Talking To Your Fridge? You Need In-House Broadband Over Powerline

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Index of Professor Horak's CommWeb Tutorial Series (including Frame Relay topic).

In a previous article, we explored Access BPL, which essentially is a set of standards for a broadband local loop provisioned over medium voltage distribution power lines.Those lines run from the headend (i.e., near-end) transformer at the utility substation to the neighborhood (i.e., far-end) transformer that steps the voltage down from the medium voltage (MV) distribution grid to the low voltage (LV, nominally 110 volts in the U.S. and some 39 other countries, and 220 volts or so in much of the rest of the world) that connects to your home or business via a drop cable. At the far-end transformer location, the broadband connection to the premises may be through the transformer (unusual) to the LV drop, around the transformer to the drop via a coupler or extractor, or via a Wi-Fi enabled extractor.

In-house PLC technologies may be more recent that Access BPL, but they aren't exactly new, either. Some key telephone systems and intercom systems have used it for decades. Standards for In-house BPL, a home networking technology, however, are a relatively recent development. Thanks to the HomePlug Powerline Alliance, formed in 2000 by 13 vendors including Cisco and Intel, the HomePlug 1.0 standards, were published in 2001. Those standards are loosely based on Ethernet, as both are based on bus technology, i.e., the use of a shared electrical path, with up to 16 nodes (i.e., devices) transmitting in both directions.

In fact, HomePlug uses the Ethernet framing format, with some modifications. HomePlug compatible devices include PCs, routers, bridges and other devices that use Ethernet, USB and Wi-Fi (IEEE 802.11) technologies. Any such device can plug into standard electrical sockets via a bridge or adapter about the size of a typical power adapter and, thereby, connect directly with the low voltage electric lines (110/220 volts at 50-60 Hz) in your home or office. So every electric outlet effectively becomes a port into a high speed LAN.

The speed rating is an impressive 14 Mbps using the unlicensed frequency band 4.5-21 MHz, according to the standards, with some manufacturers touting much higher data rates using proprietary techniques.HomePlug makes use of a version of OFDM (Orthogonal Frequency Division Multiplexing) specially tailored for powerline environments. OFDM splits the signal into a stream of data symbols for massively parallel simultaneous transmission over a number of narrowband, low data rate subcarrier frequencies. (Note: OFDM is the transmission technique used in 802.11a (aka Wi-Fi5) and 802.11g, 802.16 and WiMax). HomePlug 1.0 specifies 84 equally spaced subcarriers; within each, several differential modulation techniques are employed. As many as 16 nodes can be supported.

Attenuation, or loss of signal strength, is a fact of life. As an electromagnetic signal travels through a medium (e.g., electrical signals through copper conductors) and across various components (e.g., fuse boxes, splices, surge suppressors and circuit breakers), the signal loses some of its strength. Within the limits of the loss budget, which considers the strength of the transmitter, the sensitivity of the receiver and the various attenuating factors between the two, the system will perform adequately.

HomePlug currently offers a range of as much as 300 meters without repeaters, which is well more than the 100 meters supported by 10/100BaseT -- and without the need for running Cat 5 data-grade cable.

Note: UPSs (Uninterruptible Power Supplies) contain transformers, which stop the data communications signal in its tracks. UPSs also typically condition the electric current by running it through a trickle-charge battery pack to smooth the AC waveform in order to filter out power spikes and dips and to compensate for short power interruptions -- this conditioning also strips out the data communications signal. By the way, extension cords should be avoided -- particularly the skinny ones that you use for things like Christmas tree lights -- as they involve one more set of plugs and add to the overall run length with a cord of uncertain performance characteristics.

Interference issues can be significant. EMI (Electromagnetic Interference) sources include brush motors, switching power supplies, fluorescent lights and halogen lamps, all of which produce impulse noise that can affect communications signal integrity over the shared electrical bus. HomePlug deals with these challenges through a combination of forward error correction (FEC) and automatic repeat request (ARQ).As RFI (Radio Frequency Interference) from amateur radio can impact certain frequencies, HomePlug employs spectral density notches around the HAM radio frequency bands, thereby reducing the number of OFDM carriers that can be used in the United States. As noise on the powerline can be highly local to the receiver and as the quality of the channel between any between any two links connecting transmitter and receiver over the common electrical bus will vary, HomePlug 1.0 uses a channel adaptation technique to turn off heavily impaired subcarriers.

Security is always an issue, and particularly so with technologies using a shared bus topology. As multiple premises typically are served from a common electrical transformer, the physical reach of an in-house BPL network can extend well beyond the walls of an individual home or business. HomePlug 1.0 standards include several security options, including 56-bit DES (Data Encryption Standard). In order to secure a given logical network (i.e., in-house), all transmissions between stations are encrypted with a unique, shared network encryption key.

Ethernet rules the LAN domain, and that's a fact. So, it's no surprise that HomePlug 1.0 is based on the Ethernet MAC (Medium Access Control) protocol. That protocol not only is widely deployed and well understood, but also allows HomePlug 1.0 to interface virtually seamlessly with most PCs, with DSL, cable or PON modems (where Access BPL is not used), with Wi-Fi where appropriate and, for that matter, with just about any DTE (Date Terminal Equipment) or data network.

HomePlug employs two frame formats, both of which involve fairly small payloads. This approach facilitates QoS (Quality of Service), which is critical in support of VoIP (Voice over Internet Protocol). HomePlug also uses a variation of the CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance), the channel access protocol used widely in Wi-Fi networks, for example. In conjunction with a distributed priority resolution mechanism that supports up to four priority classes based on VLAN tags (802.11q), this approach further ensures GoS (Grade of Service) consideration (true QoS is a stretch) for delay-sensitive traffic such as VoIP.

HomePlug AV: 1.0 Amped UpHomePlug AV is built from the ground up to support entertainment applications such as HDTV (High Definition TV) and Home Theater. HomePlug AV will run in the range of 2-28 MHz, offering a raw signaling speed of up to 200 Mbps through the use of OFDM. Once TCP/IP and other overhead considerations are taken into account, the actual throughput will be in the range of 100 Mbps.

HomePlug AV will offer inherent GoS consideration through the use of IEEE 802.1Q VLAN (Virtual Local Area Network) tags for marking high-priority traffic such as VoIP (Voice over Internet Protocol) and the streaming audio and video components of HDTV. HomePlug AV improves on 1.0 security through the use of 128-bit AES (Advanced Encryption Standard), which is virtually unbreakable.

Plug & Play?

Tests in some 500 homes showed that 80% of outlet pairs can connect at 5 Mbps or better, and 98% at 1 Mbps or better. That all depends on the condition of the inside wire, of course. I live in a beautiful old (1909) four-square farmhouse with some remaining knob-and-tube wiring that somehow evaded the restoration and upgrade process some years ago; so I'm a bit leery. But, heck, I have some problems with my 802.11b/g network as well.

Some systems are targeted toward commercial office building and hotels and motels that can't easily be rewired with Cat 5/6 for DSL or PON, and that aren't suitable for WLANs. Since some such buildings have their own transformers, issues of sharing bandwidth with neighbors are avoided.The HomePlug 1.0 limitation of 16 nodes can be overcome with a dash of proprietary technology supplies by systems such as those from Asoka and Telkonet. Proprietary technology also is required to deal with the three-phase power supplies found in some commercial buildings. One also must consider bandwidth, which is just too limited at HomePlug 1.0 best-case rates of 14 Mbps. Some proprietary systems use technology from Intellion, supporting raw signaling rates up to 85 Mbps, which comes very close to 100BaseT performance.

In-house BPL devices, which must comply with Part 15 of the FCC Rules for radiated emissions limits, have been available in stores for many years, although the HomePlug compatible devices are relatively recent.

Who Turned Off The Lights?

In-house BPL may be plug and play, but recess is over during power failures, or so it seems. That can be a big problem in a convergence scenario where we are running voice, data and video over an integrated network.

In the data and video domains, we are used to shutting down when the lights go out, but that's not the case in telecom. Dialtone is line powered and is protected by UPS (Uninterrupted Power Supply) battery systems and backup generators, so conventional phones still work when the lights go out. Some fancy phones, of course, require battery backup, and PBXs and key systems require UPS battery backup.VoIP is another matter, as the hard phones certainly are different and may even be in the form of softphones, or software residing on a desktop or laptop computer equipped with a microphone and speakers. VoIP generally requires a broadband connection like DSL, cable modem or PON. Since unconventional VoIP dial tone is not line powered, voice over these loops requires battery backup at the NID (Network Interface Device). Since BPL runs over the same electric grid that powers it, power failures are a big deal. I don't see that addressed in the standards.

Commercial Service Offerings

Although BPL services are not widely available, a small number of companies have begun offering commercial service in the last year or so. Current Communications, which currently operates only in the Cincinnati area, offers the following service options:

In partnership with Ohio-based power utility Cinergy, Current Broadband plans to extend the service offerings to Ohio, Indiana and Kentucky.The City of Manassas, Virginia, which owns its own power utility company, has developed a partnership with ComTek for city wide BPL. Priced at $28.95 per month for residential service and $39.95 per month for commercial service, access speeds are a minimum of 300 kbps, fully symmetric. This compares to $42.95 that Comcast Corp. charges cable-modem customers who also subscribe to its cable television services. Cable throughput in the area is allegedly 600-800 kbps downstream and 128-256 kbps upstream. Plans call for tiered service at much higher data rates.

Other companies currently offering commercial BPL service include Idaho Power (Idacomm), Pennsylvania Power & Light (PPL Telcom) and Central Virginia Electric Coop. Earthlink has been working with Consolidated Edison in New York, and plans to offer BPL service in Manhattan; this is after a successful pilot with Progress Energy outside of Raleigh, North Carolina. Even AT&T had a trial underway with Pacific Gas and Electric (PG&E) in Menlo Park, California, until shifting its focus away from the consumer market in response to the FCC's shifted position on unbundled local loops.

Rules and Regulations

The FCC's primary interest is in Access BPL, as you might expect. The BPL modems that plug into the wall have to comply with FCC Part 15 rules, of course, just as do cordless phones, garage door openers and Wi-Fi components.

Advantages and ChallengesIn its favor, In-house BPL can take advantage of an inside wire system that's already in place and is largely suitable. That certainly lowers the cost when compared to running Cat 5/6 wire for data communications. It also avoids issues of physical barriers to Wi-Fi connectivity, which performs best under line-of-sight conditions.

Challenges include that nagging potential for interference, not to mention brownouts and blackouts. Competition from Wi-Fi definitely will be an issue, especially given pre-N devices, which are currently availability well in advance of the release of the standard.

Into The Future: In Search of The Killer App

The future of BPL is anybody's guess, of course, but some market estimates reach $2.5 billion by 2010. In the face of competition on the from well entrenched DSL and cable modems, and future competition from developing technologies such as PON and WiMax, that number may be a bit on the optimistic side for Access BPL. In-house BPL is interesting and certainly has a market niche to exploit where buildings can't easily be rewired and the promise of HomePlug AV at 200 Mbps is pretty impressive, but 802.11 continues to evolve, with pre-N devices already on the market. But, then, the overall broadband market is huge and $2.5 billion isn't what it used to be.

In-house BPL has one really interesting application that we haven't discussed, and that may be all it needs to take off and eclipse that seemingly optimistic $2.5 billion market forecast. That killer app has to do with networking home electric appliances.Just imagine a house equipped with an intelligent IP-addressable refrigerator, washing machine and dryer, dishwasher, television set, stereo, furnace and central air conditioner. Imagine the software in those intelligent devices being updated via an in-house BPL connection perhaps to access BPL (or DSL, PON, cable modem, WiMax or satellite) to the Internet. Imagine routine monitoring scans and automatic fixes for operational bugs. Imagine the manufacturers' technical support staffs being able to anticipate troubles, diagnose them and even fix many of them remotely, perhaps even before you are aware of them.

Imagine your clothes dryer calling your cell phone to alert you via an SMS message when the towels are dry. Imagine driving out of the parking garage at work and calling your oven to preheat it to 350 degrees so that you can pop that roast in just as soon as you get home. Imagine calling your intelligent IP-addressable steam iron from your cell phone while in transit to the airport for a Hawaiian vacation, just to make sure you turned it off and unplugged it.

Well, that last may be a bit of a stretch, but maybe not. One side benefit of this intelligent, networked appliance scenario is that it will give IPv6 a real boost. After all, IPv4 supports only 4,294,967,296 addresses, and that's not nearly enough to cover the extra pressure from Kenmore, KitchenAid, Maytag, Whirlpool and the like.