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