Data Link Layer

The data link Layer is the second layer of the OSI model. The data link layer performs various functions depending upon the hardware protocol used, but has four primary functions:

  1. COMMUNICATION with the Network layer above.
  2. SEGMENTATION of upper layer datagrams (also called packets) into frames in sizes that can be handled by the communications hardware.
  3. BIT ORDERING. The data link layer organizes the pattern of data bits into frames before transmission. The frame formatting issues such as stop and start bits, bit order, parity and other functions are handled here. Management of big-endian / little-endian issues are also managed at this layer.
  4. COMMUNICATION with the Physical layer below

This layer provides reliable transit of data across a physical link. The data link layer is concerned with physical addressing, network topology, physical link management, error notification, ordered delivery of frames, and flow control.

It should be noted that in most modern network interface adaptors, the Physical and Datalink functions are performed by the network interface adaptor.


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Application
Presentation
Session
Transport
Network
Data Link
Physical
Function of Layer Protocols Network Components
  • turns packets into raw bits 100101 and at the receiving end turns bits into packets.
  • handles data frames between the Network and Physical layers
  • the receiving end packages raw data from the Physical layer into data frames for delivery to the Network layer
  • responsible for error-free transfer of frames to other computer via the Physical Layer
  • this layer defines the methods used to transmit and receive data on the network. It consists of the wiring, the devices use to connect the NIC to the wiring, the signaling involved to transmit / receive data and the ability to detect signaling errors on the network media
Logical Link Control
  • error correction and flow control
  • manages link control and defines SAPs
802.1 OSI Model

802.2 Logical Link Control 		Bridge

Switch

ISDN Router

Intelligent Hub

NIC

Advanced Cable Tester

Packet filtering firewall
Media Access Control
  • communicates with the adapter card
  • controls the type of media being used:
802.3 CSMA/CD (Ethernet)

802.4 Token Bus (ARCnet)

802.5 Token Ring

802.12 Demand Priority



Created by Uluse©
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