Quick Tip: URLs - Uniform Resource Locator

URLs, or Uniform Resource Locators, are the method by which documents or data are addressed in the World Wide Web. The URL contains the following information:

- the protocol.
- the DNS name of the machine on which the page is located.
- the local name uniquely indicating the specific page.
- the location of the resource in the directory structure of the server.

To make a piece of text clickable, the page writer must provide two items of information : the clickable text to be displayed and the URL of the page to go to if the text is selected. Once the text is selected, the browser looks up the host name using DNS. Now armed with the host's IP address, the browser establish TCP connection to host. Over that connection, it sends the file name using the specified protocol.
The URL scheme is open to have protocols other than HTTP also. In short, URL's have been designed to not only allow users to navigate the Web, but to deal with FTP, news, Gopher, email, and telnet as well, making all the specialized user interface programs for those other services unnecessary, and thus integrating nearly all Internet access into a single program, the Web Browser.
The growing use of the Web has turned up an weakness in URL scheme. A URL points to one specific host. For pages that are heavily referenced, it is desirable to have multiple copies far apart, to reduce network traffic. The advent of systems such as Akami are meant to meet that need, distributing content over multiple servers on a global level.

WWW - The Server Side

For all the incoming connectionts from different clients, every website is associated with a server process listening to TCP port 80. The client sends a request after the connection is made and the server sends the reply and then the connection is released. The protocol that is responsible for requests and replies is called HTTP.

The steps that occur between the user clicking and a page being displayed are:
- The browser determines the URL.
- The browser asks DNS for IP address.
- DNS replies.
- Browser makes a TCP connection to the port.
- It then sendsthe GET command.
- The server sends the file.
- The TCP connection is released.
- The browser displays the text of the file.
- The browser fetchesand displays all images of the file.

Not all servers speak HTTP, Old servers use FTP, Gopher or other protocols. Given the number of different protocols, it was thought impractical to make browser understand different protocols. However, since there is a need to make information available (where the server talks in protocols other than HTTP), a solution was required. This solution is something called a proxy server. A proxy server takes a HTTP request from the browser and translates these requests into the FTP/Gopher/other protocols. The proxy server is a separate logical server.
A proxy server also serves to provide an important function called caching. Through caching, a proxy server keeps a local copy of the pages that pass through it. If a user requests for a page, if the page is present on the cache of the proxy server, it serves the page to the user. this way it serves to reduce load on final server.

MIMO (Multiple Input Multiple Output) technology

1. MIMO is a new wireless technology conceived in the mid 90’s
2. It is based on an entirely new paradigm for digital signal processing that multiplies the data rate throughput achievable in wireless communication products.
3. Greatly improves the reliability, range and robustness of the connection providing a much better user experience that is closer to “wired” Ethernet quality.
4. MIMO technology is now being introduced to the Wi-Fi market.

MIMO is a smart antenna technique that increases speed, range, reliability and spectral efficiency for wireless systems.
MIMO is one technology being considered for 802.11n, a standard for next-generation 802.11 that boosts throughput to 100M bit/sec.

• Smart antenna techniques use multiple antennas to improve wireless performance and reliability.
– Antennas themselves are “dumb” pieces of metal.
– “Smartness” comes from signal processing that is applied to the multiple antennas.
– There are differing degrees of smartness.
• Conventional, “single-dimension” (1D) smart antenna techniques transmit just one data stream per channel
– RF beamforming.
– Digital beamforming.
– Digital receive diversity combining.
• MIMO makes smart antennas “multi-dimension”.
– Multiple data streams in the same channel.
– 2-D signals.

BENEFITS OF MIMO TECHNOLOGY:
For Business
• Enables truly wireless office – replaces Ethernet
– Improves wireless reliability and robustness
– Reduces infrastructure cost - Doubles coverage area of each AP
– Rates to 108 Mbps in each channel – similar to wired Ethernet speed
• Improves VoIP performance
– Extends handset battery life
– Increases call capacity
For Consumers
• One AP covers your whole home with reliable service
– Penetrates more walls at higher rates
– No need to sit in the right place to use your laptop
• Supports new wireless multimedia applications
– Whole-home coverage for high-speed broadband access
– Reliable SDTV and HDTV video transport in home networks
– Multi-service applications – voice, video, data