# A Dual-Connectivity Mobility Link Service for Producer Mobility in the Named Data Networking
## 7 Simulation Investigation
### Simulation Results  
In the simulation investigation, we measured the NDN packet (Interest, Data) sequence in an effort to prove that the proposed scheme could prevent the loss of Interests even in the occurrence of a handover of the NMP. Figure 7a shows the Interest reception sequence at the NMP. The NMP receives the 140 th Interest at 7.02015 s and it receives the 141 st Interest at 9.46955. The figure shows that no loss of Interest occurred even though NMP moved from AP 1 to AP 2. There is a gap of 2.449 s between the reception of the two Interests. The NMP takes 2.4 s to move out of the shadow area (40 m). The NMP and nNAR have a 49.5 ms interaction. In this time, they can exchange four control messages, as the link delay between them is 10 ms. This process is repeated each time the NMP encounters a new AP, as shown in Figure 7a. The NDN packet sequence at the consumer is shown in Figure 7b. The 140 th and the 141 st Data packets are delivered at 7.05008 s and at 9.50909 s after the handover of the NMP has occurred,  
Figure 5: NDN packet sequence at NDN producer and consumer. respectively. The NDN consumer sends the 141 st Interest at 7.05 s and it receives the corresponding 141 st Data packet at 9.50909 s. The delay is 2.459 s, which is less than the default Interest lifetime (4 s). Although there is a time when the consumer does not receive Data for each time there is a handover event of the NMP, seamless Data delivery is always guaranteed to the consumer. Figure 8 shows the NDN packet sequence at the NDN routers. Shown in Figure 8a, the pNAR continues to receive Interests from the consumer even though the NMP has moved to nNAR. After recovering the broken link with the NMP, the pNAR sends the buffered Interests to the NMP. Furthermore, it can be confirmed that the NDN data packets sent from the NMP are delivered to the consumer via pNAR until the routing information by the NLSR is propagated over the network. After the average OSPF convergence time (6 s) has elapsed since the NMP has attached at nNAR, the NAR at which the NDN consumer is attached updates its FIB table. Figure 8b shows that the Interests sent by the consumer are transferred to the nNAR at which the NMP is attached, and that the Data packets corresponding to the Interest are also transferred to the consumer via the nNAR. Figure 9 shows the Round-Trip Time (RTT) between the consumer sending the Interest packet and receiving the Data packet. The RTT increases up to 2.45909 s by the time the NMP is in the shadow area. As the NMP moves toward the center of the nNAR, the RTT decreases continuously. After the routing information is updated by the NLSR, the data packet reaches the consumer via the nNAR, not the pNAR. This was confirmed by the difference between the RTT of the 265 th NDN packet and the RTT of the 266 th NDN packet; the 265 th and 266 th Interests are forwarded to different NARs. The consumer sees that the RTT between sending the Interest and receiving the Data packet is reduced by 20 ms from 60 ms to 40 ms. This is due to the facts that the number of hops the data packet goes through is reduced by two and that each link delay is 10 ms. If the core router to have optimal performance under the constraint that the router's buffer size must be small, the buffer size of the router must be greater than or equal to 2T * C \(\div\sqrt{N}\)[38]. 2T means the Round-Trip Time between producer and consumer, and C stands for bottleneck link capacity between the router and producer. N is the number of flows which share a bottleneck link. We assumed that the capacity of the wired link is 1 Gbps and has a delay of 1 ms, and total 10 consumers send interest to the producer. According to the calculation in the simulation environment,  
Figure 6: Simulation Network Topology. the ideal buffer size required for NAR is about 316K bytes. Figure 10 shows the size of the required buffer according to the time it takes for the NMP to restore the connection with pNAR after the link down event occurs.