Hi Pankaj,
Can we say that what we receive from upper layer is SDU(service data unit) and after applying the layer specific header we get PDU(protocol data unit).
Yes, quite correct. A datagram from an upper layer has to be serviced by the layer receiving it, hence the name Service Data Unit. After the receiving layer processes the datagram, adding its own headers, trailers and possibly other transformation, the result is called the Protocol Data Unit. In successive fashion, this layer's PDU is treated as an SDU by a lower layer.
Best regards,
Peter
