Let's try real simple.

by R. Proffitt Moderator - 12/22/08 8:44 AM

In Reply to: Dial-Up speed problem! Need expert advise. by karansawan

Let's say you move a ZIP file across your dial up connection.

If you had software to unpack that and push the unpacked content across the virtual serial link, you could see a higher bit rate than what the actual link supports.

Hopefully this is enough of an explainer why you see bursts of speed. It's almost a bad decision to report these speeds to the end user since it most often ends badly with some feeling hurt over having to learn so much.
Bob