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Are your Internet packets going to head for a lost and unstable horizon? (an article by Bob Metcalfe)

A television producer posed me atop Treasure Island overlooking the San Francisco Bay Bridge. Her camera aimed down past me at the bridge's commuter lanes, all clogged with cars stopped bumper to bumper. We were dramatizing traffic jams on the Internet.

I told her camera what I've been telling you since Ethernet's first "collisions" in the early 1970's: Packets are just like cars. Packets can get caught in traffic jams and nowadays often do, which is why we're all revving up for the Information Superhighway.

Glancing down in midsentence at the bay beneath the bridge, I saw suddenly that to understand today's World Wide Wait, I'd have to admit that Internet packets are not really all that much like cars.

When packets find themselves in Internet traffic jams, they don't lip-sync golden oldies until eventually getting to work late for a meeting. When packets get stopped in traffic on an Internet bridge, they, unlike cars, are summarily dumped into the bay without even getting a chance to call in sick on their cellular phones.

When an Internet protocol family doen't hear that its packet has arrived safely at work, members don't worry. They just wake up another copy of their lost packet, hand it lunch, and send it off toward work again.

For Internet packets, every day is like Bill Murray's Groundhog Day.

Now, although slow servers are much to blame for bogging down the Internet, lost packets are high among the Internet's dirty little secrets.

A year ago I uncovered evidence that packet losses along some Internet routes during rush hours were hitting an outrageous 10 percent. Hey, even packet losses below 1 percent can halve your Internet throughput.

Today, packet losses too often reach 20 percent, 40 percent, or 80 percent during some of the Internet's more gridlocked 15 minute intervals. At those rates, Web downloads are not just slow, but they often hang with inexplicable (if any) error messages.

Point your browser at the trend statistics at http://www.ra.net/statistics. To count packets lost this very minute, see http://www.compute.merit.edu/netnow.

So let's expand my simplistic formula for Internet delay: D=H*Q*(R+P/C)/(1-L). D is for delay, H for hops, Q for queues, R for routing, P for packet length, C for circuit speed, and now L is for the percentage of packets lost into various bays along the way.

Note that as packet losses (L) approach 100 percent (1.0), packet delays (D) ramp to infinity.

John Quarterman has long been publishing measurements of delay that seem to refute my infamous predictions of Internet collapse. You can buy his data (it's the best around) at http://www.mids.org. [see also MIDS Internet Weather Report]

Quarterman reports the good news that the Internet's average delays, as measured to 4,500 sites every 4 hours, have in fact over the past few years been trending down. But note that his gorgeous graphs do have many colorful spikes, each evidence of poor response and an opportunity for collapse.

I've asked Quarterman why even his long-term averages show frequent periods of major packet loss. And I've asked him how he computews his averages when many sample delays are infinate. Stay tuned...

So here's something else to fix in the Internet: packet loss accountability.

How many of your packets get through? When you abort an interminable Web download, was it because some packets got dumped into a bay somewhere? Internet service providers are already counting packet discards int heir routers; how about some loss reports along with their bills?

Now it's great that TCP/IP, like Ethernet, backs off as traffic increases. Backing off keeps networks stable. Lost packets are Mother Nature's way of telling your software to let up off the gas before driving the internet down.

But beware of our latest crop of Internet opportunists offering software that helps you flood the Internet to make up for lost packets.

These products increase rather than decrease packet rates as losses mount. They start the painful downloading ove every Web page in sight while you are figuring out which ones you actually want. If too many people start using such irresponsible software, the Internet could go unstable and - dare I say it - Colapse.

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