The network subsystem architecture adds three control mechanisms that are placed at the different stages of a TCP connection's life time. Figure 1 shows the various phases in the connection setup and the corresponding control mechanisms: (i) when a SYN packet is processed it triggers the SYN rate control and selective drop (ii) when the 3-way handshake is completed the prioritized listen queue selectively changes the ordering of accepted connections in the listen queue (iii) when the HTTP header is received the HTTP header controls decide on dropping or re- prioritizing the requests based on application layer information. Each of these mechanisms can be activated at varying degrees of overload where the earliest and simplest control is triggered at the highest load level.
1:
Proposed kernel mechanisms.