Re: 57600 modems

Robert Raese (
Wed, 27 Nov 1996 08:44:27 -0800

Michel Carleer wrote:

> The complete route of a signal from a PC to an SP is:
> PC-----DAC(modem)-------ADC(phone company entry
> point)------------------------------DAC(phone company exit
> point)-------ADC(modem)-----SP
> Of course the route from the SP to your PC is just the reverse from above.
> In other words, the only slow analog portions of a telephone connexion are
> the two short connexions between the telco and the end users.

Can somebody help me understand Michel's tutorial:

I am a bit confused. Michel's description sounds like the possible
transmission speeds are soley a function of the type of line they are on
- ie. digital or analog?

In other words, the maximum from PC to the phone company is 28.8 (33.6)
because of analog limitations? Is this a function of the physical line
to the phone company?
Here's how I currently understand the model:

PC ---> DAC(modem)---> ADC (phone co. entry) ---> phone co. exit --->
Service provider
28.8 56+

PC <---------------- DAC
28.8???? 56+

He writes further:

>This is why the so called 57600 bps modems will allow you to download at
>57600, but only upload at 28800 (or 33600)

On a download, wouldn't the speed be a function of the phone company's
modem? Wouldn't the signal be slowed back down to 28.8 at the point when
the phone company converts the signal back to analog to accomodate the
signal to the voice line the PC user is utilizing? It is my
understanding that the signal sent from the phone company to the PC-user
is analog and therefore subject to certain "speed limits" Am I correct
in assuming that the phone company does this? If so, wouldn't the
download speed be restricted to the "skinniest part of the hose," so to
speak? My thought is that the "weakest link in the chain" determines the
maximum speed at which I am able to upload or download information. I
don't quite see how eliminating just one roadblock (the analog line from
the phone company to the service provider) without also eliminating the
other one (from PC user to phone company) provides any advantage

Please clarify my misconceptions, whatever they may be.