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ECT 250: Survey of E-Commerce Technology
The Internet and the WWW
Administrivia
• Assignment 1 is due tonight – 8 people have
not yet submitted it.
• Assignment 2 has been posted. You may not
submit it via e-mail.
• Friday is the last day to drop with 100% tuition
reimbursement. See the calendar for other
important dates.
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What is the Internet?
• A loosely configured global wide-area network.
• Began as a Department of Defense project.
• For detailed information about the history of the
Internet, see:
http://dir.yahoo.com/Computers_and_internet/Internet/History/
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Factors behind growth
There are four factors that led to the surge in the
popularity of the Internet:
1. The web-like ability to link from site to site.
2. The ease of use provided by Web browsers’
graphical user interface.
3. The growth of personal computers and local
area networks that can be connected to the
Internet.
4. The TCP/IP standard.
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Protocols
A protocol is a set of rules for the exchange of
data across communication lines.
Protocols need to handle the following tasks:
• Identify the different devices in the communications path.
• Establish the speed and method for transmission of data.
• Alert the receiving device to the incoming data.
• Define the method for the receiving device to confirm the
receipt of the data.
• Determine the methods of error checking and correction.
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A model for networking
• The world’s telephone companies were the early
models for networked computers because the
networks used leased telephone company lines.
• Telephone companies at the time established a
single connection between sender and receiver
for each telephone call.
• Once a connection was established, data traveled
along that path.
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Circuit switching
• Telephone company switching equipment (both
mechanical and computerized) selected the
phone lines, or circuits, to connect in order to
create the path between caller and receiver.
• This centrally controlled, single connection
model is known as circuit switching.
• Using circuit switching does not work well for
sending data across a large network.
• Point-to-point connections for each sender/
receiver pair is expensive and hard to manage.
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A different approach
• The Internet uses a less expensive and more easily
managed technique than circuit switching.
• Files and messages are broken down into packets
that are labeled with codes that indicate their
origin and destination.
• Packets travel from computer to computer along
the network until they reach their destination.
• The destination computer reassembles the data
from the packets it receives.
• This is called a packet switching network.
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Packet switching
• In a packet-switched network, each computer that
an individual packet encounters determines the
best way to move the packet to its destination.
• Computers performing this determination are
called routers.
• The programs that the computers use to determine
the path are called routing algorithms.
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Benefits of packet switching
There are benefits to packing switching:
• Long streams of data can be broken down into
small manageable data chunks, allowing the
small packets to be distributed over a wide
number of possible paths to balance traffic.
• It is relatively inexpensive to replace damaged
data packets after they arrive, since if a data
packet is altered in transit only a single
packet must be retransmitted.
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Open architecture
When it was being developed, the people working
on ARPANet adhered to the following principles:
1. Independent networks should not require any
internal changes in order to be connected.
2. The router computers do not retain information
about the packets that they handle.
3. Packets that do not arrive at their destinations
must be retransmitted from their source network.
4. No global control exists over the network.
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Control of the Internet
• No one organization controls the Internet since
no single group runs or pays for the Internet.
• Several groups oversee aspects of the development
of the Internet.
– Internet Engineering Task Force (IETF)
Oversees the evolution of Internet protocols
– Internet Registries (InterNIC)
Maintain and allocate Internet domains
– World Wide Web Consortium (W3C)
Develops standards for the WWW
• See the Internet Standardization Organizations.
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Most popular Internet protocols
The most popular Internet protocols include:
• TCP/IP
• HTTP (Hypertext transfer protocol)
• E-mail protocols (SMTP, POP, IMAP)
• FTP (File transfer protocol)
Each protocol is used for a different purpose,
but all of them are important.
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TCP/IP
• The protocols that underlie the basic operation of
the Internet are TCP (transmission control
protocol) and IP (Internet protocol).
• Developed by Internet pioneers Vinton Cerf and
and Robert Kahn, these protocols establish rules
about how data are moved across networks and
how network connections are established and
broken.
CTI plug: The Distinguished Lecturer Series
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Purposes of each protocol
• TCP controls the assembly of a message into
smaller packets before it is transmitted over
the network. It also controls the reassembly
of packets once they reach their destination.
• The IP protocol includes rules for routing
individual data packets from their source to
their destination. It also handles all addressing
details for each packet.
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Network layers
The work done by communications software is
broken into multiple layers, each of which handles
a different set of tasks.
Each layer is responsible for a specific set of tasks
and works as one unit with the other layers when
delivering information over the Internet.
Each layer provides services for the layer above it.
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TCP/IP architecture
There are five layers in the Internet model:
1. Application
2. Transport
3. Internet
4. Network interface
5. Hardware
The lowest layer is the hardware layer that handles
the individual pieces of equipment attached to the
network. The highest layer is the application layer
where various network applications run.
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Positioning within the layers
A full discussion of the Internet model is beyond
the scope of this class.
It is, however, useful to know where each protocol
resides. TCP operates in the transport layer and IP
in the Internet layer.
Some of the application layer protocols include
HTTP, SMTP, POP, IMAP and FTP.
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HTTP
• HTTP (hypertext transfer protocol) is the protocol
responsible 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.
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Client/server model
• In the client/server model there are two roles: the
client and the server.
• The client process makes requests of the server.
The client is only capable of sending a request
to the server and then waiting for the reply.
• The server satisfies the requests of the client. It
usually has access to a resource, such as data,
that the client wants. When the resource that
the client wants becomes available, it sends a
message to the client.
• This model simplifies communication.
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HTTP and client/server
• With HTTP the client is the user’s Web browser
and the server is the Web server.
• To open a session, the browser sends a request
to the server that holds the desired web page.
• The server replies by sending back the page or an
error message if the page could not be found.
• After the client verifies that the response sent was
correct, 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 background 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 programs
and hardware collectively known as mail servers.
• It is displayed and created using mail programs
such as Eudora, Pine, Unix mail, Outlook, etc.
• Protocols are necessary for the mail programs to
construct requests to receive e-mail and for the
mail 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 by
client mail programs to make requests about
mail delivery.
• A wide variety of mail programs such as Eudora,
Unix mail, and PINE, use SMTP to send mail
to a mail server.
• The SMTP specifies the exact format of a mail
message and describes how mail is to be
administered.
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POP
• POP (post office protocol) is responsible for
retrieving e-mail from a server.
• It requests that the mail server either retrieve
mail from the mail server and then delete it,
retrieve mail from the server without deleting
it, or simply ask whether new mail has come
but not retrieve it.
• When e-mail is read, POP specifies that it must
be 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 manage
e-mail without downloading it from the server.
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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 server
or from the server to the client.
• It can transfer files one at a time or many files
simultaneously.
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Files types and FTP
FTP allows the transfer of two types of files:
1. ASCII text: files containing only characters
available through the keyboard and containing
no formatting information.
Example: Files created using Notepad
2. Binary data: files containing word processed
documents, 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 active
directories
• Creating and removing local and remote directories.
We will use these functions when transferring HTML
documents created on a PC to the students.depaul.edu
machine.
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Accessing with FTP
There are two ways to access remote machines:
1. Full privilege FTP access: This requires that you
have an account on the remote computer and that
you supply your username and password.
2. Anonymous FTP: If you do not have an account
on the remote computer, you can type anonymous
as the username and your e-mail address as the
password and obtain limited access to the remote
computer.
You can use a Web browser interface for FTP.
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FTP with a browser
To use a browser as an interface with FTP:
1. Type ftp://[email protected]
2. This will bring up a window that prompts you
for 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 the browser does not
store your password. Look at Tools/Internet
Options/Content/AutoComplete.
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Browsing through files
Once you have logged into your account using
FTP you can browse through the files located in
your account.
You do this by double clicking on the folders
that appear.
Example: ftp://[email protected]
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Creating directories
To create a directory on students.depaul.edu
using the browser interface:
1. Select File
2. Select New
3. Select Folder
4. Click on the folder and give it the name
you wish it to have.
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Moving files
Once you have created a public_html directory, you
can move your HTML files into that directory.
In order to do that:
1. Open up the directory into which you wish to
move the file.
2. Open the folder where the file is located on your
local machine.
3. Select Edit/Copy or drag the file directly into the
directory.
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Internet addresses
Internet addresses are represented in several ways,
but all the formats are translated to a 32-bit number
called an IP address.
The increased demand for IP addresses will soon
make 32-bit addresses too small, and they will be
replaced with 128-bit addresses in the near future.
See the links page for more information.
How does increasing the number of bits in the
address help with increasing demand?
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Dotted quads
• IP numbers appear as a series of up to 4 separate
numbers delineated by a period.
• Examples:
students.depaul.edu: 140.192.1.100
condor.depaul.edu: 140.192.1.6
facweb.cs.depaul.edu: 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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Domain names
• Since IP numbers can be difficult for humans to
remember, domain names are associated with
each IP address.
• Examples:
students.depaul.edu: 140.192.1.100
facweb.cs.depaul.edu: 140.192.33.6
• A domain name server is responsible for the
mapping between domain names and IP
addresses.
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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 protocol
used to access the resource followed by the
location of the resource.
Example: http://www.cs.depaul.edu/
• A more complex URL may have a file name
and a path where the file can be found.
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A URL deconstructed
http://facweb.cs.depaul.edu/asettle/ect250/section501/hw/assign2.htm
hypertext
transfer
protocol
domain
path that indicates
the location of the
document in the
host’s file system
document
name
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Anatomy of an e-mail address
asettle @ cs . depaul . edu
Handle
Host/Server
Others:
• students
• hawk
• condor
Domain
Domain
Type
Others:
• com, net, org
• gov
• ja, uk, de
• New additions: info, biz,
name, pro, museum, coop,
aero. See links page.
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Telnet
• An important Internet application is Telnet.
• Telnet allows you to log onto a remote computer
attached to the Internet.
• It performs the functions of a terminal emulation
program, by allowing you to type commands
and character strings that are passed directly to
the remote computer.
• Telnet emulates a few terminals including VT-52
and VT-100.
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Internet utility programs
TCP/IP supports a variety of utility programs that
allow people to use the Internet more efficiently.
These utility programs include:
• Finger
• Ping
• Talk
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Finger
Finger is a program that runs on Unix computers
and allows a user to obtain limited information
about other network users.
The information that can be obtained includes:
• Which users are currently logged on
• Where each user logged onto the network from
• How long the user has been on the network
• When the user last logged onto the system
Finger is sometimes disabled for security reasons.
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Ping
• Ping (Packet InterNet Groper) tests the connectivity
between two Internet hosts and determines if a
host is active on the network.
• It works by sending a packet to the specified address
and waiting for a reply.
• Ping is typically used to troubleshoot connections.
• To run ping, you simply type ping followed by the
IP address or domain name of the machine you are
interested in.
Example: ping students.depaul.edu
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Talk
• Talk is a program that runs on Unix computers
and allows a user to interactively communicate
with another user on the network.
• To use it you type talk followed by the string
username@host where username is the person
you wish to talk to and the host is the machine
where they are logged on.
Example: talk [email protected]
• It is similar to instant messaging programs such
as AOL instant messaging, Yahoo! pager, etc.
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Upcoming topics
 An introduction to FrontPage
 Publishing web pages on students.depaul.edu
(FTP, Unix commands, file permissions)
 Searching the Web
 Markup languages
 Information architecture
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