A publish/subscribe system includes a publisher and multiple subscribers. The published includes a packet generator to generate a packet with at least one of: a fixed length flow label labeling a message or a message bundle and a fixed length node label labeling at least one message bundle and indicating at least one of the nodes of a topic tree to which the flow label belongs. Each received includes a user selection data holder and a message selector. The data holder stores a selection of topics of interest to a user from the topic tree. The message selector receives a packet having a header and data, determines which flow and/or node labels are incorporated in the header and accepts the data if the user selection data holder indicates that the labels within the header are of interest to the user.