In the Cluster of European Research Projects (CERP) report, the Internet of Things (IoT) is defined as an integrated part of the future Internet, which ensures that `things' with identities can communicate with each other. IoT will be applied in different areas, e.g. smart cities, agriculture, energy, environment protection, health, home automation, etc. However, if different IoT applications are based on different architectures, this will prevent the IoT co-building, convergence, and openness. To reduce investments in the IoT area, a top-down architectural principles need to be followed to unify the design. This paper provides classification of the IoT platforms and proposes a top-level generic IoT architecture particularly suited for the creation of smart cities.