The disclosed methods and apparatus relate generally to the electronics media industry, such as cable television, home shopping services, on-line computer services and computer memory applications. The conductor segments are switchably coupled to one or the other of the transmission lines or to each other, in parallel with the transmission line structure. In another embodiment, the domain routing table indicates routes containing no intra-domain virtual link that terminates at an edge node and no consecutively concatenated intra-domain virtual links. An inverted U-shaped pole piece retainer 18 made of non-magnetic material such as stainless steel is affixed to each magnet carrier 12 and is formed with an axially extending channel. Deterioration of the optical transmission quality is detected as a resulting deterioration in an electrical output signal and noted deterioration is stored and read out. The cover is adapted to extend over at least a portion of a medical device disposed within the body of the user, and wherein the cover is dissolvable in the body of the user.