Encapsulation is the process of wrapping data in a protocol header. If one computer wants to send data to another computer, it must first package the data.
Encapsulation then wraps data with the necessary protocol information before network transmission. Therefore, as the data packet moves down through the layers of the OSI model, it receives headers, trailers, and other necessary information.
To see how encapsulation occurs, let us examine the manner in which data travels through the layers. Once the data is sent from the source, it travels through the application layer down through the other layers. The packaging and flow of the data that is exchanged goes through changes as the networks perform their services for end-users. Networks must perform the following conversion steps in order to encapsulate data:
Build the data. As a user sends data, the alphanumeric characters are converted to data that can travel across the network.
Package the data for end-to-end transport. The data is packaged for network transport. By using segments, the transport function ensures that the message hosts at both ends of the data system can reliably communicate. Add the network address to the header. The data is put into a packet or datagram that contains a network header with logical source and destination addresses. These addresses help network devices send the packets across the network along a chosen path; and are added to the local address in the data link header. Each network device must put the packet into a frame. The frame allows connection to the next directly connected network device on the link. Each device in the chosen network path requires framing in order for it to connect to the next device.
It is then converted to bits for transmission. The frame must be converted into a pattern of 1s and 0s for transmission on the medium. A clocking function enables the devices to distinguish these bits as they travel across the medium. The medium on the physical internet transportation path can vary along the path used. For example, the email message can originate on a LAN, cross a campus backbone, and go out a WAN link until it reaches its destination on another remote LAN. Headers and trailers are added as data moves down through the layers of the OSI model.
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Version 1.0 - Version Date: March 29, 2005
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