题目
[单选题]
共用题干题Whenthesystemuponwhichatransportentityisrunningfailsandsubsequentlyrestarts,the(21)informationofallactiveconnectionsislost.Theaffectedconnectionsbecomehalf-open,asthesidethatdidnotfaildoesnotyetrealizetheproblem.Thestillactivesideofahalf-openconnectionscanclosetheconnectionusinga(22)timer.Thistimermeasuresthetimethetransportmachinewillcontinuetoawaitan(23)ofatransmittedsegmentafterthesegmenthasbeenretransmittedthemaximumnumberoftimes.Whenthetimer(24),thetransportentityassumesthateithertheothertransportentityortheinterveningnetworkhasfailed.Asaresult,thetimerclosestheconnection,andsignalsanabnormalclosetotheTSuser.Intheeventthatatransportentityfailsandquicklyrestarts,half-openconnectionscanbeterminatedmorequicklybytheuseoftheRSTsegment,thefailedsidereturnsanRSTitoeverysegmentithatitreceives.WhentheRSTireachestheotherside,itmustbecheckedforvaliditybasedonthe(25)numberi,astheRSTcouldbeinresponsetoanoldsegment.Iftheresetisvalid,thetransportentityperformsanabnormaltermination.空白处(25)应选择()
A.sequence
B.acknowledgment
C.connection
D.message