Power-line Networks

Powerline networking is another technology to take advantage of unused bandwidth on an existing system of home circuitry. It operates similarly to a phoneline network. Internal or external network adapters are installed in each PC, which are plugged into a nearby power outlet. Printers or other peripherals can be shared through a connected PC, a modem of some sort providing the shared Internet connection.

Powerline technologies use a variety of media access methods, from CSMA/CD and token passing to datagram sensing multiple access (DSMA) and centralised token passing (CTP). DSMA acts much like Ethernet to mediate multiple access contentions on the wire, by sensing and randomly backing off if traffic is detected. In some powerline home network implementations, once a network device has gained access, it switches to a dynamic, centrally distributed, token passing scheme so that it has control of the network until it finishes transmission. This dual method reduces the incidence of transmission collisions while preserving limited bandwidth.

Powerline technology also employs a modulation technology called frequency shift keying (FSK) to send digital signals over the powerline. FSK uses two or more separate frequencies in narrow band; one is designated 1 the other 0 for binary transmission.

Powerline networking boasts many of the same benefits as phoneline networking. However, some powerline networks are not as fast as other networking choices. Powerlines tend to be very noisy and consequently slower (compared to phonelines). Bandwidth speed tops out at much less than 1 Mbit/s: rates typically range from 50 Kbit/s to 350 Kbit/s.

Powerline networking works best in homes where the computers are located in different rooms near power outlets, but on the same circuit. There are potential security issues, however, due to the way power is distributed. A single power line from the utility company goes to multiple homes; a power meter at each house measures actual usage. Like an old party telephone line, anyone can potentially listen in on the shared bandwidth. A powerline network relies on encryption, or data scrambling, to prevent others from accessing the data running over the home network.

Because of these limitations, powerline home networking is not expected to be as viable an option as competing home networking technologies. The expectation is that it is more likely be deployed in home automation and home security applications.