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VOIP - Mid-Call Failover To PSTN??

I could have edited the following post (which I made to another forum) to be more politically (Cisco) correct, but I'm sure you will understand our requirements:

Can anyone suggest any VOIP products which will carryout mid-call failover to PSTN should the IP network fail?

OK here is the scenario. We are looking to deploy VOIP (Cisco CCM) across two resilient MPLS clouds (dynamic routing using OSPF and BGP within the MPLS clouds). The VOIP would be supporting up to 240 concurrent calls across the MPLS network.

The problem we have is that we want to be able (assured) that should a problem occurr on the MPLS network, any in progress calls can be automatically transfered, mid-call to the other resilient MPLS network or on to the PSTN.

Due to the nature of the MPLS networks and the routing protocols used (OSPF & BGP), if we have a failure on one MPLS network, the resilient, diverserve network will automatically take over, however this incurs about a 20 to 30 second reconvergence of the network. Whilst this is fine for data traffic, voice traffic will suffer a 20 to 30 second outage, which, from the user experience is unacceptable.

We have looked at products such as the Quintum, Tenor multi-path switch ( which almost matches our needs, by managing to failover mid-call should the MPLS network become congested, but it still incurs a delay if there is a total failure of one of the MPLS networks.

What we are looking for are looking for a is a product that will seamlessly failover VOIP calls, mid-call with the smallest amount of impact on the user experience. i.e. no or little interruption of service.

We have investigated the Cisco solutions, but from what we understand, even these will experience a 20 - 30 second outage.

So does anyone have any suggestions? Any input greatly appreciated.


Re: VOIP - Mid-Call Failover To PSTN??

End-to-End convergence in a MPLS-VPN network can be reduced to less than 10 seconds by judiciously tuning the various timers. This depends a lot on the physical topology of the MPLS Core network, links in the core MPLS network, PE-CE connectivity, PE-CE routing protocol etc etc. The convergence can be even reduced to 10 seconds if the OPSF timers are tuned more aggressively.

In the case that you describe, the CCM is connected to two MPLS-VPN clouds and the switch-over has to occur between two MPLS-VPN clouds. The time to switch over between them depends on how the CCM is connected to the two MPLS-VPN clouds.

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