Hi,
Also, for a few years now, modems have had the ability to compress / decompress data within the modem. As a lot of the data on the internet consists mainly of text, computers have developed compression algorithms (processes) to reduce the amount of data sent over the internet. The process of compressing the data is a lot more difficult than un-compressing it. Think of it like a puzzle, you have to put it together, which can take a while, then after the picture has been made, you may break it down again. But breaking it down is a lot easier than making it.
Hope this helps,
Regards,
Dominic