is made up of many subnetworks. Each subnet has a name, such as 'net'
or 'btl'... Each
subnet is a connected graph, that is, a path exists from every node to every
node in the subnet. In
addition, the entire graph is (theoretically) connected. (In practice, some political
considerations have caused some sites to be unable to post articles reaching
rest of the network.).
Interchange of USENET Messages; RFC 850;