Computer Based PBX     P P P Pnene     Courtesy of the Jolly Roger
    (Originally an Apple ][ file for forgive the upper case!)

TO GET A BETTER UNDERSTANDING OF WHAT A PBX CAN DO, HERE ARE A FEW BASIC
FUNDAMENTALS.THE MODERN PBX IS A COMBINED COMPUTER,MASS STORAGE DEVICE,
AND OF COURSE A SWITCHING SYSTEM THAT CAN:
      [1] PRODUCE ITEMIZED,AUTOMATED BILLING PROCEDURES,TO ALLOW THE
        ouIDENTIFICATION AND MANAGEMENT OF TOLL CALLS. [HAHAtr]
      [2] COMBINE DAYTIME VOICE GRADE COMMUNICATION CIRCUITS INTO
        ouWIDEBAND DATA CtrNNELS FOR NIGHT TIME HIGH SPEED DATA
        ouTRANSFERS.
      [3] trNDLES ELECTRONIC MAIL [ INCLUDING OFFICE MEMOS ].
      [4] COMBINE VOICE CtrNNELS INTO A WIDEBAND AUDIO/VISUAL
        ouCONFERENCE CIRCUIT,WITH THE ABILITY TO XFER AND
        ouCAPTURE SLIDES,FLIPCtrRTS,PICTURES OF ANY KIND.
BOTH THE EXTERNAL AND INTERNAL CALLING CAPACITY OF THE PBX SYSTEM MUST BE
CAREFULLYuCONSIDERED BECAUSE MANY BUSINESS OPERATIONS RUN A VERY HIGH RATIO
OF INTERNAL STATION TO STATION DIALING AND A LOW CAPACITY SYSTEM WILL NOT
trNDLE THE REQUESTEDuTRAFFIC LOAD.
A CRITICAL FACTOR IS THE NUMBER OF TRUNKS AND THE CENTRAL OFFICE FACILITIES
THAT ARE USED FOR OUTSIDEuCONNECTIONS.ANOTHER IS THE NUMBER OF JUNCTIONS OR
[LINKS] THAT MAKE UP THE INTERNAL CALLING PATHS.
TO UNDERSTAND THE SERVICES AVAILABLE ON A TYPICAL COMPUTER RUN PBX IT IS
NECESSARY TO INTRODUCE THE SUBJECT OF TIME DIVISION SWITCHING.IN A TIME
DIVISION SWITCHING NETWORK ALLuCONNECTIONS ARE MADE VIA A SINGLE COMMON BUS
CALLED (OF COURSE) A 'TIME-DIVISION BUS'.EVERY LINE TRUNK THAT REQUIRES A
CONNECTION WITH ANOTHER IS PROVIDED WITH A PORT CIRCUIT.ALLuPORT CIRCUITS
trVE ACCESS TO THE TIME DIVISION BUS THROUGH A TIME DIVISION SWITCH.
[WHEN TWOuPORTS REQUKREuCONNECTION,THEIR TIME DIVISION SWITCHES OPERATE AT
A VERY HIGH FREQUENCY (16,000 TIMES PER SECOND).THIS TECHNIQUE,WHICH IS
CALLED 'SPEECH SAMPLING',ALLOWS MANY SIMULTANEOUS CONNECTIONS OVER THE SAME
TIME DIVKSION BUS.EACH CONNECTION IS ASSIGNED A TIME INTERVAL,THE 'TIME SLOT'
,AND THE NUMBER OF TIME SLOTSuIDENTIFIES THE NUMBER OF SIMULTANEOUS CONNECT-
IONS AMONGuPORTS.]
THE NEXT CRITICAL ITEM IS CIRCUIT PACKS.THE SYSTEM ELEMENTS THAT WE WILL BE
DESCRIBING IN FUTURE TUTORIALS [LINES/TRUNKS/SWITCHES,MEMORY AND CONTROL] ARE
CONTAINED ON PLUG IN CIRCUIT PACKS.EACH LINE CIRCUIT PACK CONTAINS A NUMBER
OF LINES,IN EXAMPLE,FOUR.BUT THE ASSIGNMENT OF STATION NUMBERS TO ACTUAL
PHONE LINE CIRCUITS IS FLEXIBLE.
THE SYSTEM MEMORY IS CONTAINED IN CIRCUIT PACKS WHICH PROVIDE THE CALL
PROCESSING FUNCTIONS.THE CIRCUIT PACKS ARE HELD IN SMALLuFRAMES CALLED
'CARRIERS'.WITHIN EACH CARRIER,THE CIRCUIT PACKS ARE PLUGGED INTOuPOSITIONS:
THE 'SLOTS'.EVERY CIRCUIT CAN BE ADDRESSED BY,SAY A FIVE DIGIT NUMBER WHICH
TELLS ITS LOCATION BY CARRIER-SLOT-CIRCUIT.... [STARTING TO GET THE IDEA?]
THEREuCAN BE THREE TYPES OF CARRIERS IN A MODERN PBX SYSTEM:
         n n nnnO LINE CARRIERS
         n n nnnO TRUNK CARRIERS
         n n nnnO CONTROL CARRIERS
THE LINE CARRIERS CONTAIN STATION LINES.IN A.T.& T.'S "DIMENSION" MODEL,FOR
EXAMPLE,A TOTAL OF 52 TO 64 LINES ARE PROVIDED.THE TRUNK CARRIERS CONTAIN
SLOTSuFOR 16 TRUNK CIRCUIT PACKS.THE CONTROL CARRIER INCLUDES PROCESSOR,
MEMORY,CONTROL CIRCUITRY,DATA CtrNNELS FOR ATTENDANT CONSOLE CONTROL AND
TRAFFIC MEASUREMENT OUTPUTS.
PBX SYSTEMS WILL DIRECTLYuREFLECT THE TYPES OF SERVICES OFFERED AT THE C.O.
      n nnnO CCSA
        ounO CCIS
         n OuPICTUREPHONES [SOONER THAN YOU THINK MYuPHRIENDS]
COMMON CONTROL SWITCHING ARRANGEMENTS ( CCSA ) PERMIT ANY UNRESTRICTEDuTELE-
PHONE STATION TO CALL ANY OTHET INTERNAL OR EXTERNAL SYSTEM STATION BY USING
THE STANDARD SEVEN DIGIT NUMBER.ALTERNATE ROUTING IS A FEATURE OF CCSA SERVICE
THE INTERFACILITY,ALTERNATE ROUTED CALLING PATHS ARE ACCOMPLISHED AT THE TELE-
PHONE COMPANY CENTRAL OFFICE LEVEL,NOT AT THE PBX LEVEL.
A SYSTEM OF INTEREST TO LARGE SCALE TELEPHONE USERS IS COMMON CtrNNEL INTER-
OFFICE SIGNALLING (CCIS).TYPICALLY,THIS TECHNIQUE EMPLOYS COMMON CtrNNELS TO
CARRY ALL INTERFACILITY SIGNALLING INSTRUCTIONS: DIAL PULSES,ON HOOK (IDLE),
OFF HOOK (BUSY),AND SO ON,BETWEEN TWOuSWITCHING CENTERS. [ GETTING WARM ].
CCISuREPLACES OLDER METHODS OF INTEROFFICE SIGNALLING SUCH AS 'IN BAND' AND
'OUT OF BAND' TECHNIQUES. BY THE WAY,REAL PHREAKS ARE SELLING THEIR BOXES TO
IDIOTS WHO STILL THINK THE'RE WORTH ALOT...THE FORMER (IN BAND)uTRANSMITS
SIGNALLING DATA WITHIN THE NORMAL CONVERSATION BANDWIDTH.IT'S SHORTCOMING IS
THAT FALSE INFORMATION MAY BE TRANSMITTED DUE TO UNIQUE TONE OR NOISE
COMBINATIONS SET UP IN THE TALKING PATH. [THIS IS THE OFFICIAL REASONING].
OUT OF BAND SIGNALLING TECHNIQUES PLACED THE INTEROFFICE DATA IN SPECIAL
CtrNNELS,GENERALLY ADJACENT TO AND IMMEDIATELY ABOVE THE VOICE PATH.TOuPRE-
SERVE INTERCtrNNEL INTEGRITY,OUT OF BAND SIGNALLING REQUIRES VERY EFFECIENT
FILTERING OR GREATER 'BAND GUARD' SEPERATION BETWEEN CtrNNELS.

Brought to you in the Cookbook courtesy of the Jolly Roger!!!!!!hohod