Inline Power, POE or POE+ -- which do you need?

POE and POE+ are the standard, but if you can live with its limitations inline-power equipment is cheap.

Cisco Inline Power, POE, and the new POE+

While the IEEE was dragging its feet settling on 802.3af, Cisco and PowerDsine released their own lower power standards (3com used PowerDsine).  When the IEEE finally settled on its standard at 15.4w, it took Cisco a while to join the club but they ultimately relented and inline power devices are currently being phased out.   The incompatibility of inline power with GigE probably pushed them to switch as well (the inline power standard uses the unused 2 pairs in 10/100 for negotiation and delivery, while while GigE uses all four pairs so a different architecture had to be engineered).  Recently Cisco released its first few devices for the new, 30w POE+ standard.

Here’s a quick breakdown of the three different types of power over Ethernet:

Cisco Inline Power

·         Cisco-proprietary

·         10/100 only

·         7W/port

·         Incompatible with all non-Cisco devices that accept power over Ethernet

Examples of Cisco inline power only devices are:

CP-7940G/7960G, AIR-AP1231G-A-K9

802.3af PoE

·         IEEE standard

·         15.4W/port

·         Compatible with gigabit Ethernet

·         Not compatible in any way with Cisco inline power – the power negotiation process is completely different

·         Enough power for most IP phones and wireless access points from all manufacturers.

Examples of devices that accept both 802.3af and Cisco power:

CP-7941G/7961G, CP-7942G/7962G, AIR-AP1131AG-A-K9, AIR-AP1242AG-A-K9 (note that for Cisco power, the APs only work with the WS-C3550-24PWR)

Examples of devices that only accept 802.3af power:

CP-7945G/CP-7965G, CP-7941G-GE/7961G-GE, AIR-AP1142N-A-K9, WS-C2960PD-8TT-L (this switch is powered via PoE, and is not a power-providing switch)

The presence of a gigabit Ethernet port on a powered device is a clear indicator that the device is 802.3af only.

802.3at PoE+

·         Backwards compatible with 802.3af; PoE+ just adds an additional class of power to the 802.3af standard

·         30W/port

·         Relatively new; currently only Cisco is shipping PoE+ phones

Because of the relative newness of PoE+, few devices require this level of power.  Only the AIR-AP1252AG-A-K9 and the CP-8900/9900 phones require PoE+ in Cisco’s lineup.  In addition, a few 3rd party IP security cameras have been released that also need PoE+

If you are in the market for a VOIP phone system and the associated Cisco networking equipment, and if the decision is primarily about cost savings, the rapid rise of 802.3af has greatly reduced the value of inline power components.  CP-7960G phones coupled with WS-C3524PWR-XL-EN or WS-C3550-24PWR-SMI or a Cat6500 with 6348V blades can be had for a fraction of the price of newer 802.3af components – $15 to $25/port versus $100-150/port with newer equipment.

Also, it is interesting that Cisco (and Avaya) have yet to join their competitor’s efforts to provide guidance for the design of Unified Communications equipment ( As pointed out in this article, Cisco’s WebEx – and cloud based products in general – neatly avoid the interoperability issue and perhaps their reluctance to join is a gesture of support for that product line, or perhaps Cisco is musing over an attempt to set their own standards (a la inline power) now (with Tandberg) that they are in such a dominant position?

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