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Thursday, July 19, 2012

Data link layer

The Data Link Layer is the 2ed layer of the seven layer OSI model. The Data Link Layer is the protocol layer which transfers data between adjacent network nodes in a wide area network or between nodes on the same local area network segment. Not only that it provides the functional and procedural means to transfer data between network entities and might provide the means to detect and possibly correct errors that may occur in the Physical Layer. So this will helpful to flow the data over a single physical link from one device to another.

This layer accepts packets from the Network layer and packages the information into data unit. They are the frames which are presented to the Physical layer for transmission. According to the OSI network architecture the data link layer protocols respond to service requests from the Network Layer and they perform their function by issuing service requests to the Physical Layer. However this is the layer which responsible for controlling the error between adjacent nodes and transfer the frames to other computer via physical layer while responsible for transferring datagram from one node to another node over a link.

Data link layer includes,


  • Devices


  • Bridges
  • Switches


  • Protocol


    • Ethernet
    • EAPS(Ethernet Automatic Protection Switching) 
    • MPLS (Multiprotocol Label Switching) 
    • PPP (Point to Point Protocol)
    • CDP(Cisco Discovery Protocol) 
    • CAN(Controller Area Network )
    • FDDI(Fiber Distributed Data Interface )
    • Frame Relay
    • HDLC(High-Level Data Link Control )
    • IEEE 802.2 (provides LLC functions to IEEE 802 MAC layers)
    • IEEE 802.11 wireless LAN
    • LAPD(Link Access Procedures, D channel )
    • Spanning tree protocol
    • Token ring
    • UDLD(Unidirectional Link Detection ) etc.


Functions and Servicers


  • Allows a device to access the network to send and receive messages
  • Offers a physical address so a devices data can be sent on the network
  • Ethernet incorporates both this layer and the Physical layer

  • Works with a devices networking software when sending and receiving messages
  • Provides error-detection capability
  • Acknowledged Connectionless service
  • Acknowledged Connection-Oriented service
  • Framing, link access
  • Frame synchronization
  • Reliable delivery between two physically connected devices:
  • Flow Control
  • Encapsulation of network layer data packets into frames
  • Error Detection
  • signals sender for retransmission or drops frame
  • Error Correction

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