In a recent post at mgraves.org, Michael Graves observed that today’s POTS [plain old telephone service] analog equipment seldom runs just off the phone line power, as it used to. It needs “wall power.” And folks who claim that POTS is more reliable than VoIP because the power comes over the phone line are likely forgetting this, or remembering their Trimline from thirty years ago that did indeed run solely on phone line power and worked during an electricity outage.

The telco knew the importance of reliable phone service and set up large banks of batteries at the central office that would power the lines at all times. If the electricity is out, the phone is still up, because the wall or desk phone they leased you (or later, that you bought yourself) ran off that line power. When cordless phones, FAX machines, and other more advanced analog sets came out, many did not or could not run off of phone line power and now required AC electric power. This new requirement undermined the reliability that the telco had put in place long ago.

To keep your advanced analog equipment online during a power outage, now you’d need the telco’s batteries as well as local batteries–an uninterruptible power supply, or UPS. This is what we have in place for PSU VoIP.

Our “central office”–actually, the data centers where the VoIP servers, gateways and other core devices reside–are covered by large UPSes and diesel generators. Anything between the core and the endpoint (your phone) that requires electricity is also on a UPS, including the PoE switch to which your phone is connected. Thus, if the electricity goes out, your VoIP phone will still be online.

Whether you go with POTS or VoIP, you need batteries, somewhere, to keep your phone service alive.