Q&A About V.FC Modems and High Speed Transmissions


Pete Norloff - OS/2Shareware BBS (703)385-4325 (1:109/347)


QUESTION:

I'm curious why we only get 2700-2800 cps on a download
when we connect at 28.8.

ANSWER:

I'll probably need to prepare a long response to this 
question because yours is not the first and will certainly 
not be the last time it will be asked.
 
Not wanting to get into a lot of detail here about how 
modems work and how getting 28.8k bps out of a voice grade 
phone line is essentially black magic, let me just say that 
I think that you will never see consistent results at these 
speeds over switched lines.  

Error correcting modems hide all the resends that are 
taking place between the modems so you don't see that part 
when there's a glitch on the line.  You just see the 
character rate drop a little.
 
Also, with V.FC/V.34 modems, the speed can change up and 
down a number of times during a file transfer as the modems 
retrain.  Basically, if you're doing better than 2000 cps 
you're doing good.  If you're lucky enough to get a really 
clean connection and get 3500 cps that's even better.
