Network Data Link Layer

The network data link layer is the layer above the physical layer in the Open System Interconnections (OSI) model. The primary concern of this layer is to convert the raw transmission facility provided by the physical layer to a reliable and error-free link.In TCP/IP model, the physical layer and the data link layer are combined as the host - to - network layer.

Data Link Layer in the OSI Model

The Open System Interconnections (OSI) model is a layered networking framework that conceptualizes how communications should be done between heterogeneous systems.Its three lower OSI layers are called the network support layers. The data link layer is the second lowest layer.

The following diagram depicts the position of the data link layer where a transmission is done from a sending machine to a receiving machine.

Functions of Data Link Layer

• Dividing the stream of bits from physical layer into data frames whose size ranges from a few hundred to a few thousand bytes

• Distributing the frames to the different systems, by adding a header to the frame containing the address of the sender and the receiver

• Regulating flow control so that a fast sender does not drown a slow receiver

• Dealing with transmission errors

• Sending acknowledgement frames in reliable connections

• Retransmitting lost frames

• Identifying duplicate frames and deleting them

• Controlling access to shared channels in case of broadcasting

• Providing well defined service interface to network layer above it