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American Airlines keeps T1 network at 99.8% availability.

With reservations for 35% to 40% of the airline miles traveled in the U.S. flowing through one system, network availability is absolutely critical.

Sabre Computer Services, a division of American Airlines, keeps its T1 network available 99.8% of the time. The data network, with a bit of voice mixed in, is used to book twice as many miles as American flies; obviously, othr airlines depend on it as well.

That makes the network "a major asset to the travel industry," declares Homer Huddleston, vice president of communications operations for Sabre Computer Services.

Sabre's T1 network, which it calls WIN (Wideband Integrated Network), provides connectivity to Tulsa from five vast reservations offices and the major airports that American serves.

To assure availability, the network is designed with dual feeds into reservation offices, major airports, and the largest travel agencies. There is also dial backup in place for additional diversity.

"We manage the network to approximately 99.8% availability," Huddleston boasts. "That is done by virtue of the diversity that's in the design as well as rapid restoral activities."

Sabre has AT&T's Software Defined Network to handle internal voice communications (MCI handles off-network outbound calls), but overflow and diverted calls do travel over the WIN network.

"We handle 125 million calls a year into our reservation offices," says Huddleston. "They come through the public network, into our automatic call distributors at those offices, and only the overflow and diversion between those offices ends up going over the voice portion of the WIN network."

From major data locations out to small airports and travel agencies, Huddleston explains, Sabre has used a multidrop circuit approach.

The WIN network is based almost exclusively on Network Equipment Technologies equipment. It uses NET's and homegrown network management packages, and NET voice compression equipment.

Huddleston says the network routinely compresses its voice traffic to 32 and 24 kb/s, and only recently began compressing it to 16 kb/s.

Multiple T3s

Sabre and American are among the elite group of T3 users. There are several T3s, actually, between Tulsa and Dallas. Dallas is American's headquarters, but Tulsa houses a major maintenance base, corporate accounting, and of course the computer center.

"We have multiple T3s between these two locations. It is not highly likely we would migrate to a lot of T3 around the country. The primary reason is that we are also in the process of rolling out an X.25 packet switch network. AANET," explains Huddleston.

AANET, a 117-node network, is being put into place over the next couple of years. It marks a change in networking strategy that allows Sabre to establish a point of presence in virtually every LATA (Local Access and Transport Area) in the U.S.

With that presence, Huddleston explains, "Then we can use individual drops from that node to travel agencies, rather than the complications of a multidrop environment where several agencies are in essence on the same line. It simplifies the architecture.

"Except for that dedicated circuit from the travel agency to its nearest node, the network is a virtual network. That gives us additional traffic efficiencies, because obviously the traffic load is quite variable.

"With the multidrop network and its dedicated circuits, all the way back to Tulsa, whether they ride on the WIN network or were part of the outlaying circuits, they remained dedicated.

"Now, as we migrate away from a multidrop environment, this will keep WIN from growing as significantly over the next few years, but we will not take out the WIN circuits. In some cases we will feed some of those 117 nodes through the WIN network," says Huddleston.
COPYRIGHT 1991 Nelson Publishing
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Copyright 1991 Gale, Cengage Learning. All rights reserved.

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Publication:Communications News
Date:Oct 1, 1991
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