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Data Link layer performs the process of combination of bits into bytes and bytes into frames. So, Data Link layer employs frames to summarize the packets which were received from the Network Layer for transmitting on a sort of media access. The function of Ethernet stations is to pass data frames between each other using a group of bits recognized as a MAC frame format. This detects errors from a Cyclic Redundancy Check (CRC) (Remember this is error detection, not error correction). The 802.3 frames and Ethernet frame are shown below. NOTE: Encapsulating a frame within a different type of frame is called tunneling.

This is a brief discussion on data encapsulation according to Cisco Certified Network Associate (CCNA) Exam. Let me start; when a host sends out data on a network to receiving device, the data travels from first to last in encapsulation form. It is covered with protocol information at every layer of the OSI model. Each layer communicates just with its neighbor layers on the receiving device. Every layer works with Protocol Data units (PDUs) to converse the information. PDUs grasp the control information fasten to the data at each layer of the OSI model. They are normally fasten to the header in front of the data field but can also be attached in the trailer or end of it. Every Protocol Data unit (PDU) fixes to the data by encapsulating it at every layer of the OSI model and each has a particular name (depending on the information provided in each header). On the receiving device, every neighbor layer just can read this PDU information. And after reading this information is stripped off and then the data is handed to the next upper layer.