This Recommendation | International Standard specifies the Relayed MultiCast Protocol for simplex group applications (RMCP-2), an application-layer protocol, which constructs a multicast tree for data delivery from one sender to multiple receivers over the Internet where IP multicast is not fully deployed. Clauses 5-8 define a basic RMCP-2 protocol without security features, and clauses 9-12 define a secure RMCP-2 protocol that adds security features to the basic protocol. Both protocols specify a series of functions and procedures for multicast agents to construct a one-to-many relayed data path and to relay simplex data. They also specify the operations of the session manager to manage multicast sessions. These protocols can be used for applications that require one-to-many data delivery services, such as multimedia streaming services or file dissemination services. Annex E defines a membership authentication procedure for use with the secure RMCP-2 protocol. Annexes A-D provide informative material related to these protocols. AnnexF contains an informative bibliography.