Typical last mile battery runtime (protecting against power cuts)

Jay Hennigan jay at west.net
Sat Feb 4 01:26:03 UTC 2023

On 2/3/23 06:11, Israel G. Lugo wrote:

> Question is, how much battery runtime can I typically expect from ISPs' 
> last mile infra.

See comments inline, this is my experience in the US. UK may be 
substantially different.

> People will have a random mix of DSL, FTTP, DOCSIS. Another alternative 
> is tethering with 4G.
> - For FTTP, I *think* (but am not sure) that the UK mostly uses PON, so 
> guess it would be runtime of OLT and onwards

This is likely to run indefinitely. OLTs are for the most part going to 
be in telco central offices and datacenters with reliable generator 
backup. PON outside plant covers long distances passively, not requiring 
any local power.

> - For DSL: runtime of DSLAM cabinet and onwards

If fed directly from the central office, indefinite. If fed from a 
remote terminal, maybe a couple of hours assuming that there are 
batteries installed at the terminal (and that the batteries are 

> - For CATV: CMTS and onwards, maybe any active equipments in the HFC to 
> the CPE?

DOCSIS/CATV is likely to go dark pretty much instantaneously on loss of 
local power unless your customer is very close to the HFC head-end. 
Outside cable plant is fed with AC power injected locally at power poles 
or at pedestals into the center conductor of the coaxial trunk line. 
This powers the trunk amplifiers and fiber-to-coax media converters. 
This isn't typically backed up at all. Cable companies figure that if 
the power is out nobody is watching TV or using the Internet. Sometimes 
there may be a small UPS but I wouldn't expect more than a few minutes 

In the case of prolonged outages I've occasionally seen a small Honda 
generator chained to a pole feeding one of the power injectors but this 
was very obviously a manual process done a while after the outage 
started where the power outage was localized and there were probably 
some VIP customers unaffected by the power outage.

> - For 4G: BSS and onwards

Cell sites typically have generator backup. Figure at least a day. A 
prolonged outage requiring refueling with weather making it difficult to 
get fuel to the site(s) could be a problem.

Jay Hennigan - jay at west.net
Network Engineering - CCIE #7880
503 897-8550 - WB6RDV

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