PoE, Comcast Modems, and Service Outages

Joe Greco jgreco at ns.sol.net
Tue Mar 29 21:46:07 UTC 2022

On Tue, Mar 29, 2022 at 03:42:54PM -0400, Josh Luthman wrote:
> There's a certain manufacturer of TDD radio where the CPU clock is at the
> same frequency as what Verizon's enodeB will transmit.  Even at miles away,
> it can and will cause PIM issues.  Again, don't rule it out.

I'm not ruling anything out, but on the flip side, here in this group 
of professional networkers, you'd think lots of people would have piped
up by now with "me too"'s if PoE ghosts killing cable CPE on a 24 hour
cycle were a common thing.

> Maybe he's just looking for a simple answer that 99% of callers will accept
> and it makes them happy.  When a customer of mine tells me they think it's
> something and I know it's off, I just let them believe in their statement.

I'm unclear on how this is making the caller happy.

I'm trying to envision under what circumstances a customer site that has
purchased PoE switches, presumably to power PoE gear, would be delighted
to hear that their not-directly-connected PoE gear would need to be
removed, presumably replaced, and then, what?  Run extension cords and
bricks to all the access points, IP phones, cameras, door terminals, 
and other PoE-powered gear?

> There's no reason to go after this tech and insult him, 

I'd agree it isn't sporting, but on the other hand, a poster here asked
for an evaluation.  I did not immediately blow it off, but instead
tossed out some thoughts for consideration.  Then blew it off.  But I
am still pondering the issue.

> all that's doing is making everyone miserable.

I am guessing lots of people laughed.  It's an El Reg grade tale of
woe.  I have to assume the poster who asked is frustrated but trying
to resolve a real issue.

So if you want the $100 test to eliminate PoE electrical effects, get
a pair of media converters and run fiber between them.  Put the CPE on
the far end.  Optimize as appropriate if you have SFP-capable switches.

... 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

More information about the NANOG mailing list