RJ48 or RJ45 Help for PRI

Answered Question
May 25th, 2008

I've read that while an RJ45 will work, an RJ48C should be used for a PRI coming from smart jack into a Cisco vwic. Today a customer has the PRI connected to a pbx. I looked at the face plate and I can't tell if it's an rj48 or rj45. Their cabling guy said it's just an rj45 cable from faceplate to their pbx.

So what will happen if I go to use the correct RJ48 when I remove PRI from PBX? Will it work for sure, or is it likely that the smartjack is RJ45 and thus the RJ48 will not work? Is the correct thing to do is to have the faceplate removed and replaced with an rj48c?

Any and all advise is appreciated.

thanks

I have this problem too.
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Correct Answer by Paolo Bevilacqua about 8 years 6 months ago

What they're saying is that a RJ45 male fits any jack.

Beside, many smartjacks are NOT keyed anyway.

In fact, original cisco PRI cables have no key.

So you're OK with regular RJ45 connectors to make a custom made cable. If possible, use proper 100 Ohm T1 cable, especially if the patch is longish.

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Paolo Bevilacqua Sun, 05/25/2008 - 04:31

Physically it's the same connector.

What matters is the pinout, going to a smartjack you want a straight cable using the proper pairs. That is NOT the same as an ethernet cable. The pinout is easy to find searching "vwic pinout" in the search function.

Hope this helps, please rate post if it does!

victor2008 Sun, 05/25/2008 - 04:36

Doesn't it depend on the smartjack? The customer has PRI going into one room (demarc). Then pri is extended to server room, and connected from smart jack to pbx. Trying to understand the physical specs and Cisco has stated the below, which implies smart jack type is important.

Q. What is the difference between RJ48 and RJ45?

* RJ48 has a keyed connector and a notched jack.

* RJ45 does not have a key or a notch.

* Both have 8 pins.

Although an RJ45 connector fits an RJ48 jack, the key on an RJ48 connector does not allow it to plug into an RJ45 jack.

Correct Answer
Paolo Bevilacqua Sun, 05/25/2008 - 04:56

What they're saying is that a RJ45 male fits any jack.

Beside, many smartjacks are NOT keyed anyway.

In fact, original cisco PRI cables have no key.

So you're OK with regular RJ45 connectors to make a custom made cable. If possible, use proper 100 Ohm T1 cable, especially if the patch is longish.

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