Strategies for high availability voice

For SMB’s who use a DSL/Cable line or other unmanaged public IP network to provide internet access, adding voip to the mix will require some thoughtful planning. Beyond bandwidth/QoS considerations, can you live with a voip provider or network outage? Because it’s gonna happen. SMB’s that need high availability won’t tolerate the loss of their phones during their normal hours.

Now, it would be best to have a redundant connection to the internet (DSL, Cable), dedicating one completely to voip, with a failover strategy to use the other if necessary. Even better would be to use a T1 with dedicated voice channels. But this isn’t always possible. So how does one go about making their voice system tolerant to the ups and downs of regular unmanaged DSL or Cable lines? One common method is to use both landline and voip. Yes that means keeping Bell around, but only using their cheapest possible dialtone service. With both, a properly designed voice system will leverage the high availability that POTS offers with the low cost and capacity of voip.

Here’s how it works. SMB’s will typically buy or keep one or two basic bell lines for their main number, which gives them network independent reliability & fax (there's nothing better). Then provision two multi-channel voip providers for incoming call rollover, simultaneous call capabilities, and better outgoing rates. Two voip providers are necessary, one serving as a primary, the second as a backup. The Bell side will provide a multi-path service with call forwarding on busy to the voip line setup. This allows multiple incoming calls and greater system capacity. Outgoing calls are routed based on lowest cost, with the outgoing voip callerID information set to display the main company number. Failover (a number where calls get routed in case you can’t reach the provider) for the primary voip provider is set to the backup provider. The backup provider’s failover is then set to cells, or another office.

The inbound call flow would look like this (POTS is the bell line, and voip providers are V1 (primary) & V2 (backup):

Inbound calls -> POTS -forward to-> V1. if unreachable, then -failover to-> V2. if unreachable, then -failover to-> Cells, Different Office, etc

Outbound call flow:

User dials outside number ->V1. if V1 unreachable, then V2. if V2 unreachable, then POTS -> PSTN

Under this scenario, if the primary voip provider goes south, calls will failover to the backup voip provider. And should happen seamlessly and transparently to both employees and inbound callers. If there is a total network outage, the voip failovers will cascade through the primary and secondary voip providers to cells, another office, or whatever number was assigned to the backup’s failover, and you’re still in business. None of this has yet touched the Bell line, so why keep it? It would be extremely rare to lose both voip & pots simultaneously. Incoming calls still originate from the Bell number and under a complete failure where the providers failovers fail, your business will still be able to take at least one call at a time. If you’re quick, or if it’s a prolonged outage, the Bell line forward on busy can be switched to cells or another office, giving you greater capacity.

Comments

[Jeff]

*NOTE: The comment below is a refugee from a previous iWeb hosted account.

Jeff K:
Good article. I implemented this exact scenario about a year ago and it is flawless.

I have dual wan coming in for fail-over, 4 POTS lines and 4 Voip providers provisioned at this location. This office enjoys fast cheap internet and great phone lines.
Sunday, May 3, 2009 - 11:37 AM