D-Link's Powerline starter kit provides a useful way of bridging or extending an Ethernet network over the mains. It includes two of the company's DHP-300 Ethernet-over-mains adapters, plus cables and set-up software on CD. More adapters can be added to the network later if needed.
The adapters are large blocks with a 3-pin mains plug built-in, plus a Fast Ethernet port. Each adapter has three lights, one for power, another for a live Ethernet connection and a third to say, "Hey, I can see other PowerLine adapters like me!"
Normally you would plug one adapter into a router or switch; this in effect becomes the master, and other adapters can then connect through it as long as they have the right network and security settings.
The set-up program uses the open-source WinPcap packet capture utility to scan for other PowerLine adapters. The version of WinPcap supplied is not the latest though, so you may want to download that and install it before proceeding.
Configuration options for the devices are minimal - give each one the same network ID and encryption key (encryption is turned on by default, but using a default key), and its own alias, and you have a network. The system then taps into the host network for DHCP and DNS.
Ethernet over mains wiring has been around for a few years now. Initially, there were different versions but the technology has now been standardised by the HomePlug Powerline Alliance, with the latest [pre-standard - see below] versions of the spec offering a theoretical 200Mbit/s (Fast Ethernet full-duplex).
As the name implies, the spec's main thrust is home networking, with that 200Mbit/s being calculated to support high-def TV. However, Powerline is also finding use now in businesses both large and small as a way of extending network coverage, for example where cables cannot be installed and wireless is impractical, such as in thick-walled listed buildings.
A pair of Powerline adapters could offer a quick and simple way of adding an Ethernet switch or a wireless AP at the other end of the building, say.
There are caveats, however. Ethernet performance can be affected by the quality of the wiring - the manufacturers advise against connecting Powerline via an extension cable for instance, while surge-suppressors can block the signal altogether. And unfortunately, there don't seem to be any tools available to test the quality of the connection or wiring.
In our case, we were disappointed to find that we were unable to get much above 12Mbit/s or so - and this was on a laptop which if cabled directly to the same switch could pull files over at 70Mbit/s or so. We tried turning off appliances that we thought might be generating noise, but it made no difference.
Sure, PowerLine speed is dependent on the wiring quality but even so, 12Mbit/s looks slow. Then again, in the real world of wireless interference, 802.11g wireless is often no faster than that.
It also seemed odd that while each client PowerLine adapter is presumably going to be connected to a networked device, it needs its own power socket. Wouldn't it make a lot more sense for the adapter to have a socket of its own, so you could plug the PC into the adapter and then the adapter into the wall, saving a socket? After all, there's already far too many socket-doublers and multi-way extension leads in use.
Still, Powerline is dead easy to set up and use, and makes it simple to bridge or extend a network. Its speed will depend on your mains cabling, but it should be at least as fast as the average WiFi network - and it won't be broadcasting your traffic to everyone within half a mile.
Our thanks to Carlos Sala, who writes to point out that while D-Link's devices - and others from other manufacturers - all conform to the Universal Powerline Association (UPA) specs, there isn't yet an agreed spec for 200Mbit/s Powerline - the specs currently only guarantee interoperability up to 95Mbit/s.
As he says: "All Powerline manufacturers (the main ones are DS2, Intellon and Panasonic) have delivered open standards describing their 200 Mbit/s technology (UPA-OPERA, HomePlug and HD-PLC respectively) and all of them are present in the main standardisation organisms (IEEE, ETSI and others), but no final proposal has been approved yet by any of these organisations. This process may still take indeed 1 or 2 more years, according to the experience with other technologies."
Well worth a look if you simply want to add a switch or wireless AP in an area of the building where you don't have Ethernet cabling.