On Sat, Jun 06, 2009 at 08:12:30PM +0100, Scott Robinson wrote: > Hi Guys,
What about the gals? And persons indeterminate? > Bit of a broadband issue here rather than Linux! Thought you may be > able to help. > > broadbandspeedchecker.co.uk reports speeds of 3360/258 although the > router (DG834GT on Sky) reports: > > ADSL Firmware Version A2pB022c.d20e > Modem Status Connected > DownStream Connection Speed 8032 kbps > UpStream Connection Speed 448 kbps > VPI 0 > VCI 38 > > Is it me being silly or is there a problem here somewhere? No problem. The modem is reporting the *potential* speed of the line, were you to have perfect transmission. In other words, it's reporting the "headline" speed of the particular specification of ADSL it's using on the line. The speed checker is reporting the speed it measured (since you don't have perfect transmission -- just like everyone else). ADSL signals are a wide spectrum of (audio) frequencies, in very narrow slices. Each frequency carries a (relatively slow) data signal, and your data is multiplexed across all of the frequencies to get high-speed data transmission. On consumer-grade copper telephone wiring, there's a lot of noise, cross-talk, and attenuation, so what your modem will do when it's first connected is work out which frequencies it's losing data on, and stop using them. Thus, for each frequency with poor transmission properties, you lose a little bit of bandwidth from your maximum. This process of working out which frequencies are noisy is the "training" process it goes through in the first 10 days or so of connection. So, if you were in the exchange with new undamaged high-grade copper cabling, you'd have no unacceptable noise on the line, and your modem would connect at 8032kbps. Since you're probably a couple of miles from the exchange, most likely running over copper wire that was put in the ground 30 years ago, and has been cut, patched, soaked, hacked at, bent, and generally mangled, you've lost over half of your transmission frequencies, and you're connecting at something rather slower. You may be able to find somewhere in your modem admin pages a display which shows the frequencies it's actually using, and at what signal levels. From this, it is possible to work out the actual theoretical maximum for your connection (at the time that those signals were measured). Hugo. -- === Hugo Mills: h...@... carfax.org.uk | darksatanic.net | lug.org.uk === PGP key: 515C238D from wwwkeys.eu.pgp.net or http://www.carfax.org.uk --- The English language has the mot juste for every occasion. ---
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