A connection from a lower to higher device. A hub to a switch, a switch to a router, a router to a server.
A port on hubs/switches that crosses over the circuits of any cable plugged into it. Uplink ports were originally designed for the purpose of daisy-chaining hubs together, but they can also be used to connect a cable modem directly to a LAN. Note: a regular cable connected to an uplink port serves the same function as a crossover cable connected to a normal port.
Represents the connectivity from a border node to an upnode.