# On the Fidelity of NS-3 Simulations of Wireless Multipath TCP Connections
## 6 Results
### MPTCP Throughput with Handover  
We study the impact on the performance of MPTCP when a handover is executed at the LTE system. Two types of handover procedures are investigated, namely X2-based handover and S1-based handover. The X2-based handover is an intra-RAT handover, which depends on the interaction between the serving and target eNodeBs via the X2 interface. In this case, the handover decision is made by the serving eNodeB based on the measurement report received from the UE. The serving eNodeB then directly notifies the target eNodeB by sending a handover request message over the X2 interface. The core-network (MME/SGW) is involved only at the end of the X2-based handover procedure. When there exists no X2 interface between the eNodeBs or when the handover is towards another RAT (inter-RAT handover), the S1-based handover procedure is utilized. In this procedure, the handover signaling happens through the MME--that is, when the serving eNodeB decides to perform a handover, it first notifies the MME via the S1 interface. Both X2 and S1 handovers are hard handovers, which implies that a short service interruption is anticipated when the handover is performed. The throughput performance of MPTCP handover is examined in the testbed by performing an S1-based handover while transmitting a 50 MB file from a sender node to a receiver node. The handover experiment is executed by gradually attenuating the transmission power level of the serving eNodeB while increasing the transmit power of the target eNodeB during the data transfer. The handover is initiated when the UE receives much less transmission power from the serving eNodeB than the target eNodeB. Thus, the LTE USB adapter of the sending node (UE) is forced to perform a handover to the target eNodeB. An X2-based handover is investigated in the simulator since it is the only type of handover currently implemented in ns-3. This requires an X2 interface link to be created between two eNodeBs in the simulation scenario. Like the testbed, the handover is performed while transferring a 50 MB file from a sending node to a receiving node. The handover is triggered in the simulator while changing the relative position between the UE and the eNodeBs. Once the distance between the UE and the serving eNodeB becomes significantly longer than the distance between the UE and the target eNodeB, the handover occurs from the serving eNodeB to the target eNodeB. \begin{table}
\begin{tabular}{l l l l l l l l l l l l l l l l l l} \hline \hline
**RTT (ms)** & \multicolumn{3}{c}{**OLLA**} & \multicolumn{3}{c}{**LLA**} & \multicolumn{3}{c}{**Cubic**} & \multicolumn{3}{c}{**Weeps**} \\ \hline  & **TB** & **Sim** & **TB** & **Sim** & **TB** & **Sim** & **TB** & **Sim** & **TB** & **Sim** & **TB** & **Sim** & **TB** & **Sim** & **TB** & **Sim** \\  & **LTE** & **LTE** & **Wi-Fi** & **Wi-Fi** & **LTE** & **LTE** & **LTE** & **Wi-Fi** & **Wi-Fi** & **LTE** & **LTE** & **Wi-Fi** & **Wi-Fi** & **LTE** & **Wi-Fi** & **Wi-Fi** \\
**Average** & 3.13 & 1.76 & 18.27 & 18.88 & 3.45 & 1.99 & 19.35 & 19.83 & 3.08 & 1.21 & 16.54 & 18.24 & 3.94 & 3.05 & 20.43 & 19.98 \\
**Std** & 1.94 & 1.29 & 2.52 & 2.54 & 1.5 & 1.14 & 2.12 & 1.30 & 1.3 & 0.11 & 0.91 & 2.47 & 0.97 & 0.53 & 0.88 & 0.75 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Setup 2 uplink RTT for 75 MB data flows. Figure 14: Setup 2 uplink MPTCP RTT for 75 MB flows. The S1-based or X2-based handover is set to happen around the middle of the data transfer. The handover-related LTE parameters are kept the same in the testbed and the simulator. For instance, we use the same handover algorithm, A2A4-Reference Signal Received Quality (RSRQ), with the testbed and simulator. The Radio Link Control (RLC) layer's transmission mode is set to Acknowledged Mode (AM) in both the testbed and simulator. Figure 15 shows the overall MPTCP throughput achieved when an LTE handover is performed in Setup 1. Higher throughput is observed with the simulator when compared to the testbed.