Sp wr2
- 1. How High-speed Dial-up Works 1.Introduction to How High-speed Dial-up Works Surfing the Internet, do you find yourself going to get a cup of tea, a comic or clean your bathroom between page loads? There are chances are you're using a dial-up connection, and a sneaking suspicion may be growing on you; eventually , is your connection actually getting slower? Sometimes, the connection speed of dial-up is limited by the bandwidth of Phone lines. But, at the same time, the average file size for Web content is getting larger and larger. So Web sites feel more comfortable bulking up their pages. It takes a lot time to squeeze all of that data through a dial-up connection. New technology offers a solution to the slow-down that doesn't necessitate broadband. Services like NetZero and EarthLink are now offering "high-speed dial-up.“ According to advertisement for these services, you can get connection speeds that are five times faster than traditional dial-up service. High-speed dial-up providers can't do anything about the modem handshake, but they can speed up the software handshake.
- 2. 2. High-speed Dial-up: Acceleration Servers The standard software handshake is usually a simplified explanation, of course, but you can get the idea of the back-and-forth that need to occur in the handshake protocol before information can be sent or received. High-speed dial-up providers have cut down on this back-and-forth by creating a system that allows the conversing machines to remember responses to questions. This makes for a much shorter conversation. This shorter handshake equals much faster connection times. The increase in speed varies by machine, but in some cases it can reduce the handshake by up to 50 percent. What might take 45 seconds with a "normal" dial-up service becomes maybe a 30-second process with a high-speed service. When you search for a Web page on the Internet, your request is routed though your ISP to the Web. After making a series of stops along the way at machines that help find the page you're looking for, your machine is connected to the computer that serves the Web page you requested. When you search for a Web page using high-speed dial-up, your request is sent from the dial-up modem in your computer to the ISP's acceleration server. Now the acceleration server is requesting and serving pages on your behalf. The acceleration server uses a broadband connection to quickly search the Internet for the server that hosts the page you're looking for. Once it finds that server, the two machines start talking and exchanging the information you need. Your ISP's acceleration server takes that information and sends it to your machine
- 3. 3. High-speed Dial-up: File Compression You know that there are two types of file compression that is the Key element of high-speed dial –up Internet. Text and other files that need to remain perfectly intact during the compression process use lossless compression. Once they are uncompressed, the files return to their original state. When these files are uncompressed, they are not exactly as they were before compression. They have lost some of the original data in the process. The loss in quality may not be important to the user when weighed against the increase in speed gained through the compression process. Eventually, the on-the-fly file compression utilized in high-speed dial-up can't be added to the file types specified above because of the nature of the data. For instance, data on secure Web sites is encrypted. When it is transmitted, the code looks like a bunch of gibberish so that no one can read it. I will describe three examples is text, image and other files. At text files ・・・ Typically, text will compress at least 50 percent using on-the-fly techniques. At image files ・・・ Typically, the image file size shrinks anywhere from 50 percent to 90 percent in the process. At many other files ・・・ It is not possible to compress the file any further in a quick way. In the case of secure Web pages, we already discussed why they cannot be compressed. The acceleration server will not touch these files -- it just passes them through something.
- 4. 4.High-speed Dial-up: Filtering and Caching If you type a URL into the address bar of your browser, you are sending a request for a specific page. When the information is sent back to your machine, the hidden code executes a program that launches the advertisement. In order for the pop-up to pop, that hidden code must display parameters that tells your machine what size the ad is, where on the screen it should appear, and other details about the ad. These ads take up valuable bandwidth, slowing down the transmission of data to your machine. When you combat this drag, high-speed dial-up providers have bundled a pop-up blocker into the software they send to subscribers. This pop-up blocker is programmed to recognize those lines of code that spell out the ad parameters. When it sees those tell-tale lines of code, it rejects the ad's request to be displayed. What this amounts to is less information being sent across the phone line to your machine. The less data that is sent, the faster the load time. High-speed dial-up uses a similar system for commonly requested Web pages. Instead of constantly requesting the same page, the acceleration server takes note of which Web pages are being commonly asked for by all subscribers. So instead of asking the HowStuffWorks server thousands of times a day, it just asks once. Then it stores the page in its memory, and every time another subscriber asks to see that, it simply transmits the page out of its memory to the user. This is called server-side caching, and it saves time by eliminating redundant requests.
- 5. 5.High-speed Dial-up: The Bottom Line We decided to try out one of the more popular high-speed dial-up providers to see how much the service sped up a dial-up connection. After signing up for the service and choosing the "out of the box" settings, HowStuffWorks tooled around the Web with both normal and high-speed dial-up connections to test the difference in speed. After log-in, we surfed repeatedly to some of the most popular sites on the Web. The results varied by site, but as an example, HowStuffWorks came up three times faster with high-speed dial-up. For the complete results, see the chart below. It would seem that a clever combination of fairly straightforward technologies has helped to overcome some of the speed bumps of dial-up Internet. These advances serve to prolong the life of dial-up Internet and provide an alternative for those who are tired of standard dial-up but not quite ready for the leap to broadband. If these advances continue, dial-up may be here to stay for quite a while. For more information on high-speed dial-up and related topics, check out the links on the next page.
- 6. 6. Lots More Information How WiFi Works ・・・ WiFi has a lot of advantages. Wireless networks are easy to set up and inexpensive. They're also unobtrusive -- unless you're on the lookout for a place to use your laptoｐ, you may not even notice when you're in a hotspot. In this article, we'll look at the technology that allows information to travel over the air. We'll also review what it takes to create a wireless network in your home.First, let's go over a few WiFi basics. How DSL Works ・・・ When you connect to the Internet, you might connect through a regular modem, through a local-area network connection in your office, through a cable modem or through a digital subscriber line (DSL) connection. DSL is a very high-speed connection that uses the same wires as a regular telephone line. How Modems Work ・・・ In this edition of HowStuffWorks, we'll show you how a modem brings you Web pages. We'll start with the original 300-baud modems and progress all the way through to the ADSL configurations! (Note: If you are unfamiliar with bits, bytes and the ASCII character codes, reading How Bits and Bytes Work will help make this article much clearer.)