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 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.
Trailer Code (xxx-T) Location Type Install Date Notes 001 WINDERMERE FL 4ESS (03/1991) Verified Jan 2022 002 ALBUQUERQUE 2 NM 4ESS (11/1977) Most likely decommissioned 003 ALBANY 3 NY 4ESS (01/1982) Most likely decommissioned 004 ANAHEIM 3 CA 4ESS (03/1981) Possibly replaced with 158-T? 005 ARLINGTON 3 VA 4ESS (04/1982) Most likely decommissioned 006 ATLANTA 5 GA 4ESS (03/1982) Could have been replaced with 007-T 007 ATLANTA 4 GA N4E Replaced Verified Nov 2023 008 AUSTIN 2 TX 4ESS (01/1987) Verified Nov 2023 009 BUFFALO 2 NY 4ESS (06/1984) Most likely decommissioned 010 BALTIMORE 10 MD 4ESS (08/1980) Verified Nov 2023 011 BIRMINGHAM 2 AL 4ESS (04/1981) May still be in service 012 BATON ROUGE 2 LA 4ESS (03/1984) Verified Nov 2023 013 NEW YORK 5410 NY 4ESS (07/1991) Most likely decommissioned 014 CHICAGO 9 IL 4ESS (08/1987) Verified Jan 2022 015 CHARLOTTE 3 NC 4ESS (05/1980) Most likely decommissioned 016 CHARLESTON 2 WV 4ESS (02/1982) Verified Nov 2023 017 CLEVELAND 3 OH 4ESS (12/1979) Most likely decommissioned 018 COLUMBIA 2 SC 4ESS (11/1981) Verified Nov 2023 019 COLUMBUS 3 OH N4E Replaced Verified Nov 2023 020 COLORADO SPRINGS 2 CO 4ESS (10/1981) Verified Nov 2023 021 CAMBRIDGE 19 MA 4ESS (12/1984) Verified Jan 2023 022 CAMDEN 3 NJ 4ESS (04/1979) (Disconnected late 2022?) 023 CINCINNATI 2 OH 4ESS (06/1979) Most likely decommissioned 024 DES MOINES 2 IA N4E Replaced Verified Jan 2023 025 DALLAS 3 TX 4ESS (12/1976) Possibly replaced with 154-T? 026 DALLAS 4 TX 4ESS (04/1981) Possibly replaced with 154-T? 027 DENVER 5 CO N4E Replaced Verified Nov 2023 028 DETROIT 3 MI 4ESS (04/1981) (Disconnected circa 2003?) 029 DAYTON 2 OH 4ESS (02/1987) Most likely decommissioned 030 FREEHOLD 2 NJ N4E Replaced Verified Nov 2023 031 FRAMINGHAM 4 MA 4ESS (05/1987) Verified Nov 2023 032 FORT WORTH 2 TX N4E Replaced Verified Nov 2023 033 GRAND RAPIDS 3 MI 4ESS (05/1984) Verified Nov 2023 034 GREENSBORO 3 NC N4E Replaced Verified Nov 2023 (N4E installed 2022) 035 GARDENA 3 CA 4ESS (06/1987) Verified Nov 2023 036 HARRISBURG 2 PA N/A Replaced Disconnected, changed to a 5ESS 037 HOUSTON 4 TX N4E Replaced Verified Nov 2023 038 HOUSTON 5 TX 4ESS (07/1988) Verified Feb 2023 039 INDIANAPOLIS 2 IN 4ESS (10/1980) Most likely decommissioned 040 JACKSON 2 MS 4ESS (04/1983) Most likely decommissioned 041 JACKSONVILLE 3 FL 4ESS (12/1976) Most likely replaced with a N4E 157-T 042 KNOXVILLE 2 TN 4ESS (12/1980) Most likely decommissioned 043 KANSAS CITY 2 MO N4E Replaced Verified Nov 2023 044 LANSING 3 MI 4ESS (05/1987) Verified Nov 2023 045 LOS ANGELES 5 CA 4ESS (02/1983) (Was this replaced with a N4E?) 046 LOS ANGELES 6 CA 4ESS (04/1988) (Was this replaced with a N4E?) 047 LOUISVILLE 2 KY 4ESS (07/1980) Verified Nov 2023 048 LITTLE ROCK 2 AR N4E Replaced Verified Nov 2023 049 MACON 3 GA 4ESS (04/1987) Verified Nov 2023 050 MIDLAND 2 TX 4ESS (10/1983) Most likely decommissioned 051 MEMPHIS 2 TN 4ESS (02/1981) Most likely decommissioned 052 MANCHESTER 3 NH 4ESS (04/1982) Most likely decommissioned 053 (presently unassigned) N/A N/A N/A 054 MINNEAPOLIS 3 MN 4ESS (05/1980) Verified Nov 2023 055 MINNEAPOLIS 4 MN 4ESS (06/1988) Most likely decommissioned 056 MONTGOMERY 2 AL N4E Replaced Verified Jun 2022 057 NORFOLK 4 VA 4ESS (04/1981) Most likely decommissioned 058 NASHVILLE 2 TN N4E Replaced Verified Nov 2023 059 NEW HAVEN 5 CT 4ESS (10/1981) Most likely decommissioned 060 NEW ORLEANS 3 LA 4ESS (06/1980) Most likely decommissioned 061 NEWARK 8 NJ 4ESS (06/1980) Most likely decommissioned 062 NEW YORK 24 NY 4ESS (04/1978) Most likely decommissioned 063 NEW YORK 51 NY 4ESS (11/1984) Most likely decommissioned 064 NEW YORK 5450 NY 4ESS (01/1981) Most likely decommissioned 065 NEW YORK 12 NY(QUEENS) N4E Replaced Verified Nov 2023 066 OJUS 3 FL 4ESS (05/1978) Most likely decommissioned 067 OAKBROOK 2 IL N4E Replaced Verified Nov 2023 (Replaced in 2023) 068 OAKBROOK 3 IL 4ESS (06/1988) Verified Aug 2023 069 OKLAHOMA CITY 2 OK 4ESS (05/1979) Most likely decommissioned (Disconnected late 2022?) 070 OAKLAND 6 CA N4E Replaced Verified Nov 2023 (Replaced in 2022) 071 OMAHA 2 NE N4E Replaced Verified Nov 2023 072 ORLANDO 3 FL 4ESS (09/1980) Most likely decommissioned 073 PEORIA 3 IL 4ESS (02/1983) Verified Nov 2023 074 PHILADELPHIA 4 PA 4ESS (05/1980) Possibly still in service 075 PHOENIX 3 AZ 4ESS (09/1980) Most likely decommissioned 076 PITTSBURGH 3 PA N4E Replaced Verified Nov 2023 (Replaced in 2021) 077 PORTLAND 3 OR N4E Replaced Verified Nov 2023 078 RICHMOND 2 VA N4E Replaced Verified Nov 2023 079 ROCKY MOUNT 3 NC 4ESS (06/1982) Most likely decommissioned 080 ROCHELLE PARK 3 NJ 4ESS (08/1982) Most likely decommissioned 081 RENO 4 NV 4ESS (05/1982) Most likely decommissioned 082 SOUTH BEND 3 IN 4ESS (04/1987) Verified Nov 2023 083 SACRAMENTO 4 CA N4E Replaced Verified Nov 2023 084 SHERMAN OAKS 5 CA N4E Replaced Verified Nov 2023 085 STOCKTON 3 CA 4ESS (03/1984) Verified Nov 2023 086 SALT LAKE CITY 2 UT 4ESS (04/1982) Verified Nov 2023 087 SAN ANTONIO 2 TX N4E Replaced Verified Nov 2023 088 SAN DIEGO 3 CA N4E Replaced Verified Jan 2023 089 SAN FRANCISCO 4 CA N4E Replaced Verified Nov 2023 090 SAN JOSE 3 CA 4ESS (03/1982) Most likely decommissioned 091 SPRINGFIELD 2 IL 4ESS (04/1985) Verified Nov 2023 092 SPRINGFIELD 3 MA 4ESS (05/1980) Confirmed decommissioned in late 2023 093 SPOKANE 2 WA 4ESS (10/1982) Most likely decommissioned (2022?) 094 SAINT LOUIS 3 MO N4E Replaced Verified Nov 2023 095 SEATTLE 4 WA 4ESS (05/1980) Most likely decommissioned (2022?) 096 SYRACUSE 2 NY 4ESS (03/1985) Verified Nov 2023 097 TAMPA FL 4ESS (11/1986) Most likely decommissioned 098 TOLEDO 2 OH 4ESS (04/1984) Verified Nov 2023 099 TULSA 2 OK 4ESS (06/1980) Most likely decommissioned 100 WASHINGTON 6 DC N4E Replaced Verified Nov 2023 101 WAYNE 2 PA 4ESS (09/1977) Possibly replaced with a N4E? 102 WICHITA 2 KS 4ESS (04/1981) Most likely decommissioned 103 WHITE PLAINS 3 NY N4E Replaced Verified Nov 2023 (Replaced in 2022) 104 WHITE PLAINS 5 NY 4ESS (08/1980) May have been replaced with 103-T 105 WAUKESHA 3 WI N4E (03/1979) Verified Feb 2023 (Replaced in 2022) 106 WEST PALM BEACH 4 FL 4ESS (08/1981) Most likely decommissioned 107 AKRON 4 OH 4ESS (04/1989) Verified Oct 2022 108 ATLANTA 7 GA 4ESS (11/1988) Most likely decommissioned 109 BLOOMINGTON 2 IN 4ESS (11/1989) Most likely decommissioned 110 CHICAGO 11 IL 4ESS (01/1990) Most likely decommissioned 111 NEW YORK 55 NY N4ES Replaced Verified Nov 2023 112 PLYMOUTH 2 MI 4ESS (12/1989) Most likely decommissioned 113 SAN BERNARDINO 2 CA 4ESS (03/1989) Verified Nov 2023 114 TUCSON 3 AZ 4ESS (10/1989) Verified Nov 2023 115 PITTSBURGH 9 PA 4ESS (12/1988) Verified Jun 2023 116 OMAHA 3 NE 4ESS (07/1990) Most likely decommissioned (see 071-T) 117 HAMILTON SQUARE 2 NJ 4ESS (07/1991) Verified Jan 2023 118 WORCESTER 3 MA 4ESS (12/1991) Most likely decommissioned 119 CHESHIRE CT 4ESS (01/1992) Confirmed decommissioned in late 2023 120 NEW YORK 25 NY 4ESS (02/1992) Most likely decommissioned (see 111-T) 121 HILLSBORO MO 4ESS (05/1992) Verified Jan 2023 122 FINKSBURG MD N4E Replaced Verified Nov 2023 (does not ID with an NSN) 123 ADAMS TX 4ESS (10/1992) Most likely decommissioned 124 PLANO IL 4ESS (12/1992) (standby tandem?) (Most likely decommissioned) 125 ELLISVILLE FL 4ESS (10/1992) Verified May 2023 126 MONTICELLO 2 GA 4ESS (10/1992) Verified Nov 2023 127 CEDAR KNOLLS 2 NJ 4ESS (10/1992) Verified Oct 2022 128 TACOMA 2 WA 4ESS (12/1992) Most likely decommissioned 129 DUNNIGAN CA N4E Replaced Verified May 2023 (male voice on ID) 130 GARDENA 4 CA 4ESS (04/1993) Most likely decommissioned (see 152-T) 131 FORT LAUDERDALE FL 4ESS (05/1993) Verified Nov 2023 132 MADISON 3 WI 4ESS (11/1992) Verified Nov 2023 133 WHITE PLAINS 4 NY 4ESS (08/1993) Most likely decommissioned (see 103-T) 134 MARKHAM ON (905-U2) 4ESS (06/1993) Most likely decommissioned 135 CHERRYVILLE NJ 4ESS (05/1993) Most likely decommissioned 136 CAMBRIDGE MA 4ESS (06/1993) Most likely decommissioned 137 ALDERGROVE BC (604-U2) 4ESS (08/1993) Most likely decommissioned 138 OXNARD CA 4ESS (07/1993) Most likely decommissioned 139 ANCHORAGE AK 4ESS (03/1996) Verified Nov 2023 140 MESA AZ 4ESS 2nd Gen (1998/1999) Possibly replaced with 149-T? 141 DURHAM NC 4ESS 2nd Gen (1998/1999) Verified Nov 2023 142 DENVER 6 CO 4ESS 2nd Gen (1998/1999) Possibly replaced 143 FORT MYERS FL 4ESS 2nd Gen (1998/1999) Possibly replaced with 151-T 144 MONROVIA MD 4ESS 2nd Gen (1998/1999) Verified Nov 2023 145 CHICAGO IL 4ESS 2nd Gen (1998/1999) Possibly replaced 146 ATLANTA GA 4ESS 2nd Gen (07/1999) Most likely decommissioned (Last traditional #4ESS) 147 CHICAGO IL (?) N4E 2012? Verified Jan 2023 148 BOSTON MA (?) N4E ? Verified Nov 2023 149 MESA AZ (?) N4E ? Verified Nov 2023 150 ATLANTA GA (?) N4E ? Verified Aug 2023 151 FORT MYERS FL (?) N4E ? Verified Nov 2023 152 GARDENA CA (?) N4E (08/2013) Verified Nov 2023 153 ??? MA (?) N4E ? Verified Nov 2023 154 DALLAS TX (?) N4E ? Verified Nov 2023 155 SCOTTSDALE AZ (?) N4E ? Verified Nov 2023 156 SYRACUSE NY (?) N4E ? Verified Nov 2023 157 JACKSONVILLE FL (?) N4E ? Verified Nov 2023 158 ANAHEIM CA (?) N4E ? Verified Nov 2023 159 WAYNE PA (?) N4E 2016? Verified Nov 2023