ECT 250: Survey of E-Commerce Technology

Networking and an introduction to the Internet

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• The HyperNews page is up!• Don’t be afraid to ask questions in class.• Get Assignment 1 in soon.

Administrivia

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In a network, communications equipment is usedto connect two or more computers allowing thesharing of various hardware, software, and dataresources.

The basic components of a data communicationssystems used to transmit information are:• A sending device• A communications link, consisting of both

communications hardware and software.• A receiving device

Networking

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Binary information is represented by the presenceor absence of an electronic pulse. This is referredto as digital signaling.

Many communications devices in place today weredesigned for voice data which uses analog signals.Data communications systems typically use theseexisting lines.

(The telecom industry is working on standards that will allow for direct digital transmission).

Data transmission

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Because the wires in place for communication useanalog signals, digital data must be converted to ananalog signal in order to be transmitted.

•The digital signal is transformed into an analogwave 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.

Piggybacking technology

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A modem is the hardware device that does theseconversions. (Short for modulate/demodulate).

Modem speeds are referred to by the number ofbits per second (bps) at which they can transmitand 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).

Modems

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A communications link is the physical mediumused for transmission of data.

There are several kinds:• Wire pairs/twisted pairs• Coaxial cables• Fiber optics• Microwave transmission• Satellite transmission

Communication links

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Sometimes called twisted pair, this media useswire pairs twisted together to form a cable. Thecable is then insulated.

Wire pairs are popular since this form of cablingis already installed and available in most places(telephone cabling).

It is, however, susceptible to electrical interference,called noise.

Wire pairs

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A coaxial cable is a single conductor wire that isthickly 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 undergroundor under the sea.

Coaxial cables

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Fiber optic cables use light instead of electricityto transmit data.

• The cables are made of ultra thin glass wires.Light beams can be transmitted for miles withlittle attenuation (reduction in signal strength).

• This media can handle many different typesof information including voice and data at thesame time.

Fiber optic cables

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In microwave transmission the signals are wirelessand can travel through the atmosphere.

Signals can, however, be blocked by the curvatureof the earth. (Line of sight transmission)

To prevent this, relay stations are located in highareas and are used to retransmit data to other relaystations.

Microwave transmission

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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 ageosynchronous orbit.

Satellite transmission

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Networks can be classified according to theirgeographical reach.

• Local area network• Metropolitan area network• Wide area network

Types of networks

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A wide area network (WAN) is a network ofcomputers, terminals, and peripheral devicesthat 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 thehost computer).

• A single WAN may use a variety of transmission methods.

Wide-area network

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A local area network is a collection of computersthat share hardware, software, and data over ashorter 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.

Local-area network

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A protocol is a set of rules for the exchange ofdata across communication lines.

Because telecommunications systems use a widevariety of hardware and software, protocols areneeded to coordinate communication.

What kinds of issues do protocols need to handle?

Protocols

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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 eachof these in more detail later.

Tasks for protocols

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• 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 WideWeb.

• 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/

What is the Internet?

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• In the 1950s the U.S. Department of Defensebecame concerned that a nuclear attack coulddisable its computing (and thus planning andcoordinating) capabilities.

• By 1969 the Advanced Research Projects AgencyNetwork (ARPANet) had been constructed.

• The first computers to be connected were ones atthe University of California at Los Angeles, SRIInternational, the University of California atSanta Barbara, and the University of Utah.

Early history of the Internet

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Early on researchers began to find new uses for theInternet, 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)

The changing Internet

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• In 1972 a researcher wrote a program that couldsend and receive messages over the Internet.E-mail was quickly adopted by Internet users.

• File transfer protocol (FTP) allowed researchersusing the Internet to transfer files easily acrossgreat distances.

• Telnet allows users of the Internet to log intotheir computer accounts from remote sites.

• All three of these applications are still widelyused. We will discuss them again later.

The new uses

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• In 1979 a group of students and programmers atDuke 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 varietyof subjects.

• Usenet survives today in what are called news-groups.

Usenet

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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 youwhat type of group it is and the remaining parts indicate the subject matter.

Newsgroups

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Some groups are moderated, which means that aperson must approve your message before it isposted.

Others are unmoderated and postings are regulatedonly by the responses that they receive.

Postings that are controversial may receive manynegative postings in response. This process is termed “flaming” the poster.

Moderation of newsgroups

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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 postingsto the group.See http://www.deja.com/usenet/

Accessing newsgroups

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Early use of the Internet

• From 1969 until the 1980s the Internet was usedprimarily by government and university researchers.

• The development of the Internet was funded inpart 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 beable to communicate outside the network.

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Commercial use of the Internet

• In 1989 the NSF allowed two commercial e-mailservices (MCI Mail and CompuServe) toestablish limited connections to the Internet.

• These connections allowed an exchange of e-mailbetween users of the commercial services and users of the Internet.

• In 1991 the NSF further eased its restrictions onInternet commercial activity and began planningfor the privatization of the Internet.

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Privatization

• The privatization of the Internet was substantiallycompleted in 1995. At that point the NSF decommissioned its backbone.

• The new structure of the Internet was based onfour network access points (NAPs), each operated by a separate company.

• The network access providers sell Internet accessrights directly to larger customers and indirectlyto smaller customers through other companiescalled Internet service providers (ISPs).

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A growing Internet

• Researchers had long considered the Internet avaluable tool.

• As the 1990s began, a larger variety of peoplethought of the Internet as a useful resource.

• The Internet grew significantly in 20 years.Year # of computers1969 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 thatproposed a machine (called the Memex) to storea person’s books, records, letters, and researchresults on microfilm. The Memex would havean index to help locate documents.

• In the 1960s, Ted Nelson described a similar system in which text on one page would havelinks to text on other pages. Nelson calledthis page linking system hypertext.

• Douglas Englebart (inventor of the mouse) createdthe first experimental hypertext system.

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• In 1990, Tim Berners-Lee and Robert Calliau wereworking on overhauling the document handlingprocedures at CERN, a laboratory for particleparticle physics in Geneva, Switzerland.

• CERN had been connected to the Internet for twoyears, but its scientists wanted to find better waysto circulate their scientific papers and data.

• Independently, Berners-Lee and Calliau proposeda hypertext development project.

CERN and hypertext

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• 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 computersas a spider web, hence the name Web.

• The CERN site is considered the birthplace of theWorld Wide Web.The CERN site: http://cern.web.cern.ch/CERN/

The birth of the Web

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• A hypertext server is a computer that stores fileswritten in hypertext markup language (HTML)and lets other computers connect to it and readthose files. It is now called a Web server.

• A hyperlink is a special tag that contains a pointerto another location in the same or in a differentHTML document.

• HTML is based on Standard Generalized MarkupLanguage (SGML), which organizations haveused for many years to manage large documentfiling systems.

Terminology

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• A Web browser is a software interface that letsusers read (or browse) HTML documents.

• Early web browsers were text based.• Although the Web caught on quickly in the

research community, broader acceptance wasslow to materialize.

• Part of the problem was that the early browserswere difficult to use.

Early Web browsers

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• In 1993, Marc Andressen led a team of researchersand developed the first software with a graphicaluser 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 NetscapeNavigator browser.

GUI Web browsers

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The Internet has grown, and continues to grow, ata phenomenal rate.

Date WWW Servers Internet Hosts12/1969 N/A 412/1979 N/A 188 12/1989 N/A 159,000 12/1993 623 2,056,00012/1996 603,367 21,819,000 12/1999 9,560,866 56,218,000 07/2000 18,169,498 93,047,785

The growth of the Internet

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There are four main factors that led to the surgein 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 tothe Internet.

• The TCP/IP standard.

Factors behind growth

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A project to develop another Internet, Internet2, isis 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/

Internet 2

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There are guidelines on the Internet for behaviorcalled netiquette. Do not forward chain mail.

• Internet hoaxes• Seemingly well-intentioned e-mail requestsCheck out http://kumite.com/myths/ beforeforwarding any messages.

Do not use all capitals in your messages.IT IS GENERALLY CONSIDERED TO BETHE SAME AS SHOUTING!

Netiquette

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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.

Netiquette