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Technology Stocks : LAST MILE TECHNOLOGIES - Let's Discuss Them Here -- Ignore unavailable to you. Want to Upgrade?

To: P.T.Burnem who wrote (1607)	7/20/1998 7:25:00 PM
From: DenverTechie	Read Replies (2) \| Respond to of 12823

Theoretical peak bandwidth of twisted pair cable is way up there, in excess of 1 MHz. Practical bandwidth is much lower. Voice only uses about 4 kHz of that. So ADSL uses the "left over" practical bandwidth at a certain bits to hertz conversion factor to achieve its results. Also, theoretical peak bandwidth of coaxial cable the cable company uses is way up there on a relative scale, in excess of 1GHz. But your questions is a good one. But there's more to it than just how many 1.5 Mb/s x/DSL channels you can put on the phone line. That real life phone line is subject to all sorts of distorting factors that reduce the practical bandwidth. Worst is attenuation (crosstalk's not so hot either). This reduces the available bandwidth based on distance from the serving Central Office (CO). At 9,000 feet from the CO I could give you about 9 Mb/s (6 - 1.5 Mb/s channels). At 12,000 feet from the CO I could give you only about 6 Mb/s (4 - 1.5 Mb/s channels). If you're really hungry I could give you 52 Mb/s (34.7 - 1.5 Mb/s channels, actually VDSL not ADSL). But to get that much bandwidth you have to be within 1000 feet of the CO. This is how phone companies originally proposed to do video over phone lines. They could provide 4 channels of 1.5 Mb/s video (about VCR quality) up to 12,000 feet from their serving office. The POTS (plain old telephone service) splitter in the ADSL modem allows all this to go on while still providing the voice service over a single line. Hope that helps. A quick overview in a nutshell. Many more details to it of course. Next?