KNXnet/IP system allows integration of different KNX networks through an IP network, used as fast backbone. Integration is realised by a particular device called KNXnet/IP Router. Due to the very limited transmission speeds foreseen for the KNX networks, the KNXnet/IP router may represent a bottleneck in routing telegrams coming from the IP network whose destination is a KNX device located in the relevant KNX network. The aim of the paper is to analyse the effect of congestion of KNXnet/IP Routers on the information flow between KNX devices attached to different KNX networks through an IP backbone.