ISDN PRI failover between 2 Router

[Mavis D]

Hello forum,

I have 2 E1 PR from different carriers configured on two different routers.

What i want to achieve is that, when PRI link (either the e1 card or the link to carrier) of one router goes down, i want all my calls to PSTN fail-over to the second router and when the pri which went down comes up, all call should go through the original pri link.

How this can be achieved?

Thank you.

[Chris Deren · Accepted solution]

I will assume you have CUCM as you did not specific what phone system you are using. To get outbound redundancy to work you need to put both of the gateways into either common route group, or both route groups into common route list that your route patters point to.

As to inbound that is out of your control and since they are from 2 different carriers you cannot configure them to be in one trunk group to share call delivery. Your only option would be to create manual forwarding at the telco level.

[Mavis D]

Hi Chris, I have a pub and a sub and 2 H.323 voice gateway's.

Correct me if i am wrong, if i point my route pattern to a route list which consist of a route group consisting of two voice gateway then all my calls (for example: all INTL calls) will go via one pri connection only i.e through the VG listed 1st in the route group, isn't it?

So this is a active-standby solution. Is there a way that i can use both PRI's as well as use them for fail-over.

[Mohammed al Baqari · Accepted solution]

Hi,

If you place both gateways on same RG, then you need to select the algorithm as circular for active/active PRIs.

Routing call based on priority list can be achieved in top-down algorithm or with RGs in single RL.

[Mohammed al Baqari]

Hi,

If you are using MGCP, then as Chris mentioned, placing both PRIs in same route-group or multiple route-groups in the same route-list will do the job.

If you are using H323/SIP, then failover between routers at PRI failure will require some additional work inside the routers on top of Route-Group/Route-List redundancy.

Please see this post.

https://supportforums.cisco.com/blog/12575431/failover-sip-or-h323-trunk-based-isdn-status-voice-gateways

[Chris Deren]

There should be on config changes needed for H323/SIP on the gateways as per the posted these are 2 separate voice routers, the changes would be applicable if both PRIs are on the same router.

[Mavis D]

Hi Mohammed, thank you for your input. I've got through your link for Failover SIP or H323 Trunk based on ISDN Status on Voice Gateways, correct me if i am wrong but from what i understand you are manually forcing the sip call service to shut down. This is not what i want to achieve. What i wanted was when isdn status of pri on one vg is down my outbound calls should traverse through another vg with a active pri.

[Mohammed al Baqari]

If your PRI is down, your SIP/H323 service won't go down. Therefore, CUCM will keep sending the calls to the 1st gateway and the gateway will reject the call with cause code as 'Unallocated Number' because your POTS dialpeers will be down. 

When CUCM receive this cause code, by default, will stop call routing to next gateway because of service parameter 'Stop Routing on Unallocated Number Flag'. Therefore, will never failover to next PRI gateway.

One way of resolving this is to change this service parameter which isn't recommended at all because it will cause failover for wrongly dialed numbers as well.

The second option is what I recommeded. What we will do is track the status of PRI and only shutdown SIP/H323 in case PRI is down. This will force CUCM to failover to next gateway.

[Mavis D]

Hmm! so putting 2 VG in a RG will not get what i am trying to achieve and i have to do addition config like either changing the service parameter or tracking the pri maybe using ip sla and then manually shut down the service.

[billfreitas]

Would "no dial-peer outbound status-check pots" achieve the same thing if the PRI goes down ?

[Michael Schmidt]

Hi Mohammed,

how can CUCM track or monitor the status of PRI on a H323 gateway.

I want configure a second gateway as hot-standby but without an ISDN link.

So calls should only be routed the the second VGW when the ISDN link is down at the first VGW.

When ISDN is up again at the first VGW the calls should be routed again via VGW1.

How can I configured this?

BR
Michael

[naser.jalouk]

https://community.cisco.com/t5/collaboration-voice-and-video/failover-sip-or-h323-trunk-based-on-isdn-status-on-voice/ba-p/3106706