An uplink port is the connectivity device port on a switch, hub or router that allows transmit circuits to be connected to receive circuits through a standard-type cable, thereby allowing the connection of one computer network to another network. This type of port differs from a regular port in that a regular port requires a crossover cable to communicate between two types of circuits. The uplink port is able to communicate between differing circuits with a standard cable, and it typically is used for connecting a modem to a router and to link devices together. This prevents the need for using a crossover cable when connecting a computer to the Internet or network through the use a router or through the linking of one network to another.
When connecting a computer to a networking device such as hub or switch, or when connecting one device to another, only one uplink port is actually used. If both ends are connected through such a port, the connection will not transfer any data and will fail to communicate between the two devices. This means that like devices will need to be connected with one end of the cable in the uplink port on one device and the other end plugged into a regular port on the other device. Should there be the need to connect two uplink ports together between devices, a crossover cable would need to be used.
Most hubs, switches and routers come equipped with an uplink port to facilitate available connection types. On some of these devices, there will be a toggle switch to flip the port between a regular connection and the uplink connection. There also are devices that will change the type of port connection they allow, depending on how it is connected, meaning that it will detect the need for an uplink port and switch itself accordingly. Some devices do not have dual purpose ports but instead come equipped with a shared port. This means that the uplink port shares connection with a normal port, and both cannot be connected at the same time.
Uplink ports are sometimes called medium dependent interface (MRI) ports. A computer cannot be directly connected to this type of port using a regular type of connection wire. A crossover wire is required to connect the port to a computer's network interface card directly. Crossover wires function much in same way as uplink ports and allow receive circuits to be connected to transmit circuits through the wire itself. An uplink does this through a normal wire, connecting the differing type of circuits within the port itself.