Preparing for switch failure, what happens when...

[NamesAsh]

Greetings,

I was tasked by my boss with the "what if" scenario, to cover what happens if our switch fails. We have a 3-cabinet Definity running 9i.05.122.2 with Definity Audix. We do not have a service contract nor do we have any real contact with anyone we feel comfortable with to service us, so we are self maintainers. I'm not even aware of anyone locally that can help any more (the company we bought the switch from ~7 years ago is no longer in business).

But I have a few ideas, and a few questions.

What we are worried about is what happens to the (analog) DID lines if the switch fails. We have an 808A Emergency Transfer Panel (5 trunk failover) that we 'could' use, but it's not wired up right now. My concern is - how does the telco perceive these DID trunks if the Definity is dead or non-responsive? Does it continue to think they are OK, and continue to route calls to them - or does the telco realize something is wrong and automatically busies those trunks out so that calls won't be routed to them (if the switch isn't winking the DID lines, what does the telco do?)? And does the 808A fail over on a CPU failure, as well as a power failure (our system is on a UPS, of course)?

My 'quick and dirty' thought is to get something like a Digium 8-port card with 8 FXO ports, and set up a relatively inexpensive Asterisk mini-PBX to handle the emergency situation (it would not need to handle all company calls, only calls to a very few extensions). A few VOIP phones would be sufficient to cover the critical calls. The Emergency Transfer Panel would be set up to fail over 3 of the DID lines, and 2 of the outgoing trunk lines. This assumes the Definity is totally dead in the water.

The answer I'm hoping to hear is that the telco will realize that most of the Definity-connected DID trunks have gone dead, and will be routing calls to the trunks that the Asterisk box is now winking.

Thanks,
Ash

 

[mikeydidit]

We are a hospital here so we have backup's to backup's. Some of what I tell you, this being said, will be more than a lot of people will ever need.

I have my main PRI group setup with a secondary preference in the trunk group form to our 12 CO trunks. This gives us 12 lines to use in case all goes down on the PRI's. We also have 12 DID lines that also fail over.

In the event that all the trunks are down, the CO then routes calls to us on POTS lines. I have 12 extensions that can receive DID calls.
Being you have analog trunks, I don't think your CO will busy these out if your end goes into trouble. Also I thought the lines on the emergency transfer switches needed to be CO trunks? You receive calls on DID but you can not call out on them unless they are CO or Tie. So POTS lines here and there will at least give you something to make calls on. Cheap insurance.

Hope this helps you.

Hell, there are no rules here - we're trying to accomplish something.
Thomas A. Edison

For the best response to a question, read faq690-6594

 

[NamesAsh]

Thanks for the reply. Sounds like you guys did it 'right'. I think our company is too frugal to do things right though. They won't even pay for caller ID. Ha.

Looking at the 808A docs, you're right, it does call out for CO trunks, and not DID. "The boss" is concerned that calls to our main operations extension will be missed, and those only come in on the DID trunk. Hmm. If the 808A is a dry contact and just swapping wires, then it "ought" to work either way.

We do have 1 'emergency' completely independent non-PBX POTS line that is used in this situation, but not everyone has that phone number.

I was thinking that the Asterisk box might be able to grab inbound calls from those 3 switched DID trunks (while the remaining DID trunks lay dead), and any outbound calls would go out the 2 switched outbound CO trunks (and the remaining CO trunks would lay dead as well). Asterisk could handle stripping off the extension information from the CO and routing the call to the proper person (or its internal voice mail).

 

[mikeydidit]

You could set it up with your CO to call forward you main DID number. In the case you lines goes down, send them to one of your POTS lines. I am not too familiar with the Asterish box you mention. But when everything is down something beats nothing every time..

Hell, there are no rules here - we're trying to accomplish something.
Thomas A. Edison

For the best response to a question, read faq690-6594

 

[Mitch672]

you should investigate "Out of service redirection" from your local telco provider. they can forward DID's to a predetermined number... You could set this up so your main # could forward to a set of POTS lines, in the case of a PRI/T1/DID failure. OOS Redirection runs about $75/month/per DID/line on Verizon.. Its pretty expensive for an entire DID range, but not too bad for a few select numbers.

mitch

 

[jfh9219]

My two cents:

Years ago I purchased a 920iPFT from the Gordon Kapes company in Illinois. You route a PRI trunk through it and when your switch is down it seizes the PRI and keeps it up. It provides up to 24 analog extensions throughout your facility and has very good ACD capabilities. You can filter incoming numbers, create hunt groups and have canned messages. For less than $10,000 at the time I got it I can't believe that everyone doesn't have one.

You can also talk to your CLEC about alternate routing whereby you predefine certain numbers and corresponding destinations which you can easily implement remotely.

For those of you that think the PSTN is invulnerable, this past Feb we lost our central office for 15 hours due to flooding resulting from a watermain break in the street. We were on the high priority to restore list, some people were out for 3 days.