Powerline networks aren’t new, and they aren’t all that glamorous. But they are faster and more reliable than they used to be. Recent innovations just might make powerline networks worth a look, particularly in the small office/home office market.

Powerline networks transmit data (phone calls and faxes as well as e-mail and Web pages) over regular electrical wiring, effectively transforming every electrical outlet in the immediate area into a network connection. Wires and sockets are used simultaneously for electricity and data, without disrupting each other. For computers, powerline networks work best when all network components are on the same circuit.

The way powerline networks work is similar to the way phoneline networks operate. They use available bandwidth from the power line to transmit data. Network adapters are installed in each computer and peripheral. A single modem can provide a shared Internet connection.

Various technologies are used to control data across the network, including centralized token passing and datagram sensing multiple access (DSMA). For example, DSMA senses and controls multiple access traffic much like Ethernet. In some implementations, a network device switches to a token passing scheme once it gains access to the network, allowing it to maintain control until it finishes transmitting. Powerline networks also use frequency shift keying (FSK) with separate frequencies for binary transmissions.

The top speed of powerline networks has recently increased. Under ideal conditions, they can now achieve speeds of up to 2M bit/sec; however, they are still at the bottom of the speed chart compared to other networking systems:

Ethernet network: 10M to 100M bit/sec

Wireless network: 700K to 11M bit/sec

Phoneline network: 100K to 10M bit/sec

Powerline network: 50K to 2M bit/sec

As for powerline network applications, there are several products on the market designed to connect as many as 20 PCs, printers and peripherals thorough a powerline network. (See examples at http://www.intelogis.com and http://www.intellon.com.) Today, most products are limited to data speeds of 350K bit/sec -- which is too slow for high bandwidth DSL and cable modems.

There are other limitations as well. For example, government regulation is a problem in some jurisdictions where there are different standards for electrical power industries and communication industries.

In addition, power lines are not designed to transmit data and are very susceptible to spikes and surges. These disruptions make the lines noisy, slowing down the data flow. On the plus side, new microchip technology is making interference on the line less of a problem, which enables increased network speeds.

Security, too, has been an issue. Today, powerline network security issues are being addressed by using data encryption to prevent unauthorized parties from accessing the network.

Another advancement involves telecommunications networks on the power grid. In Europe and Asia, there are experiments taking place that connect high-speed telecommunications networks with entire electrical power grids. In these tests, power companies are able to deliver highh-speed Internet access service and phone connections through the power lines.

For now, powerline networks are still most likely to be used for low bandwidth applications like home automation and security and small office networks. But keep your eyes open for higher speed networks. Speeds of 12M bit/sec are likely to become common before the end of the year (see http://www.inari.com/), and that’s fast enough for streaming multimedia and a multitude of other new applications.

» posted by ITworld staff

Network World

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