Communications and the Internet

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Using a computer to communicate is the most popular application of computers today.

Computer Communications: Process in which two or more computers or devices transfer data, instructions, and information

Computer Communications

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Computer Communications

Laptop

Tablet

Web Server

Cell Phone

Satellite

Satellite Dish

Bluetooth Device

Communications Towers

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You need:

1. A sender (computer)2. A communications device (modem): connects the

sender to the channel3. A communications channel (cable, radio waves)4. A communications device (modem): connects the

channel to the receiver5. A receiver (computer)

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Some applications of communications technology:

Internet/Web E-mail Blogs Wikis (collaborative documents) RSS (Really Simple Syndication) VoIP (Voice Over IP) FTP (File Transfer Protocol) Web folders Web conferencing

Computer Communications

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Network: a collection of computers and devices connected via communications devices and transmission media.

Networks

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Share hardware (e.g. printer, Internet connection)

Share software Share data (e.g. files on a hard disk)

Why Use a Network?

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A Local Area Network: a LAN is a network in limited geographical area such as home or office building (or a college campus)

Networks: LAN

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Wide Area Network: a WAN is a network that covers a large geographic area using many types of communications media.

The Internet is the world’s largest WAN.

Networks: WAN

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Internet: a world-wide network of computer networks.

The Internet

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ARPANET

Networking project by Pentagon’s Advanced Research Projects Agency (ARPA)

Goal: To allow scientists at different locations to share information

Goal: To function if part of network were disabled

Became functional September 1969

The Internet: Where did it start?

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The Internet, 1969

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The Internet, 1977

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The Internet Today

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The Internet Today

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The Internet Today

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1969: Four host nodes

1984: More than 1,000 host nodes

Today: More than 500 million host nodes

Internet Growth

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1989. Tim Berners-Lee 1991. HTML 1.0 1992. Lynx browser 1993. Mosaic browser 1994. HTML2 1995. HTML3 (draft never approved) 1995. Internet Explorer. 1998. HTML4 2014. HTML5

The World-Wide Web

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No one controls the Internet—it is a public, cooperative, and independent network.

Several organizations set standards.

Internet Control

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To connect to the Internet, you need three things:

Hardware to allow you to connect your PC to a communications channel.

Software that controls the sending and receiving of data.

Rules for sending data back and forth (called a protocol).

Connecting to the Internet

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Telephone line (dial-up) Digital Subscriber Line (DSL) Cable Satellite dish

Connection methods

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All of these require a device to connect your computer to the Internet called a modem.

  MODEM: a device that translates digital

signals from a computer into a format that can be transmitted over communication lines (e.g. phone line or cable).

A modem modulates a signal going out and demodulates a signal coming in.

Speed is measured in BITS per second (bps, b=bits, B=bytes).

Hardware

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Hardware

Dial-up

Satellite

DSL Low

DSL High

Cable Low

Cable High

0 5 10 15 20 25 30 35

0.056

0.5

1.5

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6

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Communications Channel Speed Comparison

Speed in Mbps (Megabits per second)

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Download Speed, 2011

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Phone (dial-up): cheap but slow Satellite: faster than phone, slower but usually

more expensive than DSL or cable. Available anywhere.

DSL: fast, but more expensive than an ordinary phone connection. Also, speed deteriorates as you move farther away from the phone company office. Maximum distance is around 2 miles.

Cable: fastest, but more expensive than DSL. All users in a neighborhood share the same cable channel, and as more users subscribe, the speed can deteriorate.

Hardware Tradeoffs

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At work, your network is probably connected to the Internet through either a:

1. T1 line (carries 24 separate signals, each at a rate of 64Kbps, for 1.5 Mbps)

2. T3 line (28 T1 lines = 43 Mbps; this is the type of line used for the Internet backbone).

Hardware

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How the Internet WorksHow data might travel the Internet using acable modem connection:

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In addition to the hardware, the computers on both ends of the communications line must agree on which rules they will use to send data back and forth. Such rules are called a protocol.

Protocol: a set of rules governing the exchange of information between computer systems.

Protocols: the rules

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Transmission Control Protocol (TCP). The message is divided into numbered

“packets” (like the pages in a book). Addresses each packet and sends it to its

destination. Packets are re-assembled into the original

message when they arrive

TCP/IP

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TCP

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Internet Protocol: a 32-bit addressing scheme.

Each computer on the Internet is given a numeric address that consists of 4 8-bit numbers, called an Internet Protocol (IP) address. An IP address looks like this: 74.125.95.104 * (each number has been translated into decimal)

* IP address of Google

TCP/IP

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URL: Uniform Resource Locator URL: A unique address for a web page

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12-digit IP addresses are impossible to memorize.

The Internet supports the use of a text name for each IP address. This text name is called a domain name.

www.google.com is a domain name.

URL: Domain Names

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A domain name is divided into three parts (and they are read from right to left!):

1. Top-level domain (e.g. com)2. Second-level domain (e.g. google)3. Third-level domain (e.g. www) It is possible to have four or more

domains, but most domain names consist of three parts.

URL: Domain Names

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Originally there were six top-level domains:1. www.google.COM (commercial—business)2. www.briarcliff.EDU (education)3. www.whitehouse.GOV (government)4. www.comcast.NET (network service providers)5. www.w3.ORG (non-profit organizations)6. www.af.MIL (military)

More top-level domains have been added and will be added in the future.

URL: Top-level Domain

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.aero air-transport industry Must verify eligibility for registration; only those in various categories of air-travel-related entities may register.

.asia Asia-Pacific region This is a TLD for companies, organizations, and individuals based in the region of Asia, Australia, and the Pacific.

.biz business This is an open TLD; any person or entity is permitted to register; however, registrations may be challenged later if they are not by commercial entities in accordance with the domain's charter.

.coop cooperatives The .coop TLD is limited to cooperatives as defined by the Rochdale Principles.

.info information This is an open TLD; any person or entity is permitted to register.

.int international organizations The .int TLD is strictly limited to organizations, offices, and programs which are endorsed by a treaty between two or more nations.

More Top-Level Domains

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.jobs companies The .jobs TLD is designed to be added after the names of established companies with jobs to advertise. At this time, owners of a "company.jobs" domain are not permitted to post jobs of third party employers.

.mobi mobile devices Must be used for mobile-compatible sites in accordance with standards.

.museum museums Must be verified as a legitimate museum. .name individuals, by name This is an open TLD; any person or

entity is permitted to register; however, registrations may be challenged later if they are not by individuals (or the owners of fictional characters) in accordance with the domain's charter.

.pro professions Currently, .pro is reserved for licensed or certified lawyers, accountants, physicians and engineers in France, Canada, UK and the U.S. A professional seeking to register a .pro domain must provide their registrar with the appropriate credentials.

.tel Internet communication services   .travel travel and tourism industry related sites

More Top-Level Domains

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The second-level domain is usually the name of the organization that purchased the name:

www.YAHOO.com www.BRIARCLIFF.edu docs.GOOGLE.com

URL: Second-level Domain

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The third-level domain identifies a web server on the host site.

Usually www, but it can be anything. Examples:

WWW.google.com APPS.google.com DOCS.google.com

URL: Third-level Domain

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Protocol: http: stands for "hypertext transfer protocol", the protocol (rules) used to transmit pages on the web:

HTTP://www.briarcliff.edu HTTPS://mail.briarcliff.edu/owa

URL: Protocol

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The last part of the URL is the name of the file to be displayed and the folder that the file is stored in:

https://maps.google.com/maps?hl=en&tab=wl

http://www.briarcliff.edu/departments/cis/csci100/syllabus.htm

Try changing the case of the file names.

URL: Folder and file

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HTML is the language used to create web pages.

A static web page is a page that does not change.

A web page is requested by a browser that sends an HTTP request to a web server.

A web page is returned to the browser by the web server sending an HTTP response.

The web browser's responsibility is to render the web page for the user.

Static Web Pages

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A dynamic web page is generated on the fly by a program on the web server.

The web server looks at the file extension of the requested page and uses the file extension to determine which application server it should send the request to for processing.

The application server generates an HTML page on the fly and returns it to the web server, which returns it to the user who made the request.

Dynamic Web pages

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ASP.NET. Runs on IIS. (.aspx) JSP. Runs on Apache web server

(Unix/Linux). (.jsp) PHP. Free, open source. Apache. (.php) ColdFusion. Commercial language. (.cfml) Ruby. Free, open source. Combined with the

Rails framework. (.rb) Perl. Free, open source. (.pl) Python. Free, open source. (.py)

Server-Side Scripting Languages

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JavaScript. Runs on the client. Implemented by all major browsers.

Client-Side Scripting Languages

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Web browser: allows Internet users to view web pages

Today’s four most popular browsers:1. Internet Explorer (Microsoft)2. Firefox (Mozilla)3. Safari (Apple)4. Chrome (Google)

Communications Software

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How a browser retrieves a web pageStep 1.Type in the URL.

Step 2.The web Browser sends the URL to your ISP where it is translated to an IP address and forwarded.

Step 3.The Web server at the destination finds the page and sends it back to the original IP address.

Step 4.The Web browser receives the web page (coded in HTML), interprets the HTML, and displays the page on your computer.

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HTML: HyperText Markup Language.

HTML involves creating plain text documents and embedding tags into them. The tags provide formatting information that is interpreted by a web browser.

Internet Software

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HTML tags usually come in pairs, one to turn the feature on, one to turn it off.

<h1> Heading 1</h1> <h2> Heading 2</h2> <p> paragraph </p> <b> BOLD </b> <i> Italic </i> <u>Underline</u>

Some HTML Tags

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The World Wide Web: Browser Plug-ins Plug-ins: Programs that extend the

capability of a browser You can download many plug-ins at no

cost from various Web sites Popular plug-ins:

Acrobat Reader Flash Player Java Quicktime Shockwave Player

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Improve error handling Develop the ability of the browser to be an

application platform, via HTML, CSS, and Javascript.

Adds audio, video, vector graphics (SVG), math notation (MathML), Web SQL database, geolocation data

HTML5 introduces a number of APIs that help in creating Web applications. These can be used together with the new elements introduced for applications.

Goals of HTML5

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Current scores (12/31/2012). See www.html5test.com ◦ Chrome (v. 23): 448 (of 500)◦ Opera (v. 12): 419◦ Safari (v. 6): 378◦ FireFox (v. 17): 365◦ IE (v. 9): 138

HTML5 Compatibility

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Guidelines for making your web pages accessible to handicapped users.

www.webaim.org. www.w3.org/TR/WCAG www.w3.org/TR/wai-aria

Accessibility

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The End