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Backups for Sip Trunks

Yarin Ezra
Level 1
Level 1

Hello Cisco Community.

I have a question and hopefully someone has the answer.

I have a customer who has a sip trunk configured to a system that receives calls and routes them to certain destinations, having this connection as a sip trunk makes it when the remote system fails, the sip trunk is down and calls from within the CUCM fail when routed to the sip trunk.

The customer wants to add a backup to the Sip trunk in case the remote system fails, reroute the calls to a Hunt list instead of the sip trunk.

is there a way to configure the requested backup?

the call flow works like this:

a user dials a DN XXXX which is on forward all to a Translation Pattern > the Translation pattern translates to a Route Pattern which has the Said sip trunk as a remote destination.

 

14 Replies 14

Simply put the SIP trunk into a Route Group and then put the RG into a Route List where you repeat the same for another egress point via something else than the SIP trunk, it could be a SIP trunk at another location or any other type of connection with a service provider. Set the order of the entities in the RL with the primary egress point as ordered first in the list and put the routing algorithm to top down. Then change your RP to point to this RL instead of direct to the SIP trunk.

With this routing functionality in CM will send the call via the primary link as long as it’s operational and send calls via the secondary link if the primary is down.



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It would work only if the backup destination were to be either another sip trunk or a gateway, the customer wants the backup destination to be a Line Group

That does not work as there is no such option. Line Group is an internal routing concept and it cannot be used together with route pattern(s) as these are an external routing concept.



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I agree, a few coleagues suggested using CTI Route point with the remote destination server but the CTIRP isn't registering probably because the remote server does not support that, so the other solution is probably using a route list with a primary destination as the sip trunk and a secondary destination as a Gateway with dial peers to route incoming calls to the Line group number.

would that be a reliable solution ?

I don’t see that a CTI RP would be an option, apart from this remote destination is not related to CTI RT, that’s a thing for Mobile Connect, aka Remote Destination Profile or TCT/BOT devices.

If you do the secondary call routing in your SBC gateway you would not need to have a second option in your route list. You’ll do the entire call routing modification in the SBC gateway.



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If you share your SBC configuration and a little bit of more details around the number that you would want calls to redirect to when your egress path is unavailable we can likely give you a hand with the configuration.



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What you could do is configure alternate dial peer call routing in the SBC where you have the SIP trunk demarcation from your service provider. With this you should be able to send calls to an alternate destination if the primary dial peer option is down based on no response from your provider on SIP option ping.



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Hey Roger, sorry for the delay, i cant share the Gateway configuration but i can share the destination number.

The customer wants the calls to be routed to the alternate number 9393 (Line Group) in case of a sip trunk failure.

The source number (Route pattern) is 9224 and its Gateway/RouteList is the sip trunk. incase the sip trunk fails, route all calls coming from the 9224 (Route Pattern) to the destination 9393 Via a Cisco Router Series 3900 configured as VGW.

are you able to help with the dial-peers configuration ?

Thank you so much for your help.

To make it easier and more specific to help you out would it be possible for you to share at least the current dial peer configuration? You can redact any sensitive information from it, as long as the overall use of each dial peer is kept visible.



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Hey Roger, i pulled the dial peer configuration from the VGW i need to use for the customer request.

Hope it is good enough

if anything else is needed please, contact me.

I'm sorry but that output does not seem to be coming from a gateway that acts as an SBC, ie a router that is running the Cube functionality to act as a Session Border Controller to terminate a SIP connection with a service provider.

How are you're SIP trunk setup, is it directly in CM to the SP or are it in a gateway (SBC) to the SP? IE either of these two options.

  1. CM -> SIP trunk -> SP
  2. CM -> SIP trunk -> SBC -> SIP trunk -> SP

 



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It is indeed CM > Sip Trunk > CUBE (SBC) but the backup route isn't supposed to reach the SBC to keep unnecessary load off of it.

That's why i was thinking the MGCP gateway configuration would be good.

Is there a way to achieve the spoken backup with the MGCP gateway or the CUBE for the SP is absolutely necessary.

Thank you Roger

You technically could do the reroute on whatever, but it would be quite unclean so my recommendation would be to do it on the SBC. If the connection to the SP is down it would have no load at all, so that should not really be an issue that you need to worry about. Apart from this doing this on a MGCP gateway is a quite terrible idea as that would not have any idea on how to do this reroute. You'll need to do this on a SIP, or if your old school H.323, gateway as they have the control of the call natively in IOS, whereas with MGCP it's actually CM that has the control of the call routing by the back-haul channel.

This would likely involve EEM scripting that triggers on SIP option ping for the SP connection being down and then doing the re-route via a dial peer that the script brings up by a no shut.

The use of the EEM script would be to not have call loop occur on the occasion that the call fails to the service provider when the link would still be operational, ie meaning that there is some issue with the call routing because of wrongly formatted called number, or calling for that matter.



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I guess calling it remote destination wasn't quite clever, on all cases, calls will be made internally, the so called "remote destination" is just a server inside the WAN, source calls made to that server are from the internal CUCM (lets call it CUCM1) and incase that remote server is down, calls should be sent to the VGW via Route list (since pings are down to the remote server so the VGW route group should be taken) and rerouted back into the CUCM.

I was thinking to create a dial peer that accepts calls from a specific number and reroute it to a specific number inside the cucm, in that case every call to that VGW would route back to the cucm but the only time calls will ever reach that VGW is when the SIP Trunk is down and the Route Pattern has a Route List that include firstly the Sip Trunk and secondly the Serials of the VGW ( incase the sip trunk is down, the route list should choose the second route group as a viable destination). 

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