HomePlugs were introduced around the turn of the centrury in order to extend wireless networks beyond the reach of a router or switch. They are a "no new wires" concept as you will always have a power socket near an electrical device which needs to connect to your network.
They are adapters that plug into your electrical wall sockets and create a network over your existing mains wiring. They are also the most cost effective method for connecting devices in different rooms. (Think power usage)
You may hear HomePlugs referred to as Power-Line adapters... They are essentially the same thing but based on slightly different chipsets. (Intellon for the new HomePlug technology & Intelogis for the older Power-Line technology)
"In order to ensure compatibility between products from different manufacturers, most products have adopted a standard networking protocol called HomePlug. In fact, the terms ‘powerline’ and ‘HomePlug’ are often used as though they’re interchangeable, but there are competing standards. HomePlug is the most popular, though."
A short comparison between Intellon (HomePlug) & Intelogis (Power-Line)
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.
Intellon's OFDM approach to power-line networking is highly scalable, eventually allowing the technology to surpass 100 Mbps.
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.
If you suffer from poor wireless coverage in your house you can effectively extend your range without the need to run lots of ethernet cable around your home (which can often involve drilling holes, lifting carpets etc...) HomePlugs can also be a better solution than a repeaters as a repeaters can reduce your available bandwidth.
There are two types of HomePlug - Wired and Wireless although some manufacturers now make combined HomePlugs for the best of both worlds. For example if speed and reliability are paramount (such as in gaming) then you may want to consider a direct connection to the HomePlug through a wired connection.
HomePlugs are designed to plug and play so they are very easy to setup. Essentially:
This diagram explains how a wired HomePlug network may look:
If you have combined Wireless & Wired HomePlugs your setup may look more like this:
The posibilities are varied and exciting... If you want to discuss your setup or help others in the Sky community with their setups why not take a look in our Broadband, Setup & Connection forum?