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The POWER of PoE

There are some who believe it could be the best business opportunity for ITS professionals since the emergence of 10BASE-T hubs in the 1980s.

March 1, 2006  

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While travelling to a BICSI education seminar in Prague last year, I was suddenly taken aback by how many mains (power) adapter plugs I was carrying.

AC mains to DC adapter plugs for mobile phone, digital camera and PDA plus the AC/DC unit for my laptop.

In addition to these I also had several mains plug/socket converters to cater to the array of mains plugs/sockets used throughout Europe.

In total I had several kilograms of these devices, which took up a considerable volume of my luggage. My mobile phone and its mains adapter plug was the heaviest of the group, weighing in at 98 grams for the phone and 332 grams for the mains adapter plug, for a total of 430 grams.

Until I saw those figures, I had always thought we had come a long way with miniaturization of the mobile phone since the first one was introduced 21 years ago.

So as you can imagine discovering Power over Ethernet (PoE) was a eureka moment for me because at last I could see the light at the end of the tunnel — a plastics and copper recycling factory full to the brim with mains transformer plugs!

With Internet protocol (IP) convergence and the fact that many of the electronic devices we use today consume less than 15 watts of power requiring a DC input, PoE is truly the universal power socket.

Already, I hear the cynics sneer as they respond that their laptop PC requires more than 15 watts. However, I believe that will soon change.

Already, an innovative British company has now produced a desktop PC that requires only a dozen watts, taking all its power via the RJ45 work area socket using PoE. To capture the devices that will still require more than 15 watts, PoE is rapidly moving up the power and network speed levels.

Today one can purchase devices that pass Gigabit and support 37 watts power forwarding. And, an IEEE standard already addresses PoE issues: IEEE802.3af, IEEE Standard for Information Technology — Telecommunications and Information Exchange Between Systems — Local and Metropolitan Area Network –Specific Requirements — Part 3:Carrier Sense Multiple access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications — Data Terminal equipment (DTE) Power via Media Dependent Interface (MDI), defines building Ethernet end-span and mid-span power sourcing equipment and powered terminals.

This specification involves delivering 48 volts of direct current over unshielded twisted-pair cable.

It works with existing Category 3, 5, 5e or 6 cable, horizontal and patch cables, patch panels and standard connecting hardware, without requiring modification. There is a detection mechanism within the power sourcing equipment that authenticates compliant devices.

Only equipment that identifies with a PoE signature will receive power, preventing damage to non-compliant devices

PoE will transform the office of the future. In the next two to five years, I predict that all structured cabling work area outlets will be equipped with a “live” PoE port.

To put things into perspective. imagine today calling in the electrician to install a patch cable in the fuse panel each time you wish to use a mains power socket.

A practice of making mains sockets live on an ad-hoc basis would be considered ridiculous, yet we currently accept similar situations in ITS with the RJ45 socket.

In a few years we will look back at today’s practice of calling in the ITS technician to install a patch cable in the telecommunications room (TR) to make the work area RJ45 outlet live, and say how ridiculous our ITS practices were then.

From experience at a recent seminar, I know that this “all live” concept for ITS outlets is going to upset those professionals whose business includes making moves, adds and changes (MACs) on patch cables in TRs, but eventually all prehistoric and inefficient practices will eventually disappear. It’s better to be prepared for change.

When ITS professionals start providing PoE to all work area drops in two-five years’ time, they may be faced with a significant problem of how to interface the drops onto the PoE devices in the floor serving the TRs.

This is a physical space problem that designers must consider when they are creating today’s structured cabling system solutions, which will eventually be used for PoE. Today, approximately 25-50% of the drops are made live with Ethernet — how does a designer interface for a future use of 100% of the drops? Let’s look at some numbers:

TRs in future commercial offices–“all-live” PoE drops

Assume TR serves 100 work areas (maximum recommended in TDMM)

* 400 total drops feeding into TR (This will not decrease since they will replace the traditional mains power socket and the transformer plug.)

* All drops will be live; therefore total number of active drops is 400.

So the problem is how does a designer interface onto 400 active PoE ports in the future? But first if all drops are live we can provide a one-to-one relationship of active port to work area drop.

This will eliminate the requirement for physical layer management. Why then is the flexibility afforded by RJ45 equipment/patch cords necessary? There are much better ways to interface active ports to drops than using RJ45 interfacing e.g. RJ21 and new forms of this interface.

LAN switch manufacturers are now releasing high density PoE modules that can support 96 ports per module/blade using RJ21. The best port count available for an RJ45 blade is 48 and new interfaces on the market today allow a single LAN switchblade to support 192 ports.

Another benefit to using the RJ121 is the cost per port drops because of reduction in power supplies and management/ supervisor modules. When you do the math, you’ll be pleasantly surprised with the cost savings on the LAN switching elements, and remember to add the ongoing savings for MACs in the TR.

This leads to the question why terminate user cable drops onto RJ45 patch panels? My prediction is that the RJ45 interface will disappear from TRs in large office installations within the next five years, and new PoE products minus RJ45 will enter the market.

Endless Benefits

Today there are more than 200 devices that work with PoE, including pan tilt zoom security cameras, wireless access points, VoIP telephones, industrial devices, access control, electric razors, lighting controllers, clocks and audio speakers.

The PoE standards body (IEEE 802.3af) is currently investigating boosting the power levels to above 50 watts, which will drive us even faster towards the world of IP and convergence over Ethernet.

When implementing wireless LAN access points and other devices thousands of dollars can be saved by providing mains power wiring to the powered device by using PoE switches in the TR.

Another benefit is that PoE switches are most likely to be protected by the TR’s uninterruptible power supply (UPS), and not many wireless access points fed directly with mains power are protected with a UPS supply.

If you are currently using your office LAN to provide VoIP, then you are probably already using PoE to power your VoIP phone, which will have a power requirement of four to seven watts.

Next time you see the lights flash on your VoIP phone, remind yourself where the power come from, and think of PoE and my bag of mains transformers plugs banging against my legs as I walk through airports.

John Laban, RCDD, is Technical Director of Annor, Ltd., a U.K.-based firm providing structured cabling design and installation services. He is also the former BICSI European Region Director and may be reached at The following article appeared in a past issue of BICSI News.