What is RJ11 ? RJ11 RJ11 - Registered Jack 11 - is used for the landline telephone. It is an international standard that is used to connect the landline telephone to the Telecommunications network. RJ11 uses a 6-slot connector. In it RJ11 has 6 slots (positions) and two conductors, the standard is written 6P2C. The information transmitted on the line can be digital (DSL) or analog. The telephone cable that arrives at the subscriber has 4 conductors grouped into 2 colored pairs called twisted pairs. Only the 2 central conductors are used for the line.