John Graham-Cumming
You are in a 747 flying from San Francisco to London. The captain announces that the 12-hour flight will be much shorter this time as the plane now has twice as many seats. Do you believe him?
Many Internet users fall for this line when they buy “faster” modems. For what is commonly called speed is actually bandwidth – the number of bits that can be transmitted in a second – the digital equivalent of seats on that 747.
High bandwidth is necessary but there’s an equally important factor in how long it takes a Web page to download: latency, the time a single bit takes to get from a website to your computer. It’s the bit’s “flying time” and is limited by the speed of light and congestion on the Internet. And these delays add up.
For example, The Guardian’s Web page, , has around 16 000 bytes to be downloaded. Each byte is eight bits, a total of 128 000 bits. With a 28,8 kilobytes per second modem that transfers 28 800 bits per second, you’d expect the page to appear in five seconds (128 000 divided by 28 800). It doesn’t.
That’s because TCP, the protocol that governs the download, doesn’t receive the page in one go. Each piece consists of a number of segments of around 536 bytes.
TCP first asks for one segment and checks that it receives it. Then it asks for two segments, checks, asks for four and so on until it is using all the bandwidth it can. This careful checking and doubling helps to stop a program from hogging the Internet. But each check requires a back and forth message. And that delays the communication by twice the latency or “flying time”.
If the network is congested or packets get lost, the doubling process is slowed adding additional messages, called ACKs (acknowledgments) across the Internet. When the latency is large – perhaps the Web server is far away or the Internet is congested – there’s a big delay before you see the page.
But there are remedies. Get the highest bandwidth modem you can, 56 kilobytes per second or better – if there aren’t enough seats on the 747 you’re not going anywhere. Then make sure your Internet service provider (ISP) handles that speed.
Download a copy of Net.Medic from VitalSigns Software, , to check the modem is running at the speed that the computer expects.
Install an up-to-date browser that uses the HTTP 1.1 protocol (both Netscape and Internet Explorer do) as this can make a big difference to download times.
Next look into PeakJet 2000 from PeakSoft at which guesses the pages you are likely to download and gets them while you are busy reading another page.
Talk to various ISPs about their connections to the Internet backbone and check out their record with other people. Net.Medic will pinpoint if your ISP is having congestion problems.
Ask your ISP if it has a proxy server. This is a giant version of the cache in your browser and stores copies of commonly accessed pages at the ISP, making them very quick to access.
Consider using some software to tune your TCP stack. This is a fairly technical topic but PPP Boost from C3 Systems at does all the work for you – just select the “recommended” settings – and it’s free, too.
Why fly your 747 to Los Angeles when you can pick up what you want in New York or Amsterdam? Where possible use mirror sites which are exact copies of Internet sites stored in different places around the world.
Choosing a site near you will get the best performance. You can determine this by using the “ping” utility built into Windows. To find the difference in latency between your personal computer and, say, Yahoo! in the United Kingdom and Yahoo! in the United States, go to the Start Menu, select Run, then type ping . Note the time values given in milliseconds. Do the same for and compare them.
Lastly, try to avoid being stacked up round Heathrow waiting for a landing slot. Lunch hours, for example, when many people go Net surfing, is a bad time to try any site.