## 4 Test Results
### RR Performance Predictions for Individual Sections and End-to-End
Firstly, implementing this particular RR system was the only accomplishable solution, as the resource-demanding planting of optical cables was not an option, nor was adding new intermediate nodes in an attempt to reduce the RR sections' lengths or replacing the RR devices with new ones that have shifted frequency bands to 13 GHz and 18 GHz. Furthermore, using higher-gain (and thus larger) antennas within the limited space on the rooftop mounts would bring about a pronounced susceptibility to strong winds and ice accumulation, both causing antenna smearing during storms, as some constructions cannot withstand the increased weight and mechanical stress. Therefore, the only realistic option was to reduce the modulation order until the target prediction norm (availability) was reached for each RR section, as well as for the end-to-end connection. Moreover, differentiating and prioritizing of services according to their importance and traffic type (i.e., defining the appropriate QoS parameters) needed to be done. So, for example, for the OAM packets and synchronizing messages, the target throughput was chosen to be 20 Mb/s. However, the internet traffic that is targeted at 200 Mb/s is of the lowest priority, implying that it primarily suffers from propagation phenomena such as fading. RR Performance Prediction with Reduced Modulation Order  
Let us now present the predictions for the same RR sections as above, but with a reduced modulation order, which have to fulfil the (un)availability norm for short haul microwave links with a fixed data rate. As can be seen on the screenshot in Figure 11, for the first RR section, the predicted availability is 99.98% for 128 QAM modulation, vertical polarization, and a throughput of 323 Mb/s, implying that the annual unavailability is 65.5 min, which is within the relevant norm [5]. From the screen shot for the second RR section, presented in Figure 12, it is reasonable to expect that 128 QAM modulation and throughput of 323 Mb/s were chosen over-pessimistically, as in this RR section, 256 QAM modulation would likely satisfy the norm too. However, the norm needs to be fulfilled end-to-end, so that is why the lower-order QAM was chosen to make the unavailability lower (just 24.2 h annually for vertical polarization). Further on, the third RR section also fulfills the norm with 128 QAM modulation. As for vertical polarization, the annual unavailability amounts to 63 min, Figure 13.  
The fourth very short RR section definitely fulfills the norm with 2048 QAM modulation and maximal throughput of 500 Mb/s; as for vertical polarization, the annual unavailability amounts to just 37.8 min (Figure 14). Figure 11: Prediction for the first RR section; 128 QAM, 323 Mb/s. Figure 12: Prediction for the second RR section; 128 QAM, 323 Mb/s. Figure 14: Prediction for the fourth RR section; 2048 QAM, 500 Mb/s. Figure 13: Prediction for the third RR section; 128 QAM, 323 Mb/s. Finally, from the screenshot for the fifth RR section, presented in Figure 15, it can be seen that the norm is satisfied for 256 QAM modulation and a throughput of 368 Mb/s, using the installed hybrid RR equipment of the second generation. Thus, as the end-to-end throughput equals the minimal one out of all five RR sections, we consider it to take the value of 368 Mb/s. Moreover, the end-to-end unavailability is the sum of five individual section unavailabilities, and amounts to 305.3 min per year (for vertical polarization of all RR sections), which is above the annual norm of 210 min [5]. Therefore, in order to fulfill the end-to-end norm in this regard, we \"downgraded\" the last RR section modulation order from 256 QAM to 128 QAM, thus satisfying the norm for the rate of 323 Mb/s (Figure 16). This not only reduces the RR throughput but also that of the Ethernet traffic.