WhichtwostatementsabouttheDiffServmodelaretrue?()
A.Aclasscanbeidentifiedasasingleapplication，multipleapplicationswithsimilarserviceneeds，orbebasedonthesourceordestinationIPaddresses.
B.AdrawbackoftheDiffServmodelisthatitdoesnotprovidebackwardcompatibilitywithdevicesthatcanonlyusetheToSfield.
C.DiffServusestheDiffServfieldintheMACheadertomarkframesintobehavioraggregates（BAs）.
D.TheDiffServfieldoccupiesthesameeightbitsoftheMACheaderthatwerepreviouslyusedfortheToSfield.
E.Thefirstsixhigh-orderbitsoftheDiffServfieldareusedtoidentifytheResourceReservationProtocol（RSVP）value.
F.TheprimarygoalofDiffServisscalability.
正确答案：参考A, F
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