Transcript 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
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Satellite
Web Server
Satellite Dish
Communications
Towers
Bluetooth
Device
Laptop
Cell
Phone
Tablet
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1. A sender (computer)
2. A communications device (modem): connects the
sender to the channel
3. A communications channel (cable, radio waves)
4. A communications device (modem): connects the
channel to the receiver
5. A receiver (computer)
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Some applications of communications
technology:
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Internet/Web
E-mail
Blogs
Wikis (collaborative documents)
RSS (Really Simple Syndication)
VoIP (Voice Over IP)
FTP (File Transfer Protocol)
Web folders
Web conferencing
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Network: a collection of computers and
devices connected via communications
devices and transmission media.
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Share hardware (e.g. printer, Internet
connection)
Share software
Share data (e.g. files on a hard disk)
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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)
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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.
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Internet: a world-wide network of computer
networks.
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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
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1969: Four host nodes
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1984: More than 1,000 host nodes
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Today: More than 500 million host nodes
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1989.
1991.
1992.
1993.
1994.
1995.
1995.
1998.
2014.
Tim Berners-Lee
HTML 1.0
Lynx browser
Mosaic browser
HTML2
HTML3 (draft never approved)
Internet Explorer.
HTML4
HTML5
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No one controls the Internet—it is a public,
cooperative, and independent network.
Several organizations set standards.
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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).
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Telephone line (dial-up)
Digital Subscriber Line (DSL)
Cable
Satellite dish
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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).
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A modem modulates a signal going out and
demodulates a signal coming in.
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Speed is measured in BITS per second (bps,
b=bits, B=bytes).
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Communications Channel Speed Comparison
Cable High
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Cable Low
6
DSL High
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DSL Low
1.5
Satellite
0.5
Dial-up
0.056
0
5
10
15
20
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Speed in Mbps (Megabits per second)
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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.
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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).
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How data might travel the Internet using a
cable 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.
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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
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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
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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.
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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)
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It is possible to have four or more domains,
but most domain names consist of three
parts.
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Originally there were six top-level domains:
1.
2.
3.
4.
5.
6.
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www.google.COM (commercial—business)
www.briarcliff.EDU (education)
www.whitehouse.GOV (government)
www.comcast.NET (network service providers)
www.w3.ORG (non-profit organizations)
www.af.MIL (military)
More top-level domains have been added
and will be added in the future.
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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.
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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
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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
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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
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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
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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.
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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.
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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.
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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)
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JavaScript. Runs on the client. Implemented
by all major browsers.
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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)
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Step 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.
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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>
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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:
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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.
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Current scores (12/31/2012). See
www.html5test.com
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Chrome (v. 23): 448 (of 500)
Opera (v. 12): 419
Safari (v. 6): 378
FireFox (v. 17): 365
IE (v. 9): 138
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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
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