## 4 Test Results  
### RR Performance Predictions for Individual Sections and End-to-End  
Let us now present performance prediction of each of the five RR sections of the observed end-to-end connection Satorova Gomila-Leotar, measured by means of the original software tool SmartBudget, which is produced by the equipment manufacturer. The tests were initially done for maximal and fixed modulation order, namely 2048 QAM and maximal throughput of 500 Mb/s. Practically speaking, this means that the assumption of short-haul sections was adopted. As can be read from the screenshot presented in Figure 6, the availability equals 99.40% for vertical and 99.37% for horizontal polarization of the first RR section, and thus does not satisfy the norm for a short-haul RR link with fixed transmission rate. Consequently, the annual unavailability time prediction equals 3123 min and 3294 min, respectively, for the abovementioned polarizations, both of which are significantly longer than the maximal allowed value of 210 min per year [5]. Analogously, for the second RR section, it can be seen from the corresponding screenshot in Figure 7 that the annual unavailability time prediction equals 1389 min and 1475 min for vertical and horizontal polarizations, respectively. Both values are significantly longer than the maximal allowed value of 210 min per year [5], and therefore do not satisfy the norm for a short-haul RR link with fixed transmission rate. Figure 6: Prediction for the first RR section; 2048 QAM, 500 Mb/s. Figure 7: Prediction for the second RR section; 2048 QAM, 500 Mb/s. Furthermore, for the third RR section, the screenshot in Figure 8 shows that the annual unavailability time prediction equals 4992.4 min and 5174.7 min for vertical and horizontal polarizations, respectively. Both values are significantly longer than the maximal allowed value of 210 min per year [5], and therefore they do not satisfy the norm for a short-haul RR link with fixed transmission rate. However, for the fourth RR section, the related screenshot in Figure 9 shows that the annual unavailability time prediction equals 37.8 min and 64.2 min for vertical and horizontal polarizations, respectively. These values are below the norms (even for an international RR link). This is in accordance with expectations for the 4 km-long link and the frequency band centered around 23 GHz. Finally, as can be seen in the screenshot in Figure 10, the fifth, 25 km-long RR section, using the frequency band centered around 13 GHz, also does not satisfy the availability norm, as the annual unavailability time prediction equals 3311 min and 3473.8 min for vertical and horizontal polarizations, respectively, which are both significantly longer than the maximal allowed value of 210 min per year [5]. Figure 8: Prediction for the third RR section; 2048 QAM, 500 Mb/s. Figure 10: Prediction for the fifth RR section; 2048 QAM, 500 Mb/s. Figure 9: Prediction for the fourth RR section; 2048 QAM, 500 Mb/s. The potential countermeasures leading to better availability of both the individual sections and the end-to-end connection include the following:  
* increase the node count (i.e., reduce the lengths of critical sections);
* choose lower-band (6 L, 6 U, 8 GHz) RR devices that are less susceptible to fading;
* increase the antennas' diameter in order to get better antenna gain, which implies a rise of the fading margin and signal-to-noise ratio;
* optimize the order of frequency channels and polarization in accordance with RR sections lengths;
* reduce the modulation order;
* differentiate and prioritize services according to their importance and traffic class, and then define the QoS parameters; or
* give up on an RR system and look for alternative technical solutions (i.e., optical transport).