- The data link layer is the second layer from the bottom in the OSI (Open System Interconnection) network architecture model. It is responsible for the node-to-node delivery of data.
- The data link layer has two sub-layers: logical link control and media access control.
- There are six major functions of the data link layer including framing, addressing, error control, flow control and access control.
The data link layer or layer 2 is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between adjacent network nodes in a wide area network (WAN) or between nodes on the same local area network (LAN) segment. The data link layer provides the functional and procedural means to transfer data between network entities and might provide the means to detect and possibly correct errors that may occur in the physical layer.
What is data link layer?
The Data Link Layer is the second layer in the OSI Layered Model. With its intricate functions and liabilities, this layer is among the most complex ones. The data link layer presents itself to the upper layer as the communication medium while concealing the specifics of the underlying hardware.
The data link layer is concerned with the local delivery of frames between devices on the same LAN. These protocol data units are known as data-link frames, and they do not leave the confines of a local network. Data-link protocols can concentrate on local delivery, addressing, and media arbitration because inter-network routing and global addressing are higher-layer functions. In this sense, the data link layer resembles your local traffic cop; it attempts to mediate disputes between parties vying for access to a medium, regardless of the parties’ final destination. Frame collisions happen when multiple devices attempt to use the same medium at the same time. Device detection, recovery, and potential mitigation or prevention mechanisms are all outlined in data-link protocols.
The data stream is converted to signals by the data link layer bit by bit and sent over to the underlying hardware. The data link layer receives electrical signals from the hardware, assembles them into a recognisable frame format, and transfers the data to the upper layer.
The data link layer has two sub-layers: logical link control and media access control. The former deals with protocols, flow control, and error control and the latter deals with actual control of media
Ethernet is an example of a data link protocol for local area networks (multi-node networks), while ADCCP, HDLC, and PPP are examples of point-to-point (dual-node) connections. The lowest layer of the descriptive model in the Internet Protocol Suite (TCP/IP), the link layer, houses the functionality of the data link layer.
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5 functions of data link layer
1. Framing
In the data link layer, the packet that is received from the network layer is referred to as a frame. DLL splits up packets from the network layer at the sender’s end into smaller frames, which it then sends bit by bit to the physical layer. Additionally, it appends a few unique bits to the header and end of the frame (for error control and addressing). DLL gathers bits from the Physical layer at the receiver’s end, assembles them into a frame, and transmits them to the Network layer.
2. Addressing
To guarantee node-to-node delivery, the data link layer encapsulates the source and destination’s MAC address/physical address in the header of each frame. The device’s MAC address is the distinct hardware address assigned to it during manufacturing.
3. Error control
Noise, attenuation, and other factors are among the many causes of data corruption. Therefore, the data link layer is in charge of identifying errors in transmitted data and making the necessary corrections using error detection and correction techniques, respectively. To enable the recipient to verify whether the data they have received is accurate, DLL appends error detection bits to the frame’s header. It increases physical layer reliability by including mechanisms to identify and retransmit lost or damaged frames.
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4. Flow control
A buffer overflow and potential frame loss may result from the receiver’s receiving speed being slower than the sender’s sending speed. Therefore, DLL is in charge of establishing flow control and synchronising the sender and receiver’s speeds.
5. Access control
There is a high likelihood of collision when multiple devices share a communication channel, so the DLL must determine which device is in control of the channel. CSMA/CD and CSMA/CA can be used to prevent collisions and frame loss in the channel.
The data link layer is the second layer of the OSI Layered Model. This layer is one of the most complicated layers and has complex functionalities and liabilities. The data link layer hides the details of the underlying hardware and represents itself to the upper layer as the medium to communicate. In addition, there are various benefits of the data link layer including framing, addressing, error control, flow control and access control.
