Semaphore Networks

07 June 2010

I’ve just finished reading Keith Roberts’ novel Pavane. It describes an alternate history of late twentieth-century England, in a Europe ruled by a proscriptive Catholic church that has cracked down on technology and progress. The petrol engine is all but vetoed; electricity is heresy. Coal power is as advanced as things get.

The book takes the form of a series of linked short stories, described as measures; the rigid, stately dance of the pavane is an important metaphor for the wheels of repression and revolution, and though only directly referenced at one point, hangs over the entire book. It’s a beautifully written piece, especially as a piece of SF; delicate and ethereal in its description of the myth and magic rooted in English history, solid in its telling of a world where backstory has to be uncovered, rather than laid out.

Right now, though, I wanted to share a quotation, both for the vision it describes and the design it fictionalises.

In Roberts’ England of the late twentieth-century, the primary long-distance communication method is sempahore. Towers of various sizes, from giant, 12-man beasts, to little repaters, litter the landscape, and messages are transmitted, encrypted, across the nation. The Guild of Signallers is a powerful group as a result, and semi-autonomous from the church. These messages are not just sent point-to-point, either; they travel the land, bundled up with routing instructions, finding new routes when towers break down.

And, in one marvellous passage, coaxial messaging is explained:

The actual transmitted information, what the Serjeant called the payspeech, occupied only a part of the signalling; a message was often almost swamped by the codings necessary to secure its distribution. The current figures for instance had to reach certain centres, Aquae Sulis among them, by nightfall. How they arrived, their routing on the way, was very much the concern of the branch Signallers through whose stations the cyphers passed. It took years of experience coupled with a certain degree of intuition to route signals in such a way as to avoid lines already congested with information; and of course while a line was in use in one direction, as in the present case with a complex message being moved from east to west, it was very difficult to employ it in reverse. It was in fact possible to pass two messages in different directions at the same time, and it was often done on the A Class towers. When that happened every third cypher of a northbound might be part of another signal moving south; the stations transmitted in bursts, swapping the messages forward and back. But coaxial signalling was detested even by the Guildsmen. The line had to be cleared first, and a suitable code agreed on; two lookouts were employed, chanting their directions alternately to the Signallers, and even in the best-run station total confusion could result from the smallest slip, necessitating reclearing of the route and a fresh start.

I really liked that.

It’s not a representative passage of the book as a whole, though; Roberts isn’t obsessed with the machinery of a low-tech world, but the thought behind his world-building is evident throughout, and I loved (in this case) the construction not only of the mechanics of sempahore towers, and the shape of the network, but also documenting the skills and learning necessary to master it. It felt worth sharing, overlapping so many interests all at once.