Power over Ethernet questions.

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Why use PoE ?

There are a number of reason why you would use PoE, but in most cases the overriding reason is cost.

It can cost between $100 and $200 to run an ethernet cable to a wireless access point. But it can cost a further $400 to run an electrical conduit to power that access point.

The alternative is to install Power Sourcing Equipment (PSE) called Endspan Equipment into the ethernet switch, or by adding Midspan Power Insertion Equipment after the ethernet switch. This will combine the data and power at the source to be sent through the ethernet cable. The power from the cable can then be extracted at the endpoint with a Powered Device (PD) to operate the access point.

This solution removes the need to run expensive electrical conduit and will cost considerably less than $400.

Is there a PoE Standard ?

Yes, the Institute of Electrical Electronics Engineers (IEEE) 802.3af Task Force has ratified the technology into the Ethernet standard. The IEEE 802.3af standard covers the interoperability of using PoE products and covers the PSE - Endspan or Midspan, the Powered Device (PD) and the cabling requirements. It is endorsed by all network players that power IP-connected devices, such as voice-over-IP (VoIP) phones, wireless LAN (WLAN) access points (APs) and advanced security devices, over the existing Ethernet cabling infrastructure.

How is the power put onto the ethernet cable ?

The power can be added to the ethernet cable if the switch has a built-in power source in the form of PSE is called Endspan Equipment. Alternatively the power can be added to the cable after the switch by using a PSE called Midspan Equipment.

How is the power extracted from the cable ?

To extract the power from the cable the connected device needs to be a Powered Device (PD) such as the Isonas IP reader.