FTP transfers files by breaking them into packets and sending them over the network connection. When a large file is being transferred, the packets are queued for transmission in an output buffer until the entire file has been sent. At the receiving end, the packets are stored in the input buffer until the complete file has been received.
To handle spooling file transfers, FTP uses a technique called flow control. Flow control manages the transmission of data between two devices by controlling the amount of data that can be sent before an acknowledgement is required. If too much data is transmitted without acknowledgement, the receiving device’s buffer can become overloaded and cause data loss or performance issues.
To prevent this, FTP employs a sliding window flow control mechanism. The sender limits the number of packets that it can send before receiving an acknowledgement from the receiver. This means that only a certain number of packets are transferred at a time, reducing the risk of buffer overload. As the receiver acknowledges receipt of each packet, the sender is allowed to send more packets, effectively “sliding” the window forward.
In addition to flow control, FTP also employs error detection and correction mechanisms to ensure the integrity of the transferred data. These mechanisms include checksums and cyclic redundancy checks (CRC) that are performed on both sides of the transfer to verify data integrity. If errors are detected during the transfer, FTP will retransmit the affected packets until all packets are successfully transmitted and received.
