A registered jack-11 (RJ-11) is a 6-position 2-conductor telephone connector/jack (6P2C) with 4 positions unused. It is commonly used to connect the telephone handset to the base unit, and the entire telephone to the wall outlet. One of its primary functions is to connect different data equipment and telecommunication devices with services normally provided by telephone exchanges or long-distance carriers. Overall it is the most popular modular form of registered jack. It is found in houses and offices where old telephone-wired systems are connected with the ISP's line.