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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.

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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)

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RJ45 Connector Pin Numbering

RJ45 Male Connector

RJ45 TOP FRONT

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