* Alcatel offers distributed or centralized processing
Pushing voice over IP out to branch offices will eventually be required for enterprises to reap maximum ROI with the technology. In the spirit of some our recent newsletters that address giving branch-office and other remote users parity of network services, let’s take a look at the issues that arise in the voice world.
With most vendor IP telephony implementations, there is centralized intelligence in an IP PBX or cluster of IP PBXs in a headquarters office or data center. VoIP features are pushed out to distributed sites where voice-capable WAN access routers or IP phones contain some signaling capabilities that work in concert with the centralized IP phone switch(es).
A big draw is that you can centralize the processing and software feature upgrades so that capabilities downloaded to all the remote sites remain consistent. This prevents you from ending up with the hodge-podge of telephony equipment and software versions that happened in the TDM world. Plus, you don’t need to repeat the same capital investments at each site.
On the other hand, you have to rely on the WAN for your signaling. So what about disaster recovery?
The various vendors take different approaches. Most of them use some sort of fall-back capability to a local processor that serves as a redundant call processing “brain” to the central site. However, sometimes, the rich feature set of the IP PBX is lost and just basic connectivity is retained during this period. If you think a temporary loss of features would be disruptive, the question to ask your vendor is what IP PBX feature set is available in failover mode?
To address this issue, Alcatel last month added a “distributed intelligence” option to its centralized VoIP architecture that allows multiple locations to behave as a single entity, so one can take over for another in the case of a failure. This option requires a VoIP call processor module in the router at each site. In centralized mode, the Alcatel OmniPCX IP PBX at headquarters calls the router at the branch site to reestablish the signaling link.
As a lower-cost alternative, the company backs up its signaling link using the PSTN; the site that has been cut off dials an alternative gateway through the PSTN via a modem capability embedded in Alcatel local gateways and reestablishes the signaling over an alternative path, says Jeanne Bayerl, director of product marketing at Alcatel.
She advises that for supporting fewer than 50 to 60 users, it is most cost-effective to go with centralized processing. “The distributed-intelligence is the most reliable,” she says, for sites with 60 to 100 users at remote location. The added intelligence costs “a couple thousand dollars more – but when you divide it up among users, you’re not paying that much more for an extra processor out there.”
