## 6 Conclusions  
RR transmission systems are an important constituent of each operator network (e.g., for interconnecting the base stations of wireless access systems that we consider here), LTE in particular. Specifically, we focus on a non-uniform environment encompassing various technologies of RR systems such as legacy SDH NGN, hybrid Ethernet/TDM, and all-IP, which together have to provide targeted availability and end-to-end Ethernet/IP QoS.  
As Carrier Ethernet has become dominant in RR systems, it has become even more important to ensure an appropriate end-to-end QoS level, so our goal was to analyze the RR performance consistency with the Ethernet/IP layer QoS.  
In this regard, a question arises whether and to what extent fulfilling the former classic recommendations for performance prediction--specifically, the (un)availability of an RR chain of stations for fixed data rates--determine the Ethernet QoS on the end-to-end level.  
The measurements were done on the operating network, which, at the physical media layer (RR), included the at-the-time actual propagation impairments, for which we followed the recommendation to adopt the most over-pessimistic predictions.  
After extensive practical testing and analysis of the achieved results, it came out that the impact of RR-level impairments that determine the RR performance prediction  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Spearman \(\rho\)** & **p-Value** & **BER** & **H0** \\
**QoS vs. RR Unavailability** & **p-Value** & **BER** & **H0** \\ \hline
0.723 & 0.031 & \(10^{-3}\) & Rejected \\
0.164 & 0.087 & \(10^{-5}\) & Rejected \\
0.021 & 0.124 & \(10^{-6}\) & Accepted \\
0.007 & 0.323 & \(10^{-9}\) & Accepted \\ \hline \hline \end{tabular}
\end{table}
Table 5: Correlation of QoS vs. RR unavailability.  
affected the Ethernet QoS to the extent that BER values increased to the acceptability threshold values.  
The only achievable solution in this regard was to downgrade the modulation order until the target norm is reached for each section, as well as for the end-to-end connection.  
Although at this time, testing did not target analyzing the individual impact of any RR impairment--fading in particular (which would have needed long-term testing)--the test model could be extended or focused by tracking each propagation effect, once it was identified and isolated.  
Making more tests with more diversified conditions would definitely enhance the representability of the achieved results, but unfortunately, we had no resources available for more a ambitious task in this respect.  
Our goal with this research was just to pave the way for network operators to develop such correlative cross-layer testing on a larger scale in terms of both test diversity and repeating rate.  
Conceptualization, S.Z. and V.L.; methodology, S.Z., A.L. and V.L.; software, S.Z.; validation, A.L., M.H. and V.L.; formal analysis, A.L.; investigation (actual testing), S.Z. and M.H.; resources, S.Z.; data curation, A.L.; writing--original draft preparation, S.Z. and A.L.; writing--review and editing, V.L.; visualization, S.Z.; supervision, V.L.; project administration, A.L.; funding acquisition, S.Z. All authors have read and agreed to the published version of the manuscript.  
The research leading to the published results was supported by the Ministry of Civil Affairs of Bosnia and Herzegovina, under Grant No. 02-7143/20.  
The authors declare no conflict of interest.