## 4 Numerical Results  
In this section, we proceed to provide an illustrative example of the proposed mixed reservation- and priority-based traffic coexistence strategy. Specifically, we consider three services that have to be supported by the 5G NR air interface--URLLC, eMBB, and mMTC. According to the 5G International Mobile Telecommunications-2020 (IMT-2020) requirements specified in [4] and network slicing recommendations in 3 GPP Technical Specification (TS) 23.501 and TS 38.300, URLLC should receive the highest priority and be served as there are absolutely no other types of traffic in the system reaching the drop probability of \(10^{-5}\). On the other hand, mMTC requirements are the loosest out of all these three types of services, requiring that no more than 1% of traffic is not delivered within 10 s. The eMBB service is characterized by the balanced requirements. Thus, in our numerical example, we assign the priorities accordingly. The default system parameters utilized to produce the reported results in this section are shown in Table 1. Note that here, we explicitly compare two slice isolation schemes: (i) full reservation, where the whole set of resources, \(C=39\) PRBs, is equally divided between the slices, and (ii) partial reservation with priorities, where a set of resources is allocated to the shared pool. Note that in both cases, URLLC traffic is well isolated from the rest of the traffic and, thus, we will only consider performance degradation experienced by eMBB and mMTC. We start with Figure 4 with the two critical metrics of interest, eMBB and mMTC session drop, \(p_{B_{2}}\), \(p_{B_{3}}\), and pre-emption probabilities, \(p_{pre_{2}}\), \(p_{pre_{3}}\), for two considered schemes as a function of the offered traffic load of URLLC, \(\rho_{1}=\lambda_{1}b_{1}^{\min}/\mu_{1}\). Note that the full reservation scheme is indicated by \(g_{k}=13\) PRBs, while the mixed reservation- and priority-based is indicated by \(g_{k}=10\). In the latter case, there is the shared pool of nine PRBs that are shared between all types of traffic. By analyzing the session drop probability demonstrated in Figure 4a, one may observe that the mixed reservation- and priority-based mechanism outperforms full reservation in terms of the mMTC drop probability for low and moderate values of the \(\rho_{1}\). For both eMBB and mMTC traffic, the system is characterized by two regimes: (i) up until approximately \(\rho_{1}=15\), the mixed scheme performs better, (ii) after \(\rho_{1}=15\), the full reservation scheme outperforms the mixed one. The rationale is that prior to \(\rho_{1}=15\) both eMBB and mMTC traffic efficiently utilize the shared pool of resources available. However, when the offered traffic load of highest priority URLLC sessions further increases, they start to occupy the shared pool of resources, aggressively leading to the performance loss of eMBB and mMTC traffic. The price one has to pay for better session drop probability in the mixed reservation- and priority-based scheme is higher session pre-emption probability demonstrated in Figure 4b for the same system parameters. Here, we see that the session pre-emption probability is lower for the full reservation scheme across almost the whole range of the URLLC-offered traffic load \(\rho_{1}\). Notably, the mMTC traffic suffers less with the corresponding probabilities being quite close to each other. The rationale here is that short-lived lightweight traffic is better suited for priority service due to fine granularity in terms of the number of sessions that need to be interrupted to accommodate the arriving higher priority session. However, the elastic eMBB traffic suffers most with the difference reaching three times at approximately \(\rho_{1}=20\). Note that the pre-emption of a rare but long eMBB session has much higher negative impact compared to mMTC sessions, thus making the full reservation scheme better suited for the former type of traffic.