 Q-Signal In the NTSC color system, the Q signal represents the chrominance on the green-magenta axis. Q.920 One of the two ITU-T Recommendations in which the Link Access Protocol-D (LAPD) is formally specified. Q.921 Along with Q.920, this ITU-T Recommendation specifies the LAPD protocol, an OSI layer-2 protocol. The connection-oriented service establishes a point-to-point D channel link between a customer and a carrier's switch. Data is sent over the link as Q.921 packets. Q.931 Whereas the D channel is packet-switched, B channels are circuit-switched. They are established, maintained and torn down using ITU-T Recommendation Q.931 (also known as ITU-T I.451). In Q.931, the ITU-T specified how 'H' channels-multiple contiguous channels on T-1 or E-1/CEPT frames-can be bound together and switched across an ISDN network. Quarter Common Intermediate Format, a mandatory part of the ITU-T H.261 compression standard that requires that non-interlaced frames of NTSC video be sent with 144 luminance lines and 176 pixels. When operating in the QCIF mode the number of bits that result from encoding a single image cannot exceed 64 K bits where K equals 1024. Quality of Service (QoS) defines a level of performance in a communications network. For example, video traffic requires low delay and jitter; data traffic does not, but will burst and thereby impede the transmission of voice traffic. Any channel that transports both must, therefore, reserve and execute preferential treatment for video. Glossary of Terms quality reduction One way of compressing data in which some compromises are made in picture resolution, frame rate and image size in order to accommodate the bandwidth available for transmission. quantization Quantization is one step in the process of converting an analog event into its digital representation. It involves the division of a continuous range of signal values into contiguous parts, a unique value being assigned to each part. Prior to quantization the signal is sampled at regular intervals (typically at a ra