TELECOM Digest OnLine - Sorted: Re: DSL Speed

Re: DSL Speed

Choreboy (choreboyREMOVE@localnet.com)
Sat, 25 Jun 2005 01:09:15 -0400

Tony P. wrote:

> In article <telecom24.287.9@telecom-digest.org>, hancock4@bbs.cpcn.com
> says:

>> Choreboy wrote:

>>> Couldn't technology analogous to a megaphone be applied to dialup as
>>> well as DSL?

>> Yes.

>>> Ah, crosstalk! It seems to me that if DSL uses the same wire dialup
>>> used, the same crosstalk will be present.

>> Not necessarily. Remember AM and FM radio waves go through the same
>> air, but AM is much more sensitive to lightning and other static than
>> is FM.

>> DSL service may be arrangeed to minimize crosstalk.

> You've hit it on the head. Both AM and FM use radio bandwidth, but
> each uses a different form of modulation. AM stands for Amplitude
> Modulation -- the amplitude is how high a particular sine wave rises or
> falls. FM is frequency modulation, the carrier frequency varies
> depending on what signal is being fed to it.

Broadcast AM uses a channel 10 kHz wide. Broadcast FM mono uses 150 kHz.

> It's sort of the same setup on DSL with the data signals occupying a
> higher frequency.

Frequency shift keying and phase modulation could be called forms of
FM. Modems have used them for decades.

I think dialups use a carrier of 2kHz or so. I think the baud rate is
the samples per second. I think the 14.4k modem used 2400 baud with
phase modulation so precise that each sample yielded 6 bits. Amazing!
It's incredible that they found a way to get 56k out of a carrier
somewhere around 2k.

Do you mean DSL has a much higher carrier frequency? I haven't found
anything about it, but it could explain how it can carry 50 times more
bits.

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