Asterisk PRI Questions

jclester used Ask the Experts™
Hello all,

I've been using Asterisk in my home with Broadvoice for sometime now, and am in the process of migrating our company from a 3Com NBX to an Asterisk server.

I'm pretty sure that I can figure out how to get Asterisk to connect to our PRI, however it is new to me, and I have a couple of questions.

First, we actually have two PRIs through the same carrier... is there any reason that I can't use one for our NBX and the other for our Asterisk server while I migrate the system?

Any idea as to what would happen if the same DID is configured on both servers?  Will both locations ring until one system or the other answers the call?

Thanks I appreciate the help.
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Most Valuable Expert 2012

I am assuming that you have two smartjacks: one for each PRI in your wall.

That being said, if you plug one in the Asterisk box, and one into the NBX, one box will be responsible for DIDs configured for that particular PRI, and the other box will be responsible for the DIDs that are assigned to that PRI.

So, if 800-662-5555 comes down PRI A, and PRI A is plugged into Asterisk, asterisk will field the call. Regardless if th NBX is configure to handle the call. It just won't come down the pipe.

If your DIDs are configured to "roll over" then it would be anyone's guess as to which pipe the call will actually come down, so you have to have duplicate dialplans on both boxes.
Most Valuable Expert 2012

Also, here are some guides I have written that will get your Asterisk box up and running:

A website to provision Polycom phones for free:

And... I have a new article that is currently unpublished, but hopefully will be published soon that tells you how to install DAHDI to run your PRIs. (Not configure them though. That's a separate issue).

DrDamnit Hi

is not better to use PRI card with two SPANs to handle the two PRIs
and he can configure it from the same server to handle DIDs .. ?
I recommend this scenario, hence he can manage all DIDs and route them easily ..

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Thanks for the info...

The PRIs are set to roll over, (the DID's do not come down specific PRIs), and yes, I do have two smart jacks.

I do already have Asterisk and Dahdi installed on the new server, I think the config will be the only new area for me.

I have used Dahdi for Analog phones in my home, so I assume a lot of the process is similar.

Memo, the card I have in the server I'm building is the Digium TE212P, which does support dual T1s, but i don't understand what you're suggesting I do.

To recap, the goal is to keep the old PBX up while building the new Asterisk PBX... I have two PRIs that are rolling over incoming calls.  

Also, I have no idea how I managed to put Cisco PIX firewalls as the default zone for this question... I don't think I can remove it now, so sorry about that.  (Lack of sleep).
Most Valuable Expert 2012

It would be better to use a dual span T1 card; however, in his question he stated that he wants to use the NBX box at the same time as the asterisk box to do a smooth transition.

Using a dual span card will put both PRI's directly into the Asterisk box, which is counter to his immediate goals.

I, personally, would prefer that approach: just go cold turkey to Asterisk, but his users might hate it.

There are several drawbacks that are *not* free as in beer:

1. If both PRI's are connected to the asterisk box, then he needs at least an additional PRI port *out* of the asterisk box to feed the NBX PBX. So that means instead of buying a single dualspan card, he'd have to have a dual span + a single span at minimum, or a quad span card.

2. He'd have to get the asterisk box working and up in order to feed the NBX box, and judging by his original quesion, he's not an asterisk expert.... yet... (he will be soon though!).

3. If he wanted to do a different kind of splitting, it is possible using a device like an Adtran total access (in any number of different models and / or configurations), but that again is several hundred if not a thousand dollars just to play around.
Most Valuable Expert 2012

Does the old PBX have a way to do SIP trunking?
Most Valuable Expert 2012

Given what you just posted (rollover + te212p), I would suggest the following:

if you have the ability to trunk calls to the old PBX, (an additional PRI card, SIP trunking, etc...) then put both the PRI's into the TE212, and then use the dial plan to route whatever calls / numbers / did's you want to the legacy PBX.

If you do not have the ability to trunk calls, call your provider and tell htem that you need to remove roll over, and assign certain numbers to one PRI and the rest to the other PRI.

Then break out the jobs between the various PBX's to slowly transition everyone onto the new system.

Once you get everything pretty much working, you can slowly migrate the DIDs onto a single PRI until you hit capacity, and then dump the rest, and re-instantiate rollover.


I don't believe the legacy PBX has the ability to trunk calls, but I will confirm.

Both suggestions sound like great options, and I think I'll have the provider remove rollover as you suggested.

I already have the majority of our dialplan built on the Asterisk system, so this sounds like a good option for me.

Nope, not an expert yet, but I'm working towards it.  I took the bootcamp in Vegas a couple years ago and I've been hooked ever since.


Thanks again.
Most Valuable Expert 2012

I went through Bootcamp years ago at Digium in Huntsville. :-)

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