Togetherwiththenetworklayer,thetransportlayeristheheartoftheprotocol().Thenetworklayerprovidesend-to-end(请作答此空)deliveryusingdatagramsorvirtualcircuits.Thetransportlayerbuildsonthenetworklayertoprovidedatatransportfromaprocessona()machinetoaprocessonadestinationmachinewithadesiredlevelofreliabilitythatisindependentofthephysical()currentlyinuse.Itprovidestheabstractionsthatapplicationsneddtousethenetwork..Withoutthe()layer,thewholeconceptoflayeredprotocolswouldmakelittlesense. A.packet
A.data B.command C.recor正确答案A
