Node to node synchronization accuracy requirements of dynamic frame packing

The evolution of industrial communication inexorably moves towards Ethernet based networks. One important reason for using Ethernet at the shop floor is to participate on the continuous advancements of standard Ethernet. In contradistinction to the star topology, used commonly in home and office networks, in the industrial automation most common network structure is line. It is due to the fact that it simply follows the architecture of plants (production line). Depending on the size of an automation facility the size of such a network structure may contain up to 100 nodes. Thus, the node to node synchronization jitter, with its cumulative behavior, becomes a relevant performance factor for high demanding applications such as motion control. This paper examines influence of the synchronization jitter on the industrial Ethernet networks by taking the example of PROFINET IO, a common representative of an industrial Ethernet based protocol. It uses a Time Division Multiple Access (TDMA) procedure together with the communication scheduling to fulfill hard real-time requirements. Additionally the protocol uses Dynamic Frame Packing (DFP) in order to optimize bandwidth utilization. The efficiency of both mechanisms strongly depends on the node to node synchronization accuracy.