AT&T 4ESS and N4E Tandem List

 

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