Powerline Ethernet: When WiFi won't and CAT-5 Can't

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's standard for Power over Ethernet, POE, is now commercially 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 a consumer 802.11b Access Point can be had for between $50-100 while an enterprise AP is often ten times that cost. 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 advertised bandwidth a mere 50-75 feet from their access point. My experience with many consumer quality products corroborates these coverage numbers. But I've also placed enterprise class APs in my office with only marginal improvement, certainly nothing like the 300 foot coverage the product literature claims. 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. 802.11x LANs will automatically adjust throughput based on signal strength, but it's difficult to maintain signal quality over highly obstructed paths.

Here's an example of a highly obstructed path in my home. The office in which my 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.

The obvious 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 You 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. HomePlug 1.0 products offer transmission rates of up to 14 Mbps and provide DES encryption for confidentiality. The more recent HomePlug AV can push peak rates up to 200 Mbps and offers 128-bit AES encryption (based on a shared secret/password). Other than changing the default password for your network, HomePlug devices 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 WPA-Personal 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 original powerline network delivered 9.2 Mpbs over my 14-year old wiring. With my recent upgrade to 200 Mbps HomePlug AV devices, I get sufficient bandwidth so that my WLANs achieve over 50 Mbps. 

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...

Comments

[Security Skeptic]

Hi,

Follow the "Home Backbone LAN" directions in the article. You should be able to attach your Airport Express to a HomePlug Ethernet Adapter in one of the remote rooms, then put another airport adapter "near" your Extreme and plug it into the Extreme's "internal network" Ethernet port. Configure the network to allow you to roam as I did. I'd get the fastest HomePlug adapters you can afford. Remember that wiring quality may affect the actual throughput.

[Tom Wheaton]

Perhaps you can help me. I have an old house in Mexico with brick, stone and adobe walls up to 70cm thick, and my internet access point is about 25 meters to the farthest bedroom. I have a wireless network (Apple Airport Extreme) that works fine in one-third of the house. I added an Airport Express in the living room in an attempt to extend the range of the network, but that only worked intermittently, never very well, and that recently gave up the ghost. I want to be able to use Airplay to stream Netflix, etc. using a VPN and to provide a wireless internet connection for guests in the bedrooms.

I would like to use the electrical system to expand the network to the rest of the house. Is it possible to use powerline adapters in various areas of the house, and then attach some kind of wireless router to them to extend my wireless network? If so, what equipment do I need and what problems should I look out for? I have a two year old iMac with 4 gigs of RAM, an Intel Core 2 Duo Intel Core 2 Duo with a processor speed 2.66 GHz, running Lion.