Framing in Data Link Layer

Framing is the process by which the Data Link Layer divides the stream of bits received from the Network Layer into manageable units called frames for transmission over the Physical Layer.

Purpose of Framing

1. Error detection and control: Frames include headers/trailers that allow error checking.
2. Flow control: Frames make it easier to manage the rate of data transmission.
3. Synchronization: Helps the receiver identify the start and end of each frame.

Components of a Frame

• Header: Contains control information, source and destination addresses.
• Data (Payload): The actual message or packet from the Network Layer.
• Trailer: Usually contains error detection info like CRC (Cyclic Redundancy Check).

Methods of Framing

1. Character Count (Char Count)

• Concept: Each frame starts with a field that specifies the number of characters in the frame.

• How it works:

  [Char Count][Data][Checksum]
  

  • The first byte (or field) tells the receiver how many characters to read for this frame.

• Pros: Simple to implement.

• Cons: If the count itself gets corrupted, the frame can be misinterpreted.