Together with the network layer,the transport layer is the heart of the protocol( )The network layer provides end-to-end( ) delivery using datagrams or virtual circuits.The transport layer builds on the network layer to provide data transport from a process on a( )machine to a process on a destination machine with a desired level of reliability that is independent of the physical ( ) currently in use.It provides the abstractions that applications nedd to use the network..Without the( ) layer,the whole concept of layered protocols would make little sense. A.transport B.network C.hierarchy D.service A.packet B.data C.command D.record A.connection B.terminal C.source D.destination A.traffic B.connection C.lines D.networks A.network B.transport C.link D.physical