The following two types of phone jacks can be used with ISDN telephone lines:
RJ11, the standard analog phone jack. The RJ11 has four wires. The wire from the wall to the NT1 usually has RJ11 jacks.
RJ45, a jack slightly wider than the RJ11 that has six wires. The wire from the NT1 to the ISDN adapter usually has RJ45 jacks.
The following figure puts together ISDN hardware and interfaces to illustrate the relationships described in this "ISDN Hardware" section.
MHMiriam HarlineFigure 4.2 ISDN hardware and interfaces