How High-speed Dial-up Works

A PTT employee explains to a customer about subscribing to the new high-speed internet service at the post office in Hanoi, Vietnam.
A PTT employee explains to a customer about subscribing to the new high-speed internet service at the post office in Hanoi, Vietnam.  See more Internet connection pictures.

While surfing the Internet, do you find yourself going to get a cup of coffee, grab a magazine or retile your bathroom between page loads? If so, chances are you're using a dial-up connection, and a sneaking suspicion may be growing on you: Is your connection actually getting slower?

It is and it isn't. As always, 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. More people are using broadband connections that can handle a bigger load, 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 ads for these services, you can get connection speeds that are five times faster than traditional dial-up service.

When you think of dial-up Internet service, the first thing that probably comes to mind is the strange sort of "R2-D2 in a blender" type chirping that the modem makes as it connects. This song is called the handshake protocol, and it is the first thing that bogs down the speed of dial-up Internet.

The handshake protocol, as the name implies, begins the conversation that allows data to be sent to and from your computer using the Internet. There are actually two separate handshakes that occur in this process. The first half is the modem initializing the Internet connection. We'll call that the modem handshake. The second part is the software handshake. That deals with authenticating the user's access to the ISP (Internet Service Provider). When your computer is chirping away, it is introducing itself to your ISP. High-speed dial-up providers can't do anything about the modem handshake, but they can speed up the software handshake.

On the next page learn about the standard software handshake and how it can be accelerated.­



High-speed Dial-up: Acceleration Servers

High-speed dial-up allows your machine to establish a connection with your ISP in a fraction of the time it takes with standard dial-up.

The standard software handshake goes something like this:

Your machine: Hello, my name is Sparky.

ISP Server: Hello, Sparky.

Your machine: I am John's computer.

ISP Server: John who?

Your machine: John Smith.

ISP Server: I know 32,422 John Smiths.

Your machine: He is one of your customers.

ISP Server: Does he have an account number?

Your machine: Yes.

ISP Server: What is that number?

Your machine: 5546743897

ISP Server: Ah, yes. OK, go ahead, 5546743897. You have access.

This is a simplified explanation, of course, but you can get the idea of the back-and-forths 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:


Your machine: Hello, my name is Sparky.

ISP Server: Ah, hello, Sparky. Aren't you John Smith's machine.

Your machine: Yes, his account number is 5546743897.

ISP Server: Go ahead, 5546743897. You have access.

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. Once this connection is established, data can flow freely from the Web server to your computer. Once the information leaves the Web server and hits your dial-up connection, that's where the bottleneck begins in the typical Internet transaction.

But high-speed dial-up providers have come up with some pretty clever ways to open up that bottleneck. By loading special software into a server, they turn it into what they call an acceleration server. And by sandwiching the acceleration server into the chain between your dial-up connection and the Web, they can speed up the process considerably.

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.

The high-speed dial-up data path

Acceleration servers speed up the dial-up data transfer using several techniques:

  • Compression
  • Filtering
  • Caching

Next, we'll go over how these acceleration servers drop the pedal on your dial-up.


High-speed Dial-up: File Compression

The key element of high-speed dial-up Internet is file compression. If you've read How File Compression Works, then you know that there are two types of file compression: lossy and lossless.

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.


Photos and graphics can be transmitted using lossy compression. 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. For example, a picture that originally had 2 million colors may only have 16 thousand after lossy compression. The loss in quality may not be important to the user when weighed against the increase in speed gained through the compression process. Companies like NetZero let the user control how much compression is used on photos and certain sites.

File compression is an evolving technology, and it doesn't work on every file type yet. The below information will help you understand what will and will not be accelerated by high-speed dial-up.


  • HTML/Java-based Web pages
  • Text
  • JPG/GIF-based graphics
  • E-mail

Not Accelerated

  • Streaming media (audio or video)
  • Secure Web pages
  • Music/photos sent as e-mail
  • Downloads

At this point, 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. When this gibberish reaches the acceleration server, it can't compress the code: If the compression software were to change even one character in the encrypted transmission, that would render the data unusable.

Here is how a typical acceleration server compresses different file types:

  • For text files, including the HTML text of a Web page and the text in an e-mail message, the acceleration server compresses the text on the fly and sends it down your modem line. Typically, text will compress at least 50 percent using on-the-fly techniques.
  • For image files, including GIF and JPG images on Web pages as well as many banner ads, the acceleration server reads the image from the Web site and recompresses it to reduce its size. Typically, the image file size shrinks anywhere from 50 percent to 90 percent in the process.
  • In many other files, including video files, Zip files and MP3 music files, compression has already taken place. For example, an MP3 file is already one-tenth the size of the original track on the CD. 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 as-is.

In the next section, we will learn how high-speed dial-up accelerators filter out useless data to increase speed.


High-speed Dial-up: Filtering and Caching

When you type a URL (like into the address bar of your browser, you are sending a request for a specific page. If that page uses pop-up advertising, there are pop-up parameters hiding in its programming code. 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.

To 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.



The first time your browser loads a Web page, it has to load the entire thing, along with all of the images it displays. If the browser saves the images and text, then the second time it loads the same page it can check for duplicates. If an image has not changed, there is no need to download it again. This process of saving a file in the hopes of reusing it in the future is called caching. For a complete explanation of the caching process, see How Caching Works.

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 if it can see the homepage of, it just asks once. Then it stores the page in its memory, and every time another subscriber asks to see HowStuffWorks, 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.

There is a second side to caching -- client-side caching. Internet browsers like Explorer or Netscape are made to cache frequently viewed pages to cut down on load times.

Client-side caching

The browser stores the cached pages on your computer's hard disk. High-speed dial-up software enhances this feature. In addition to storing frequently viewed pages, it also looks for elements in those pages that remain constant. For instance, instead of caching the entire HowStuffWorks homepage, most of which changes every day, it looks for things that don't change. On our homepage, the logo, the header, the navigation, and the search bar stay the same every day. The software makes note of that consistency, saves those elements, and then only loads what has changed every time you come to the HowStuffWorks homepage.

You can see how caching saves time by avoiding unnecessary data transmission. The most amazing thing about this tool is that with the combination of server-side caching and client-side caching, the system learns about your surfing habits. It uses what it learns to streamline your connection process as much as possible. So the more you use it, the faster it gets.

Compression, filtering and caching are the three key steps in dial-up acceleration. But what actually happens when you put all three techniques together? Does performance really improve? And is the improvement enough to be noticeable?

The answer is yes, and in the next section we will try out NetZero to see how well it actually works with real-world Web pages.


High-speed Dial-up: The Bottom Line

Web page load time comparison
Web page load time comparison

Now that you understand how it works, let's take a moment to look at how well it works. We decided to try out one of the more popular high-speed dial-up providers, NetZero, 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.

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.