Tech Stuff - Telephone Wiring
This section contains information on telephone cabling for ISDN.
U Interface
North American Demarcation point. A 2 -wire interface (single pair) that is usually but not universally provisioned using an RJ45 connector (more correctly an 8 position modular connector). ISDN wiring uses LAN based pair numbering NOT telephony pair numbering.
| Pin No. |
strand color |
Name |
| 1 |
white and orange |
N/C |
| 2 |
orange |
N/C |
| 3 |
white and green |
N/C |
| 4 |
blue |
U Interface |
| 5 |
white and blue |
U interface |
| 6 |
green |
N/C |
| 7 |
white and brown |
Optional -48 VDC |
| 8 |
brown |
Optional -48 VDC (return) |
Power for telephones is optional and if present is supplied on pins 7 & 8.
S/T Interface
Europe's demarcation point and via an NT1 for North American users. a 4 wire interface universally provisioned using an RJ45 (8 position modular connector). ISDN wiring uses LAN based pair numbering NOT telephony pair numbering.
| Pin No. |
strand color |
Name |
| 1 |
white and orange |
N/C |
| 2 |
orange |
N/C |
| 3 |
white and green |
RX+ |
| 4 |
blue |
Tx+ |
| 5 |
white and blue |
TX- |
| 6 |
green |
RX- |
| 7 |
white and brown |
Optional -48 VDC |
| 8 |
brown |
Optional -48 VDC (return) |
RJ45 Connector Pin Numbering
RJ45 Male Connector
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