Howto:How ISDN wiring works

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ISDN Primary rate (PRI) wiring differs from Ethernet and from ISDN Basic rate (BRI) wiring. Here is how to do primary rate and basic rate wiring correctly.

Applies To

This information applies to

  • IP3000
  • IP3000DD
  • IP6000
  • IP400
  • IP800
  • IP202
  • IP302
  • IP305

More Information


With a newer ISDN PRI network termination, the IP3000 can be connected using a straight, 8-wire category 5 cable. A 4 wire cable, either LAN or telephony cable, will often not work. Also, some network terminations do not feature an RJ45 connector, so an individual cable must be created.

On the IP3000 box bottom, there is a wiring diagram. If you are unclear about the pinout, the following pinout picture will probably help:

How ISDN wiring works - RJ45.gif

PRI uses pairs 1 and 2 according to the following picture (pair 1: 4+5, pair 2: 1+2), as opposed to BRI, which uses pairs 1 and 3.

How ISDN wiring works - Rj45-pairs.gif

To check the cable you are going to use, simply plug it into PRI1 and PRI2 of the same IP3000. Both PRI1/2 leds must light, otherwise the cable is broken or unsuited. This even works if the 2 PRIs are not licensed.

Related Articles

Pinout of the BRI connector

Pinout of the PRI connector