Abstract: A method, program and user node for use in a communication system implemented over a network comprising a plurality of user nodes, each being associated with a respective presence status indicating an availability of the user node for communication within the communication system. The method comprises, at each of a first one or more of the user nodes: maintaining a contact list specifying a selection of contacts from the plurality of user nodes; associating a presence update priority level with each of the contacts, the presence update priority level relating to an estimated likelihood of communication between the first user node and the respective contact; and transmitting a presence message to each of a plurality of the contacts in dependence on the respective presence update priority level, each of the presence messages comprising at least one of: a request for the presence status of the contact, and a notification of the presence status of the first user node.

Abstract: A method, program and user node for use in a communication system implemented over a network comprising a plurality of user nodes, each being associated with a respective presence status indicating an availability of the user node for communication within the communication system. The method comprises, at each of a first one or more of the user nodes: maintaining a contact list specifying a selection of contacts from the plurality of user nodes; associating a presence update priority level with each of the contacts, the presence update priority level relating to an estimated likelihood of communication between the first user node and the respective contact; and transmitting a presence message to each of a plurality of the contacts in dependence on the respective presence update priority level, each of the presence messages comprising at least one of: a request for the presence status of the contact, and a notification of the presence status of the first user node.