The Data Link layer provides reliable, sufficient transportation between adjacent machines and it has the function of error notification, invite retransmission, perform framing, physical addressing, network topology, sequencing the frames and flow control. This means the data will be delivered using numerous of Data Link protocols to ensure transport the Ip packets over various types of Lan's and Wan's to the allowable host.
It specifies the encapsulation of a packet (Network layer Pdu) into a frame (Data Link layer Pdu) and the techniques for getting the encapsulated packet on and off each medium (Ethernet link, satellite link, wireless link). The technique used for getting the encapsulated packet on and off media is called the Media way operate (Mac) method.
Optical Encode
The Data Link frame includes:
Data - the packet from the upper layer (service data unit)
Header - Contains operate information, and is added to the front of the protocol data unit (Pdu)
Trailer - added to the rear of the Pdu
There are 4 organizations that define the Data Link standards :
- Institute of Electrical and Electronic Engineering (Ieee)
- American National Standards design (Ansi)
- International organization for Standardization (Iso)
- International Telecommunication Union (Itu)
The Ieee subdivided the Data Link layer into 2 sublayers. There are Media way operate (Mac) and Logical Link operate (Llc).
Media way operate is defined in the 802.3 specification. It defines how packets are placed on the physical way media. The Mac sublayer maintains a table of Mac address (physical address) of devices. Carry on protocol way to the physical network medium. The error notification, sequencing of frame and flow operate are used within this sublayer.
Logical Link operate is defined in the 802.2 specification. It supports both connectionless and connection-oriented services. It manages transportation between devices over a singular line of a network. Identifying Network layer protocols and then encapsulating them. Sequencing operate bits and flow operate are used within this sublayer.
Osi Model - Data Link Layeroptical encoder