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.

For example, a DNS server will resolve a name https://freeknowledg.blogspot.in/ to a particular IP address to uniquely identify the computer on which this website is hosted.

This tutorial has been prepared for the students as well as professionals to ramp up quickly. This tutorial is also easily understood by general person with an interest in becoming computer literate.

Before proceeding with this tutorial you should have a basic knowledge of Computers, which will help you in understanding this tutorial easily and quickly.

Internet Overview

Internet

Internet is defined as an Information super Highway, 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 name https://freeknowledg.blogspot.in/ 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

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.

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:

Facebook
Twitter
Yahoo
Google+
Flickr
Orkut

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.Online Television

Online Games
Songs
Videos
Social Networking Apps

Internet allows us to use many services like:

Internet Banking
Matrimonial Services
Online Shopping
Online Ticket Booking
Online Bill Payment
Data Sharing
E-mail

Internet provides concept of electronic commerce, that allows the business deals to be conducted on electronic systems

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.
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 among the computers in that Intranet.

Benefits

Intranet is very efficient and reliable network system for any organization. It is beneficial in every aspect such as collaboration, cost-effectiveness, security, productivity and much more.

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.

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:

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:

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.

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.

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.

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:
internet_technologies_tutorial

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:

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.

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.

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 the layer above.

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.

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:

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:

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.

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.

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 webmaster@tutorialspoint.com.

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.

For example, https://freeknowledg.blogspot.in/p/cloud-computing.html is an URL to the index.html which is stored on the knowledge tree web server under internet_technology directory.

URL Types

There are two forms of URL as listed below:

Absolute URL
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 https://freeknowledg.blogspot.in/p/cloud-computing.html. where:

http is the protocol.
freeknowledg.blogspot.in is the server name.
cloud-computing.html 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

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 https://freeknowledg.blogspot.in/p/cloud-computing.html, we can use the relative URL which can take the form like /cloud-computing.html.

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:

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
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.

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.

TYPES OF NAME SERVERS

Following are the three categories of Name Servers that manages the entire Domain Name System:

Root Server
Primary Server
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.freeknowledg.blogspot.in 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.

The root DNS server replies with delegation that I do not know the IP address of www.freeknowledg.blogspot.in but know the IP address of DNS Server.

The local DNS server then asks the com DNS Server the same question.

The in DNS Server replies the same that it does not know the IP address of www.freeknowledg.blogspot.in but knows the address of freeknowledg.blogspot.in

Then the local DNS asks the freeknowledg.blogspot.in DNS server the same question.

Then freeknowledg.blogspot.in DNS server replies with IP address of freeknowledg.blogspot.in.

Now, the local DNS sends the IP address of www.freeknowledg.blogspot.in to the computer that sends the request.

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 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.

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 Multi-point Control Unit (MCU).

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.

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:

Dial-up Connection
ISDN
DSL
Cable TV Internet connections
Satellite Internet connections
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:

Serial Line Internet Protocol (SLIP)
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:

Basic Rate Interface (BRI)
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:

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:

Asymmetric DSL (ADSL)
Symmetric DSL (SDSL)
High bit-rate DSL (HDSL)
Rate adaptive DSL (RDSL)
Very high bit-rate DSL (VDSL)
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:

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:

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:

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).

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:

Stream Data Transfer.

Reliability.

Efficient Flow Control

Full-duplex operation.

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

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:

TCP of process-1 informs TCP of process – 2 and gets its approval.
TCP of process – 1 and TCP of process – 2 and exchange data in both the two directions.
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.

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.

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.

Control connection is made between control processes while Data Connection is made between

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.

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.

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

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, webmaster@tutorialspoint.com 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:

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

Subject

BCC

FROM

The From field indicates the sender’s address i.e. who sent the e-mail.

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

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:

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.

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 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:

Original IMAP
IMAP2
IMAP3
IMAP2bis
IMAP4

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.
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.

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 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.

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.

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.

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?

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)

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.

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.

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.

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

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.

E-mail Security

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.
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

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 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.