The Bell Glossary courtesy of Exodus



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ACD: Automatic Call Distributor - A system that automatically distributes calls

to operator pools (providing services such as intercept and directory

assistance), to airline ticket agents, etc.


Administration: The tasks of record-keeping, monitoring, rearranging,

prediction need for growth, etc.


AIS: Automatic Intercept System - A system employing an audio-response unit

under control of a processor to automatically provide pertinent info to callers

routed to intercept.


Alert: To indicate the existence of an incoming call, (ringing).


ANI: Automatic Number Identification - Often pronounced "Annie," a facility for

automatically identify the number of the calling party for charging purposes.


Appearance: A connection upon a network terminal, as in "the line has two

network appearances."


Attend: The operation of monitoring a line or an incoming trunk for off-hook or

seizure, respectively.


Audible: The subdued "image" of ringing transmitted to the calling party during

ringing; not derived from the actual ringing signal in later systems.


Backbone Route: The route made up of final-group trunks between end offices in

different regional center areas.


BHC: Busy Hour Calls - The number of calls placed in the busy hour.


Blocking: The ratio of unsuccessful to total attempts to use a facility;

expresses as a probability when computed a priority.


Blocking Network: A network that, under certain conditions, may be unable to

form a transmission path from one end of the network to the other. In general,

all networks used within the Bell Systems are of the blocking type.


Blue Box: Equipment used fraudulently to synthesize signals, gaining access to

the toll network for the placement of calls without charge.


BORSCHT Circuit: A name for the line circuit in the central office. It

functions as a mnemonic for the functions that must be performed by the

circuit: Battery, Overvoltage, Ringing, Supervision, Coding, Hybrid, and



Busy Signal: (Called-line-busy) An audible signal which, in the Bell System,

comprises 480hz and 620hz interrupted at 60IPM.


Bylink: A special high-speed means used in crossbar equipment for routing calls

incoming from a step-by-step office. Trunks from such offices are often

referred to as "bylink" trunks even when incoming to noncrossbar offices; they

are more properly referred to as "dc incoming trunks." Such high-speed means

are necessary to assure that the first incoming pulse is not lost.


Cable Vault: The point which phone cable enters the Central Office building.


CAMA: Centralized Automatic Message Accounting - Pronounced like Alabama.


CCIS: Common Channel Interoffice Signaling - Signaling information for trunk

connections over a separate, nonspeech data link rather that over the trunks



CCITT: International Telegraph and Telephone Consultative Committee- An

International committee that formulates plans and sets standards for

intercountry communication means.


CDO: Community Dial Office - A small usually rural office typically served by

step-by-step equipment.


CO: Central Office - Comprises a switching network and its control and support

equipment. Occasionally improperly used to mean "office code."


Centrex: A service comparable in features to PBX service but implemented with

some (Centrex CU) or all (Centrex CO) of the control in the central office. In

the later case, each station's loop connects to the central office.


Customer Loop: The wire pair connecting a customer's station to the central



DDD: Direct Distance Dialing - Dialing without operator assistance over the

nationwide intertoll network.


Direct Trunk Group: A trunk group that is a direct connection between a given

originating and a given terminating office.


EOTT: End Office Toll Trunking - Trunking between end offices in different toll

center areas.


ESB: Emergency Service Bureau - A centralized agency to which 911 "universal"

emergency calls are routed.


ESS: Electronic Switching System - A generic term used to identify as a class,

stored-program switching systems such as the Bell System's No.1 No.2, No.3,

No.4, or No.5.


ETS: Electronic Translation Systems - An electronic replacement for the card

translator in 4A Crossbar systems. Makes use of the SPC 1A Processor.


False Start: An aborted dialing attempt.


Fast Busy: (often called reorder) - An audible busy signal interrupted at twice

the rate of the normal busy signal; sent to the originating station to indicate

that the call blocked due to busy equipment.


Final Trunk Group: The trunk group to which calls are routed when available

high-usage trunks overflow; these groups generally "home" on an office next

highest in the hierarchy.


Full Group: A trunk group that does not permit rerouting off-contingent foreign

traffic; there are seven such offices.


Glare: The situation that occurs when a two-way trunk is seized more or less

simultaneously at both ends.


High Usage Trunk Group: The appellation for a trunk group that has alternate

routes via other similar groups, and ultimately via a final trunk group to a

higher ranking office.


Intercept: The agency (usually an operator) to which calls are routed when made

to a line recently removed from a service, or in some other category requiring

explanation. Automated versions (ASI) with automatic voiceresponse units are

growing in use.


Interrupt: The interruption on a phone line to disconnect and connect with

another station, such as an Emergence Interrupt.


Junctor: A wire or circuit connection between networks in the same office. The

functional equivalent to an intraoffice trunk.


MF: Multifrequency - The method of signaling over a trunk making use of the

simultaneous application of two out of six possible frequencies.


NPA: Numbering Plan Area.


ONI: Operator Number Identification - The use of an operator in a CAMA office

to verbally obtain the calling number of a call originating in an office not

equipped with ANI.


PBX: Private Branch Exchange - (PABX: Private Automatic Branch Exchange) An

telephone office serving a private customer, Typically , access to the outside

telephone network is provided.


Permanent Signal: A sustained off-hook condition without activity (no dialing

or ringing or completed connection); such a condition tends to tie up

equipment, especially in earlier systems. Usually accidental, but sometimes

used intentionally by customers in high-crime-rate areas to thwart off



POTS: Plain Old Telephone Service - Basic service with no extra "frills".


ROTL: Remote Office Test Line - A means for remotely testing trunks.


RTA: Remote Trunk Arrangement - An extension to the TSPS system permitting its

services to be provided up to 200 miles from the TSPS site.


SF: Single Frequency. A signaling method for trunks: 2600hz is impressed upon

idle trunks.


Supervise: To monitor the status of a call.


SxS: (Step-by-Step or Strowger switch) - An electromechanical office type

utilizing a gross-motion stepping switch as a combination network and

distributed control.


Talkoff: The phenomenon of accidental synthesis of a machine-intelligible

signal by human voice causing an unintended response. "whistling a tone".


Trunk: A path between central offices; in general 2-wire for interlocal, 4-wire

for intertoll.


TSPS: Traffic Service Position System - A system that provides, under stored-

program control, efficient operator assistance for toll calls. It does not

switch the customer, but provides a bridge connection to the operator.


X-bar: (Crossbar) - An electromechanical office type utilizing a "fine-motion"

coordinate switch and a multiplicity of central controls (called markers).

There are four varieties:

No.1 Crossbar: Used in large urban office application; (1938)

No 3 Crossbar: A small system started in (1974).

No.4A/4M Crossbar: A 4-wire toll machine; (1943).

No.5 Crossbar: A machine originally intended for relatively small

suburban applications; (1948)

Crossbar Tandem: A machine used for interlocal office switching.




Revised in '94 CBIV,.......... -= Exodus =-