Amnesia 8/Amnesia - Issue 08 (1992-05-31)(Eclipse).adf/text/Article32

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                             PHREAKER'S DICTIONARY



       A & A BUREAU--ABUSE AND ANNOYANCE BUREAU. THE PERSONNEL IN THIS
       LINE OF WORK SPEND THEIR TIME HELPING CUSTOMERS GET RID OF NUTS,
       OBSCENE CALLERS, HARASSING COLLECTORS, ETC.

       ACCESS--THE EXISTENCE OF PATHS WITHIN A NETWORK FROM AN INPUT
       TERMINAL TO A SET OF OUTPUT TERMINALS IN THE ABSENCE OF TRAFFIC
       IS INDICATED BY THE TERM, ACCESS. FULL ACCESS PERMITS CONNECTING
       TO ALL OUTPUT TERMINALS BY UNIQUE PATHS; MULTIPLE ACCESS
       INDICATES THAT ALL OUTPUT TERMINALS CAN BE REACHED IN MORE THAN
       ONE WAY; PARTIAL ACCESS REFERS TO THE ABILITY TO REACH ONLY A
       FRACTION OF THE OUTPUT TERMINALS.

       ACCESSIBILITY--(AVAILABILITY)--THE NUMBER OF TRUNKS OF THE
       REQUIRED ROUTE IN A SWITCHING NETWORK WHICH CAN BE REACHED FROM
       AN INLET.

       ADAPTOR--A DEVICE DESIGNED TO SWITCH A NUMBER OF VOICE-FREQUENCY
       TELEPHONE CHANNELS COMING FROM A NON-TIME-DIVISION SWITCHING
       SYSTEM TO A TIME-DIVISION MULTIPLEX HIGHWAY.

       ALTERNATE ROUTING--A PROCEDURE BY WHICH SEVERAL ROUTES INVOLVE
       DIFFERENT SWITCHING STAGES OR SWITCHING NETWORKS. USUALLY THE
       ROUTE HAVING THE FEWEST SWITCHING STAGES IS TESTED FIRST.

       ANALOG TRANSMISSION--THE TRANSMISSION OF CONTINUOUSLY VARIABLE
       SIGNALS RATHER THAN DESCRETELY VARIABLE SIGNALS. PRIOR TO THE USE
       OF DIGITAL ENCODING AND PCM, IT WAS THE ONLY WAY OF TRANSMITTING
       VOICE SIGNALS OVER TELEPHONE CHANNELS.

       AREA CODE--A THREE-DIGIT PREFIX DIALED AHEAD OF THE NORMAL
       SEVEN-DIGIT TELEPHONE NUMBER TO PERMIT DIRECT DISTANCE DIALING.

       ASYNCHRONOUS SYSTEM--A SYSTEM IN WHICH THE TRANSMISSION OF EACH
       INFORMATION CHARACTER IS INDIVIDUALLY SYNCHRONIZED USUALLY BY THE
       USE OF START AND STOP ELEMENTS.

       AVERAGE HOLDING TIME--THE AVERAGE DURATION OF A CALL EXPRESSED IN
       SECONDS OR MINUTES.

       BIT--THE SMALLEST BINARY UNIT OF INFORMATION. A CONTRACTION OF
       THE WORDS BINARY DIGIT.

       BIT RATE--THE RATE OR SPEED AT WHICH BITS ARE TRANSMITTED. BITS
       PER SECOND IS A COMMON MEASURE.

       BLOCKING (CONGESTION)--A CONDITION WHERE THE IMMEDIATE
       ESTABLISHMENT OF A NEW CONNECTION IS IMPOSSIBLE DUE TO THE LACK
       OF AVAILABLE PATHS, OR THE INABILITY TO INTERCONNECT TWO IDLE
       NETWORK TERMINALS BECAUSE SOME OF THE APPLICABLE LINKS BETWEEN
       THEM ARE USED FOR OTHER CONNECTIONS.

       BOOLEAN ALGEBRA--A FORM OF NONQUANTITATIVE ALGEBRA FOR DEALING
       WITH LOGIC FUNTIONS, ORIGINALLY EXPRESSED BY BRITISH
       MATHEMATICIAN GEORGE BOOLE (1815-1864).
       B.O.S.--BUSINESS OFFICE SUPERVISOR. SHE'S THE BOSS TO THE SERVICE
       REPS.

       BROADBAND EXCHANGE (BEX)--PUBLIC SWITCHED COMMUNICATION SYSTEM
       FEATURING FULL DUPLEX (FDX) CONNECTIONS OF VARIOUS BANDWIDTHS. A
       WESTERN UNION FACILITY.

       B.S.I.--BUSINESS SERVICES INSTRUCTOR. A TRAFFICE EMPLOYEE WHO
       WILL COME OUT AND TEACH YOU HOW TO USE YOUR PHONE SYSTEM.

       BUSY HOUR--AN UNINTERRUPTED PERIOD OF 60 MINUTES IN WHICH THE
       TOTAL TRAFFIC OF A SAMPLE IS A MAXIMUM.

       BYTE--A UNIT OF INFORMATION IN ELECTRONIC COMPUTER TERMINOLOGY
       CONSISTING OF 8 BITS, REFERRED TO AS EXTENDED BINARY CODED
       DECIMAL INFORMATION OF AN EBCDIC CODE.

       CALL CONGESTION RATIO--THE RATIO OF THE TIME DURING WHICH
       CONGESTION EXISTS TO THE TOTAL TIME CONSIDERED. IT IS AN ESTIMATE
       OF THE PROBABILITY THAT AN EXTERNAL OBSERVER WILL FIND A SYSTEM
       IN A CONGESTED CONDITION.

       CALLING RATE--AVERAGE CALLS PER SUBSCRIBER PER HOUR.

       CALL STORE--THE MEMORY SECTION OF A STORED PROGRAM CONTROL
       SWITCHING SYSTEM IN WHICH TEMPORARY INFORMATION USED IN THE
       PROCESSING OF CALLS THROUGH THE EXCHANGE IS CONTAINED. IT IS ALSO
       REFERRED TO AS THE PROCESS STORE.

       CENTRAL OFFICE--EXCHANGES WHERE SUBSCRIBER LINES AND PRIVATE
       BRANCH EXCHANGE LINES TERMINATE. THERE THEY ARE SWITCHED TO
       PROVIDE THE DESIRED CONNECTION WITH OTHER SUBSCRIBERS. SUCH AN
       EXCHANGE IS CALLED AN END OFFICE AND IS DESIGNATED AS A CLASS 5
       OFFICE IN THE U.S.

       CENTRAL PROCESSOR--THE MAIN COMPUTER ELEMENT OF A STORED PROGRAM
       CONTROL SWITCHING SYSTEM, WHICH UNDER THE DIRECTION OF THE STORED
       PROGRAM ESTABLISHES SWITCHING NETWORK CONNECTIONS AND ALSO
       MONITORS AND ANALYZES THE SYSTEM TO INSURE PROPER OPERATION.
       ROUTINE PROCESS TESTING, MAINTENANCE AND ADMINISTRATIVE FUNTIONS
       ARE ALSO CARRIED OUT.

       CENTREX--A PABX SYSTEM IN WHICH THE SWITCHING EQUIPMENT IS
       LOCATED CENTRALLY AND AWAY FORM THE LOCATION BEING SERVED. DIRECT
       INWARD DIALING (DID) AND DIRECT OUTWARD DIALING (DOD) AS WELL AS
       AUTOMATIC NUMBER IDENTIFICATION (ANI) ARE PROVIDED BY SUCH A
       SYSTEM.

       CHARACTERS--THE ELEMENTS OF A MESSAGE. ONE COMPUTER CHARACTER
       CONSISTS OF 8 BITS OR 1 BYTE AND IS KNOWN AS AN EBCDIC CHARACTER.

       CIRCUIT SWITCHING--TELECOMMUNICATIONS SWITCHING IN WHICH THE
       INCOMING AND OUTGOING LINES ARE CONNECTED BY A PHYSICAL PATH, AS
       THROUGH CROSSPOINTS OR SWITCH CONTACTS.
       CLASS OF SERVICE--THE SERVICES AND FACILITIES OFFERED TO EACH
       INDIVIDUAL TERMINAL CONNECTED TO A SYSTEM. THIS INFORMATION IS
       USUALLY STORED WITH THE DIRECTORY OR EQUIPMENT NUMBERS OF THE
       ASSOCIATED TERMINAL, AND IS ACCESSED BY THE CALL PROCESSORS WHEN
       A CONNECTION IS REQUIRED TO OR FROM THAT TERMINAL.

       CLOCK--EQUIPMENT TO PROVIDE A TIME BASE FOR A SWITCHING SYSTEM.
       IN TIME-DIVISION SWITCHING IT IS USED TO CONTROL SAMPLING RATES,
       DURATION OF SIGNAL DIGITS, ETC.

       C.O.A.M.E.--CUSTOMER OWNED AND MAINTAINED EQUIPMENT.

       CODEC--THE COMBINATION OF A CODER AND DECODER, AS USED IN
       TIME-DIVISION SWITCHING SYSTEMS TO CODE THE INCOMING MESSAGE AND
       DECODE THE MESSAGE BEING RETURNED TO THE CALLER. IT IS A
       CONTRACTION OF THE WORDS, CODER AND DECODER.

       COMMON CONTROL--AN EXCHANGE CONTROL METHOD IN WHICH THE DIALED
       SIGNALS ARE RECEIVED AND REGISTERED SEPARATELY FROM THE SWITCHING
       ELEMENTS BEFORE THEY ARE USED TO CONTROL THESE SWITCHES. ALSO
       DEFINED AS A CONTROL METHOD, WHICH IDENTIFIES THE INPUT AND
       OUTPUT TERMINALS OF THE SWITCHING NETWORK AND THEN CAUSES A
       CONNECTING PATH TO BE ESTABLISHED BETWEEN THEM. SUCH SYSTEMS ARE
       ALSO DESIGNATED AS MARKER SYSTEMS.

       CONCENTRATION STAGE--A SWITCHING STAGE IN WHICH A NUMBER OF INPUT
       LINES ARE CONNECTED TO A SMALLER NUMBER OF OUTPUT LINES OR
       TRUNKS, AS IN THE CONNECTION OF A LARGE NUMBER OF SUBSCRIBER
       LINES TO A SMALLER NUMBER OF TRUNKS BASED ON THE GRADE OF SERVICE
       DESIRED.

       CONGESTION FUNCTION--ANY FUNCTION USED TO RELATE THE DEGREE OF
       CONGESTION TO THE TRAFFIC INTENSITY.

       CONNECTING ROW--ALL THOSE CROSSPOINTS DIRECTLY ACCESSIBLE FROM AN
       INLET. ONLY ONE CONNECTION CAN BE ESTABLISHED VIA A CONNECTING
       ROW AT ANY INSTANT.

       COUPLER--A DEVICE USED TO PREVENT ELECTRICAL FLASHBACK AND
       MAINTAIN NORMAL ELECTRICAL FLOW ON A TELEPHONE LINE. USED AS A
       BUFFER BETWEEN C.O.A.M.E. AND TELEPHONE COMPANY EQUIPMENT.

       CROSSBAR SWITCH--A SWITCH HAVING A PLURALITY OF VERTICAL PATHS, A
       PLURALITY OF HORIZONTAL PATHS AND ELECTROMAGNETICALLY OPERATED
       MECHANICAL MEANS FOR CONNECTING ANY OF THE VERTICAL PATHS WITH
       THE HORIZONTAL PATHS.

       CROSSPOINT--A CROSSPOINT COMPRISES A SET OF CONTACTS THAT
       OPERATES TOGETHER AND EXTENDS THE SPEECH AND SIGNAL WIRES OF THE
       DESIRED CONNECTION. EACH CONNECTION IN A SPACE-DIVISION SWITCHING
       NETWORK IS ESTABLISHED BY CLOSING ONE OR MORE CROSSPOINTS.

       CROSSTALK--AN UNWANTED TRANSFER OF SIGNALS FROM ONE CIRCUIT TO
       ANOTHER AS MAY OCCUR BETWEEN SWITCHING ELEMENTS OR CIRCUIT
       WIRING.

       C.W.A.--THE COMMUNICATION WORKERS OF AMERICA. THE C.W.A.
       REPRSENTS 90 PERCENT OF THE UNIONIZED TELCO WORK FORCE.

       DAY-TO-BUSY HOUR RATIO--THE RATIO OF THE 24 HOUR DAY TRAFFIC
       VOLUME TO THE BUSY HOUR TRAFFIC VOLUME. IN SOME COUNTRIES THE
       RECIPROCAL OF THIS RATIO IS USED.

       D.D.D.--DIRECT DISTANCE DIALING. ALSO KNOWN AS ONE-PLUS DIALING.

       DELAY SYSTEM--A SWITCHING SYSTEM IN WHICH A CALL ATTEMPT, WHICH
       OCCURS WHEN ALL ACCESSIBLE PATHS FOR THE REQUIRED CONNECTION ARE
       BUSY, IS PERMITTED TO WAIT UNTIL A PATH BECOMES AVAILABLE.

       DIAL PULSE--THE SIGNALING PULSE WHICH IS FORMED BY THE
       INTERRUPTION OF THE CURRENT IN THE DC LOOP OF A CALLING
       TELEPHONE. SUCH INTERRUPTIONS ARE PRODUCED BY THE BREAKING OF THE
       DIAL PULSE CONTACTS OF THE CALLING TELEPHONE SUBSET DURING THE
       DIALING PROCESS.

       DIAMOND-RING TRANSLATOR--AN ARRAY OF RING-TYPE INDUCTION COILS
       ASSOCIATED WITH CODED WIRING IN SUCH A MANNER THAT THE
       TRANSLATION OF DIRECTORY NUMBERS TO EQUIPMENT NUMBER OR VICE
       VERSA CAN BE ACCOMPLISHED IN AN EXCHANGE. IT IS NAMED AFTER ITS
       ORIGINATOR, T.L.DIMOND OF THE BELL TELEPHONE LABORATORIES.

       DIRECT CONTROL--AN EXCHANGE CONTROL METHOD IN WHICH PULSES,
       DIALED BY THE SUBSCRIBERS, CONTROL DIRECTLY THE ROUTE SELECTION
       SWITCHES OF THE SYSTEM. FOR EACH DIGIT DIALED THE EQUIVALENT OF
       ONE SET OF SELECTOR SWITCHES IS REQUIRED WITH THIS CONTROL
       METHOD.

       DIRECTOR--A CONTROL ELEMENT WHICH PROVIDES A MEASURE OF COMMON
       CONTROL IN STEP-BY-STEP OR STROWGER EXCHANGES.

       DISTRIBUTING FRAME--A STRUCTURE FOR TERMINATING THE WIRES OF A
       TELEPHONE EXCHANGE IN SUCH A MANNER THAT CROSS-CONNECTIONS CAN BE
       MADE READILY. EXAMPLES ARE THE MAIN DISTRIBUTION FRAME (MDF) AT
       THE ENTRY OF AN EXCHANGE, INTERMEDIATE DISTRIBUTION FRAMES (IDF)
       BETWEEN SECTIONS OF AN EXCHANGE, AND POWER DISTRIBUTION FRAMES
       (PDF).

       DISTRIBUTION STAGE--A SWITCHING STAGE BETWEEN A CONCENTRATION
       STAGE AND OUTLETS AND SERVES AS A MEANS OF SELECTING TRUNKS TO
       THE DESIRED TERMINATIONS.

       DUV--DATA UNDER VOICE (AT&T SYSTEM). ELECTROMECHANICAL SWITCHING
       SYSTEM--AN EXCHANGE SYSTEM IN WHICH BOTH THE SPEECH PATHS AND THE
       CONTROL EQUIPMENT ARE SWITCHED BY ELECTROMECHANICAL
       COMPONENTS--SUCH AS RELAYS, ROTARY SWITCHES, ETC.

       ELECTRONIC SWITCHING SYSTEM--AN EXCHANGE SYSTEM IN WHICH AT LEAST
       THE CONTROL EQUIPMENT IS COMPOSED OF ELECTRONIC CIRCUITS AND
       COMPONENTS, GENERALLY OF A SOLID-STATE TYPE.

       EMD SWITCH--THE SPEECH-PATH SWITCHING ELEMENT USED IN A SIEMENS
       ROTARY SWITCHING SYSTEM. EMD IS AN ABBREVIATION OF
       EDELMETALL-MOTOR-DREHWAHLER, WHICH TRANSLATES IN ENGLISH TO
       NOBLE-METAL MOTOR SWITCH.

       END OFFICE--A CENTRAL OFFICE OR CLASS 5 OFFICE.

       ENTRAIDE--A SWITCHING SYSTEM INPHICH OUTLETS FROM A GIVEN
       CONNECTING STAGE ARE CONNECTED TO INLETS OF THE SAME OR A
       PREVIOUS STAGE. IN SUCH SYSTEMS CALLS MAY TRAVERSE A STAGE MORE
       THAN ONCE. USUALLY THESE REENTERING LINKS ARE USED AS LAST CHOICE
       PATHS AND THE RESULTING NETWORK IS HETEROGENEOUS. SUCH AN
       ARRANGEMENT IS USED IN ITT'S PENTACONTA CROSSBAR SYSTEM.

       ERLANG--THE UNIT OF TRAFFIC INTENSITY, WHICH IS MEASURED IN
       CALL-SECONDS PER SECOND OR CALL-MINUTES PER MINUTE. ALSO, ONE
       ERLANG EQUALS 3600 CALL-SECONDS PER HOUR. IT IS NAMED AFTER A. K.
       ERLANG, THE DANISH ENGINEER AND MATHEMATICIAN WHO FIRST ADOPTED
       IT.

       ESS--ELECTRONIC SWITCHING SYSTEM.

       EXCHANGE--ALL NUMBERS WITHIN A GIVEN THREE-DIGIT PREFIX AREA. CAN
       ALSO BE USED TO DESCRIBE A GEOGRAPHICAL AREA THE SIZE OF A CITY.

       FX--FOREIGN EXCHANGE CALLS. THE TERM APPLIED TO CALLS MADE TO A
       CENTRAL OFFICE OTHER THAN THE ONE LOCATED IN THE CALLING CUSTOMER
       AREA.

       H.C. INSTRUMENT--AN ORDINARY TELEPHONE WITH NO EXTRAS.

       I.D.E.W.--INTERNATIONAL BROTHERHOOD OF ELECTRICAL WORKERS. A
       UNION THAT REPRESENTS SEVEN PERCENT OF ALL UNIONIZED TELEPHOE
       WORKERS.

       INTERSTATE--TELEPHONE SERVICE THAT CROSSES STATE LINES. SUCH
       SERVICES COME UNDER THE JURISDICTION OF THE F.C.C.

       INTRASTATE--TELEPHONE SERVICES THAT REMAIN WITHIN THE BOUNDARES
       OF A STATE. SUCH SERVICES COME UNDER THE JURISDICTION OF THE
       P.S.C.

       JOINT PRACTICES--AN INTER-COMPANY GUIDE AKIN TO THE GENEVA RULES
       OF WAR. THE J.P. COVERS SUCH THINGS AS INTERVALS, OFFERINGS, AND
       PROCEDURES.

       K.K.6--SIX-BUTTON TELEPHONE. THE STANDARD TELEPHONE FOUND IN MOST
       OFFICES. THE K.K.6 CAN HANDLE FIVE LINES. THE SIXTH BUTTON IS
       USED FOR HOLD.

       LAYOUT CARD--SCHEMATIC DRAWINGS OF THE ELECTRICAL CIRCUITS
       REQUIRED FOR A TELEPHONE INSTALLATION.
       LINK (TRUNK) THE CONNECTION BETWEEN THE TERMINALS OF ONE SWITCH
       AND THE TERMINALS ON A SWITCH OF THE NEXT STAGE CORRESPONDING TO
       A SINGLE TRANSMISSION PATH.

       LINK (ONE-WAY AND TWO-WAY)--A ONE-WAY LINK IS USED ONLY FOR THE
       ESTABLISHMENT OF CONNECTIONS IN ONE DIRECTION, WHILE A TWO-WAY
       LINK IS USED FOR THE ESTABLISHMENT OF CONNECTIONS IN EITHER
       DIRECTION.

       LINK SYSTEM--A SYSTEM IN WHICH: (1) THERE ARE AT LEAST TWO
       CONNECTING STAGES; (2) A CONNECTION IS MADE OVER ONE OR MORE
       LINKS; (3) THE LINKS ARE CHOSEN IN A SINGLE LOGICAL OPERATION;
       AND (4) LINKS ARE SEIZED ONLY WHEN THEY CAN BE USED IN MAKING A
       CONNECTION.

       LOGIC FUNCTION--THE RELATIONSHIP OF TWO OR MORE BOOLEAN VARIABLES
       AS EXPRESSED BY BOOLEAN ALGEBRA.

       LOGIC GATES--ELECTRICAL OR ELECTRONIC CIRCUITS WHICH CONTROL THE
       TRANSFER OF SIGNALS AND PRODUCE THE REQUIRED OUTPUTS FOR SPECIFIC
       INPUT COMBINATIONS TO IMPLEMENT BOOLEAN LOGIC FUNCTIONS.

       LOGIC (HARD-WIRED)--CONTROL LOGIC IN AN EXCHANGE, WHICH IS WIRED
       IN CIRCUIT FORM.

       LOGIC (SOFT-WIRED)--CONTROL LOGIC IN AN EXCHANGE, WHICH IS HELD
       IN SOFTWARE COMPUTER PROGRAMS.

       LONG DISTANCE--TECHNICALLY, ANY CALL THAT TERMINATES MORE THAN
       SEVENTEEN MILES FROM THE SOURCE.

       LONG LINES--A DIVISION OF AT&T RESPONSIBLE FOR THE DAY-TO-DAY
       OPERATION OF THE LONG DISTANCE NETWORK. WHILE THE LOCAL TELCO
       HANDLES ALL MAINTENANCE, LONG LINES DIRECTS OVERALL SUPERVISION.

       LOOP DISCONNECT PULSING--SUBSET DIAL PULSING IN WHICH THE
       SUBSCRIBER DC LOOP IS INTERRUPTED TO PRODUCE PULSES FOR SIGNALING
       AN EXCHANGE.

       MARKER--CIRCUITS WHICH INCORPORATE THE FUNCTION OF BUSY TESTING,
       LOCATING AND FINALLY CONTROLLING THE ESTABLISHMENT OF A
       PARTICULAR PATH THROUGH THE SWITCHING NETWORK.

       MARKETING REP--THE SALES PEOPLE OF THE BELL COMPANIES. ALSO KNOWN
       AS ACCOUNT EXECUTIVE.

       MARKING--THE USE OF ELECTRICAL POTENTIALS AND GROUNDS AT CERTAIN
       POINTS IN A SWITCHING NETWORK TO CONTROL ITS OPERATION.

       MATRIX--A SIMPLE SWITCHING NETWORK IN WHICH A SPECIFIED INLET
       (MATRIX ROW) HAS ACCESS TO A SPECIFIED OUTLET (MATRIX COLUMN) VIA
       A CROSSPOINT PLACED AT THE INTERSECTION OF THE ROW AND COLUMN IN
       QUESTION. A COMPLETE MATRIX IS ONE IN WHICH EACH INLET HAS ACCESS
       TO EACH OUTLET, WHILE AN INCOMPLETE MATRIX IS ONE IN WHICH EACH
       INLET MAY HAVE ACCESS TO ONLY SOME OF THE OUTLETS.

       MEAN DELAY OF CALLS DELAYED--THE TOTAL WAITING TIME OF ALL CALLS
       DIVIDED BY THE NUMBER OF DELAYED CALLS.

       MESSAGE SWITCHING--A METHOD OF RECEIVING AND STORING A MESSAGE
       FOR A MORE APPROPRIATE TIME OF RETRANSMISSION. WITH SUCH A
       METHOD, NO DIRECT CONNECTION IS ESTABLISHED BETWEEN THE INCOMING
       AND OUTGOING LINES AS IN THE CASE OF CIRCUIT SWITCHING.

       MULTIFREQUENCY SIGNALING--SIGNALING BETWEEN SUBSCRIBERS AND THE
       CENTRAL OFFICE THROUGH A COMBINATION OF AUDIO FREQUENCIES, AS
       WITH PUSHBUTTON DIALING. ALSO, IN MANY CASES SIGNALING BETWEEN
       EXCHANGES IS ACCOMPLISHED BY COMBINATIONS OF FREQUENCIES.

       MULTIGROUP--A COMBINATION OF TWO OR MORE PCM MULTIPLEX CHANNELS.

       NONLISTED NUMBERS--TELEPHONE NUMBERS THAT DO NOT APPEAR IN THE
       DIRECTORY BUT THAT ARE AVAILABLE IF THE INQUIRER CALLS DIRECTORY
       ASSISTANCE.

       NONPUBLISHED NUMBERS--TELEPHONE NUMBERS NOT MADE AVAILABLE TO THE
       PUBLIC. ALSO KNOWN AS SILENT NUMBERS.

       OCCUPANCY--THE AVERAGE PROPORTION OF TIME THAT A TRAFFIC CARRYING
       FACILITY IS BUSY.

       PACKET SWITCHING--ESSENTIALLY THE SAME AS MESSAGE-SWITCHING.

       PANEL-SWITCHING SYSTEM--A COMMON CONTROL ELECTROMECHANICAL
       SWITCHING SYSTEM, WHICH WAS USED WIDELY IN THE U.S. PRIOR TO ITS
       VIRTUAL REPLACEMENT BY CROSSBAR AND OTHER SYSTEMS. THE BANKS OF
       SELECTORS TAKE THE FORM OF FLAT VERTICAL PANELS, FROM WHICH THE
       NAME OF THE SYSTEM WAS DERIVED. SOME PANEL INSTALLATIONS ARE
       STILL IN USE IN THE U.S.

       PATH--A SET OF LINKS JOINED IN SERIES TO ESTABLISH A CONNECTION.
       PATHS DIFFER IF ONE OR MORE LINKS DIFFER.

       P.B.X.--PRIVATE BRANCH EXCHANGE. COMMONLY KNOWN AS A SWITCHBOARD.
       MINI-CENTRAL OFFICE EQUIPMENT FOR BUSINESS CUSTOMERS WITH FROM 10
       TO 2,000 TELEPHONES.

       PRIMARY CENTER--A SWITCHING CENTER CONNECTING TOLL CENTERS, WHICH
       CAN ALSO SERVE AS A TOLL CENTER FOR ITS LOCAL END OFFICES. IN THE
       U.S. IT IS DEFINED AS A CLASS 3 OFFICE.

       PRIVATE AUTOMATIC BRANCH EXCHANGE (PABX)--A PRIVATE AUTOMATIC
       TELEPHONE EXCHANGE WHICH PROVIDES FOR THE CONNECTION OF CALLS
       GOING TO AND COMING FROM THE PUBLIC TELEPHONE NETWORK (USUALLY A
       CENTRAL OFFICE EXCHANGE) AS WELL AS INTRAEXCHANGE CALLS BETWEEN
       THE SERVED EXTENSIONS.

       PROBABILITY OF DELAY--THE PROBABILITY THAT A CALL ATTEMPT, IF
       OFFERED, CANNOT BE COMPLETED IMMEDIATELY.

       PROBABILITY OF LOST CALLS (PROBABILITY OF LOSS)--THE PROBABILITY
       THAT A CALL ATTEMPT, IF OFFERED, WILL BE LOST.

       PROGRAM STORE--THE MEMORY SECTION OF A STORED PROGRAM CONTROL
       SWITCHING IN WHICH SEMI-PERMANENT INSTRUCTIONS AND TRANSLATIONS
       ARE CONTAINED. THESE ARE FED TO THE CENTRAL PROCESSOR TO PERMIT
       IT TO PROVIDE STORED PROGRAM CONTROL.

       PUBLIC SWITCHED NETWORK--ANY SWITCHING SYSTEM THAT PROVIDES
       CIRCUIT SWITCHING FACILITIES FOR USE BY THE PUBLIC. TELEPHONE,
       TELEX, TWX, AND BROADBAND SWITCHED NETWORKS ARE THE PUBLIC
       SWITCHED NETWORKS IN THE U.S.

       PULSE AMPLITUDE MODULATION (PAM)--A FORM OF PULSE MODULATION IN
       WHICH A NUMBER OF CHANNELS ARE MULTIPLEXED BY TIME SAMPLING, BUT
       ONE IN WHICH THE PULSE AMPLITUDES VARY IN ACCORDANCE WITH THE
       AMPLITUDE OF THE ANALOG SIGNAL LEVELS.

       PULSE CODE MODULATION (PCM)--A FORM OF PULSE MODULATION IN WHICH
       A NUMBER OF CHANNELS ARE MULTIPLEXED BY TIME SAMPLING AS IN PAM,
       BUT WITH EACH AMPLITUDE REPLACED BY A GROUP OF BINARY PULSES
       WHICH IDENTIFY THE AMPLITUDE.