Logic Link Control (LLC) Layer and Medium Access Control
(MAC) layers are the sublayers of the Data link layer in the OSI
reference model.
OSI reference model: OSI stands for Open
Systems Interconnection. OSI is a 7 layer architecture which
contains 7 layers. Each layer having its own specific
functionality. All these 7 layers in the OSI model are used to
transmit data.
Data Link Layer: In computer networking, the
data link layer is the 2nd layer of the OSI reference model. The
main function of this layer is to transmit data between nodes. The
data link layer transmits data between network entities and also
detects the errors which occurred on the physical layer.
Datalink layer contains two sublayers:
- The logical link control (LLC) sublayer
- The medium access control (MAC) sublayer
The logical link control (LLC) sublayer:
- The main functionality of the LLC layer is that it multiplexes
the protocols over the MAC layer while sending and de-multiplex the
protocols while receiving.
- This layer controls the flow control.
- The error-checking of the data link layer is performed by
LLC.
- LLC can also track the acknowledgments.
- While transmitting data, if LLC detects any frame lost,
immediately it sends back to the source to transmit over
again.
- The LLC layer comes above the MAC layer and acts as an
interface between the upper layers and the MAC layer.
The medium access control (MAC) sublayer:
- MAC address: MAC address is defined and the Media Access
Control address. It is a unique address that is allocated to the
NIC of the device. It is used as an address to transmit
data within ethernet or WiFi.
- This layer acts as an interface between the physical layer and
the LLC layer in the OSI model.
- The main responsibility of the MAC layer is that it
encapsulates the frames during transmission so that, whether they
are suitable.
- The MAC layer identifies and verifies the address of source
stations and destinations.
- MAC layer performs multiple access resolution when there are
more dara frames.
- MAC layer coordinates with the physical layer to seize a shared
channel by using multiple MAC entities to avoid collisions.
- Ethernet is an example of a medium that is defined through the
MAC sublayer.