Caller ID
For the protein involved in the synthesis
of major histocompatibility complex II,
see CLIP (protein).
Caller ID, known also as Caller Identifica-
tion (CID), or more properly Calling Num-
ber Identification (CNID), is a telephone
service, available on POTS (plain old tele-
phone service) lines, that transmits a caller’s
number to the called party’s telephone equip-
ment during the ringing signal, or when the
call is being set up but before the call is
answered. Where available, caller ID can also
provide a name associated with the calling
telephone number, in some cases for a higher
fee. The information made available to the
called party may be made visible on a tele-
phone’s own display or on a separate at-
tached device.
Caller ID may be used to track down or
limit the impact of prank calls, telemarketers,
and other intrusions. However, it can also im-
pede communication by enabling users to be-
come evasive. The concept behind caller ID is
the value of informed consent; however, it
also poses problems for personal privacy.
Another problem is that the possibility of
caller ID spoofing makes it unreliable.
Calling-line identification
In some countries, the terms caller display,
calling line identification presentation
(CLIP), call capture, or just calling line
identity are used; call display is the predom-
inant marketing name used
in Canada
(though customers often call it caller ID). The
idea of CNID as a service for POTS sub-
scribers originated from automatic number
identification (ANI) as a part of toll free num-
ber service in the United States.
However, CNID and ANI are not the same
thing. Caller ID is made up of two separate
pieces of information: the calling number and
the billing (or subscriber) name where avail-
able. When an originating phone switch
sends out a phone number as caller ID, the
telephone company receiving the call is re-
sponsible for looking up the name of the sub-
scriber in a database. It is for this reason that
mobile phone callers appear as WIRELESS
CALLER, or the location