Cable Plant Training

Here are a couple places with varying explanation of how cable internet works. Some are very basic, take them for what they're worth.

http://computer.howstuffworks.com/cable-modem9.htm
http://computer.howstuffworks.com/cable-modem.htm
http://bradyvolpe.com/docsis-101/docsis101_rf-fundamentals/
http://www.linktionary.com/c/cabledata.html

Here's a good one, more to do with television but many of the basics apply to an internet cable plant as well. Check out the diagrams.
http://people.seas.harvard.edu/~jones/cscie129/nu_lectures/lecture13/CATV/CATV.html

A couple of these links get a little in-depth. But alot of this is good reading.