Get the Whitepaper called Insertion, Evasion, and Denial of Service: Eluding Network Intrusion Detection.
You can download it from the following link: https://packetstormsecurity.com/files/download/103299/ied-nids.pdf
Source: https://packetstormsecurity.com/files/103299/Insertion-Evasion-And-Denial-Of-Service-Eluding-Network-Intrusion-Detection.html