Is IEEE 802.3af PoE truly downwards compatible?
When I learn of cables that carry mixed analog-digital signals, I tend to be cautious, to say the least. Take for instance DSL, a technology that I am currently using for the first time ever. At its inception, tears ago, when a read that they were planning to send the Internet digital signal in the same conductor as the regular old-fashioned POTS, I was pretty skeptical. And, sure enough, my DSL breaks and the POTS phone stops working every once in a while.
Anyway, my question is about PoE. The latest Ethernet (1GB) uses all 8 conductors of the RJ-45 cable. They somehow manage to modulate the digital signal on top of it (which conductors are used for DC?). Does it *really* work? What happens to some Ethernet devices that were manufatured before PoE? Won't they break?
Hmm, perhaps PoE is strictly 10baseT and 100baseT standard? That way they can send the DC through the unused conductors.
Thanks for your insight.
-Ramon
read more and respond »Posted 5 years ago by Ramon F Herrera in Cisco Systems
