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					              The Internet
               -How it works
               - Web 2.0
Art 321 Dr. J Parker
      Digital Communication
How do computers send information along
 wires (phone lines, cable TV) and wireless
 networks (including bluetooth)?

This is actually a very complex subject. We
 can get to understand the basics if we try
 to avoid the jargon and the math.


                                              2
        Digital Communication
We know that all information is stored in a
 computer as numbers, binary numbers.

  Binary numbers can have digits that are 1 or 0,
    corresponding to an on/off state of a switch or
    transistor.
  We can also arbitrarily assign a voltage to ‘0’
    and one to ‘1’. When a device detects a
    particular voltage it can then be converted into
    a digit. And vice-versa.

                                                   3
       Digital Communication
Let’s say that 0 is +2 volts and 1 is +5 volts.
  Here’s how we can send 1’s and 0’s:




                                                  4
      Digital Communication
This sends 2 volts which is a zero.




                                      5
      Digital Communication
This sends 5 volts which is a one.




                                     6
      Digital Communication
Binary numbers as lights – we did that
  before. Let’s do it again.
Let’s send messages using lights in another
  way.




                                              7
Digital Communication




                        8
        Digital Communication
We’d never do exactly that, though.

Real electronic signals are never digital. Voltages
 are never precisely 2 or 5, and there are many
 voltages between 2 and 5 (infinitely many).




                                                      9
        Signals for Communication
     Let’s draw a line at 2v and 5v


8

4

0

4

-8




                                      10
   Signals for Communication
Eliminate everything outside the allowed
  voltages of 2 and 5.




                                           11
Signals for Communication

 Rescale and we have a (nearly) digital signal!




                                            12
    Signals for Communication
This is how we send a binary number along a wire!
As the voltage moves past a point the numbers
can be read off.




                                                13
           Data Transmission
This is how data gets sent to computers on a
network.

The sending computer generates the digital
voltages that get sent along a wire to a receiving
computer.

Along one wire, only one signal (one direction) can
be sent. Two wires can send information both
ways at the same time (full duplex)

                                                     14
          Communications
So a computer can send to a receiver along
a wire. Good.
But there can be many computers on the
same wire …




                                             15
            Overview LAN
Any computer here can send to any or all
others. However, they have to take turns.




                                            16
            Radio networks
How would you communicate between
computers that can’t be connected by wires?

By radio, of course.

That’s what they did at the University of
Hawaii to link their computers. They called it
‘Alohanet’

                                             17
Alohanet




           18
                  Alohanet
Here are 4 radio transmission stations, used
instead of wires. Often they try to send at the same
time and the result is a mess, a signal that is a
combination of the transmission. It is called a
collision.




                                                   19
                   Alohanet
Collisions result in no data being transmitted, and
all colliding data must be re-sent.

Collisions




                                                      20
                     Alohanet
If more than one person shouts into the hose/pipe, the
sound is garbled and nobody can understand. That’s a
collision. They need to repeat the message.




                                                         21
                   Inspiration
Why do we care about
Alohanet?                Second, it is the same
                         idea as is used on
Well first, it was the   Ethernet that is used
original wireless        everywhere on the
network                  planet.

                         Ethernet is the network
                         used by almost all PCs
                         and Macs in the world.
                                                  22
                 Ethernet
Instead of a radio, computers ‘shout’ into a
wire or cable. If a collision occurs then it is
detected, and they have to resend their data
(shout again).




                                              23
                   Packets
Now, sending data one byte at a time is like
speaking one letter at a time. It is more efficient
to send a bunch of bits or bytes ( a block) as a
unit.

Usually these have a fixed size.

A block of data plus some other info is a
packet.
                                                 24
                    Packets

Here’s a packet: (for example)

<code: packet type>
  <destination>
  <sequence number>
  <date/time>
  <sender> <…>
  <data …………………………………….>
  <error detection code>

                                 25
                 Packets
The destination is critical. On an ethernet
system all computers connected on that net
can receive all data on the network.

A computer discards all data not addressed
to it. All data goes to everyone, receiver
notes it, others discard it.

Sniffers can look at all packets and display
them! These nets are not secure.
                                               26
                 Packets
A block of data (a file, say) is split into
smaller pieces each the right size to put into
a packet. The sequence numbers order
these pieces.
If a packet arrives in the wrong order, the
data can still be put together correctly.
If a packet gets lost the missing packet can
be requested and resent..


                                             27
                Packets
Error detection codes are computed for each
data packet, and are numbers that can be
used to tell if something bad happened in
the transmission.
Sender computes the code for the data sent.
Receiver computes the code for the data
received.
If the two differ, and error occurred (EG
broken wire or electrical interference).
                                          28
          Wireless networks

Like Alohanet, the data is sent to a radio
transmitter and sent – receiver decodes and
sends to computer. Most of the rest of the
scheme will still work (packets, error detection,
etc).




                                                    29
           Nets and the Web
We now have a basis for understanding larger
(global) networks and building more complex
systems like the Web.

Bigger networks (my house, your house, the U of
C) connect to each other using basically the same
scheme as used for the small ones. These (Cities)
connect via faster links to each other through
collections of computers (servers) and those to
bigger ones, etc. etc.
                                                30
                                              Internet
     How does the Internet work, then?
Internet Service Provider               Network Access point
                    Point of Presence

                              T1
                    T3




                                                               31
                                Internet
    How does the Internet work, then?

•   Internet Service Provider – local computer that you connect to.
•   High-level networks connecting to each other through Network Access
    Points or NAPs. Network Access point
• Point of Presence - a place for local users to access the company's
    network, often through a local phone number or dedicated line.
•     T1 - a high speed digital connection that supports transfer speed up to
    1.54 megabits per second.
•    T3 lines are a common aggregation of 28 T1 circuits that yields 44.736
    Mbps total network bandwidth.
In the real Internet, dozens of large Internet providers interconnect at
NAPs in various cities, and trillions of bytes of data flow between the
individual networks at these points. The Internet is a collection of huge
corporate networks that agree to all intercommunicate with each other at
the NAPs. In this way, every computer on the Internet connects to every         32
other.
                  Internet
How does the Internet work, then?




                                    33
     The Web II and Web 2.0

The ‘Web’ sits on top of the Internet, and is
really an artifact of software.

Web 2.0 is merely more of the same, but
with more interactive features.

EG Blogs, Wikis, Podcasts, etc.
                  Blogs
     A BLOG is a weB LOG, an online public
diary of sorts.

A simple blog is just a web site with a bunch of
opinions, text, images, etc.

A real blog has users subscribe, and the
subscribers get told automatically when there
is new content
                 Blogs
    I will give an overview of how this works.

To do blogging and podcasting ‘by hand’ is
just too much, and so with the knowledge of
the basic system, we will look at practical
ways to DO it.

Free software whenever possible.
                   RSS
RSS?

Rich Site Summary is a way to deliver
regularly changing web content.
(AKA Really Simple Syndication)

Many news-related sites, weblogs and other
online publishers syndicate their content as an
RSS Feed to whoever wants it.
                   RSS
 Anything that can be broken down into discrete
items can be syndicated via RSS:
- the "recent changes" page of a wiki
- a changelog of CVS checkins
- the revision history of a book.
Once information about each item is in RSS
format, an RSS-aware program can check the
feed for changes and react to the changes in an
appropriate way.
                 RSS
 RSS defines a grammar (a set of HTML-
like tags) for sharing news.

Each RSS text file contains both static
information about your site, plus dynamic
information about your new stories
surrounded by matching start and end
tags.
                 RSS
 An RSS feed always starts with an <rss>
element (tag), which contains an attribute
called version, which specifies the version of
the RSS feed.
Here we focus on the RSS 2.0 format
because it's the most commonly used today.

<rss version="2.0">
…
</rss>
<rss version="2.0">
 <channel>
  <item>
   <guid isPermaLink="false">
    http://www.blogger.com/feeds/11571454126425128
   </guid>
   <pubDate>Fri, 01 Sep 2012 21:08:00 +0000</pubDate>
    <title> Art 311 </title>
   <description>
     <div xmlns="http://www.w3.org/1999/xhtml">My article
      <a href="http://www.ucalgary.ca">How RSS works
       </a> is on the homepage this week.</div>
   </description>

<link> http://www.minkhollow.ca/blog/2009/09/xx.html </link>
     <author> Jim </author>
    </item>
 </channel>
</rss>
                  RSS                 Subscriber


            You can tell the RSS          Subscriber
Your web    feed when there’s a new
site or     item.
files are                               Subscriber
            Subscribers are told
here, on
            about new content
your        automatically.
computer
            Subscribers can
or rented   schedule checks for
server.     new content.
            RSS will periodically
            look for new items.         Subscriber
                            RSS
The structured nature of the RSS
Document permits the process to be
successful.

The RSS software can read the file and
tell what is in it, who wrote it, etc.
                           Blogs
Back to blogs then.

Get someone else to host, unless you
REALLY need security and want to
do a lot more work.

I suggest wordpress.com
                          Blogs
My own 299 blog is at
  drjimparker.wordpress.com

Go to wordpress.com and sign up for a
new account. You will be mailed an
authentication and can fill out some
profile material.
                           Blogs
How to read these?

There are many aggregators, as they
are called.

Example: RSS Bandit
   http://rssbandit.org/
                 Wikis
 A Wiki is a web page or site (collection of
pages) that can be built collaboratively.
Many people can share the wiki and can
add and edit material there.
Requires special software run on the web
server.
                 Wikis
First wiki software: WikiWikiWeb 1994

Wiki is a Hawaiian word meaning ‘fast’.

Like a blog, it uses a relational database.
So we don’t want to maintain this
ourselves. It’s complicated and boring.
                    Wikis
I have created a wiki for us at
http://sites.google.com/site/art299coursewiki/

To use the Wiki you should create a Google
account – you will be asked to if to try to edit the
wiki.

If you do not wish to get a Google account, I will
give you a dummy account. Do not share with
anyone outside of the class.
                         Wikis




The login page will be loaded for you.
                    Wikis




Then the new wiki page with editing ability.
                    Wikis

You can now
type in here,
add images,
etc.



 Then you
 can save
 It. Don’t
 Forget!

You do all editing through the browser!.
                   Wikis
 I want everyone to make a small edit to
the wiki.

Add one line with your name and ID
number and a link to your web page.

http://sites.google.com/site/art299coursewiki/
              Podcasts
A Podcast (or Vodcast) is simply an RSS
feed.

Doing the work by hand, as for wikis, is
nasty. So let’s use a tool – Podbean.

http://faq.podbean.com/2007/02/23/how-
to-set-up-my-podcast-in-itunes-music-
store/
              Podcasts
Create a Podbean account – it’s free and
comes with may Gb of space.

Doing the work by hand, as for wikis, is
nasty. So let’s use a tool – Podbean.

Then log in to your dashboard.
http://faq.podbean.com/2007/02/23/how-
to-set-up-my-podcast-in-itunes-music-
store/
         Podcasts
Click on the upload tab, and then on
the ‘MediaManage’ sub-tab.
Click on the Upload button to begin
transferring the file to PodBean. Don’t
close the window until it has finished.
Click on the Upload button to begin
transferring the file to PodBean. Don’t
close the window until it has finished.
              Podcasts
That’s the upload stage. Now we publish.
Click on the publish tab.

Fill in the information asked for. Drop down
tabs will allow the sound file uploaded to be
selected with a simple click.
             Podcasts
Click on the publish button and we’re
done..
Podcasts

				
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