August 13, 2003

By Karen Kenworthy


Wow. I'm feeling really old today. My oldest brother, Bill, has just turned 50!

If I close my eyes, I can still see him in his little cowboy outfit, roaming the neighborhood, righting wrongs and protecting the weak. Today, with eyes wide open, he's a righteous man, father of six of the most wonderful children on earth, and grandfather of two. He's a loyal and loving brother, and an inspiration to those fortunate enough to know him.

Hmm, I guess he hasn't changed that much after all ...

Site for Sore Eyes

Maybe it's because Bill (unlike me) is getting older. Or perhaps I need to re-visit my eye doctor. But for some reason I've been thinking a lot about vision problems lately.

As children, most of us saw clearly. No text was too small for our sharp, young eyes. But as we age, many of us must resort to eyeglasses. And over the years, those lenses get thicker and stronger, compensating for our increasingly poorer eyesight.

Other folks must struggle with vision problems their entire life. Without magnification, text can be indecipherable. Letters that don't contrast strongly with their background can be difficult to decode too.

That's why I recently made a small, but important, change to my web site. Now, in the menu bar that stretches across the top of each page, you'll see a new choice. Click this link, labeled "Preferences", and you'll see a new web page allowing you to control the way web pages are displayed.

First, you can choose between six different text sizes. Two selections cause all text to appear smaller than before. One causes the web site to use its original text sizes. But three choices -- "Larger", "Even Larger", and "Largest" -- boost the size of text displayed by the site.

Another setting allows you to control the color of text. Placing a checkmark in a box labeled "High Contrast (B&W)" forces all text to be drawn in black. Clearing this box tells the web site to revert to its original, lovely, color scheme.

Once you've made your selections, they will affect every page displayed by They'll be remembered too, if your web browser allows my site to store a "cookie". This little file, stored on your computer, contains no personal information other than your font size and color choices. And it cannot be viewed by other web sites. Only the web server that created the cookie can retrieve its contents.

Land of Lost Packets

Recently, reader Brian Gillespie wrote, asking an intriguing question:

"... my inquisitive mind is begging for an answer: When a ping packet gets lost on the net, where does it go? Or, when any packets get lost, where do they go?"

That's a very good question. We've talked a lot about "packets" lately. Those little bundles of data travel around the Internet at nearly the speed of light, bearing web pages, e-mail messages, and all the other traffic that traverses the 'net.

The e-mail message you're reading now was originally composed here at the secluded Power Tools workshop, all in one piece. But before it could be sent, the message was broken into smaller blocks, or packets. Each packet was carefully numbered and addressed to your e-mail server, then sent on its way.

In the fullness of time, your e-mail server received each packet. Like a jigsaw puzzle, the message was reassembled one piece at a time. Once all pieces, err packets, were in place, the rebuilt message was stored in your inbox, awaiting your retrieval.

When you collected your e-mail, this message and all others waiting for you, were again broken into packets. Each was sent to your computer where they were again reassembled, stored, and eventually displayed.

When Good Packets Go Bad

Most of the time, packets arrive at their destination quickly and reliably. Even when traveling across the world, and passing through a dozen intermediate computers and routers, their journeys are successful, and seldom take longer than a fraction of a second.

But occasionally, a packet goes astray. Despite the senders care and diligence, the data never reaches its destination. As Brian asked, where did the packet go? And why was it lost?

Sometimes, a packet's contents become corrupted. It may be the result of a failing circuit somewhere along the packet's path. Or some random electrical or magnetic interference may alter the packet's data.

Whatever the cause, the data flaw is always detected. That's because each packet includes a "checksum", the result of a mathematic formula based on the specific pattern of 1s and 0s making up the packet's data.

At every stage of its journey, the packet's checksum is computed, and compared to the checksum found in the packet itself. If the two don't agree, the packet must have been altered. Somewhere along the route, one of our binary buddies has failed us.

If a computer or router receives a corrupted packet, it behaves as if the packet had never arrived. The data isn't forwarded to the final recipient (since the recipient address found in the packet may be were the data damage occurred). And it isn't returned to the sender (since that address might not be valid either).

Instead, the packet is simply discarded, going to the great "bit bucket" in the sky. Eventually, the original sending computer will realize that one of its packets has not been acknowledged by the recipient. It will then resend the unfortunate packet, which in most cases will be delivered intact.

Haste Makes Waste

Fortunately, packet corruption is rare nowadays. Fiber optics have made many transmission paths much less sensitive to in-flight interference. And the electronic circuits that relay packets are more reliable than ever.

But packet failures are still common. Why? It's all about speed ...

I'm old enough to remember 300 bit-per-second modems. You could literally read text as it arrived on-screen. Later, many of us used dialup connections, in theory hauling as many as 56,000 bits every second. Data moved so quickly, I thought I'd never need a faster connection. :)

Today, "high-speed" connections are common. Many of us can send and receive over one million bits each second. ISPs, and others with a great need for speed, can move data even faster. Some connections transport 13.271 gigabits (13,271,000,000 bits!) in a single second. And faster circuits are on the way.

This wide range of "bandwidths" (that's engineer-speak for how quickly a device or circuit moves data) helps make the Internet affordable. Everyone is able to buy just the "pipe" (that's what techie types called network connections) they need.

But this diversity creates a problem too. Consider the life of the computer or router that joins two different-speed pipes. Day after day, it picks up packets arriving via one pipe, and sends them on their way out the other.

[Reality Check: Few of these devices connect just two pipes. Usually they have three or more network connections. In addition to passing packets from one pipe to the other, they must also decide which outgoing connection is the "closest" to the final destination, making the packet's total trip as short as possible.]

On a slow day, this job is easy. But when the 'net is especially busy this poor device has a problem. Packets can arrive via a high-speed connection faster than they can depart via a slower-speed connection. When this happens, a backlog of un-relayed packets builds up in the computer or router's memory.

Often, 'net traffic will relent before this memory (called a "buffer") is filled with undelivered packets. But during sustained busy periods, we won't be so lucky. The device's memory will overflow, and excess arriving packets must be discarded. Once again, they disappear without a trace, making their way to binary heaven.

And that, finally, answers Brian's question. When packets get lost, they simply go away, vanishing into the ether(net). :)

If you'd like to keep an eye on packets leaving your favorite server, take a look at the latest version of my 'Net Monitor. It tests web servers and e-mail servers, making sure they are awake and on the job. It can also test your connection to other computers on the Internet, letting you know when those connections fail, or become unreliable.

The 'Net Monitor's has also learned another trick that we'll talk about the next time we get together. But if you'd like to try the program in the meantime, drop by the 'Net Monitor's home page at:

And if you're a programmer, check out the program's free Visual Basic source code too!

Or if you prefer, get the latest version of every Power Tool, including the new 'Net Monitor, on CD. The disc also includes three bonus Power Tools, not available anywhere else. You'll find every back issue of my newsletter, and a few articles, in the CD's library. The CD even includes a special license that lets you use your Power Tools at work.

Best of all, buying a CD is the easiest way to support the web site and this newsletter. To find out more about the CD, visit:

Until we meet again, if you see my brother Bill, wish him a Happy Birthday. Be sure to speak loudly and clearly, so his old ears can make out what you're saying. And if you see me on the 'net, send me a packet. And don't forget to wave and say "Hi!"

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