PoE, Comcast Modems, and Service Outages

Joe Greco jgreco at ns.sol.net
Wed Mar 30 19:57:59 UTC 2022

On Wed, Mar 30, 2022 at 05:52:06PM +0000, Livingood, Jason wrote:
> >  Their crappy equipment needing rebooting every few weeks, not ridiculous.
> > Their purchasing gear from incompetent vendors who cannot be standards
>     compliant for PoE PD negotiation, tragically plausible.
> Many customers buy their own cable modem. You can lease an Xfinity 
> device as well and those function pretty nicely these days but YMMV. 
> But typically a device reboot is a way to quickly solve a few 
> different kinds of problems, which is why techs will often recommend 
> it as an initial step (you can generally assume that there's data 
> behind what occurs when any one of tens of thousands of support reps 
> suggesting something to a customer - support at scale is data-driven).

No one's doubting all of that -- support is best when data-driven, scale
or otherwise.  But that's actually the issue here.  There's no data that
I know of to suggest widespread PoE ghost current buildups, and, given
the audience here, no one else has popped up with a clear "me too".

PoE is typically negotiated by modern switches, 24v Unifi special
jobbies aside, so it's all DC on cables that are already handling
differential signalling.

> >    He's got graphs showing it every 24 hours?  Liar, liar, pants on fire,
>     lazy SOB is looking for an excuse to clear you off the line.
> Could well be from noise ingress - lots of work goes into finding & 
> fixing ingress issues. Hard to say unless we look in detail at the 
> connection in question and the neighborhood node.

No doubt.  There's huge amounts of room for problems to be introduced
into last mile networks.  But, again, this isn't about general problems.
This is about a tech claiming it's due to PoE, and that he's seen it
often before.

I certainly have a lot of sympathy for cable techs, but that doesn't
mean I want to swallow any random garbage they want to blame issues on.
Please just tell me it's the chipmunks getting feisty and nibbling on
the copper if you want to feed me a line...

... JG
Joe Greco - sol.net Network Services - Milwaukee, WI - http://www.sol.net
"The strain of anti-intellectualism has been a constant thread winding its way
through our political and cultural life, nurtured by the false notion that
democracy means that 'my ignorance is just as good as your knowledge.'"-Asimov

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