This document specifies the Distributed Denial-of-Service Open Threat Signaling (DOTS) signal channel, a protocol for signaling the need for protection against Distributed Denial-of-Service (DDoS) attacks to a server capable of enabling network traffic mitigation on behalf of the requesting client. The DOTS data channel is defined in an associated document. The document updates RFC 8872. The document is almost Ready from an OPS perspective, but there are a couple of issues worth clarification before approval. 1. Appendix A describes the changes from RFC 8782. I could not find however any information in the document concerning backwards compatibility and the path of upgrade that an operator should be aware about when migrating an existing client, server or the whole network from RFC 8782 support. If I missed it, please point and maybe detail this information in the Appendix. If not, it would be useful to add. 2. I could not find any information about the supplementary overload that the changes in signaling brought by this update may bring. If such an analysis was made, it would be useful to mention its results. No significant extra-load is fine. If anything different, it would be useful to add more details.