http://www.cisco.com/c/en/us/td/docs/ios/voice/cdr/developer/guide/cdrdev/cdrcsv.html

• Configure FTP Server
• Configure IOS

Sample IOS Config

gw-accounting file
 primary ftp 123.123.123.123/cdrs/ username anonymous password 0 1234
 secondary ftp 123.123.123.124/cdrs/ username anonymous password 0 1234
 acct-template callhistory-detail
 maximum cdrflush-timer 15
 cdr-format detailed

IIS Config

• Enable FTP on IIS

• Enable Anonymous access

• Lock down FTP access to only allow access from designated devices

• Enable Read / Write access to Windows Folder used for FTP to the user 'IUSR'