Special thanks to Intellon
for their assistance with this
article.
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.
In this edition of HowStuffWorks,
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.
Networking!
Please be sure to read the companion article How
Home Networking Works, which provides information
about configuring your computers, routers
and firewalls,
Ethernet
networking and sharing an Internet connection. There are
also companion articles about phone-line
networking and wireless
networking. By the time you finish this series of
articles, you will be able to choose a network
technology that suits your needs and then configure the
whole thing!
The Technology Like HomePNA,
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.
Pros and Cons 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.
Photo courtesy Intellon New power-line networking products are based
on Intellon's PowerPacket
technology.
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.
Photo courtesy Intellon This card plugs into a PCI slot in your
computer and into a wall outlet to create a power-line
network.
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.
Cost And Installation Intelogis provides a
kit that connects two computers and one printer for $59.
Additional adapters cost about $40. There are specific
versions for computers or printers, so make sure you get the
correct one. Since the network does not affect power usage or
consumption, no additional monthly costs are incurred.
The cost of PowerPacket technology is expected to be
comparable to HomePNA solutions and significantly less than
802.11 wireless solutions.
Image courtesy of Intellon A power-line network provides access all over
your
home.
How to Install a Power-line
Network The physical connection between each
computer and the Intelogis power-line network uses the
computer's parallel
port. A wall device is plugged directly into the
electrical outlet (it will not operate properly if plugged
into a surge
protector).
To install an Intelogis PassPort power-line
network, you plug a wall device like this into an
outlet.
A parallel cable is plugged into the wall device and into
the parallel
port of the computer. The power-line network must be the
last item connected to the parallel port. For this reason, if
you have anything else connected to the parallel port, such as
a scanner or
Zip
drive, it must have a pass-through for the parallel port.
Unless you have a second parallel port on your computer, your
printer must be connected to the network through a wall device
of its own. Something to keep in mind is that current
power-line networks do not support bidirectional printing.
"Bidirectional" means that data is sent in both directions,
allowing your printer to send information back to your
computer, such as how much ink is left and if there is a paper
jam. This will not keep your printer from working, but it is
worth noting that you will lose the use of such features.
Initial PowerPacket devices connect via a USB or
Ethernet cord from the computer to a small wall adapter.
Subsequent devices will have the circuitry built in, meaning
the only connection needed would be the power cord.
Once the physical connections are made, installation of the
software is a snap. The software automatically detects all
nodes (computers and printers) on the network. Whether your
Internet connection is by cable
modem, DSL or normal
modem,
the included proxy server software allows you to share the
Internet with your other computers. You can easily add
computers by simply plugging a new adapter in and installing
the software. Additional printers can be added using the
printer plug-in adapter. File and
printer sharing is done through Windows.
There are two common types of home networks: peer-to-peer
and client/server. Client/server networks have a
centralized administrative system that provides information to
all of the other devices. Peer-to-peer means that each
device can talk directly to each other device on the network
without consulting a central system first. Intelogis Passport
technology uses a client/server network. The first computer
that you install the software on becomes the Application
Server. In essence, it is the director of the network,
controlling the flow of data and telling each device on the
network where to find the other devices. Intellon's
PowerPacket technology uses a peer-to-peer network.
The Future Intellon's PowerPacket technology
is compatible with wireless and HomePNA solutions, making
power-line an ideal option to serve as the backbone for a
multi-technology home network. In this case, consumers will
not have to discard their existing network solutions in favor
of a new standard.
The one common thread among all of the networking options
is the need for power. While a wireless solution may indeed
shun wires, its access point is still going to be plugged in
at some point. That power cord, for example, can tie the
wireless network into the home's overarching power-line
network.
There are two other networking technologies to discuss:
phone-line and wireless networks. Click on the title below to
go to one of these articles for more information, or proceed
to either A Word
About Macs or The
Future of Home Networking.
