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From: rhorn@infinet.UUCP (Rob Horn)
Newsgroups: comp.society.futures
Subject: Long haul fiber optics
Message-ID: <8711231923.AA00352@infinet.uucp>
Date: Mon, 23-Nov-87 14:23:14 EST
Article-I.D.: infinet.8711231923.AA00352
Posted: Mon Nov 23 14:23:14 1987
Date-Received: Fri, 27-Nov-87 23:54:11 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
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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
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