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TUCoPS :: Phreaking General Information :: ess27.htm

Electronic Switching System for Beginners

Electronic Switching System for Beginners

Electronic Switching System for Beginners


How it works:

     Well, if you did not know by now ESS stands for Electronic Switching
System.  There are basically two uses for switches, one is the local
switch the other one is the tandem switch otherwise known as the long haul
switch. The local switch also called the CO (Central Office).  The CO will
handle all the calls in your area.  The long haul switch will handle calls
going to another NPA (Numbering Plan Area) or as you know it as your
current area code.)

     If you are dialing out to another number in your area the call will
go from your local switch to that persons local switch but if you are
calling LD(Long Distance) the call will go from local switch to a tandem
switch and from that tandem switch will connect to another tandem switch
to a local switch. Here is what is happening..

     A local call-

                         (Your's)   (Their's)
          Your House ----- C.O. ----- C.O. ----- Their House

     A long distance call-

            (Your's)    (Your's)        (Their's)    (Their's)
Your House -- C.O. -- Tandem Switch -- Tandem Switch -- C.O. -- Their House

Types of Switches:

     In 1960 the first ESS was being tested and for six years the test's
ran and proved to be successfull.  The 1ESS was a local switch which came
out in 1965 and was used for areas with multiple telephone lines.  The ESS
was being used by AT&T at the time.

     About ten years later in 1976 the 1AESS switch came out which had
the 1A processor which is also used in the 4ESS which came out in the same
time. The processor enabled the seitch to handle twice as many lines so it
upgraded the ESS to the 1EASS so now the switch went from 60,000 lines to
130,00. Like mostly everything else it will not use all of the lines before
it will give "all circuits busy" message because of purpose like 911 calls
and such. This might help you in the near future but about 60% of local
switches in the Denver area are 1AESS and the 1AESS also has a proprietart

     The 2BESS switch came out around 1970's and was not as advanced as
the 1AESS but it had it's time.  It is now a outdated switch but it is still
found in todays world  used by AT&T.

     The 5ESS is a local switch (CO) and is a UNIX based switch. It is
also one of the fastest switches out and is used by AT&T.  The 5ESS is
one of the next upgrades in switches from the 1AESS.

     The DMS-100 (Digital Multiplex System) is used by Northen Telecom. 
The DMS-100 has two properties that help keep maintenance on it.  First it
has the telco employees and then it has its interenal maintenance running.
The DMS-100 can support as many lines as the 1AESS or the 5ESS switches.

     The DMS-200 is also used by Northern Telecom and provides and
provides TOPS (Telephone Operator Position System) which is the world's
premier operator service, from Northen Telcom.

     The DMS-250 is Northern Telecom's Tandem switch (Long Haul) which
will transfer the calls to another CO in a different NPA (as expalained
above). In some cases the DMS-500 are Northern Telcom's main long haul

     The 4ESS which is explained in the paragraph above is a Tandem
switch which means that it handles long distance calls (The Long Haul).
The switch came out in the mid 1970's.  The 4ESS is still being widely
used today by AT&T.

     If you would like more information on ESS here is a list of articles
that you can read up on.

All of the following can be found on Disorder's Homepage or
Unholiness Rising (303)980-2404

Address (

The Tao of ESS (Deadkat and Disorder)
5 ESS from top to bottom (Firm G.R.A.S.P.)
Digital Multiplex System (DMS) 100 (Knight Lightning)

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