Orange McAfee, Inc. 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. A companion document defines the DOTS data channel, a separate reliable communication layer for DOTS management and configuration purposes. This document obsoletes RFC 8782.