Description
This article is from the Data Communications Cabling FAQ, by Peter Macaulay pmac@fox.nstn.ca with numerous contributions by
others.
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.
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