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off-hook

The active state of a telephone circuit. The term is derived from old telephone sets where the receiver, when in use, was lifted from a hook attached to a switch. The opposite condition is on-hook.

on-hook

The inactive state of a customer telephone circuit. The term is derived from old telephone sets where the receiver, when not in use, was placed on a hook attached to a switch. The opposite condition is off-hook.

OGT

Out-Going Trunk; a telephone line that is used only for placing calls.

OKI ADPCM

A form of ADPCM encoding. See also ADPCM, PCM.

ones density

The requirement for digital transmission lines in the PSTN that eight consecutive zeros cannot exist in a digital data transmission. On a T1 line, zero (0) means no voltage, no pulse. Since the bus clock is driven by the T1 line, too many consecutive zeroes can cause the clocking to fail. See also B8ZS.

Open System Interconnect (OSI)

A model for digital communication, developed by the International Organization for Standardization (ISO). The OSI model defines seven separate layers of communication. ISDN follows this protocol model to ensure end-to-end connectivity.

operator workstation

A type of network interface which connects to operator headsets.

OSI

See Open System Interconnect (OSI).

out parameter

When developing a CT Access service API, refers to an argument which provides a pointer to a buffer to receive output from a function.

outbound application

An application designed to place outbound calls.

outbound call

A call placed by an application to a remote party.

out-of-band

In telephony, information carried outside of the audio or voice channel.

out-of-band signaling

Refers to signaling methods where signaling information is carried by a separate channel. In addition to technical advantages, out-of-band signaling helps prevent unauthorized tampering with the network. See also in-band signaling.

output gain

In telephony, gain applied to output.

overflow

Saturation condition of output channel after all of the inputs to a conference have been combined.

overlap receiving mode

An AG ISDN ACU mode, in which an inbound call causes the ACU to send a ACU_CONN_IN message to the application even if the called number and/or calling number are not complete (i.e. the "Sending Complete" IE is not present). The ACU then sends any additional incoming digits in ACU_DIGIT_IN messages. See also ACU stack mode.

overlay

Software that is not always memory resident; it is loaded on request.