The difference between this function and the ftp_fput() is that this function uploads the file asynchronously, so your program can perform other operations while the file is being downloaded.
ftp_nb_fput() uploads the data from the file pointer handle until it reaches the end of the file. The results are stored in remote_file on the FTP server. The transfer mode specified must be either FTP_ASCII or FTP_BINARY. The difference between this function and the ftp_fput() is that this function uploads the file asynchronously, so your program can perform other operations while the file is being downloaded.