The Major Duties of Data Link Layer

Welcome to the third article on the OSI Reference Model by CoreNetworkZ Tech Solutions. Today, I explain the second layer and its applications in a practical computer network. I will teach you today about the Data Link Layer, the sub-divisions of this layer, the devices working in this layer, and the protocols working in the Data Link Layer.

The second layer in the OSI Reference model is the Data Link Layer. It lies between the Physical and Network layers. The data link layer is responsible for assigning physical addresses for the devices connected to the network.

The difference between a logical address and a hardware address is critical to know. Logical addresses (The best example is an IP address) are not permanent. But, a hardware address (MAC address) is permanent.

The primary function of the Data Link Layer is to deliver frames between the source and destination. However, you must understand that the scope of the Data Link Layer is in the same LAN only.

Let us check how the Data Link Layer creates a frame. The data link layer takes bits from the Physical layer and converts them to frames. All communications done in the Data link layer are in frames.

During my training sessions, many trainees asked me if the Data Link Layer has sub-divisions. The answer is yes.

The Data link layer has two divisions in the IEEE version (of Ethernet). They are:

1. Logical Link Control (LLC)
2. Media Access Control (MAC)

I published two articles about them and suggest you read them by visiting the relevant links.

CoreNetworkZ Tech Solutions is a network engineering company, and we train our employees on network devices. A few readers, like Sanal Ragav, asked me this question in the comment section. So, you might be eager to know what devices work in the Data Link Layer.

Let us check the devices that work in the Data Link Layer.

1. Switch
2. NIC
3. Bridge

Let us check an important topic asked in the network engineer job interviews. As a CoreNetworkZ Tech Solutions job interview board panelist, I saw many job applicants do not know the responsibilities of the Data Link Layer. I do not want you to be one of them. So, I suggest you study them carefully.

1. Define Physical Addresses.

2. Communication in the same network in the form of Frames.

3. Data Link Layer defines the hardware topology of the network.

One reader, Merin, asked me to write a tutorial on the protocols working in this layer. Yes, she is right. This tutorial is not complete without mentioning the protocols working in this layer.

These seven network applications work in the second layer of the OSI Reference Model.

1. CIF : Cells in Frames Ethernet
2. FDDI : Fiber Distributed Data Interface
3. GARP : Generic Attribute Registration Protocol
4. GMRP : Multicast Registration Protocol.
5. GVRP :GARP VLAN Registration Protocol
6. LLC :Logical Link Control.
7. SNAP :SubNetwork Access Protocol

The seven layer structure is:

1. Physical layer
   
   
2. Data link layer
   
   
3. Network layer
   
   
4. Transport layer
   
   
5. Session layer
   
   
6. Presentation layer
   
   
7. Application layer

Today, you have learned the fundamentals, applications, supported protocols, and duties of the Data Link Layer. Let me conclude this article with references and further readings for research students.

I suggest you read this Cisco and IBM tutorial for further studies.

1. https://www.ibm.com/docs/en/zos-basic-skills?topic=review-data-link-layer-layer-2
2. https://learningnetwork.cisco.com/s/article/osi-model-reference-chart