In the OSI model of computer networking, the data link layer is layer two of seven and corresponds to the host-to-network layer of the TCP/IP reference model. Its main aim is to reliably transfer data between two adjacent machines whilst efficiently detecting and correcting errors in transmission. Packets from the network layer are packed into frames and transferred to the network layer on another machine. Data link layer protocols respond to the network layer and issue requests to the physical layer. The data link layer in LANs can contain Media Access Control and Logical Link Control sub-layers.
Unacknowledged connectionless service can be offered by the data link layer. It is used in LANs and other reliable mediums or real-time traffic situations. No connection is established when the source machine sends individual frames to a machine, frames are not acknowledged.
Acknowledged connectionless service works on the same principles as unacknowledged connectionless service except each individual frame is acknowledged on reception. It is used on unreliable media such as wireless.
Acknowledged connection-oriented service is also provided by the data link layer, data is sent and acknowledged. The data link establishes a connection to send data then releases it once the data has been successfully sent.
In order to transfer data between layers, a bitstream is split into frames containing the frames source and destination information. Errors can occur during transmission of frames which are rectified using a suitable protocol. Frames are transferred between LAN devices by the data link layer. A frame contains a header which includes the source and destination address of the frame. Frames are delivered using...
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...evel messages into frames. Sent data needs to be checked for errors when using some protocols and the data link layer monitors and corrects errors that occur on lower levels of the network.
Carter, N. (2009). What is layer 2 and why should you care?. Available: http://www.accel-networks.com/blog/index.php?q=/2009/09/what-is-layer-2-and-why-should-you-care.htm. Last accessed 23 March 2010.
Kozierok, C M. (2005). Data link layer (layer 2). Available: http://www.tcpipguide.com/free/t_DataLinkLayerLayer2.htm. Last accessed 18 March 2010.
whatIs.com. (2009). Data link layer. Available: http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci211899,00.html . Last accessed 20 March 2010.
Yang, S (2009). CO2017 lecture notes. Leicester: University of Leicester. 53-63.
Yang, S (2009). CO2017 lecture slides. Leicester: University of Leicester. 57-74.
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