You can get references to any nDataStream (user) from the nSession object if you call getDefaultDataGroup(). You can also access nDataStreams by implementing the nDataGroupListener interface. Please refer to DataGroup management (see Managing DataGroup Membership) for more information. This will deliver callbacks as users are connected/disconnected. There are various writeDataStream methods available. These methods also support batching of multiple events to a single group or batching of writes to multiple DataStreams.