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New York airports speed auto traffic.


To eliminate long exit lines at parking lots and minimize the chance for human error, the Port Authority of New York and New Jersey is spending $33.5 million.

Fiber reliability makes it look like money well spent.

To be completed by 1991 at Kennedy, Laguardia, and Newark International airports, the revenue-control system will track traffic in and out of lots and let travelers prepay parking fees--with cash or credit car--at automated parking machines in baggage areas and other terminal locations.

Private, high-speed, fault-tolerant fiber optic networks at each airport will carry all possible traffic among parking lots, airport computers, and microwave transmission facilities.

Fiber was favored over copper to achieve higher reliability in harsh environments beset by high water tables and electrical noise.

A star configuration was rejected because of the high cost of laying fiber to link a CPU with all parking lots and network nodes--17 exit lanes and 13 entrances at Laguardia, 30 exits and 32 entrances at Newark, 31 exits and 28 entrances at Kennedy.

A star configuration also did not allow for easy expandability as new parking lots, or additional entrance and exit lanes, are added.

Finally, this architecture provided no fault tolerance.

Ring Solution

Nynex proposed a fiber-based, drop-and-insert, counter rotating ring. "With this configuration," explains Jairo Orjuela, associate director of project management at Nynex, "we only had to run a single fiber backbone at each airport to link all the lots."

Data is sent to the lots and transmitted back to the host computer along this backbone, using a time-division-multiplexing technique which allocates separate time slots in the fiber for each node.

With the backbone's 25-megabit bandwidth, 30 high-speed time slots are available to carry asynchronous data at speeds up to 768 kb/s each (or synchronous transmissions at 56 kb/s), and 300 slow-speed time slots offer asynchronous capacity of 64 kb/s each.

With only about half the slots currently assigned, the system will be able to grow easily and inexpensively.

For voice, separate slow-speed time slots are used for each entrance lane. At exit lanes, two slow-spped time slots must carry voice transmissions through an intercom system available for use by customers and cashiers.

High-spped time slots are also used to transport syschronous data at 56 kb/s to and from microwave facilities, which transmit data between the airports and a Port Authority control facility.

The backbone's two fibers are configured in counter rotation. They're laid out in concentric circles--primary and secondary--each carrying traffict the opposite way.

"If the fibers are severed at any location," says Orjuela, "the previous node redirects incoming transmissions back along the secondary fiber to the node located after the break. A similar phenomenon occurs on the return loop."

Thus, network traffic can continue though access to a single node is unavailable.

Because two fibers are involved in this topology, each node has dual optical transceivers--one for each fiber.

The secondary transceiver can be called into service on the primary fiber if needed.

For additional protection, nodes are outfitted with backup power supplies.

Through a network-management system, the exact location of any fiber break or equipment failure is immediately reported back to a terminal on a system administrator's desk.

The network-management package is comprised of this terminal--used to display network alarms and statistics--and network-management modules located at each node. With this terminal, and administrator can configure and control the various network components. If an administrator requires assistance diagnosing and dealing with a malfunction, they simply dial the Nynex maintenance staff, which has remote access to the system.

"The entire network is designed to be highly fault-tolerant, with built-in automatic rerouting capabilities and equipment switchovers," Orjuela says. "But in the unlikely event of an equipment or fiber failure, the network-management system ensures that we can quickly restore the previous fault-tolerant condition."

"Parking is a major revenue generator at airports," Michelfelder adds, "and this network makes sure that all entrance- and exit-lane transaction data is safely transmitted to the data center for processing. the result: all transactions will be accounted for, and the likelihood of losses due to human error--or equipment failure--is virtually eliminated."
COPYRIGHT 1990 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1990 Gale, Cengage Learning. All rights reserved.

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Title Annotation:fiber-optic networks
Publication:Communications News
Date:Dec 1, 1990
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