In our facility, an extended power failure would eventually deplete the battery backups on our switches and the data network will go down. We would still have dial tone. Dial tone is critical.
While most people would walk down the stairs and out of the building, the disabled do not have that choice. If they happened to get overlooked, how do they call for assistance when the network is down?
I have not seen much about the cost of building in redundancy to match the reliability provided by telephone companies. That cost appears to be tremendous. How would you make a business case to get the money?
In most larger organizations, a power failure will bring down the local PBX switch once the battery is drained as well, leading to telecommunications failure similar to that which you describe for VoIP. Therefore, most power failure implications are similar for both types of systems. One exception to this is a Centrex-type system, whereby the PBX is located at the telecommunication service provider's location, and the phones are powered via the phone jacks.
However, investments can be made for more resilience, and should be, as the issues you speak of are not unusual and can be critical. VoIP networks depend on power, so one of the ways to assure reliability in extended outages is via generator or large data center level battery backups. A second way is to purchase the VoIP solution as a hosted service, whereby the phone company maintains the equipment at their own facilities which have such power backup and generators. The weak link in this hosted VoIP system, though, is that often the phones require power, and so does the IP network which still needs to remain up and running.
This was first published in May 2005