Network Concepts ^^^^^^^^^^^^^^^^ NODE A bulletin board system that calls another bulletin board system (a hub) in order to transfer mail. A node doesn't receive its mail directly from any other BBS (that is, no one calls it to transfer mail.) HUB A bulletin board system which may or may not call another hub system in order to transfer mail, but is called by one or more nodes to transfer mail. REGIONAL HUB A hub which calls another hub in order to transfer mail. It's called a regional hub because when designing a network, a hub is usually placed in each of the major regions serviced in order to minimize long distance phone charges. For example : P&BNetHub / \ \ / \ \ / \ \ RUBYS BBS1 BBS2 / \ / \ BBS3 BBS4 P&BNetHub is the NATIONAL HUB because it does not call anyone for mail. BBS1 and BBS2 are NODES, directly linked to P&BNetHub. BBS3 and BBS4 are nodes connected to RUBYS. RUBYS is a node of P&BNetHub and also a REGIONAL HUB since it calls P&BNetHub to transfer mail. Each hub that is a regional hub has a HUB ID. This ID is used by the regional hub to identify itself when it calls the hub "above" it to transfer mail. The network shown above would consist of four nodes, one regional hub and one national hub (P&BNetHub).