QAM: Quadrature amplitude modulation
Quadrature amplitude modulation (QAM) is a method for encoding digital data in an analog signal in which each combination of phase and amplitude represents one of sixteen four-bit patterns. This is required for fax transmission at 9600 bits per second.

Q-in-Q
Q-in-Q, defined in the IEEE 802.1Q-in-Q, is a provider bridge extensions in 802.1Q VLAN tag, also known as stackable VLANs. It enables service providers to use a single VLAN to support customers who have multiple VLANs.

QoS Parameters
Quality of service (QoS) parameters are the parameters that control the priority, reliability, speed and amount of traffic sending over a network. Typical QoS parameters include: throughput, bandwidth, transit delay, jitter, loss ratio, and error rate.

QoS: Quality of Service
Quality of Service (QoS) refers to the ability of a network to provide higher priority services, including dedicated bandwidth, controlled jitter and latency (required by some real-time and interactive traffic), and improved loss characteristics, to selected network traffic over various WAN, LAN and MAN technologies. At the same time, making sure that providing priority for one class of traffic does not make other flows fail. QoS refers to a broad collection of networking technologies and techniques.

QPPB: QoS Policy Propagation on BGP
QoS Policy Propagation on BGP(QPPB) is a feature that classifies packets by IP precedence based on BGP community lists, BGP autonomous system paths, and access lists. After a packet is classified, other quality of service features such as committed access rate (CAT) and Weighted Random Early Detection (WRED) can specify and enforce policies to fit a business model.

QPSK: Quaternary Phase Shift Keying
Quaternary Phase Shift Keying (QPSK) is a digital frequency modulation technique used for sending data over coaxial cable networks. Because it's both easy to implement and fairly resistant to noise, QPSK is used primarily for sending data from the cable subscriber upstream to the Internet.

QRSS: Quasi-random Signal Sequence
Quasi-random Signal Sequence (QRSS) is a test pattern widely used to simulate voice signals.

Quartet Signaling
Quartet Signaling is a signaling technique used in 100VG-AnyLAN networks that allows data transmission at 100 Mbps over four pairs of UTP cable at the same frequencies used in 10BaseT networks.

Query
Query is a type of messages used to inquire about the value of some variable or set of variables.

Queue
Queue, in routing, means a backlog of packets waiting to be forwarded over a router interface.

Queuing Delay
Queuing Delay refers to the amount of time that data must wait before it can be transmitted onto a statistically multiplexed physical circuit.

Queuing Theory
Queuing Theory, also known queueing theory, refers to scientific studies governing the formation or lack of formation of congestion on a network or traffic lines or queues.

QUIPU
QUIPU is a public domain software package developed to study the X.500 OSI Directory and to provide extensive pilot capabilities.