Testing data transfer at the application layer of a wind power surveillance computer system. One technique includes preparing a test message with a message id, transferring the test message from a first computer entity to a second computer entity, stamping the test message with a time stamp, when transfer is initiated, stamping the test message with a transfer id and a corresponding transfer time stamp, when the test message is received at the second entity, transferring the test message from the second computer entity at the application layer to the first computer entity, stamping the test message with an arrival time stamp, when the test message arrives at the first entity, storing the message id and the transfer id with corresponding time stamp and corresponding transfer time stamp, and the arrival time stamp, and comparing the stored time stamp with the transfer time stamp and with the arrival time stamp.