Moving Data in the Network: PDU, Encapsulation / De-encapsulation ![]() To begin with, this is a quick reminder of our networking protocol stack. The OSI Model/ protocol stack also described by the TCP/ IP Model/ protocol stack has been discussed earlier. However for the sake of this discussion, I will make popular reference to the OSI Model. ![]() Protocol Data Unit (PDU) is the term which describes data as moves through the layers of the OSI model. It consists of protocol control information and user data. Below is a list of what PDU is called per layer of the OSI model
Protocol Encapsulation and De-encapsulation ![]() Encapsulation As data moves from one layer of the TCP/ IP protocol stack to a lower layer at the source, information known as headers is added at each layer to the actual data being sent. The header along with the actual data now becomes the data at the next lower layer as the lower layer’s header is added. This is referred to as encapsulation. It only means that the initial data is encapsulated in a virtual envelope with a header then sent to the next lower layer. On its arrival, the virtual envelope (with the previous header) is repackaged into another new virtual envelope for the current layer and a header for the current layer is added to the new virtual envelope. The process repeats itself until it gets to layer 1 where the envelope is eventually transmitted to its destination. The exception is on layer 2 where not only a header is added but a footer called Trailer is also added. De-encapsulation
PDUs are labeled for easy direction and re-assembly after De-encapsulation. This allows the PDUs to have order on arrival thus eases re-assembly. On arrival at the destination, the reverse of encapsulation occurs. This is known as De-encapsulation. The virtual envelopes are stripped off and the header helps the process with the information contained in it. This helps the PDU to be delivered to the exact network application awaiting the data. References http://aaronshi.blogspot.ie/2012/11/data-link-layer-add-both-header-and.html https://s-media-cache-ak0.pinimg.com/originals/3e/53/42/3e534245a610e82dd09bf17e5c828c84.jpg http://www.omnisecu.com/images/tcpip/encapsulation-decapsulation-boxes.jpg http://www.omnisecu.com/tcpip/tcpip-encapsulation-decapsulation.php http://www.tcpipguide.com/free/diagrams/osiencap.png http://www.tcpipguide.com/free/t_IPDatagramEncapsulation.htm https://www.techopedia.com/definition/25292/protocol-data-unit-pdu http://www.webopedia.com/TERM/P/PDU.html |
CategoriesAuthor I have a passion for networking and use this medium for tutorials in Networking Archives
April 2017
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