Call Center Glossary of Terms

Dialed Number

The number that the caller dialed to initiate the call.

Dialed Number Identification Service

A string of digits that the telephone network passes to the ACD, VRU or other devise, to indicate which number the caller dialed. The ACD can then process and report on that type of call according to user-defined criteria. One trunk group can have many DNIS numbers.


The use of a binary code 1s and 0s to represent information.

Direct Call Processing

See Talk Time.

Dual-Tone Multifrequency

A signaling system that sends pairs of audio frequencies to represent digits on a telephone keypad. It is often used interchangeably with the term Touchtone (an AT + T trademark).

Dynamic Answer

An ACD feature that automatically reconfigures the number of rings before the system answers calls, based on real-time queue information. Since costs dont begin until the ACD answers calls, this feature can save callers or the call center money when long distance charges apply. Electronic Mail (E-mail). Electronic text mail.

Envelope Strategy

A strategy whereby enough agents are scheduled for the day or week to handle both the inbound call load and other types of work. Priorities are based on the inbound call load. When call load is heavy, all agents handle calls, but when it is light, some agents are reassigned to work that is not as time-sensitive.

Erlang B

A formula developed by A.K. Erlang, widely used to determine the number of trunks required to handle a known calling load during a one hour period. The formula assumes that if callers get busy signals, they go away forever, never to retry (lost calls cleared). Since some callers retry, Erlang B can underestimate trunks required. However, Erlang B is generally accurate in situations with few busy signals.

Erlang C

Calculates predicted waiting times (delay) based on three things: the number of servers (reps); the number of people waiting to be served (callers); and the average amount of time it takes to serve each person. It can also predict the resources required to keep waiting times within targeted limits. Erlang C assumes no lost calls or busy signals, so it has a tendency to overestimate staff required.

Erlang, A.K

A Danish engineer who worked for the Copenhagen Telephone Company in the early 1900s and developed Erlang B, Erlang C and other telephone traffic engineering formulas.


One hour of telephone traffic in an hour of time. For example, if circuits carry 120 minutes of traffic in an hour, that's two Erlangs.

Error Rate

Either the number of defective transactions or the number of defective steps in a transaction.

Escalation Plan

A plan that specifies actions to be taken when the queue begins to build beyond acceptable levels.

Exchange Line

See Trunk.

Executive Summary

A brief summary of the key points of a more detailed report or study.

Facsimile / FAX

Technology that scans a document, encodes it, transmits it over a telecommunications circuit, and reproduces it in original form at the receiving end.

Fast Clear Down

A caller who hangs up immediately when they hear a delay announcement.

Fax on Demand

A system that enables callers to request documents, using their telephone keypads. The selected documents are delivered to the fax numbers they specify.


A step by step diagram of a process.

Flushing Out the Queue

Changing system thresholds so that calls waiting for an agent group are redirected to another group with a shorter queue or available agents.


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