How to use Standard 802.3af POE Injectors w/ Cisco 7940/60
It was recently brought up on the IRC channel that the 7940 and 60
phones from Cisco do not support the 802.3af Power Over Ethernet
standard. At first, I didn't believe it, so I grabbed a 7960 and
tried it with a standard 3COM POE injector and found it to be true.
Only the 79xx G models support 802.3af.
But hope is not lost! Denon suggested that they would work if you
simply reversed the polarity of 2 of the pairs of wire. He said
that by swapping 4 with 7, and 5 with 8 you could use a standard
POE injector to power the phone.
Since I had a crimp tool and some cable laying around, I gave it
a whirl and it works. If you aren't familiar with making cable,
don't try this at home.
Basically, you just wire one side of the cable as standard 568b
and then reverse 4 and 7, and 5 and 8 on the other side. Then,
simply plug your Cisco into a standard POE injector, like the
3CNJPSE ($23.00) and voila! Your phone works.
I've included color mappings for convenience, and you can
reference the following fine site for pretty pictures:
http://www.lanshack.com/make-cat5E.asp
Damin's POE Cable
568b
----
1 OrWh
2 Or
3 GrWh
4 Bl
5 WhBl
6 Gr
7 BrWh
8 Br
Cisco Side
----------
1 OrWh
2 Or
3 GrWh
4 BrWh
5 Br
6 Gr
7 Bl
8 WhBl
P.S. This hasn't blown up my 7960 yet, but I'm not an electrical
engineer,
therefore, use at your own risk and I am DEFINITELY not responsible if you
flip the wrong pairs and turn your unit into a smoking pile of rubble. If
you are that concerned and/or inexperienced with making cables, look on
Ebay and get a used Cisco POE injector, or Power supply. They are
relatively cheap nowadays.
Revised: 2/26/2004 - GJB
--
Vice President of N2Net, a New Age Consulting Service, Inc. Company
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