Tuesday, April 23, 2013

Bits in the wires: Homeplug



By now you've probably been exposed to at least some form of connectivity that doesn't involve a traditional
wired connection.  Most likely it's Wi-Fi but what happens when you just can't get a good signal?

Maybe you've got your game room in a converted basement or want to have internet access in your shiny metal RV garage.  Running wires isn't always a viable option especially in older construction or where distance exceeds the specification for maximum cable length.  It's still 328 feet for Ethernet by the way.

Wireless networking options can be very finicky.  For one thing if you're trying to push a signal below ground level (such as our basement example) you'll soon find out the limits of an annoying little thing called wave propagation.  Nothing kills a wireless signal faster than an obstruction and good old terra firma (the ground) is one heck of an obstruction. 

Another kind of obstruction isn't as obvious.  It's called the "Faraday effect" and it can squelch a wireless signal simply because there are too many conductive surfaces that can absorb it.  Your big metal RV garage can act like a "Faraday cage" and diffuse a wireless signal before it ever gets near your wireless device.

So if network cabling and wireless aren't an option are you stuck? 

Not necessarily.  There's a third option that's become more popular and it uses wires but not the ones you typically associate with computers.  It's called Powerline networking or "Homeplug" and you've likely already guessed from the name that it has something to do with power lines. 

Powerline networking in a nutshell simply uses your home's electrical wires as a transmission medium to connect to your other network devices.  It's based on an IEEE standard just like Wi-Fi called IEEE 1901.
The most recent incarnation of the standard is called Homeplug AV2 and it promises speeds up to 500Mbps with some companies claiming to top out at Gigabit speeds.  Of course those are theoretical maximums.  A good rule of thumb is to not expect better than 1/3 of the rated speed.

Powerline networking is a great option when others fail you but it has it too has its drawbacks.  For one thing the signal can be affected by the way your house is wired or the kinds of devices you have plugged into your other wall outlets or even the outlets themselves.   

You also have to plug the adapter directly into your wall outlet so no surge suppressors or UPS's allowed.   Those devices can kill the signal. 

Don't worry about electrical surges damaging them though, most vendors have integrated power protection into the Powerline adapters.  Some models even come with a pass-through so you don't have to give up an outlet.   Just don't plug your vacuum cleaner into it unless you want to lose signal.  Powerline network connections are sensitive to transformers and that 12 Amp Dyson is a big one.

Generally you purchase Powerline networking adapters in pairs since it takes a minimum of 2 to get going.  Installation couldn't be easier as you generally just plug the adapters into a wall outlet, plug in an Ethernet cable between your networked device and the adapter and wait for your pair of adapters to sync up.  The only other thing to consider is which device you want to be the "coordinator".  A coordinator is usually the first device and will control the communication between all other powerline adapters. 



Security is simple as well.  By default, today's Powerline networking equipment is already protected with 128 bit AES encryption.  Generally that's enough unless you have power outlets outside your home or live in an apartment.  The first concern is obvious the second may not be. 

Since Powerline networking has no authentication mechanisms outside of the network name, someone who could see your Powerline adapters could just plug in and connect to your private network.  This can happen if you happen to share a fuse box with a neighbor. 

Don't be too concerned about broadcasting to your entire neighborhood though, the signal does have a limited range and likely won't make it out of the confines of your home.  In some cases it may not make it past a few rooms if you happen to have GFCI outlets on the circuit.  The signal is very sensitive to power protection circuits which is why you can't plug adapters into UPS's or surge suppressors.

If that's not enough protection for you, however.  There's one more way to secure the Powerline network.  Simply change the Powerline Network name.  That's usually accomplished by pressing a button on one of the networking devices for a period of time, waiting for status lights to flash a certain sequence then go to the other devices and repeat the procedure till the devices all sync up. 

Similar to a wireless network with a WPA passphrase securing its connections a Homeplug network is virtually impossible to hack into without more effort than your slacker neighbor has the ability or the patience for.  Think of a Homeplug network name like a combination of a WPA passphrase and an SSID on a wireless network.


Some adapters like ZyXel even come with configuration software so you can set your own network name instead of relying on an auto generated one from the previous procedure.  That's usually enough to keep prying eyes out of your Powerline network but if you're really paranoid you can also set what's known as the DAK or Device Access password.  The DAK is a 16 Letter key usually printed on the bottom of the actual device.   

That can prevent a rogue Powerline adapter from changing settings on remote adapters by preventing  changes to your Powerline adapters from a remote location unless that DAK password is entered.  In effect, it prevents someone from hijacking your powerline network.  The down side is you have to manually enter the information into your configuration  software which can be tedious if you have a lot of adapters.  

So what else do you have to worry about with Powerline Networking?


Well, much like wireless devices, compatibility can be an issue.  For one thing, even though there's one standard for Homeplug not all versions are compatible.  For example, new devices using the Homeplug AV2 standard will not talk to older Homeplug 1.0 devices. 

Earlier devices were slower and implemented security in a way that won't allow them to work with newer devices.  They can, however, be used in parallel with newer devices, the two types just won't see each other.
Also, some devices that are configured to be the "coordinator" will refuse to connect to other devices that are capable of assuming that role.  I actually have a pair of Zyxel and Cisco Homeplug AV adapters and only one of the two Cisco units will talk to the Zyxel units. 

Powerline is generally a last ditch option to get connectivity where other methods fail so I wouldn't reccommend basing an entire network topology on it.  The standard can support up to 64 individual adapters but 16 is the practical maximum for good performance. 

I've personally used Homeplug adapters for about 5 years now and I've been generally happy.   That said, I've seen my theoretical 200Mbit speeds drop to 5Mbits for no apparent reason.  Luckily, that doesn't happen too often.

It's definitely been a more reliable option than wireless especially when streaming Internet video.  Wireless signals tend to be more erratic than Powerline networks even with the advent of 802.11 N and multipath or MIMO.  Peak wireless transfer speeds do tend to be higher, however.

Some have reported reliability issues with Powerline adapters from Cisco and Netgear and it can be difficult to get even a matched pair to renegotiate security between two devices.  I've never had an issue with my Zyxel PL401A V3's but I did with My Cisco PL300's.

There is one other option that's similar to Powerline networking that uses coaxial cabling called MoCA
(Multimedia over Coax Alliance) which is promoted by cable companies (of course) and serves as the basis for many of those "whole home DVR" offerings.

Admittedly,  I've had limited experience with MoCA devices but found them to be generally more costly and far less reliable than Homeplug.

The MoCA standard is currently in version 2.1 and promises 800Mbps to 1Gbps of bandwidth but factors such as the type of Coax cable, number of splitters and quality of terminations can have a serious effect on performance.  

This latest incarnation of the standard tries to address some of these issues by trying to prioritize sensitive traffic like HD video streams using what's called PQOS or Parameterized Quality of Service.  PQOS is much like the Quality of Service found in modern network switching and routing equipment that ensures certain types of data are classified and given priority on the wire.

AT this point Powerline Networking is the more mature standard and is more focused on traditional data connectivity than streaming video and multimedia traffic like MoCA. 
Although MoCA isn't as well known as Homeplug it's worth mentioning here since it's likely your home DVR's are communicating via it's mechanisms. 

Anyway, that's it for my discussion of alternate networking options.  Check out the links below for more information.

Post a Comment