Huawei Alibaba Huawei Huawei DDoS Open Threat Signaling (DOTS) Working Group is for developing the standard signaling mechanisms, together with the DDoS related telemetry and threat handling requests and data transmitted by them used in DDoS problem space. Although IP Flow Information Export (IPFIX), Packet Sampling (PSAMP), and Packet Selection methods are useful for network security inspection, there are still some gaps existing to identify some categories of DDoS attacks. To fill in the gaps, this document describes the connection sampling mechanism and explains why it is needed for detecting DDoS attacks. It also defines several new IPFIX Information Elements (IEs). Then, it presents some examples to show how to use these new IPFIX IEs together with the existing IPFIX IEs to detect specific DDoS attacks.