Thus spake "Steven M. Bellovin" <smb@research.att.com>
And in fact, there are technical reasons as well. Downstream IP transmission on a cable plant uses any arbitrary channel; if there's a lot of downstream traffic, just displace the Home Gerbil Channel or some such and allocate more bandwidth to IP. Upstream traffic uses the band below channel 1, and it's not easy to add more unless you split the tree and put in another fiber node. This is done for the sake of the repeaters -- the downstream repeaters are fed by a high-pass filter, and the upstream repeaters are fed by a low-pass filter. If too many people are fielding home servers, it affects everyone.
So DOCSIS has a technical limitation which may or may not apply. This is reasonable justification for limiting upstream bandwidth, not for specifying that users can't run servers. If users can run servers effectively in the limited available upstream bandwidth, then there is no _technical_ reason to prevent them. Other last-mile technologies provide symmetric bandwidth yet providers still prohibit servers; this is clearly a business issue, not a technical one. S Stephen Sprunk "Stupid people surround themselves with smart CCIE #3723 people. Smart people surround themselves with K5SSS smart people who disagree with them." --Aaron Sorkin