Q
QAM	Quadrature amplitude modulation. Technique for modulating digital data onto high-frequency carrier tones that is a combination of amplitude modulation and phase-shift keying.
QoS	Quality of service. Measure of performance for a transmission system that reflects its transmission quality and service availability. QoS refers to the ability of a network to provide better service to selected network traffic over various underlying technologies. QoS is not inherent in a network infrastructure; rather, you must institute QoS by strategically deploying features that implement it throughout the network.
Q-series recommendations	ITU-T standards that define switching and signaling. Well-known Q-series recommendations include Q,921 for the ISDN data-link layer and Q.931 for out-of-band signaling in ISDN connections.
QSIG	Q (point of the ISDN model) Signaling. Common-channel signaling standard based on Q.931 and used by many digital PBXs.