Togetherwiththenetworklayer,thetransportlayeristheheartoftheprotocol(请作答此空).Thenetworklayerprovidesend-to-end()deliveryusingdatagramsorvirtualcircuits.Thetransportlayerbuildsonthenetworklayertoprovidedatatransportfromaprocessona()machinetoaprocessonadestinationmachinewithadesiredlevelofreliabilitythatisindependentofthephysical()currentlyinuse.Itprovidestheabstractionsthatapplicationsneddtousethenetwork..Withoutthe()layer,thewholeconceptoflayeredprotocolswouldmakelittlesense.
A.transport B.network C.hierarchy D.service正确答案C
