Layer 4: Transport Layer End-to-end communication between processes Application Different services provided TCP reliable byte stream 432 Transport UDP unreliable datagrams Link (Datagram single packet message) Physical 18Layer 4: Transport Layer 7 4 3 2 1 End-to-end communication between processes Different services provided: TCP = reliable byte stream UDP = unreliable datagrams (Datagram = single packet message) 18 Application Transport (Inter)Network Link Physical