The Cisco IPS 4520 Sensor is now obsolete (past End-of-Life and End-of-Support status).
End-of-Sale Date: 2015-04-26
End-of-Support Date: 2020-04-26
Cisco's End-of-Life Policy
You can view a listing of available Next-Generation Intrusion Prevention System (NGIPS) offerings that best meet your specific needs
If you want support information for the Cisco IPS 4520 Sensor documentation, it may be available through Cisco.com Search or in the Cisco Community