11/29/2009 06:58:49 PM

Many organizations conduct a site survey prior to deploying Wireless LANs in a facility, and often discover the most appropriate access point placement is a location where they cannot provide power. Since WLAN access points must typically connect to a wired network using CAT-5, an obvious technology solution for such circumstances is to provide electrical power of the Ethernet cabling to the access point. The IEEE is developing just such a standard for Power over Ethernet, POE, and pre-standard products are available from many vendors.

POE solves the problem, “when you can’t reach power, use CAT-5 to deliver it”. POE helps make wireless deployment in enterprise facilities a slam dunk. Residential deployment of wireless, however, isn’t always a slam dunk, and POE isn’t likely to solve the problem. Some homes are simply radio frequency (RF)-challenged.

RF-Challenged Homes

What factors contribute to making a home RF-challenged. Let’s begin with expense. Enterprises will commonly use industrial grade access point technology: better radios, stronger antenna, adjustable power offer better coverage than consumer products. This is only one of a number of reasons why an enterprise AP is often ten times the cost of a consumer Access Point. Enterprises will invest in a site survey, deploy multiple APs, and manage multiple radio channels to serve a single facility. This drives the cost and complexity well beyond home office budgets.

Consumers are often disappointed when they get less than 11 Mbps a mere 50-75 feet from their access point. My experience with consumer grade products corroborates these coverage numbers. But I’ve placed an enterprise class AP in my office with only marginal improvement. So what’s the deal?

Obstructions

Radio signals propagate out from the typical dipole (omnidirectional) antenna, in a more or less a spherical manner, unless they hit something. Walls, doors, furniture, kitchen appliances obstruct and diffuse radio signals: the signals bounce around obstructions and still carry on, but they can’t be sustained over as long distances, or with sufficient power to support maximum throughput. If you have only one AP and lots of obstructions, you may not have sufficient signal strength in every corner of your home. If you have multiple access points, WiFi devices will automatically connect to the AP with strongest signal, but even with WiFi extenders it may be hard to maintain signal quality throughout a home with numerous highly obstructed paths.

Here’s an example of a highly obstructed path in my home. The office in which my Etherloop DSL connection is terminated is in one wing of our L-shaped house (Picture the bottom right-hand corner of a L drawn backwards). If I were to place an AP in my office, and wanted to use wireless from my laptop back to my office from my bedroom (at the top of the L), I only need 75-80 feet of direct radio coverage, seemingly within the product vendor’s claims. But three interior walls and two exterior walls (the bend in the L), render the signal to my bedroom useless for networking.

One solution is to move the AP to a more central location in the home. But to do so, I (and others with similar obstruction challenges) must run CAT-5 to the AP location. “And therein lies the rub…” ^[1].

In residential or home office, CAT-5 is an oxymoron: it’s ugly so you want to hide it, but concealing it with tacky plastic runners violates interior design principles, and retrofitting a home, or pre-installing CAT-5 is expensive, especially if you want it done by someone with a clue.

If Can’t Deliver Power over Ethernet, Why Not Deliver Ethernet over Power?

In homes, the omnipresent wiring is residential power lines. Most occupied rooms have two or more outlets. Where the obvious answer in enterprise facilities is to run power over ethernet, the obvious answer in homes is to run Ethernet over Power, a.k.a., Powerline Ethernet or HomePlug Networking.

Powerline Ethernet runs over residential power lines using a Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol to arbitrate the shared medium; a Physical layer designed for transmission over electrical wiring; and Orthogonal Frequency Division Multiplexing (OFDM) in a bursty transmission mode of operation appropriate for a shared Ethernet medium (for more information see this CommsDesign article and the Powerline Communications Network Technology eLibrary).

Plug Powerline Adapters into your power outlets to form a network over your home electrical wiring. Transmission rates of up to 14 Mbps are DES-encrypted for confidentiality (based on a shared secret/password). Other than changing the default password for your network, it’s entirely self-discovering and self-configuring. You can use your powerline network as you would any LAN subnet:

Your only Home Network. Directly connect PCs and home entertainment devices via to HomePlug adapters using USB and Ethernet NICs, then uplink the powerline network via a hublet or switch to a broadband router. This replaces a WLAN. It tethers you to a power outlet, but if you are using a laptop for more than a few hours, perhaps you’ll have to situate yourself close to an outlet, anyway.

Home Backbone LAN. Here’s one way to centrally situate your home network access point, or to create a second WLAN in your home without running CAT-5 cabling. Connect one HomePlug adapter to your broadband router or SOHO firewall’s trusted Ethernet port. Place a second HomePlug adapter in a central location, as free from obstructions as possible. Connect an access point to the second HomePlug, or you can buy an integrated Wireless Access Point and HomePlug adapter solution.

By employing the second alternative, I’m able to roam from one WLAN to another, from room to room on both floors in my home. I configure both access points with the same ESSID and security (e.g., same WEP keys, authentication method), and DHCP assign addresses from the same subnet, but use a different radio frequency (channel) for each access point. Both access points uplink to the same DMZ port on my firewall. My powerline network delivers 9.2 Mpbs over my 14-year old wiring, and I get 11 Mbps on my WLANs, with exceptional coverage.

One Medium Does Not Rule Them All

Wireless LANs are the most heavily marketed medium for home networking. Perhaps they satisfy the 90% rule. But for those who find themselves in the 10% situation, there’s no need to add wiring if you have electrical outlets in convenient locations. Powerline Ethernet is as simple a solution to deploy as I’ve ever encountered in networking…

unless you live in that rare home with separately metered sections. Even here, think positively: ask, “what medium works best to bridge this gap?” Where there’s Ethernet, there’s a way…