. *Making Phone calls on
Internet
*Using special phone s/w to send or receive
telephone calls
*Connect to special directory, the directory
contains list of people who connect internet
using that phone s/w.
*Find the IP address to connect phone call.
*High speed – High quality voice files
*The s/w breaks up the voice file into a series
of packets to be sent using TCP/IP.

43. *How Internet
Telephony Works

44. IP Telephony service
Dial special code first, as a way of routing the call.
Call  PSTN Special IP voice gateway
Gateway converts the voice signal to digital data &
compress
Voice packet convert them back into their original form,
sends through PSTN.
The call travels on PSTN , the person receiving the call
picks up the phone & talks.
The same way the receiver speaks the call travels to the
sender.