This is a basic presentation regrading basics of Computer Networking

1. By: Akhil Kaushik
Assistant professor, CSE Deptt

3.  Email stands for Electronic Mail
 Email is very quicker than snail mail
 It is basically an informal mail formats most
popular over the internet
 Ex: Yahoo, Gmail, Rediff, Hotmail, etc
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4.  As Email is an informal method of
communication, a lot of abbreviations &
slangs are used
 Ex: LOL = Lots Of Laughter
IMHO = In My Humble Opinion
BRB = Be Right Back
BTW = By The Way
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5. Smiley Meaning Smiley Meaning
:- ) I’m happy =):- ) Uncle Sam
:- ( I’m sad ;- ) I’m winking
: - ( o ) I’m yelling : + ) Big nose
:- )) Double chin :- {) Mustache
8 - ) Wears Glass C : -) Large brain
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6.  Sending a message to many people was inconvenient
 Message had no internal structure
 Sender never knew if a mail was delivered
 Forwarding emails was not easy
 Hard to create & send mails containing a mixture of
text, drawings, facsimile & voice
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7.  Mailboxes: to store & manage incoming email
 Mailing List: a list of email addresses
 Carbon copies: cc
 Blind carbon copies: bcc
 High-priority emails
 Encrypted emails
 Alternative recipient if original sender is not
available
 Ability to read boss’s email if he is away
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8. Email normally consists of:
1. User Agent: which allow people to read and
send email
- Local programs, interface b/w user & email
system
2. Message Transfer Agent: which move the
message from source to destination -
Daemons, runs at the background
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9.  Composition: process of creating emails
 Transfer: moving emails from sender to receiver,
also establish connection
 Reporting: tell the sender what hap to email
 Displaying: incoming emails so users can read it
 Disposition: what user does after receiving email
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10. 1. Internet Message Access Protocol
(IMAP):
It is a standard protocol for accessing email from
local server. (Port no-143)
It is a client/server based protocol in which email
is received and held for us by the mail server
We don’t need to transfer files on local pc from
mail server every time
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11. 2. Post Office Protocol (POP):
POP provides a simple, standardized
way for users to access mailboxes and download
messages to their computers (Port no-110)
In POP, all the messages will be downloaded to
the local pc from the mail server
Thus after messages have been downloaded,
internet connection can be terminated
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12. 3. Simple Mail Transfer Protocol (SMTP):
SMTP is used by Mail Transfer
Agent(MTA) to deliver our email to recipient’s mail
server.
(Port no-25)
SMTP is used only for sending emails, not for
receiving them
SMTP also works on the client server basis
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14.  WWW is an architectural framework for accessing
documents which are spread out over a no. of
machines over internet
 It a web of pages of information which is spread
around the world
 People have become aware of power of internet
thru’ WWW
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15.  It began in 1989 at CERN, the European center
for nuclear research
 It was designed to get collaboration of scientists
from across the globe
 It provides info to user on every subject
 It is basically a client server architecture
 The web pages are written in HTML or Java
 It also supports hypermedia i.e. hypertext pages
with audio, video or animation
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16.  WWW is a collection of standard protocols or
instructions, sent back & forth over internet to gain
access to information
 Internet is a network of networks – a more
physical entity
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17.  Client looks at web as vast world wide collection
of documents called pages
 Links: Each page may contain links or pointers to
related pages anywhere in world
 Hypertext: Pages which point to other pages
 Browser: Interface used for viewing pages. It
fetches requested page and displays them
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18.  Every website has a server process
 It is listening to port 80 on which incoming clients
(browsers) are connected
 Once connection is established, client sends a
request and server replies for that
 The protocol used for defining legal request and
replies in HTTP
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19. URL has 3 parts:
1. Name of protocol (ex: html)
2. Name of machine where page is located
3. Name of file containing page
Ex: http://wwww4.org/www/project.html http-
name of protocol
wwww4.org – name of machine
www/project.html – name of file
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20.  Browser determine the URL
 Browser asks DNS for IP address of URL
 Browser establishes a TCP connection to port 80
on m/c with the resolved IP address
 Browser then sends a command for file
 The specified m/c sends the requested file
 TCP connection is released
 Browser displays all text in the file
 Browser establishes a new TCP connection to
port 80 to fetch and display every images
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22.  Multimedia means combination of 2 or more
continuous media
 Media components maybe:
1. Text
2. Images or Graphics
3. Animation
4. Sound
5. Video
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23.  Multimedia applications are classified into two
types:
1. Based on timing considerations (Delay Sensitive)
2. Based on data loss tolerance (Loss Tolerant)
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24. Multimedia applications are categorized into three
classes:
1. Streaming stored audio/ video: Ex- Stored
audio songs, famous lectures, etc
2. Streaming live audio/ video: Ex- Internet
radio, Cricket match broadcast
3. Interactive audio/ video: Ex- Internet
teleconferencing and internet telephony
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25. Expectations of multimedia from internet are:-
1. Real time characteristics
2. High bandwidth
3. Multicasting support
4. Error characteristics of medium
5. Security
6. Mobility
7. Session individually
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26. “Searching the internet requires part
skills, part luck & little bit of art”

27.  Search engine is a software program that
searches for sites based on words that you
designate as search terms
 Search engines look thru’ their own database of
info to find what you are looking for
 Search engines don’t search the entire web page,
thus they make overlook the info
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28.  Search engines automatically create web site
listings by using spiders that crawl “web pages”,
index their info and optimally follows that site’s
links to other pages
 Spiders return to already crawled websites looking
for updates or changes
 Ex: Google, Altavista, Yahoo, AOL, MSN, etc
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29.  It is a search tool that sends user requests to
several other search engines and/or databases
and aggregates the result into a single list or
displays them according to their source
 It enable users to enter search criteria once &
access several search engines simultaneously
 It has a virtual database to compile the result
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31.  E-com stands for electronic commerce
 E-com refers to all commerce transactions
conducted over the internet
 E-com includes online banking, investing, bill
paying, buying & selling online
 Ex: e-bay, paying phone bill by credit card
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32.  E-com grew b/w 1993 & 2000 and influenced the
mainstream business
 To a customer, most popular use of e-com is
showing online catalogue, selecting items online &
paying it electronically i.e. retail purchase
 E-com become feasible when browsers included a
security feature for transactions
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33.  Credit cards are convenient for making large
purchases, but they incur overhead as user have
to enter credit card details
 Many groups have proposed an alternative known
as digital money or digital cash, which is
electronically equivalent of cash that people carry
with them to make small purchases & have less
overhead
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34.  An easy way to understand digital cash is in form
of debit card
 A person begins with electronic visit to bank to
authorize a withdrawal from their bank account
and place the money in digital wallet
 Bank returns the wallet, which users store on
their pc and specify them to make electronic
payment
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35.  Whenever user sends data online, there are 2
possibilities:
1. Automated security: It requires encryption i.e.
browser automatically encrypts the message
before sending it
2. Warning: If the browser doesn’t have specified
secure transfer, it issues a warning. Then, it
depends on user to send data or not
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36.  The most widely used technology is Secure
Socket Layer
 When the browser encrypts info, process is
entirely hidden from the user
 A user must look at security icon displayed by
browser (picture of padlock either locked or
unlocked) to check if encryption is used
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37.  Here, 2 different keys are used for encryption &
decryption
 Before encryption, browser must obtain app.
Encryption key of server and must verify
authenticity of both server & key
 All steps are automatically done by the browser
w/o bothering the user
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38.  It is a mechanism for authentication
 It allows a receiver to know who sent a given
electronic document in the same way as
conventional signature
 It is created by encrypting info about document
using the sender’s private key
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39.  Digital signature is different from digitized
signature, which is merely a scanned version of
conventional signature
 Another difference b/w digital signature & digitized
signature is that digital signature can’t be
duplicated
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40.  It refers to the structured transmission of data b/w
organizations by electronic means
 It is used to transfer electronic documents from
one pc to another, i.e. from one trading partner to
another trading partner
 It is more than emails and is normally not used for
monetary transactions
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41.  EDI implies a sequence of strictly formatted
messages between two parties
 In EDI, the usual processing of received
messages is by computer only
 Human intervention in the processing of a
received message is typically intended only for
error conditions, for quality review, and for special
situations
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43.  As electronic data & financial data can be crucial
for a company, security is a major aspect for
network
 Organizations face a lot of threat to security of
their info on the n/w, like:
1. Data may be stolen, misused or altered
2. Attack on hardware
3. Crash the systems, etc
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44.  Confidentiality: Data is kept private
 Authenticity: Verifying the identity of
communicating party
 Authority: Data only for authorized users
 Integrity: Data is not altered
 Availability: Data is available when required
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45. a) Physical Security Threat
b) Software Security Threat
c) Inconsistent Usage Threat (Passwords)
d) Denial of service attack
e) Virus, worms & Trojan horses
f) Data diddling & data destruction
g) Unauthorized Access
- Hacking
- Shoulder surfing
- Spoofing
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46.  Cryptography word is derived from the Greek
word kruptos, meaning hidden
 The art and science of keeping messages secure
by altering or transforming them
 It provides privacy, authorization & authentication
 It avoids eavesdropping & data diddling
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47.  Plaintext - Text that is in readable form
 Cipher text - Results from plaintext by applying
the encryption key
 Encryption - Process of converting plain text into
cipher text.
 Decryption - Process of converting cipher text
back to plain text.
 Key - Rules used to convert a plain text into
cipher text.
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48.  Also known as “Private Key Encryption”
 In this cryptography, the same key is used for
encryption & decryption
 Ex: 1. DES (Data Encryption Standard),
2. AES (Advanced Encryption Standard)
 The prevalent issue here is the distribution of the
secret key to the receiver
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50.  Also known as “Public Key Encryption”.
 In this cryptography, different keys are used for
encryption & decryption at both ends
 Example: 1. RSA (Rivest Shamir Adleman)
2. Diffie-Hellman Algorithm
 The primary concern here is the complexity of the
encryption & decryption process
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53.  Firewall is a software/ hardware which enforces
an access control policy b/w an internal n/w in an
organization & internet
 It can also be used b/w 2 parts of same internal
n/w
 A firewall blocks some traffic & permits some,
based on policy specified
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54.  It can’t protect against attacks that don’t go thru’
firewall
 It can’t protect against traitors or idiots inside the
n/w
 It can’t protect against bad things being allowed
thru’ them. Ex: Trojan horse use IRC protocol
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55. Application/ Proxy Gateways:
 First firewall
 Considered most secure
 Slowest of all
 They run a special s/w called “proxy server”,
that runs on Application layer of OSI model
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56. Packet Filtering:
 Here, routers have ACLs turned on
 Every data packet must pass thru’ firewall and
access lists
Circuits Gateways:
 Least used & least secured firewall as it do not
check data in the packet
 It used to make LAN invisible behind it
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57. Stateful packet Inspection:
 It checks contents of packet to know type of
communication
 More rigorous in packet inspections
Internet Connection Firewall:
 ICF is used by Windows XP
 It means ports on firewall are checked
 It prevents hackers to from scanning the pc
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