  Time-Sensitive Networking (TSN) aims to extend the IEEE 802.1Q Ethernet
standard with real-time and time-aware capabilities. Each device's transmission
of time-critical frames is done according to a so-called Gate Control List
(GCL) schedule via the timed-gate mechanism described in IEEE 802.1Qbv. Most
schedule generation mechanisms for TSN have a constraining assumption that both
switches and end-systems in the network must have at least the TSN capabilities
related to scheduled gates and time synchronization. However, many TSN networks
use off-the-shelf end-systems, e.g., for providing sensor data, which are not
scheduled and/or synchronized.
  In this paper, we propose a more flexible scheduling strategy that considers
a worst-case delay analysis within the scheduling synthesis step, leveraging
the solution's optimality to support TSN networks with unscheduled and
unsynchronized end-systems while still being able to guarantee bounded latency
for critical messages. Our method enables real-world systems that feature
off-the-shelf microcontrollers and sensor nodes without TSN capabilities
connected to state-of-the-art TSN networks to communicate critical messages in
a real-time fashion. We evaluate our approach using both synthetic and
real-world test cases, comparing it with existing scheduling mechanisms.
Furthermore, we use OMNET++ to validate the generated GCL schedules.
