Describe data encapsulation.
1 Answer
Answer :
In figure which gives an overall view of the OSI layers, D7 means the data unit at layer 7, D6 means the data unit at layer 6, and so on. The process starts at layer 7 (the application layer), then moves from layer to layer in descending, sequential order. At each layer, a header, or possibly a trailer, can be added to the data unit.
Commonly the trailer is added only at layer 2. When the formatted data unit passes through the physical layer (layer 1), it is changed into an electromagnetic signal and transported along a physical link.
Upon reaching its destination, the signal passes into layer 1 and is transformed back into digital into digital form. The data units then moves back up through the OSI layers. As each block of data reaches the next higher layer, the headers and trailers attached to it at the corresponding sending layer are removed, and actions appropriate to that layer are taken. By the time it reaches layer 7, the message is again in a form appropriate to the application and is made available to the recipient.
Encapsulation
Figure reveals another aspect of data communications in the OSI model; encapsulation. A packet (header and data) at level 7 is encapsulated in a packet at level 6. The whole packet at level 6 is encapsulated in a packet at level 5 and so on.
In other words, the data portion of a packet at level 5, and so on.
In other words, the data portion of a packet at level N-1 carries the whole packet (data and header and maybe trailer) from level N. The concept is called encapsulation; level N-1 is not aware of which part of the encapsulated packet is data and which part is the header or trailer. For level N-1, the whole packet coming from level N is treated as one integral unit.