Data aggregation in an internet of things (IoT) system refers generally to collecting data such that the data can be processed in a useful manner. Existing approaches to data aggregation in IoT systems, such as a system including a network of sensors for example, often focus on network logical topology and data transmission scheduling and routing schemes. An IoT system can aggregate data at an application-protocol layer. For example, an IoT node in an IoT system can send a data aggregation request message that is capable of retrieving data from a plurality of different applications. In response, the IoT node may receive data that is representative of a set of nodes that are located downstream in the IoT system from the IoT node.