Cluster user login method, state updating method, processing equipment, IMS network entity and communication system

The invention relates to a method of user registration and a method of updating the user state in an open group, belonging to the field of mobile communication. The method of user registration in the group comprises the following steps: the user identity in an implicit registration set is registered; the information of a related user in the implicit registration set is updated. The method of updating the user state comprises the following steps: the user identity in a dynamic group is registered; when the state of the user identity in the dynamic group changes, the information of the related user in the implicit registration set is updated correspondingly based on the information of state changes. The invention also provides a user state processing device, an IMS network entity and a communication system correspondingly. The invention has the advantages that the qualified user in the dynamic group can be registered using less resource.