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Power Considerations

One of the great things about the traditional PSTN is that it keeps working when the power goes out. I've repeatedly read articles recommending that people sustain traditional POTS service, at least in part because of this fact. Their theory being that VOIP service isn't sustained during a power outage. But this need not be the case, given just a little forethought.

Prior to migrating to Asterisk, we had been using a Panasonic KX-TG4000 KSU (below). This phone system has four FXO interfaces for analog lines.


Panasonic KX-TG4000B
Panasonic KX-TG4000B KSU with built-in battery backup

It also features a built-in battery backup so our phones stay up through power outages. In migrating to VOIP within our home and office, I felt it necessary to strive for this kind of reliability. It has certainly made my wife happier.

There are a number of factors involved in my consideration of power for the phone system as a whole.

Asterisk Servers

I have long been a believer in embedded systems and my Asterisk servers reflect this fact. During my initial experimentation with Asterisk, I ran it on traditional PC hardware. But eventually I migrated to a mini-itx system, and then later to embedded systems like the Soekris Net 4801 and HP T5700 thin clients.

HP T5700 Thin Client
Rear view of a H-P T5700 Thin Client

The embedded systems offer a number of advantages, but two of the biggest are low noise and low power consumption. Both of the embedded platforms mentioned draw less than twelve watts. That means that they can be kept running a long time from a relatively low cost UPS.

Along with low power consumption comes the added benefit of low heat output. This can be important if you lose power and your air conditioner stops running. Living in South Texas when the AC unit stops, the whole place can heat up quickly.

UPS Power For Network Components

Various key network devices also need to be on UPS power. In my case this includes:

  • DSL modem
  • Router
  • Netgear 24 port gigabit switch
  • Power over Ethernet insertion devices
  • Wifi access point
  • Charging cradle for Aastra cordless handset

I recommend that you keep your phones and network components on their own UPS. All of the devices listed have very low power requirements. This means that an inexpensive UPS (1500 KVA, approx. $120) can keep the entire network running for a good long while.

My office is actually in what some people would call the "Garage Apartment". I prefer to think of it as the "Carriage House" or "Executive Suite". There are a couple of underground CAT 5 runs from the office to the house, so it's all one network.

There is a small networking cabinet in the house that contains a 16 port switch and a Linksys ATA for the home phones. This gear needs to stay powered up 24/7 /365 so I also had to provide a second, smaller UPS (700 KVA) in the house.

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