UPoE "four-pair" not on spare pairs

[peter.w.ma]

I have the following setup:

- WS-C3560X-24U-S (with C3KX-PWR-1100WAC)

- Version: 15.0(2)EZ / C3560E-UNIVERSALK9-M

- C3KX-PWR-715WAC

I am trying to source power to a PD (internal custom design) that does not support CDP nor LLDP, but does support 802.3at Type 4.  My goal is to source at least 50W, which implies the need for 4-pair "UPOE".

As expected, the switch reports Type 4 and does provide power.  I measure 56VDC across the data pairs, and about 0.8VDC across "spare" pairs.

I configure a few ports as follows (still at experimental stage of things):

no cdp run

no lldp run

interface range GigabitEthernet0/1 -4

power inline consumption 60000

power inline four-pair forced

shut

no shut

Despite the "four-pair forced", I still see just 0.8VDC across the "spare" pairs.

Tried to save the config and reload, with the same result.

Any pointers would be greatly appreciated.  Thanks.

[Philip D'Ath]

Have you seen the Cisco PoE adaptors?  You plug them into the cable, and they give you plan simple DC out?

[Philip D'Ath]

Bummer, there are some caveats with using this module.  I don't think it supports your switch above.  The part number was WS-UPOE-12VPSPL.

http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4500/hardware/configuration/notes/OL_25751.pdf

[Philip D'Ath]

Perhaps it will work.

http://www.cisco.com/c/en/us/products/collateral/switches/catalyst-4500-series-switches/white_paper_c11-670993.html

This mentions the 3560 and using "forced" mode.  Search for "Splitter".

[peter.w.ma]

Thanks, Philip...

I am designing my own set of PDs for a very tightly-spaced application.  Having an external splitter box on every ethernet link would not be feasible.  And quite tragic actually, considering what PoE is for!

Whatever the case, the original question remains:  why is the 3560-X with "four-pair forced" not actually forcing power onto all four pairs?

[Philip D'Ath]

What about buying one of these splitters and ripping it apart to see how it works?  It must be doing something to make that same four pair mode work.

I bet it is doing something tricky like creative a resistive and/or capacitive load between two wires to tell the switch to start supplying power.

[peter.w.ma]

:-)  I had just submitted a quote request for one.  Was thinking the exact same thing,when I noticed that there is an LED that indicates when "four-pair forced" in activated.  Presumably it detects when four pairs are powered.

I have an eval board from Microsemi that is supposedly UPoE compatible, and it definitely is not seeing power on the spare pair.  Can get up to 43W through the data pair -- before the switch's Imax cuts out.

[Paul Chapman]

Hi Peter and Philip -

I noticed a caveat in the link Philip sent stating the following:

UPOE uses the same CDP and LLDP power negotiation mechanism and algorithms for inline power negotiation with an extended range of allowing requests up to 60W contingent on PSE hardware capability and power budget. With UPOE, we introduce a new CDP and LLDP TLV to accommodate the 4-pair PoE functionality. It is mandatory for any PD requiring 4-pair PoE functionality to implement at least these CDP/LLDP TLVs and have them enabled administratively or by default.

It would appear that CDP/LLDP is mandatory for the 4-pair option to work.

PSC

[peter.w.ma]

From the Software Config Guide 15.0(2)SE - Configuring Interface Characteristics - UPOE:

If the enddevice is PoE-capable on both signal and spare pairs but does not support the CDP or LLDP extensions required for UPoE, a 4-pair forced mode configuration automatically enables power on both signal and spare pairs from the switch port.

To enable the power on the pairs, follow these steps:

	Command	Purpose
Step 1	interface terminal	Changes the mode to global configuration.
Step 2	interface { fastethernet | gigabitethernet } slot/port	Selects the interface to configure.
Step 3	[no] power inline four-pair forced	Automatically enables or disables power on both signal and spare pairs from a switch port.
Step 4	end	Exits configuration mode.

The following example shows how to automatically enable power on both signal and spare pairs from switch port Gigabit Ethernet 2/1:

Switch# configure terminal

Enter configuration commands, one per line. End with CNTL/Z.

Switch(config)# interface gigabitethernet 2/1

Switch(config-if)# power inline four-pair forced

Switch(config-if)# end

Do not enter this command if the enddevice cannot source inline power on the spare pair or if the enddevice supports the CDP or LLDP extensions for UPoE.

This leads me to believe that one can achieve 4-pair power, even without CDP/LLDP.  It appears that is the very reason for the "four-fair forced" command.  So this is my conundrum.