We have the same problem with the local cable company. We have a small network on a cable modem and people can not connect into our network from outside. When I asked the cable company about it, they told me that their firewall prevents that, but if I wanted to purchase the business package then they would open the firewall for others to connect to our system.
You really need to talk to your provider to see if they will allow this. Tell them that you are testing to see whether it would be worthwhile to set up a "business system".
Rob
