Figure 2
From: Efficient integration of secure and safety critical industrial wireless sensor networks
The black channel principle, where safety-related and non safety-related communication co-exist on the same standard transmission system (Profinet and WirelessHART). The black channel is excluded from functional safety certification as the safe transmission function (Profisafe) comprises all of the measures to deterministically discover all possible faults and hazards that could be infiltrated by the black channel.