From: bmk@mvuxi.att.com (Bernard Mckeever)
Subject: Switch Applications
Date: 8 Mar 90 14:39:53 GMT
Sender: news@accuvax.nwu.edu
Reply-To: bmk@cbnews.ATT.COM
Organization: AT&T Bell Laboratories
In an earlier posting the following was asked:
>In all my experience with various small scale telephony projects, I
>have never really assimilated the various switch types used in central
>offices through the years.
>Perhaps Larry Lippman ( @kitty ) or Bernard McKeever or other who has
>had experience in this area could provide a summary of the various CO
>switches, the dates of their prominence, and the common applications
>they found themselves in (big cities, toll centers, etc).
>For instance, most #2 ESS offices seem to serve a smaller number of
>customers and operate more slowly than, say #1 ESS. Any insight into
>these issues would be appreciated.
>Thanx!
>John Boteler
Well I have to apologize for taking so long with a reply but I have
been out of town for a few weeks on business and just got caught up on
the news in this group. I am in the middle of a transfer to Denver so
this reply may be a little short.
Switching systems come in two basic flavors, LOCAL and TANDEM. Now of
course the LOCAL TANDEM switch does a little of both. The local switch
connects lines to lines and lines to LOCAL TRUNKS [interoffice/
intraexchange]. The TANDEM switch connects TOLL TRUNKS
to TOLL TRUNKS and TOLL TRUNKS to TOLL CONNECT TRUNKS. The LOCAL
TANDEM may connect to TOLL TRUNKS directly as may some local switches.
Easy so far. Most local [exchange] switches and local tandem switches
use 2-wire trunks. Most toll switches use 4-wire trunks. In addition
to the intended use as a "public" switch, most of the systems
mentioned also saw life, in smaller versions, as PBXs.
Now that we have the basics, and the CAPS, out of the way a few words
from our sponsor. Much of the information that follows comes from
available sources. My thanks to Notes on the Network, Notes on Direct
Distance Dialing, and of course Engineering and Operations in the Bell
System. The opinions expressed are mine and the accurate information
and other good stuff belongs to them. Whatever you do, don't throw
away old references just because a new one is issued, you may lose a
bit of history in the process.
LOCAL SWITCHING
Automatic switching equipment started to appear in general use in
1919. [invented in 1889 by A. B. Strowger] The Step by Step [SXS]
equipment was installed and [I believe] manufactured by Automatic
Electric. In 1926 Western Electric introduced its own version the
#1SXS. This system, as many can attest, is still used in many areas.
Your basic local system, SXS was "improved" to provide 2-wire toll
service as early as 1920. By 1940 SXS Tandem was able to provide
Centralized Automatic Message Accounting [CAMA]. SXS spawned several
variations used as Community Dial Offices [CDO]. In the beginning SXS
was not considered economical for large cities so a new development
began on a switcher for large cities.
The 1st Panel office was placed in service in 1921. This too was a
local switch later adapted to local tandem operations. Peaking in the
1950s, the last Panel office was retired on Sept.11,1982 in Newark
N.J.
In 1938 the #1XB system was introduced as a "metropolitan" office.
The #1XB was faster and bigger than earlier electro-mechanical offices
but, not quite "common control".
That was the job of the #5XB introduced in 1948. #5XB is capable of
providing "most" of the features we associate with the modern
switching network. A variation the #5XB is the XBT [crossbar tandem]
designed to provide only toll switching connections.
NOTE: At the end of this article I will list several small application
modifications on the above switching systems.
TOLL SWITCHING
In addition to the mentioned toll function provided by local switchers,
several toll only switches were developed.
WOOPS I am running out of time. What follows is only a short list. Is
someone has the time feel free to fill in the blanks. If I have NET
access at my new location I will try to follow-up.
1943 [Philadelphia] #4 Crossbar System improved in 1953 it became known
as the #4A Crossbar System [what else]
Electronic Switching Systems [stored program control]
#1ESS
1st trial 1960 in Morris Ill. Introduced in 1965 Succasunna N.J.
Local Metropolitan applications. Upgraded several times. 1968 local
tandem 1974 2-wire toll 1976 #1AESS [New Processor] 1977 4-wire toll
#2ESS
1970 Local Suburban
1976 #2BESS same application [I have no idea what happened to the
#2AESS]
#3ESS
1976 Local Rural
#4ESS
1976 Large 4-wire toll
#5ESS
1982 ALL OF THE ABOVE [after a little development]
Misc. Switching Systems [no particular order]
1979 10A RSS local small rural [a remote linked to a #1A or #2B ESS]
5A RMS and ORM are remote and optical remote modules of a #5ESS switch
#1/1A ESS HILO small/medium 4-wire toll on a 2-wire path
And last but not least all sorts of CAMA and operator switching systems.
I know I have missed a few of the systems and did not provide all
the detail available. Sorry for the abrupt ending but.......
Hope to be in touch soon,
Bernie McKeever