Typical last mile battery runtime (protecting against power cuts)

Mark Tinka mark at tinka.africa
Sat Feb 4 04:47:58 UTC 2023

On 2/3/23 19:25, Brian Turnbow via NANOG wrote:

> They have been discussing it here in Italy as well.
> The isp/telecommunication industry here is tryng to get Cos/pops/cabinets listed as critical infra and removed from rolling power cuts.

I would say plan for the worst, because there will always be some other 
department or governmental function that says they are more critical 
than the next one. And even if they may designate certain functions as 
critical, electrical distribution grids are not always built to that 
degree of granularity, and those critical functions are often caught in 
the crossfire as other non-critical loads are shed from the network.

And even after all that, if the blackouts need to intensify, all bets 
are off, since the main purpose then becomes preventing grid frequency 
drop, rather than servicing loads.

> Here this is mainly ran from pops that have ups and generator systems so several hours to days of uptime depending on site.

If major data centres need to spend more on fuel than they planned for, 
I'd suggest making a generous allocation for an increase in co-lo costs 
for your next budget cycle, as the data centres will, invariably, pass 
those costs on the longer the city has to shed power from the grid.

> OTOH I have seen providers daisy chain customer sites in a ring that crash miserably when 2 customers loose power isolating all in between sites.
> But that is not the norm...

This is one of the reasons we refuse to turn customer sites into Metro-E 
PoP's, or PoP's of any kind.

> Street cabinets for fttc services here have low times if any.
> Same thing for mini dslams mounted on poles in the middle of nowhere.
> 0 to 2 hours for these.
> Most have batteries/capacitors in the cabinet but not all and they are not designed for extended power outages 2 hours max.
> Some are remotely powered from the CO, but that does not seem to be a thing anymore. Too costly
> DSL ran from COs are protected as for fiber above.

A lot of this will be driven by what competitors do. If there is no 
competition that can keep their street cabinets going, the others won't. 
It's a great opportunity for anyone willing to make lemonade out of the 

> Don't operate a 4g network, so take this info accordingly ,  but here it depends on the tower from what I have seen.
> All towers I have seen have  battery backup , a lot have generators too.
> I would say they have higher times than the fttc times above.

In dense metro's, mobile sites will be well invested. It starts to get 
tricky when you go out into the sticks.

Also, when the power goes out, so does the wi-fi. That means everybody 
moves their traffic away from the home wi-fi and on to the nearest cell 
tower. While radio bandwidth and signal coverage does not suffer that 
much, it hits the backhaul hard, between the tower and the mobile 
carrier's core. So nice flashing LTE/4G/5G signals on your phone 
translates to GPRS-esque performance. In some cases, we have seen mobile 
operators downgrade radio coverage to 3G, in order to manage this. Who 
knew 3G performed a bad as GPRS or EDGE, in 2023 :-)?

In the most extreme of case, the cell site could run out of power as 
well, as there isn't enough time for the batteries to recharge between 
outage cycles, or the field teams can't replenish fuel for the 
generators in time.

In the absolutely extreme cases (as we see here in South Africa, for 
example), cell sites can be raided and batteries stolen, especially if 
there is darkness all around. I would not expect this to be the case in 
the UK, especially if power outages are not the norm and people live a 
fairly middle-class life, but if I were Vodafone, for example, I'd have 
my risk department planning for such an eventuality already.


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