I live in an apartment building in Czech Republic, Europe. I have a cable internet connection with a static IP connected to an Ubuntu server I set up. Recently out building lost power, though the elevators and emergency lights continues functioning on some secondary emergency power supply.

I was thinking of buying an UPS unit to keep my cable modem, router, and MiniITX Ubuntu server running during a power outage. I know that when I lived in the US, telephone(edit-removed: /DSL) connections will continue to function because they have their own power source.

So, if I hooked up a UPS, would my connection remain alive? Or do cable internet connections rely on repeaters/signal boosters/etc. which use the local power source?

  • 2
    correction, in the US, POTS telephones still work because they're powered by the telco's equipment. wireless phones & consumer DSL modems are powered by the location's power, so they won't function during a power outage without battery/generator backup. Oct 22 '09 at 19:25

It is impossible for any of us to say.

I have seen some places that have batteries in the cabinets, some that are powered from the exchange and some with no backup power what so ever.

Without actually seeing it, I doubt you will be able to find out.

If it is a small apartment, a solution may be to talk to the person in charge and ask to take a look at the cabinet - or even offer to pay for a UPS for it, but short of this, I doubt anyone else will be able to tell you.


I had this setup. UPS power on computers, switch, router, and modem. When power went out, I would still lose Internet connection even though everything was on backup power. This was likely something on the ISP's side that lost power also.

I believe the only way to maintain power is if your internet provider had backup power on every router, repeater, and equipment involved in getting connection to your residence. This will vary will every location and company. No way to say yes or no for sure until you try it or ask your internet company about it.


This discussion might be useful to understand how the CMTS and your Cable Modem get powered.


My local cable co (back in the day when I had broadband) had about a 1 hour battery backup in their cabinet. A little frustrating since our typical power outage lasts 2-3 hours and my home batteries last around 4 hours! My servers would stay up and running, but the cable co was down!


I'm not sure about a building in the Czech Republic but I can provide some information on what happens in the US. Here, the answer depends on the scenario.

  1. A local outage in your immediate area.

You will only lose power to devices that you don't have on backup. There are very few active devices along an hfc line. The most notable is one that converts the fiber to coax, but this is powered and has a battery backup.

  1. A outage that effects your local CMTS and local distribution center
  2. City wide power outage
  3. State wide outage

Because people who sign up for digital voice are using this service (or could potentially use this service) as a lifeline, ISPs are under the same voice regulations as your typical lec. The gear must stay up for certain periods of time and be under repair SLAs for uptime. I'm fairly certain that the holdout would be the battery in the EMTA unit, as this lasts for ~8-12 standby hours, a timeframe that surpasses the lengths of most outages. Each of the components that deals with phone (similar to the "co" of a lec) is on generator to ensure uptime. These "co's" may or may not include CMTS hardware (though it would make sense that they would).

An important point here is that the CMTS units are not located in every neighborhood. These units more than likely serve several thousand customers (depending on the units involved, uplink and backplane capacity, and desired oversubscription ratio). More than likely, there are one or more cmts units centrally located to an area. I can't say for certain how your local ISP handles their unit placement, as i am unaware of the CMTS hardware and fiber routes being used. Since these units can be remote to the neighborhood, it is much easier to provide backup generation for each unit. However, I am unsure of the uptime of these units and if they are involved in digital voice. The CMTS may pass the digital voice frequency to a dedicated pbx (similar to a dslam/pbx relationship for dsl) or the CMTS may process the signal then downlink to a pbx for voice routing.

Answer compiled from here: http://www.dslreports.com/forum/r23030874-

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