In this Network Hands On, I’d like to revisit the question I tried to address in my last column – “If Powerline/Homeplug devices can communicate across circuits, will devices in the next house or office, or even down the street, be able to connect to mine?”

I’ve always been sceptical that this might be possible and ran a few tests with a neighbour to check, but it seems I didn’t quite appreciate how AC power is distributed in the UK and didn’t do as much testing as necessary.

Several of you wrote in pointing out where I went wrong, but I’m most grateful to David Mowbray of Sheffield University who sent the following.

“I read with interest your article concerning Powerline networks in the March edition of PCW. However, the issue of security and your test of a possible connection to a next door house has additional complications.

“The power cables running down a street contain three separate supplies, referred to as the three phases. While all three of these phases will be fed into large buildings, as this allows powerful equipment to be driven, only one of these phases will be fed into an individual house. Hence along the street one-third of the houses will be connected to one phase, one-third to another and so on. If two houses are connected to different phases then no connection will be possible between Powerline networks in these houses.

“Although a third of houses will be connected to a given phase, the connections are made at random, so two adjacent houses could be on the same phase but only with a one-third probability.

“Hence to fully test the security of this system you need to try to establish a connection first with the house next door, then the next one down the street and so on. You should also test two houses on the other side of the road.

“As you say, encryption should be turned on, so the above is less of an issue but could be important if you were deliberately trying to establish a network between neighbouring houses. Also it is possible that in some large buildings different parts of the building may draw their power from different phases.”

I’ll leave the issue for now and simply reiterate that it’s unlikely to be an issue for most domestic users, and agree with David that if you’re worried then you should make full use of the encryption offered to scramble and thus protect your data.

Practical encryption
Most of the Powerline/Homeplug devices I’ve tried have fallen into one of two categories: those that use software to set up and manage encryption, and those that do it all in the hardware. Of the two, the latter are still in the minority but are the easiest to configure, as with Solwise NET-PL-200AV Push adapter, which was reviewed in the January issue.

The Solwise Push adapter is a £50 ex Vat 200Mbits/sec Homeplug device. Encryption can be configured using software if you want, but there is also a button that can set it for you. Referred to by the developers as Simple Connect, this tells the adapter to find others on the network then decide on a randomly generated, 128-bit AES key, also called the private network name, to scramble data.