Last week we discussed the delights of power-line networking based on the HomePlug standard.
HomePlug nodes can communicate at up to 14M bit/sec. Note that we wrote “can” and “up to” – anything that degrades the signal, such as interference and gremlins or more than 16 HomePlug devices, will cause the power-line system to back off to find a reliable throughput rate.
You’ll find that each node pair in a HomePlug network likely will connect at different data rates because each individual path across the power lines will have different transmission characteristics.
Actually, the maximum of 16 devices is the figure most vendors quote, but a paper from the Massachusetts Institute of Technology, Moving HomePlug to Industrial Applications with Powerline Communication Network, says that for best performance you should network only up to 15 nodes using the HomePlug 1.0 standard.
So, what are the limitations other than the number of devices? First, distance: HomePlug signals will travel a maximum of about 300 meters of wire, notwithstanding interference from electric motors, fluorescent lights, halogen lamps, switching power supplies and dimmer switches. You also should avoid connecting HomePlug devices to power sockets using extension cables and multi-outlet power strips with surge suppressors.
There also are wiring limitations. While HomePlug signals have no problem passing through circuit breakers, they won’t pass through power transformers and will not reliably cross phases.
This latter issue is not that bad in practice. In a report titled HomePlug 1.0 powerline communication LANs – protocol description and performance results published in the International Journal of Communication Systems, the authors note that: “Despite these impediments, tests of the present version of the HomePlug 1.0 power-line devices in some 500 homes show that 80% of outlet pairs will be able to communicate with each other at about 5M bit/sec or higher, and 98% will be able to support data rates greater than 1M bit/sec: Field tests suggest that the power-line network will provide connectivity in situations where some wireless networks will fail due to large attenuations caused by distance or obstructions such as intervening walls or furniture.”
Also check out the paper HomePlug Field Test Results: A White Paper issued by the HomePlug Powerline Alliance.
An important issue with HomePlug is privacy. HomePlug signals can “escape” from your power wiring and be picked up by your neighbors. To get around this, HomePlug provides data security based on 56-bit DES encryption.
Using a vendor-supplied utility you enable encryption by setting a password into each HomePlug transceiver – all devices that are to communicate must use this password.
In our tests of Netgear and Linksys products, we found that HomePlug technology works amazingly well. As we noted last week, all the products were easy to install but the documentation and management utilities could be improved. We found the utilities were inconsistent in detecting the transceivers, which could not be easily explained because when they were found the connections were considered good or excellent.
That snafu aside, we had no problem getting reliable connections between transceivers. Indeed, we are hooked. Power-line networking is a powerful tool to have in your “we need a quick connection for a reasonable price” tool box.
The International Journal of Communication Systems report we mentioned earlier concludes with: “In-home [power-line communications] have the potential for significant improvements. . . . The HomePlug Powerline Alliance announced plans for the development of next-generation powerline specifications . . . called HomePlug AV . . . intended to provide 100M bit/sec throughput, and will be designed to support distribution of data and multi-streaming entertainment, including high definition television and standard definition television, throughout the home.”
The HomePlug AV specification has moved forward reasonably quickly, and the HomePlug Powerline Alliance notes on their Web site that “HomePlug AV products will likely be available for the 2004 holiday season.” We know what we want for Christmas.
So tell us your home networking tales – best response by the 16th gets a rosebush. Entries to gearhead@gibbs.com.
