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PoE Switch does not Power Up IP Phone

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Article ID: 11385

Matrix N-Series DFE
SecureStack C3, C2, B3, B2, A2

Attached an IP Phone (for example, Siemens Optipoint 4000) to a "
"-suffixed unit of one of the above-stated product lines, using an 8-conductor UTP cable.

The host unit's Power over Ethernet (PoE) is not powering up the phone, though both devices support PowerDsine pre-802.3af-standard power detection.

The IP Phone PoE client is one example of a pre-802.3af-standard device which uses the spare pairs (4-5 / 7-8) for power.

The above-stated Enterasys products use the data pairs (1-2 / 3-6) to supply power, as do most modern-day switches.

The 802.3af standard states that the device receiving power should be able to receive power using either method. The IP Phone doesn't support this as it is pre-standard.

The Enterasys products do have a PoE detection mode capability (default = '
set inlinepower detectionmode auto
') to accommodate both the 802.3af-standard "Resistive" method and the pre-standard "Capacitive" method (9872). But since this has nothing to do with which pairs are used to provide power, it will not correct the described incompatibility.

Functions as Designed (FAD).

Workaround: Use a pre-standard mid-span PoE source, or an external power supply, for the IP Phone.

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