They only lean toward MAC/IP topologies in BPL. In lower-bandwidth scenarios (metering) they go a variety of ways, largely because extended distances mean signals from a given node won't be visible across the entire network, which forces a repeater mechanism of some kind. It gets complex fairly quickly, especially in commercial systems, where huge banks of fluorescent lights create some unpredictable behavior.

Making things worse are the customers who have heard about BPL and say, "Why can't you just replace all these devices with something that does broadband and greater throughput?"

Actually, the way they do this is using an address layer like most any other protocol. A bunch of different topologies exist, but generally speaking, each monitored node will be uniquely addressable with a value embedded in the data frames rather than just by frequency. Multiple frequencies are used to dynamically adjust to the presence of various types of noise.

How about a jar full of mosquitoes instead? - Tim

People said the same thing when they launched the Zune. Go figure. - Tim