Best way to use multiple trunks on multiple PBX

[VeeDubb65]

I'm working on cleaning up a mitel system that I inheritted from a guy who didn't seem to care much about his job.

We've got 3 3300's, call them A, B, and C.

The call center consoles are attached to A.

A and B are clustered.

C has hospitality enabled, and is not clustered. Technically there's a console attached, but it's only for setting wake-up calls.

Right now we have 4 PRI trunks, and 6 LS. 

For the PRI's, A has 2. B and C each have one, and there are no routes in place to share between A, B and C. A does run out of lines once in a while, B less often, and C almost never. The circumstances that would make one or another run out of lines are all very different, so all three running out at once is unlikely to ever happen.

All 6 of the LS trunks are connected to C, but they're not actually configured. The inbound numbers for those lines are unpublished, and there are no routes that use them. Looking through the ARS, you can see that they may have been configured as 2nd-choice routes in the past, but no calls have touched them for years.

What I'd like to know is what the best method would be to make proper use of all of our trunks, and provide the best total service quality and redundancy. Ideally, I'm thinking that the best option would be to move those 6 LS trunks around so that each PBX has 2. Then use route lists like the following:


A
1st choice PRI group on A
2nd choice route to B
3rd choice route to C
4th choice LS on A, COS restrictricted so only A can use it.

B
1s choicet PRI group on B
2nd choice route to C
3rd choice route to A
4th choice LS on B, COS restrictricted so only B can use it.

C
1st choice PRI group on C
2nd choice route to A
3rd choice route to B
4th choice LS on C, COS restrictricted so only C can use it.

If I build that out right, it should put all the PRI's into a single pool of 92 lines, while still keeping lines to the outside world, even if 2 PBXs go offline. If the PRIs all went down but left the LS trunks up, each PBX would keep 2 lines open for outbound calling.


That brings the questions:

1. Is this even a sane idea, or is there a clear reason why this wouldn't be a good idea?
2. How to I do this without creating a loop? Alternatively, do I care if this creates a loop?
3. Is there a better way to accomplish this?

[acejavelin]

Based only on what you have said... Disconnect the LS trunks and save the $300/month

A
1st choice PRI group on A
2nd choice route to C
3rd choice route to B

B
1s choicet PRI group on B
2nd choice route to C
3rd choice route to A

C
1st choice PRI group on C
2nd choice route to A
3rd choice route to B

That brings the questions:

1. Is this even a sane idea, or is there a clear reason why this wouldn't be a good idea?
2. How to I do this without creating a loop? Alternatively, do I care if this creates a loop?
3. Is there a better way to accomplish this?

1. It's an excellent idea... and you do not have to be clustered to share trunks, you can do IP trunking without clustering but be aware these will need to be Enterprise sites, not Stand-alone, which may affect the licensing of C.

2. The PBX's know how to handle tromboning or looping, it generally isn't a concern in such a small network.

3. Perhaps, depends on your resources and situation... But this would be a good start.

[VeeDubb65]

Thanks for the sanity check. You've basically confirmed exactly what I was thinking. We may still keep the copper, just because we're in a rural-ish area and we've seen PRI problems in the local CO a few times. On the flip side, $300/month is $300/month.

We actually have two other trunks I haven't mentioned, which are also copper LS trunks. They're connected to controller A, and all 3 controllers use those as the 1st-choice route for outbound 911, so we've always got a clean line waiting for 911 calls.

As for the Enterprise vs standalone, I just double checked: All 3 are Enterprise.