Download User News Network

ECT 250: Survey of E-Commerce Technology
Networking and an introduction to
the Internet
Administrivia
• The HyperNews page is up!
• Don’t be afraid to ask questions in class.
• Get Assignment 1 in soon.
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Networking
In a network, communications equipment is used
to connect two or more computers allowing the
sharing of various hardware, software, and data
resources.
The basic components of a data communications
systems used to transmit information are:
• A sending device
• A communications link, consisting of both
communications hardware and software.
• A receiving device
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Data transmission
Binary information is represented by the presence
or absence of an electronic pulse. This is referred
to as digital signaling.
Many communications devices in place today were
designed for voice data which uses analog signals.
Data communications systems typically use these
existing lines.
(The telecom industry is working on standards that
will allow for direct digital transmission).
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Piggybacking technology
Because the wires in place for communication use
analog signals, digital data must be converted to an
analog signal in order to be transmitted.
•The digital signal is transformed into an analog
wave in a process called modulation.
•The analog wave is transmitted.
•The analog signal is converted back into a digital
signal during a process called demodulation.
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Modems
A modem is the hardware device that does these
conversions. (Short for modulate/demodulate).
Modem speeds are referred to by the number of
bits per second (bps) at which they can transmit
and receive data.
• The earliest modems has speeds around 300 bps.
• Later modems had speeds ranging from 9600
to 33,600 bps.
• Today modems have speeds of 56,000 bps (or
56 Kbps).
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Communication links
A communications link is the physical medium
used for transmission of data.
There are several kinds:
• Wire pairs/twisted pairs
• Coaxial cables
• Fiber optics
• Microwave transmission
• Satellite transmission
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Wire pairs
Sometimes called twisted pair, this media uses
wire pairs twisted together to form a cable. The
cable is then insulated.
Wire pairs are popular since this form of cabling
is already installed and available in most places
(telephone cabling).
It is, however, susceptible to electrical interference,
called noise.
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Coaxial cables
A coaxial cable is a single conductor wire that is
thickly shielded.
• It sends a very powerful signal.
• It is used for cable television.
• These cables can transmit data at a very fast
rate.
Bundles of these cables can be laid underground
or under the sea.
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Fiber optic cables
Fiber optic cables use light instead of electricity
to transmit data.
• The cables are made of ultra thin glass wires.
Light beams can be transmitted for miles with
little attenuation (reduction in signal strength).
• This media can handle many different types
of information including voice and data at the
same time.
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Microwave transmission
In microwave transmission the signals are wireless
and can travel through the atmosphere.
Signals can, however, be blocked by the curvature
of the earth. (Line of sight transmission)
To prevent this, relay stations are located in high
areas and are used to retransmit data to other relay
stations.
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Satellite transmission
The basic components of satellite transmission:
• Earth stations: Send and receive signals.
• Transponder: Receives a transmission from
an earth station, amplifies the signal, changes
the frequency, and retransmits the data to the
receiving earth station.
The entire process takes only a few seconds.
Communications satellites are positioned in a
geosynchronous orbit.
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Types of networks
Networks can be classified according to their
geographical reach.
• Local area network
• Metropolitan area network
• Wide area network
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Wide-area network
A wide area network (WAN) is a network of
computers, terminals, and peripheral devices
that is located over a very large area.
• It can span a state, country, or the world.
• The central hubs or servers are usually
powerful minicomputers or mainframes.
(The server is usually referred to as the
host computer).
• A single WAN may use a variety of
transmission methods.
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Local-area network
A local area network is a collection of computers
that share hardware, software, and data over a
shorter geographical area than a WAN.
(Usually limited to a single building or compound).
A LAN can also be very small.
Example: LAN in my apartment contains one PC,
one printer, and two laptops.
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Protocols
A protocol is a set of rules for the exchange of
data across communication lines.
Because telecommunications systems use a wide
variety of hardware and software, protocols are
needed to coordinate communication.
What kinds of issues do protocols need to handle?
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Tasks for protocols
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.
Common Internet protocols include TCP/IP, SMTP,
POP, IMAP, FTP, and HTTP. We will discuss each
of these in more detail later.
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What is the Internet?
• A loosely configured global wide-area network.
• Includes more than 31,000 different networks in
over 100 different countries.
• Millions of people visit and contribute to the
Internet, through e-mail and the World Wide
Web.
• 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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Early history of the Internet
• In the 1950s the U.S. Department of Defense
became concerned that a nuclear attack could
disable its computing (and thus planning and
coordinating) capabilities.
• By 1969 the Advanced Research Projects Agency
Network (ARPANet) had been constructed.
• The first computers to be connected were ones at
the University of California at Los Angeles, SRI
International, the University of California at
Santa Barbara, and the University of Utah.
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The changing Internet
Early on researchers began to find new uses for the
Internet, beyond its original purpose of controlling
weapons systems.
These new applications included the following:
• Electronic mail
• File transfer protocol
• Telnet
• User’s News Network (Usenet)
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The new uses
• In 1972 a researcher wrote a program that could
send and receive messages over the Internet.
E-mail was quickly adopted by Internet users.
• File transfer protocol (FTP) allowed researchers
using the Internet to transfer files easily across
great distances.
• Telnet allows users of the Internet to log into
their computer accounts from remote sites.
• All three of these applications are still widely
used. We will discuss them again later.
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Usenet
• In 1979 a group of students and programmers at
Duke and the University of North Carolina
started Usenet, short for User News Network.
• Usenet allows anyone who connects to the
network to read and post articles on a variety
of subjects.
• Usenet survives today in what are called newsgroups.
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Newsgroups
There are several thousand newsgroups covering a
highly varied groups of subjects.
Examples:
– alt.cats
– comp.databases
– rec.climbing
– soc.penpals
The first part of the name of each group tells you
what type of group it is and the remaining parts
indicate the subject matter.
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Moderation of newsgroups
Some groups are moderated, which means that a
person must approve your message before it is
posted.
Others are unmoderated and postings are regulated
only by the responses that they receive.
Postings that are controversial may receive many
negative postings in response. This process is
termed “flaming” the poster.
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Accessing newsgroups
Newsgroups can be accessed in two ways:
1. Using special software (trn, rn, etc.)
2. Using a browser on the Web.
As an example, DejaNews is a web site that
allows access to a variety of newsgroups as
well as providing an archive of old postings
to the group.
See http://www.deja.com/usenet/
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Early use of the Internet
• From 1969 until the 1980s the Internet was used
primarily by government and university
researchers.
• The development of the Internet was funded in
part by the National Science Foundation (NSF)
and commercial network traffic was prohibited.
• As personal computers became more powerful,
and affordable in the 1980s, companies created
their own networks. These users wanted to be
able to communicate outside the network.
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Commercial use of the Internet
• In 1989 the NSF allowed two commercial e-mail
services (MCI Mail and CompuServe) to
establish limited connections to the Internet.
• These connections allowed an exchange of e-mail
between users of the commercial services and
users of the Internet.
• In 1991 the NSF further eased its restrictions on
Internet commercial activity and began planning
for the privatization of the Internet.
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Privatization
• The privatization of the Internet was substantially
completed in 1995. At that point the NSF
decommissioned its backbone.
• The new structure of the Internet was based on
four network access points (NAPs), each
operated by a separate company.
• The network access providers sell Internet access
rights directly to larger customers and indirectly
to smaller customers through other companies
called Internet service providers (ISPs).
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A growing Internet
• Researchers had long considered the Internet a
valuable tool.
• As the 1990s began, a larger variety of people
thought of the Internet as a useful resource.
• The Internet grew significantly in 20 years.
Year
# of computers
1969
4
1990
313,000
• The largest growth in the Internet was yet to
come.
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A prehistory of the Web
• In 1945, Vannevar Bush wrote an article that
proposed a machine (called the Memex) to store
a person’s books, records, letters, and research
results on microfilm. The Memex would have
an index to help locate documents.
• In the 1960s, Ted Nelson described a similar
system in which text on one page would have
links to text on other pages. Nelson called
this page linking system hypertext.
• Douglas Englebart (inventor of the mouse) created
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the first experimental hypertext system.
CERN and hypertext
• In 1990, Tim Berners-Lee and Robert Calliau were
working on overhauling the document handling
procedures at CERN, a laboratory for particle
particle physics in Geneva, Switzerland.
• CERN had been connected to the Internet for two
years, but its scientists wanted to find better ways
to circulate their scientific papers and data.
• Independently, Berners-Lee and Calliau proposed
a hypertext development project.
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The birth of the Web
• Over the next two years Berners-Lee developed
the code for a hypertext server program and
made it available on the Internet.
• He envisioned the set of links between computers
as a spider web, hence the name Web.
• The CERN site is considered the birthplace of the
World Wide Web.
The CERN site: http://cern.web.cern.ch/CERN/
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Terminology
• A hypertext server is a computer that stores files
written in hypertext markup language (HTML)
and lets other computers connect to it and read
those files. It is now called a Web server.
• A hyperlink is a special tag that contains a pointer
to another location in the same or in a different
HTML document.
• HTML is based on Standard Generalized Markup
Language (SGML), which organizations have
used for many years to manage large document
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filing systems.
Early Web browsers
• A Web browser is a software interface that lets
users read (or browse) HTML documents.
• Early web browsers were text based.
• Although the Web caught on quickly in the
research community, broader acceptance was
slow to materialize.
• Part of the problem was that the early browsers
were difficult to use.
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GUI Web browsers
• In 1993, Marc Andressen led a team of researchers
and developed the first software with a graphical
user interface for viewing pages over the Web.
• This first GUI browser was named Mosaic.
• Mosaic widened the appeal of the Web by making
access easier and adding multimedia capabilities.
• Andressen later went on to develop the Netscape
Navigator browser.
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The growth of the Internet
The Internet has grown, and continues to grow, at
a phenomenal rate.
Date
WWW Servers Internet Hosts
12/1969
N/A
4
12/1979
N/A
188
12/1989
N/A
159,000
12/1993
623
2,056,000
12/1996
603,367
21,819,000
12/1999 9,560,866
56,218,000
07/2000 18,169,498
93,047,785
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Factors behind growth
There are four main factors that led to the surge
in popularity of the Internet:
• The web-like ability to link from site to site.
• The ease of use provided by the browsers’
graphical user interface.
• The growth of personal computers and local
area networks that could be connected to
the Internet.
• The TCP/IP standard.
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Internet 2
A project to develop another Internet, Internet2, is
is being led by over 170 U.S. universities working
in partnership with industry and government.
This new network is designed to allow development
and deployment of advanced network applications
and technologies.
For more information see: http://www.internet2.edu/
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Netiquette
There are guidelines on the Internet for behavior
called netiquette.
 Do not forward chain mail.
• Internet hoaxes
• Seemingly well-intentioned e-mail requests
Check out http://kumite.com/myths/ before
forwarding any messages.
 Do not use all capitals in your messages.
IT IS GENERALLY CONSIDERED TO BE
THE SAME AS SHOUTING!
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Netiquette
 Do not post ads via e-mail or newsgroups
unless you are sure that you are posting
appropriately.
 Do read postings and related FAQs from a
newsgroup before posting to it.
 Always remember that the Internet is filled
with individuals with strong opinions and an
even stronger desire to espouse their views.
Do not get caught up in a flame-war.
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