Why uploading a file through FTP takes more time every 10 minutes

See more:

VB6

general

FTP

Hello all,
I wrote a simple FTP program to transfer 4 text files to a device in a loop.(for testing we wanted to have a ftp tool which will be uploading 4 txt files continuosly without stop).

The tool seems to be working fine, uploading the files repeatedly in an endless loop.
But, we witnessed something interesting in the log files.

We observed that every 10 minutes (exact, the file uploading process takes more time compared to rest of the transfer process i.e. suppose a file which normally takes 2 seconds to upload, the same file takes around 6 minutes to upload, every 10 minutes of file uploading process.

Does anyone has any clue why this could happen? We have not set any kind of timeouts in the program as well as the tool instantly begins the transfer of next file once it finishes uploading the previous file.

Any kind of help or suggestions will be appreciated.

Thanks
Dinesh.