Wasn't that the one that failed in numerous exchanges all across the
> country as a result of a software bug?
The software problem you're referring to was the infamous crash of the AT&T long distance network in 1990 when a software upgrade was applied to the over 100 AT&T/Western Electric #4ESS long-haul tandems in the US. It brought down most if not all the #4ESS switches to a screeching halt for the better part of a day.
AT&T had to do an about-face and go back to a previous software version until they got the bug fixed!
Here's an article written about the incident:
formatting link
Dave Perrussel Webmaster - Telephone World
formatting link