FXO failover for 911

Answered Question
Apr 3rd, 2008
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I have one FXO 911 line setup at multiple locations. Basically if someone at a firestation makes a 911 call. I have their calling search space set to a group for that building. That way 911 or 9911 calls are passed out the single FXO line I have for each building.


I need a failover basically if the 911 line goes down for any reason, It will use the PRI which is not located at the building but at the main building handling all the PRI lines. I have this setup in the Calling search space list. Basically 3 partitions.


So the first partition would be the fire station, next one would be the main building with the PRI. The correct route patterns are linked to this partition.


When I disconnect the 911 line to test this redundancy out. CCM doesnt seem to check if the line is working before trying to pass the pattern, so I come up with a busy signal. If I remove the firestation partition, calls work correctly to the next location. Doesnt seem to failover to the PRI. Any possible way I can make CCM check the analog fxo line then rolling the call over to a PRI ?


Also I have another question if this would help if 2 people in the same building call 911 with only 1 911 line in that building to pass person #2 that is calling 911 out to the PRI.


Sorry for it being so long.

Correct Answer by mattcalderon about 8 years 11 months ago

Yes the second endpoint needs to be a member of the hunt group. A second partition will not send the second call to the applicable endpoint. The outgoing call will hunt through the list and if the FXO is the only endpoint in the hunt, it will not know to hunt to the pri. Add the PRI to your hunt and see how that goes.


Are you sure you are not using H323? If you sent it right to the gateway and the gateway shows as unregistered that sounds exactly like what you see in ccm for h323.

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heathrw Thu, 04/03/2008 - 16:01
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I would create a seperate route lists purely for emergency calls (1 for each site) and then add your route Groups so if it fails on the first RG because the FX port is in use it goes to the next one in the list. You would need to have a 9.911 pattern and partition for each building and added to the correct CSS

mattcalderon Thu, 04/03/2008 - 18:03
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Now I am under the assumption that you are using a MGCP gateway due to the fact you are specifying endpoints in call manager. If you are using H323 please answer back


MGCP will not know if you do not have an active line plugged into the FXO port. All MGCP will do is register that endpoint and let call manager know if that endpoint is off-hook or not. I have seen many times where users have unplugged the gateways ONLY PSTN line for an extra fax machine and then when a 911 call is made....Nothing!! When you debug the call, you see the call hit the port and go off hook, but there is nothing there to send the digits out over.


Call manager will know though if the line is busy and then will route the call accordingly to your backup which is the PRI. So if 2 users attempt to dial 911, call manager will know that the first endpoint is busy and will route the call to the PRI.


This is why some of our customers insist on monthly 911 tests.

m0city_snet Thu, 04/03/2008 - 18:14
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Correct. I am using a MGCP Gateway.


I have no problem converting the whole network to H323. Can you explain the negatives, If i do this. I know CCM will not control the calls once it reach the router anymore but if it means that if say the line is dead the call will roll over to the PRI on another area that would be cool.


At least I can take care of the problem if the line is busy is the call will route to the PRI if someone else calls. I wasnt sure if the FXO will report offhook and onhook. That clears one problem.


But yeah, I guess I have to do daily or weekly checks on my network which would be a hassle,t but wouldnt be a problem I guess. Can H323 see that a line is down and roll a call another way ?


Thanks for your help with this !!!

mattcalderon Thu, 04/03/2008 - 18:27
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I dont think H323 would give what you are looking for. See when a PRI goes down the dial-peer goes down or the endpoint unregisters. When a FXO is not plugged in, the call will still go to that port on the card. I dont believe, and i may be corrected, that neither MGCP or H323 will give you the type of redundancy you are looking for.

m0city_snet Fri, 04/04/2008 - 06:00
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I guess I understand there is no way to detect if the line is down or not.


I am using MGCP and when I tested it out. I called from one phone and when I use the other phone it didnt know if the phone was busy or not to rollover to PRI. Does it have to be set up in route group or setting up 2 partitions in CSS wont work. And if not, why do they give you the option to set up more then 1 partition in CSS if it wont provide redundancy ?


I been having problem setting up the FXO using route group and route list. It seems to not route right. I have to setup a pattern directly pointing to the gateway is why. I think i setup everything fine but when I use the dial pattern it gives me a fast busy. In the route list it shows the device is "NOT REGISTERED".

Correct Answer
mattcalderon Fri, 04/04/2008 - 06:43
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Yes the second endpoint needs to be a member of the hunt group. A second partition will not send the second call to the applicable endpoint. The outgoing call will hunt through the list and if the FXO is the only endpoint in the hunt, it will not know to hunt to the pri. Add the PRI to your hunt and see how that goes.


Are you sure you are not using H323? If you sent it right to the gateway and the gateway shows as unregistered that sounds exactly like what you see in ccm for h323.

m0city_snet Fri, 04/04/2008 - 21:28
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Thanks this resolved one of the problems.


I did a shut on a port as well and did a call. It seems to roll the call over to the PRI. I have not done a pull of the cord as the cord is located on another premise. I will do it sometime next week.


But rolling calls to the next line in the route group works though. Thanks alot. One thing I had to do is when I setup my route list I had to reset the route list in Call manager. That is something I never thought of doing. Once I reset it established and worked fine.


Thanks alot again matt !

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