VOIP Phone - POE via Router

Hi All,

I am new to the VOIP technology through physical phones so think this will be the best place to clarify some of my queries. I am in the process of purchasing a Panasonic KT-UT123 SIP Voip Phone for home use(SIP Trunking). I have figured that this does not come with a power adaptor and is primarily to be used with POE. My question is
1) Can this phone be powered if the RJ45 cable is connected at the other end to a normal wireless router?
2) If no, then what else do we need to power this phone? Would a POE adaptor/injector help?
3) Can you please let me know some models of POE adaptor/injector that will fit this requirement. Also I am a little confused as to how the POE adaptor works but that can be understood once we clarify the initial questions. Thanks in advance!

As you don't have a PoE capable switch, you need a midspan power injector. These have two Ethernet ports and a power input. Broadband Buyer have several options - though other retailers are available.

The differences between the various models are whether or not they support Gigabit, also whether they support the newer high power 802.3ah standard.

The chances are that you need neither of these enhancements for your phone and a non Gigabit capable 802.3af injector will suffice. It's up to you whether to connect the injector at the phone end of the cable or the router end - as you have power at the router end, the router end will probably be neater.

Hi David,

Thanks for the reply. I have checked a few injectors on ebay/amazon etc but I am a bit confused about the AC power adapter part. None of these specify if they include an adapter or not rather some specify that the adapter needs to be bought separately. I dont understand the point of selling these without a power adpater since I believe it will not work without a power supply? If an AC power supply is mandatory, then are there generic power adapters available which would fit into these injectors? Would be greatful if you can point to some links on ebay for these. Thanks again!

There's two sorts of power over Ethernet - standards compliant (802.3af and 802.3ah) and proprietary. The proprietary solutions usually move the existing power supply to the other end of the cable, so may involve reusing the existing power supply. 802.3af and 802.3ah put 48V power over the Ethernet cable - I wouldn't expect people to have 48V power adaptors lying around.


Your phone uses 802.3af PoE, which means you need an 802.3af or 802.3ah power injector. 802.3ah sources are backwards compatible with 802.3af sinks.


All the 802.3af midspan injectors I've deployed are the sort with the mains power supply and the PoE injector in a single box, so you connect mains and two Ethernet cables. I'd expect any 802.3af injector needing a separate power supply to come with the power supply.

The Solwise Gigabit 802.3ah unit sold by Broadband Buyer is from a series resold by several brands, including HP. This is an "all-in-one" design, which I find neater to install.

Thanks David for the clarification. After a day of frantic research and support from good samaritans like you, I now have a much better idea of how these work. Guess I now have to find a cheap POE injector or a power adapter to work with the phone. One query.. if I plan to use a power adapter with the voip phone, does it make a difference if I use a generic 2.1mm X 5.5mm power adapter or do I need to specifically buy the Panasonic KX-A239 adapter recommended for this phone. Also anything specific related to voltage or watts that I need to notice would help. Thanks

You have two power options with your phone - a local power adapter that plugs in to the base of the phone (Panasonic KX-A239 or equivalent) or 802.3af / 802.3ah Power over Ethernet. I'm not sure the local power adapter is available in the UK, and it's arguable the messier option anyway - why have two cables going to the phone when you can get away with one?


Any good quality 802.3af or 802.3ah midspan power injector will suffice - that's the beauty of a standard. Any 802.3af compliant source should power any 802.3af compliant sink. How the injector hardware is powered is irrelevant, so long as it is powered correctly. As I said, I prefer the 'one box' injectors, where the mains power supply and the injector hardware itself is in the same box.

There's some cheap Chinese units on eBay - but I'd go for something a little more expensive to protect your fairly expensive phone. TP-LINK is probably the cheapest brand, but you have to be careful - not all their PoE injectors are 802.3af or 802.3ah types, and the reviews on Amazon indicate the quality may be a little suspect.

I pointed out the Solwise unit earlier in this thread, which is from a series rebadged by other brands including HP. If I wanted a single port midspan, that's what I'd buy. Connect the unit to the mains, the unpowered side to your switch (in your router, I presume) and the powered side to the phone. It doesn't matter whether the midspan goes at the router or the phone end - that's the beauty of PoE.


If you intend to buy more 802.3af devices, it may be worth buying an 8 port Gigabit PoE switch rather than a midspan injector.

http://www.amazon.co.uk/Panasonic-Power-Adapter-PQLV... is the PSU for the phone concerned, if you wanted to go that route.