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
