Texas-size testing job

Communications News, May, 1990 by John Jesitus

TEXAS-SIZE TESTING JOB

The University of Texas at Austin literally has a testing job as big as all Texas on its hands. It maintains 5000 miles of leased transmission lines supporting the school's statewide voice, video, and data network.

Network locations include research giants such as the M.D. Anderson Cancer Center in Houston and the Southwestern Medical Center in Dallas. Fifteen campuses stretch from Galveston to El Paso and from Dallas to Brownsville. Thirty telecomm staffers, half of them in centrally located Austin, ride herd on the network.

Over half the University of Texas' 100,000 students are at Austin. A Northern Telecom SL-100 switch there supports over 50,000 lines and 1000 PBXs at satellite institutions.

"Most of our voice connections are the equivalent of a small town," explains Communications Analyst John Kilgore. The school's packet-switched IBM SNA data network--which is "spread all over the place," he says--supports not only internal users but connections to nearly all Texas colleges and many out-of-state schools via major academic networks like Internet. "We just turned up a 56-kb/s data circuit between Midland-Odessa and El Paso, a 400-mile circuit. At the same time we were turning up another 200-mile circuit between Midland-Odessa and Lubbock. It's like that all the time."

Dreaming Of Zero Error

Microwave links provide intra-city hookups for component sites. Data-network error rates are [10.sup.-6], "not real good" by Kilgore's standards but plenty usable. "We'd like to see at least [10.sup.-9]."

Austin uses two Phoenix Microsystems 5575A test units and one 5148 to turn up and troubleshoot transmission lines on a daily basis. At least one 5575 at each of 14 other sites will be installed.

"They're fairly easy to use," Kilgore says of the Phoenix units--though no line tester he has seen is simple. "They all assume you know what you're doing," he remarks.

A 5575 T1 MicroBERT test set at each end of a circuit allows drop-and-insert testing. Austin transmits a BERT test to a remote end, and vice versa. Signals are compared to establish an error rate.

This process identifies bipolar variations and monitors signal levels. The test unit generates loopback codes to specific transmission equipment to find where problems start.

Picking the 5575 and 5148 made sense; Southwestern Bell uses the 5575 to test its own lines. "We can talk their language if we've got a problem," Kilgore says.

Maintaining the university's 1.544-Mb/s, full-T1 video instruction network presents the greatest challenge. It uses bidirectional compressed video signals to deliver classroom instruction between two cities.

World War III

"If I get one bit error in a video frame, it's going to cause the codec to reframe," Kilgore says. "It makes the television picture go to hell in a handbasket and the audio sound like World War III."

On a voice-only DS1 most people won't notice a bit error rate of [10.sup.-9], but in video [10.sup.-12] is "barely usable," he says.

In late March the school's TAGER (The Association for Graduate Education and Research) video network added a 12-mile fiber link tying its Robotics Institute in Ft. Worth to the University of Texas at Arlington (see p. 15).

"We wanted a system whereby we could lead a seminar at the institute, send it back to [the Arlington] campus and tie into the University of Texas TAGER network," says Craig Vanbebber, corporate relations manager at the Arlington campus.

Microwave links tie Dallas/Ft. Worth businesses into the show. The new fiber supports two 45-Mb/s full-motion digital video signals in each direction, letting remote participants be seen as well as heard.

Users of Arlington's CAD network may now log into the Robotics Institute network to manufacture parts remotely.

Such applications will let multi-location companies centralize functions.

"They won't have engineers strewn about the country, not knowing what the others are doing," according to Vanbebber.

For this application, optical fiber proved much cheaper than microwave-transmission facilities, in addition to being invisible.

A microwave link would have required an "ungodly high tower" and dishes at either end, he says.