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.Reducing packet latencycan be effectively achieved via a dedicated processor like aDSP and by employing end-to-end compression techniquesrather than node-to-node compression/decompression.Allthese factors contribute to reducing bandwidth and equip-ment costs as well as improving the network response timefor user applications.80 DECIBELSee alsoVoice CompressionDECIBELDECIBELDecibel (dB) is a unit of measurement expressing gain orloss.It is used to measure such things as sound, electrical ormechanical power, and voltage.In the telecommunicationsindustry, the decibel is used to conveniently express the gainor loss in transmission systems, whether the medium is cop-per, optical fiber, or wireless.The decibel is actually the relationship of some referencepoint and another point that is above or below the referencepoint.The base reference point is 0 dB, and subsequent mea-surements are relative to that reference point.There are anumber of decibel notations, each indicating the context ofthe measurement, such asdBi is the antenna gain in dB relative to an isotropicsource.dBm is the power in dB relative to 1 milliwatt.dBW is the power in dB relative to 1 watt.dBmV is referenced to 1 millivolt.It is often used as ameasure of signal levels (or noise) on a network.The dB scale related to power is different from the dBscale related to voltage.In power measurements, the powerlevel doubles every 3 dB, instead of every 6 dB as in voltage.Likewise, the dB scale related to audio output is differentfrom the dB scales relating to voltage and power.Audio IntensitySince the range of audio intensities that the human ear candetect is so large, the scale frequently used to measure them isDECIBEL 81a scale based on multiples of 10.This type of scale is sometimesreferred to as a  logarithmic scale. The threshold of hearing isassigned a sound level of 0 dB.Asound that is 10 times moreintense is assigned a sound level of 10 dB.Asound that is 10times more intense (10 × 10) is assigned a sound level of 20 dB.Asound that is 10 times more intense (10 × 10 × 10) is assigneda sound level of 30 dB.Asound that is 10 times more intense(10 × 10 × 10 × 10) is assigned a sound level of 40 dB.Table D-1 lists some common and not so common sounds with an esti-mate of their intensity and decibel level.SummaryThere are a variety of test instruments available to handlevirtually any measurement requirement, including analogimpulse meters to measure quick bursts of sound.Thesedevices typically have output jacks for connections to chart-ing devices that plot continuous noise levels across a roll ofpaper.Digital devices output measurements to light-emittingTABLE D-1 Decibel Levels of Selected SoundsNo.of TimesGreater thanSource Threshold of Hearing DecibelsThreshold of hearing (TOH) 100 0Rustling leaves 101 10Whisper 102 20Normal conversation 106 60Busy street traffic 107 70Vacuum cleaner 108 80Heavy truck traffic 109 90Walkman at maximum level 1010 100Power tools 1011 110Threshold of pain to the ear 1012 120Airport runway 1013 130Sonic boom 1014 140Perforation of eardrum 1016 16012 feet from a battleshipcannon muzzle 1020 22082 DIGITALLY ENHANCED CORDLESS TELECOMMUNICATIONSdiode (LED) screens.Band filters allow selection of narrowfrequency ranges to isolate specific noises for measurement.Optional calibrators are available for in-field adjustments.See alsoHertzDIGITALLY ENHANCED CORDLESSDIGITALLY ENHANCED CORDLESSTELECOMMUNICATIONSTELECOMMUNICATIONSThe Digital Enhanced Cordless Telecommunications (DECT)standard defines a protocol for secure digital telecommunica-tions and is intended to offer an economical alternative toexisting cordless and wireless solutions.DECT uses TimeDivision Multiple Access (TDMA) technology to provide ten1.75-MHz channels in the frequency band between 1.88 and1.90 GHz.Each channel can carry up to 12 simultaneous two-way conversations.Speech quality is comparable to conven-tional land-based phone lines.Frequency bands have beenmade available for DECT in more than 100 countries.Whereas conventional analog cordless phones have arange of about 100 meters, the DECT version can operatereliably up to 300 meters [ Pobierz caÅ‚ość w formacie PDF ]