Power-line networking is one of several ways to connect the computers in your home. It uses the electrical wiring in your house to create a network.
Power-line networking is based on the concept of “no new wires.” The convenience is even more obvious in this case because while not every room has a phone jack, you will always have an electrical outlet near a computer. In power-line networking, you connect your computers to one another through the same outlet.
Because it requires no new wiring, and the network adds no cost to your electric bill, power-line networking is the cheapest method of connecting computers in different rooms.
In this article, we’ll talk about power-line networking and the technology used to make it happen. We’ll also discuss the advantages and disadvantages of using a power-line network.
Pros and Cons of Power-line Networking
There are two competing power-line technologies. The original technology is called Passport, by a company named Intelogis. A new technology called PowerPacket, developed by Intellon, has been chosen by the HomePlug Alliance as the standard for power-line networking.
Here are the advantages of a power-line network:
- It’s inexpensive. (This author bought a complete Intelogis’ PassPort kit to connect two computers for $50.)
- It uses existing electrical wiring.
- Every room of a typical house has several electrical outlets.
- It’s easy to install.
- A printer, or any other device that doesn’t need to be directly connected to a computer, doesn’t have to be physically near any of the computers in the network.
- It doesn’t require that a card be installed in the computer (although there are companies working on PCI-based systems).
The new PowerPacket technology provides a couple of other advantages as well. It is fast, rated at 14 megabits per second (Mbps). This speed allows for new applications, such as audio and video streaming, to be available throughout the house.
There are some disadvantages to connecting through power-lines when using the older Intelogis technology:
- The connection is rather slow — 50 Kbps to 350 Kbps.
- The performance can be impacted by home power usage.
- It can limit the features of your printer.
- It only works with Windows-based computers.
- It uses large wall devices to access an electrical outlet.
- It can only use 110-V standard lines.
- It requires that all data be encrypted for a secure network.
- Older wiring can affect performance.
According to Intellon, PowerPacket technology eliminates many of these concerns, citing the following advantages:
- It is very fast, rated at 14 Mbps.
- It “avoids” disruptions in the power-line, maintaining the network’s connections and speeds.
- It does not limit the features of your printer.
- It can be compatible with other operating systems (depending on driver availability).
- It may have the necessary circuitry embedded within the device, necessitating only a standard power cord to access an outlet.
- It works independent of line voltage and frequency of current.
- It includes encryption.
- In tests, it showed no signal degradation due to older wiring.
Now let’s find out how each of these technologies works.
Methods
Intellon and Intelogis use different methods to establish power-line networks.
Intellon
Intellon’s PowerPacket technology, which serves as the basis for the HomePlug Powerline Alliance standard, uses an enhanced form of orthogonal frequency-division multiplexing (OFDM) with forward error-correction, similar to the technology found in DSL modems. OFDM is a variation of the frequency-division multiplexing (FDM) used in phone-line networking. FDM puts computer data on separate frequencies from the voice signals being carried by the phone line, separating the extra signal space on a typical phone line into distinct data channels by splitting it into uniform chunks of bandwidth.
In the case of OFDM, the available range of frequencies on the electrical subsystem (4.3 MHz to 20.9 MHz) is split into 84 separate carriers. OFDM sends packets of data simultaneously along several of the carrier frequencies, allowing for increased speed and reliability. If noise or a surge in power usage disrupts one of the frequencies, the PowerPacket chip will sense it and switch that data to another carrier. This rate-adaptive design allows PowerPacket to maintain an Ethernet-class connection throughout the power-line network without losing any data.
The latest generation of PowerPacket technology is rated at 14 Mbps, which is faster than existing phone-line and wireless solutions. However, as broadband access and Internet-based content like streaming audio and video and voice-over-IP become more commonplace, speed requirements will continue to increase. Along these lines, Intellon’s OFDM approach to power-line networking is highly scalable, eventually allowing the technology to surpass 100 Mbps.
Intelogis
The older power-line technology used by Intelogis relies on frequency-shift keying (FSK) to send data back and forth over the electrical wires in your home. FSK uses two frequencies, one for 1s and the other for 0s, to send digital information between the computers on the network. (See How Bits and Bytes Work to learn more about digital data.) The frequencies used are in a narrow band just above the level where most line noise occurs. Although this method works, it is somewhat fragile. Anything that impinges on either frequency can disrupt the data flow, causing the transmitting computer to have to resend the data. This can affect the performance of the network. For example, this author noticed that when he was using more electricity in the house, such as running the washer and dryer, the network slowed down. Intelogis includes line-conditioning power strips with its network kit and encourages you to insert them between the wall outlet and your computer equipment to help reduce the amount of electrical-line noise.
Because the current crop of power-line networks are designed to work on 110-volt electrical systems, the technology is not very useful to countries outside of North America that use different standards.