At which layer of the OSI model does the function of flow control primarily occur?

Flow control is a key function that ensures data is transmitted at a rate that the receiver can handle, preventing overloading. This functionality is primarily associated with the Transport Layer of the OSI model. The Transport Layer, which is the fourth layer, is responsible for end-to-end communication and error recovery, as well as providing mechanisms to control the flow of data between sender and receiver.

At this layer, protocols such as Transmission Control Protocol (TCP) implement flow control techniques like sliding window and acknowledgments to manage the amount of data being sent before requiring an acknowledgment from the receiving side. This ensures that the sender does not overwhelm the receiver with too much data at once.

While flow control is important in other layers—particularly in the Data Link Layer, which also deals with framing and reliable delivery on a local network—the primary and more sophisticated mechanisms for flow control occur at the Transport Layer. The focus at this layer is on managing data between hosts across the entire network, making it crucial for large-scale data transmission.