As I understand 802.3af, the phones go through a negotiation with the
unit supplying the power. I don't think it's a matter of -48VDC on a
particular pair. I remember a schematic from years ago--it had each of
the receive pair and the transmit pair going into a transformer winding,
and that winding had a center tap for PoE. This is not something that
*I* am going to screw with.
The IP501 telephone set is the same for both PoE and local power. With
the PoE cable, the 802.3af electronics (the negotiator) is a plastic
thing in the cable. For the local power, there is a plastic thingie
toward the wall end of the cable, and you plug the wall wart into the
plastic thingie. <Notice the advanced technical jargon here>
With local power, there is still only one cable one the desk--the power
plugs into the cable towards the wall. Except for a power interruption,
this has all the advantages of PoE.
William M Conlon wrote:
I saw that Polycom offered a cable (not stocked anywhere), at $40 a pop
for 802.3af connections. That's what made me think the phone itself is
NOT 802.3af compliant.
Presumably, for $40, there's more than a fuse in that special cable.
On Mar 5, 2006, at 4:31 PM, Paul Hales wrote:
For Polycom IP500/501's and IP300/301's you need a special polycom POE
cable.
When you buy Polycom phones you can usually specify POE or powerpack.
PaulH
On Sun, 2006-03-05 at 16:23 -0800, William M Conlon wrote:
When I bought two Polycom 501 SIP phones, I naively thought they were
Power-over-Ethernet (IEEE 802.3af) because they were "powered over
ethernet." Silly me.
Polycom must have some odd voltage or funny way of injecting the
power, because the POE switch I bought for them (Netgear [EMAIL PROTECTED])
won't power them, though if I use the Polycom-supplied AC adapter and
ethernet power injector cable, they work with the switch in either
its powered or unpowered ports.
Anyhow, I hadn't seen any mention of how people power these phones,
as I had planned on centralizing phone power on a UPS to supply my
Asterisk server and POE switch. Now the question is:
Can the Polycom AC-powered injector be used with a standard ethernet
patch cable:
switch :: Polycom injector cable :: RJ45 coupler :: patch cable ::
Polycom 501
which would allow me to power the Polycom AC adapters by my UPS. Or
do I need to provide a UPS at each phone and run the ethernet like
switch :: patch cable :: RJ45 coupler :: Polycom injector cable ::
Polycom 501
thanks.
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Bill
William M. Conlon, P.E., Ph.D.
To the Point
345 California Avenue Suite 2
Palo Alto, CA 94306
vox: 650.327.2175 (direct)
fax: 650.329.8335
mobile: 650.906.9929
e-mail: mailto:[EMAIL PROTECTED]
web: http://www.tothept.com
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--
Michael Welter
Telecom Matters Corp.
Denver, Colorado US
+1.303.414.4980
[EMAIL PROTECTED]
www.TelecomMatters.net
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