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911 from Local Gateway

I have a quick question that I just thought about today.

I have a site that has a Local Voice Gateway for 911 calls. This all works, but I was wondering what happens if someone calls 911 and they hang up and 911 attempts to call back.

Will, that call connect back to the extension that dialed or just ring endlessly?

Currently, all outbound calls go out our main PRI except for 911 calls which go out the local voice gateway because this site hits a different PSAP.

I'm thinking I might have an issue here.

Thanks for any advice that can be provided.

VIP Collaborator

The inbound call from the PSAP would be handled like any other inbound call from the PSTN. If you are sending internal CLID out with the 911 call, that is the number that the PSAP operator would call back and you would want it to ring on the originator's phone. If you are sending generic CLID out over the gateway, then that is the CLID the PSAP operator would call back and you would want it to ring somewhere. (I'm assuming you are not using Emergency Responder here, because call-back behavior is part of the design/implementation.)

So, to make sure that calls inbound on that gateway reach "someone" you'll need to figure out what the PSAP operator will be dialing. Then make sure that there is a DN or translation pattern in CUCM that matches that inbound dialed number, and make sure that the gateway has a CSS that can reach that number.

Does that help?



In addition to what Maren said, it's common to use POTS lines for 911 locally, so you'll have to consider that if that's what you have. You'll basically need to reserve one line for 911 only (assuming there's also SRST). With POTS it technically doesn't matter what ELIN CER sends because POTS is going to overwrite it anyway, but for callback you can configure connection plar on that port to the ELIN. CER will never know the difference.


Edit: I overlooked the fact you seem to not have CER. In that case, you'll still need connection plar on the FXO to some phone, maybe a security desk if there's one, or a manager's phone, or a shared line. Just don't plar it to an auto-attendant.


Sorry, everyone, I should have been clear and given more information.


We do have CER, and we use that for our main site, this remote site hits a different PSAP so to make that work we have a local Voice Gateway with a POTS line that is used for 911 only for this remote site.


When someone dials 911 from the remote site, it goes out this local voice gateway and 911 is presented with the local phone # in that area for the POTS line.


Everyone has given great responses, and here is my thinking which I think falls in line with everyone's comments; the local area # (let’s say is) 717-555-1234, if 911 had to call back that would be the number they would use. My thought process is to have the voice gateway answer a call and send it to the front desk. This is a small office with about 8 phones.


I guess my question is, is the configuration difficult on the local voice gateway to get incoming calls to go to the front desk? @Evgeny Izetov, you mentioned a connection plan on the FXO… how would I do that?


I inherited this setup, while I was a UCCX admin for a long time, that’s where my knowledge was. CUCM, CER, and Voice gateways are all new to me.


Again, all advice is very much appreciated.


First, in your situation the connection plar opx is a decent choice. Here is a link to information and configuration examples:

But the config would look something like this:

voice-port 0/1/0
connection plar opx 4085554321
dial-peer voice 9999 voip (or pots)
 destination-pattern 4085554321
 session-target ip.of.cucm.server
 [other commands as needed...]

And then on CUCM have that reach out to the receptionist at the remote location.




Because you have CER, you can make it work so that PSAP callback rings the phone that actually dialed 911 (even though you have a POTS line). In CER look for that site Emergency Response Location (ERL) and you should see what calling number CER is using (ELIN). If people followed the guide when deploying CER, it could look something like 10911.4045551212, where the last 10 digits is the ELIN. Then you'd need to configure the ELIN as connection plar just like in the above post by Maren. The callback will work assuming that the rest of the configuration is correct, i.e. the 4045551212 hits the 913XXXXXXXXXX number on CTI Route Point.


OK, this is making sense, but I don’t want to mess anything up.


I have attached a copy of the Voice Gateway Config (I removed any revealing information and replaced it with information I know how to tie back) can someone take a look at it and advise how I should proceed and maybe config changes.


At the remote site, there is one POTS line used exclusively for 911 (we’ll say the # is 7175551234). The POTS line is connected to Port1 on the VG (AALN/S0/SU1/0).


Furthermore, yes we have CER, but when someone from this Site dials 911, there is a CSS and PT that sends the 911 call to the VG bypassing CER altogether.


Would adding a Plar to the VG and sending it to CER still get back to the receptionist's desk? I’m thinking the answer is yes based on @Maren Mahoney’s response.


However, I noticed the config already had some dial-peer configurations in place and this is where I don’t want to mess up! :) However, from what I was told some of the configurations is old and not used, but I'm not sure. Although when I tested 911 from this site it goes to the correct PSAP and they see the correct Phone # and provide the correct location. I'm just not sure if they had to callback if it would work.


As always everyone's advice is appreciated.

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