Built upon the connectionless UDP protocol, FASP does not expect any feedback on every packet sent, and yet provides fully reliable data transfer over best effort IP networks.
Its control model is designed to fill the available bandwidth of the end-to-end path over which the transfer occurs with only "good" and needed data.
To counteract attacks by monitoring the encrypted information during long transfers, the AES is operated in cipher feedback mode with a random, public initialization vector for each block.
In addition, an integrity check of each data block takes place, in which case, for example, a man-in-the-middle attack would be noticed.
Acting on this information is complicated because the receiver has it and the sender needs it, but its lifetime is often less than the transmission delay; and measurements are noisy.