# A QoS-Enabled Medium-Transparent MAC Protocol for Fiber-Wireless 5G RAN Transport Networks
## 4 Results
Flows with a lower IFG (higher load) produced more packets, and therefore, these flows exhibited higher delay increment rates. As a result, it was observed that while CEXP flows with IFGs of 8 and 16 maintained an average packet delay lower than the target of 100 us, the CEXP flow with IFG4 did not and surpassed the above target even at 1 km of fiber length. The greater service time for packets that reside at the back of the queue was also attested by the vertical error bars denoting the delay jitter, confirming that as fiber length (and, consequently, the SF duration) increased, more packets were generated, and packets at the back of the queue experienced higher delays than packets that were at the front of the queue, inevitably leading to higher delay jitter values, which started at around 20 us at 1 km of fiber, reaching up to 75 us at 10 km of fiber. The above discussion showcases that gMT-MAC's gated service policy cannot meet the eCPRI Key Performance Indicators (KPIs) for low-layer CBR FH traffic, both in terms of delay (100 us) and delay jitter (65 ns), whereas the reserved time slot qMT-MAC policy managed to obtain both goals, offering delay values that increased only due to the added propagation delay, while exhibiting zero delay jitter. In this test, all flows for both protocols exhibited zero packet drops, since the aggregated load of 43.75% of the test scenario could be served in a timely manner by both protocols and no buffer overflow events took place. Figure 7 displays the qMT-MAC vs. the SoA gMT-MAC performance comparison for a combination of all three types of traffic versus load. Specifically, this test considered a  
Figure 6: (a) Throughput vs. fiber length for three combined CEXP flows with IFG 4, 8, and 16, respectively, (b) Delay vs. fiber length for three combined CEXP flows with IFG 4, 8, and 16, respectively. network with each wavelength being shared amongst three nodes, while each node serves a different flow type, i.e., one node serves a CEXP flow, one node serves an EXP flow, and one node serves a BE flow. 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) remains 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. In this test, the produced load refers to individual EXP and BE traffic, which were assumed to have the same load, i.e., the load in both EXP and BE flows increased concurrently. By means of Figure 7a, it can be seen that CEXP traffic had a constant throughput output for all loads under both protocols, since in the case of qMT-MAC, CEXP traffic is served in reserved time-slots, while in gMT-MAC, the Round Robin nature of served traffic means that no node is being led to starvation. With respect to EXP and BE traffic flows, however, we noticed that qMT-MAC and gMT-MAC differ greatly, as under gMT-MAC operation, EXP and BE were treated with the same priority and achieved the same plateau of 400 Mbps, while under the qMT-MAC protocol, once the aggregated produced traffic by both flows reached the remaining capacity of the channel at a normalized load of 0.4, EXP traffic flow was prioritized over BE traffic. Specifically, as the load continued to increase beyond 0.4, EXP traffic throughput increased linearly until it reached the maximum value of 800 Mbps. On the contrary, BE throughput decreased steadily as the load increased more than 0.4, since the network's capacity was absorbed by EXP traffic, leading the queue to starvation once the load reached 0.8 and beyond. Figure 7b displays the average delay vs. load for both protocols and all traffic flows. It can be observed that CEXP traffic flows were served in a timely manner under both protocols, and the produced delays stayed below 100 us for all loads, since qMT-MAC reserved the slots for CBR traffic, while gMT-MAC served nodes under the Round Robin paradigm; therefore, each node was guaranteed an equal portion of the Polling Sequence.