ZyXEL PowerLine HomePlug/AV PLA401 

I worked for many years in the networking industry, seeing first the widespread use of big thick COAX cable to network computers, then thinner twisted pair wiring into centralised switching rooms. Wired technology was never widely adopted in the home for obvious reasons, but the idea of making use of the existing mains power cabling was often anticipated.
ZyXEL PLA401 HomePlug power-line Ethernet bridge

Despite the ready availability of power cables to every point of every house, running data over an environment that was designed to carry high voltage and high power was never going to be easy. Every time you switch on an electrical appliance power spikes ripple around the house wiring causing potential havoc to low-voltage, high frequency data transmissions.


Despite a few niche players with proprietary technologies, mains networking effectively languished and with the advent of wireless networking almost disappeared from conversation. With the standardisation of wireless technology you could get access to the Internet without a mess of cables. The initial standards were fairly slow but that has been improved over time. Right now if you have a network in your home the chances are it's wireless.

An industry consortium, the HomePlug Powerline Alliance, has however now made interoperable power line networking a reality - but have they missed the boat?

Although it's undoubtedly going to be hard converting people away from wireless powerline does have some strong advantages in it's favour. While sold on ease of use, wireless technologies do suffer a number of very real limitations that people 'put up with' for the convenience of easy connectivity.

Limitations of Wireless networking

Firstly and most obviously is the propagation of the wireless signal. If you are lucky you can get the signal through one wall, maybe two if the walls aren't too thick or are of the stud-partition variety. More than that you're likely to have no signal at all. Where you do manage to get signal, you may suffer from reduced data rates - well below the rate you'll have seen emblazoned across the box!

Until recently the whole focus of home networking has been to provide shared access to some fairly slow resources, most commonly your Internet connection and your printer. Internet connections are getting faster, but they tend to still be significantly slower than the raw speed of a wireless network - and with everyone attempting to access the slow Internet connection, wireless has never been the bottle neck.

Things are changing. Home 'media centres' - either almost standard Windows PCs or dedicated small home servers are becoming popular. These can attach to your network and allow you to 'stream' audio/visual content to any computer in your house. More and more devices want to connect to the network and want to consume more and more bandwidth. Wireless technology is not great in these environments - all the systems are transmitting on the same frequencies and special algorithms prevent them over-writing each other. This generally only work well when the network is no more than 10% loaded and degrades the higher the attempted usage. For video streaming you need to guarantee a data rate between devices, otherwise the video will stall and you'll have those annoying glitches to spoil your entertainment.

Then there is the issue of 'security' - when everyone is talking about identity fraud and shredding any paperwork carrying their details, broadcasting your network traffic to anyone walking down the street would seem to be taking an unnecessary risk. While wireless networks allow data to be encrypted, and strongly recommend that you so do - a lot of wireless networks remain unencrypted. Why? Because setting up encryption is a non-trivial task, has to be set up on every device and each device has it's own way of doing things.

Finally there are the usual health concerns expressed over exposure to electromagnetic radiation. There is no proof to suggest that these concerns are real, but there is always that nagging doubt. We balance that small risk against the convenience that wireless home networking brings us. But if there were a better alternative that avoids that risk?

The role of Power Line networking

HomePlug products overcome many of the limitations inherent and concerns associated with wireless networks. There have been two standards. The PLA401 supports the more recent HomePlug/AV variant - the AV standing for audio-visual. As the name suggests this system has 'designed out' the limitations inherent in wireless networks with respect to real-time transmission. Without going into details, it's possible for two devices to agree a data rate between them and for that bandwidth to be guaranteed - vital for video and audio streaming.

Being a wired technology there is no need to worry about electromagnetic radiation - however slim the likelihood.

The maximum raw data rate available with PowerPlug AV is 200Mbps (mega-bits per second), which translates into a usable data bandwidth of 150Mbps. This is shared in an efficient way between all the stations on the network. This performance is comparable with raw data rates of current generation WiFi networks, but because of the way it is used offers much better usable data rates between stations and can also guarantee real-time performance for video streaming. The data rate will decrease if you have particularly bad wiring in your house, however in my tests I managed virtually full rate across separate ring mains in my house, and we have a lot of noisy electrical equipment here.

Access is obviously not restricted by walls!

HomePlug security

Power Line systems are inherently more secure than wireless technology simply because your data is not being broadcast. Although the data transmission in most locations cannot 'leak' beyond your house, 128 bit strong encryption has been built into the technology anyway. This primarily protects from someone plugging a device into your network to snoop (unlike wireless where they simply have to stand outside your house!).

The PLA401 has encryption enabled by default to stop casual snooping. While it is always recommended that encryption keys be set for wireless networks, the same is generally not true of power line services. The default keys are generally sufficient in all cases except those where you believe you do not have physical security. An office might be an example.

ZyXEL HomePlug in use

ZyXEL are one of the adopters of the PowerLine Alliance standards. As a standard you should be able to buy products from a range of manufacturers, much as you can do with wireless. The HomePlug website lists many supporters of the technology.

ZyXEL support HomePlug in a number of their home networking products. In this case I have a pair of PLA401 devices. Each of these resembles a big power-brick that you plug straight into the wall. Although quite chunky, you can fit the unit into a double wall socket and still use the other socket.

The documentation boasts a one minute set-up - simply plug the device into the wall then connect your computer to it. Well - I tried it and they are as good as their word. There is simply no configuration required, which is as it should be. Each PLA device located the other on the network and immediately started communicating.

The PLA401 has a single RJ45 network connection. Into this you should be able to plug any device that has an Ethernet interface. Most laptops and desktop computers will work fine regardless of operating system. I connected a Vista PC and a Linux box. Network attach devices such as media PCs and network printers will also work. The Ethernet port on the PLA401 will work at 10Mbps or 100Mbps and will auto-negotiate to match the speed and type of your device. Because your computer connects via Ethernet rather than wireless you are also spared the vaguaries of wireless support often found in even the most recent operating systems.

The PLA401 came with a quick start guide, which wasn't required. A more complete manual is available on the included CD, which also includes a configuration utility to change the network encryption keys should you consider this necessary for your environment. You can also use this to find out what data rate you can achieve on your particular wireing.

Powerline and Wireless

You could use Powerline technology to wire the whole of your house, however wireless still has some benefits (sitting in the garden on a hot summers day under the shade of a tree with your laptop and a cup of tea being just one of them). It is perfectly possible to use both technologies together by plugging the Ethernet port of a wireless access point into PLA401 Ethernet port.

I found PowerLine particularly useful in extending the range of my wireless network. My house is long and thin with broadband piped in at one end and my study at the other. There is no way I can get wireless from one end to the other, even with the purchase of a high quality aerial. Until now I've had a collection of wireless 'bridges' to get the signal down the length of the house. With Powerline I can span the distance using the mains wireing of the house. Works perfectly.

As well as the PLA401, ZyXEL also build HomePlug compliant interfaces into a number of other products including routers and, most interesting, some of the 'media servers' the company is producing.


HomePlug and Powerline technology should have a great future - I hope it does. It has many benefits over wireless that will only become more apparent as homes implement more sophisticated internal multi-media networks.

Price-wise, a twin-pack PLA401, containing two units, is currently £92.70 including VAT from DABs - link below. This is quite expensive, however the technology is new and as volumes increase I'd expect the prices to fall.

Details on the ZyXEL HomePlug range can be found on the ZyXEL web site.

For those that would like a technical overview of the HomePlug technology, there is a very good whitepaper on the PowerLine alliance web-site.

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Comment by vinaya, 21 Feb 2008 10:33

had a query regarding Homeplug Solution:

We want to implement the Homeplug solution using Homeplug 1.0 adapters for about 600 flats.

Following are the questions:

Maximum number of devices that can be supported by Homeplug (for a scenario were there are going to 2-3 buildings)
What @ isolation issue between the flats in the building?
As per the specification for one family 253 devices but not more than 10 can talk at a time, so if this is the case that for an building having 20 flats each having 10 Homeplug Adapters? Will it work? Is it required to provide isolation for each flat? Can u please suggest any solution for the same?

Waiting for reply.



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