Introduction to Data link layer
  1. It divides the stream of bits into small manageable packets called as frames.  
  2. The data link layer transforms the physical layer, a raw transmission facility, to a link responsible for node-to-node (hop-to-hop) communication. 
  3. It provides Hop-Hop connection.

Functionality :

  1. Access control
  2. Error control
  3. Flow control
  4. Framing
  5. Physical addressing.

1.Framing:-

Taking streams of bits from the network layer and divides into small manageable units is called frames.

A large stream of bits can be sent throughout the channel but doing so will have some issues like :

When an error occurred, you have to check the entire message and then retransmit the whole bitstream. When a message is carried in one very large frame, even a single-bit error would require the retransmission of the whole message. When a message is divided into smaller frames, a single-bit error affects only that small frame.

 

SFD (Start frame delimiter):- It tells the start of the frame.

EFD(End frame delimiter):-   these bit tells End of the frame.

 

Types of framing:-

1. Fixed-size Framing:

Size of each frame is fixed. Here we don't need any delimiter because the size of frames is confirmed and it itself acts as the delimiter.

 

2. Variable Size Framing:-

Here we have to define delimiter. We have to tell the beginning and end of each frame. For this, we have two approaches.

Character Stuffing and Bit Stuffing.

 

 

 

Contributor's Info

Created:
0Comment