# On the Fidelity of NS-3 Simulations of Wireless Multipath TCP Connections
## 7 Conclusions  
The paper studies the fidelity of ns-3 simulations for dual-homed wireless nodes using Linux-based MPTCP kernel implementation embedded in the ns-3 DCE module. The study is hinged on comparing the ns-3 DCE simulation results with a testbed that allows several dual-homed (LTE and WiFi) wireless nodes to communicate to one another via real Wi-Fi and LTE networks in a controlled environment using different MPTCP congestion control algorithms (LIA, OLIA, Cubia, and wVegas).  
The investigated scenarios reveal apparent differences between the simulator and testbed throughput performance. Generally, it is observed that the data volume, the existence of a bottleneck link, and the employed congestion control algorithm impact the fidelity of the simulation results.  
For instance, in uplink MPTCP packet transfer, the throughput results of the ns-3 simulator are not in a close match with the testbed results with short-lived flows. However, ns-3 DCE generally replicates the testbed throughput results to a good extent for long-lived flows except when the Cubic algorithm is used in a network configuration with a bottleneck link.  
It is found that the MPTCP downlink throughput obtained by ns-3 DCE reasonably matches the throughput measured by the testbed when no bottleneck exists, except for wVegas. However,it slightly underestimates the MPTCP throughput for most of the studied algorithms with the presence of a bottleneck link in the network configuration.  
Moreover, the ns-3 DCE overestimates the MPTCP throughput during handover compared with the testbed when no bottleneck link exists in the simulated network since it does not implement the S1-based handover as the testbed. However, the simulator's MPTCP throughput results reasonably match the testbed results during the handover with the existence of a bottleneck for most of the studied congestion control algorithms as the subflow rates tend to stabilize faster after the handover disturbance.  
Furthermore, it is found that the measured RTT values of the simulator and testbed for Wi-Fi and LTE subflows well justify the mentioned throughput performance. The main reason of the discrepancy between the simulator and testbed results lies in that the ns-3 DCE RTT values significantly differ from their testbed counterparts, although the signal level and MCS values are kept the same for both. This can be attributed to the simplified control plane of the simulator LTE implementation.  
We believe that the ns-3 simulator can replicate the MPTCP throughput results of multihomed (Wi-Fi and LTE) nodes of a real testbed to a good extent only for long-lived uplink connections using LIA, OLIA, or wVegas algorithm and downlink connections using LIA, OLIA, or Cubic algorithm. This also applies to handover scenarios if S1-based handover is implemented.  
[PERSON] built the testbed and the simulation model. She conducted the experiments using the testbed and the simulator. She also contributed to paper writing. [PERSON] designed the network architecture of the testbed. He contributed to the design of the setup topologies and the simulation setting. He also participated in reviewing and writing the paper. All authors have read and agreed to the published version of the manuscript.  
This work was made possible by the UAE University UPAR grant number 31N226.  
The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.