# A Performance Evaluation for Software Defined Networks with P4
## 5 Results and Analysis of Tier 1--Single Type of Traffic Run
### Case Study 3--UDP  
In case study 3, UDP traffic was generated via file downloads using iPerf. Clients downloaded a file of 1 GB from respective servers for multi-path and grid topologies, and considered a UDP transmission of 1200 s for the Internet topology. The results of the experiments are presented in Figure 6 together with a summary of the results given in Table 3.  
For all three experiments, Figure 6a-c show that _SDN+P4_ achieved a higher and constant throughput in comparison to _SDN+Ov5_. The initial delay in _SDN+Ov5_ was longer than for _SDN+P4_, because the route discovery delay is significant in _SDN+Ov5_ but less so with _SDN+P4_. With a successful population of FlowRules, consuming a greater time for route discovery, bottlenecks can result in real-time applications that involve a demanding service, such as, Vehicle-to-Everything (V2X).  
In Figure 6a, the fixed size UDP download completed earlier for _SDN+P4_ (in approximately 510 s (Figure 6a), than for _SDN+Ov5_ which took approximately 640 s, (Figure 6b). In both _SDN+P4_ and _SDN+Ov5_, traffic traversed the same route for topologies I and II.  
Figure 6: Throughput of UDP data transfer in case study 3. (**a**) UDP transfer of 1 GB data using iPerf in multi-path topology. (**b**) UDP transfer of 1 GB data using iPerf in grid topology. (**c**) UDP transfer for 1200 s using iPerf in the Internet topology.  
In contrast to Figure 6a,b, the UDP traffic file download in iPerf ran for a fixed 1200 s in the Internet topology. As shown in Figure 6c, _SDN+P4_ (red) achieved a higher throughput than _SDN+Ov5_ (blue). In all cases the P4 switches process packet forwarding in _SDN+P4_ faster than non-P4 switches in _SDN+Ov5_.  
For case study 3, Figure 7a-c present jitter for UDP packets. As observed in Figure 7a,b, jitter in _SDN+Ov5_ (the blue lines) indicate a lower jitter than that collated by _SDN+P4_. Albeit being recorded for a fraction of a few seconds in a quasi-periodic trend, an argument can be presented that these should not contribute towards an application that requires stringent jitter constraints. The primary reason for this quasi-periodic pattern of higher jitter is the higher throughput that was recorded by _SDN+P4_. This has been corroborated by [PERSON] et al. [75]. In Table 3, _SDN+Ov5_ recorded an average jitter of 0.298 ms while _SDN+P4_ produced an average of 0.231 ms using Equation (1).  
\[\frac{1}{M}\sum_{f=1}^{M}\sum_{i=1}^{N_{f}}{J_{fi}}/{N_{f}} \tag{1}\]  
Here \(M\) represents the number of flows in the network, \(N_{f}\) denotes the number of packets in flow \(f\) and \(J_{fi}\) represents the jitter in packet \(i\) of flow \(f\). With the application of Equation (1) and the analysis of jitter, _SDN+P4_ recorded a reduction in jitter of 22% in comparison to _SDN+Ov5_.  
Table 3 summarises the performance metrics in terms of throughput, packet loss, delay, amount of data transmitted and transmission time for this group of experiments, averaged over the respective connections given in Table 1. In all cases, _SDN+P4_ has demonstrated a significant improvement in network related statistics in comparison to _SDN+Ov5_. For example, the grid topology has demonstrated a 13% improvement in throughput for _SDN+P4_ in comparison to _SDN+Ov5_. _SDN+P4_ has reduced the packet loss from 22% to 9%, a reduction of 59%. Recorded delay for UDP traffic has reduced from  
Figure 7: Jitter of UDP data transmission in case study 3. (**a**) Jitter experienced for UDP Transmission in multi-path topology. (**b**) Jitter experienced for UDP Transmission in grid topology. (**c**) Jitter experienced for UDP Transmission in the Internet topology.  
1.95 s for _SDN+OvS_ to 0.32s for _SDN+P4_, a reduction of 83%. Lastly, the total transmission time has reduced by 14% due to the faster download speed achieved by _SDN+P4_ over that achieved with _SDN+OvS_. Although the above results for each case study were conducted on software switches, the experiments can be conducted on hardware switches to further support our hypothesis for improved results [21].