Patent ID: 7752273

Claim:
A group communication system based on presence information for use in an instant message and presence service system that sends and receives presence information and an instant message among a plurality of client devices each comprising a presentity that provides presence information; a watcher that observes presence information on presentities other than said presentity; and an IM (Instant Message) transmission/reception unit that sends and receives an instant message, wherein at least one client device of said plurality of client devices comprises: a processor for implementing the functions of the client device; a group management unit that, when presence information provided by the presentity of said one client device changes to a specific status, determines whether a group agent corresponding to the specific status of the client already exist, and if the group agent corresponding to the specific status of the client already exists, sends a control command to that group agent device to request that the client be added as a member to the group agent device, otherwise the group management unit generates a group agent device corresponding to the specific status of the client; and a presence issuing unit that issues the specific status and an identifier used to contact said generated group agent device; and wherein said group agent device comprises: a member management unit that manages, as members thereof, at least said client device that generated said group agent device and a client device that sends an instant message to said group agent device; and an IM delivery unit that transfers an instant message, which is sent to said group agent device, to all client devices that are members managed by said member management unit except at least the sender of the instant message.