21.0 ISDN Cabling

     21.1 ISDN U-loop
     ISDN Basic Rate Interface (BRI) is provided by a carrier from
     a central office (CO) switch to the customer premise with a
     two wire U-loop RJ-45 connector on the center pins 4-5.

         RJ45 Plug
         =========
         1  N/C
         2  N/C
         3  N/C
         4  U-loop network connection
         5  U-loop network connection
         6  N/C
         7  N/C
         8  N/C

     21.2 ISDN Network Termination (NT)
     The Network Termination is a Power Supply and NT1.  In North
     America this functionality can be provided in the terminal
     equipment (i.e. ISDN digital modem) or separate as follows;
  ________              ________
        | Power  |            |        |========== TE
      =========| Supply |============|  NT1   |
 U-loop |________|   U+PS2    |________|========  S/T bus
 2-wire              4-wire                       4-wire
     
         RJ45 Plug for U+PS2
         ===================
         1  N/C
         2  N/C
         3  N/C
         4  U-loop network connection
         5  U-loop network connection
         6  N/C
         7  -48 VDC 
         8  -48 VDC Return

     The ISDN cables can be silver satin patch cables (the kind that
     make 10Base-T Ethernet installers cringe).  The S/T bus can also
     be silver satin but most installers use CAT 3 or CAT 5 with one
     drop per terminal equipment.  It is true that only 4-wires are
     needed on the S/T bus but see below for optional power needs.

     21.3 ISDN S/T Bus (Point-to-Point)
     One logical terminal is on the S/T bus which can be 1km long.

     21.4 ISDN S/T Bus (Short Passive)
     Up to eight terminals on the S/T bus which can be within 100 to
     200m.

     21.5 ISDN S/T Bus (Extended Passive)
     Up to eight terminals on the S/T bus which can be up to 500m.

     21.6 ISDN S/T Bus (NT1 Star)
     Up to eight terminals on the S/T bus which are wired from a
     central NT1 and can be up to 1km in length each.

     21.7 ISDN S/T Bus Pinout
     The S/T bus connects the NT1 with the terminal equipment.  See
     section 10.0 for plug identification and pin numbering.  Note,
     if power is not required an RJ11 (6-pin) plug could be used.
     Some NT1 devices have a switch to turn off power if it is not
     required by the terminal equipment.  For safety reasons the
     power should not be put on the S/T bus if it is not required.
     Typically, ISDN PC cards do not require power from the S/T bus,
     but ISDN telephones do require power from the S/T bus.  Check
     your vendor equipment specifications carefully.

         RJ45 Plug for ISDN S/T bus  
         ==========================   
         1  N/C
         2  N/C
         3  White/Green .....  Receive +
         4  Blue ............  Transmit+
         5  White/Blue ......  Transmit-
         6  Green ...........  Receive -
         7  White/Brown .....  -48VDC (option)     
         8  Brown ...........  -48VDC Return (option)

     21.8 ISDN Cabling Guidelines
     The North American ISDN Users Forum (NIUF) has produced a document
     titled _ISDN Wiring and Powering Guidelines_ NIUF #433-94 which 
     describes residence and small business ISDN cabling.  See section
     30.0 for the NIUF document ordering address.