Q.931 (also called Q931) is a signaling protocol for Integrated Services Digital Network (ISDN) communications, that is used in voice over IP (VoIP). The Q.931 protocol is involved in the setup and termination of connections. Q.931 and TCP/IP work at different layers and share few features. Q.931 has reliable layers but does not provide retransmission or flow control.

Quadrature amplitude modulation, also know as QAM, is a method of combining two amplitude-modulated (AM) signals into a single channel, thereby doubling the effective bandwidth. QAM is used with pulse amplitude modulation (PAM) in digital systems, especially in wireless applications.