Data Link Layer
Data link layer and Physical layer are very much connected with each other.The data link layer responsible to transform physical layer data to raw transmission for upper layer. This layer also responsible if data is transferred properly or not. If data is lost it quickly tells transport layer for re-transmit the data. To perform such confirmation data link layer used CRC(Cyclic Redundancy Check) function. While Network layer belongs to IP and router this layer belongs to switch. If you study TCP/IP model Data link layer and Physical layer combined as Link layer.
This Layer define rule for device to sending data over a particular medium or not. For that it data link have protocols that defines the header and trailer format which is helpful to devices to send data successfully to its destination or received data from source.
This Layer define rule for device to sending data over a particular medium or not. For that it data link have protocols that defines the header and trailer format which is helpful to devices to send data successfully to its destination or received data from source.
As Data link layer and Physical layer are very closed that's why some hardware like Network inteface card(NIC) also called Ethernet card and Token card etc associated with this layer. Some network devices like bridges also operate with layer 2 in term of decision making what operation is perform on data frame although receive or send. Many protocols also work on this layer like Serial link interface protocol in short is called SLIP that is related to TCP/IP other are ATM,Ethernet,Token Ring,Point to Point protocol (PPP),IEEE 802.11 and FDDI.
IEEE group responsible for creating many interfaces and standards in network technologies. So the project IEEE 802 conceptually divided into two sub layers that are Media Access Control (MAC) and Logical Link Control(LLC). These division make it easy to understand how these layer works.Following are the function perform by data link layer.
Media Access Control:Media access control refers to control medium access.It is responsible for set rules for managing to avoid error or conflict between medium. As network shared many devices or many network shared a single medium. It is responsible for controlling these medium access. For example Token ring passes token media access control and Ethernet used Collision method CSMA/CD media access control. It also provide addressing mechanism.
Logical Link Control: As name describe it belongs to establish logical link between devices on network. This usually mentioned as DLL sub layer,it provide services to network layer above it or it provide interface between network layer and media access control.It also responsible for acknowledgement tracking,multi point network operation, synchronize data link and frame sequence number.
Data Frame: Before sent data over physical layer data link control responsible for encapsulation the data coming from upper layer into frame. It also provide facility to de-capsulation data frame from physical layer to upper layer.
Addressing:As we mentioned above hardware like NIC work on data link layer. Every device on a network has it unique address sometime called machine address but usually called Mac address. With the help of Mac address data link layer ensure which data for whom machine. It is last layer in OSI model that ensuring address of destination.
Error Handling:Error handling also perform on data link layer over physical layer. CRC used to detect if data received correctly to destination.
IEEE group responsible for creating many interfaces and standards in network technologies. So the project IEEE 802 conceptually divided into two sub layers that are Media Access Control (MAC) and Logical Link Control(LLC). These division make it easy to understand how these layer works.Following are the function perform by data link layer.
Media Access Control:Media access control refers to control medium access.It is responsible for set rules for managing to avoid error or conflict between medium. As network shared many devices or many network shared a single medium. It is responsible for controlling these medium access. For example Token ring passes token media access control and Ethernet used Collision method CSMA/CD media access control. It also provide addressing mechanism.
Logical Link Control: As name describe it belongs to establish logical link between devices on network. This usually mentioned as DLL sub layer,it provide services to network layer above it or it provide interface between network layer and media access control.It also responsible for acknowledgement tracking,multi point network operation, synchronize data link and frame sequence number.
Data Frame: Before sent data over physical layer data link control responsible for encapsulation the data coming from upper layer into frame. It also provide facility to de-capsulation data frame from physical layer to upper layer.
Addressing:As we mentioned above hardware like NIC work on data link layer. Every device on a network has it unique address sometime called machine address but usually called Mac address. With the help of Mac address data link layer ensure which data for whom machine. It is last layer in OSI model that ensuring address of destination.
Error Handling:Error handling also perform on data link layer over physical layer. CRC used to detect if data received correctly to destination.
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