Monday, July 26, 2010

Succulents and (tele)protection mechanisms

My wife and I cultivate succulents, plants that store water. Cacti are succulents, but we don’t collect them – only the cuddly and outwardly types. What I find so interesting about succulents is that the various types are relatively unrelated – there was never a proto-succulent that evolved into many subspecies. Instead many different kinds of plants developed similar mechanisms to cope with the same problem – that of conserving water. For example, the American Agave (from which Tequila is made) family looks so similar to the African Aloe (from which Aloe Vera is derived) family, that it is hard to tell them apart.

The same thing happens in different families of technologies. For example, in-building wiring in the UK uses ring circuits, where wiring goes from the fuse box to each of the receptacles, and back to the fuse box. In this way one can get away with smaller-diameter conductors than needed with a "radial circuit", since there are two parallel paths from the fuse box to each receptacle. Furthermore, if a wire is disconnected along one direction from the fuse box, there is still electricity at all of the receptacles. This is similar to what we call in communications engineering a 1+1 protection mechanism. In 1+1 protection the information is sent around a ring in both directions, and a copy that makes it (first or best) to the destination is extracted.

On the other hand, high-voltage electric distribution systems use a mechanism called "teleprotection" in order to bypass faults. When a fault is detected large relays switch in order to bypass the fault. This is similar to what we call fast reroute (FRR), in which detection of a communications network failure triggers rerouting of information around the failed link or element.

So, two of the protection mechanisms used in communications were independently discovered and implemented in electric wiring as well. I find that as interesting as succulents.