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Ups and downs of FT1.


Sometimes obtaining even the most typical services--like fractional T1 for your network--is a struggle.

"If anything can go wrong, it will go wrong," warns Ed Hodgson, communications and computing manager for Schindler Elevator, based in Morristown, N.J.

Hodgson discovered that the telcos, in many cases, had no idea at all how to arrange local access via T1 with B8ZS (bipolar eight zero substitution) and ESF (extended superframe format) services.

B8ZS allows 64-kb/s clear data per channel, inserting two violations of the bipolar line-encoding technique rather than one for every seven consecutive zeros.

ESF is a T1 standard that uses 24 frames instead of the old standard 12. It not only provides for frame synchronization but adds a cyclic redundancy check, which allows for error and end-to-end performance monitoring.

Hodgson wanted to go the inexpensive route--CSUs playing the role of an FT1 mux--but they only handle one channel, whether a DS0 or multiple DS0s. "We had 384 kb/s split into two 192-kb/s from remote LAN gateways with parallel backup, and an additional two 64 kb/s for stat-mux access."

He originally wanted to run a link from Morristown to a facility in Toledo, Ohio.

The "simple" service was to be ready by March 5 of this year. It was May 15 before he actually was able to use it.

The first roadblock: the LECs do not support B8ZS/ESF on a tariffed basis.

Next, it seemed all carriers had problems testing clear-channel B8ZS and ESF.

Ear And Mouth

"They use the old ear-and-mouth method," Hodgson groans. "If you can hear it and speak over it, the technicians figure it's working."

Many carrier personnel do not know anything about B8ZS or ESF.

Hodgson discovered the testing problem when he realized the carrier planned to carry his service as eight DS0 channels, not as a single block.

"When you select local access, tell the LEC which channels you want toi use on local-access T1s. If you want channels one to eight, tell them." And make sure all the DS0s have the same routing. The IXC won't necessarily do that.

"We got CRCs [cyclic redundancy checks] on the ESF frames. The DS0s were routed over different facilities. We had 90% errors coming over."

After checking costs, Hodgson discovered backbone network costs can be greater than DS1.

Local access, in many cases, is via zero-mileage T1. In Schindler Elevator's case, a digital route between Randolph, N.J., and Philadelphia with 56-kb/s DDS costs just $100 more per month than analog service. "That's cheap when you consider the control and lower error rate."

He'll drop all analog service, starting with leased lines.

When planning the new network, Schindler Elevator looked at LiTel, Southern Cable, Cable & Wireless, AT&T, MCI, and US Sprint.

"Generally, the difference in cost at the different locations was the cost to get to a POP," says Hodgson.

AT&T's POP in Morristown is in line of sight from his headquarters office. They won the bid there.

For a run to Schindler's North Carolina facility, Cable & Wireless was the low bidder, but they were using several fiber-optic carriers.

Carolina Telephone was one of the few telcos that Hodgson found was a pleasure to work with. If their engineers said it was feasible, their salespeople arranged to get it done.

To top off the Carolina installation, plans to purchase primary-rate ISDN services for the switch there.

"With Jersey Bell and PRI, it was like talking to a stone wall," he laments.
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.

Article Details
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Title Annotation:fourth of seven articles on T1 communications; fractional T1
Author:Harler, Curt
Publication:Communications News
Date:Oct 1, 1990
Previous Article:Econo-LAN & brouters end utility data snags.
Next Article:T1 backbone cures school growth pains.

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