Enscapsulation

Understanding Encapsulation and Decapsulation in Networking

The term “encapsulation” refers to the process of adding headers and trailers around data as it moves through different layers of a network protocol stack. For example, when you send an email using your favorite email program (like Outlook or Thunderbird), the email is sent from the Application layer to the Transport layer. The Transport layer encapsulates the data and adds its own header (containing information like the port number to be used) before passing it to the Internet layer. The Internet layer then encapsulates the data again, adding a header with source and destination IP addresses. Finally, the data reaches the Network Access layer, which is the only layer that adds both a header and a trailer. At this point, the data is ready to be transmitted through a physical network link.

The term “decapsulation” refers to the process of removing headers and trailers as the data passes from lower to upper layers. This process happens on the receiving computer when data is being interpreted at each layer.

Frame, Packet, and Segment

Frame: A "frame" refers to the encapsulated data defined by the Network Access layer. It includes a header and a trailer that encapsulate the data section.

Packet: A "packet" refers to encapsulated data defined by the Internet layer. A packet typically includes a header containing the source and destination IP addresses.

Segment: A "segment" refers to encapsulated data defined by the Transport layer. A segment includes a header with information such as source and destination port numbers, sequence numbers, and acknowledgment numbers.