Or Layer 2
We know the second layer in OSI model is Data Link Layer but , there is an another name in the Industry is Ether Layer.
Data Link Layer or Ether Layer works on Ethernet Standards of IEEE (802.1q , 802.11 , 802.1d , 802.1w etc.). PDU of Data Link Layer is Frame and a Frame consists of Ethernet Header and Trailer , header comes from Network Layer and trailer is added extra by Data Link Layer. Which consists the information like type of Data , MAC address of destination and source , data minimum 1500 bytes , FCS frame check sequence , SFD start frame delimeter. What are these Flags , ‘ they are guides of FRAME.’
What does these flags do?
- Preamble — 7 bytes , it is used for the synchronization.
- SFD — Start Frame Delimeter , 1 byte is used to tell the OS that next byte is Start of Destination MAC address.
- Destination MAC — 6 bytes , Hexadecimal ID provided by manufacturer of device where the data is to be sent from the Switch.
- Source MAC — 6 bytes , MAC address of the device which sent the data.
- Type — 2 bytes , determines the type of protocol used (Ethernet , WEP , WPA etc.).
- DATA — minimum 1500 bytes , supported by CISCO switches .
- FCS — 4 bytes , it is used as a part of Frame’s trailer , it determines if any error has occurred or not.
Data Link Layer is subdivided in two layers :
- LLC (link layer control): Which is used to determine if any error or collision occurred in the path of Frame , it is used to determine and avoid the outer Natural Interference. So that the robustness of the Network remains sustain
- MAC (media access control): This layer is used to gather the information from the upper layer and make it direct to the receiver. In MAC layer ARP protocol is used to convert the IP address into the MAC address and vice versa inside the collision domain.
In Data Link Layer , PDU is a simple term for encapsulation. In Data Link Layer the Packet from Network Layer gets encapsulated into the Frame in the form of header and trailer as we have seen above. The packet gets encapsulated so that they can acknowledge themselves where to go. By IEEE for encapsulation of packet we use 802.1q encapsulation protocol.
Trailer Part is necessary lets complete it in next Story!
CSMA /CD …
