The main reason not to stick a tone on the DSL line is that the line coding (2B1Q) used by SDSL uses the baseband (low frequency part of the spectrum). For line codings that don't use the baseband (CAP, DMT and variants like G.lite), the DSLAM (telco central office DSL equipment) is always set up so that the DSL can be combined with a voice circuit over the same pair, so it still doesn't put a tone on the line. On Mon, 14 May 2001, Alex Bligh wrote:
as for relibility, I cant tell you the number of times a Verizon tech, would be out to install a phone line and steal one of our dsl lines cuase it did not have a tone.
As a (serious) question, why not stick a tone on it? How much can an oscillator at the CO plus some trivial passive low pass filters (one set per line), cost? (Or, if you aren't the DLEC, stick it at cust prem). Just don't use the trace tone... (translation to US terminology may be required)
-- Alex Bligh Personal Capacity