Power Supply : ISDN functional devices like NT1, TE and TA require significantly more power than conventional analog telephones, the reason being that ISDN devices have some internal memory to identify its address and bearer service attributes and to support the ISDN protcols. Therefore, the normal power provided by the Central office (C.O.) to the analog telephones is not enough for ISDN devices.  The NT1 requires approximately 400mw and the TE would require about 200 mw of power.  For this reason, three main power sources, namely power source 1,  power source 2 and power source 3 have been defined in ITU-T physical layer recommendation I.430 and all the three are optional.
             Power source 1 is located in the NT and it can derive power from the network or from a local ac power source or batteries. A maximum of 40V can be provided by the NT through power source 1. Out of thie the TE may draw up to 1 watt of power in a normal condition. This power is called the phantom power.
          Power source 2 is also an optional source located at NT and it derives power locally at the NT, such as via batteries or a.c. power source. It uses an additional third wire pair to distribute upto 40V from the NT.
          Power source 3 is optional and it may be present in the TE and it provides an optional source of power for TE-TE connection. If employed, it would use the an optional fourth pair.
         In North America, the operating telephone companies do not supply power for the customer premises equipment. Therefore the NT1 or the TE is plugged directly into an ac or dc power source in the home. In several European countries, the operating company is responsible for delivering power to the TE over the transmit and receive power loops. Power source 2 provides a mechanism so that a single battery-backup capability in a house or buisness can support all ISDN devices, obviating the need for a battery in every piece of ISDN equipment.

Physical Connector: The physical connector for the BRI is an eight pin RJ-45 or RJ-48 jack based on ISO 8877.

RJ11 - the standard analog phone jack. The RJ11 has 4 wires. The wire from the wall to the NT-1 will usually have RJ11 jacks.
RJ45 - this jack is slightly wider than the RJ11, and has 8 wires. The wire from the NT-1 to the ISDN adapter will usually use RJ45 jacks.
 
The connector assigments for an RJ45 jack is shown in the table given below:
 
I.430 Connector Assignments
       Pin No:           TE              NT          Polarity      Required?
           1 Power Source 3 Power Sink 3             +           No
           2 Power Source 3 Power Sink 3            -           No
           3 Transmit Receive            +           Yes
           4 Receive  Transmit            +           Yes
           5 Receive Transmit            -           Yes
           6 Transmit Receive            -           Yes
           7 Power Sink 2 Power Source 2            -            No
           8 Power Sink 2 Power Source  2            +            No