Issues with xDSL
The PSTN networks were originally designed to carry analog voice within a narrowband range of 0 to 4 kHz. There are filters along the lines to condition the signals and eliminate frequencies above 4 kHz. To service multiple customers, service providers deployed bridge taps. Long loops also deploy load coils, which help to flatten 0- to 4-kHz frequency response. Bridge taps, load coils, filters, cross talk, noise, and radio-frequency interference pose significant challenges to the deployment of xDSL in real life. A significant fraction of the DSL downstream bandwidth is unusable because of the distance and the length of the copper cables. (DSL downstream rates are severely restricted due to signal attenuation in the copper lines, ...
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