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You're being ADSL

Posted on 2 Jul 2002 at 17:12

While ADSL in the US seems to be standard fare, in good old Blighty we're taking it a bit more slowly. And we're right to be wary, says Steve Cassidy

A couple of columns ago I mentioned a network hardware vendor NBase-Xyplex based in Israel, which told me a couple of surprising things about the ISP marketplace for network equipment. The company makes a range of network bridges and routers that manage the amount of bandwidth a number of users are given, and so important is this activity to the ISPs that different ones may have radically different preferences. NBase-Xyplex will make you a router that boots Linux so you can customise what you want it to do at a very fine level, which no doubt suits the highly-technical types who inhabit ISP network design - once there's a software standard in place, all the world's problems are solved, right?

Well not exactly. The other way that NBase-Xyplex makes its money in is TCs (terminal controllers), boxes with an Ethernet on the back and a vast array of serial connectors on the front. In the dim and distant past when Ethernet was expensive, this was how rooms full of dumb terminals talked to minicomputers. These days TCs are less widespread, but ISPs love them because just about every bit of network-building hardware - hubs, switches, bridges, routers and the rest - has a serial port to which a Telnet client can connect to monitor activity and change settings.

The majority of these devices could also be told that they have an IP address and be interrogated via Telnet that way, but ISPs really don't want their hub and router control systems on the same network as traffic from the great unwashed public. Rather than use clever IP addressing tricks or packet encryption, their preferred fix is to stuff a TC into the rack and link all the serial ports back to it, so the router and switch supervisor functions can reach their destination without troubling the Ethernet, which comprises the ISP's bread-and-butter transportation.

Why is this important? Back to the BT part of the story. The chastening part of the ADSL trial that PC Pro's article covered was that even with only 900 households in the system and a closed private IP range, there was a steady stream of trivial hacking attacks on the machine that held the ADSL connection. A lot of 14-year-old kids out there fancy themselves as the next Keanu Reeves, and it's to keep the control systems away from their probing young minds that ISPs are buying TC boxes. The industry term is 'out of band control' where 'band' means the main stream of data passing through some device.

BT learned from that trial a few priorities for rolling out ADSL on a more widespread basis. It knows it can't let every potential 512Kbits/sec user on at that speed, because to buy that much bandwidth would be hugely uneconomical. It also knows that early adopters (that is, PC Pro readers) will tweak the system if given half a chance, and that wannabe hackers (who aren't PC Pro readers, I hope) are hovering around. And it knows that it has to preserve the revenue it gets from existing high-rental connections from its larger Net users.

It turns out that most people in the trial wanted to play Quake with one another and look at a very small selection of information provision sites, while stretching the limits of the tightly-defined compatibility standards BT's tech support team were prepared to deal with. The fix is, therefore, simple - an ADSL system that looks and feels far more like a newspaper than a data pipeline. BT feeds its users today's headlines or movies on demand, so that they're not using their onward connections and, therefore, not hitting the massive bottleneck between that screaming 512Kbits/sec and the load-balanced, bridged-off, virtually-hosted, time-shared 64Kbits/sec line they're all connected to.