On Aug 1, 2016 12:48 PM, "Ivan Avery Frey via talk" <talk@gtalug.org> wrote:
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> On Mon, Aug 1, 2016, 10:58 Steve Petrie, 
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> snip
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>> I do realize that the DSL modem provides a dial up "line" in parallel
>> with the high-bandwidth DSL link.
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>> However, there is still a difference between: 1. a telephone link over a
>> twisted pair of physical copper wires, and 2. an emulation of a
>> telephone link, over a DSL modem.
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> The DSL modem does not provide a dial up "line" in parallel with the DSL link. DSL operates over the same wires as the traditional phone service. One does need a small filter to prevent the DSL signals from interfering with the use of the telephone link. 

The modem also bands traffic with unused tones as well as using the low pass filter on the line. Tone 1 = POTS, Tone 2-5 guard against cross talk.

The initialization handshake chooses the optimum frequency's for data based on the signal to noise ratio as determined by a variety of physical factors. The better the SNR the more bits in the mux-bucket.

List of tones and more may be found here.

http://www.kitz.co.uk/adsl/adsl_technology.htm

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Russell
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