Theatre Design & Technology - Summer 1989 - 46

tually lower than the thick coaxial cable. Transmission distances are much
longer in FDDI, with several kilometers possible between stations using
single-mode, low-dispersion, lowattenuation glass fibers. This thin cable is easier to handle and occupies
less space than copper conductor cables, and even less expensive fiber may
be used for shorter distances. Finally,
fiber-optic cable is completely immune to electrical interference of all
types and produces none of its own,
eliminating the need for certification
of systems with the FCC or similar
regulatory agencies.
In its fullest implementation, FDDI
transmits messages from any station
or node to any other via a multi-token
ring system, which allows virtually
any number of tokens to be passed
simultaneously and provides for
many levels of priority to be assigned
to both the nodes and the message
packets. There are two concentric and
redundant rings, both of which normally carry the sanle messages and
are compared by each node to aid in
error correction and system analysis.
Each nybble (half a data byte) is sent in
a coded parity bit error-correcting format so that ring redundancy is not
required.
The system is designed to be so
thoroughly fail-safe that if one of the
redundant rings is umeliable or even
severed complete!)\ no data is lost or
affected and the system automatically
reports the location of the fault I Even
if a particular node becomes faulty or
loses operating power, an optical bypass automatically diverts both in-

corning light signals directly to their
respective outputs, and the lack of
cornn1Unication with that node is reported. Whenever new nodes are
added, an automatic interrogation procedure fully integrates them into the
system.
But what about using such a powerfulnetwork in the theatre? How difficult is it going to be for system
designers to give their communication interfaces the comprehensive capabilities required? Actually, it turns
out that it will be very easy. Major
component manufacturers are already
manufacturing modular FDDI connectors, compatible cable, and, most
importantly, complete integrated chip
sets, making the addition of an FDDI
communication port potentially as
easy as adding a hard disk drive.
Communication cards are now being designed using a five-chip integrated circuit set which automatically
performs encoding, decoding, error
correction, ring-integrity checking,
redundancy, token passing, priori ty arbitration, timing correction, fault detection, node-address generation,
message-packet data storage and retrieval, local multi-port buffer memory management, and local processor
conlli1Unications management.
These chips are brand new and not
particulary cheap, but, as integrated
circuit prices decrease, this will soon
be the most cost-effective way to create any type of networking capability.
Even in the short term, I believe that
whatever costs might be saved by using lower-cost non-FDDI hardware,
much more than that will be spent in

software development simply to create a system that only approaches
FDDI's sophistication.
Once FDDI becomes our standard,
we can then define standard theatre
network messages, assign dedicated
node addresses, and generally become
part of the expanding FDDI standard.
The same FDDI fiber-optic backbone
of our technical theatre systems can
also provide communication between
front-of-house and backstage, box office and accounting, production and
management, design department and
scene shop, payroll and personnel. It
can be an electronic mail and messaging system and can be used for virtually any other communications
purpose in the foreseeable future. It
can do all this and at the same time
fulfill our requirements for a comprehensive real-time control system. A
100-megabit per second (100 000
OOOb/s) data communication rate with
over 2(48) (256 000 000 000 000) node
addresses available ensures nonobsolescence for a long time.
THE FUTURE

So, if all this is possible nm\) what will
the future hold and how does FDDI fit
in? In fact, FDDI II is close to being a
standard of its own; completely compatible with FDDI and possessing the
same physical interface, it adds a
number of enhancements. The major
feature of FDDI II is a time-division
multiplexed mode providing individual routes within the network with a
variety of guaranteed data transfer
rates. This allows the system to auto-

JOEL E. RUBIN &ASSOCIATES
Strategic Planners/Resource Specialists
Consulting Services to Facilities and Companies
for Performing Arts Technology, Marketing, and
Planning
19
44

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