transport protocol (TP)
Conceptually, the transport layer only recognizes end systems in the network and no node computers in transit systems, no Internetworking, etc. The transport layer is the fourth layer in the OSI reference model and thus lies above the physical and logical network layers.
One of the tasks of this layer is to provide two communicating application processes with transparent, seamless and secure end-to-end data transmission, regardless of the media used in layers 1 to 3. A distinction is made between connection-oriented and connectionless transmission. The best-known transport protocols from the Internet world are the connection-oriented Transmission Control Protocol( TCP) and the connectionless User Datagram Protocol( UDP).
In addition, there are the OSI transport protocols( OSI-TP), which support five different transport classes (TP0 to TP4), and there was the Sequenced Packet Protocol( SPP) as a connection-oriented transport protocol of the XNS protocols. Other vendor-specific protocols are Novell's IPX/ SPX protocols, IBM's NetBIOS, DEC's Local Area Transport Protocol( LAT), Microsoft's NetBEUI or the AppleTalk for the Mac world.