Installation guide

Glossary
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ShoreTel 14.2 Planning and Installation Guide 495
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CLASS Custom Local Area Signalling Services, a family of telephone
services offered from local telephone companies, usually for a
monthly fee; includes features such as CallerID, Call Waiting, call
return, repeat dialing, call rejection, call trace, priority ringing, and
selective call forwarding.
Class of Service Abbreviated as CoS or COS; a set of features and privileges
associated with a particular user or extension, used for grouping
similar users together.
CO Central Office; the building where the telephone company’s
telephone switching equipment that services the local area is
located.
CO Line See
Trunk.
Conference Three or more parties joined together in a single call, such that each
party can hear and be heard by the others.
DHCP Dynamic Host Configuration Protocol, a protocol for downloading
network information (such as IP addresses) to client workstations.
DID Direct Inward Dial, a signaling mechanism used by telephone
companies to indicate to a customer’s PBX what telephone number
was dialed by the calling party. It can be used with analog lines but
is used mostly with digital (that is, T-1) connections.
DTMF Dual-Tone Multi-Frequency, a technique of providing two tones for
each button on a telephone to signal dialing digits; also known as
Touch Tone.
End User For documentation purposes, a person using the telephone system
from the inside, such as from an extension or a call control
application, as opposed to a caller who dials in from outside the
system; often shortened to “user.” See also
Caller.
Erlang Formula A mathematical way of predicting a randomly arriving workload
(such as telephone calls) based on known information (such as
average call duration). Although traditionally used in telephone
traffic engineering to determine the required number of trunks,
Erlang formulas have applications in call center staffing as well.
External Call A telephone call directed to or from outside the telephone system,
and over the Public Switched Telephone Network (PSTN).