# Error Recovery in the Time-Triggered Paradigm with FTT-CAN
## 8 Conclusions  
In any real network, transmission errors are unavoidable and thus, a method to guarantee the delivery of messages, despite error occurrence, is necessary. This is especially true if a high reliability system is needed. In this paper, we presented a methodology to recover 1-bit errors in a simplex Controller Area Network (CAN or CAN-FD) running a time-triggered protocol. We showed that using on-line traffic scheduling plus a specifically designed server to handle retransmissions allows very large error recovery bandwidth savings while maintaining a high reactivity to errors, when compared with other error recovery approaches for time-triggered communication on CAN available in the literature. Conversely, the properties of our mechanism are closer to those of event-triggered CAN. However, the real-time guarantees in this case depend completely on the accuracy of the error model since the retransmissions are normally uncontrolled. Our solution explicitly controls retransmissions using a server, thus enforcing the properties of the considered error model. This is attained by including a run-time module that checks the arriving error patterns and limits the server execution to the patterns used in its configuration (see Section 5.2). Thus, the impact on the system timeliness of errors occurring beyond the model is strictly bounded.  
To implement our mechanism we used the FTT-CAN protocol, taking advantage of its on-line scheduling of the time-triggered traffic. We provided a detailed description of the proposed method, including the considered fault model, choice of server, and its parameterization and clear problem definition. We also identified the most demanding error scenarios and determined the level of replication needed to guarantee error recovery in the next FTT-CAN cycle. All of the methods were discussed in detail, including the corresponding algorithms.  
We tested the proposed error recovery mechanism simulating several well-known benchmarks, as well as random message sets and we compared it with other methods available in the literature. We showed that the proposed method is effective in recovering errors in time-triggered messages using approximately two orders of magnitude less average bandwidth than other approaches, while the instantaneous bandwidth required by our method (average of the random sets) is also always lower than the one used by other methods, allowing for the application of the error recovery method to message sets with greater bandwidth utilization. On the other hand, our method can only recover errors in the following protocol cycle while other approaches can recover in the cycle in which the error occurred. This may force our mechanism to use shorter cycles to handle fast messages appropriately.  
Currently, we are working to extend our approach to other than the Poisson single bit error model, so that we can accurately apply our method to situations with error bursts and periods of sustained higher interference. The optimization and reduction of the complexity in the schedulability and analysis techniques is another direction to pursue as future work.  
This work has been supported by the Portuguese Government through a grant from Fundacao para a Ciencia e Tecnologia (UID/EEA/50008/2013--Instituto de Telecomunicacoes), and by the European Regional Development Fund (FEDER) through a grant of the Operational Programme of Competitivity and Internationalization of Portugal 2020 (PRODUTECH II SIF, POCI-01-0247-FEDER-024541).  
[PERSON] proposed the recovery method, built the simulator/optimizer and performed the simulation study. [PERSON] participated in simulator coding/debugging and in writing the initial draft of the paper. [PERSON] and [PERSON] supervised all the work, analyzed and discussed the results and thoroughly revised all article versions. All authors reviewed the final article version.  
The authors declare no conflict of interest.