Internet Principles
In 1984 William Gibson in his sci-fi novel Neuromancer coined the term Cyberspace. It refers
to the non-physical terrain created by computer systems. Online systems, for example, create a
cyberspace within which people can communicate with one another (via e-mail), do research, or
simply window shop. Like physical space, cyberspace contains objects (files, mail messages,
graphics, etc.) and different modes of transportation and delivery. Unlike real space, exploring
cyberspace does not require any physical movement other than pressing keys on a keyboard or
moving a mouse. Some programs, particularly computer games, are designed to create a special
cyberspace, one that resembles physical reality in some ways but defies it in others. In its ex-
treme form, called virtual reality, users are presented with visual, auditory, and even tactile feed-
back that makes cyberspace feel real. The dreams of William Gibson is becoming a reality in the Internet world.
1.1 Introduction to Internet
A network of computers refers to a group of computers connected with each other as per a topol-
ogy. The computers in a network are capable of sharing the resources among themselves, the
resources such as memory, peripherals, etc. They communicate with each other in a defined way.
Internet refers to a global network connecting millions of computers. More than 100 countries
are linked into exchanges of data, news and opinions. Unlike online network services, which are
centrally controlled, the Internet is decentralized by design. Each Internet computer, called a
host, is independent. Its operators can choose which Internet services to use and which local
services to make available to the global Internet community. Remarkably, this anarchy by design
works exceedingly well. There are a variety of ways to access the Internet. Most of the Internet
users gain access through a commercial Internet Service Provider (1SP) as illustrated in Figure
1.1. Usually we connect our Home PC to the Internet through the landline telephone connection
using a device called modem as shown in Figure 1.2. So, the following two factors decide the
characteristics of the Internet services.
1 modem
2 Connectivity for communication
1.1.1 Modem
A modem (short form of modulator-demodulator) is a device that enables a computer to trans-
mit data over, for example, telephone or cable lines. Computer information is stored digitally,
whereas information transmitted over telephone lines is transmitted in the form of analog waves.
A modem converts between these two forms.
Fortunately, there is one standard interface for connecting external modems to computers
called RS-232. Consequently, any external modem can be attached to any computer that has an
RS-232 port, which almost all personal computers have. There are also modems that come as an
expansion board that you can insert into a vacant expansion slot. These are sometimes called
onboard or internal modems.
While the modem interfaces are standardized. a number of different protocols for formatting
data to be transmitted over telephone lines exist. Some, like CCITT V.34, are official standards,
while others have been developed by private companies. Most modems have built-in support for
the more common protocols-at slow data transmission speeds at least, most modems can
communicate with each other. At high transmission speeds, however, the protocols are less
standardized.
Characteristics ofa Modem
Aside from the transmission protocols that they support, the following characteristics distinguish
one modem from another:
1. Speed of transmission
Internet Principles 3
At slow rates, modems are measured in terms of baud rates. The slowest rate is 300 baud (about
25 characters per secondcps). At higher speeds, modems are measured in terms of bits per sec-
ond (bps). A fast modem transmits at 57,600 bps, although they can achieve even higher data
transfer rates by compressing the data. Obviously, the faster the transmission rate, the faster you
can send and receive data. Note, however, that you cannot receive data any faster than it is being
sent. If, for example, the device sending data to your computer is sending it at 2,400 bps, you
must receive it at 2,400 bps. It does not always pay, therefore, to have a very fast modem. In
addition, some telephone lines are unable to transmit data reliably at very high rates.
2. Modes supported
Many modems support a switch to change between voice and data modes. In data mode, the
modem acts like a regular modem. In voice mode, the modem acts like a regular telephone.
Modems that support a voice/data switch have a built-in loudspeaker and microphone for voice
Communication.
3. Aut0-answer
An aut0-answer modem enables your computer to receive calls in your absence. This is only
necessary if you are offering some type of computer service that people can call in to use.
4. Data compression
Some modems perform data compression, which enables them to send data at faster rates. How-
ever, the modem at the receiving end must be able to decompress the data using the same compression technique.
5. Flash memory
Some modems come with flash memory rather than conventional ROM. which means that the
communication protocols can be easily updated if necessary.
6. Fax capability
Most modern modems are fax modems, which means that they can send and receive faxes
1.1.2 Connectivity for Communication
Connectivity is considered to be the backbone of the Internet world. Apart from ordinary tol
ephone line we are also using broad band connectivity such as ISDN connections.
1.1.3 Standards of Data Communication
The CCITT (Comité Consultatif International Téléphonique et Télégraphique ) is an organiza-
tion that sets international communications standards. It has developed the X.400 standard
which attempts to provide a universal way of addressing messages. To date, though, the de facto
addressing standard is the one used by the Internet system because almost all e-mail systems
have an Internet gateway.
CCITT has defined many important standards for data communications, including the
following:
Group 3: The universal protocol for sending fax documents across telephone lines. The
Group 3 protocol specifies CCITT T.4 data compression and a maximum transmission rate
of 9,600 baud. There are two levels of resolution: 203 by 98 and 203 by 196.
Group 4: A protocol for sending fax documents over ISDN networks. The Group 400
protocol supports images of up to 400 dpi (dots per inch) resolution.
V.21: The standard for full-duplex communication at 300 baud in Japan and Europe. In the
United States, Bell 103 is used in place of V.21.
V.22: The standard for half-duplex communication at 1,200 bps in Japan and Europe. In the
United States, the protocol defined by Bell 212A is more common.
V22bis: The worldwide standard for full-duplex modems sending and receiving data
across telephone lines at 1,200 or 2,400 bps.
V.29: The standard for half-duplex modems sending and receiving data across telepnone
lines at 1,200, 2,400, 4,800, or 9,600 bps. This is the protocol used by fax modems.
V.32: The standard for full-duplex modems sending and receiving data across phone ines
at 4,800 or 9,600 bps. V.32 modems automatically adjust their transmission speeds base on the quality of the lines.
V.32bis: The V.32 protocol extended to speeds of 7.200, 12,000, and 14,400 bps.
V.34: The standard for full-duplex modems sending and receiving data across phone lineS
at up to 28,800 bps. V.34 modems automatically adjust their transmission speeds based on
the quality of the lines.
V42: An error-detection standard for high-speed modems. V.42 can be used with digital
telephone networks. See MNP for a competing standard.
VA2bis: A data compression protocol that can enable modems to achieve a data transter
rate of 34,000 bps.
The standard for full-duplex modems sending and receiving data across phone lines
at up to 56,600 bps.
X.25: The most popular packet-switching protocol for WANs.
X400: The universal protocol for e-mail. X.400 defines the envelope for e-mail messages
so all messages conform to a standard format.
X.500: An extension to X.400 that defines addressing formats so all e-mail systems can be
linked together.
1.1.4 ISDN Connections
ISDN is the abbreviation of integrated services digital network, an international communications
standard for sending voice, video, and data over digital telephone lines or normal telephone
wires. ISDN supports data transfer rates of 64 Kbps (64,000 bits per second). Typically an ISDN
connection has some Bearer-channels (B-channel) which are the main data channel and some
Delta-channels (D-channel ), the channel that carries control and signaling information
There are two types of ISDN as shown in Table 1.1.1.
1 Basic Rate (BRI) ISDN that consists of two 64-Kbps B-channels and one D-channel for
transmitting control information.
2 Primary Rate ISDN. In the United States of America and a few other countries this type of
ISDN consists of 23 B-channels and one D-channel. In the Europe these have 30 B-channels and one D-channel.The original version of ISDN employs baseband transmission. Another version, called B.
ISDN, Uses broadband transmission and is able to support transmission rates of 1.5 MBPS. B-
ISDN requires fiber optic cables and is not widely available at present. The baseband and
broadband transmission are discussed in section 1.1.6.
1.1.5 DSL (Digital Subscriber Lines) Connection
DSL is the acronym for Digital Subscriber Lines. DSL technologies use sophisticated modula-
tion schemes to pack data onto copper wires. They are sometimes referred to as last-mile tech-
nologies because they are used only for connections from a telephone switching station to a
home or office, not between switching stations. DSL is similar to SDN in as much as both oper-
ate over existing copper telephone lines and both require the short runs to a central telephone
office (usually less than 20,000 feet). However, DSL offers much higher speeds-up to 32 Mbps
for upstream traffic (client to server), and from 32 Kbps to over 1 Mbps for downstream traffic
(server to client).
There two main categories being
0 Asymmetric digital subscriber line (ADSL)
1 Symmetric digital subscriber line (SDSL)
Depending upon the speed some also classify as follows:
2 High-data-rate DSL (HDSL)
3 Very high DSL (VDSL).
Asymmetric Digital Subscriber Line (ADSL)
Asymmetric digital subscriber line is a new technology that allows more data to be sent over
existing copper telephone lines. ADSL supports data transfer downstream rate from 1.5 to 9
Mbps and upstream rate from l6 to 640 Kbps. ADSL requires a special ADSL modem. ADSL is
growing in popularity as more areas around the world gain access to Internet.
Symmetric Digital Subscriber Line (SDSL)
Symmetric digital subscriber line is a technology that allows more data to be sent over existing
copper telephone lines. SDSL supports data rates up to 3 Mbps. SDSL works by sending digital
pulses in the high-frequency area of telephone wires. Since these high frequencies are not used
by normal voice communications, SDSL can operate simultaneously with voice connections over
the same wires. SDSL requres a special SDSL modem. SDSL is called symmetric because it
supports the same data rates for upstream and downstream traffic. ADSL is more popular in
North America, whereas SDSL is being developed primarily in Europe. A comparison of ADSL
and SDSL is shown in Table 1.1.2.
1.1.6 Broadband and Baseband Transmissions
Broadband transmission is a type of data transmission in which a single medium (wire) can carry
several channels at once. Cable TV, for example, uses broadband transmission. In contrast,
baseband transmission allows only one signal at a time.
Most communications between computers, including the majority of local-area networks use
only baseband communications. An exception is B-ISDN network., which employ broadband
transmission.
1.2 Client Server Model
Internet works in a client server model. This section throws some light on the servers that are
used in the marketplace today. Server Platforms refers to the operating system that drives the
Server.
1.2.1 Application Servers
Application Servers are the type of middleware, which occupy a large chunk of computing terri-
tory between database servers and the end user, and they often connect the two.
1.2.2 Audio/Video Servers
Audio/Video Servers bring multimedia capabilities to Web sites by enabling them to broadcast
streaming multimedia content.
1.2.3 Chat Servers
Chat Servers enable a large number of users to exchange information in an environment similar
to Internet newsgroups that offer real-time discussion capabilities.
1.2.4 Fax Servers
Fax Servers are ideal solution for organizations looking to reduce incoming and outgoing tel-
ephone resources but that need to fax actual documents.
8 Web Technology anu
1.2.5 FTP Servers
FTP Servers serve one of the oldest Internet services. It makes it possible to move one or more
files securely between computers while providing file security and organization as well as trans-
fer control.
1.2.6 Groupware Servers
A groupWare server is a software designed to enable users to collaborate, regardless of location
Via the Internet or a corporate intranet and to work together in a virtual atmosphere.
1.2.7 IRC Servers
IRC Servers provide an option for those seeking real-time discussion capabilities, Internet Relay
Chat consists of various separate networks (or "nets) of servers that alloW users to connect to
each other via an IRC network.
1.2.8 List Servers
List servers offer a way to better manage mailing lists, whether they be interactive discussions
open to the public or one-way lists that deliver announcements, newsletters, or advertising.
1.2.9 Mail Servers
Mail servers move and store mail over corporate networks (via LANS and WANs) and across the
Internet.
1.2.10 News Servers
News servers act as a distribution and delivery source for the thousands of public news groups
currently accessible over the USENET news network.
1.2.11 Proxy Servers
Proxy servers sit between a client program (typically a Web browser) and an external server
(typically another server on the Web) to filter requests, improve performance, and share
connections.
1.2.12 Web Servers
A web server is a computer system (Hardware and software) that delivers (serves up) Web pages.
Every Web server has an IP address and possibly a domain name. For example, if you enter theURL http: //www.stxaviers.com/index. html in your browser, this sends a request to the
server whose domain name is stxavier. com.
index. html and sends it to your browser.
The server then fetches the page namned
Any computer can be turned into a Web server by installing server software and connecting
the machine to the Internet. There are many Web server software applications, including public
domain software from NCSA and Apache, and commercial packages from Microsoft, Netscape
and others.
1.3 Protocol
A protocol is a program written as per mutually accepted standard that two computers use to
communicate with each other. Computers use protocols (protocol programs) to format
consistently their messages so that other computers can understand them, acknowledge the
receipt of messages, indicate that they are finished sending a message and so on. In the network
when one computer requests for the service of another, it is called a client. In order to establish
the needed connectivity, both the client machine and the server machine must have a common
protocol program. This is illustrated in Figure 1.3.
In short a protocol is an
protocol determines the following:
agreed-upon format for transmitting data between two devices. The
Server
the type of error checking to be used
data compression method, if any
how the sending device will indicate that it has finished sending a message
how the receiving device will indicate that it has received a messageThere are a variety of standard protocols from which programmers can ch0ose, Each has na
ticular advantages and disadvantages; for example, some are simpler than others, some are mo
reliable, and some are faster.
From a user's point of view, the only interesting aspect about protocols is that your compite.
or device must support the right ones if you want to communicate with other computers Th
protocol can be implemented either in hardware or in software.
Some standard protocols used in networks are listed below:
1. Simple Mail Transfer Protocol (SMTP)
2. Post Office Protocol version 3 (POP3)
3. Point to point Protocol/Serial Line Interface Protocol (POP/SLIP)
4. Transmission Control Protocol/Internet Protocol (TCP/IP)
5. Hyper Text Transfer Protocol (HTTP)
6. File Transfer Protocol (FTP)
7. Internet Mail Access Protocol (IMAP)
8. Internet Relay Chat (IRC)
9. Network News Transfer Protocol (NNTP)
10. Telnet
11. Gopher
12. Light weight Directory Access Protocol (LDAP)
1.3.1 Simple Mail Transfer Protocol
Simple Mail Transfer Protocol is used for sending e-mail messages between servers. Most e-
mail systems that send mail over the Internet use SMTP to send messages from one server to
another; the messages can then be retrieved with an e-mail client using either POP or IMAP. I
addition, SMTP is generally used to send messages from a mail client to a mail server. This is
why you need to specify both the POP or IMAP server and the SMTP server when you configure
your e-mail application.
1.3.2 Post Office Protocol (POP )
Post Office Protocol is a protocol used to retrieve e-mail from a inail server. Most e-mail appil
cations (e-mail client) use the POP protocol, although some can use the newer protocol Sucn a
IMAP (Internet Message Access Protocol). There are two versions of POP. The first, callee
POP2, became a standard in the mid-80's and requires SMTP to send messages. The newer Ve
sion, POP3, can be used with or without SMTP.
1.3.3 TCP/IP on the Internet
TCP/IP is the widely accepted protocol used in the networks. It is a protocol suite that consists
of several protocols including two primary protocols, Transmission Control Protocol (TCP) and
Internet Protocol (IP). The TCP/IP Protocol (protocol program) works asynchronously to handle
multiple message traffic simultaneously from multiple sources to multiple destinations as shown
in Figure 1.4. TCP (TCP Protocol program) handles the data integrity. It makes sure data gets to
the destination without errors. TCP is also responsible for disassembling and assembling the
data. It divides large messages into smaller packets of at the most 15 KB size. Each of this packet
1S called a segment. TCP numbers these segments and hands over to the IP. IP is the Protocol
(protocol program) that controls how data moves around on the network. After TCP divides the
message into segment, IP labels them with source and destination. These packets are now called
IP Datagrams. IP also takes care of sending the datagrams by determining the route. These
datagrams may hop several networks before reaching the destination.
At the destination the IP verifies the labels and passes them to the TCP. The TCP (at the des-
tination) checks if all the segments have been received. If any of the segments are missing it
informs this to the source TCP and requests the segment to be sent again. It is called retry. After
verification, the TCP assembles the message from these data segments and supplies to the destination program.
Packet Switching (Routing)
Routing (Packet Switching) refers to the job of transferring the data packets (IP datagrams) to an
appropriate computer. A special computer that does routing is called router. We have already
seen that Internet is a network of networks. So when a packet of data (IP datagram) starts from a
computer, it is submitted to the router of the network to which the computer belongs to. The
router verifies the IP address of the destination. The destination network may not be directly
reached. The router finds the next network to which the datagram must be submitted and does it.
Similarly the datagram passes several routers and finally reaches the final destination network.
Every router uses routing tables and routing algorithms to accomplish the job.
A
The routing algorithm will choose the next network to which the datagram may be routed de-
pending upon the data traffic and the shortest route. Datagrams of the same message may travel
through different routes to reach the final destination. But finally the TCP protocol takes care of
verifying if all the datagrams have reached. For example, suppose a Computer C1 in network A
wants to communicate with a Computer C2 in network F as shown in Figure 1.5.
When a message has to be sent from A to F, the message is disassembled into IP datagrams.
Some datagrams may travel in the path C1ACDFC2 whereas some may travel through
CIABEFC2. However, C2 verifies if all the datagrams have reached. Then it assembles the
sage and supplies to the application program in C2.
Tracing the Route (Tracert Command)
type
munication in a Network
In Windows or Windows NT when we are connected to Internet we can see the route from our
computer to any Internet host. This is got by the tracert command in command prompt. In Win.
dows NT, first open the DOS cmd prompt by running cmd command. In the DOS cmd promp"
tracert<doma in>
the rnes-
For example, we can type tracert Isu.edu
A router is a special computer that manages the traffic from network to network. The router de-
termines the path of travel for a datagram in TCP/IP. Routers keep track of the next computer to
which the datagram has to hop. They use routing tables and routing algorithms to do routing.
In Windows NT, we can see the IP address of the router in our network by running the
WINIPCFG.EXE program. When we run the program click more info and then select PPP
Adapter in the dropdown 1list. In the middle of the dialog box the IP address of the router is
shown in the field Default Gateway. This is the IP address of the router to which your computer
will send a TCP/IP datagram when it is addressed to a computer that is not on your local net-
work. This is illustrated in Figure 1.6.
1.3.4 HyperText Transfer Protocol (HTTP )
HyperText Transfer Protocol is the underlying protocol used by the World Wide Web. HTTI
defines how messages are formatted and transmitted, and what action Web servers and browser
should take in response to various commands. For example, when you enter a URL in you
browser., this actually sends an HTTP command to the Web server directing it to fetch and trans
mit the requested Web page. The other main standard that controls how the World
works is HTML, which covers how Web pages are formatted and displayed.
Wide We
HTTP is called a stateless protocol because each command is executed independently, witho
any knowledge of the commands that came before it. This is the main reason that it is difficult
implement Web sites that react intelligently to user input. This shortcoming of HTTP is bei
addressed in a number of new technologies, including ActiveX, Java, JavaScript and cookies.
1.3.5 File Transfer Protocoi (FTP)
File Transfer Protocol or FTP, is a protocol used to upload files from a workstation to
server or download files from a FTP server to a workstation. It is the way that files get trans-
ferred from one device to another in order for the files to be available on the Internet. Wher
appears in a URL it means that the user iS connecting to a file server and not a Web server and
that some form of file transfer is going to take place. Most FTP servers require the user to loe
to the server in order to transfer files.
In contrast, Hyper Text Transfer Protocol, or HTTP, is a protocol used to transfer files froma
Web server onto a browser in order to view a Web page that is on the Internet. Unlike FTP
where entire files are transferred from one device to another and copied into memory, HTTP
only transfers the contents of a web page into a browser for viewing. FTP is a two-way system
as files are transferred back and forth between server and workstation. HTTP is a one-way sys-
tem as files are transported only from the server onto the workstation's browser. When httn
appears in a URL it means that the user is connecting to a Web server and not a file server. The
files are transferred but not downloaded, therefore not copied into the memory of the receiving
device.
1.3.6 Wireless Application Protocol (WAP)
Wireless Application Protocol defines a secure specification that allows users to access Internet
information instantly via handheld wireless devices such as mobile phones, pagers, two-way
radios, smartphones and communicators. WAP supports most wireless networks. WAP is sup-
ported by all operating systems. Ones specifically engineered for handheld devices now include
PalmOS,. EPOC, Windows CE, FLEXOS, OS/9, and JavaOS. WAPs that use displays and access
the Internet run using microbrowsers. Microbrowsers are browsers with small file sizes that can
accomnodate the low memory constraints of handheld devices and the low-bandwidth con-
straints of a wireless-handheld network.
Although WAP supports HTML and XML, the WML language (an XML application) is spe-
cifically devised for small screens and one-hand navigation without a keyboard. WML is scal-
able from two-line text displays up through graphic screens found on items such as smart phones
and communicators. WAP also supports WMLScript. It is similar to JavaScript, but makes mini-
mal demands on memory and CPU power because it does not contain many of the unnecessary
functions found in other scripting languages. Because WAP is fairly new it is still an initiative
that was started by Unwired Planet, Motorola, Nokia, and Ericsson.
1.3.7 Bluetooth
Bluetooth refers toa short-range radio technology aimed at simplifying communications among
Net devices and between devices and the Internet. It also aims to simplify data synchronizationbetween Net devices and other computers. Products with Bluetooth technology must be quali-
fied and pass interoperability testing by the Bluetooth Special Interest Group prior to release.
1.3.8 Simple Object Access Protocol (SOAP)
Simple Object Access Protocol proposed by Microsoft provides a way for applications to com-
municate with each other over the Internet. indenendent of platform. Unlike I1OP, SOAP piggy
backs a DOM onto HTTP (port 80) in order to penetrate server firewalls, which are usuaiy
COnngured to accept port 80 and port 21 (FTP) requests. SOAP relies on XML to define the Tor-
mat of the information and then adds the necessary HTTP headers to send it.
1.3.9 Internet Inter-ORB Protocol (I1OP)
Internet Inter-ORB Protocol is a protocol developed by the Object Management Group (OMG)
to implement CORBA solutions over the World Wide Web. IIOP enables browsers and servers
to exchange integers, arrays, and more complex objects, unlike HTTP, which only supports
transmission of text.
1.4 Internet IP Address
Internet Principles
In the global network Internet, each node is identified with unique number called IP addressS.
The IP address of a machine is an array of four numbers separated by period, as shown below-
18.10.200. 14
185.25.85. 141
Each number in the above array is an eight-bit inte ger (That is it is between 0 and 255 and
called an Octet). There are three classes of networks in the Internet depending on the numbers or
hosts it can handle. They are
Class A networks
Class Bnetworks
Class C networks
Class A networks can handle a large number of hosts. ClassB networks are capable of han-
dling a moderate number of hosts.
Class C networks can handle only a small number of hosts. The maximum number of host
handled by each network are tabulated in Table 1.4.1.
1.4.1 Class a Network
The first octet of a Class A network 1P address represents the network ID and has a value f
1 to 126. So, there are only 126 Class A networks. However for each Class A network the
ond. third and the fourth octet represent the host ID, which can be any number between 0
256 and hence can have 16,177,2 14 hosts. (Note: 256 * 256 * 256 =16.177.216).
Class A Networks
The general form of an IP address of a Class A network host is
N.H1.H2.H3.
Where
N ranges from l to 126
H1, H2, H3 are numbers from 0 to 255.
1.4.2 Class B Networks
The first octet of a Class B network IP address is a value from 128 to 191. The general format of
a Class B network IP address is
Where
NI.N2.Hl. H2
NI ranges from 128 to 191
N2 ranges from 0 to 255
HI and H2 may range from 0 to 255.
NI and N2 form the network ID and H1 and H2 represent the host ID. There can be up to 16,38
Class B networks on the Internet, each of which can have up to 65,534 hosts.
(Note: Ni takes one of the 64 values from 128 to 191 and N2 takes O to 255. 254 * 254 = 65536
1.4.3 Class C Networks
Class C networks are designed to handle the situation where there would be very large numb
of networks that contained a small number of networks which in turn contained a small number of hosts. Small organizations having upto 254 hosts can go in for Class C networks. The general
format of the IP address is
NI.N2.N3.H
Where
NI ranges from 192 to 233
N2, N3 may vary from 0 to 255
H may vary fron 2 to 255.
There can be upto 2,097,092 Class C networks on the Internet, each of which can have upto
254 hosts. The following table 1.3.2 summarizes the facts on the IP address formats of various
Classes of networks on the Internet.
1.5 Domain Name
A name that identifies one or more IP addresses. For example, the domain name microsoft.com
represents about a dozen IP addresses. Domain names are used in URLs to identify particular
Web pages. For example, Consider the URL
http://www. stxaviers. com/index. html
The domain name is stxaviers. com. Every domain name has a suffix that indicates which
top level domain (TLD) it belongs to. There are only a limited number of such domains. For
example:
gov-Government agencies
edu-Educational institutions
org-Organizations (nonprofit)
mil-Military
com--commercial business
net-Network organizations
ca-Canada
th-Thailand
Because the Internet is based on IP addresses, not domain names, every Web server requires a
Domain Name System (DNS)) server to translate domain names into IP addresses as shown in
Figure 1.7.
Uniform Resource Locator (URL)
URL is the abbreviation of Uniform Resource Locator, the global address of documents a
other resources on the World Wide Web. The first part of the address indicates what protocol
use, and the second part specifies the IP address or the domain name where the resouree:
located.
For example, the two URLs below point to two different files at the domain stxaviers com
The first specifies an executable file that should be fetched using the FTP protocol; the second
specifies a Web page that should be fetched using the HTTP protocol:
ftp://www. stxaviers.com/nov2002result.exe
http://www.. stxaviers.com/index. html
1.6 Internet Services
In this section we discuss some important services available through Internet.
1.6.1 Gopher Service
The Internet Gopher protocol is designed primarily to act as a distributed document delivery
system. While documents (and services) reside on many servers, Gopher client software presents users with a hierarchy of items and directories much like a file system. In fact, the Gopher
interface is designed to resemble a file system since a file system is a good model for locating
documents and services
In essence, the Gopher protocol consists of a client connecting to a server and sending the
server a selector (a line of text, which may be empty) via a TCP connection. The server responds
with a block of text terminated with a period on a line by itself, and closes the connection. The
server between transactions retains no state with a client. The simple nature of the protocol stems
from the need to implement servers and clients for the slow protocols.
1.6.2 Instant Messaging
It is a type of communication service that enables you to create a private chat room with another
individual. Typically, the instant messaging system alerts you whenever somebody on your pri-
vate list is online. You can then initiate a chat session with that particular individual.
There are several competing instant messaging systems. Unfortunately, there's no standard.
1.6.3 Internet Relay Chat
A virtual room where a chat session takes place is called a chat room. If two computers are con-
nected through Intermet the Internet Relay Chat (IRC) application provides a platform for the
users to chat. Technically, a chat room is really a channel, but the term room is used to promote
the chat metaphor
1.6.4 Bulletin Board System (BBS)
BBS is an electronic message center. Most bulletin boards serve specific interest groups. They
allow you to dial in with a modem, review messages left by others, and leave your own message
if you want. Bulletin boards are a particularly good place to find free or inexpensive software
products.
1.6.5 Usenet News Group Service
A worldwide bulletin board systemn that can be accessed through the Internet or through many
online services is called a Usenet service. The Usenet contains more than 14,000 forums, called
newsgroups, that cover every imaginable interest group. It is used daily by millions of people around the world.
1.7 Electronic Mail
Electronic mail is the transmission of messages over communications networks. The message
can be notes entered from the kevboard or electronic files stored on disk. Most mainframes
minicomputerS, and computer networks have an e-mail system. Some elecironic-mail systems are
Confined to a single computer system or network. but others have gateways to other computer
Systems, enabling users to send electronic mail anywhere in the world. Companies that are fully
Computerized make extensive use of e-mail because it is fast, flexible, and reliable.
Most e-mail systems include a rudimentary text editor for composing messages, but many al-
10w yOu to edit your messages using any editor you want. You then send the message to the re.
CIpient by specifying the recipient's address. You can also send the same message to several
Sent messages are stored in electronic mnailboxes until the recipient fetches them. To see if
you have any mail, you may have to check your electronic mailbox periodically, although many
Systems alert you when mail is received. After reading your mail, you can store it in a text file.
Torward it to other users, or delete it. Copies of memos can be printed out on a printer if vou
want a paper copy.
All online services and Internet Service Providers (ISPs) offer e-mail and also support gate-
ways so that you can exchange mail with users of other systems. Usually, it takes only a few
seconds or minutes for mail to arrive at its destination. This is a particularly effective way to
communicate with a group because you can broadcast a message or document to everyone in the
group at once.
Although different e-mail systems use different formats, there are some emerging standards
that are making it possible for users on all systems to exchange messages. In the PC world, an
important e-mail standard is MAPI. MAPI is the abbreviation of Messaging Application Pro-
gramming Interface, a system built into Microsoft Windows that enables different e-mail appli-
cations to work together to distribute mail. As long as both applications are MAPI-enabled, they
can share mail messages with each other. The recent addition to Email is the Voice Email in
which a Voice file is communicated.
1.8 World Wide Web
Many people use the terms Internet and World Wide Web interchangeably, but in fact the two
terms are not synonymous. The Internet and the Web are two separate but related things. The
Internet is a massive network of networks, a networking infrastructure. It connects millions of
computers together globally, forming a network in which any computer can communicate with
any other computer as long as they are both connected to the Internet. Information that travels over the Internet does so via a variety of languages known as protocol.
1.8.1 Web Technologies
The Web uses the HTTP protocol, only one of the laaguages spoken over the Internet, to transmit data. Web services, which use HTTP to allow applications to communicate in order to exchange business logic, use the Web to share information. The Web also utilizes browsers, such as Internet Explorer or Netscape, to access Web documents called Web pages that are linked to
each other via hyperlinks. Web documents also contain graphics, sounds, text and video.
The Web is just one of the ways that information can be disseminated over the Internet. The
Internet, not the Web, is also used for e-mail, which relies on SMTP, Usenet news groups, in-
stant messaging and FTP. So the Web is just a portion of the Internet, albeit a large portion, but
the two terms are not synonymous and should not be confused.
Web is a system of Internet servers that support specially formatted documents. The
documents are formatted in a script called HTML (HyperText Markup Language) that supports
links to other documents, as well as graphics, audio, and video files. This means you can jump
from one document to another simply by clicking on hot spots. Not all Internet servers are part
of the World Wide Web. There are several applications called Web browsers that make it easy
to access the World Wide Web. Two of the most popular being Netscape Navigator and
Microsoft's Internet Explorer. In a web page information are presented using the following
technologies:
1 HTML
2 Javascript
3.Java Applets
4. Java Server Pages (JSP)
5. Active Server Pages (ASP)
6. Java Servlets
In the above list the browser machine executes the first three whereas the last three run in the
server machine. XML is a new technology, which is widely used in data formatting and communication. The web pages also contain objects such as cookies and plug-ins, which are explained
in the following sections.
1.8.2 Plug-in
A hardware or software module that adds a specific feature or service to a larger system is called
a plug-in. For example, there are number of plug-ins for the Netscape Navigator browser that
enable it to display different types of audio or video messages.
1.8.3 Cookie
Cookie is a message given to a Web browser by a WNeb server. The browser stores the mesSsage
in a text file (in the client machine itself) and uses each tỉme the browSer requests a page fro
the server. The main purpose of cookies is to identify users and possibly prepare customiZed
Web pages for them. When you enter a Web site using cookies, you may be asked to fill out a
form providing such information as your name and interests. This information is packaged into a
cookie and sent to your Web browser. The next time you go to the same Web site, your browser
WIlI send the cookie to the Web server. The server can use this information to present you with
Custom Web pages. So, for example, instead of seeing just a generic welcome page you might
See a welcome page with your name on it. The name cookie derives from UNIX objects called
magic cookies. These are tokens that are attached to a user or program and change depending on
the areas entered by the user or program.
CoOkies are messages that a Web server transmits to a Web browser so that the Web seryer
can keep track of the user's activity on a specific Web site. The message that the Web server
Conveys to the browser is in the form of an HTTP header that consists of a text-only string. The
text is entered into the memory of the browser. The browser in turn stores the cookie informa-
Web sites use cookies for several different reasons:
To collect demographic information about who is visiting the Web site. Sites often use this
information to track how often visitors come to the site and how long they remain on the
site.
To personalize the user's experience on the Web site. Cookies can help store personal
information about you so that when you return to the site you have a more personalized
experience. When you visit a web site again and see your name mysteriously appear on the
screen, it is because, on a previous visit you gave your name to the site and it was stored in
a cookie. When you returned you would be greeted with a personal message. A good
example of this is the way some online shopping sites will make recommendations to you
based on previous purchases. The server keeps track of what you purchase and what items
you search for and stores that information in cookies.
Web sites will often use cookies to keep track of what ads it lets you see and how often
you see ads.
Cookies do not act maliciously on computer systems. They are merely text files that can be
deleted at any time. They are not plug-ins nor are they programs. Cookies cannot be used to
spread viruses and they cannot access your hard drive. This does not mean that cookies are not
relevant to a user's privacy and anonymity on the Internet. Cookies cannot read your hard drive
to find out information about you:; however, any personal information that you give to a Web
site, including credit card information, will most likely be stored in a cookie unless you have
tion on the hard drive so when the browser is closed and reopened at a later date the cookie information is still available.
turned off the cookie feature in your browser. The cookie will only contain information that you
freely provide to a Web site.
Cookies have six parameters that can be passed to them:
The name of the cookie.
The value of the cookie.
The expiration date of the cookie- this determines how long the cookie will remain active
in your browser.
1.9.1
The path the cookie is valid for-this sets the URL path the cookie is valid in. Web pages
outside of that path cannot use the cookie.
The domain the cookie is valid for this takes the path parameter one step further. This
makes the cookie accessible to pages on any of the servers when a site uses multiple servers
in a domain.
The need for a secure connection--this indicates that the cookie can only be used undera
secure server condition, such as a site using SSL.
Both Netscape and Microsoft Internet Explorer (IE) can be set to reject cookies if the user
prefers.
1.9 Internet Security
As the Internet connects millions of computers across the globe, the security and privacy are two
vital issues in this new era of Information Technology. This section introduces two widely-used
security technologies of the web, SSL and S-HTTP.
Secure Sockets Layer (SSL) and Secure HTTP (S-HTTP)
Secure Sockets Layer, is a protocol developed by Netscape for transmitting private documents
via the Internet. SSL works by using a public key to encrypt data that's transferred over the SSL
connection. Both Netscape Navigator and Internet Explorer support SSL, and many Web sites
use the protocol to obtain confidential user information, such as credit card numbers. By convention, URLs that require an SSL connection start with https: instead of http: .
Another protocol for transmitting data securely over the World Wide Web is Secure HTTP
(S-HTTP). Whereas SSL creates a secure connection between a client anda server, over which
any amount of data can be sent securely, S-HTTP is designed to transmit individual messages
securely. SSL and S-HTTP, therefore, can be seen as complementary rather than competing
technologies. The Internet Engineering Task Force (IETF) has approved both protocols as a
standard.
1.9.2 Encryption
The word encryption m means translation of data into a secret code. Encryption is the most effec
tive way to achieve data security. To read an encrypted file, you must have access to a secret
key or password that enables you to decrypt it. Unencrypted data is called plain text ; encrypled
data is referred to as cipher text.
There are two main types of encryption. They are
1 Asymmetric encryption (also called public-key encryption) and
2 Symmetric encryption.
1.9.3 Asymmetric Encryption (public-key encryption )
Whitfield Diffie and Martin Hellman invented public key cryptography in 1976. For this reason
it is sometime called Diffie-Hellnan encryption.
This is a cryptographic system that uses two keys-a public key known to everyone and a
private or secret key known only to the recipient of the message. When A wants to send a secure
message to B, he uses B's public key to encrypt the message. B then uses his private key to de-
crypt it. An important element to the public key system is that the public and private keys are
related in such a way that only the public key can be used to encrypt messages and only the
corresponding private key can be used to decrypt them. Moreover, it is virtually impossible to
deduce the private key if you know the public key.
Public-key systems, such as Pretty Good Privacy (PGP), are becoming popular for transmit-
ting information via the Internet. They are extremely secure and relatively simple to use. The
only difficulty with public-key systems is that you need to know the recipient's public key to
encrypt a message for him or her. What's needed, therefore, is a global registry of public keys,
which is one of the promises of the new LDAP technology.
1.9.4 Symmetric Encryption
In Symmetric encryption the same key is used to encrypt and decrypt the message.
1.10 Electronic Commerce (E-Commerce) and Electronic Data Interchange (EDI)
EDI stands for the transfer of data between different companies using networks, such as the
Internet. As more and more companies get connected to the Internet, EDI is becoming increas-
ingly important as an easy mechanism for companies to buy, sell, and trade information. ANSI
has apprOved a set of EDI standards known as the X12 standards. E-Commerce refers to trans-
acting business on-line. This includes, for example, buying and selling products with digital cash
and via Electronic Data Interchange (EDI).
1.10.1 Digital Cash
Digital cash refers to a system that allows a person to pay for goods or services by transmitting
a number from one computer to another. Like the serial numbers on real dollar bills, and rupee
bills the digital cash numbers are unique. Each one is issued by a bank and represents a specified
sum of real money. One of the key features of digital cash is that, like real cash, it is anonymous
and reusable. That is, when a digital cash amount is sent from a buyer to a vendor, there is no
way to obtain information about the buyer. This is one of the key differences between digital
cash and credit card systems. Another key difference is that a digital cash certificate can be
reused.
Digital cash transactions are expected to become popular shortly. However, there are a
number of competing protocols and it is unclear which ones will become dominant. Most digital
cash systems start with a participating bank that issues cash numbers or other unique identifiers
that carry a given value, such as five dollars. To obtain such a certificate, you must have an ac-
count at the bank; when you purchase digital cash certificates, the money is withdrawn from your
account. You transfer the certificate to the vendor to pay for a product or service, and the vendor
deposits the cash number in any participating bank or retransmits it to another vendor. For large
purchases, the vendor can check the validity of a cash number by contacting the issuing bank
1.10.2 Digital Signature
A digital code that can be attached to an electronically transmitted message that uniquely identi-
fies the sender is called a digital signature.. Like a writen signature, the purpose of a digital
signature is to guarantee that the individual sending the message really is who he or she claims
to be. Digital signatures are especially important for electronic commerce and are a key compo-
nent of most authentication schemes. To be effective, digital signatures must be unforgeable.
There are a number of different encryption techniques to guarantee this level of security.
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