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Overview And Details Of Internet Technologies . Help To Reading and learning The Concept Of Internet Technologies.
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Internet Technologies Internet refers to network of networks. In this network each computer is
recognized by a globally unique address known as IP address. A special
computer DNS (Domain Name Server) is used to give name to the IP Address
so that user can locate a computer by a name.
Internet Internet is defiend as an Information super Higway, to access information
over the web. However, It can be defined in many ways as follows:
Internet is a world-wide global system of interconnected computer networks.
Internet uses the standard Internet Protocol (TCP/IP).
Every computer in internet is identified by a unique IP address.
IP Address is a unique set of numbers (such as 110.22.33.114) which identifies
a computer location.
A special computer DNS (Domain Name Server) is used to give name to the IP
Address so that user can locate a computer by a name.
For example, a DNS server will resolve a
namehttp://www.tutorialspoint.com to a particular IP address to uniquely
identify the computer on which this website is hosted.
Internet is accessible to every user all over the world.
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Evolution The concept of Internet was originated in 1969 and has undergone several
technological & Infrastructural changes as discussed below:
The origin of Internet devised from the concept of Advanced Research Project
Agency Network (ARPANET).
ARPANET was developed by United States Department of Defense.
Basic purpose of ARPANET was to provide communication among the various
bodies of government.
Initially, there were only four nodes, formally called Hosts.
In 1972, the ARPANET spread over the globe with 23 nodes located at different
countries and thus became known as Internet.
By the time, with invention of new technologies such as TCP/IP protocols, DNS,
WWW, browsers, scripting languages etc.,Internet provided a medium to
publish and access information over the web.
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Advantages Internet covers almost every aspect of life, one can think of. Here, we will
discuss some of the advantages of Internet:
Internet allows us to communicate with the people sitting at remote locations.
There are various apps available on the wed that uses Internet as a medium for
communication. One can find various social networking sites such as:
o Facebook
o Twitter
o Yahoo
o Google+
o Flickr
o Orkut
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One can surf for any kind of information over the internet. Information regarding
various topics such as Technology, Health & Science, Social Studies,
Geographical Information, Information Technology, Products etc can be surfed
with help of a search engine.
Apart from communication and source of information, internet also serves a
medium for entertainment. Following are the various modes for entertainment
over internet.
o Online Television
o Online Games
o Songs
o Videos
o Social Networking Apps
Internet allows us to use many services like:
o Internet Banking
o Matrimonial Services
o Online Shopping
o Online Ticket Booking
o Online Bill Payment
o Data Sharing
o E-mail
Internet provides concept of electronic commerce, that allows the business
deals to be conducted on electronic systems
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Disadvantages However, Internet has prooved to be a powerful source of information in
almost every field, yet there exists many disadvanatges discussed below:
There are always chances to loose personal information such as name, address,
credit card number. Therefore, one should be very careful while sharing such
information. One should use credit cards only through authenticated sites.
Another disadvantage is the Spamming.Spamming corresponds to the
unwanted e-mails in bulk. These e-mails serve no purpose and lead to
obstruction of entire system.
Virus can easily be spread to the computers connected to internet. Such virus
attacks may cause your system to crash or your important data may get
deleted.
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Also a biggest threat on internet is pornography. There are many pornographic
sites that can be found, letting your children to use internet which indirectly
affects the children healthy mental life.
There are various websites that do not provide the authenticated information.
This leads to misconception among many people.
Intranet Overview Intranet Intranet is defined as private network of computers within an organization
with its own server and firewall. Moreover we can define Intranet as:
Intranet is system in which multiple PCs are networked to be connected to each
other. PCs in intranet are not available to the world outside of the intranet.
Usually each company or organization has their own Intranet network and
members/employees of that company can access the computers in their
intranet.
Every computer in internet is identified by a unique IP address.
Each computer in Intranet is also identified by a IP Address, which is unique
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Benefits Intranet is very efficient and reliable network system for any organization.
It is beneficial in every aspect such as collaboration, cost-effectiveness,
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Communication
Intranet offers easy and cheap communication within an organization.
Employees can communicate using chat, e-mail or blogs.
Time Saving
Information on Intranet is shared in real time.
Collaboration
Information is distributed among the employees as according to
requirement and it can be accessed by the authorized users, resulting in
enhanced teamwork.
Platform Independency
Intranet can connect computers and other devices with different
architecture.
Cost Effective
Employees can see the data and other documents using browser rather
than printing them and distributing duplicate copies among the employees,
which certainly decreases the cost.
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Workforce Productivity
Data is available at every time and can be accessed using company
workstation. This helps the employees work faster.
Business Management
It is also possible to deploy applications that support business operations.
Security
Since information shared on intranet can only be accessed within an
organization, therefore there is almost no chance of being theft.
Specific Users
Intranet targets only specific users within an organization therefore, once
can exactly know whom he is interacting.
Immediate Updates
Any changes made to information are reflected immediately to all the users.
Issues Apart from several benefits of Intranet, there also exist some issues.. These
issues are shown in the following diagram:
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Applications Intranet applications are same as that of Internet applications. Intranet
applications are also accessed through a web browser. The only difference
is that, Intranet applications reside on local server while Internet
applications reside on remote server. Here, we've discussed some of these
applications: Par
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Document publication applications
Document publication applications allow publishing documents such as
manuals, software guide, employee profits etc without use of paper.
Electronic resources applications
It offers electronic resources such as software applications, templates and
tools, to be shared across the network.
Interactive Communication applications
Like on internet, we have e-mail and chat like applications for Intranet,
hence offering an interactive communication among employees.
Support for Internet Applications
Intranet offers an environment to deploy and test applications before
placing them on Internet.
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Internet vs. Intranet Apart from similarities there are some differences between the two.
Following are the differences between Internet and Intranet:
Intranet Internet
Localized Network. Worldwide Network
Doesn't have access to Intranet Have access to Internet.
More Expensive Less Expensive
More Safe Less Safe
More Reliability Less Reliability
Extranet Overview Extranet Extranet refers to network within an organization, using internet to connect
to the outsiders in controlled manner. It helps to connect businesses with
their customers and suppliers and therefore allows working in a
collaborative manner.
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Implementation
Extranet is implemented as a Virtual Private Networks (VPN) because it
uses internet to connect to corporate organization and there is always a
threat to information security. VPN offers a secure network in public
infrastructure (Internet).
Key Points
The packet is encapsulated at boundary of networks in IPSEC complaint routers.
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It uses an encryption key to encapsulate packets and IP addresses as well.
The packet is decoded only by the IPSEC complaint routers or servers.
The message is sent over VPN via VPN Tunnel and this process is known as
tunneling.
VPN uses Internet Protocol Security Architecture (IPSEC) Protocol to
provide secure transactions by adding an additional security layer to TCP/IP
protocol. This layer is created by encapsulating the IP packet to a new IP
packet as shown in the following diagram:
Benefits Extranet proves to be a successful model for all kind of businesses whether
small or big. Here are some of the advantages of extranet for employees,
suppliers, business partners, and customers:
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Issues Apart for advantages there are also some issues associated with extranet.
These issues are discussed below:
Hosting
Where the extranet pages will be held i.e. who will host the extranet pages.
In this context there are two choices:
Host it on your own server.
Host it with an Internet Service Provider (ISP) in the same way as web pages.
But hosting extranet pages on your own server requires high bandwidth
internet connection which is very costly.
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Security
Additional firewall security is required if you host extranet pages on your
own server which result in a complex security mechanism and increase
work load.
Accessing Issues
Information can not be accessed without internet connection. However,
information can be accessed in Intranet without internet connection.
Decreased Interaction
It decreases the face to face interaction in the business which results in lack
of communication among customers, business partners and suppliers.
Extranet vs. Intranet The following table shows differences between Extranet and Intranet:
Extranet Intranet
Internal network that can be accessed externally. Internal network that can not be
accessed externally.
Extranet is extension of company's Intranet. Only limited users of a company.
For limited external communication between
customers, suppliers and business partners.
Only for communication within a
company.
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Internet Reference Models Reference Model Reference Model offers a means of standardization which is acceptable
worldwide. Since people using the computer network are located over a
wide physical range and their network devices might have heterogeneous
architecture. In order to provide communication among heterogeneous
devices, we need a standardized model i.e. a reference model, which would
provide us way how these devices can communicate regardless their
architecture.
We have two reference models such as OSI model and TCP/IP reference
model, however, the OSI model is a hypothetical one but the TCP/IP is
absolutely practical model.
OSI Model OSI is acronym of Open System Interface. This model is developed by
theInternational organization of Standardization (ISO) and therefore
also referred as ISO-OSI Model.
The OSI model consists of seven layers as shown in the following diagram.
Each layer has a specific function, however each layer provide services to
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Physical Layer
The Physical layer is responsible for the following activities:
Activating, maintaining and deactivating the physical connection.
Defining voltages and data rates needed for transmission.
Converting digital bits into electrical signal.
Deciding whether the connection is simplex, half duplex or full duplex.
Data Link Layer
The data link layer performs the following functions:
Performs synchronization and error control for the information which is to be
transmitted over the physical link.
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Enables error detection, and adds error detection bits to the data which are to
be transmitted.
Network Layer
Following are the functions of Network Layer:
To route the signals through various channels to the other end.
To act as the network controller by deciding which route data should take.
To divide the outgoing messages into packets and to assemble incoming packets
into messages for higher levels.
Transport Layer
The Transport layer performs the following functions:
It decides if the data transmission should take place on parallel paths or single
path.
It performs multiplexing, splitting on the data.
It breaks the data groups into smaller units so that they are handled more
efficiently by the network layer.
The Transport Layer guarantees transmission of data from one end to other end.
Session Layer
The Session layer performs the following functions:
Manages the messages and synchronizes conversations between two different
applications.
It controls logging on and off, user identification, billing and session
management.
Presentation Layer
The Presentation layer performs the following functions:
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This layer makes it sure that the information is delivered in such a form that the
receiving system will understand and use it.
Application Layer
The Application layer performs the following functions:
It provides different services such as manipulation of information in several
ways, retransferring the files of information, distributing the results etc.
The functions such as LOGIN or password checking are also performed by the
application layer.
TCP/IP Model TCP/IP model is practical model and is used in the Internet. TCP/IP is
acronym of Transmission Control Protocol and Internet Protocol.
The TCP/IP model combines the two layers (Physical and Data link layer)
into one layer i.e. Host-to-Network layer. The following diagram shows
the various layers of TCP/IP model:
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Application Layer
This layer is same as that of the OSI model and performs the following
functions:
It provides different services such as manipulation of information in several
ways, retransferring the files of information, distributing the results etc.
The functions such as LOGIN or password checking are also performed by the
application layer.
Protocols used: TELNET, FTP, SMTP, DN, HTTP, NNTP are the protocols employed
in this layer.
Transport Layer
It does the same functions as that of transport layer in OSI model. Here are
the key points regarding transport layer:
It uses TCP and UDP protocol for end to end transmission.
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TCP is reliable and connection oriented protocol.
TCP also handles flow control.
The UDP is not reliable and a connection less protocol also does not perform
flow control.
Protocols used: TCP/IP and UDP protocols are employed in this layer.
Internet Layer
The function of this layer is to allow the host to insert packets into network
and then make them travel independently to the destination. However, the
order of receiving the packet can be different from the sequence they were
sent.
Protocols used: Internet Protocol (IP) is employed in Internet layer.
Host-to-Network Layer
This is the lowest layer in TCP/IP model. The host has to connect to network
using some protocol, so that it can send IP packets over it. This protocol
varies from host to host and network to network.
Protocols used: ARPANET, SATNET, LAN, packet radio are the protocols which are
used in this layer.
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Internet Domain Name System Overview When DNS was not into existence, one had to download a Host
file containing host names and their corresponding IP address. But with
increase in number of hosts of internet, the size of host file also increased.
This resulted in increased traffic on downloading this file. To solve this
problem the DNS system was introduced.
Domain Name System helps to resolve the host name to an address. It
uses a hierarchical naming scheme and distributed database of IP addresses
and associated names
IP Address IP address is a unique logical address assigned to a machine over the
network. An IP address exhibits the following properties:
IP address is the unique address assigned to each host present on Internet.
IP address is 32 bits (4 bytes) long.
IP address consists of two components: network component andhost
component.
Each of the 4 bytes is represented by a number from 0 to 255, separated with
dots. For example 137.170.4.124
IP address is 32-bit number while on the other hand domain names are easy to
remember names. For example, when we enter an email address we always enter a
symbolic string such as [email protected].
Uniform Resource Locator (URL) Uniform Resource Locator (URL) refers to a web address which uniquely
identifies a document over the internet.
This document can be a web page, image, audio, video or anything else present on the
web.
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For
example, www.mywebsite.com/internet_technology/index.htmlis an
URL to the index.html which is stored on mywebsite web server under
internet_technology directory.
URL Types
There are two forms of URL as listed below:
1. Absolute URL
2. Relative URL
ABSOLUTE URL
Absolute URL is a complete address of a resource on the web. This
completed address comprises of protocol used, server name, path name
and file name.
For example http:// www.mywebsite.com / internet_technology /index.htm.
where:
http is the protocol.
mywebsite.com is the server name.
index.htm is the file name.
The protocol part tells the web browser how to handle the file. Similarly we
have some other protocols also that can be used to create URL are:
FTP
https
Gopher
mailto
news
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RELATIVE URL
Relative URL is a partial address of a webpage. Unlike absolute URL, the
protocol and server part are omitted from relative URL.
Relative URLs are used for internal links i.e. to create links to file that are part of same
website as the WebPages on which you are placing the link.
For example, to link an image on
mywebsite.com/internet_technology/internet_referemce_models, we can
use the relative URL which can take the form
like/internet_technologies/internet-osi_model.jpg.
Difference between Absolute and Relative URL
Absolute URL Relative URL
Used to link web pages on different
websites
Used to link web pages within the same
website.
Difficult to manage. Easy to Manage
Changes when the server name or
directory name changes
Remains same even of we change the server
name or directory name.
Take time to access Comparatively faster to access.
Domain Name System Architecture The Domain name system comprises of Domain Names, Domain Name
Space, Name Server that have been described below:
Domain Names
Domain Name is a symbolic string associated with an IP address. There are
several domain names available; some of them are generic such as com,
edu, gov, net etc, while some country level domain names such as au, in,
za, usetc.
The following table shows the Generic Top-Level Domain names:
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Domain Name Meaning
Com Commercial business
Edu Education
Gov U.S. government agency
Int International entity
Mil U.S. military
Net Networking organization
Org Non profit organization
The following table shows the Country top-level domain names:
Domain Name Meaning
Au Australia
In India
Cl Chile
Fr France
Us United States
Za South Africa
Uk United Kingdom
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Jp Japan
Es Spain
De Germany
Ca Canada
Ee Estonia
Hk Hong Kong
Domain Name Space
The domain name space refers a hierarchy in the internet naming structure.
This hierarchy has multiple levels (from 0 to 127), with a root at the top.
The following diagram shows the domain name space hierarchy:
In the above diagram each subtree represents a domain. Each domain can
be partitioned into sub domains and these can be further partitioned and so
on.
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Name Server
Name server contains the DNS database. This database comprises of
various names and their corresponding IP addresses. Since it is not possible
for a single server to maintain entire DNS database, therefore, the
information is distributed among many DNS servers.
Hierarchy of server is same as hierarchy of names.
The entire name space is divided into the zones
Zones
Zone is collection of nodes (sub domains) under the main domain. The
server maintains a database called zone file for every zone.
If the domain is not further divided into sub domains then domain and zone refers to
the same thing.
The information about the nodes in the sub domain is stored in the servers
at the lower levels however; the original server keeps reference to these
lower levels of servers.
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TYPES OF NAME SERVERS
Following are the three categories of Name Servers that manages the entire
Domain Name System:
1. Root Server
2. Primary Server
3. Secondary Server
ROOT SERVER
Root Server is the top level server which consists of the entire DNS tree. It
does not contain the information about domains but delegates the authority
to the other server
PRIMARY SERVERS
Primary Server stores a file about its zone. It has authority to create,
maintain, and update the zone file.
SECONDARY SERVER
Secondary Server transfers complete information about a zone from
another server which may be primary or secondary server. The secondary
server does not have authority to create or update a zone file.
DNS Working DNS translates the domain name into IP address automatically. Following
steps will take you through the steps included in domain resolution process:
When we type www.mywebsite.com into the browser, it asks the local DNS
Server for its IP address.
Here the local DNS is at ISP end.
When the local DNS does not find the IP address of requested domain name, it
forwards the request to the root DNS server and again enquires about IP
address of it.
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The root DNS server replies with delegation that I do not know the IP
address of www.mywebsite.com but know the IP address of DNS
Server.
The local DNS server then asks the com DNS Server the same question.
The com DNS Server replies the same that it does not know the IP address of
www.mywebsite.com but knows the address of tutorialspoint.com.
Then the local DNS asks the tutorialspoint.com DNS server the same question.
Then mywebsite.com DNS server replies with IP address of
www.mywebsite.com.
Now, the local DNS sends the IP address of www.mywebsite.com to the
computer that sends the request.
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Internet Services Internet Services allows us to access huge amount of information such as
text, graphics, sound and software over the internet. Following diagram
shows the four different categories of Internet Services.
Communication Services There are various Communication Services available that offer exchange of
information with individuals or groups. The following table gives a brief
introduction to these services:
S.N. Service Description
1 Electronic Mail
Used to send electronic message over the internet.
2 Telnet
Used to log on to a remote computer that is attached to internet.
3 Newsgroup
Offers a forum for people to discuss topics of common interests.
4 Internet Relay Chat (IRC)
Allows the people from all over the world to communicate in real time.
5 Mailing Lists
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Used to organize group of internet users to share common information
through e-mail.
6
Internet Telephony (VoIP)
Allows the internet users to talk across internet to any PC equipped to receive
the call.
7
Instant Messaging
Offers real time chat between individuals and group of people. Eg. Yahoo
messenger, MSN messenger.
Information Retrieval Services There exist several Information retrieval services offering easy access to
information present on the internet. The following table gives a brief
introduction to these services:
S.N. Service Description
1 File Transfer Protocol (FTP)
Enable the users to transfer files.
2
Archie
It’s updated database of public FTP sites and their content. It helps to search
a file by its name.
3 Gopher
Used to search, retrieve, and display documents on remote sites.
4
Very Easy Rodent Oriented Netwide Index to Computer Achieved
(VERONICA)
VERONICA is gopher based resource. It allows access to the information
resource stored on gopher’s servers.
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Web Services Web services allow exchange of information between applications on the
web. Using web services, applications can easily interact with each other.
The web services are offered using concept of Utility Computing.
World Wide Web (WWW) WWW is also known as W3. It offers a way to access documents spread
over the several servers over the internet. These documents may contain
texts, graphics, audio, video, hyperlinks. The hyperlinks allow the users to
navigate between the documents.
Video Conferencing Video conferencing or Video teleconferencing is a method of communicating
by two-way video and audio transmission with help of telecommunication
technologies.
Modes of Video Conferencing
POINT-TO-POINT
This mode of conferencing connects two locations only.
MULTI-POINT
This mode of conferencing connects more than two locations through
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Multi-point Control Unit (MCU).
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Internet Connectivity Here in this tutorial, we will discuss how to connect to internet i.e. internet
service providers, software and hardware requirements, configuring internet
connection etc.
Internet Service Providers (ISP) Internet Service Provider (ISP) is a company offering access to internet.
They offer various services:
Internet Access
Domain name registration
Dial-up access
Leased line access
ISP Types
ISPs can broadly be classified into six categories as shown in the following
diagram:
ACCESS PROVIDERS
They provide access to internet through telephone lines, cable wi-fi or fiber
optics.
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MAILBOX PROVIDER
Such providers offer mailbox hosting services.
HOSTING ISPS
Hosting ISPs offers e-mail, and other web hosting services such as virtual
machines, clouds etc.
VIRTUAL ISPS
Such ISPs offer internet access via other ISP services.
FREE ISPS
Free ISPs do not charge for internet services.
Connection Types There exist several ways to connect to the internet. Following are these
connection types available:
1. Dial-up Connection
2. ISDN
3. DSL
4. Cable TV Internet connections
5. Satellite Internet connections
6. Wireless Internet Connections
Dial-up Connection
Dial-up connection uses telephone line to connect PC to the internet. It
requires a modem to setup dial-up connection. This modem works as an
interface between PC and the telephone line.
There is also a communication program that instructs the modem to make a
call to specific number provided by an ISP.
Dial-up connection uses either of the following protocols:
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1. Serial Line Internet Protocol (SLIP)
2. Point to Point Protocol (PPP)
The following diagram shows the accessing internet using modem:
ISDN
ISDN is acronym of Integrated Services Digital Network. It establishes
the connection using the phone lines which carry digital signals instead of
analog signals.
There are two techniques to deliver ISDN services:
1. Basic Rate Interface (BRI)
2. Primary Rate Interface (PRI)
Key points:
The BRI ISDN consists of three distinct channels on a single ISDN line: t1o
64kbps B (Bearer) channel and one 16kbps D (Delta or Data) channels.
The PRI ISDN consists of 23 B channels and one D channels with both have
operating capacity of 64kbps individually making a total transmission rate of
1.54Mbps.
The following diagram shows accessing internet using ISDN connection:
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DSL
DSL is acronym of Digital Subscriber Line. It is a form of broadband
connection as it provides connection over ordinary telephone lines.
Following are the several versions of DSL technique available today:
1. Asymmetric DSL (ADSL)
2. Symmetric DSL (SDSL)
3. High bit-rate DSL (HDSL)
4. Rate adaptive DSL (RDSL)
5. Very high bit-rate DSL (VDSL)
6. ISDN DSL (IDSL)
All of the above mentioned technologies differ in their upload and download
speed, bit transfer rate and level of service.
The following diagram shows that how we can connect to internet using DSL
technology:
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Cable TV Internet Connection
Cable TV Internet connection is provided through Cable TV lines. It uses
coaxial cable which is capable of transferring data at much higher speed
than common telephone line.
Key Points:
A cable modem is used to access this service, provided by the cable operator.
The Cable modem comprises of two connections: one for internet service and
other for Cable TV signals.
Since Cable TV internet connections share a set amount of bandwidth with a
group of customers, therefore, data transfer rate also depends on number of
customers using the internet at the same time.
The following diagram shows that how internet is accessed using Cable TV
connection:
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Satellite Internet Connection
Satellite Internet connection offers high speed connection to the internet.
There are two types of satellite internet connection: one way connection or
two way connection.
In one way connection, we can only download data but if we want to
upload, we need a dialup access through ISP over telephone line.
In two way connection, we can download and upload the data by the
satellite. It does not require any dialup connection.
The following diagram shows how internet is accessed using satellite
internet connection:
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Wireless Internet Connection
Wireless Internet Connection makes use of radio frequency bands to
connect to the internet and offers a very high speed. The wireless internet
connection can be obtained by either WiFi or Bluetooth.
Key Points:
Wi Fi wireless technology is based on IEEE 802.11 standards which allow the
electronic device to connect to the internet.
Bluetooth wireless technology makes use of short-wavelength radio waves and
helps to create personal area network (PAN).
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Internet Protocols Transmission Control Protocol (TCP) TCP is a connection oriented protocol and offers end-to-end packet delivery.
It acts as back bone for connection.It exhibits the following key features:
Transmission Control Protocol (TCP) corresponds to the Transport Layer of OSI
Model.
TCP is a reliable and connection oriented protocol.
TCP offers:
o Stream Data Transfer.
o Reliability.
o Efficient Flow Control
o Full-duplex operation.
o Multiplexing.
TCP offers connection oriented end-to-end packet delivery.
TCP ensures reliability by sequencing bytes with a forwarding acknowledgement
number that indicates to the destination the next byte the source expect to
receive.
It retransmits the bytes not acknowledged with in specified time period.
TCP Services
TCP offers following services to the processes at the application layer:
Stream Delivery Service
Sending and Receiving Buffers
Bytes and Segments
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Full Duplex Service
Connection Oriented Service
Reliable Service
STREAM DELIVER SERVICE
TCP protocol is stream oriented because it allows the sending process to
send data as stream of bytes and the receiving process to obtain data as
stream of bytes.
SENDING AND RECEIVING BUFFERS
It may not be possible for sending and receiving process to produce and
obtain data at same speed, therefore, TCP needs buffers for storage at
sending and receiving ends.
BYTES AND SEGMENTS
The Transmission Control Protocol (TCP), at transport layer groups the
bytes into a packet. This packet is called segment. Before transmission of
these packets, these segments are encapsulated into an IP datagram.
FULL DUPLEX SERVICE
Transmitting the data in duplex mode means flow of data in both the
directions at the same time.
CONNECTION ORIENTED SERVICE
TCP offers connection oriented service in the following manner:
1. TCP of process-1 informs TCP of process – 2 and gets its approval.
2. TCP of process – 1 and TCP of process – 2 and exchange data in both the two
directions.
3. After completing the data exchange, when buffers on both sides are empty, the
two TCP’s destroy their buffers.
RELIABLE SERVICE
For sake of reliability, TCP uses acknowledgement mechanism.
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Internet Protocol (IP) Internet Protocol is connectionless and unreliable protocol. It ensures no
guarantee of successfully transmission of data.
In order to make it reliable, it must be paired with reliable protocol such as
TCP at the transport layer.
Internet protocol transmits the data in form of a datagram as shown in the
following diagram:
Points to remember:
The length of datagram is variable.
The Datagram is divided into two parts: header and data.
The length of header is 20 to 60 bytes.
The header contains information for routing and delivery of the packet.
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User Datagram Protocol (UDP) Like IP, UDP is connectionless and unreliable protocol. It doesn’t require
making a connection with the host to exchange data. Since UDP is
unreliable protocol, there is no mechanism for ensuring that data sent is
received.
UDP transmits the data in form of a datagram. The UDP datagram consists
of five parts as shown in the following diagram:
Points to remember:
UDP is used by the application that typically transmit small amount of data at
one time.
UDP provides protocol port used i.e. UDP message contains both source and
destination port number, that makes it possible for UDP software at the
destination to deliver the message to correct application program.
File Transfer Protocol (FTP) FTP is used to copy files from one host to another. FTP offers the
mechanism for the same in following manner:
FTP creates two processes such as Control Process and Data Transfer Process at
both ends i.e. at client as well as at server.
FTP establishes two different connections: one is for data transfer and other is
for control information.
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Control connection is made between control processes while Data
Connection is made between<="" b="" style="box-sizing: border-box;">
FTP uses port 21 for the control connection and Port 20 for the data
connection.
Trivial File Transfer Protocol (TFTP) Trivial File Transfer Protocol is also used to transfer the files but it
transfers the files without authentication. Unlike FTP, TFTP does not
separate control and data information. Since there is no authentication
exists, TFTP lacks in security features therefore it is not recommended to
use TFTP.
Key points
TFTP makes use of UDP for data transport. Each TFTP message is carried in
separate UDP datagram.
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The first two bytes of a TFTP message specify the type of message.
The TFTP session is initiated when a TFTP client sends a request to upload or
download a file.
The request is sent from an ephemeral UDP port to the UDP port 69 of an TFTP
server.
Difference between FTP and TFTP
S.N. Parameter FTP TFTP
1 Operation Transferring Files Transferring Files
2 Authentication Yes No
3 Protocol TCP UDP
4 Ports 21 – Control, 20 – Data Port 3214, 69, 4012
5 Control and Data Separated Separated
6 Data Transfer Reliable Unreliable
Telnet Telnet is a protocol used to log in to remote computer on the internet.
There are a number of Telnet clients having user friendly user interface. The
following diagram shows a person is logged in to computer A, and from
there, he remote logged into computer B.
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Hyper Text Transfer Protocol (HTTP) HTTP is a communication protocol. It defines mechanism for communication
between browser and the web server. It is also called request and response
protocol because the communication between browser and server takes
place in request and response pairs.
HTTP Request
HTTP request comprises of lines which contains:
Request line
Header Fields
Message body
Key Points
The first line i.e. the Request line specifies the request method i.e.Get or Post.
The second line specifies the header which indicates the domain name of the
server from where index.htm is retrieved.
HTTP Response
Like HTTP request, HTTP response also has certain structure. HTTP
response contains:
Status line
Headers
Message body
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E-mail Overview Email Email is a service which allows us to send the message in electronic mode
over the internet. It offers an efficient, inexpensive and real time mean of
distributing information among people.
E-Mail Address
Each user of email is assigned a unique name for his email account. This
name is known as E-mail address. Different users can send and receive
messages according to the e-mail address.
E-mail is generally of the form username@domainname. For example,
[email protected] is an e-mail address where webmaster is
username and tutorialspoint.com is domain name.
The username and the domain name are separated by & (at) symbol.
E-mail addresses are not case sensitive.
Spaces are not allowed in e-mail address.
E-mail Message Components E-mail message comprises of different components: E-mail Header,
Greeting, Text, and Signature. These components are described in the
following diagram:
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E-mail Header
The first five lines of an E-mail message is called E-mail header. The header
part comprises of following fields:
From
Date
To
Subject
CC
BCC
FROM
The From field indicates the sender’s address i.e. who sent the e-mail.
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DATE
The Date field indicates the date when the e-mail was sent.
TO
The To field indicates the recipient’s address i.e. to whom the e-mail is
sent.
SUBJECT
The Subject field indicates the purpose of e-mail. It should be precise and
to the point.
CC
CC stands for Carbon copy. It includes those recipient addresses whom we
want to keep informed but not exactly the intended recipient.
BCC
BCC stands for Black Carbon Copy. It is used when we do not want one or
more of the recipients to know that someone else was copied on the
message.
GREETING
Greeting is the opening of the actual message. Eg. Hi Sir or Hi Guys etc.
TEXT
It represents the actual content of the message.
SIGNATURE
This is the final part of an e-mail message. It includes Name of Sender,
Address, and Contact Number.
Advantages E-mail has prooved to be powerful and reliable medium of
commmunication. Here are the benefits of E-mail:
Reliable
Convenience
Speed
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Inexpensive
Printable
Global
Generality
Reliable
Many of the mail systems notify the sender if e-mail message was
undeliverable.
Convenience
There is no requirement of stationary and stamps. One does not have to go
to post office. But all these things are not required for sending or receiving
an mail.
Speed
E-mail is very fast. However, the speed also depends upon the underlying
network.
Inexpensive
The cost of sending e-mail is very low.
Printable
It is easy to obtain a hardcopy of an e-mail. Also an electronic copy of an e-
mail can also be saved for records.
Global
E-mail can be sent and received by a person sitting across the globe.
Generality
It is also possible to send graphics, programs and sounds with an e-mail.
Disadvantages Apart from several benefits of E-mail, there also exists some disadvantages
as discussed below:
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Forgery
Overload
Misdirection
Junk
No response
Forgery
E-mail doesn’t prevent from forgery, that is, someone impersonating the
sender, since sender is usually not authenticated in any way.
Overload
Convenience of E-mail may result in a flood of mail.
Misdirection
It is possible that you may send e-mail to an unintended recipient.
Junk
Junk emails are undesirable and inappropriate emails. Junk emails are
sometimes referred to as spam.
No Response
It may be frustrating when the recipient does not read the e-mail and
respond on a regular basis.
E-mail Protocols E-mail Protocols are set of rules that help the client to properly transmit the
information to or from the mail server. Here in this tutorial, we will discuss
various protocols such as SMTP, POP, and IMAP.
SMPTP SMTP stands for Simple Mail Transfer Protocol. It was first proposed in
1982. It is a standard protocol used for sending e-mail efficiently and
reliably over the internet.
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Key Points:
SMTP is application level protocol.
SMTP is connection oriented protocol.
SMTP is text based protocol.
It handles exchange of messages between e-mail servers over TCP/IP network.
Apart from transferring e-mail, SMPT also provides notification regarding
incoming mail.
When you send e-mail, your e-mail client sends it to your e-mail server which
further contacts the recipient mail server using SMTP client.
These SMTP commands specify the sender’s and receiver’s e-mail address, along
with the message to be send.
The exchange of commands between servers is carried out without intervention
of any user.
In case, message cannot be delivered, an error report is sent to the sender
which makes SMTP a reliable protocol.
SMTP Commands
The following table describes some of the SMTP commands:
S.N. Command Description
1 HELLO
This command initiates the SMTP conversation.
2
EHELLO
This is an alternative command to initiate the conversation. ESMTP indicates
that the sender server wants to use extended SMTP protocol.
3 MAIL FROM
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This indicates the sender’s address.
4
RCPT TO
It identifies the recipient of the mail. In order to deliver similar message to
multiple users this command can be repeated multiple times.
5 SIZE
This command let the server know the size of attached message in bytes.
6
DATA
The DATA command signifies that a stream of data will follow. Here stream
of data refers to the body of the message.
7 QUIT
This commands is used to terminate the SMTP connection.
8
VERFY
This command is used by the receiving server in order to verify whether the
given username is valid or not.
9
EXPN
It is same as VRFY, except it will list all the users name when it used with a
distribution list.
IMAP IMAP stands for Internet Mail Access Protocol. It was first proposed in
1986. There exist five versions of IMAP as follows:
1. Original IMAP
2. IMAP2
3. IMAP3
4. IMAP2bis
5. IMAP4
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Key Points:
IMAP allows the client program to manipulate the e-mail message on the server
without downloading them on the local computer.
The e-mail is hold and maintained by the remote server.
It enables us to take any action such as downloading, delete the mail without
reading the mail.It enables us to create, manipulate and delete remote message
folders called mail boxes.
IMAP enables the users to search the e-mails.
It allows concurrent access to multiple mailboxes on multiple mail servers.
IMAP Commands
The following table describes some of the IMAP commands:
S.N. Command Description
1 IMAP_LOGIN
This command opens the connection.
2 CAPABILITY
This command requests for listing the capabilities that the server supports.
3
NOOP
This command is used as a periodic poll for new messages or message status
updates during a period of inactivity.
4 SELECT
This command helps to select a mailbox to access the messages.
5
EXAMINE
It is same as SELECT command except no change to the mailbox is
permitted.
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6 CREATE
It is used to create mailbox with a specified name.
7 DELETE
It is used to permanently delete a mailbox with a given name.
8 RENAME
It is used to change the name of a mailbox.
9
LOGOUT
This command informs the server that client is done with the session. The
server must send BYE untagged response before the OK response and then
close the network connection.
POP POP stands for Post Office Protocol. It is generally used to support a single
client. There are several versions of POP but the POP 3 is the current
standard.
Key Points
POP is an application layer internet standard protocol.
Since POP supports offline access to the messages, thus requires less internet
usage time.
POP does not allow search facility.
In order to access the messaged, it is necessary to download them.
It allows only one mailbox to be created on server.
It is not suitable for accessing non mail data.
POP commands are generally abbreviated into codes of three or four letters. Eg.
STAT.
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POP Commands
The following table describes some of the POP commands:
S.N. Command Description
1 LOGIN
This command opens the connection.
2 STAT
It is used to display number of messages currently in the mailbox.
3
LIST
It is used to get the summary of messages where each message summary is
shown.
4 RETR
This command helps to select a mailbox to access the messages.
5 DELE
It is used to delete a message.
6 RSET
It is used to reset the session to its initial state.
7 QUIT
It is used to log off the session.
Comparison between POP and IMAP
S.N. POP IMAP
1 Generally used to support single client. Designed to handle multiple clients.
2 Messages are accessed offline. Messages are accessed online
although it also supports offline
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mode.
3 POP does not allow search facility. It offers ability to search emails.
4 All the messages have to be
downloaded.
It allows selective transfer of
messages to the client.
5 Only one mailbox can be created on the
server.
Multiple mailboxes can be created
on the server.
6 Not suitable for accessing non-mail
data.
Suitable for accessing non-mail data
i.e. attachment.
7
POP commands are generally
abbreviated into codes of three or four
letters. Eg. STAT.
IMAP commands are not
abbreviated, they are full. Eg.
STATUS.
8 It requires minimum use of server
resources.
Clients are totally dependent on
server.
9 Mails once downloaded cannot be
accessed from some other location.
Allows mails to be accessed from
multiple locations.
10 The e-mails are not downloaded
automatically.
Users can view the headings and
sender of e-mails and then decide to
download.
10 POP requires less internet usage time. IMAP requires more internet usage
time.
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E-mail Working E-mail System E-mail system comprises of the following three components:
Mailer
Mail Server
Mailbox
Mailer
It is also called mail program, mail application or mail client. It allows
us to manage, read and compose e-mail.
Mail Server
The function of mail server is to receive, store and deliver the email. It is
must for mail servers to be sunning all the time because if it crashes or is
down, email can be lost.
Mailboxes
Mailbox is generally a folder that contains emails and information about
them.
Working of E-mail Email working follows the client server approach. In this client is the mailer
i.e. the mail application or mail program and server is a device that
manages emails.
Following example will take you through the basic steps involved in sending
and receiving emails and will give you a better understanding of working of
email system:
Suppose person A wants to send an email message to person B.
Person A composes the messages using a mailer program i.e. mail client and
then select Send option.
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The message is routed to Simple Mail Transfer Protocol to person B’s mail
server.
The mail server stores the email message on disk in an area designated for
person B.
The disk space area on mail server is called mail spool.
Now, suppose person B is running a POP client and knows how to communicate
with B’s mail server.
It will periodically poll the POP server to check if any new email has arrived for
B.As in this case, person B has sent an email for person B, so email is
forwarded over the network to B’s PC. This is message is now stored on person
B’s PC.
The following diagram gives pictorial representation of the steps discussed
above:
Email Operations Here we will discuss the operations that can be performed on an e-mail. But
first of all we will learn how to create an email account.
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Creating Email Account There are various email service provider available such as Gmail, hotmail,
ymail, rediff mail etc. Here we will learn how to create an account using
Gmail.
Open gmail.com and click create an account.
Now a form will appear. Fill your details here and click Next Step.
This step allows you to add your picture. If you don’t want to upload now, you
can do it later. Click Next Step.
Now a welcome window appears. Click Continue to Gmail.
Wow!! You are done with creating your email account with Gmail. It’s that easy.
Isn’t it?
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Now you will see your Gmail account as shown in the following image:
Key Points:
Gmail manages the mail into three categories namely Primary,
Socialand Promotions.
Compose option is given at the right to compose an email message.
Inbox, Starred, Sent mail, Drafts options are available on the left pane which
allows you to keep track of your emails.
Composing and Sending Email Before sending an email, we need to compose a message. When we are
composing an email message, we specify the following things:
Sender’s address in To field
Cc (if required)
Bcc (if required)
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Subject of email message
Text
Signature
You should specify the correct email address; otherwise it will send an error back to the
sender.
Once you have specified all the above parameters, It’s time to send the
email. The mailer program provides a Send button to send email, when you
click Send, it is sent to the mail server and a message mail sent
successfully is shown at the above.
Reading Email Every email program offers you an interface to access email messages. Like
in Gmail, emails are stored under different tabs such as primary, social, and
promotion. When you click one of tab, it displays a list of emails under that
tab.
In order to read an email, you just have to click on that email. Once you
click a particular email, it gets opened.
The opened email may have some file attached with it. The attachments are
shown at the bottom of the opened email with an option called download
attachment.
Replying Email After reading an email, you may have to reply that email. To reply an email,
click Reply option shown at the bottom of the opened email.
Once you click on Reply, it will automatically copy the sender’s address in to
the To field. Below the To field, there is a text box where you can type the
message.
Once you are done with entering message, click Send button. It’s that easy.
Your email is sent.
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Forwarding Email It is also possible to send a copy of the message that you have received
along with your own comments if you want. This can be done
using forward button available in mail client software.
The difference between replying and forwarding an email is that when you
reply a message to a person who has send the mail but while forwarding
you can send it to anyone.
When you receive a forwarded message, the message is marked with a >
character in front of each line and Subject: field is prefixed with Fw.
Deleting Email If you don’t want to keep email into your inbox, you can delete it by simply
selecting the message from the message list and clicking delete or pressing
the appropriate command.
Some mail clients offers the deleted mails to be stored in a folder called
deleted items or trash from where you can recover a deleted email.
E-mail Features Now a day, the mail client comes with enhanced features such as
attachment, address book, and MIME support. Here in this chapter we will
discuss all of these features which will give you a better understanding of
added feature of a mail client program.
Attachment Ability to attach file(s) along with the message is one of the most useful
features of email. The attachment may be a word document, PowerPoint
presentation, audio/video files, or images.
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In order to attach file(s) to an email, click the attach button. As a result, a
dialog box appears asking for specifying the name and location of the file you
want to attach.
Once you have selected the appropriate file, it is attached to the mail.
Usually a paper clip icon appears in the email which indicates that it has an
attachment.
When adding an attachment it is better to compress the attached files so as to
reduce the file size and save transmission time as sending and downloading
large files consumes a lot of space and time.
Address Book Address book feature of a mail program allows the users to store
information about the people whom they communicate regularly by sending
emails. Here are some of the key features of an Address book:
Address book includes the nick names, email addresses, phone number etc. of
the people.
Using address book allows us not to memorize email of address of a person, you
just have to select recipient name from the list.
When you select a particular name from the list, the corresponding email
address link automatically get inserted in to the To: field.
Address book also allows creating a group so that you can send a email to very
member of the group at once instead of giving each person email address one
by one.
MIME Types MIME is acronym of Multipurpose Internet Mail Extensions. MIME
compliant mailer allows us to send files other than simple text i.e. It allows
us to send audio, video, images, document, and pdf files as an attachment
to an email.
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Suppose if you want to send a word processor document that has a group
of tabular columns with complex formatting. If we transfer the file as text,
all the formatting may be lost. MIME compliant mailer takes care of messy
details and the message arrives as desired.
The following table describes commonly used MIME Types:
1. Type Subtype Description File
extension(s)
2. Application
postscript
tex
troff
Printable postscript document
TEX document
Printable troff document
.eps, .ps
.tex
.t, .tr, .roff
3. Audio
aiff
au
midi
real
audio
Apple sound
Sun Microsystems sound
Musical Instrument Digital Interface
Progressive Network sound
.aif, .aiff,.aifc
.au, .snd
.midi, .mid
.ra, .ram
4. image
gif
jpeg
png
triff
Graphics Interchange Format
Joint Photographic Experts Group
Portable Network Graphics
Tagged Image Modeling Language
.gif
.jpeg, .jpg, .jpe
.png
.tiff, .tif
5. Model vrml Virual reality Modelling Language .wrl
6.
Text
plain
sgml
html
Hyper Text Markup Language
Unformatted text
Standard Generalized Markup
language
.html, .htm
.txt
.sgml
7. Video
avi
mpeg
quicktime
sgi-movie
Microsoft Audio Video Interleaved
Moving Pictures Expert Group
Apple QuickTime movie
silicon graphic movie
.avi
.mpeg, .mpg
.qt, .mov
.movie
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E-mail Etiquettes The term etiquette refers to conventional rules of personal behavior. But
while communicating via email, we cannot know about the body language
and tone of voice etc. Therefore a set of guidelines for acceptable behavior
on email that have been evolved is known as Email Netiquette.
Here are set of guidelines that should be followed while working with email:
Try to make your message as short as possible. It will make your message easy
to read and understood.
Be careful about spelling and grammar while typing a message.
Use emoticons, smiles when required.
Email address entered must be correct.
The subject heading of a message should be clear and descriptive.
Follow the same rules as if you are writing a letter or a memo.
Sending a message that has already been forwarded or replied many times may
contain many angled brackets. It is better to remove the angled brackets from
the message.
While sending mails to multiple persons, specify their email addresses in the
BCC: field so that the spammers cannot come to know about addresses of other
recipients to whom you have sent a copy.
Keep size of attachment as small as possible.
Always add your signature at the end of email.
Before you send, make it sure everything is fine because you cannot call back a
sent mail.
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E-mail Hacking Email hacking can be done in any of the following ways:
Spam
Virus
Phishing
Spam
E-mail spamming is an act of sending Unsolicited Bulk E-mails
(UBI) which one has not asked for. Email spams are the junk mails sent by
commercial companies as an advertisement of their products and services.
Virus
Some emails may incorporate with files containing malicious script which
when run on your computer may lead to destroy your important data.
Phishing
Email phishing is an activity of sending emails to a user claiming to be a
legitimate enterprise. Its main purpose is to steal sensitive information such
as usernames, passwords, and credit card details.
Such emails contains link to websites that are infected with malware and
direct the user to enter details at a fake website whose look and feels are
same to legitimate one.
E-mail Spamming and Junk Mails Email spamming is an act of sending Unsolicited Bulk E-mails (UBI) which
one has not asked for. Email spams are the junk mails sent by commercial
companies as an advertisement of their products and services.
Spams may cause the following problems:
It floods your e-mail account with unwanted e-mails, which may result in loss of
important e-mails if inbox is full.
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Time and energy is wasted in reviewing and deleting junk emails or spams.
It consumes the bandwidth that slows the speed with which mails are delivered.
Some unsolicited email may contain virus that can cause harm to your
computer.
Blocking Spams
Following ways will help you to reduce spams:
While posting letters to newsgroups or mailing list, use a separate e-mail
address than the one you used for your personal e-mails.
Don’t give your email address on the websites as it can easily be spammed.
Avoid replying to emails which you have received from unknown persons.
Never buy anything in response to a spam that advertises a product.
E-mail Cleanup and Archiving In order to have light weighted Inbox, it’s good to archive your inbox from
time to time. Here I will discuss the steps to clean up and archive your
Outlook inbox.
Select File tab on the mail pane.
Select Cleanup Tools button on account information screen.
Select Archive from cleanup tools drop down menu.
Select Archive this folder and all subfolders option and then click on the
folder that you want to archive. Select the date from theArchive items older
than: list. Click Browse to create new .pst file name and location. Click OK.
E-mail Providers
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There are several email service providers available in the market with their
enabled features such as sending, receiving, drafting, storing an email and
much more.
The following table shows the popular email service providers:
S.N. Service and Description
1.
Gmail
Gmail is an email service that allows users to collect all the messages. It also
offers approx 7 GB of free storage.
2. Hotmail
Hotmail offers free email and practically unlimited storage accessible on web.
3.
Yahoo Mail
Yahoo Mail offers unlimited storage, SMS texting, social networking and
instant messaging to boot.
4.
iCloud Mail
iCloud Mail offers ample storage, IMAP access, and an elegantly functional
web application.
5. ATM Mail
ATM Mail is a free email service with good spam protection.
6.
Mail.com and GMX Mail
Mail.com and GMX Mail offers reliable mail service with unlimited online
storage.
7.
Shortmail
Shortmail offers easy and fast email service but with limited 500 characters
per message.
8. Inbox.com
Inbox.com offers 5 GB of free online storage. IMAP is not supported by
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Inbox.com
9. Facebook Messages
Facebook Messages includes the message conversation.
10.
My Way Mail
My Way Mail offers clean and fast free email service but lacks in secure
messaging.
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Websites Overview Website is a location on web and is hosted on a web server. It is a set of
related web pages. It is accessed using Internet address known as Uniform
Resource Locator
Static Websites Static websites are also known as flat or stationary websites. They are
loaded on the client’s browser as exactly they are stored on the web server.
Such websites contain only static information. User can only read the
information but can’t do any modification or interact with the information.
Static websites are created using only HTML. Static websites are only used
when the information is no more required to be modified.
Dynamic Websites Dynamic websites shows different information at different point of time.
It is possible to change a portion of a web page without loading the entire
web page. It has been made possible using Ajax technology.
Server-side dynamic web page
It is created by using server-side scripting. There are server-side scripting
parameters that determine how to assemble a new web page which also
include setting up of more client-side processing.
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Client-side dynamic web page
It is processed using client side scripting such as javascript. And then
passed in to Document Object Model (DOM).
Internet Forums An internet forum is message board where people can hold conversation by
posting messages.
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Key Points
A forum can contain several sub forums.
Each of sub forums may contain a number of topics.
Within a forum’s topic, each new discussion started is called a thread.
This thread can be replied by as many people as so wish.
Blog The term Blog is taken from web log. It is a kind of web site that is
updated regularly, with content about almost anything. In other words, blog
is aContent Management System (CMS), an easy way of publishing
articles on the internet.
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Blogging Terminologies
BLOG
A type of website used to publish content on the internet.
BLOGGER
A person who writes for a blog.
BLOGGING
Writing for blogs is referred as blogging.
BLOGOSPHERE
A term is used to refer all the blogs on the web.
What to Blog about
Following discussion will help you to figure out what to write about and as
well as what to name your blog.
Write what you know about. For example, if you have good computer
knowledge. You can write what you know about the subject.
You can share your experience. You can also write what you gained from that
experience, what you learned.
Detail your personal research.
Share your memory of someone.
E-commerce E-Commerce or Electronics Commerce is a methodology of modern
business which addresses the need of business organizations, vendors and
customers to reduce cost and improve the quality of goods and services
while increasing the speed of delivery. E-commerce refers to paperless
exchange of business information using following ways.
Electronic Data Exchange (EDI)
Electronic Mail (e-mail)
Electronic Bulletin Boards
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Electronic Fund Transfer (EFT)
Other Network-based technologies
Features
E-Commerce provides following features:
NON-CASH PAYMENT
E-Commerce enables use of credit cards, debit cards, smart cards,
electronic fund transfer via bank's website and other modes of electronics
payment.
24X7 SERVICE AVAILABILITY
E-commerce automates business of enterprises and services provided by
them to customers are available anytime, anywhere. Here 24x7 refers to 24
hours of each seven days of a week.
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ADVERTISING / MARKETING
E-commerce increases the reach of advertising of products and services of
businesses. It helps in better marketing management of products /
services.
IMPROVED SALES
Using E-Commerce, orders for the products can be generated anytime,
anywhere without any human intervention. By this way, dependencies to
buy a product reduce at large and sales increases.
SUPPORT
E-Commerce provides various ways to provide pre sales and post sales
assistance to provide better services to customers.
Portfolio Online portfolio is collection of images, multimedia, emails, blog entries,
and hyperlinks that are managed online. It can be seen as a kind of
learning record that provides actual evidence of achievement.
Types
There are three types of online portfolio:
1. Developmental (e.g. working)
2. Reflective (e.g. learning)
3. Representational (e.g. showcase)
Developmental portfolio contains all the things that an individual has done
over a period of time.
Reflective portfolio contains personal reflection on the content.
Representational online portfolio refers to learner’s achievement in a
particular work.
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Website Designing Web designing has direct link to visual aspect of a web site. Effective web
design is necessary to communicate ideas effectively.
Web desinging is subset of web development. However these terms are used
interchangeably.
Key Points
Design Plan should include the following:
Details about information architecture.
Planned structure of site.
A site map of pages
Wireframe Wireframe refers to a visual guide to appearace of web pages. It helps to
define structre of web site, linking between web pages and layout of visual
elements.
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Following things are included in a wireframe:
Boxes of primary graphical elements
Placement of headlines and sub headings
Simple layout structure
Calls to action
Text blocks
Wireframe can be created using program like Visio but you can also use a pen and
paper.
Web Designing Tools Here is the list of tools that can be used to make effective web designs:
Coda 2
Coda 2 is a powerful web development & designing tool, comes with better user
interface, text editing, file management, clips, sites, design and better Mysql
support.OmniGraffle
OmmniGraffle is mainly used for wireframing. The downside of this tool is that It
doesnot have interactive prototyping and It is available only for Mac.Pen and Paper
Pen and paper can be used to draw the appeance of the how the web site will look
like.Vim
Vim is great web desiging tool.It supports full customizable auto-intending of code,
multiple buffers for storing cut/copied code, and recording of actions for automated
repetition.
S.N. Tool Description
1.
Photoshop CC
This is a great web designing tool provided by Adobe. The latest Photoshop
CC 2014 supports many new features such as smart objects, layer comps,
smart guides, Typekit integration, font search, and workflow enhancements.
2.
Illustrator CC
Illustrator CC is also a web designing tool comes with powerful features like
AutoCad libraries, white overprint, fill and stroke proxy swap for text,
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automatic corner generation, unembed images and touch type tools etc.
3.
4.
5.
Sublime Text
Sublime Text is a source code editor with Python application programming
interface. It's functionality can be extended using plugins.
6.
7.
8.
Imageoptim
It is basically used for optimizing images on a website in order to load them
faster by finding best compression parameters and by removing unnecessary
comments.
9.
Sketch 3
Sketch 3 is a web desiging tool developed specifically for designing interfaces,
websites, icons etc.
10.
Heroku
It is also a great web development tool which supports Ruby, Node.js,
Python, java and PHP.
11.
Axure
It supports prototyping, documentation, and wireframing tools for making
interactive website design.
12.
Hype 2
The Hype 2 offers: Easiest way to Animate & add interactivity, Hardness the
power of HTML5, Mobile responsiveness, and WYSIWYG features.
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13.
Image Alpha
This tool helps to reduce file sizes of 24-bit PNG files. It does so by applying
lossy compression and convert it to PNG8+alpha format which more efficient.
14. Hammer
This tool is suitable for non programmers and good only for small projects.
15.
JPEGmini Lite
It is an image optimizing tool and supports photos in any resolution up to 28
Megapixels.
16.
BugHerd
This tool helps to see how the projects is going and what everyone is working
on. It also helps to identify issues in development.
Web Page Anatomy A web site includes the following components:
Containing Block
Container can be in the form of page’s body tag, an all containing div tag.
Without container there would be no place to put the contents of a web
page.
Logo
Logo refers to the identity of a website and is used across a company’s
various forms of marketing such as business cards, letterhead, brouchers
and so on.
Naviagation
The site’s navigation system should be easy to find and use. Oftenly the
anvigation is placed rigth at the top of the page.
Content
The content on a web site should be relevant to the purpose of the web site.
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Footer
Footer is located at the bottom of the page. It usually contains copyright,
contract and legal information as well as few links to the main sections of
the site.
Whitespace
It is also called as negative space and refers to any area of page that is
not covered by type or illustrations.
Web design Mistakes One should be aware of the following common mistakes should always keep
in mind:
Website not working in any other browser other internet explorer.
Using cutting edge technology for no good reason
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Sound or video that starts automatically
Hidden or disguised navigation
100% flash content
Website Development Web development Web development refers to building website and deploying on the web.
Web development requires use of scripting languages both at the server
end as well as at client end.
Before developing a web site once should keep several aspects in mind like:
What to put on the web site?
Who will host it?
How to make it interactive?
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How to code it?
How to create search engine friendly web site?
How to secure the source code frequently?
Will the web site design display well in different browsers?
Will the navigation menus be easy to use?
Will the web site loads quickly?
How easily will the site pages print?
How easily will visitors find important details specific to the web site?
How effectively the style sheets be used on your web sites?
Web Development Process Web development process includes all the steps that are good to take to
build an attractive, effective and responsive website. These steps are shown
in the following diagram:
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Web development tools Web development tools helps the developer to test and debug the web
sites. Now a days the web development tooll come with the web browsers
as add-ons. All web browsers have built in tools for this purpose.
Thsese tools allow the web developer to use HTML, CSS and JavaScript etc..
These are accessed by hovering over an item on a web page and selecting
the “Inspect Element” from the context menu.
Featues
Following are the common featuers that every web development tool
exhibits:
HTML AND THE DOM
HTML and DOM viewer allows you to see the DOM as it was rendered. It
also allows to make changes to HTML and DOM and see the changes
reflected in the page after the change is made.
WEB PAGE ASSESTS, RESOURCES, AND NETWORK INFORMATION
Web development tools also helps to inspect the resources that are loaded
and available on the web page.
PROFIING AND AUDITING
Profiling refers to get information about the performance of a web page or
web application and Auditing provides developers suggestions, after
analyzing a page, for optimizations to decerease page load time and
increase responsiveness.
Skills Required For being a successful web developer, one should possess the following
skills:
Understanding of client and server side scripting.
Creating, editing and modifying templates for a CMS or web development
framework.
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Testing cross browser inconsistencies.
Conducting observational user testing.
Testing for compliance to specified standards such as accessibility standards in
the client region.
Programming interaction with javaScript, PHP, and Jquery etc.
Websites Publishing Website publishing is the process of uploading content on the internet. It
includes:
uploading files
updating web pages
posting blogs
Website is published by uploading files on the remote server which is provided by the
hosting company.
Prerequisites for Website Publishing In order to publish your site, you need the following things:
Web development software
Internet Connection
Web Server
Web development software
It is used for building web pages for your web site. Dreamweaver and
WordPress are example of web development softwares.
Internet Connection
Internet connection is required to connect to a remotely located web server.
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Web Server
Web server is the actual location where your website resides on. A web
server may host single or multiple sites depending on what hosting service
you have paid for.
Websites URL Registration A domain name is the part of your Internet address that comes
after "www".For example, in www.tutorialspoint.com the domain name
istutorialspoint.com.
A domain name becomes your Business Address so care should be taken to
select a domain name. Your domain name should be easy to remember and
easy to type.
Domain Extensions The final letter at end of internet address is known as top level domain
names. They are called top level because they are read from right to left,
and the part after the dot is the highest in a hierarchy.
The following table shows the Generic Top-Level Domain names:
Domain Meaning
.com Commercial Busness
.edu Education
.gov U.S. government agency
.int International Entity
.mil U.S. military
.net Networking organization
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.org Non profit organization
Registering Domain Name Registering a Domain Name is very simple. You can take following step to
get your desired domain name registered:
Think of a name that justifies your business need. To find out the available
names you can enter a name at commercial domain name registrar such as
GoDaddy.
If the domain name entered by you is available, then select that particular
domain name.
Now it will ask you for other additional services such as Email inbox, hosting etc.
that host also provides. You may choose what’s best for you.
Now they will ask you for your personal information which is stored in WHOIS
database.
It will then ask for payment information. Pay for the purchase you have made.
Make sure you enter the correct payment information.
Once you are done with all above steps, you are ready to use their tools to
upload your stuff to your site.
Domain Name Registrar There are a number of domain name registrars available in the market.The
following table contains some of popular domain name registrars:
S.N. Domain Name Registrar
Address Creation, LLC
Addressonthe web, LLC
101domains, INC
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Atomicdomainnames, LLC
BigRock Solutions Ltd
Black Ice Domain, Inc
Block Host LLC
Domain Monkeys, LLC
Domain Mantra, Inc.
DomainName, Inc.
Dot Holding Inc.
DotMedia Ltd
Extend Names, Inc.
Extremely Wild
Fast Domain Inc.
Google Inc
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Websites Hosting Overview Web hosting is a service of providing online space for storage of web
pages. These web pages are made available via World Wide Web. The
companies which offer website hosting are known as Web hosts.
The servers on which web site is hosted remain switched on 24 x7. These
servers are run by web hosting companies. Each server has its own IP
address. Since IP addresses are difficult to remember therefore, webmaster
points their domain name to the IP address of the server their website is
stored on.
It is not possible to host your website on your local computer, to do so you
would have to leave your computer on 24 hours a day. This is not practical
and cheaper as well. This is where web hosting companies comes in.
Types of Hosting The following table describes different types of hosting that can be availed
as per the need:
S.N. Hosting Description
1.
Shared Hosting
In shared hosting, the hosting company puts thousand of website on the
same physical server. Each customer has their own allocation of physical web
space and a set of bandwidth limit. As all websites share same physical
memory, MYSQL server and Apache server, one website on the server
experiencing high traffic load will affect performance of all websites on the
server.
2.
Virtual Private Server (VPS)
It is also known as Virtual Dedicated Server. It is a server which is partitioned
into smaller servers. In this customer is given their own partition, which is
installed with its own operating system. Unlike shared hosting, VPS doesn’t
share memory or processor time rather it allocates certain amount of
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memory and CPU to use which means that any problem on a VPS partition on
the same drive will not affect other VPS customers.
3.
Dedicated Server
In this kind of hosting, single dedicated server is setup for just one customer.
It is commonly used by the businesses that need the power, control and
security that a dedicated server offers.
4.
Reseller Hosting
A reseller acts as a middle man and sells hosting space of someone else’s
server.
5.
Grid Hosting
Instead of utilizing one server, Grid Hosting spreads resources over a large
number of servers. It is quite stable and flexible. The servers can be added or
taken away from the grid without crashing the system.
Web Hosting Companies Following are the several companies offering web hosting service:
S.N. Hosting Company
1. Blue Host
2. Go Daddy
3. Host Gator
4. just Host
5. Laughing Squid
6. Hivelocity
7. liquid Web
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8. Media TempleServInt
9. Wired Tree
10. Wild West Domains
11. Wix
12. WIPL
13. Big Rock
Website Security Consideration Websites are always to prone to security risks. Cyber crime impacts your
business by hacking your website. Your website is then used for hacking
assaults that install malicious software or malware on your visitor’s
computer.
Hackers may also steal important customer data such as credit card information,
destroy your business and propagate illegal content to your users.
Security Considerations Updated Software
It is mandatory to keep you software updated. It plays vital role in keeping
your website secure.
SQL Injection
It is an attempt by the hackers to manipulate your database. It is easy to
insert rogue code into your query that can be used to manipulate your
database such as change tables, get information or delete data.
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Cross Site Scripting (XSS)
It allows the attackers to inject client side script into web pages. Therefore,
while creating a form It is good to endure that you check the data being
submitted and encode or strip out any HTML.
Error Messages
You need to be careful about how much information to be given in the error
messages. For example, if the user fails to log in the error message should
not let the user know which field is incorrect: username or password.
Validation of Data
The validation should be performed on both server side and client side.
Passwords
It is good to enforce password requirements such as of minimum of eight
characters, including upper case, lower case and special character. It will
help to protect user’s information in long run.
Upload files
The file uploaded by the user may contain a script that when executed on
the server opens up your website.
SSL
It is good practice to use SSL protocol while passing personal information
between website and web server or database.
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Search Engine Optimization What is SEO Search Engine Optimization refers to set of activities that are performed
to increase number of desirable visitors who come to your site via search
engine. These activities may include thing you do to your site itself, such as
making changes to your text and HTML code, formatting text or document
to communicate directly to the search engine.
Types of SEO
SEO can be classified into two types: White Hat SEO and Black Hat or
Spamdexing
WHITE HAT SEO
An SEO tactic, technique or method is considered as White Hat if it follows
the followings
If it conforms to the search engine's guidelines.
If it does not involves any deception.
It ensures that the content a search engine indexes and subsequently ranks is
the same content a user will see.
It ensures that a Web Page content should have been created for the users and
not just for the search engines.
It ensures the good quality of the web pages.
It ensures the useful content available on the web pages.
Always follow a White Hat SEO tactic and don't try to fool your site visitors. Be honest
and definitely you will get something more.
BLACK HAT OR SPAMDEXING:
An SEO tactic, technique or method is considered as Black Hat or
Spamdexing if it follows the followings:
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Try to improve rankings that are disapproved of by the search engines and/or
involve deception.
Redirecting users from a page that is built for search engines to one that is more
human friendly.
Redirecting users to a page that was different from the page the search engine
ranked.
Serving one version of a page to search engine spiders/bots and another version
to human visitors. This is called Cloaking SEO tactic.
Using Hidden or invisible text or with the page background color, using a tiny
font size or hiding them within the HTML code such as "no frame" sections.
Repeating keywords in the Meta tags, and using keywords that are unrelated to
the site's content. This is called Meta tag stuffing.
Calculated placement of keywords within a page to raise the keyword count,
variety, and density of the page. This is called Keyword stuffing.
Creating low-quality web pages that contain very little content but are instead
stuffed with very similar key words and phrases. These pages are
called Doorway or Gateway Pages
Mirror web sites by hosting multiple web sites all with conceptually similar
content but using different URLs.
Mirror web sites by hosting multiple web sites all with conceptually similar
content but using different URLs.
Creating a rogue copy of a popular web site which shows contents similar to the
original to a web crawler, but redirects web surfers to unrelated or malicious
web sites. This is called Page hijacking.
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Key Elements to ethical SEO Keyword research
It allows you to see which keywords users actually employ to find products
and services within your chosen market, instead of making guesses at the
keywords you believe are the most popular.
Content development
Content development involves:
Navigational flow and menu structure
Site copy or articles
Headings and sections
Web development
Web development involves:
Text-based site development wherever possible.
Clean and logical site structure.
Proper markup of key page elements.
Link Building
Building links will make up about 60% of your work. There are ways to
automate this process using shortcuts, workarounds, and submission
services.
Internal linking is also very important. Treat the way you link to your own
content same as you would link from an external site.
Webmaster Tools
Webmaster dashboard is provided by both Google and Bing that gives
insight into activity by the search engine on any site that has been
registered and verified via dashboard.
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Dashboards offer a number of tools which allow us to understand how the
search engine sees your site. These are the only way to identify crawling,
indexing, and the ranking issue with your site.
SEO Do’s and Do’nts DO's
There are various other tips which can help you to optimize your web site
for many Search Engines:
Create logs of pages and each page should however contain a minimum of about
200 visible words of text to maximize relevance with Google.
Create a Sitemap, Help, FAQ, About Us, Link to Us, Copyright,
Disclaimer, and Privacy Policy pages on mandatory basis.
Create a home page link to each and every web page and provide easy
navigation through all the pages.
Pay attention to your dynamic page URLs. Google can crawl and index dynamic
pages as long as you don't have more than 2 parameters in the URL.
Check your complete site for broken links. Broken links will reduce your other
pages rank as well.
Do'nts
Here is the list of Do'nts that one should keep in mind all the times:
Don't keep hidden text on your web pages.
Don't create alt image spamming by putting wrong keywords.
Don't use Meta tags stuffing.
Don't use frames and flash on your site.
Don't exchange your links with black listed sites.
Don't try to fool your site visitors by using miss spelled keywords.
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Don't send spam emails to thousand of email IDs.
Don't use too much graphics on your site.
Don't create too many doorway pages.
Don't try to create duplicate content of pages.
Don't submit your website many times in a single search engine.
Don't use sub-directory depth more than 1-2.
Don't create too many dynamic pages. Try to convert them into static pages.
Don't bloat your pages with code.
Don't nest your pages.
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Website Monetization Website monetization refers to making money from the website. It is
done by converting existing traffic to a particular website into revenue.
Methods of Monetization Display Advertising
It refers to the banners and text ads. This method is good for the websites
that have significant traffic, valuable audience, relevant and active
advertisers.
Affiliate Marketing
It refers to steering the visitors to products and services of a third party
merchant. It is good for the websites that are product centric and have easy
integration into content.
Lead generation
It refers to capturing the customer information and selling it to a third
party.
Email rental
It refers to renting out your email lists to third parties. In this you will send
an email on their behalf to your distribution list.
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WWW Overview Overview WWW stands for World Wide Web. A technical definition of the World
Wide Web is : all the resources and users on the Internet that are using the
Hypertext Transfer Protocol (HTTP).
A broader definition comes from the organization that Web inventor Tim
Berners-Lee helped found, the World Wide Web Consortium (W3C).
The World Wide Web is the universe of network-accessible information, an
embodiment of human knowledge.
In simple terms, The World Wide Web is a way of exchanging information
between computers on the Internet, tying them together into a vast
collection of interactive multimedia resources.
Internet and Web is not the same thing: Web uses internet to pass over the
information.
Evolution World Wide Web was created by Timothy Berners Lee in 1989
at CERN inGeneva. World Wide Web came into existence as a proposal by
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him, to allow researchers to work together effectively and efficiently
at CERN. Eventually it became World Wide Web.
The following diagram briefly defines evolution of World Wide Web:
WWW Architecture WWW architecture is divided into several layers as shown in the following
diagram:
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Identifiers and Character Set
Uniform Resource Identifier (URI) is used to uniquely identify resources
on the web and UNICODE makes it possible to built web pages that can be
read and write in human languages.
Syntax
XML (Extensible Markup Language) helps to define common syntax in
semantic web.
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Data Interchange
Resource Description Framework (RDF) framework helps in defining
core representation of data for web. RDF represents data about resource in
graph form.
Taxonomies
RDF Schema (RDFS) allows more standardized description
of taxonomiesand other ontological constructs.
Ontologies
Web Ontology Language (OWL) offers more constructs over RDFS. It
comes in following three versions:
OWL Lite for taxonomies and simple constraints.
OWL DL for full description logic support.
OWL for more syntactic freedom of RDF
Rules
RIF and SWRL offers rules beyond the constructs that are available
from RDFsand OWL. Simple Protocol and RDF Query Language
(SPARQL) is SQL like language used for querying RDF data and OWL
Ontologies.
Proof
All semantic and rules that are executed at layers below Proof and their
result will be used to prove deductions.
Cryptography
Cryptography means such as digital signature for verification of the origin
of sources is used.
User Interface and Applications
On the top of layer User interface and Applications layer is built for user
interaction.
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WWW Operation WWW works on client- server approach. Following steps explains how the
web works:
1. User enters the URL (say, http://www.tutorialspoint.com) of the web page
in the address bar of web browser.
2. Then browser requests the Domain Name Server for the IP address
corresponding to www.tutorialspoint.com.
3. After receiving IP address, browser sends the request for web page to the web
server using HTTP protocol which specifies the way the browser and web server
communicates.
4. Then web server receives request using HTTP protocol and checks its search for
the requested web page. If found it returns it back to the web browser and
close the HTTP connection.
5. Now the web browser receives the web page, It interprets it and display the
contents of web page in web browser’s window.
Future There had been a rapid development in field of web. It has its impact in
almost every area such as education, research, technology, commerce,
marketing etc. So the future of web is almost unpredictable.
Apart from huge development in field of WWW, there are also some
technical issues that W3 consortium has to cope up with.
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User Interface
Work on higher quality presentation of 3-D information is under
deveopment. The W3 Consortium is also looking forward to enhance the
web to full fill requirements of global communities which would include all
regional languages and writing systems.
Technology
Work on privacy and security is under way. This would include hiding
information, accounting, access control, integrity and risk management.
Architecture
There has been huge growth in field of web which may lead to overload the
internet and degrade its performance. Hence more better protocol are
required to be developed.
Web Pages web page is a document available on world wide web. Web Pages are
stored on web server and can be viewed using a web browser.
A web page can cotain huge information including text, graphics, audio,
video and hyper links. These hyper links are the link to other web pages.
Collection of linked web pages on a web server is known as website.There is
unique Uniform Resource Locator (URL) is associated with each web page.
Static Web page
Static web pages are also known as flat or stationary web page. They are
loaded on the client’s browser as exactly they are stored on the web server.
Such web pages contain only static information. User can only read the
information but can’t do any modification or interact with the information.
Static web pages are created using only HTML. Static web pages are only
used when the information is no more required to be modified.
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Dynamic Web page
Dynamic web page shows different information at different point of time.
It is possible to change a portaion of a web page without loading the entire
web page. It has been made possible using Ajax technology.
SERVER-SIDE DYNAMIC WEB PAGE
It is created by using server-side scripting. There are server-side scripting
parameters that determine how to assemble a new web page which also
include setting up of more client-side processing.
CLIENT-SIDE DYNAMIC WEB PAGE
It is processed using client side scripting such as JavaScript. And then
passed in to Document Object Model (DOM).
Scripting Laguages Scripting languages are like programming languages that allow us to write
programs in form of script. These scripts are interpreted not compiled and
executed line by line.
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Scripting language is used to create dynamic web pages.
Client-side Scripting
Client-side scripting refers to the programs that are executed on client-
side. Client-side scripts contains the instruction for the browser to be
executed in response to certain user’s action.
Client-side scripting programs can be embedded into HTML files or also can be kept as
separate files.
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Following table describes commonly used Client-Side scripting languages:
S.N. Scripting Language Description
1.
JavaScript
It is a prototype based scripting language. It inherits its naming conventions
from java. All java script files are stored in file having .js extension.
2. ActionScriptIt is an object oriented programming language used for the
development of websites and software targeting Adobe flash player.
3.
Dart
It is an open source web programming language developed by Google. It
relies on source-to-source compiler to JavaScript.
4.
VBScript
It is an open source web programming language developed by Microsoft. It is
superset of JavaScript and adds optional static typing class-based object
oriented programming.
Server-side Scripting
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Following table describes commonly used Server-Side scripting languages:
S.N. Scripting Language Description
1.
ASP
Active Server Pages (ASP)is server-side script engine to create dynamic web
pages. It supports Component Object Model (COM) which enables ASP
web sites to access functionality of libraries such as DLL.
2.
ActiveVFP
It is similar to PHP and also used for creating dynamic web pages. It uses
native Visual Foxpro language and database.
3. ASP.net
It is used to develop dynamic websites, web applications, and web services.
4. Java
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Java Server Pages are used for creating dynamic web applications. The Java
code is compiled into byte code and run by Java Virtual Machine (JVM).
5.
Python
It supports multiple programming paradigms such as object-oriented, and
functional programming. It can also be used as non-scripting language using
third party tools such as Py2exe or Pyinstaller.
6.
WebDNA
It is also a server-side scripting language with an embedded database
system.
Web Browser web Browser is an application software that allows us to view and explore
information on the web. User can request for any web page by just entering
a URL into address bar.
Web browser can show text, audio, video, animation and more. It is the
responsibility of a web browser to interpret text and commands contained in
the web page.
Earlier the web browsers were text-based while now a days graphical-based
or voice-based web browsers are also available. Following are the most
common web browser available today:
Browser Vendor
Internet Explorer Microsoft
Google Chrome Google
Mozilla Firefox Mozilla
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Netscape Navigator Netscape Communications Corp.
Opera Opera Software
Safari Apple
Sea Monkey Mozilla Foundation
K-meleon K-meleon
Architecture
There are a lot of web browser available in the market. All of them interpret
and display information on the screen however their capabilities and
structure varies depending upon implementation. But the most basic
component that all web browser must exhibit are listed below:
Controller/Dispatcher
Interpreter
Client Programs
Controller works as a control unit in CPU. It takes input from the keyboard
or mouse, interpret it and make other services to work on the basis of input
it receives.
Interpreter receives the information from the controller and execute the
instruction line by line. Some interpreter are mandatory while some are
optional For example, HTML interpreter program is mandatory and java
interpreter is optional.
Client Program describes the specific protocol that will be used to access a
particular service. Following are the client programs tat are commonly
used:
HTTP
SMTP
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FTP
NNTP
POP
Starting Internet Explorer
Internet explorer is a web browser developed by Microsoft. It is installed by
default with the windows operating system howerver, it can be downloaded
and be upgraded.
To start internet explorer, follow the following steps:
Go to Start button and click Internet Explorer.
The Internet Explorer window will appear as shown in the following
diagram:
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Accessing Web Page
Accessing web page is very simple. Just enter the URL in the address bar
as shown the following diagram:
Navigation
A web page may contain hyperlinks. When we click on these links other
web page is opened. These hyperlinks can be in form of text or image.
When we take the mouse over an hyperlink, pointer change its shape to
hand.
Key Points
In case, you have accessed many web pages and willing to see the previous
webpage then just click back button.
You can open a new web page in the same tab, or different tab or in a new
window.
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Saving Webpage
You can save web page to use in future. In order to save a webpage, follow
the steps given below:
Click File > Save As. Save Webpage dialog box appears.
Choose the location where you want to save your webpage from save in: list
box. Then choose the folder where you want to save the webpage.
Specify the file name in the File name box.
Select the type from Save as type list box.
o Webpage, complete
o Web Archive
o Webpage HTML only
o Text File
From the encoding list box, choose the character set which will be used with
your webpage. By default, Western European is selected.
Click save button and the webpage is saved.
Saving Web Elements
Web elements are the pictures, links etc. In order to save these elements
follow the steps given below:
Right click on the webpage element you want to save. Menu options will
appear. These options may vary depending on the element you want to save.
Save Picture As: This option let you save the picture at specific location
with its name. When you click this option, a dialog box is opened where you
can sepcify its name and location.
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Favourites
The Favourites option helps to save addresses of the webpages you visited
oftenly. Hence you need not to remember long and complex address of
websites you visit often.
In order to open any webpage, you just need to double click on the
webpage that you have marked from bookmarks list.
ADDING A WEB PAGE TO YOUR FAVOURITES
In ordered to add website to your favourite list, follow the steps given
below:
Open webpage that you want to add to your favourite.
Click on favourite menu and then click on Add to
Favourites opton.Addfavourites dialog box appears.
You can also click Favourites button available in the toolbar. Favourites panel will open
in the left corner of the internet explorer window.
Clickadd button, AddFavourites dialog box will apppear.
In AddFavourites dialog box, the Name: text box will contains the name of the
web page that you want to add to favourites.
Click the Create in button, Favoutites folder will appear. Move to the folder
where you want to store the favourites by clicking on the folder name.
Now click OK button to save the favourites.
OPENING FAVOURITES
In order to open favourites, follow the steps given below:
In the Favourite Panel, take the mouse over the site that you want to open. Now
click on the address to open that site.
Favourite can also be opened from the Favourites menu by selecting the
appropriate one.
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ORGANIZING FAVOURITES
Favourites can be organized by categorizing web pages, creating folder for
each category and then storing web pages into them. In order to organize
favourites, follow the steps given below:
Click Favourites menu > Organize Favourites. Organize favourites dialog
box will appears.
In order to organize the webpages, drag the individual webpage to the
respective folder. Similarly to delete a favourite, Click on delete button.
Web Server Overview Web server is a computer where the web content is stored. Basically web
server is used to host the web sites but there exists other web servers also
such as gaming, storage, FTP, email etc.
Web site is collection of web pages whileweb server is a software that respond to the
request for web resources.
Web Server Working Web server respond to the client request in either of the following two
ways:
Sending the file to the client associated with the requested URL.
Generating response by invoking a script and communicating with database
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Key Points
When client sends request for a web page, the web server search for the
requested page if requested page is found then it will send it to client with an
HTTP response.
If the requested web page is not found, web server will the send anHTTP
response:Error 404 Not found.
If client has requested for some other resources then the web server will contact
to the application server and data store to construct the HTTP response.
Architecture Web Server Architecture follows the following two approaches:
1. Concurrent Approach
2. Single-Process-Event-Driven Approach.
Concurrent Approach
Concurrent approach allows the web server to handle multiple client
requests at the same time. It can be achieved by following methods:
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Multi-process
Multi-threaded
Hybrid method.
Multi-processing
In this a single process (parent process) initiates several single-threaded
child processes and distribute incoming requests to these child processes.
Each of the child processes are responsible for handling single request.
It is the responsibility of parent process to monitor the load and decide if
processes should be killed or forked.
Multi-threaded
Unlike Multi-process, it creates multiple single-threaded process.
Hybrid
It is combination of above two approaches. In this approach multiple
process are created and each process initiates multiple threads. Each of the
threads handles one connection. Using multiple threads in single process
results in less load on system resources.
Examples Following table describes the most leading web servers available today:
S.N. Web Server Descriptino
1
Apache HTTP Server
This is the most popular web server in the world developed by the Apache
Software Foundation. Apache web server is an open source software and can
be installed on almost all operating systems including Linux, UNIX, Windows,
FreeBSD, Mac OS X and more. About 60% of the web server machines run
the Apache Web Server.
2. Internet Information Services (IIS)
The Internet Information Server (IIS) is a high performance Web Server from
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Microsoft. This web server runs on Windows NT/2000 and 2003 platforms
(and may be on upcoming new Windows version also). IIS comes bundled
with Windows NT/2000 and 2003; Because IIS is tightly integrated with the
operating system so it is relatively easy to administer it.
3.
Lighttpd
The lighttpd, pronounced lighty is also a free web server that is distributed
with the FreeBSD operating system. This open source web server is fast,
secure and consumes much less CPU power. Lighttpd can also run on
Windows, Mac OS X, Linux and Solaris operating systems.
4.
Sun Java System Web Server
This web server from Sun Microsystems is suited for medium and large web
sites. Though the server is free it is not open source. It however, runs on
Windows, Linux and UNIX platforms. The Sun Java System web server
supports various languages, scripts and technologies required for Web 2.0
such as JSP, Java Servlets, PHP, Perl, Python, and Ruby on Rails, ASP and
Coldfusion etc.
5.
Jigsaw Server
Jigsaw (W3C's Server) comes from the World Wide Web Consortium. It is
open source and free and can run on various platforms like Linux, UNIX,
Windows, and Mac OS X Free BSD etc. Jigsaw has been written in Java and
can run CGI scripts and PHP programs.
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Proxy Server Overview Proxy server is an intermediary server between client and the interner.
Proxy servers offers the following basic functionalities:
Firewall and network data filtering.
Network connection sharing
Data caching
Proxy servers allow to hide, conceal and make your network id anonymous by hiding
your IP address.
Purpose of Proxy Servers Following are the reasons to use proxy servers:
Monitoring and Filtering
Improving performance
Translation
Accessing services anonymously
Security
Monitoring and Filtering
Proxy servers allow us to do several kind of filtering such as:
Content Filtering
Filttering encrypted data
Bypass filters
Logging and eavasdropping
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Improving performance
It fasten the service by process of retrieving content from the cache which
was saved when previous request was made by the client.
Transalation
It helps to customize the source site for local users by excluding source
content or substituting source content with original local content. In this the
traffic from the global users is routed to the source website through
Translation proxy.
Accessing services anonymously
In this the destination server receives the request from the anonymzing
proxy server and thus does not receive information about the end user.
Security
Since the proxy server hides the identity of the user hence it protects from
spam and the hacker attacks.
Type of Proxies Following table briefly describes the type of proxies:
Forward Proxies
In this the client requests its internal network server to forward to the
internet.
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Open Proxies
Open Proxies helps the clients to conceal their IP address while browsing
the web.
Reverse Proxies
In this the requests are forwarded to one or more proxy servers and the
response from the proxy server is retrieved as if it came directly from the
original Server.
Architecture The proxy server architecture is divided into several modules as shown in
the following diagram:
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Proxy user interface
This module controls and manages the user interface and provides an easy
to use graphical interface, window and a menu to the end user. This menu
offers the following functionalities:
Start proxy
Stop proxy
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Exit
Blocking URL
Blocking client
Manage log
Manage cache
Modify configuration
Proxy server listener
It is the port where new request from the client browser is listened. This
module also performs blocking of clients from the list given by the user.
Connection Manager
It contains the main functionality of the proxy server. It performs the
following functions:
It contains the main functionality of the proxy server. It performs the following
functions:
Read request from header of the client.
Parse the URL and determine whether the URL is blocked or not.
Generate connection to the web server.
Read the reply from the web server.
If no copy of page is found in the cache then download the page from web
server else will check its last modified date from the reply header and
accordingly will read from the cache or server from the web.
Then it will also check whether caching is allowed or not and accordingly will
cache the page.
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Cache Manager
This module is responsible for storing, deleting, clearing and searching of
web pages in the cache.
Log Manager
This module is responsible for viewing, clearing and updating the logs.
Configuration
This module helps to create configuration settings which in turn let other
modules to perform desired configurations such as caching.
Search Engines Introduction Search Engine refers to a huge database of internet resources such as
web pages, newsgroups, programs, images etc. It helps to locate
information on World Wide Web.
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Search Engine Components Generally there are three basic components of a search engine as listed
below:
1. Web Crawler
2. Database
3. Search Interfaces
Web crawler
It is also known as spider or bots. It is a software component that
traverses the web to gather information.
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Database
All the information on the web is stored in database. It consists of huge web
resources.
Search Interfaces
This component is an interface between user and the database. It helps the
user to search through the database.
Search Engine Working Web crawler, database and the search interface are the major component of
a search engine that actually makes search engine to work. Search engines
make use of Boolean expression AND, OR, NOT to restrict and widen the
results of a search. Following are the steps that are performed by the
search engine:
The search engine looks for the keyword in the index for predefined database
instead of going directly to the web to search for the keyword.
It then uses software to search for the information in the database. This
software component is known as web crawler.
Once web crawler finds the pages, the search engine then shows the relevant
web pages as a result. These retrieved web pages generally include title of
page, size of text portion, first several sentences etc.
These search criteria may vary from one search engine to the other. The retrieved
information is ranked according to various factors such as frequency of keywords,
relevancy of information, links etc.
User can click on any of the search results to open it.
Architecture The search engine architecture comprises of the three basic layers listed
below:
Content collection and refinement.
Search core
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User and application interfaces
Search Engine Processing Indexing Process
Indexing process comprises of the following three tasks:
Text acquisition
Text transformation
Index creation
TEXT ACQUISITION
It identifies and stores documents for indexing.
TEXT TRANSFORMATION
It transforms document into index terms or features.
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INDEX CREATION
It takes index terms created by text transformations and create data
structures to suport fast searching.
Query Process
Query process comprises of the following three tasks:
User interaction
Ranking
Evaluation
USER INTERACTION
It supporst creation and refinement of user query and displays the results.
RANKING
It uses query and indexes to create ranked list of documents.
EVALUATION
It monitors and measures the effectiveness and efficiency. It is done offline.
Examples Following are the several search engines available today:
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Search
Engine Description
Google It was originally called BackRub. It is the most popular search
engine globally.
Bing It was launched in 2009 by Microsoft. It is the latest web-based
search engine that also delivers Yahoo’s results.
Ask It was launched in 1996 and was originally known as Ask Jeeves. It
includes support for match, dictionary, and conversation question.
AltaVista It was launched by Digital Equipment Corporation in 1995. Since
2003, it is powered by Yahoo technology.
AOL.Search It is powered by Google.
LYCOS It is top 5 internet portal and 13th largest online property according
to Media Matrix.
Alexa It is subsidiary of Amazon and used for providing website traffic
information.
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Internet Collaboration Overview Online Chatting Online chatting is a text-based communication between two or more
people over the network. In this, the text message is delivered in real time
and people get immediate response.
Talkomatic was the world first online chat system. It was developed byDoug
Brown and David R. Woolley in 1973.
Chat Etiquette
Chat etiquette defines rules that are supposed to be followed while online
chatting:
Avoid chat slang
Try to spell all words correctly.
Don’t write all the words in capital.
Don’t send other chat users private messages without asking them.
Abide by the rules created by those running the chat.
Use emoticons to let other person know your feelings and expressions.
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Web Based Chat Services
Following web sites offers browser based chat services:
Website Description
It was founded by Mark Zuckerberg with his college roommates at
Harvard university. Facebook lets the user to create personal profile,
post status & photos, and receive notifications.
eBuddy It is an instant messaging service. It supports multiprotocol instant
messaging clients.
Convore It offers real time web based chat system.
MeBeam It offers video based chat between the clients to create video
conferencing rooms for up to 16 people.
Yahoo!
Messenger
It offers PC-PC, PC-phone, Phone-to-PC, file transfer, webcam
hosting, text messaging service etc.
WhatsApp It is an instant messaging service application available on smart
phones.
Gmail It offers instant chatting, sending and receiving mails, and video
calling services.
Instant Messaging (IM) Instant messaging is a software utility that allows IM users to
communicate by sending text messages, files, and images. Some of the IMs
also support voice and video calls.
Application Description
Nimbuzz It is native iPhone app. It supports voice and video chats, file
sharing, and group chats with panache.
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eBuddy eBuddy IM helps to have all your buddies from multiple IM
accounts in one single list.
Imo.in It has capability to link all your IM accounts together. You can log
on to all of your IM accounts by just logging into imo.in.
MeBeam It offers video based chat between the clients to create video
conferencing rooms for up to 16 people.
Yahoo!
Messenger
It offers PC-PC, PC-phone, Phone-to-PC, file transfer, webcam
hosting, text messaging service etc.
GoogleTalk It is an IM by Google and one of the most widely used.
Lync Lync is an IM developed by Microsoft. It is widely used in corporate
sector for internal and external communication as well.
Internet Relay Chat (IRC) Internet Relay Chat is a protocol developed by Oikarinen in August 1988.
It defines set of rules for communication between client and server by some
communication mechanism such as chat rooms, over the internet.
IRC consist of separate networks of IRC servers and machines. These allow
IRC clients to connect to IRC. IRC client runs a program client to connect to
a server on one of the IRC nets. After connecting to IRC server on IRC
network, user can join with one or more channels and converse over there.
IRC Commands
Following commands are used while connected to an IRC server. Almost of
the below commands will work with most of IRC clients and servers.
Command Description
/away (message) Leaves a message let the others know why you are gone.
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/clear Clears the text from current window.
/clearall Clears all the text from all of the opened windows.
/dcc chat (username) Opens a chat window with the username that you specify.
/help Brings up a list of all the commands or the help window.
/ignore (on/of)
(username) Allows you to ignore or not ignore a user.
/ignore (+/-)
(username) Alternative to ignore or not ignore a user.
/join (#channel) Joins a particular chat group.
/nick (username) Changes the username
/part (channel) Leaves specified channel.
/ping (username) Pings a specified user and it let you know how far they
are in seconds
/whowas (username) Shows information about specified user that was in
earlier.
/ping (channel) Pings all users in specified channel.
Video Conferencing Video conferencing or Video teleconferencing is a method of
communicating by two-way video and audio transmission with help of
telecommunication technologies.
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Modes of Video Conferencing
POINT-TO-POINT
This mode of conferencing connects two locations only.
MULTI-POINT
This mode of conferencing connects more than two locations through Multi-
point Control Unit (MCU).
Video Sharing Video sharing is an IP Multimedia System (IMS) service that allows
user to switch voice calls to unidirectional video streaming session. The
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video streaming session can be initiated by any of the parties. Moreover,
the video source can be the camera or the pre-recorded video clip.
Mailing List Mailing List In order to send same email to a group of people, an electron list is created
which is know as Mailing List. It is the list server which receives and
distributes postings and automatically manages subscriptions.
Mailing list offers a forum, where users from all over the globe can answer
questions and have them answered by others with shared interests.
Types of Mailing List
Following are the various types of mailing lists:
RESPONSE LIST
It contains the group of people who have responsed to an offer in some
way. These people are the customers who have shown interest in specific
product or service.
COMPILED LIST
The compiled list is prepared by collecting information from various sources
such as surveys, telemarketing etc.
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ANNOUNCEMENTS
These lists are created for sending out coupans , new product
announcements and other offers to the customers.
DISCUSSION LIST
This list is created for sharing views on a specific topic suchas computer,
environment , healt, education etc.
How does mailing list work? Before joining a mailing list, it is mandatory to subscribe to it. Once you are
subscribed, your message will be sent to all the persons who have
subscribed to the list. Similarly if any subscriber posts a message, then it
will be received by all subscribers of the list.
Finding Mailing List There are a number of websites are available to maintain database of
publically accessible mailing list. Some of these are:
http://tile.net./lists
http://lists.com
http://topica.com
http://isoft.com/lists/list-q.html
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Mailing lists can also be found using Google website. In Google, move to directory and
the follow: Computers > Internet >Mailing List > Directories.
Subscribing to Mailing List To subscribe to a list, you need to send an email message to the
administrative address mailing list containing one or more commands. For
example, if you want to subscribe to Harry Potter list in gurus.com where
name of the list server us Majordomo, then you have to send email to
[email protected] containing the text, Subscribe harry potter in its
body.
After sending the email, you will receive a confirmation email for your subscription. This
email will include list of commands that will help you to perform various operations
such as unsubscribing, receiving acknowledgement, and find out what list you are
subscribed to.
There are many list servers available, each having its own commands for
subscribing to the list. Some of them are described in the following table:
List Server Command Example
LISTSERV subscribe listname yourname subscribe commdhtml rahul
Majordomo subscribe listname subscribe commdhtml
ListProc subscribe listname yourname subscribe commdhtml rahul
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Usenet Newsgroup Usenet (USEr NETwork) Like mailing lists Usenet is also a way of sharing information. It was started
by Tom Truscott and Jim Ellis in 1979. Initially it was limited to two sites
but today there are thousands of Usenet sites involving millions of people.
Usenet is a kind of discussion group where people can share views on topic
of their interest. The article posted to a newsgroup becomes available to all
readers of the newsgroup.
Newsgroup Classification
There exist a number of newsgroups distributed all around the world. These
are identified using a hierarchical naming system in which each newsgroup
is assigned a unique name that consists of alphabetic strings separated by
periods.
The leftmost portion of the name represents the top-level category of the
newsgroup followed by subtopic. The subtopic can further be subdivided
and subdivided even further (if needed).
For example, the newsgroup comp.lang.C++ contains discussion
on C++language. The leftmost part comp classifies the newsgroup as one
that contains discussion of computer related topics. The second part
identifies one of the subtopic lang that related to computer languages. The
third part identifirs one of the computer languages, in this case C++.
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The following table shows the top-level hierarchies of Usenet Newsgroup:
Comp.* Computer related topics including computer
hardware, software, languages etc.
Comp.lang.java.beans
Comp.database.oracle
News.* Newsgroup and Usenet topics News.software.nntp
Rec.* Artistic activities, hobbies, or recreational
activities such as books, movies etc. Rec.arts.animation
Sci.* Scientific topics Sci.bio.botany
Soc.* Social issues and various culture Soc.culture.india
Talk.* Conventional subjects such as religion,
politics etc. Soc.politics.india
Humanities.* Art, literature, philosophy and culture Humanities.classics
Misc.* Miscellaneous topics i.e. issues tat may not Misc.answers
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fit into other categories Misc.books.technical
Working of Usenet Newsgroup
When a newsreader such as outlook express connects to a news server, it
downloads all the new messages posted in the subscribed newsgroup. We
can either reply a message after reading or post a news article to the news
server.
The article posted to a news server is appended to the file maintained for
that newsgroup Then the news server shares article with other news
servers that are connected to it.
Then each news server compares if both carry the same newsgroup. If yes,
then by comparing the files it checks that if there are any new articles in
the file, if so they are appended to the file.
The updated file of the news servers is then sent to other news servers
connected to it. This process is continues until all of the news servers have
updated information.
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Reading Articles
If user wants to read article, user has to connect to the news server using
the newsreader. The newsreader will then display a list of newsgroups
available on the news server where user can subscribe to any of the news
group. After subscription the newsreader will automatically download
articles from the newsgroup.
After reading the article user can either post a reply to newsgroup or reply
to sender by email. The newwsreader saves information about the
subscribed newsgroups and articles read by the user in each group.
Posting an Article
In order to send new article to a newsgroup, user first need to compose an
article and specify the names of the newsgroup to whom he/she wants to
send. An article can be sent to one or more newsgroup at a time provided
all the newsgroups are on same news server.
It is also possible to cancel the article that you have posted but if someone has
downloaded an article before cancellation then that person will be able to read the
article.
Replying an Article
After reading the article user can either post a reply to newsgroup or reply
to sender by email. There are two options available Reply and Reply group.
Using Reply, the reply mail will be sent to the autor of the article while
Reply group will send a reply to whole of the newsgroup.
Cancelling an Article
To cancle an article after it is sent, select the message and click Message >
Cancel message. It will cancle the message from the news server. But if
someone has downloaded an article before cancellation then that person will
be able to read the article.
Usenet netiquette
While posting an article on a newsgroup, one should follow some rules of
netiquette as listed below:
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Spend some time in understanding a newsgroup when you join it for first time.
Article posted by you should be easy to read, concise and grammatically correct.
Information should be relevant to the article title.
Don’t post same article to multiple newsgroups.
Avoid providing your business email address while subscribing to a newsgroup
as may be used by spammers.
Avoid using capital letters as someone may interpret as shouting.
Prefer to use plain text wherever possible in your article.
Mailing list vs. Newsgroup
S.N. Mailing List Newsgroup
1.
Messages are delivered to
individual mailboxes of subscribed
member of group.
Messages are not posted to individual
mailboxes but can be viewed by anyone
who has subscribed to that newsgroup.
2.
Working with mailing list is easier
than newsgroup. It is easy to
compose and receive emails.
Working with a particular newsgroup
requires proper knowledge of that
newsgroup.
3. In order to send or receive mails,
you required an email program. It requires a newsgroup reader.
4. Messages are delivered to certain
group of people. Messages are available to public.
5. Mailing list does not support
threaded discussion. Newsgroup supports threaded discussion.
6. Messages delivered to listed
subscribers can not be cancelled.
Article posted on a newsgroup can be
cancelled.
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Internet Security Introduction Internet security refers to securing communication over the internet. It
includes specific security protocols such as:
Internet Security Protocol (IPSec)
Secure Socket Layer (SSL)
Internet Security Protocol (IPSec)
It consists of a set of protocols designed by Internet Engineering Task Force
(IETF). It provides security at network level and helps to create
authenticated and confidential packets for IP layer.
Secure Socket Layer (SSL)
It is a security protocol developed by Netscape Communications
Corporation. ). It provides security at transport layer. It addresses the
following security issues:
Privacy
Integrity
Authentication
Threats Internet security threats impact the network, data security and other
internet connected systems. Cyber criminals have evolved several
techniques to threat privacy and integrity of bank accounts, businesses, and
organizations.
Following are some of the internet security threats:
Mobile worms
Malware
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PC and Mobile ransomware
Large scale attacks like Stuxnet that attempts to destroy infrastructure.
Hacking as a Service
Spam
Phishing
Email Phishing Email phishing is an activity of sending emails to a user claiming to be a
legitimate enterprise. Its main purpose is to steal sensitive information such
as usernames, passwords, and credit card details.
Such emails contains link to websites that are infected with malware and
direct the user to enter details at a fake website whose look and feels are
same to legitimate one.
What a phishing email may contain?
Following are the symptoms of a phishing email:
SPELLING AND BAD GRAMMAR
Most often such emails contain grammatically incorrect text. Ignore such
emails, since it can be a spam.
BEWARE OF LINKS IN EMAIL
Don’t click on any links in suspicious emails.
THREATS
Such emails contain threat like “your account will be closed if you didn’t
respond to an email message”.
SPOOFING POPULAR WEBSITES OR COMPANIES
These emails contain graphics that appear to be connected to legitimate
website but they actually are connected to fake websites.
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Data Encryption Introduction Encryption is a security method in which information is encoded in such a
way that only authorized user can read it. It uses encryption algorithm to
generate ciphertext that can only be read if decrypted.
Types of Encryption
There are two types of encryptions schemes as listed below:
Symmetric Key encryption
Public Key encryption
SYMMETRIC KEY ENCRYPTION
Symmetric key encryption algorithm uses same cryptographic keys for
both encryption and decryption of cipher text.
PUBLIC KEY ENCRYPTION
Public key encryption algorithm uses pair of keys, one of which is a
secret key and one of which is public. These two keys are mathematically
linked with each other.
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Hashing In terms of security, hashing is a technique used to encrypt data and
generate unpredictable hash values. It is the hash function that generates
the hash code, which helps to protect the security of transmission from
unauthorized users.
Hash function algorithms
Hashing algorithm provides a way to verify that the message received is
the same as the message sent. It can take a plain text message as input
and then computes a value based on that message.
Key Points
The length of computed value is much shorter than the original message.
It is possible that different plain text messages could generate the same value.
Here we will discuss a sample hashing algorithm in which we will multiply
the number of a’s, e’s and h’s in the message and will then add the number
of o’s to this value.
For example, the message is “ the combination to the safe is two, seven,
thirty-five”. The hash of this message, using our simple hashing algorithm
is as follows:
2 x 6 x 3 ) + 4 = 40
The hash of this message is sent to John with cipher text. After he decrypts
the message, he computes its hash value using the agreed upon hashing
algorithm. If the hash value sent by Bob doesn’t match the hash value of
decrypted message, John will know that the message has been altered.
For example, John received a hash value of 17 and decrypted a message
Bob has sent as “You are being followed, use backroads, hurry”
He could conclude the message had been altered, this is because the hash
value of the message he received is:
(3x4x1)+4 = 16 . This is different from then value 17 that Bob sent.
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Digital Signature Digital signatures allow us to verify the author, date and time of
signatures, authenticate the message contents. It also includes
authentication function for additional capabilities.
A digital signature should not only be tied to the signing user, but also to the message.
Applications There are several reasons to implement digital signatures to
communications:
Authentication
Digital signatures help to authenticate the sources of messages. For
example, if a bank’s branch office sends a message to central office,
requesting for change in balance of an account. If the central office could
not authenticate that message is sent from an authorized source, acting of
such request could be a grave mistake.
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Integrity
Once the message is signed, any change in the message would invalidate
the signature.
Non-repudiation
By this property, any entity that has signed some information cannot at a
later time deny having signed it.
Firewall Security Firewall is a barrier between Local Area Network (LAN) and the Internet. It
allows keeping private resources confidential and minimizes the security
risks. It controls network traffic, in both directions.
The following diagram depicts a sample firewall between LAN and the
internet. The connection between the two is the point of vulnerability. Both
hardware and the software can be used at this point to filter network traffic.
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There are two types of Firewall system: One works by using filters at the network layer
and the other works by using proxy servers at the user, application, or network layer.
Key Points
Firewall management must be addressed by both system managers and the
network managers.
The amount of filtering a firewall varies. For the same firewall, the amount of
filtering may be different in different directions.
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HTML Introduction HTML stands for Hyper Text Markup Language. It is a formatting
language used to define the appearance and contents of a web page. It
allows us to organize text, graphics, audio, and video on a web page.
Key Points:
The word Hypertext refers to the text which acts as a link.
The word markup refers to the symbols that are used to define structure of the
text. The markup symbols tells the browser how to display the text and are
often called tags.
The word Language refers to the syntax that is similar to any other language.
HTML was created by Tim Berners-Lee at CERN.
HTML Versions
The following table shows the various versions of HTML:
Version Year
HTML 1.0 1991
HTML 2.0 1995
HTML 3.2 1997
HTML 4.0 1999
XHTML 2000
HTML5 2012
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HTML Tags Tag is a command that tells the web browser how to display the text,
audio, graphics or video on a web page.
Key Points:
Tags are indicated with pair of angle brackets.
They start with a less than (<) character and end with a greater than (>)
character.
The tag name is specified between the angle brackets.
Most of the tags usually occur in pair: the start tag and the closing tag.
The start tag is simply the tag name is enclosed in angle bracket whereas the
closing tag is specified including a forward slash (/).
Some tags are the empty i.e. they don’t have the closing tag.
Tags are not case sensitive.
The starting and closing tag name must be the same. For example <b> hello
</i> is invalid as both are different.
If you don’t specify the angle brackets (<>) for a tag, the browser will treat the
tag name as a simple text.
The tag can also have attributes to provide additional information about the tag
to the browser.
Basic tags The following table shows the Basic HTML tags that define the basic web
page:
Tag Description
<html> </html> Specifies the document as a web page.
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<head> </head> Specifies the descriptive information about the web documents.
<title> </title> Specifies the title of the web page.
<body> </body> Specifies the body of a web document.
The following code shows how to use basic tags.
<html>
<head> Heading goes here…</head>
<title> Title goes here…</title>
<body> Body goes here…</body>
</html>
Formatting Tags The following table shows the HTML tags used for formatting the text:
Tag Description
<b> </b> Specifies the text as bold. Eg. this is bold text
<em> </em> It is a phrase text. It specifies the emphasized text.
Eg.Emphasized text
<strong>
</strong>
It is a phrase tag. It specifies an important text. Eg. this is
strong text
<i> </i> The content of italic tag is displayed in italic. Eg. Italic text
<sub> </sub> Specifies the subscripted text. Eg. X1
<sup> </sup> Defines the superscripted text. Eg. X2
<ins> </ins> Specifies the inserted text. Eg. The price of pen is now 2015.
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<del> </del> Specifies the deleted text. Eg. The price of pen is now 2015.
<mark> </mark> Specifies the marked text. Eg. It is raining
Table Tags Following table describe the commonaly used table tags:
Tag Description
<table> </table> Specifies a table.
<tr> </tr> Specifies a row in the table.
<th> </th> Specifies header cell in the table.
<td> </td> Specifies the data in an cell of the table.
<caption> </caption> Specifies the table caption.
<colgroup> </colgroup> Specifies a group of columns in a table for formatting.
List tags Following table describe the commonaly used list tags:
Tag Description
<ul> </ul> Specifies an unordered list.
<ol> </ol> Specifies an ordered list.
<li> </li> Specifies a list item.
<dl> </dl> Specifies a description list.
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<dt> </dt> Specifies the term in a description list.
<dd> </dd> Specifies description of term in a description list.
Frames Frames help us to divide the browser’s window into multiple rectangular
regions. Each region contains separate html web page and each of them
work independently.
A set of frames in the entire browser is known as frameset. It tells the browser how to
divide browser window into frames and the web pages that each has to load.
The following table describes the various tags used for creating frames:
Tag Description
<frameset>
</frameset>
It is replacement of the <body> tag. It doesn’t contain the tags
that are normally used in <body> element; instead it contains
the <frame> element used to add each frame.
<frame>
</frame> Specifies the content of different frames in a web page.
<base>
</base>
It is used to set the default target frame in any page that
contains links whose contents are displayed in another frame.
Forms Forms are used to input the values. These values are sent to the server for
processing. Forms uses input elements such as text fields, check boxes,
radio buttons, lists, submit buttons etc. to enter the data into it.
The following table describes the commonly used tags while creating a
form:
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Tag Description
<form> </form> It is used to create HTML form.
<input> </input> Specifies the input field.
<textarea>
</textarea>
Specifies a text area control that allows to enter multi-line
text.
<label> </label> Specifies the label for an input element.
CSS Introduction CSS is acronym of Cascading Style Sheets. It helps to define the
presentation of HTML elements as a separate file known as CSS file
having .cssextension.
CSS helps to change formatting of any HTML element by just making
changes at one place. All changes made would be reflected automatically to
all of the web pages of the website in which that element appeared.
CSS Rules
CSS Rules are the styles that we have to create in order to create style
sheets. These rules define appearance of associated HTML element. The
general form of CSS syntax is as follows:
Selector {property: value;}
Key Points
Selector is HTML element to which CSS rule is applied.
Property specifies the attribute that you want to change corresponding to the
selector.
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Property can take specified value.
Property and Value are separated by a colon (:).
Each declaration is separated by semi colon (;).
Following are examples of CSS rules:
P { color : red;}
h1 (color : green; font-style : italic }
body { color : cyan; font-family : Arial; font- style : 16pt}
Embedding CSS into HTML Following are the four methods to add CSS to HTML documents.
1. Inline Style Sheets
2. Embedded Style Sheets
3. External Style Sheets
4. Imported Style Sheets
Inline Style Sheets
Inline Style Sheets are included with HTML element i.e. they are placed
inline with the element. To add inline CSS, we have to declare style
attribute which can contain any CSS property.
Syntax:
<Tagname STYLE = “ Declaration1 ; Declaration2 “> …. </Tagname>
Let’s consider the following example using Inline Style Sheets:
<p style="color: blue; text-align: left; font-size: 15pt">
Inline Style Sheets are included with HTML element i.e. they are placed inline with the
element.
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To add inline CSS, we have to declare style attribute which can contain any CSS property.
</p>
Output −
Embedded Style Sheets
Embedded Style Sheets are used to apply same appearance to all
occurrence of a specific element. These are defined in <head> element by
using the<style> element.
The <style> element must include type attribute. The value of typeattribute specifies
what type of syntax it includes when rendered by the browser.
Syntax
<head> <title> …. </title>
<style type =”text/css”>
…….CSS Rules/Styles….
</head>
Let’s consider the following example using Embedded Style Sheets:
<style type="text/css">
p {color:green; text-align: left; font-size: 10pt}
h1 { color: red; font-weight: bold}
</style>
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External Style Sheets
External Style Sheets are the separate .css files that contain the CSS
rules. These files can be linked to any HTML documents using <link> tag
with rel attribute.
Syntax:
<head> <link rel= “stylesheet” type=”text/css” href= “url of css file”>
</head>
In order to create external css and link it to HTML document, follow the
following steps:
First of all create a CSS file and define all CSS rules for several HTML elements.
Let’s name this file as external.css.
p
{
Color: orange; text-align: left; font-size: 10pt;
}
h1
{
Color: orange; font-weight: bold;
}
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Now create HTML document and name it as externaldemo.html.
<html>
<head>
<title> External Style Sheets Demo </title>
<link rel="stylesheet" type="text/css" href="external.css">
</head>
<body>
<h1> External Style Sheets</h1>
<p>External Style Sheets are the separate .css files that contain the CSS rules.</p>
</body>
</html>
Imported Style Sheets
Imported Style Sheets allow us to import style rules from other style
sheets. To import CSS rules we have to use @import before all the rules in
a style sheet.
Syntax:
<head><title> Title Information </title>
<style type=”text/css”>
@import URL (cssfilepath)
… CSS rules…
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</style>
</head>
</style>
Let’s consider the following example using Inline Style Sheets:
<html>
<head>
<title> External Style Sheets Demo </title>
<style>
@import url(external.css);
</style>
</head>
<body>
<h1> External Style Sheets</h1>
<p>External Style Sheets are the separate .css files that contain the CSS rules.</p>
</body>
</html>
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JavaScript Introduction JavaScript is a lightweight, interpreted programming language with object-
oriented capabilities that allows you to build interactivity into otherwise
static HTML pages.
JavaScript code is not compiled but translated by the translator. This translator is
embedded into the browser and is responsible for translating javascript code.
Key Points
It is Lightweight, interpreted programming language.
It is designed for creating network-centric applications.
It is complementary to and integrated with Java.
It is complementary to and integrated with HTML
It is an open and cross-platform
JavaScript Statements JavaScript statements are the commands to tell the browser to what action
to perform. Statements are separated by semicolon (;).
JavaScript statement constitutes the JavaScript code which is translated by the browser
line by line.
Example of JavaScript statement:
document.getElementById("demo").innerHTML = "Welcome";
Following table shows the various JavaScript Statements −
Sr.No. Statement Description
1. switch case A block of statements in which execution of code depends
upon different cases. The interpreter checks each case
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against the value of the expression until a match is found.
If nothing matches, a default condition will be used.
2. If else The if statement is the fundamental control statement that
allows JavaScript to make decisions and execute
statements conditionally.
3. While The purpose of a while loop is to execute a statement or
code block repeatedly as long as expression is true. Once
expression becomes false, the loop will be exited.
4. do while Block of statements that are executed at least once and
continues to be executed while condition is true.
5. for Same as while but initialization, condition and
increment/decrement is done in the same line.
6. for in This loop is used to loop through an object's properties.
7. continue The continue statement tells the interpreter to immediately
start the next iteration of the loop and skip remaining code
block.
8. break The break statement is used to exit a loop early, breaking
out of the enclosing curly braces.
9. function A function is a group of reusable code which can be called
anywhere in your programme. The keyword function is used
to declare a function.
10. return Return statement is used to return a value from a function.
11. var Used to declare a variable.
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12. try A block of statements on which error handling is
implemented.
13. catch A block of statements that are executed when an error
occur.
14. throw Used to throw an error.
JavaScript Comments JavaScript supports both C-style and C++-style comments, thus:
Any text between a // and the end of a line is treated as a comment and is
ignored by JavaScript.
Any text between the characters /* and */ is treated as a comment. This may
span multiple lines.
JavaScript also recognizes the HTML comment opening sequence <!--.
JavaScript treats this as a single-line comment, just as it does the // comment.-
->
The HTML comment closing sequence --> is not recognized by JavaScript so it
should be written as //-->.
Example
<script language="javascript" type="text/javascript">
<!--
// this is a comment. It is similar to comments in C++
/*
* This is a multiline comment in JavaScript
* It is very similar to comments in C Programming
*/
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//-->
<script>
JavaScript variable Variables are referred as named containers for storing information. We can
place data into these containers and then refer to the data simply by
naming the container.
Rules to declare variable in JavaScript
Here are the important rules that must be followed while declaring a
variable in JavaScript.
In JavaScript variable names are case sensitive i.e. a is different from A.
Variable name can only be started with a underscore ( _ ) or a letter (from a to
z or A to Z), or dollar ( $ ) sign.
Numbers (0 to 9) can only be used after a letter.
No other special character is allowed in variable name.
Before you use a variable in a JavaScript program, you must declare it.
Variables are declared with the var keyword as follows −
<script type="text/javascript">
<!--
var money;
var name, age;
//-->
</script>
Variables can be initialized at time of declaration or after declaration as
follows −
<script type="text/javascript">
<!--
var name = "Ali";
var money;
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money = 2000.50;
//-->
</script>
Javascript Data Type There are two kinds of data types as mentioned below −
Primitive Data Type
Non Primitive Data Type
The following table describes Primitive Data Types available in javaScript
Sr.No. Datatype Description
1. String
Can contain groups of character as single value. It is represented in
double quotes.E.g. var x= “tutorial”.
2. Numbers
Contains the numbers with or without decimal. E.g. var x=44, y=44.56;
3. Booleans
Contain only two values either true or false. E.g. var x=true, y= false.
4. Undefined
Variable with no value is called Undefined. E.g. var x;
5. Null
If we assign null to a variable, it becomes empty. E.g. var x=null;
The following table describes Non-Primitive Data Types in javaScript
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Sr.No. Datatype Description
1. Array
Can contain groups of values of same type. E.g. var x={1,2,3,55};
2. Objects
Objects are stored in property and value pair. E.g. var rectangle = {
length: 5, breadth: 3};
JavaScript Functions Function is a group of reusable statements (Code) that can be called any
where in a program. In javascript function keyword is used to declare or
define a function.
Key Points
To define a function use function keyword followed by functionname, followed by
parentheses ().
In parenthesis, we define parameters or attributes.
The group of reusabe statements (code) is enclosed in curly braces {}. This
code is executed whenever function is called.
Syntax
function functionname (p1, p2) {
function coding…
}
JavaScript Operators Operators are used to perform operation on one, two or more operands.
Operator is represented by a symbol such as +, =, *, % etc. Following are
the operators supported by javascript −
Arithmetic Operators
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Comparison Operators
Logical (or Relational) Operators
Assignment Operators
Conditional (or ternary) Operators
Arithmetic Operators
Arithmatic Operators
Following table shows all the arithmetic operators supported by javascript −
Operator Description Example
+ Add two operands. 10 + 10 will give
20
- Subtract second operand from the first. 10 – 10 will give
0
* Multiply two operands. 10 * 30 will give
300
/ Divide numerator by denominator 10/10 will give 1
% It is called modulus operator and gives remainder
of the division.
10 % 10 will give
0
++ Increment operator, increases integer value by
one
10 ++ will give
11
-- Decrement operator, decreases integer value by
one
10 – will give 9
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Comparison Operators
Following table shows all the comparison operators supported by javascript
−
Operator Description Example
== Checks if values of two operands are equal or not, If
yes then condition becomes true.
10 == 10 will
give true
!= Not Equal to operator
Checks if the value of two operands is equal or not, if
values are not equal then condition becomes true.
10 !=10 will
give false
> Greater Than operator
Checks if the value of left operand is greater than the
value of right operand, if yes then condition becomes
true.
20 > 10 will
give true
< Less than operator
Checks if the value of left operand is less than the
value of right operand, if yes then condition becomes
true.
10 < 20 will
give true
>= Greater than or equal to operator
Checks if the value of left operand is greater than or
equal to the value of right operand, if yes then
condition becomes true.
10 >=20 will
give false
<= Less than or equal to operator
Checks if the value of left operand is less than or
equal to the value of right operand, if yes then
condition becomes true.
10 <=20 will
give true.
Logical Operators
Following table shows all the logical operators supported by javascript −
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Operator Description Example
&& Logical AND operator returns true if both
operands are non zero.
10 && 10 will give
true.
|| Logical OR operator returns true If any of the
operand is non zero
10 || 0 will give
true.
! Logical NOT operator complements the logical
state of its operand.
! (10 && 10) will
give false.
Assignment Operators
Following table shows all the assignment operators supported by javascript
−
Operator Description Example
= Simple Assignment operator
Assigns values from right side operands to left
side operand.
C = A + B will assign
value of A + B into C
+= Add AND assignment operator
It adds right operand to the left operand and
assign the result to left operand
C += A is equivalent
to C = C + A
-= Subtract AND assignment operator
It subtracts right operand from the left
operand and assign the result to left operand
C -= A is equivalent
to C = C - A
*= Multiply AND assignment operator
It multiplies right operand with the left
operand and assign the result to left operand
C *= A is equivalent
to C = C * A
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/= Divide AND assignment operator
It divides left operand with the right operand
and assign the result to left operand
C /= A is equivalent
to C = C / A
%= Modulus AND assignment operator
Modulus AND assignment operator, It takes
modulus using two operands and assign the
result to left operand
C %= A is equivalent
to C = C % A
Conditional Operator
It is also called ternary operator, since it has three operands.
Operator Description Example
?: Conditional
Expression
If Condition is true? Then value X : Otherwise
value Y
Control Structure Control structure actually controls the flow of execution of a program.
Following are the several control structure supported by javascript.
if … else
switch case
do while loop
while loop
for loop
If … else
The if statement is the fundamental control statement that allows
JavaScript to make decisions and execute statements conditionally.
Syntax
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if (expression){
Statement(s) to be executed if expression is true
}
Example
<script type="text/javascript">
<!--
var age = 20;
if( age > 18 ){
document.write("<b>Qualifies for driving</b>");
}
//-->
</script>
Switch case
The basic syntax of the switch statement is to give an expression to
evaluate and several different statements to execute based on the value of
the expression. The interpreter checks each case against the value of the
expression until a match is found. If nothing matches, a default condition
will be used.
Syntax
switch (expression)
{
case condition 1: statement(s)
break;
case condition 2: statement(s)
break;
...
case condition n: statement(s)
break;
default: statement(s)
}
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Example
<script type="text/javascript">
<!--
var grade='A';
document.write("Entering switch block<br/>");
switch (grade)
{
case 'A': document.write("Good job<br/>");
break;
case 'B': document.write("Pretty good<br/>");
break;
case 'C': document.write("Passed<br/>");
break;
case 'D': document.write("Not so good<br/>");
break;
case 'F': document.write("Failed<br/>");
break;
default: document.write("Unknown grade<br/>")
}
document.write("Exiting switch block");
//-->
</script>
Do while Loop
The do...while loop is similar to the while loop except that the condition
check happens at the end of the loop. This means that the loop will always
be executed at least once, even if the condition is false.
Syntax
do{
Statement(s) to be executed;
} while (expression);
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Example
<script type="text/javascript">
<!--
var count = 0;
document.write("Starting Loop" + "<br/>");
do{
document.write("Current Count : " + count + "<br/>");
count++;
}while (count < 0);
document.write("Loop stopped!");
//-->
</script>
This will produce following result −
Starting Loop
Current Count : 0
Loop stopped!
While Loop
The purpose of a while loop is to execute a statement or code block
repeatedly as long as expression is true. Once expression becomes false,
the loop will be exited.
Syntax
while (expression){
Statement(s) to be executed if expression is true
}
Example
<script type="text/javascript">
<!--
var count = 0;
document.write("Starting Loop" + "<br/>");
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while (count < 10){
document.write("Current Count : " + count + "<br/>");
count++;
}
document.write("Loop stopped!");
//-->
</script>
This will produce following result −
Starting Loop
Current Count : 0
Current Count : 1
Current Count : 2
Current Count : 3
Current Count : 4
Current Count : 5
Current Count : 6
Current Count : 7
Current Count : 8
Current Count : 9
Loop stopped!
For Loop
The for loop is the most compact form of looping and includes the following
three important parts −
The loop initialization where we initialize our counter to a starting value. The
initialization statement is executed before the loop begins.
The test statement which will test if the given condition is true or not. If
condition is true then code given inside the loop will be executed otherwise loop
will come out.
The iteration statement where you can increase or decrease your counter.
Syntax
for (initialization; test condition; iteration statement){
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Statement(s) to be executed if test condition is true
}
Example
<script type="text/javascript">
<!--
var count;
document.write("Starting Loop" + "<br/>");
for(count = 0; count < 10; count++){
document.write("Current Count : " + count );
document.write("<br/>");
}
document.write("Loop stopped!");
//-->
</script>
This will produce following result which is similar to while loop −
Starting Loop
Current Count : 0
Current Count : 1
Current Count : 2
Current Count : 3
Current Count : 4
Current Count : 5
Current Count : 6
Current Count : 7
Current Count : 8
Current Count : 9
Loop stopped!
Creating Sample Program Following is the sample program that shows time, when we click in button.
<html>
<body>
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<button onclick="this.innerHTML=Date()">The time is?</button>
<p>Click to display the date.</p>
<button onclick="displayDate()">The time is?</button>
<script>
function displayDate() {
document.getElementById("demo").innerHTML = Date();
}</script>
<p id="demo"></p>
</body>
</html>
Output
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PHP Introduction PHP is acronym of Hypertext Preprocessor (PHP) is a programming
language that allows web developers to create dynamic content that
interacts with databases.PHP is basically used for developing web based
software applications.
PHP started out as a small open source project that evolved as more and
more people found out how useful it was. Rasmus Lerdorf unleashed the
first version of PHP way back in 1994.
Key Points
PHP is a recursive acronym for "PHP: Hypertext Preprocessor".
PHP is a server side scripting language that is embedded in HTML. It is used to
manage dynamic content, databases, session tracking, even build entire e-
commerce sites.
It is integrated with a number of popular databases, including MySQL,
PostgreSQL, Oracle, Sybase, Informix, and Microsoft SQL Server.
PHP is pleasingly zippy in its execution, especially when compiled as an Apache
module on the Unix side. The MySQL server, once started, executes even very
complex queries with huge result sets in record-setting time.
PHP supports a large number of major protocols such as POP3, IMAP, and LDAP.
PHP4 added support for Java and distributed object architectures (COM and
CORBA), making n-tier development a possibility for the first time.
Uses of PHP PHP has now become a poupular scripting language among web developer
due to the following reasons −
PHP performs system functions, i.e. from files on a system it can create, open,
read, write, and close them.
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PHP can handle forms, i.e. gather data from files, save data to a file, through
email you can send data, return data to the user.
You add, delete, modify elements within your database through PHP.
Access cookies variables and set cookies.
Using PHP, you can restrict users to access some pages of your website.
It can encrypt data.
Characteristics Five important characteristics make PHP's practical nature possible −
Simplicity
Efficiency
Security
Flexibility
Familiarity
"Hello World" Script in PHP To get a feel for PHP, first start with simple PHP scripts. Since "Hello,
World!" is an essential example, first we will create a friendly little "Hello,
World!" script.
As mentioned earlier, PHP is embedded in HTML. That means that in
amongst your normal HTML (or XHTML if you're cutting-edge) you'll have
PHP statements like this −
<html>
<head>
<title>Hello World</title>
</head>
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<body>
<?php echo "Hello, World!";?>
</body>
</html>
It will produce following result −
Hello, World!
If you examine the HTML output of the above example, you'll notice that
the PHP code is not present in the file sent from the server to your Web
browser. All of the PHP present in the Web page is processed and stripped
from the page; the only thing returned to the client from the Web server is
pure HTML output.
All PHP code must be included inside one of the three special markup tags
ate are recognised by the PHP Parser.
<?php PHP code goes here ?>
<? PHP code goes here ?>
<script language="php"> PHP code goes here </script>
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