# A Dual-Connectivity Mobility Link Service for Producer Mobility in the Named Data Networking
## 6 Analytical Investigation
### Cost Modeling
#### 6.1.2 Producer Mobility Link Service  
When an NMP moves to a new NAR's coverage, it restores the connection with the pNAR by sending a face update message to the peer PLMS at the pNAR. Then, it re-synchronizes the transaction states with the peer PMLS by sending a status report message per transaction. Therefore, the handover cost of the PLMS is the sum of the cost of transmitting these control message between pNAR and NMP and the cost of transmitting the (N-K) data segments from the NMP to the pNAR. K means the number of segments that have already been transmitted to the pNAR. As the PLMS can retrieve only the lost data segments using the status report message from pNAR, it does not need to send entire transaction. The hop distance from nNAR to pNAR and weight of wire and wireless link were reflected to the formula. This process allows the NMP to retransmit the portion of the entire data that had not been transmitted to the pNAR. Therefore, the handover overhead of the PLMS applying the NAR crossing rate of the NMP can be represented as  
\[C_{S}^{(PMLS)}= \mu_{a}\{(M_{Update}+M_{Status}) \tag{2}\] \[\qquad*(H_{PtoN}*\alpha+H_{Wireless}*\beta)\}\] \[+\mu_{a}\{((N-K)*M_{Data})\] \[\qquad*(H_{PtoN}*\alpha+H_{Wireless}*\beta)\}\]  
The default parameter values are set as follows: \(P_{Int}\) = 44 bytes, \(M_{Update}\) = 28 bytes, \(M_{Status}\) = 31 bytes, \(P_{Data}\) = 1 MB, \(M_{Data}\) = 1033 bytes, and N = 1024, according to [18; 32; 33; 34]. In addition, \(\alpha\) is set to 1, \(\beta\) is set to 1.5, and R is set to 400 m, based on [35]. We set the value of \(H_{Wireless}\) to 1 and the value of \(H_{PtoN}\) to 1 according to the simulation topology.  
Figure 5a shows the handover overhead of original NDN and the PLMS according to parameter K and \(H_{Hop}\) from the consumer and a new NAR. The handover overhead of the original NDN is always greater than that of PMLS. This is because the consumer in the original NDN mobility scheme must request entire transaction, even if it has already received part of the transaction, whereas the PLMS can retrieve only the lost data segments using the status report message. Therefore, the handover cost of the PLMS decreases as the more segments have already been transmitted to the pNAR. In other words, the smaller the number of segments to be sent after handover, the lower the handover cost. On the other hand, in the original NDN, as the consumer must regenerate an Interest packet even though part of the data segment has already received, the handover cost of the original NDN is proportional to the number of hops (\(H_{Hop}\)) from the consumer to the new NAR. Also, the larger the total size of data which the producer must send back to the consumer, the greater the handover cost of the original NDN would also increase. By contrast, in PLMS, the handover operation occurs only between the producer and the previous NAR, so the handover overhead is constant regardless of \(H_{Hop}\).  
Figure 5b shows the handover overhead versus velocity (v). In original NDN mobility and PLMS, the handover overhead increases in direct proportion to increases in the vehicle speed, but the handover overhead of the original NDN mobility is higher than that of PLMS. This is because the signaling required for handover is limited to 1 hop in the case of PLMS, while the signaling required  
for original NDN mobility increases according to the number of hops between the consumer and the new NAR.