Believe it was 1995 or '96. We had 20 remote sites connected with "128K" ISDN connections. There were a pair of PRIs at our main data center. Ascend PRI router (concentrator?) on one end, Ascend ISDN boxes at the remote site. (IRC, Ascend was formed by former Hayes modem engineers). Occasionally there would be issues bringing up a site and I would be invited (allowed?) into the Telco Central Office to troubleshoot. Standard ISDN troubleshooting tools were a laptop, a portable sniffer (Toshiba laptop with 96K of memory and Network General Ethernet adapter), a BERT tester and, occasionally an oscilloscope. For the more difficult sessions I would work with a remote Anixter engineer (before they were bought and screwed up by SBC) who was a veritable rocket scientist. We'd been running clean for a couple of years, and I was on vacation at Disney Florida with my wife and small children when I got the call that one of our supervisors had somehow managed to wipe the configs on the PRI boxes. I spent the next two hours on a bench under the Epcot ball walking one of our best desktop people through reconfiguring the boxes from memory. I do not miss ISDN, 56/64K, T-1, T-3, SONET. Currently running on privately owned fiber and never want to go back.