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 physical address is also known as the hardware address because it is a built-in address.
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.
So, the frame delivery happens between devices connected to the same Local Area Network.
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.
Subdivision in Data-link Layer
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)
Let us check the devices that work in the Data Link Layer.
Data-link Layer devices
- Switch
- NIC
- Bridge
Responsibilities of Data Link Layer
Define Physical Addresses.
Communication in the same network in the form of Frames.
Data Link Layer defines the hardware topology of the network.
Major Data Link Layer Protocols
- CIF : Cells in Frames Ethernet
- FDDI : Fiber Distributed Data Interface
- GARP : Generic Attribute Registration Protocol
- GMRP : Multicast Registration Protocol.
- GVRP :GARP VLAN Registration Protocol
- LLC :Logical Link Control.
- SNAP :SubNetwork Access Protocol
The Seven Layer Structure
The seven layer structure is:
