Re: Mid-span ethernet monitor

On 6/8/2025 6:52 AM, Theo wrote:

Edward Rawde <invalid@invalid.invalid> wrote:

"Don Y" <blockedofcourse@foo.invalid> wrote in message news:1020c8h$2oq18$1@dont-email.me...

I need a device that can sit midspan (at a "splice point") and monitor
an ethernet connection for integrity.  At the very least, that continuity
exists to both ends of the span.
>
While these are PoE/PoE+ drops, I don't want to place any significant
burden on the PSEs; an external power supply is therefor likely.

>
In that case I'd just put an unmanaged four port non PoE switch at mid run
and look into getting access to the LEDs on the switch which tell me what
the link is doing.
The last design I did which had an ethernet port used KS8721BL

 Won't that prevent PoE passing through the link?  This switch will terminate
the PoE and won't pass power or PoE signalling through to the far end.

Yes.  And, the switch will have to signal to the PSE that it is present
in order to receive power (even if the PD is NOT) and then mimic the
state of the PD after the testing is complete.
An active solution also has to preserve transit times (or, at least
represent a constant delay across the switch for timing-sensitive
protocols)

I suppose you could have some kind of relay box that normally passes the
line through but interposes an ethernet switch (or something else) in the
middle for testing purposes.  When you're in test mode the PoE drops, but
maybe you don't mind that.  Or maybe you do a PoE receiver and PoE injector
to let PoE pass the tester switch.  Some switches can do pair tests:
https://www.engineerkhan.com/networking/testing-an-ethernet-cable-from-a-cisco-switch/

You're not just looking for a failed conductor/pair but, also, miswired pairs.
Using a switch (or even a 1-port router) means you expect the connections to
it to be correctly pinned.
It's a much simpler problem to solve if you assume someone "certified"
has made the changes.  However, that is often not the case (witness the
number of Code violations that you see licensed electricians making
in the name of expedience or economy; how careful do you think folks
will be with network drops?)

Don't know what a relay would do to signal integrity though.
(it probably has to be mechanical due to isolation requirements)
 Theo