# A QoS-Enabled Medium-Transparent MAC Protocol for Fiber-Wireless 5G RAN Transport Networks
## 4 Results
However, again, we noticed that under gMT-MAC, EXP and BE packets were treated equally, resulting in both flows quickly surpassing the threshold of 250 us at loads of 0.3 and above, with the delay reaching a maximum value of ~15 ms for all loads greater than 0.4. In the qMT-MAC case, however, EXP traffic increased at a very slow pace, and the produced results surpassed the 250 us threshold only when the load approached 0.8, while, on the contrary, BE delay increased rapidly when the load increased above 0.3 and, at the highest point, reached values close to 100 ms. This performance difference is evident since EXP traffic has clear priority over BE traffic in the creation of the PS, and to this end, it is served quickly, achieving sufficient delay budgets for all loads less than the network's capacity. BE delay under qMT-MAC decreased when the load is greater than 0.7; however, this was due to the fact that only a handful of BE packets reached their destination in these high-load conditions (as confirmed by Figure 7c, discussed later on), and since the delay statistic was only measured for non-dropped packets, these few packets that remained took advantage of the very few transmission opportunity windows that came up following EXP packet drops, which were accounted for at loads greater than 0.8. Figure 7: Performance evaluation vs. load for three combined flows (CEXP, EXP, and BE). Finally, Figure 7c displays the percentage of packet drops for each protocol and each flow. The results in Figure 7c confirmed the results displayed in Figure 7a,b, showing that CEXP traffic flows exhibited zero packet drops for both protocols, while for the EXP and BE traffic classes, packet drops were in tandem and greater than zero for loads >0.4 under the gMT-MAC protocol due to buffer overflows. Under the qMT-MAC protocol, however, the EXP traffic class maintained a clear advantage, since the EXP traffic flow exhibited non-zero packet losses only when the load approached the system's capacity at 0.8, again due to buffer overflows, while for BE traffic, non-zero packet losses occurred and increased rapidly when the load surpassed 0.3 and reached up to 100% at load values of 0.7. Beyond a 0.7 load value, BE packet drops showed a limited decline, as at the same time, packet drops occurring in the EXP queue resulted in some infrequent gaps in the PS, which translated to transmission opportunity windows for the BE flow. Figure 8 presents the performance evaluation of the qMT-MAC protocol under the three PS execution policies, aiming to further enhance the priority of EXP packets over BE packets, i.e., EXP priority and Pre-emption priority. This simulation considered a network where a node concurrently serves an EXP and a BE flow. Again, CEXP traffic has an IFG of five, denoting a constant 0.2 (20%) normalized load generation, while the remaining 80% of bit rate capacity (800 Mbps) remained free for the EXP and BE flows. The fiber length was set at 1 km, and the normalized load displayed at the x-axis took values of 0.1-1.0 with a step of 0.1. Similar to the results of Figure 7, the produced load refers to individual EXP and BE traffic, which were assumed to have the same load, i.e., both EXP and BE flows increased concurrently. Figure 8a presents the throughput performance results vs. load, while t 8b presents the packet drop percentage vs. load. As can be seen in both figures, results are grouped based on the type of flow, while the same trends as in the case of Figure 7 were observed. CEXP traffic exhibited constant throughput output and zero packet drops irrespective of the PS execution policy, while EXP flows gained priority over BE flows, resulting in a linear increase of the achieved throughput until the system's capacity was reached at a 0.8 load and packet drops started to occur. On the contrary, the lower priority of BE flows resulted in a throughput decrease and higher packet drops at loads higher than 0.4 when the aggregated CEXP/EXP/BE load reached the system's capacity.