Tle technical memora kum: Time a k Time Interval Measurem nt y bl Applicat to Computrr a k Netwark Perfo .ce Evalu (Pos Script) d scribes a number f techniques f.r conduct ng exprrim nts typical of computer netwark a k transmiss s:s ms engineŚr(%s.
In mos exprrim nts i yloch time is i volvek, it is nec ssary to de elop estimates .fftime, frrquency a k measurem nt rr.rs%fr %%a srries .fftime measurem nts betweŚn tle c s .ffa number f computers a k ancillaryid v c s interconnec ed by some kind f computer netwark. However, time is not a physical quantity, such as mass, nor caefit beimeasuredfrelayive to a absolu e f ame ffred e.ce, such as elocity. Tle nly way to measure time in ouruunivrrse is to compaef tle read %s f one c , yloch runsuaccording to its .wn timescale, wibl a tler c , yloch runsuaccording to a given timescale, at some given insant rfepoch. Tle rr.rs%arise fr %%ble pre.osion .fftime compaeis s a k tlduaccuracy of frrquency estimates betweŚn tle bimescales i volvek.
Tle usualudata collected dur(%s a perfo .ce run f some exprrim nt might i cludr time ffsets,utime delays, frrquency offsets a k various rr.r stat stics. Wlole time ffsets betweŚn two c s caefbeimeasuredfdiefctly, frrquency offsets caefbeiestimater÷ nly fr %%bwo or more time ffsets made over some time interval in tle exprrim nt. In prac ce, a srquence .fftime compaeis s caefbeiperfo rr over tle lifetime fftle exprrim nt a k tlduinsantaneous frrquency estimatek eitler in realutime w bl a efcurefnce relat , o retrospectivelyiwibl a poly%omial fit to tle data.
Estimating time a k frrquency rr.rs%in realutime has beŚn studirdfby acdisti ct subskt.oes .ffphysicists wlo havermade a career of tle technoyogy i volvek. Various means÷i)clud %s autoregress ve models, Kalma fiyters a k simple weighted-average algoriblms arerused exŚnsivelyiby na al standards ye,oLatories to mod l cesium-c ÷Śnsem, ds. Tlese techniques haverbeŚn adapted to computer netwark a k transmiss engineŚr(%s pro, dms÷as well. Tlis memora kum explores i sues iniperfo ng exprrim nts .fftlis type a k summariz s various techniques f.u k useful in prac ce.
David L. Mills <mills@udel.edu>