PoE standard (cisco ILP vs 802.3af)

[Kyujin Choi]

I have CCNP switch official guide book, page 306 says below.

For cisco ILP, inline power is provided over data pairs 2 and 3 (RJ45 1,2 and 3,6)

For 802.3af power can be supplied in the same fashion (1 2 3 6) or over paris 1 and 4 (RJ45 4,5 and 7,8)

Can you give me when those bold option is used in terms of PoE?

Thanks.

[William Bell]

I believe the 802.3af standard actually allows both pinout configurations.They are known as Mode A and Mode B.  Mode A uses the data pairs while Mode B uses the "spare" pairs. I have always been under the impression that Mode A would be what one would find on devices that terminate a connection. For example, a Cisco Catalyst switch that provides 802.3af power will use the Data Tx/Rx pairs (pins 1,2,3,6).  Further, my belief is that Mode B would be used by "mid-span" devices that insert power. For example, in-line power patch panels or in-line power injectors.  These panels use the "spare" pairs to carry DC power (pins 4,5,7,8).

The equipment that provides the power (i.e. the power sourcing equipment) determines which Mode (i.e. pins) is used. The powered device that is 802.3af compliant must be capable of supporting both modes.

Here is a quick reference chart:

https://supportforums.cisco.com/docs/DOC-10259

The chart doesn't directly answer your question, but you may find it handy as you are getting a feel for the material.

HTH.

Regards,
Bill

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