The Internet and the World Wide Web

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Review

From Week 1• Overview of eCommerce

• Definition• Components• Comparison to Traditional Commerce• Why eCommerce: Unique features• Appropriateness of eCommerce

• History of the Internet

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Week Two Topics

Technology Components• Packet Switching• Protocols: TCP/IP, FTP, HTTP, eMail

• Purpose, use of various protocols

• TCP/IP Architecture• IP Addresses, URLs, Domains• Publishing on the Web: In Depth

• File Transfer Protocol

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• A loosely configured global wide-area network.

•Loosely configured = open architecture, no single control

•Network = connection of computers

•Wide Area = large geographical coverage

What is the Internet?

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Primary technology factors behind growth discussed tonite:

The TCP/IP standard and packet switching.

The web-like ability to link from site to site enabled through HTML and HTTP.

Factors Behind Growth

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• The world’s telephone companies were the earlymodels for networked computers because thenetworks used leased telephone company lines.

• Telephone companies at the time established asingle connection between sender and receiverfor each telephone call.

• Once a connection was established, data traveled

along that path.

A Model for Networking

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• Telephone company switching equipment (bothmechanical and computerized) selected thephone lines, or circuits, to connect in order tocreate the path between caller and receiver.

• This centrally controlled, single connection model is known as circuit switching.

• Using circuit switching does not work well forsending data across a large network.

• Point-to-point connections for each sender/receiver pair is expensive and hard to manage.

Circuit switching

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• The Internet uses a less expensive and more easilymanaged technique than circuit switching.

• Files and messages are broken down into packetsthat are labeled with codes that indicate theirorigin and destination.

• Packets travel from computer to computer alongthe network until they reach their destination.

• The destination computer reassembles the datafrom the packets it receives.

• This is called a packet switching network.

A Different Approach

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View of Packet Switching

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• In a packet-switched network, each computer thatan individual packet encounters determines thebest way to move the packet to its destination.

• Computers performing this determination arecalled routers.

• The programs that the computers use to determinethe path are called routing algorithms.

• Utilizes Transmission Control Protocol/Internet Protocol TCP/IP

Packet switching

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Routing Messages

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There are benefits to packing switching:

• Long streams of data can be broken down intosmall manageable data chunks, allowing thesmall packets to be distributed over a widenumber of possible paths to balance traffic.

• It is relatively inexpensive to replace damageddata packets after they arrive, since if a datapacket is altered in transit only a single packet must be retransmitted.

Benefits of Packet Switching

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A protocol is a set of rules for the exchange of data acrosscommunication lines.

Protocols need to handle the following tasks:

• Format messages• Order Data in message• Compress message• Provide Error checking on message

Protocols

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The most popular Internet protocols include:

• TCP/IP: Transmission Control Protocol/Internet Protocol

• FTP: File Transfer Protocol

• HTTP: Hypertext Transfer Protocol

• E-mail protocols: SMTP, POP, IMAP

Each protocol is used for a different purpose, but all of them are important.

Most Popular Internet Protocols

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• The protocols that underlie the basic operation ofthe Internet are TCP (transmission controlprotocol) and IP (Internet protocol).

• Establish rules about how data are moved across networks and how network connections are established and

broken.

TCP/IP

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• TCP controls the assembly of a message intosmaller packets before it is transmitted overthe network. It also controls the reassemblyof packets once they reach their destination.

• The IP protocol includes rules for routing individual data packets from their source totheir destination. It also handles all addressingdetails for each packet. More on addressing later.

Purposes of Each

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TCP/IP Architecture

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Full discussion of the TCP/IP Architecture beyond the scope of this class.

Useful to understand where each protocol resides:

•TCP operates in the transport layer.

•IP operates in the Internet layer.

•HTTP, SMTP, POP, IMAP and FTP operate in the application layer.

General Layer Properties

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File transfer protocol

• FTP (file transfer protocol) is a part of TCP/IP that allows files to be transferred between computers connected using TCP/IP.

• It uses the client/server model.

• FTP permits files to be transferred in both directions, that is, from the client to the serveror from the server to the client.

• It can transfer files one at a time or many filessimultaneously.

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Files types and FTP

FTP allows the transfer of two types of files:

1. ASCII text: files containing only charactersavailable through the keyboard and containingno formatting information.Example: Files created using Notepad

2. Binary data: files containing word processeddocuments, worksheets, graphics, etc.

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Other Functions of FTP

FTP has other useful functions:

• Displaying remote and local computers’ directories

• Changing the current client’s or server’s activedirectories

• Creating and removing local and remote directories.

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Accessing with FTP

There are two ways to access remote machines:

1. Full privilege FTP access: This requires that youhave an account on the remote computer and thatyou supply your username and password.

2. Anonymous FTP: If you do not have an accounton the remote computer, you can type anonymousas the username and your e-mail address as thepassword and obtain limited access to the remotecomputer.

You can use an FTP client program or Web browser

interface for FTP.

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Once you have logged into your account using FTP you canbrowse through the files located in your account.

You do this by double clicking on the folders that appear.

Browsing Through Files

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To use a browser as an interface with FTP:

1. Type ftp://yourlogin@students.comsats.edu.pk

2. This will bring up a window that prompts youfor your password.

3. Type in your password (being careful to type it correctly) and hit enter.

4. The files in your main directory will appear. Note: Be sure to check that browser doesn’t store password. Look at Tools/Internet Options/Content/AutoComplete.

FTP with a Browser

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To create a directory on students.depaul.eduusing the browser interface:

1. Select File2. Select New3. Select Folder4. Click on the folder and give it the name

you wish it to have.

Creating Directories

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Once you have created a public_html directory, youcan move your HTML files into that directory.In order to do that:

1. Open up the directory into which you wish tomove the file.

2. Open the folder where the file is located on yourlocal machine.

3. Select Edit/Copy or drag the file directly into thedirectory.

Moving Files

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• HTTP (hypertext transfer protocol) is the protocolresponsible for transferring and displaying Web pages.

• It has continued to evolve since being introduced.

• Like other Internet protocols, HTTP uses the client/server model of computing. Thus, to understand how HTTP works, we need to first discuss the client/server model.

HTTP

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Client/Server model

• In the client/server model there are two roles: theclient and the server.

• The client process makes requests of the server.The client is only capable of sending a requestto the server and then waiting for the reply.

• The server satisfies the requests of the client. Itusually has access to a resource, such as data,that the client wants. When the resource thatthe client wants becomes available, it sends amessage to the client.

• This model simplifies communication.

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Client/Server Model

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HTTP and Client/Server

• With HTTP the client is the user’s Web browserand the server is the Web server.

• To open a session, the browser sends a requestto the server that holds the desired web page.

• The server replies by sending back the page or anerror message if the page could not be found.

• After the client verifies that the response sent wascorrect, the TCP/IP connection is closed and the HTTP session ends.

• Each new page that is desired will result in a new

HTTP session and another TCP/IP connection.

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One Page, Multiple Requests

• If a Web page contains objects such as movies,sound, or graphics, a client must make a request for each object.

• For example, a Web page containing a back-ground sound and three graphics will result in five separate server request messages to retrieve the four objects plus the page itself.

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Mail protocols

• Electronic mail is managed and stored by programsand hardware collectively known as mail servers.

• It is displayed and created using mail programssuch as Eudora, Pine, Unix mail, Outlook, Web interface mail programs.

• Protocols are necessary for the mail programs toconstruct requests to receive e-mail and for themail servers in downloading and/or deleting e-mail.

• The e-mail protocols we will discuss use the client/server model.

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SMTP

• SMTP (simple mail transfer protocol) is used byclient mail programs to make requests aboutmail delivery.

• A wide variety of mail programs such as Eudora,Unix mail, and PINE, use SMTP to send mailto a mail server.

• The SMTP specifies the exact format of a mailmessage and describes how mail is to be administered.

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POP

• POP is responsible forretrieving e-mail from a server.

• It requests that the mail server either retrievemail from the mail server and then delete it,retrieve mail from the server without deletingit, or simply ask whether new mail has comebut not retrieve it.

• When e-mail is read, POP specifies that it mustbe downloaded to your computer from the

server. Read e-mail is not kept on the server.

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IMAP

IMAP (Internet Message Access Protocol) is a newer protocol that, like POP, can ask if there is new mail, download e-mail, and delete e-mail.

IMAP has capabilities that POP does not:

• It defines how a client program asks a mail server to present available mail.

• It can allow you to manipulate and managee-mail without downloading it from the server.

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Internet Addresses

Internet addresses are represented in several ways,but all the formats are translated to a 32-bit numbercalled an IP address; a function of Internet Protocol (IP)

The increased demand for IP addresses will soonmake 32-bit addresses too small, and they will bereplaced with 128-bit addresses (IP v6.0) in the near future.

How does increasing the number of bits in the address helpwith increasing demand?

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Dotted Quads

• IP numbers appear as a series of up to 4 separatenumbers delineated by a period.

• Examples:140.192.1.100140.192.1.6 140.192.33.6

• Each of the four numbers can range from 0 to 255, so the possible IP addresses range from 0.0.0.0 to 255.255.255.255

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Elements of Internet Addressing

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Domain Names

• Since IP numbers can be difficult for humans toremember, domain names are associated witheach IP address.

• Examples: 140.192.1.100140.192.33.6

• A domain name server is responsible for the mapping between domain names and IP addresses.

• Domain names and IP addresses are registered separately. Registering domain name doesn’t imply getting an IP address. IP address is from hosting service.

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Uniform Resource Locator

• People on the Web use a naming convention called the uniform resource locator (URL).

• A URL consists of at least two and as many as four parts.

• A simple two part URL contains the protocolused to access the resource followed by thelocation of the resource.Example: www.google.com

• A more complex URL may have a file nameand a path where the file can be found.

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Anatomy of an eMail Address

abc @ yahoo . com

HandleHost/Server Domain

Type

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Domain types

.com Commercial organizations

or businesses .edu

Educational institutions .gov

U.S. government agencies .mil

U.S. military .net

Network computers .org

Nonprofit organizations and foundations

.biz business firms

.info information providers

.aero Air transport industry

.coop Cooperatives

.museum Museums

.name Individuals

.pro Professionals

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HTML

HTML – Hypertext Markup Language One of the languages with the parent

SGML – Standard Generalized Markup Language

HTML provides Web page designers with a fixed set of markup “tags” that are used to format a Web page

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HTML Example

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HTML TOOLS