Passive PoE options for SD49225T-HNI and other similar OEM models

[Left Coast Geek]

the 100m length for ethernet has nothing to do with PoE, it was baked into the frame timings back when things were 10Mbit on coax and twisted pair, and related to the round trip CSMA/CD (carrier sense multiple avoidance/collision detect) timing window and gap between ethernet packets. signals on a twisted pair or a coax cable travel at 60-70% or so of the speed of light, any signal takes about 500 nanoseconds to travel 100m, another 500 ns getting back with zero turnaround, at 10baseT speeds, thats about 10 bits round trip time, and all the ethernet protocol and packet timing is baked around this upper limit for round trip. When ethernet was upgraded to 100baseT then latter 1000baseT, the timings remain even though the datarates are now 100X faster (so that 1000ns round trip is now 1000 bits instead of 10).

(retired network and systems software engineer)

 

[Flintstone61]

we couldn't afford string that long.

 

[cctv-dave]

(retired network and systems software engineer)

Appreciate your input.
What I've noted from all these companies building extended ethernet is that they have reduced the timings so they are still within spec.
And importantly there is no higher latency over the longer connection (the extra 200m distance being covered by the signal in ns not ms so un-noticable), so live doesn't suffer either as some people who are anti-ePoE have a habit of claiming.