A type of interface used to connect workstations or printers to 5ESS (digital phone) jacks, and then to MITnet. This is a modular interface with little plastic connectors on the ends that snap into place. The connectors are also known as RJ-45 connectors. The MIT ISDN phone system uses this type of wiring. The name comes from the fact that the wiring is unshielded and pairs of wires are twisted together to eliminate crosstalk on them.