# QoS-Aware Flexible Handover Management in Software-Defined Mobile Networks
## 4 Performance Evaluation
### Handover Signaling Cost  
As discussed in [50; 51], there is no unit for the cost parameter, and the cost can be defined to be proportional to the time to transmit or process the signaling messages. In other words, the handover signaling cost is generally proportional to the handover frequency multiplied by the rate of handover users and the cost of the exchanged signaling messages for handover. The handover frequency is in an inverse proportion to the average residence time. The cost of the exchanged signaling messages is proportional to the distance between nodes, which is defined as the hop distance multiplied by the signaling message size. The processing cost of the node can also be included in this cost. Since the SDN-based PMIP and Class 1 of the proposed scheme are in reactive modes, signaling messages are exchanged after the MN moves to AS 2. In the case of the SDN-based EPC and Class 3 procedures, the strictest handover procedure can be provided through the L2 trigger and buffering. The difference between the two procedures is the direct participation of the MN in the handover procedure. In the SDN-based EPC, the MN requests the handover to the controller based on the wireless signal strength. This procedure is assumed to be included in the L2 trigger in Table 2. On the other hand, AS 1 plays this role in the proposed scheme based on the statistics of the MN's traffic. Thus, the L2 trigger is performed by AS 1 instead of the MN in the proposed scheme for Classes 2, 3 and 4 in Figure 2. The required signaling process of other classes exactly follows the handover procedures, as explained in Figure 2. Based on Table 2, the signaling cost per unit of the residence time in the proposed scheme is as follows. In the following signaling costs, FU, RS, PI, PO, RA, and FM mean flow entry updates, router solicitation message, packet-in message, packet-out message, router advertisement message, and flow-mod message, respectively. On the other hand, the signaling costs per unit of the residence time in the SDN-based PMIP and SDN-based EPC are the same as in Equations (1) and (4), respectively. \[ \begin{array}{l}SC_{\rm{dass1}}^{\rm{prop}}=\frac{1}{E(T)}\cdotp(SC_{FU})= \frac{1}{E(T)}\cdotp(d_{MN-AS2}(\frac{l_{RS}}{R_{ui}}+\beta)+d_{AS2-Ctrl}(\frac{ l_{H}}{R_{ui}}+\alpha)+d_{Ctrl-AS2}(\frac{l_{H}}{R_{ui}}+\alpha)+d_{AS2-MN}(\frac{l_{H}}{R_{ui}}+ \beta)+d_{AAS2-MN}(\frac{l_{H}}{R_{ui}}+\alpha))\\ \cdot(\frac{l_{H}}{R_{ui}}+\beta)+d_{CHl-CS}(\frac{l_{H}}{R_{ui}}+\alpha))\end{array}  \tag{1}\]  
\[ \begin{array}{l}SC_{\rm{dass2}}^{\rm{prop}}=\frac{1}{E(T)}\cdotp(SC_{FU}+SC_{ L2}+BC_{CS})=\frac{1}{E(T)}\cdotp(d_{AS1-Ctrl}(\frac{l_{H}}{R_{ui}}+\alpha)+(d_{Ctrl-AS1}+d_{Ctrl- CS})\cdot(\frac{l_{H}}{R_{ui}}+\alpha)+d_{AN-AS2}\\ \cdot(\frac{l_{H}}{R_{ui}}+\beta)+d_{AS2-Ctrl}(\frac{l_{H}}{R_{ui}}+\alpha)+d_ {CHl-AS2}(\frac{l_{H}}{R_{ui}}+\alpha)+d_{AS2-MN}(\frac{l_{H}}{R_{ui}}+\beta)+ d_{CHl-CS}(\frac{l_{H}}{R_{ui}}+\alpha)+B_{CS})\end{array}  \tag{2}\]  
\[ \begin{array}{l}SC_{\rm{dass2}}^{\rm{prop}}=\frac{1}{E(T)}\cdotp(SC_{FU}+SC_{ L2}+BC_{AS2}+BC_{AS3})=\frac{1}{E(T)}\cdotp(d_{AS1-Ctrl}(\frac{l_{H}}{R_{ui}}+ \alpha)+(d_{Ctrl-AS1}+d_{Ctrl-AS2}+d_{Ctrl-AS3}+d_{Ctrl-CS})\\ \cdot(\frac{l_{H}}{R_{ui}}+\alpha)+d_{AN-AS2}(\frac{l_{H}}{R_{ui}}+\beta)+d_ {AS2-CNtrl}(\frac{l_{H}}{R_{ui}}+\alpha)+d_{CHl-AS2}(\frac{l_{H}}{R_{ui}}+ \alpha)+d_{AS2-MN}(\frac{l_{H}}{R_{ui}}+\beta)+B_{CS2}+BC_{AS3})\end{array}  \tag{3}\]