Methods and systems for an integrated solution to the rate based denial of service attacks targeting the Session Initiation Protocol are provided. According to one embodiment, header, state, rate and content anomalies are prevented and network policy enforcement is provided for session initiation protocol (SIP). A hardware-based apparatus helps identify SIP rate-thresholds through continuous and adaptive learning. The apparatus can determine SIP header and SIP state anomalies and drop packets containing those anomalies. SIP requests and responses are inspected for known malicious contents using a Content Inspection Engine. The apparatus integrates advantageous solutions to prevent anomalous packets and enables a policy based packet filter for SIP.