<Li> The layer 1 (Physical layer) PDU is the bit or, more generally, symbol (can also be seen as "stream"). </Li> <Li> The layer 2 (Data link layer) PDU is the frame . </Li> <Li> The layer 3 (Network layer) PDU is the packet . </Li> <Li> The layer 4 (Transport layer) PDU is the segment for TCP or the datagram for UDP . </Li>

The protocol data unit (pdu) of application layer is