On 16/11/2010 22:59, Sean Breheny wrote:
> I understand that, I was just wondering where the 35kbit/sec number
> comes from. It sounds like a rule of thumb and not a theoretical
> limit. If it were a theoretical limit, it should apply in a lab-type
> setting, too, and yet it would be fairly easy to inject a signal into
> a telephone codec which got any arbitrary sequence of codes out of the
> ADC, which could then deliver a data rate of 64 kbits/sec. Even with a
> kilometer of wire in front of the codec, it could be done in the lab
> by doing system identification on the wire to determine the transfer
> function and then pre-distorting the signal to compensate.
>
> In fact, this must actually be possible (not quite 64kbps) in a
> real-world situation on a high-quality phone line since 56 kbps modems
> do work on at least one analog end.
>
> Sean

The practical limit is 33kbps because most telco do not implement full=20
V92. Its 33k analogue for upstream (max) and the pseudo 56k ISDN (to=20
suit USA ISDN) on downstream only. Hence end to end rather than Internet=20
you are limited to top analogue upstream of each end.

You can get 64K end to end (or 128k). You have a modem called and ISDN=20
TA and it does all the stuff you suggest. Except they designed it for=20
error free 144k.

Before DSL was available, the ISDN was very popular if you could afford=20
it and get it. Eventually they lowered the line rental to same as=20
analogue and you simply paid twice as much if you used 128K instead of 64k.

NO Flat rate! Still no Flat rate! cents per minute to use the Internet.=20
Even today, if they can supply POTS or  ISDN but not DSL, there is no=20
true flat rate, it's effectively 10 times the cost of DSL for same=20
amount of typical time (which is MUCH less data!).
--=20
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