Message formatting and encapsulation

If you have recently sent a letter to your loved ones via the post office, then you have formatted and encapsulated the message (see Figure 2.2.). That is, in a blank letter, you wrote your message by saluting the recipient of the letter, and that represents the formatting of the letter. Then, inserting the folded letter into an envelope where you will identify the sender and the recipient represents the encapsulation of the letter:

Similarly, messages are formatted and encapsulated during computer communication, too. The frame is the envelope's equivalent, while the bits are the equivalent of the letter and its contents. Similar to the letter being placed in an envelope, the bits are placed in the frame too, and that represents the encapsulation process. When the receiving computer receives the frame and unpacks the frame by taking out the bits from the frame, then that represents the de-encapsulation process. Like the envelope, the frame also contains the source address and destination address.