IoTconsultancy.nl InterDigital RISE AB This document specifies the use of the Constrained Application Protocol (CoAP) for group communication, using UDP/IP multicast as the underlying data transport. Both unsecured and secured CoAP group communication are specified. Security is achieved by use of the Group Object Security for Constrained RESTful Environments (Group OSCORE) protocol. The target application area of this specification is any group communication use cases that involve resource- constrained networks. The most common of such use cases are also discussed. This document replaces [RFC7390] and updates [RFC7252] and [RFC7641].