The following is a work in progress in trying to maintain an active catalog of the Number 4 Electronic Switching System (#4ESS) Class 4 Tandem list for the AT&T long distance network. This list is a successor to the original list made by the late telephone historian and researcher Mark Cuccia (1961-2014) to try to encompass the changes in the #4ESS network since his passing.
The #4ESS switch was first installed in Chicago, IL in 1976 as the successor to the 4A crossbar switch. Over 100 #4ESS switches were installed in the PSTN by the early 1990s for AT&T Long Lines, and a number of them were also used for the regional Bell operating companies. A second batch of #4ESS switches (what I call “2nd Generation”) were installed in 1998-1999 and were the last #4ESS switches installed in the PSTN, with the one in Atlanta (number 146-T) being the last one ever.
Starting in or around 2012, a new batch of #4ESS type Class 4 switches were starting to show up in the PTSN. This is the successor switch called the Next Generation 4ESS or N4E. The N4E emulates the #4ESS software in a new hardware environment. The main difference to the end user is that the tandem recordings are very clean (no magnetic drums) and sound a bit robotic in nature.
This list not only contains the #4ESSes in the network, but the new N4E switches as well. In some cases, there are N4E switches that are replacing 4ESS switches, and in some cases they are brand new to the network (those numbering 147 and higher). It is assumed that the new N4Es are replacing the #5ESS switches that were originally installed to be “edge tandems” in the AT&T network and upgrading them to full Class 4 tandems.
The locations for the new N4E switches (147 and higher) are best guesses, and in some cases appears to be replacing existing #4ESS switches and taking on new identities, while in other cases they take on the old trailer code (known as the Network Switch Number of NSN) of the #4ESS that they replaced.
Confirmed 4ESS or N4E - Survey as of April 2025 NSN Switch Name, ST Type Install Date Last Verified Date 007 ATLANTA 4 GA N4E Replaced Mar 2025 008 AUSTIN 2 TX 4ESS 01/01/87 Mar 2025 014 CHICAGO 9 IL 4ESS 08/01/87 Jun 2024 019 COLUMBUS 3 OH N4E Replaced Mar 2025 024 DES MOINES 2 IA N4E Replaced Mar 2025 027 DENVER 5 CO N4E Replaced Mar 2025 030 FREEHOLD 2 NJ N4E Replaced Mar 2025 031 FRAMINGHAM 4 MA 4ESS 05/01/87 Mar 2025 032 FORT WORTH 2 TX N4E Replaced Mar 2025 034 GREENSBORO 3 NC N4E Replaced Mar 2025 035 GARDENA 3 CA 4ESS 06/01/87 Mar 2025 037 HOUSTON 4 TX N4E Replaced Mar 2025 040 JACKSON 2 MS N4E Replaced Mar 2025 043 KANSAS CITY 2 MO N4E Replaced Mar 2025 044 LANSING 3 MI 4ESS 05/01/87 Mar 2025 048 LITTLE ROCK 2 AR N4E Replaced Mar 2025 056 MONTGOMERY 2 AL N4E Replaced Mar 2025 058 NASHVILLE 2 TN N4E Replaced Mar 2025 065 NEW YORK 12 NY(QUEENS) N4E Replaced Mar 2025 067 OAKBROOK 2 IL N4E Replaced Mar 2025 068 OAKBROOK 3 IL 4ESS 06/01/88 Nov 2024 070 OAKLAND 6 CA N4E Replaced Mar 2025 071 OMAHA 2 NE N4E Replaced Mar 2025 076 PITTSBURGH 3 PA N4E Replaced Mar 2025 077 PORTLAND 3 OR N4E Replaced Mar 2025 078 RICHMOND 2 VA N4E Replaced Mar 2025 083 SACRAMENTO 4 CA N4E Replaced Mar 2025 084 SHERMAN OAKS 5 CA N4E Replaced Mar 2025 087 SAN ANTONIO 2 TX N4E Replaced Mar 2025 088 SAN DIEGO 3 CA N4E Replaced Mar 2025 089 SAN FRANCISCO 4 CA N4E Replaced Mar 2025 094 SAINT LOUIS 3 MO N4E Replaced Mar 2025 096 SYRACUSE 2 NY 4ESS 03/01/85 Mar 2025 098 TOLEDO 2 OH 4ESS 04/01/84 Apr 2025 100 WASHINGTON 6 DC N4E Replaced Mar 2025 103 WHITE PLAINS 3 NY N4E Replaced Mar 2025 105 WAUKESHA 3 WI N4E Replaced Mar 2025 110 CHICAGO 11 IL N4E Replaced Mar 2025 111 NEW YORK 55 NY N4E Replaced Mar 2025 115 PITTSBURGH 9 PA 4ESS 12/01/88 Jun 2023 129 DUNNIGAN CA N4E Replaced Nov 2024 139 ANCHORAGE AK 4ESS 03/01/96 Mar 2024 142 DENVER CO 4ESS 1998/1999 Nov 2024 144 MONROVIA MD 4ESS 1998/1999 Apr 2025 147 Chicago IL? N4E 2012? Mar 2025 148 Boston MA? N4E ? Mar 2025 149 Mesa AZ? N4E ? Mar 2025 150 Atlanta GA? N4E ? Mar 2025 151 Fort Myers, FL? N4E ? Mar 2025 152 Gardena CA? N4E 2012? Mar 2025 153 MA? N4E ? Mar 2025 154 Dallas TX? N4E ? Mar 2025 155 Scottsdale AZ? N4E ? Mar 2025 156 Buffalo? N4E ? Mar 2025 157 Jacksonville FL? N4E ? Mar 2025 158 Anaheim, CA? N4E ? Mar 2025 159 Wayne PA? N4E 2016? Mar 2025 Assumed still in service, but not 100% sure NSN Switch Name, ST Type Install Date Last Verified Date 012 BATON ROUGE 2 LA 4ESS 03/01/84 Nov 2023 029 DAYTON 2 OH 4ESS 02/01/87 033 GRAND RAPIDS 3 MI 4ESS 05/01/84 045 LOS ANGELES 5 CA 4ESS 02/01/83 117 HAMILTON SQUARE 2 NJ 4ESS 07/01/91 Jan 2023 121 HILLSBORO MO 4ESS Unknown Jan 2023 124 PLANO IL 4ESS 12/01/92 129 DUNNIGAN CA N4E Replaced May 2023 133 WHITE PLAINS 4 NY 4ESS 08/01/93 135 CHERRYVILLE NJ 4ESS 05/01/93 Assumed disconnected, but not 100% sure NSN Switch Name, ST Type Install Date Last Verified Date 122 FINKSBURG MD N4E Replaced Mar 2024