Q

Q band The portion of the radio spectrum in the range of 36–46 GHz, as specified by the ITU-R. Applications are military in nature. See also electromagnetic spectrum and ITU-R.

Q Bit (Qualified Data Bit) - A bit in the X.25 protocol that resides in the data packet header (within the X.25 frame). It is the first bit in the threebyte header that indicates whether or not data is intended for the end DTE (in which case, the bit is set to 0) or X.29 instructions for a PAD device (in which case, the bit is set to 1).

Q series - The series of ITU-T Recommendations specifying protocols relating to switching and signaling.

Q Signaling (QSIG) - See QSIG.

Q.920/Q.921 - ITU-T specifications for the ISDN UNI data-link layer. See also UNI.

Q.922A - ITU-T specification for frame-relay encapsulation.

Q.931 - The ITU-T Recommendation for the user network interface (UNI) for integrated services digital network (ISDN) basic call control, such as call setup and teardown.The specifications include user-touser and network-to-network call control messages for both circuit-switched and packet-switched networking. ISDN signaling and control takes place over the D channel. Q.931 also is included in the ITU-T H.323 protocol suite for multimedia communications over packet networks. See also D channel, H.323, ISDN, and ITU-T.

Q.93B - ITU-T specification for signaling to establish, maintain, and clear BISDN network connections. An evolution of ITU-T recommendation Q.931. See also Q.931.

Q - 1. One of the two letters, along with Z, that traditionally did not appear on a telephone dial or keypad. The thought was that Q could be confused with O, and that Z could be confused with 2. Q now appears with P, R, and S on number 7. Alphanumeric dialing was, and remains, a North American practice. Telephones in most other countries do not sport letters. 2. Q interface or Reference Point Q in ISDN. See Reference Point Q.

QAM (Qaudrature Amplitude Modulation) - A modulation technique used for digital signals. The line format or transmission format (for wireless applications) is analog. QAM is a breeding of phasemodulation and amplitude-modulation. The many different variations of QAM allow for extended constellations and formats thereof. Two simple QAM formats have 16 different signals by using four different phase shifts and four different amplitudes, or eight different phase shifts and two different voltage levels. Both methods provide four bits per baud. To convert a digital bit stream to a QAM signal, the bit stream is accepted four bits at a time. Those bits are converted to a symbol, which represents a constellation, or, more technically, a voltage level and phase shift. With four bits, there are 16 possible constellations. This enables four bits to be sent with one baud cycle. Some versions of QAM incorporate 256 constellations, which enables 16 bits to be transmitted in a single baud cycle.

QCIF (Quarter Common Intermediate Format) - In the ITU-T H.320 umbrella standard for videoconferencing and multimedia communications over narrowband ISDN (N-ISDN), a mandatory video format that supports resolution of 176 × 144 pixels, which is exactly 1 ⁄4 the resolution of CIF at 352 × 288 pixels. See also CIF, H.320, ITU-T, multimedia, N-ISDN, pixel, resolution, video, and videoconferencing.

QLLC (Qualified Logical Link Control) - A data-link layer protocol defined by IBM that allows SNA data to be transported across X.25 networks.

QoS (Quality of Service) - A measure of parameters that affect the level of performance a network offers a specific type of traffic. QoS parameters include access priority, bandwidth availability, latency, jitter, and packet loss. Toll quality, real-time compressed and uncompressed voice and video require fairly immediate network access, guaranteed availability of bandwidth throughout the call, low latency, zero jitter, and zero loss. E-mail is at the opposite end of the QoS spectrum, as it is highly tolerant of a low level of priority; high levels of latency, jitter, and loss; and does not require any bandwidth availability guarantees during the course of a mail transfer. QoS also must ensure that granting a QoS level to one traffic type or call does not violate the data flow requirements of another traffic type or call.The circuit-switched public switched telephone network (PSTN) offers all applications the highest level of QoS. Asynchronous transfer mode (ATM) offers multiple QoS levels appropriate for different traffic types. Frame relay, Internet Protocol (IP), and Ethernet networks can employ various priority mechanisms to offer differential grade of service (GoS) levels, but cannot guarantee QoS. See also ATM, compression, Ethernet, frame relay, GoS, IP, jitter, latency, loss, and PSTN.

QPSK (Quadrature, Quadriphase, or Quaternary Phase-Shift Keying) - A modulation technique that achieves dibit transmission by defining four phase shifts separated by 90 degrees (0°, 90°, 180°, and 270°). IEEE 802.11a (Wi-Fi5) wireless LAN (WLAN) standards call for binary phase-shift keying (BPSK) at 6 Mbps and QPSK at 12 Mbps. IEEE 802.11b (Wi-Fi) calls for BPSK at 1 Mbps and QPSK at 2 Mbps. Bluetooth specifies BPSK for use in the 868 and 915 MHz bands, and QPSK for use in the 2.4 GHz band. µ/4 differential quaternary phase shift keying (µ/4 DQPSK) can be viewed as the superposition of two QPSK constellations offset by 45 degrees relative to each other. See also 802.11a, 802.11b, Bluetooth, BPSK, modulation, phase, PSK, µ/4 DQPSK, and WLAN.

QPSX (Queued Packet Synchronous eXchange) - A technology that formed the basis for the Distributed Queue Dual Bus (DQDB) defined in the IEEE 802.6 standard for metropolitan area networks (MANs). QPSX was developed at the University of Western Australia. See also 802.6, DQDB, IEEE, and MAN.

QSIG (Q Signaling) - A standard that defines services and signaling protocols for interconnecting TDM-based PBXs based on the ITU-T ISDN standard Q.931. QSIG is a Common Channel Signaling (CCS) protocol that runs over the ISDN D-channel for signaling between nodes in a Private Integrated Services Network (PISN). QSIG supports call setup, call teardown, and transparency of features such as message waiting, camp-on, and callback. The ISO (International Organization for Standardization) has adopted QSIG as Private Signaling System No. 1 (PSS1). See also CCS, ISDN, ISO, Q.931, and Q series.

Quad IW (Quad Inside Wire) - Older standard telephone wire used by telephone companies. Quad has four wires, the colors are red, green, black, and yellow. Some quad wiring is not twisted, so it is susceptible to RFI. The colors for line one are green and red, and the colors for line two are yellow and black.

Quad Lock Conduit - Conduit that is designed to be direct buried. The four individual conduits allow communications companies to lease conduit space to each other in a way that is easy to track for fiberoptic cable installers/splicers, etc.

Quad Word - In computer memory, a word is 16 bits, which is one data unit processed by the bus. Newer computers and other processing systems are built with 32- and 64-bit busses, which gives them the ability to process double words (32 bits) and quad words (64 bits).

quadbit - 1. A set of four bits. Some line coding techniques encode blocks of 4 bits of data at a time, rather than 1 or 2 bits.The 4B/5B technique, for example, encodes a 4-bit block of data into a 5-bit block of signal in order to provide sufficient clocking pulses and signal transitions to synchronize the network and to provide some level of error detection. 4B/5B is used in 100Base-TX, 100Base-FX, and Fiber Distributed Data Interface (FDDI) LANs. Compare to nibble. See also 4B/5B, line coding, and synchronization. 2. Referring to a modulation technique that impresses 4 bits on a baud, so that the bit rate is quadruple the baud rate. Such a technique employs 16 signal states. 16-QAM is a quadbit technique achieved by defining two amplitude values for each of eight phase shifts. See also 16-QAM, amplitude, amplitude modulation, baud, baud rate, bit, bit rate, dibit, modulation, phase, QAM, quartet, signal, tribit, and unibit.

quadraplex - A circuit or device that supports simultaneous transmission or reception of four independent signals. Quadraplex communications technology is a simple form of multiplexing that improved on diplex (two independent signals) and was considered quite revolutionary in the early days of telegraphy, when the four signals could be transmitted in one direction, only.The term is generally considered obsolete. See also diplex and multiplex.

Quadrature Amplitude Modulation (QAM) - A line-code method primarily used in twisted-pair telephony applications that increases the number of bits sent per baud (line state) by representing multiple bits as a combination of phase and amplitude levels. See also QAM.

Quadrature Amplitude Modulation (QAM) - See QAM.

quadrature phase-shift keying (QPSK) - See QPSK.

quadriphase phase-shift keying (QPSK) - See QPSK.

quadruple play - A marketing term used by broadband service providers to describe the triple play combination of voice, high speed data, and television services over a single local loop, plus wireless services. While there is no standard approach, quadruple play wireless services generally are designed to operate as cordless telephony when within range of a base station on the subscriber premises and as cellular telephony when out of range. As contemporary high-end cellular terminal devices are capable of supporting voice, data, image, and video, and as broadband cellular and other wireless networks are capable of supporting transmission rates in the range of hundreds of kbps and even Mbps, wireless capability is a significant addition to an integrated suite of service.The term triple play is a baseball analogy, referring to the very rare act in which the defense makes three outs on the same play. See also broadband, cellular radio, cordless telephone, local loop, and triple play.

quality of service (QoS) - See QoS.

quantization and compaction encoding - Referring to a step in the video compression process that reduces the number of bits required to represent a color pixel. Compaction techniques include run-length encoding, Huffman coding, and arithmetic coding.

quantize - To express in multiples of a quantum number, in other words an integer or basic unit. In telecommunications, the term refers to the conversion of the amplitude of an analog sine wave into a digital signal, which necessarily requires expressing the amplitude value in binary terms. See also quantizing noise.

Quantizing Distortion - A form of distortion that can occur in telecommunication circuitry at the physical, data-link, or network level. It is a result of a digital signal being corrupted to some degree, thus causing an improper reproduction of the original audio in the digital-to-analog conversion process. Quantizing distortion can cause a person’s voice to sound “robotic,” delayed, or choppy during a wireless phone conversation.

quantizing noise - A type of distortion that occurs when an analog waveform is encoded into a digital signal and then decoded back into an analog signal. The digital-to-analog conversion process occurs at sampling intervals and always involves some amount of approximation as the amplitude of the waveform is quantized, which involves converting each sample amplitude value to the nearest of 256 (2 ⁸ ) standard approximate binary values.When the approximate digital values are reconverted and the analog waveform is reconstructed, the effect of the approximation manifests as quantizing noise. If the sampling rate is too low (i.e., infrequent) and/or the approximation is too extreme, the result is a phenomenon known as aliasing in which the reconstructed signal is inaccurate, or even unintelligible, and the resulting voice quality unacceptable. See also aliasing, amplitude, analog, binary, digital, distortion, noise, quantize, and waveform.

quantum leap - 1. In physics, an abrupt, or step, change in the energy state of an elemental unit, such as a molecule, atom, or subatomic particle. Such particles do not smoothly transition from one energy state to another; rather, they jump or leap from a state of rest to an excited state, for example, accompanied by the absorption or emission of a particle carrying the equivalent energy. Such changes are dramatic and instantaneous, but small in magnitude. 2. In the vernacular, a change that is abrupt and large in magnitude.

quantum - The elementary quantity of radiant energy, a photon. See also photon.

Quarter Common Intermediate Format (QCIF) - See QCIF.

quartet - A four-bit byte.Also known as a nibble. Compare with quadbit. See also bit, byte, and nibble.

quaternary phase-shift keying (QPSK) - See QPSK.

Quatraplex - A synonym for quadraplex. See quadraplex.

Query Language - A programming language designed for manipulating data in data bases.

Query - A name given to a programming string that asks a question about data in a relational data base. Queries are common in call-accounting applications.

Queue - 1. Queue is a way of saying waiting line in telephony. The two types of queues are line queues (very uncommon) and ACD (Automatic Call Distribution System) call queues. Some telephone systems have a feature called line queuing. If you try to dial out and you cannot get an outside line, you are put in queue, or in a waiting line for the next available trunk. Some systems can provide music, as if you were on hold for the line and some can ring your phone back. The other queuing is ACD specific. ACD systems place incoming calls in queue for the next available agent and evenly distribute calls among the agents so that the workload is not unbalanced and sales opportunities are fair. 2. Generally, an ordered list of elements waiting to be processed. 3. In LAN and WAN routing, a backlog of packets waiting to be forwarded over a router interface.

Queued Packet Synchronous Exchange (QPSX) - See QPSX.

Queuing Delay - In LAN and WAN data transfers over X.25 and frame relay, the amount of time that data must wait before it can be transmitted onto a statistically multiplexed physical circuit.

Quick Connect - A name given to 66M150 block and AT&T 110 (one-ten) block connectivity.

QuickConnect - A feature of V.92 modems that reduces the time required for handshaking by approximately 50 percent, to about 10–15 seconds. QuickConnect trains the modem on the first call and remem bers the characteristics of the circuit.Assuming that the circuit is the same on the next call, the circuit characteristics do not have to be relearned, which results in faster connect times, yielding obvious advantages to the end user and Internet service provider (ISP), alike. See also handshaking, ISP, modem, and V Series.

quintet - A five-bit byte. See also bit and byte.

QWERTY - The standard layout for English-language computer keyboards, so named for the top left six alphabetical characters.The QWERTY layout was patented by Christopher Sholes in 1868 for use with the first mechanical typewriter, which he also invented. Sholes sold the patent rights to Remington in 1873.The original layout was in alphabetical order, which caused the typebars to become entangled frequently once the typist gained proficiency and speed.Although the original justification is lost in time and there have developed a number of theories about it, the QWERTY layout certainly split up commonly used pairs of letters (e.g., s and t) and mitigated the issue of typebar entanglement.