Data Link Layer
The second layer of the OSI model is the data link layer. This layer performs important roles in the communication between computers. It comes directly after the physical layer and is responsible for taking binary code and formatting it into a frame. Sound confusing? Don’t worry. We’ll break it all down.
First of all, remember that computers speak in binary code–a language comprised solely of different combinations of zeros and ones. You’ve probably seen binary code before, even if you can’t read it.
So, you may be wondering what we by the data link layer taking binary code and formatting it into a frame. What’s a frame? And how does this relate to networking?
Frames are an important part of networking, as they make communication between different computers and devices possible. How exactly? Frames contain all the pertinent “contact information” for your computer. In other words, frames are a unit of data over a network, and these units include your computer’s address. They also include the computer address of the recipient of the information, as well as the ability to check for data errors.
Let’s recall for a moment a simple network. Imagine two computers connected over a network by a cable (the physical layer). Each computer has its own unique address. Before data is transferred across the cable from one computer to another, each computer’s address and other information must be established. This means knowing the address of the sender and of the receiver.
The data link layer takes all this information from binary code and formats it into a frame that can be used in the data transmission process. Pretty cool, huh? This process has been likened to the packaging of envelopes, as the data link layer prepares everything for transfer across the network.
In doing so, the data link layer performs another important function in making sure that there is no error in the information to be sent. If errors are found, it requests for the information to be sent again.
There are several reasons that there may be an error in information (such as interference), but the data link layer irons out these kinks before getting the physical/mac address of the computers. After doing so, the information is all primed and ready to be sent across the network. From here, the next stage of the process is the network layer that will help send the information off for delivery.