rhorn@infinet.UUCP (Rob Horn) (11/23/87)
The fastest long distance fiber optic link in commercial operation today is a 1.7 Gigabit/sec link between Philadelphia and Chicago. More typical speeds are 280 Mbit/sec and 450 Mbit/sec (approx.). These are typically resold in units of 56/64 Kbit/sec (voice) or 1.544 Mbit/sec (T1). The fastest long distance (>50 km) links that I know of having worked in the laboratory are presently about 8 Gbit/sec. The approach for reaching 20 Gbit/sec is very clear, and will probably work for traffic up to around 100 Gbit/sec. For various reasons it is very unlikely that speeds above 10 Gbit/sec will be available on a single data channel. The higher speed links use frequency allocation multiplexing of multiple slower (if you consider 2-10 Gbit/sec slow) links. One of the major reasons for this is the difficulty of processing data at those speeds. 10 Gbit/sec corresponds to 100 pico-seconds/bit. Because transistor switching speeds in VLSI are several hundred picoseconds the electronics cannot use VLSI. Light only travels 3 cm in 100 pico-seconds leading to some significant physical design problems. So you can imagine the problems involved in processing data at 100 Gbit/sec. (Actually one of the cuter design features of one of these high speed receivers was a tuned delay line: a piece of coax cut to the precise length needed, and a multiplexor tap: T-connections spaced out along a wave guide. At 100 Gbit/sec a bit is smaller than the diameter of some coax.) Rob Horn UUCP: ...harvard!adelie!infinet!rhorn Snail: Infinet, 40 High St., North Andover, MA (Note: harvard!infinet path is in maps but not working yet)