Signalling protocol (layer 3) for B-ISDN (similar to Q-931)

Quadrature Amplitude Modulation

Method of modulating digital signals onto a radio-frequency carrier signal involving both amplitude and phase coding. QAM is a modulation scheme mostly used in the downstream direction.

Quality Index

Qualified Logical Link Control

Data link layer protocol defined by IBM that allows SNA data to be transported across X.25 networks.

Quality of Service

The requirements a network must provide to an individual flow of information (e.g., a voice call, an interactive video conference, a data file transfer) so that the information is optimally delivered.

Quality of Service Parameters

Parameters that control the amount of traffic the source in an ATM network sends over an SVC. If any switch along the path cannot accommodate the requested QoS parameters, the request is rejected, and a rejection message is forwarded back to the originator of the request.

Quasi-Random Signal

A digital test signal consisting of a bit sequence that approximates a random signal.

Quasi-Random Signal Sequence

The process that divides the continuous range of values of a signal into non-overlapping (but not necessarily equal) sub-ranges. It then assigns a discrete value of the output to each sub-range. Whenever the signal value falls within a given sub-range, output has the corresponding discrete value.

Software package developed to study the OSI Directory and provide extensive pilot capabilities.