Glossary - Q

Q.2931

A ITU-TSS signaling standard for ATM to support SVCs. Based on the signaling standard for ISDN.

Q.93B

Older name for ITU-TSS signaling standard for ATM to support SVCs. Currently called Q.2931.

Q.931

(network, isdn, ATM, frame relay)

A ITU-T signaling standard for ISDN to support SVCs. Basis for the signaling standard developed for Frame Relay and ATM. See Q.933, Q.2931, Q-SIG).
ITU-T Recommendation for specifying the UNI signaling protocol in N-ISDN.

Q.933

A ITU-T Recommendation for specifying the UNI signaling protocol in Frame Relay to support SVCs. Based on the signaling standard for ISDN. See Q.931.

Q.2110

A ITU-T recommendation for specifying the UNI SSCOP.

Q.2130

A ITU-T recommendation for specifying the UNI SSCF.

Q.2931

A ITU-T Recommendation derived from both Q.931and Q.933 to provide SVC specifications and standards.

QAM

Quadrature Amplitude Modulation (communications)
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.
Quadrature Shift Keying modulation method, which, of practical modulation techniques, has the best bandwidth efficiency per information symbol (baud). It is used in most modems.
A modulation technique that encodes a signal by modulating its amplitude to represent data. The data can be represented by changing the signal to any of 16 or 32 different states.

Quality Assurance Management

QBE

Query By Example Process that allows a user to build a SQL query using examples. The user is supposed to know the SQL language.

QD

Queuing delay (physical level, ATM)

QoS

Quality of Service (ATM)
Five broad categories outlined by the ATM Forum's UNI 3.0; implementation details and precise characteristics are to be determined in the future. Refers to the set of ATM performance parameters that characterize the traffic over a given virtual connection (VC). These parameters include the CLR, CER, CMR, CDV, CTD and the average cell transfer delay.

QoS Classes

Quality of Service Classes
Five service classes are defined by the ATM Forum in terms of the QoS parameters:

• Class 0 is effectively a "best effort" attempt at delivery; it is intended for applications that do not require a particular class of service. This class of service is sometime called Class 5.
• Class 1 specifies the parameters for circuit emulation, CBR (uncompressed) video and for VPN. It specifies performance requirements and indicates that ATM's quality of service should be comparable with the service offered by standard digital connections. AAL1 supports this kind of connection-oriented service.
• Class 2 specifies the parameters for VBR audio and video. AAL2 supports this delay-dependent, connection-oriented class. It specifies necessary service levels for packetized video and voice.
• Class 3 specifies the parameters for connection-oriented data transfer protocols, particularly frame relay. AAL3/4 and mostly AAL5 supports this delay-independent class of service.
• Class 4 specifies interoperability requirements for connectionless protocols, including IP IPX, and SMDS. AAL3/4 or AAL5 can be used to support this class.
• Class 5 see class 0.

Q-SIG (standard, ITU-T)

Signaling standard developed by the ECMA and based on the normalised CCITT signaling (Q.931). It is supposed to allow coherent exchanges between public and private signaling systems.

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