home router battery backup

Jordan jnh at vt11.net
Mon Jan 17 22:39:25 UTC 2022

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?

> Mike


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