There is a growing trend for real-time Ethernet in nearly all industrial branches. While each industry has its own Ethernet-based protocols in networks, the High Availability Seamless Redundancy (HSR) network is currently of interest to the automation industry. A key factor and main benefit of HSR is its built-in fault-tolerance against the failure of a single communication link. However, it lacks mechanisms to guarantee certain bandwidth to applications. In this paper we propose a mechanism to guarantee packet arrival within a certain time while still offering best-effort traffic in order to support for mixed criticality traffic. Furthermore, a mathematical model is developed, that describes the upper latency limit of the proposed mechanism. We compare HSR with and without the proposed extension using an OMNeT++ simulation and show its advantages and weaknesses.
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