In the Figure 1.24, a general term for the unit of encapsulation at each layer (
ID: 2085950 • Letter: I
Question
In the Figure 1.24, a general term for the unit of encapsulation at each layer (message, segment, datagram, and frame) is a protocol data unit (PDU). Assume layer N is above layer (N-1) in the diagram. The figure shows that a PDU at one layer (layer N) is encapsulated in the PDU created at adjacent lower layer (N-1). Other possibilities are to break one layer N PDU into several layer (N-1) PDU’s (called segmentation) or to group multiple layer N PDU’s into one layer (N-1) PDU (called blocking).
a- iff segmentation is used, is it necessary that each layer (N-1) PDU contain a copy of the layer N PDU header? Explain your answer.
b. If blocking is used, is it necessary that each layer N PDU keep its own header in the layer (N-1) PDU or can the level N header information be consolidated one level N header in the level (N-1) PDU? Explain your answer
Source Message M Application Segment Ht M Transport Datagram Hn H M Network Frame Hi Hn Ht M Link Physical Hi Hn Ht M Link Physical Link-layer switch Router Destination M Application Ht MTransport Hn He M Network Hn Ht MNetwork Hn Ht M Hi Hn Ht M Physical PhysicalExplanation / Answer
a) It depends on the N-1 layer as if it has some mechanism which can reassemble the fragments properly than its not necessary to have header copied from N layer. Example of such a case is IP on ATM.
but if N-1 layer doesnt have mechanism which can guarantee the reassembling of segments then it becomes necessary to duplicate the headers of the N layer.
b) Its necessary that each layer N PDU keep its own header in layer N-1 PDU because after blocking once the data is transmitted then at the receving end it will get tranferred from layer N-1 to layer N where this block of data or the aggregated is required to be seperated for restoration. without the header block this process will become complex.
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.