I want to upload my file it to a FTP server in parts

I want to upload my file to an FTP server. In case if my uploading process is interrupted. I want to upload rest of the bytes of the file and append it to the incomplete uploaded file on the server. Can any body Help me how to do it.

For example I am uploading a file of 20.0 Mb and when 10.0 Mb has been uploaded the an error occurs and upload process is interrupted. I want to upload the rest 10 mb and concatenate it at the last of the incomplete part.