c. Why is flow control necessary in computer networks? Compare 3 flow control schemes in data link layer: Stop-and-Wait, Go-back-N, and Selective Repeat. What are the differ- ences comparing flow control implementations in data link layer and tran...-DPDK中文网

Flow control is necessary in computer networks to prevent the sender from overwhelming the receiver with more data than it can handle, which could result in lost or corrupted data. This is especially important in situations where the sender and receiver have different processing speeds or network capacities.

There are three main flow control schemes used in the data link layer: Stop-and-Wait, Go-back-N, and Selective Repeat.

Stop-and-Wait: In this scheme, the sender sends one frame at a time and waits for an acknowledgement from the receiver before sending the next frame. The receiver acknowledges each frame as it receives them. This method is simple but inefficient because it wastes time waiting for acknowledgements.

Go-back-N: In this scheme, the sender can send multiple frames without waiting for acknowledgements. However, if a frame is lost or corrupted during transmission, all subsequent frames must be retransmitted by the sender starting from the lost/corrupted frame. This results in wasted bandwidth and slower transmission speeds.

Selective Repeat: In this scheme, both the sender and receiver maintain a window of acceptable sequence numbers. The sender can send multiple frames within its window without waiting for acknowledgements. If a frame is lost or corrupted during transmission, only that particular frame needs to be retransmitted by the sender while other frames within their respective windows continue to be transmitted and received.

The difference between flow control implementations in data link layer and transport layer lies mainly in their scope of operation. Data link layer flow control operates on individual frames while transport layer flow control operates on entire streams of data (e.g., TCP). Transport layer flow control also considers network congestion as a factor when adjusting its transmission rate whereas data link layer flow control does not typically account for network congestion.