Re: 57600 modems

Michel Carleer (mcarleer@ulb.ac.be)
Wed, 27 Nov 1996 17:10:50 +0100


Good point, Bob.
The explanation I gave come from an english computer magazine, and as I
pointed out in my message, that's about all I know on the subject. I would
also like to have a more in depth explanation. Someone can help?

Michel R.C.E. Carleer
Chimie Physique Moleculaire CPi 160/09
Universite Libre de Bruxelles
Ave. F.D. Roosevelt, 50
1050 Bruxelles
Belgique
Tel: +32-2-6502425
Fax: +32-2-6504232
e-mail: mcarleer@ulb.ac.be

----------
> From: Robert Raese <raese@ix.netcom.com>
> To: CU-SEEME-L@cornell.edu
> Subject: Re: 57600 modems
> Date: Wednesday, November 27, 1996 17:44
>
> 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+
> 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.
>
> Thanks,
>
> Bob