An RJ45 connector is commonly known as a crystalconnector. The transparent plug that connects thenetwork card or HUB to connect both ends of thetwisted-pair cable. RJ-45 is a network interface specification, similar to RJ-11, which is the "telephone interface" used toconnect telephone lines. It is called "crystal head",because its appearance crystal clear. The RJ-45 plug must be installed on both ends of the twisted-pair cable so that it can be inserted into the RJ-45 port of a NIC, Hub, or Switch for networkcommunication.