Gentlemen of Verona
One of several hats I wear is that of IT manager of the World Bridge Federation. Most of my time this last month has been taken up running the IT requirements for the World Bridge Championships in Verona in Northern Italy. The Federation holds this large competition every four years, and thousands of players turned up at Verona Fiera, a large exhibition complex similar to the NEC in Birmingham. I had an assistant, Harvey Fox, to help me out this year, and appearances by Bill Gates and Fidel Castro’s sister – who both turned up to play – ensured plenty of media interest.
Thankfully, Mr Gates was too engrossed in the complexities of his Bridge game to notice my network, which is just as well, because creating and maintaining a network for such an event in a few days often involves throwing “best practice” out the window. Nevertheless, despite hundreds of users connecting their various laptops to it, my internal network ran with few problems, which is more than I can say for the internet connection. I’d asked for two 2Mb lines with guaranteed bandwidth, which based on previous experience was the minimum we’d need, but on arrival I was told we had two 4Mb ADSL lines that were adaptive, meaning that their available bandwidth would alter.
What this meant in practice was that whenever the ISP thought we were using too much bandwidth, it would start dropping packets until my users’ browsers began to time out… The lines never quite died, but spent much time feigning the twitches of a dying animal. Richard Palmer of Merula (www.merula.net) tells me that similar practices occur in the UK: bear in mind that most of the copper wire infrastructure is still owned by BT, so the limitations of BT’s products will affect you even if you buy your ADSL service from a different ADSL company.
At this point, I need to explain the difference between bandwidth and sync rate: sync rate is the speed at which your ADSL modem talks to the ISP’s modem, whereas bandwidth is the rate at which data moves up and down the connection. Once you’re connected at the agreed sync rate you paid for, you’ll be sharing the actual bandwidth with 20 or 50 other users (depending on which package you bought from your ISP).
The only products for which BT “guarantees” a particular bandwidth are the 2Mb products, which “guarantee” a sync rate of 256Kb upload and 2Mb download. I put “guarantee” in quotes because actually there’s no service-level agreement for ADSL lines, unlike the considerably more expensive leased lines. The 512Kb and 1Mb products are what’s known as semi-fixed adaptive and their rates will vary: normally, the upload rate will slow if the line becomes marginal and attempts to keep the download speed as fast as possible. The new high-speed ADSL Max – which offers much faster speeds – has a smaller maximum signal-to-noise ratio allowance and so should tolerate more marginal lines, but the actual speeds obtained will vary on a minute-by-minute basis depending on line quality.
The amount of bandwidth your line will support is only part of the problem. Most ISPs, when any user starts using more than what’s considered a fair share of bandwidth, will start to throttle that user back by dropping packets. A product like VisualRoute (www.visualroute.com) can show you where dropped packets are happening, and if it’s within your ISP they’re probably trying to throttle your bandwidth usage.
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