modems data rates?

Question

Each computer(data terminal) transmits data in a selected data rate(for example: 1.1-19.2 kbps).
this is the rate that it transmits data to the modem.
But, each modem has another data rate that it uses to transmit to the line(to the second modem), normally in a sychronous modem the data rate is much higher than the data rate of the terminal.
Why are there two different data rates?
if the comuter will transmit in 19.2 kbps and the modem will transmit for example in 2.048 mbps, what would happen with that extra data rate that is not being used.

Answer 1

modem banks are not paired up like that. a perfect example would be the set up used in an ISP that support 56K modems.

V.92 (56Kbps) connects to ISDN (64Kbps)

* if the 56K modem was connected to another 56K modem at the ISP the greatest connection rate under ideal line conditions would be 43.6K

Answer 2

Lets make this a bit easier. Lets say you have a 52 k modem and you connect to a site that uses 14.4 k. When the modems connect, they do a 'handshake' that basically asks a few questions, like, what speed are you sending at, how is your messages formatted, etc. Modems are limited to the speed they were connected at. Your wireless network card is the same, yes, it can handle very large bandwidth, (in the GHz range), but most networks are not capable of consistently providing that type of speed, so the modems or network cards will downgrade to the speed necessary for successful communications. So to make a long explanation short, nothing happens to the extra data rate. It is available if needed for another device that connects to it at a higher data rate.