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24 Aug 2008

Home Power-Line Networking Basics

For the past several weeks, ever since moving into a new apartment, I’ve been racking my brain (and amassing a vast array of new drill bits) trying to figure out how to wire it for data. After some bad experiences trying to get MythTV to stream MPEG-2 video acceptably over 802.11g, I was convinced that the only network worth having was one built on good old UTP.

In the old apartment, I’d managed to successfully run Ethernet cabling from floor to floor and room to room without a lot of destruction or (almost equally importantly) visibility, by running it through the air ducts, along the plumbing, and through carefully-bored holes in closets and crawl-spaces. Unfortunately, none of the tricks that worked in previous places got me anywhere in the new one. All the ductwork has long horizontal runs and mysterious corners; the plumbing is sealed behind walls; there’s no attic or unfinished basement to run through … it’s just generally not friendly to guerilla networking projects.

In desperation – more than a week of MythTV-less existence was not winning me any friends – I started researching power-line and phone-line networking as alternatives to actually running new cable. Quite a lot has developed since the last time I ran a home network over phone wires (when Farallon’s PhoneNet was high tech), and there are quite a few options available.

The first decision to make is which medium you want to run data over: power lines, phone lines, or coax. Each has advantages and disadvantages.

Cable TV coax provides a high-quality medium for data transmission, but in many homes and apartment buildings that were constructed before cable TV became the norm, coax may only run to one or two locations. Also, the dominant standard for home networking over coax, HomePNA 3.0, supposedly doesn’t coexist with DOCSIS cable modems. That was enough to scare me away, since the last thing I want to do with my home LAN is interfere with my only Internet connection option.

The next-best option for a wired home LAN would seem to be phone wiring. HomePNA is also the dominant standard there, although you could probably cobble something together with VDSL equipment if you could get the gear. Unfortunately, I didn’t find many models available after filtering out the older HomePNA 1.0 and 2.0 devices, which are too slow to really compete with 100BT on Cat5. Apparently the dominant distributor of HomePNA chipsets, CopperGate, is focusing their attention mostly on integrating the technology into IPTV STBs and FiOS gateways. This was one of the few standalone HomePNA-to-Ethernet bridges that I found for sale, and at $83 per unit they’re not cheap.

The other option, and the least elegant in my opinion, is running data over the AC power lines throughout the house. Although they can be prone to creating RF interference, and can have widely varying performance even between different rooms in the same house (or even separate outlets in the same room), they do offer data communication over a basically ubiquitous medium. They’re also some of the easiest devices to find – I found them for sale both in the local computer warehouse (MicroCenter) and Best Buy.

Unfortunately, not all power-line networking devices are created equal. Over the years there have been several (mutually incompatible, naturally) attempts at producing a dominant data-over-mains standard, several of which are available:

The HomePlug 1.0 standard operates at 14Mb/s and was an attempt to reduce the number of incompatible vendor-specific protocols that were proliferating a few years ago, before WiFi took off. HomePlug 1.0 devices are available from quite a few vendors, although not all of them mark them as such. They have the benefit today of being relatively cheap and easy to find, but 14Mb (under optimal conditions) is unacceptably slow for what I needed them to do. The Netgear XE102 was among the least-expensive and easiest-to-find devices using HomePlug 1.0. Linksys apparently still sells one, the PLEBR10, but I didn’t see it for sale anywhere.

“Turbo” HomePlug 1.0 devices aren’t part of the official HomePlug standard, but exist as a sort of de facto standard because of a feature in a particular Intellon chipset (the INT5500) that was used in many devices. “Turbo” mode provides up to 85Mb/s under optimal conditions, with reports putting real-world performance down around 20-30 megabits. Theoretically, HomePlug 1.0 Turbo devices from various vendors ought to be compatible. As with HomePlug 1.0, not all vendors seem to be forthcoming about labeling their products with the standard they actually use, but as far as I know, 1.0 Turbo devices are the only ones likely to be labeled as “85 Mbps”. Netgear labels their Turbo devices as “85Mbps Powerline”, eschewing the HomePlug branding completely.

As far as I can tell, Netgear’s “Powerline HD” is a proprietary protocol used only by a handful of their power-line networking devices. It allegedly provides up to 200Mb/s, but isn’t compatible with 200 megabit devices from other vendors. The HDX101 seemed to be the most common device using this scheme, although there’s also the HDX111 which (despite being called “Powerline HD Plus”) is apparently identical except for providing a pass-thru outlet.

The newest version of the HomePlug multi-vendor standard is the ‘AV’ variant, which provides for speeds up to 200Mb/s (150Mb/s usable, after overhead) under optimal conditions, with QoS and AES encryption. HomePlug AV devices are available from several vendors, and seem to becoming the dominant power-line networking standard, displacing the 85Mb ‘Turbo’ and 200Mb proprietary devices at the top of Linksys’ and Netgear’s lineups. Netgear offers HomePlug AV – calling it “Powerline AV” – in the XAV101, priced at an MSRP of $80 ea. or two for $140 as the XAVB101. Linksys matches this with the PLE200 (PLK200 for the bundle of two), priced similarly.

At this point, I think a person would be foolish to buy anything except the newest HomePlug AV devices, since any of the earlier revisions are likely to become obsolete and hard to find soon. In particular, the proprietary 200Mb devices seem like they should be avoided like the plague.

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