Metroliner telephone article 4137

Well, I wouldn't call it less stringent; just different.

ISDN requires a relatively clean line in terms of number of gauge changes, loads etc. but only requires good frequency response in the 3-72 kHz area; and can take some phase distortion. ISDN handles signal reflections pretty badly. It also requires the line to be pretty well balanced; no single exposed pairs etc. It works poorly over "rat's nest" connections, but delivers a reliable signal over remarkably long hauls.

DSL uses powerful signal processors, and handles reflections, (i.e. small loads and gauge changes) a lot better, but is more sensitive to frequency response, crosstalk with other DSL lines, and requires good frequency response in the 40-800 kHz range. It also packs more signal per state change, so it needs better phase and singal-noise ratio. These requirements can work over "rat's nest" cabling, but will have length-speed limitations.

DSL has the advantage of dynamic adaption to line conditions, so it delivers whatever the line is available of carrying. It also degrades gracefully; and does not just drop signal during call setup as ISDN does.

Even a bad DSL line is better. Even with retreansmits end to end ping time is rarely above 10 ms; a figure that is common with good ISDN lines.

-- mrr