 This is why GDOI is called a "multicast key management system" as it uses and supports multicast messaging for very large groups.These multicast messages are unsolicited messages and are therefore called "push" messages, which are unsolicited messages sent from the controller to the members; explicit requests from a member to a controller are called "pull" messages in GDOI.Thus GDOI group key updates are pushed and can reach any number of group members with a single efficient transmission from the controller.