From: [email protected] (Scott Fender)

Subject: Re: ESS & DMS Question

In a previous posting, Lee Hardiman ([email protected]) writes:

> In article <[email protected]>, [email protected] says...

> I'm not a phreaker or anything but I keep hearing these two acronyms 

> (ESS & DMS) and I'd appreciate a little info on what the difference is 

> between the two and how it affects the phone your using.  Thanx.


> ESS stands for Electronic Switching System and is a term used to refer to 

> switches manufactured by AT&T.  DMS is a trademark of Northern Telecom.  

> Both refer to switches that use a computer to control the switch matrix. 

>  A DMS, #5ESS, nad #4ESS are digital switches.  A #1ESS uses an analog 

> switch matrix.


Also to complete, it "DMS" simply stands for "Digital Multiplex Switch".

Common DMS versions are:

   DMS-10  -serves areas a bit outside the main city centres.  It links

            small communities to a larger DMS-100 located in a larger city.

   DMS-100 -This is the local exchange.  Used all over Canada except in rare

            cases where No. 5 X-Bar is in use, and in even more rare cases

            where SxS is still running.  It is programmed in BNR proprietary

            Pascal, in PROTEL, and in Assembler (rarely these days).

            It is upgraded by software loads that take place every six months,

            with *major* software changes taking place every 18 months.

            The loads take place at 3 AM local time.  These BCS loads

            (Batch Change Supplements) can be quite take longer than expected

            sometimes, and weird things can happen.  Because of this the

            switch is always "mirrored" prior to any new load and can revert

            back to its former state if the trouble persists.  To simplify

            the load process, the loads are now done via PCL's, which are

            smaller and take advantage of more modular software currently

            written.  Each PCL is specific for each individual switch

            operating in North America.

   DMS-200 -This is a local operating company toll switch.

   DMS-250 -This switch local/toll used by the inter exchange carriers MCI,

            Sprint etc.

   DMS-300 -This is a ISC switch and can do all the conversion between the

            International circuit (CCITT System No. 5) and various North

            American systems like R1 (Regional System No. 1), SS6, and


Both AT&T's switches and NT's (BNR designed) DMS switches are quite advanced.

They can "get" you if they want to.

Take it easy guys,

                  Scott.  ([email protected])

P.S. Hope to see you all at Cafe Wim (Ottawa) this Friday.