Data link layer works between two hosts which are directly connected in some sense.

This direct connection could be point to point or broadcast. Systems on broadcast network are said to be on same link.

The work of data link layer tends to get more complex when it is dealing with multiple hosts on single collision domain.

Data link layer is responsible for converting data stream to signals bit by bit and to send that over the underlying hardware.

At the receiving end, Data link layer picks up data from hardware which are in the form of electrical signals, assembles them in a recognizable frame format, and hands over to upper layer.

Data link layer has two sub-layers:

• Logical Link Control: It deals with protocols, flow-control, and error control

• Media Access Control: It deals with actual control of media

Functionality of Data-link Layer

Data link layer does many tasks on behalf of upper layer. These are:

• Framing

   

• Addressing

   

• Synchronization

   

• Error Control

   

• Flow Control

   

There are three types of techniques available which Data-link layer may deploy to control the errors

1  Stop-and-wait ARQ

2    Go-Back-N ARQ

3   Selective Repeat ARQ