Brittle Power- PARTS 1-3 (+Notes) - Natural Capitalism Solutions

Chapter Thirteen: Designing for Resilience 193more it can itself become a source of failure. For example, redundant guidancegyroscopes and/or computers in most spacecraft are reconciled by a “voting”system—best two out of three—which protects against the failure of any oneunit. But a failure of the device which compares their readings can disable allthe redundant channels simultaneously, leaving the astronauts to make dowith a sextant and a hand calculator.Redundancy and substitutability Individual modules, nodes, or links can failwithout serious consequences if other components are available to take overtheir function right away. This requires redundant, substitutable units. (These,in turn, will be more readily available if they are small and cheap.) Multiplefilaments in a light bulb, or spare pumps in a reactor, or leaves on a tree, illustrateredundant modules. The branching veins in a single leaf, intricately connectedso that nutrients can still flow through alternative pathways after aninsect has chewed the leaf full of random holes, illustrate redundant links. TheBell System’s multiple switching centers provide redundant links and (to alesser extent) redundant nodes to reconnect those links in various patterns.The telephone analogy shows, on closer study, that redundancy is not apanacea. Telephone trunk transmission is very highly interconnected; long-distancecalls are commonly rerouted, even several times per second, without thecaller’s noticing. If a microwave, satellite, or cable link is lost (through failureof the link itself or of a node that connects it into the network), another can besubstituted. But as phone phreaks (Chapter Two) are discovering, this flexibilityof rerouting calls actually depends on a relatively small number of keyswitching nodes. This number is probably only a few. For example, to preventa single nuclear bomb from paralyzing the nation’s telephone system, the Bellsystem has redundant underground control centers in Georgia, Kansas, andNew Jersey. 55 The inference, however, is that three bombs might suffice—ormerely a coordinated electronic assault on two or three nodes via the telephonesystem itself. Some phone phreaks believe that by tying up all the input portsat several critical nodes, perhaps using microcomputer-generated dummy calls,a small group of knowledgeable people could crash the Bell system.It is indeed the very openness of the telephone system, allowing readyaccess from innumerable points, that helps to cause this vulnerability. Mostpeople become aware of the fragility of the phone system only if some mishapcuts off their own call—for example, if a tone in their voice happens to be closeto the frequencies used by switching equipment to signal a cutoff. But suchaccidents normally lose only one’s own call, not everybody’s at once. Whatmay be less obvious is that the multiplicity of relatively open phone links,especially by microwave, facilitate unauthorized access to the phone system.