Its All in a Click

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Its All in a Click
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A Web Page

• When you bring up a web page, the page is made up
  of several parts. The main part is the actual
  text page which is often enhanced with a
  graphics background. Usually, other graphics
  object are also found on the page. Another
  element found on the page is a link or
  sometimes called a hyperlink.

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A Link

• Links found on a web page are most often (the
  default) blue and underlined.
• However, both the designer of the page and/or the
  user of the browser can change this setting.
• Thus, it is not a good idea to user underlined
  text on a web page because users may think it is
  a link.

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Whats in a Link

• One of several commands could be embedded in a
  link .
• The most common command is the http command
  which tells the server what type of information
  (protocol) is coming to it.
• Other common commands include ftp, and
  mailto.

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When I Click!

• Lets take a common web action (going to another
  web page) and follow it.
• When you click on the link (http//www.carroll.k
  12.ia.us) the software looks at the protocol
  (http) and encodes the rest of the information in
  packets to send to a server.
• The information following the protocol command is
  in text thus the information will be sent to a
  DNS server.

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Ya Gotta Pack to Travel

• Your browser, working with your network card
  (NIC) takes the request (your click) and packages
  it into small chunks called packets.
• It takes several (x100) packets to encapsulate
  your request and send it along to the server.

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Packets

• Packets are made up of three parts, the header,
  body, and trailer.

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Header

• The header contains information as to where the
  packet should be going (address) and how many
  hops it has pass through along the way.
• Note if the packet passes through more than 3
  hubs/repeaters, the packet is killed.
• Note learn more about this deadly hopping by
  reading about the 5-4-3 rule in
  hubs/switches/routers.

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Body

• The body of the packet actually contains portions
  of your data.
• After the packets arrive at their destination,
  the NIC will reassemble the data.

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Trailer

• The trailer contains information as to how many
  packets are being used to encapsulate the data
  being sent.
• The trailer also contains information as to what
  part of the entire data packets this packet
  belongs.

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DNS Server

• The DNS (Domain Name Server) servers function is
  to change a text address request into a number
  number called the IP or domain address.
• Example carroll.k12.ia.us is converted to the
  domain address of 207.165.61.1
• Note a reverse domain name server does just the
  opposite translation.

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Pass it along

• The DNS server embeds the proper address and the
  shortest route into the header of the data
  packets.
• The data packets are then forwarded to the
  requested server.

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The Web Server

• The web server you requested by clicking on the
  link has been sitting there Listening for your
  request.
• A web server is configured to listen for a set
  number of requests and to actively hand a set
  number of requests.
• Example our server is set to handle 60 active
  connections and 60 listens. That means that the
  server has the ability to serve 60 users at one
  time while paying attention to 60 other users
  that have received information from the server
  and the server is waiting for another request.

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Serving your Web Request

• The web server looks at your request and finds
  the requested page located on an attached drive.
• The server finds that the requested pages
  contains several types of information (text,
  graphics, sounds, links, etc)
• The server begins sending you the data in
  separate parts. IE the basic page page.
• Then the server waits (listens) for a response
  from your browser before it sends another part of
  the page.

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Your Browser Responds

• Your browser acknowledges the sent data and
  begins to assemble the web page while waiting for
  the server to send the rest of the page data.

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World Wide Wait

• Ok, so now you can see why you have to wait for
  your web page to appear. The server sends parts
  of the page to you, then it drops the connection
  and servers someone else while it listens for
  your browser to ask for more data.
• How long the server will listen for additional
  requests is called the TTL (Time To Live). If
  your browser takes too long to respond, your
  computer will have to re-establish the connection
  again. (the wait!)

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Persistent Connections

• A server can be configured to offer a persistent
  connection. Then the server will serve your
  browser the entire page.
• This is much faster but reduces the number of
  connections that the server can handle at one
  time.
• Note your browser must also be configured to
  handle persistent connections.

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