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What is meant by data decapsulation in OSI model?

Data Decapsulation is the second type of data flow in the OSI model. Here we shall discuss about the decapsulation process.

What process takes place at the encapsulation side?

– In encapsulation process what happens is that the data obtained from the user is converted in to a form that can be transmitted over the network.
– A connection is secured between the destination and the source and the data is divided in to segments.
– These segments are then converted in to data packets having a logical address.
– These packets are then converted in to frames.
– The host is identified by the MAC address.
– At physical layer, these frames are then encoded in to bits and a signal is formed which is then transmitted over the cable.

What is a Decapsulation Process?

– Decapsulation is just the opposite process of the encapsulation.
– It is unwrapping of the data at the receiver’s side. This process takes place as follows:
– Host at the receiving end, first reads the extra 0’s and 1’s and synchronizes accordingly with the digital signal.
– Once up on the completion of the synchronization process, the whole frame is received and passed on to the data link layer.
– This layer carries out a CRC or the cyclic redundancy check on the received frame.
– This check is kind of a computation that is done by the host system.
– If the result matches with the FCS (frame check sequence), it confirms that the frame contains no errors.
– After this, the addition information and headers that was attached to the frame are stripped off by the data link layer.
– So now frame becomes a data packet.
– This packet is moved on to next layer i.e., the network layer.
– This layer checks the IP address of the data packet for a match with the IP address of the machine.
– If a match is found, then the network header attached to it is also stripped off and the remaining is passed on to the transport layer.
– The data packet is now termed as the data segment.
– This segment is further processed at this layer.
– Here, the data stream is rebuilt.
– Remember that, at this level on the sending host, the data was split in to many smaller units.
– After putting all these units together, the transport layer sends an acknowledgement to the sending host that all data has been received.
– It is worth noting here that for sending the acknowledgement, TCP is used instead of UDP.
– After all this checking, the data is passed over to the upper – layer applications.
– Sending and receiving of the data using encapsulation and decapsulation processes has been made possible by the networking protocols.
– The encapsulation takes place with the protocol information at each layer of the OSI model.
– PDUs (or the protocol data units) are used by all the layers for the communication and exchange of the information.
– These are the units that consist of control information that is attached to the data units at each layer.
– These are stripped off from the data units when read by the corresponding layers and moved on to the next layer.
– After the data packet has been extracted from the frame, the frame is discarded.
– The OSI model has been defined for minimizing the complexity of the internet.
– To ease this, the layers of the model have been divided in to two categories as stated below:
1. The upper layers: This category includes the 7th, 6th and the 5th layer. These layers have a direct connection with the user interface of the application.
2. The data flow layers: The remaining, 4th, 3rd, 2nd and the 1st layers fall under this category. These layers bear relation with the data flow. Each of these layers have a PDU as defined below:
a) Transport layer – segment
b) Network layer – packet
c) Data link layer – frame
d) Physical layer – bit

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