Power to DCE
I'm one of the quiet lurkers on this list and I'm sorry if what follows is
seen to be off the topic, but I'd like to contribute it for discussion as
it may add to what 802.3af is trying to do.
I work as Technical Director of Citylink a private "telco" in Wellington,
New Zealand. We operate a 50km fiber network where 50% of our business is a
metro network based on ethernet. We have something like 30 switches
distributed around the city and effectively sell ports to customers. It
happens that 15+ of our customers are ISPs so we are a high speed access
We also operate a distributed Internet Exchange with dual route servers, so
that both ISPs AND customers can peer with each other in a free traffic area.
A major thrust for us is to get speeds up and prices down. We regularly
extend cat-5 in buildings by installing a cheap hub in a riser powered off
We also have a device we make called a Network Interface Device (NID) that
is powered off the cat-5 and houses a hub or a switch and the fiber media
converter. This is generally pole mounted, so we use an external grade
cat-5 to deliver 10 or 100 mbps ethernet to low rise buildings. As I said,
the power comes from the customer. The more customers we get, the more
power available at the pole top. Power is also shared (with protection), so
that if one customer looses power his connection keeps running, but if
power is lost to the block, well they all loose their connections.
For your info, I've attached two photos.
00011011.jpg - is a photo of the power pack and the device we use for
inserting the power onto the cat-5. This is an early one that has one
outlet for the ethernet and one for a POTS phone line. We now use both
spare pairs for power. We also use 24vDC as I didn't like mucking around
with 48vdc when up a pole, swinging in the breeze. We regulate this down to
12v DC which is what all our component gear uses.
00040025.jpg - is a photo of a NID. This is one we developed 2 weeks ago.
It has an Apple Airport inside the NID with an 8 port hub and room for a
fiber interface. Baically this allows us to drop bandwidth to the top of a
pole from the wireless and feed it to homes using external cat-5. The hub
and the Airport are powered off the cat-5. Total load = 800mA.
Reading what you have been working on, I can confirm most of the figures. I
allow about 800mA per cat-5 feed and 24 vDC has given me enough power to do
most things. I don't put power down the signal lines as that would make
circuits non-standard, particularly at the customer end.
We also use the Cisco/Selsius phones, but only internally at this stage.
Being 12,000 miles away in the South Pacific makes support tricky. We would
really love to have a VoIP system that we could rely on enough to sell. You
can imagine the impact this would have on the local POTS market. (we have
200+ high rise buildings on the network so far).
I hope this helps your efforts, but please don't limit the discussion to
powering devices off hubs or switches, they also get powered off the cat-5.
Hope this is helpful,
PS now working on a Linux box with GbE incoming and 8x 10/100 outgoing -
pole mounted of course.
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