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Re: Talking with Yahoo Messenger

Mark Allums wries:
> In the US, a 56k dialup running at 53k (max allowed by law, and rarely
> achieved in practice) gives you just about the necessary bandwidth for
> voice over IP, *and nothing else*.

That's 56k downbound.  Upbound is 33k max.

> Not a voice-over-IP expert, and yes, I *have* heard of Nyquist.

Good.  Now read Shannon.  The number of bits per second you can push
through a channel depends on the bandwidth _and_ the signal to noise

> What modulation does Skype use?  Some type of delta modulation would be
> my guess for dialup, but I have no real idea.

None.  Skype surely uses some sort of compression, but the modem handles
the physical layer using complex multitone modulation schemes.
John Hasler

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