HomePlug Powerline Alliance

HomePlug is an industry trade group for power line communication. This organization of about 70 companies defines power line communication specifications. HomePlug 1.0 and AV are the two specifications for home networking technology that connects devices to each other through the power lines in a home. HomePlug certified products connect PCs and other devices that use Ethernet, USB, and 802.11. Many devices have HomePlug built in and to connect them to a network all one has to do is to plug the device into the wall in a home with other HomePlug devices. Since surge protectors and similar devices may interfere with the high-frequency signals used by HomePlug, the directions included with HomePlug devices recommend plugging them directly into the wall outlets without using extension cords or outlet strips.

Operation

In residences and small businesses with Split phase wiring (common in North America), roughly half the 120-volt outlets in the building will be on each hot phase, and HomePlug signals may or may not be able to get from one side to the other. If one is unlucky, this may prevent some rooms from being connected via HomePlug.

Among other things, HomePlug brings back the ability to use Ethernet in bus topology, implied by its standard description (carrier sense multiple access and collision detection) and very desirable in some circumstances. This is achieved by use of advanced OFDM modulation that allows co-existence of several distinct data carriers in the same wire. The use of OFDM also allows turning off (masking) one or more of the sub-carriers which overlap previously allocated radio spectrum in a given geographic region. In North America, for instance, HomePlug AV only uses 917 of 1155 sub-carriers.

Security

Since the signals may travel a short distance outside the user's residence or business, like many other home networking technologies, HomePlug includes the ability to set an encryption password. As with many other networking products, most HomePlug devices are "secure by default". The HomePlug specification requires that all devices are set to a default out-of-box password—although a common one. Users should change this password.

To simplify the process of configuring passwords on a HomePlug network, each device has a built-in master password, chosen at random by the manufacturer and hard-wired into the device, which is used only for setting the encryption passwords. A printed label on the device lists its master password.

The data at either end of the HomePlug link is not encrypted (unless an encrypted higher-layer protocol such as TLS or IPSEC is being used), only the link between HomePlug devices is encrypted.

Since HomePlug devices typically function as transparent network bridges, computers running any operating system can use them for network access. However, some manufacturers only supply the password-setup software in a Microsoft Windows version; in other words, enabling encryption requires a computer running Windows [1]. Once the encryption password has been configured, Windows will no longer be needed, so in the case of a network where all computers run other systems a borrowed laptop could be used for initial setup purposes.

Current and proposed functionality

The HomePlug powerline alliance has defined the following specifications:

• HomePlug 1.0 — Released June 2001 — Specification for connecting devices via power lines in the home. Theoretical speed of 14 Mbit/s.
• HomePlug AV — Released December 2005 — Designed for transmitting HDTV and VoIP around the home. Theoretical PHY datarate of up to 189 Mbit/s.
• HomePlug Access BPL (BPL) — under development — A working group to develop a specification for to-the-home connection.
• HomePlug Command & Control (HPCC) — Released October 9, 2007 — It's a low-speed, very low-cost technology intended to complement the alliance's higher-speed powerline communications technologies. The specification enable advanced, whole-house control of lighting, appliances, climate control, security and other devices.

1.0

The original HomePlug 1.0 specification allows for speeds up to 14 Mbit/s half-duplex.

On May 28, 2008 Telecommunications Industry Association (TIA) incorporated HomePlug 1.0 powerline technology into the newly published TIA-1113 international standard. TIA-1113 defines modem operations on user-premises electrical wiring. The new standard is the world's first multi-megabit powerline communications standard approved by an American National Standards Institute (ANSI)-accredited organization.

Many old 85 Mbit/s devices are erroneously referred to be HomePlug. They are instead based on Intellon's proprietary 85 Mbit/s Turbo mode. The error is induced by the fact that INT5500 Chip Set is compatible with both HomePlug 1.0 specifications and Intellon Turbo technology and the two technology are called HomePlug 1.0 with Turbo on the whole.

AV

The HomePlug AV specification was designed to provide sufficient bandwidth for applications such as HDTV and VoIP. Utilizing adaptive modulation on up to 1155 OFDM sub-carriers, turbo convolution codes for error correction, two-level MAC framing with ARQ, and other techniques, HomePlug AV can achieve near the theoretical maximum bandwidth across a given transmission path. Key distribution techniques and the use of 128 bit AES encryption are specified as mandatory in the specification. Furthermore, even the interception of data exchanged between HomePlug AV devices poses a "significant challenge" for an attacker due to the adaptive techniques used to modulate the signal between two given points.

HomePlug 1.0 devices cannot interoperate with HomePlug AV devices without the use of a suitable bridge, although both can co-exist on the same cable.

BPL

The alliance is developing a specification called HomePlug BPL for last-mile access networks.

Command & Control

Command & Control is a lower speed specification intended for applications such as HVAC or lighting control.

Interoperability

The alliance certifies products for HomePlug compliance. Devices marked with the certification mark will interoperate with each other. However, they will not work with other powerline technologies from Panasonic or DS2 which offer similar speeds.

According to the organization, existing HomePlug (1.0, Turbo and AV) devices will not interoperate with products based on the new G.hn standard (for power lines, phone lines and coaxial cables) developed by ITU-T. On March 2009, Rob Ranck (then president of HomePlug) said during an interview with EE Times:

The heart of the issue is that HomePlug uses turbo coding forward error correction while G.hn is proposing low density parity check (LDPC). The two are incompatible and supporting both techniques would make HomePlug chips large and expensive, Ranck said.

— EE Times, "Debate breaks out over home net standards", March 2009,

Differences in Forward error correction (FEC) are also one of the reasons why HomePlug 1.0 devices do not interoperate with HomePlug AV devices:

Though it is possible to build a backward-interoperable device, the complexity would be prohibitively expensive to our customers. Such a device would have to include the ability to switch between FEC techniques and many other features, which places cost at an unworkable level.

— EDN, "Voices: Intellon’s Mark Hazen on the HomePlug AV powerline-networking alternative",

Coexistence

HomePlug, along with other organizations such as CEPCA, UPA and HD-PLC, is participating in developing the IEEE P1901 standard for powerline communications. P1901 defines a set of multiple non-interoperable PHY and MAC specifications and a coexistence protocol between them. Although different P1901 devices may not interoperate, they will coexist with each other.

See also

• G.hn
• HomePNA
• HomeRF
• HomeIR

• IEEE P1901
• Multimedia over Coax Alliance
• Power line communication
• Power over Ethernet

External links

• HomePlug
• List of certified HomePlug products
• Technical whitepapers on the HomePlug website
• IEEE P1901