# Error Recovery in the Time-Triggered Paradigm with FTT-CAN
## 6 Results and Discussion
### LSW Optimization with Random Sets and BW Required by the Error Recovery Mechanism  
Multiple runs of the LSW optimization module were carried out to assess the performance of the three methods referred in the previous section, concerning the minimum LSW value required to attain the desired error responsivity, as a function of the message set utilization. The bandwidth utilization range varied between 5% and 70%, in steps of 1%. Message payload length varied from 1 to 8 bytes and message periods from 2 to 15 ECs, with implicit deadline (i.e., equal to period), both with uniform distribution. LEC was set to 2.5 ms and one thousand message sets were generated for each utilization value. The results are presented in Figure 11, averaging the obtained minimum LSW of the 1000 sets of each utilization point.  
_Static TT_ shows a better performance than _Automatic Retransmission_ (smaller minimum required LSW) but only for low utilization values (less than 8%). The _Controlled Retransmission_ method always shows better performance than all of the other ones. When compared to _Automatic Retransmission_, it is slightly better for sets with utilization lower than 15% and grows for larger utilizations, requiring up to about 16% less in the LSW parameter. The picture also shows that our method allows for attaining much higher utilization levels than the competing ones, for the same reliability goal, allowing up to 70% utilization against 20% and 55% from _Static TT_ and _Automatic Retransmission_, respectively.  
Figure 12 represents the bandwidth required by the different error recovery mechanisms as a function of the message set utilization, being obtained with random message sets using LEC equal to 2.5 ms, an Aggressive environment, and the other parameters as in the previous experiences. In _Static TT_, the required bandwidth is proportional to the number of copies needed for each message, also including error signaling, being always more than 300% of the corresponding message utilization bandwidth, as four copies per message are required to attain the desired reliability level. Thus, more than 70% of the total bandwidth is allocated to the recovery mechanism, even for message sets with a utilization of only 20%. _Automatic Retransmission_ reserves slack time in each EC to recover the maximum number of errors considered (equal to _max_1 cycle_), which in the studied cases is 3 or 4, corresponding to 19.0% or 25.2% of the available bandwidth. Therefore, the overhead is essentially constant, having a step in the utilization transition from 19% to 20%, corresponding to the situation in which the errors that need to be handled changes from 3 to 4 per EC. As for the _Controlled Retransmission_ mechanism, the reserved bandwidth is the one of the error server. The server configuration depends on the fault arrival rate and maximum _RepLevel_ configuration value, and using \(T_{S}\) equal to \(1/\lambda\), the necessary capacity varies between \(8\times 3\times C_{MAX}\) and \(14\times 3\times C_{MAX}\), which is only 0.084% and 0.147% of the 1 Mbps available bandwidth. This figure clearly shows the superiority of our method, since its required bandwidth is at least two orders of magnitude inferior to the other methods.  
Figure 11: Average requirement for minimum LSW vs message set bandwidth utilization.