home router battery backup

Michael Thomas mike at mtcc.com
Mon Jan 17 23:29:45 UTC 2022

On 1/17/22 2:39 PM, Jordan wrote:
> On Thu, Jan 13, 2022 at 02:06:39PM -0800, Michael Thomas wrote:
>> For my ISP, they maintain backup power for both DSL and POTS.  I
>> suspect that for a lot of DSL that would hold true because it's
>> relatively easy for them to power since they already have the
>> battery backup requirements for POTS.  The setup they have here
>> is a DSLAM and SIP->POTS termination in a pedestal with fiber
>> backhaul.  They use the old copper that used to go back to the CO
>> to power the pedestal.
> Do you happen to know what voltage is placed across the copper pairs
> for this purpose?  Maybe 130V like T1 span repeaters?  More?
> I used to have three POTS lines at home from BellSouth, before the
> AT&T acquisition, with DSL on one of them, all supposedly served
> from the same Lucent SLC.  One of these, the one originally used
> for DSL, would always go down for both voice and data when the SLC
> lost power-- no DC, no dialtone, no DSL, while the other two
> remained up.  Despite several claims of a resolution, this was
> never properly fixed, so eventually I just had them move DSL over
> to one of the unaffected lines.
> I could never understand what failure mode would result in losing
> just a single POTS line like this while the carrier equipment was
> running from battery, while others remained in service.
> Speculating, perhaps only the A or B-side was backed up, and an
> open diode or other defect caused a single ine card to draw only
> from the "other" source?  But, at this time (circa 2000) the remote
> DSLAM was definitely a separate piece of equipment, right, joined
> to a shared subscriber pair with passive splitters?

I have absolutely no idea, but if I had to guess it is the same voltage 
as the local loop but I suppose they could use ring voltage too.

Mike, definitely not a EE

More information about the NANOG mailing list