An SFP uplink port is a piece of hardware produced by Cisco Systems. A port is a socket on a computerized device like a laptop, a printer or a router. Ports have designs that match the plugs that fit into them. Different ports have different sizes and specifications, which prevents the incorrect type of connector being plugged into them. SFP stands for "Small Form-factor Pluggable" and applies to a range of components for Cisco switches. One of these components is an uplink module, which contains two or four ports.
A switch is a network device. The main elements of a network are called Data Terminating Equipment. This term applies to computers, printers, faxes and any other pieces of equipment that serves the users of the network. The network that links these devices together is composed of cables and network equipment. A switch is the most commonly used network device. It makes connections between all the DTEs on the network, each of which is connected to the switch by a stretch of cable.
Transmit and Receive
Network cable contains several pairs of wires. Each pair represents the negative and positive path of a complete circuit. These circuits are not bi-directional - they only carry data in one direction. DTEs expect to receive data on one circuit and they always send data on another circuit. Network hardware is designed with this factor in mind, so a switch will send data on the cable's receive circuit and listen for data on the cable's transmit circuit. This method fails if two DTEs or two network devices are connected together by one cable. One solution is to use a crossover cable that switches over the transmit and receive paths in the connector at one end so the transmit path is sent to the receive pins in the port at one end of the cable and vice versa.
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An uplink port is a component that enables two network devices to connect together with a standard, "straight through" cable instead of using crossover cable. The transmit and receive contacts inside the port are switched. Thus the uplink port can connect to a regular port of another device. It would be a mistake to connect two uplink ports together with straight through cable.
The Small Form-factor Pluggable design of uplink module contains four ports for 1 Gigabit per second data rate or two ports with a 10 Gigabits per second rate. Each port has two lights that indicate activity and the status of that port. The ports are mounted on a small chassis that slots into the switch's casing.