VTU Module-2 | Data Link Control (DLC) services

18EC71 | COMPUTER NETWORKS | Module-2 VTU Notes

Framing, Flow and Error Control, and Data Link Layer Protocols play crucial roles in ensuring reliable communication over a network. These concepts are fundamental components of the Data Link Layer in the OSI model. Let's delve into each of them:

1. Framing:

Framing involves dividing a stream of data into manageable frames for transmission across a network. Each frame typically consists of a header and a trailer, delineating the start and end of the frame, and often includes error-checking information. The framing process helps receivers identify and extract meaningful data from the transmitted stream, ensuring accurate and orderly communication.

2. Flow Control:

Flow control mechanisms are employed to manage the rate of data transmission between devices, preventing overload or congestion. This is crucial when the sender's rate of data production exceeds the receiver's ability to process it. Techniques such as feedback mechanisms, windowing, and buffering are employed to regulate the flow of data and maintain a balance between sender and receiver capacities.

3. Error Control:

Error control mechanisms are implemented to detect and correct errors that may occur during data transmission. This involves adding error-checking information to the data, allowing the receiver to identify and request retransmission of corrupted frames. Techniques like checksums and cyclic redundancy checks (CRC) are commonly used to verify data integrity and ensure reliable communication.

4. Data Link Layer Protocols:

• Simple Protocol: The Simple Protocol is a basic communication protocol that involves sending data frames one at a time, with each frame requiring acknowledgment from the receiver before the next one is sent. While simple, it can result in inefficiencies, especially in scenarios where network latency is a factor.
• Stop and Wait Protocol: The Stop and Wait protocol is a flow control mechanism where the sender transmits a single frame and then waits for an acknowledgment from the receiver before sending the next frame. Although straightforward, it may lead to underutilization of the network as the sender spends a significant amount of time waiting.
• Piggybacking: Piggybacking is an optimization technique where data acknowledgments are sent along with new data frames. Instead of separate acknowledgment frames, the receiver includes acknowledgment information in its response to the sender's data. This helps in utilizing network resources more efficiently and reducing the overall transmission delay.

In summary, Framing, Flow and Error Control, and Data Link Layer Protocols are essential elements in network communication, ensuring the reliable and efficient exchange of data between devices. These concepts contribute to the overall robustness and performance of networked systems.