I finally found a forum on Tadiran Coral PBX's!!!
Question - how critical is having a CSU between the telecom provider's smart jack and a Tadiran Coral PRI card? The circuit is a T-1 PRI point to point running QSIG between two circa 1997 Tadiran Corals w/ PRI cards at two sites. I have heard both sides - the upcoming new telecom provider says "you don't need them", PBX vendor says they provide "advantages" such as a loop back point on customer side and "line conditioning" and always recommends installing them. The CSU's aren't used with the current telecom provider's service that uses Cisco ONS shelves with T-1 port cards and the voice service is very reliable. The main site was upgraded two years a go with ver.15.x, dual MEX-IP2 processors, and PUGW card (VOIP not implemented yet). The other site is running ver. 10.39.x Any advice regarding if CSU's are truly needed would be greatly appreciated.  

Yep, I got this forum started cos I couldn't find anyone anywhere else!

But sorry I can't help on the CSU issue specifically . I've worked around the world on Corals but using E1 not T1. In theory to connect via QSIG you just need 2 pairs (1x Tx, 1x Rx) so Corals next to each other just use a piece of jumper wire. But going into the public network is another issue as it goes through exchanges etc. Because it's a leased circuit and going through exchanges you don't know what it's connected to on its way to you.

Personally I'd leave them in place. It may work without them but I wouldn't trust it.

It also comes down to demarcation. Telcos I've worked with have a demarcation point ie a point at which they take responsibility for and say anything past it is your responsibility. The CSU is usually this point. If they can prove it works to that point then they've done their job. Without that there is no point to which there is a line of responsibility. Maybe US telcos operate different, I'm not sure. But that's what I'd work on.

Thanks for the reply and so quickly. I'll know in a few weeks when cutover takes place, if things don't work, I'll tell the project mgr better purchase some CSU's quick.

Late to the post, but be aware...there is a "known' issue with the jumpers on the tadiran IPX Pri card. If they are not set correctly the card will not behave well.

I would use a CSU.