  Recent technological advances have fostered the development of complex
industrial cyber-physical systems which demand real-time communication with
delay guarantees. The consequences of delay requirement violation in such
systems may become increasingly severe. In this paper, we propose a
contract-based fault-resilient methodology which aims at managing the
communication delays of real-time flows in industries. With this objective, we
present a light-weight mechanism to estimate end-to-end delay in the network in
which the clocks of the switches are not synchronized. The mechanism aims at
providing high level of accuracy with lower communication overhead. We then
propose a contract-based framework using software-defined networking where the
components are associated with delay contracts and a resilience manager. The
proposed resilience management framework contains: (1) contracts which state
guarantees about components behaviors, (2) observers which are responsible to
detect contract failure (fault), (3) monitors to detect events such as run-time
changes in the delay requirements and link failure, (4) control logic to take
suitable decisions based on the type of the fault, (5) resilience manager to
decide response strategies containing the best course of action as per the
control logic decision. Finally, we present a delay-aware path finding
algorithm which is used to route/reroute the real-time flows to provide
resiliency in the case of faults and, to adapt to the changes in the network
state. Performance of the proposed framework is evaluated with the Ryu SDN
controller and Mininet network emulator.
