In this tutorial, we are going to learn about data link layer in OSI. 

The data link layer is the second layer from the bottom in the OSI model. This layer is one of the most difficult to understand, with several functionalities and risks. The data connection layer hides the underlying hardware features and represents itself to the upper layer as a communication medium.

Sub – layers of Data Link Layer in OSI:

Following are the two sub-layers in the data link layer:

Protocols, flow control, and error control are all covered by logical link control.

Media Access Control is concerned with the real management of media.

Services of Data Link Layer in OSI:

1. Framing: 

Before transmission across the link, Data Link Layer protocols encapsulate each network frame in a Link layer frame. A frame has a data field and a number of data fields in which we put a network layer datagram. It defines the frame’s structure as well as the channel access protocol that is useful to send the frame over the link.

2. Reliability: 

It provides a dependable delivery service, that is, it reliably transmits network layer datagrams. Transmissions and acknowledgement are useful for providing a trustworthy delivery service. This layer primarily provides a dependable delivery service over links since they have greater error rates and may be repaired locally, rather than forcing data to be re-transmitted.

3. Flow control: 

A receiving node is capable of receiving frames at a quicker rate than it is capable of processing them. The receiver’s buffer can overflow without flow control, causing lo frames. To deal with this issue, the data connection layer employs flow control to keep the sending node on one side of the link from overwhelming the receiving node on the other.

4. Error detection:

Signal attenuation and noise can both cause errors. One or more mistakes can be detected using the Data Link Layer protocol. We accomplish this by including error detection bits in the frame, which the receiving node subsequently check.

5. Error correction: 

Error rectification is identical to error detection, with the exception that the receiving node not only detects but also determines where the faults occurred in the frame.