Brief about Data link Protocol

 
         The primary function of the Data link layer is to provide an error-free communications link between adjacent devices in a network. The various tasks the data link layer has to perform include:
 
         *Link connection management between any two adjacent nodes in a  network.
         *Framing of the data received from upper layers to make it suitable for  transmission.
         *Addressing to identify the transmitter of the frame and the intended  receiver.
         *Sequencing of the frames to enable a smooth and fast transmission.
         *Acknowledgement of the receipt data frames.
         *Timeout.
         *Error control.
         *Flow control.
 
 
 
  The  ISDN D-channel Layer 2 Protocol
 

     Link access procedures on the D-channel,LAPD, is the layer 2 protocol on the  D-channel. LAPD defines the logical connection on  the D-channel between the  user's device(TE or TA) and the network(NT2 or LE) across the S (or S/T)  reference point. It supports serial, synchronous, full-duplex communication across  either a point-to-point or point-to-multipoint physical connection.

       LAPD is also called  as  Digital subscriber signaling system No. 1 (DSS1) a   name designated by the ITU-T.