Laser Beam Links Token Ring LANs Between Buildings
 
Microbytes Daily News Service
Copyright (c) 1989, McGraw-Hill, Inc.
A new device from Laser Communications Inc. uses infrared laser
beams to connect token rings in separate buildings into a
single physical LAN. The transceiver units attach to rooftops
and can transmit data up to a kilometer (0.6 miles) across
unobstructed space at 4 megabits per second, the company says.
 
The LACE Token Ring System units follow similar devices for
ethernet LANs and T1/T2 connections previously released by LCI.
All the products use similar modulation and laser technology,
and all offer the benefit of connecting disparate facilities
without cable or microwave links. Because they replace wiring
at the physical layer, LACE units also operate at full network
speeds, much faster than modem links, and require no special
error correction, LCI says.
 
LACE systems, including two transceivers and the interface units,
sell for $26,649 and are available now.
 
Running cables between buildings is often complicated by the
need to obtain permits and right-of-way licenses, while
microwave links must be approved by the FCC and are subject to
security problems such as eavesdropping. By contrast, LACE
devices can be installed by trained in-house technicians and
require no approvals, the company said.
 
The new token ring units are fully IEEE 802.5 and IBM Token
Ring-compatible and attach to the network via indoor interfaces
that act like repeaters. The interface units are nodes on the
network, so the laser beam simply substitutes for wiring. Error
detection and correction is handled by higher-level software
protocols.
 
Each LACE unit can both transmit and receive data simultaneously,
allowing full duplexed operation. The transmit lens uses a
focused infrared laser diode (not an infrared LED), emitting a
beam of invisible coherent light that spreads from a few inches
across at the point of transmission to 8 feet across at the point
of reception. The two units must be carefully aligned and
calibrated so that the receiver is within 4 feet of the center of
the beam.
 
The path between the units must be completely free of
obstructions or interference, such as from vented heat. In the
event of a blockage, the network would attempt retransmission.
LCI admits that a thick fog would shut down communication.
 
Coincidentally, an Australian company recently announced a
similar infrared laser system for AppleTalk networks that
supports both LocalTalk (230,400 bps) and TOPS FlashTalk
(768,000 bps) data rates. The DPX-725, from Dataplex Pty. Ltd.,
also requires line-of-site installation and can transmit up to
1 kilometer between units. The units sell for between $13,000-
$15,000 Australian, or roughly $10,140 to $11,700 US dollars.
 
Contacts
 
Laser Communications Inc., 1848 Charter Lane, Suite F, Lancaster,
PA 17601; (717) 394-8634 or (800) 527-3740;
 
Dataplex Pty. Ltd., 7-9 John St, PO Box 541, Lilydale,
Victoria, 3140, Australia; (03) 735-3333; fax (03) 735-3830.
 
                              --- Andy Reinhardt
 
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