1. A method, comprising: computing, by a management node, a minimum number of observer nodes required to observe network traffic of each node of a plurality of nodes inside a node domain in a shared-media communication network; selecting, by the management node, a subset nodes inside the node domain to act as an observer for one or more subject nodes in the network, wherein the number of nodes in the subset of nodes is based on the minimum required number of observer nodes; receiving, at the management node from the selected subset of nodes, a message containing an indication of traffic activity or traffic inactivity at the one or more subject nodes, the indication being derived from the selected subset of nodes observing network traffic at the one or more subject nodes; and determining, by the management node, which of the one or more subject nodes are active based on the received message.