# QoS-Aware Flexible Handover Management in Software-Defined Mobile Networks
## 4 Performance Evaluation
### Packet Loss  
The packet loss (PL) for an MN can be defined as the sum of the lost packets for all handovers in a session [52]. This means that it can be proportional to the handover latency (HL). Since SDN-based PMIP, Class 1 and Class 4 do not support the buffering mechanism, all the packets during HL will be lost. Compared to these methods, SDN-based EPC, Class 2 and Class 3 have buffering mechanisms. Therefore, PL can occur only during L2 handover (\(T_{L2}\)), the transmission time for L2 statistical reports (\(T_{stat}\)) and the time for the flow-mod message (\(T_{FM}\)). It can be noted that SDN-based PMIP and SDN-based EPC have the same HL as Class 1 and Class 2/Class 3, respectively. Therefore, PL can be defined as follows:  
\[ \begin{array}{l}\small\begin{array}{l}\small\begin{array}{l}\small{P}{ \rm{I}}^{\rm{prop}}_{\rm{class1}}=\frac{1}{E(T)}{\cdot}p{\cdot}{H}^{\rm{prop}}_{ \rm{class}}\cdot{\lambda}_{\rm{{s}}}\cdot E(S)\end{array}\end{array}\end{array}  \tag{7}\]  
\[\begin{array}{l}\small \begin{array}{l}\small\begin{array}{l}\small{P}{ \rm{I}}^{\rm{prop}}_{\rm{class4}}=\frac{1}{E(T)}{\cdot}p{\cdot}{H}^{\rm{prop}}_{ \rm{class4}}\cdot{\lambda}_{\rm{{s}}}\cdot E(S)\end{array}\end{array}  \tag{8}\]  
\[\begin{array}{l}\Figure 3a,b show the signaling cost according to the rate of user mobility and average cell residence time, respectively. From both figures, it can be seen that Class 3, which has the same signaling cost as SDN-based EPC, has the highest signaling cost because it supports buffering and pre-updates for flow entries, guaranteeing the strictest handover policy (loss-less with minimum handover delay). Since Class 2 also supports a buffering mechanism which requires data delivery and buffering cost, it has a higher signaling cost than Class 1 and Class 4 which do not support a buffering mechanism. On the other hand, Class 1, which has the same signaling cost as SDN-based PMIP, has the lowest signaling cost because it does not provide buffering and pre-updates for flow entries but only performs flow entry updates in response to the router solicitation from the MN. In addition, both figures show that the signaling cost can increase when users are more mobile because signaling occurs based on the number of handover operations. From the comparison between Class 2 and Class 4, we can see that signaling costs for buffering operations are much higher than those with only pre-updates for flow entries. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Value** & **Parameter** & **Value** \\ \hline \(\lambda_{\text{s}}\) & 0.1 (flows/s) & L\({}_{\text{STAT}}\) & 96 Byte \\ E(s) & 10 (packets/flow) & L\({}_{\text{RS}}\) & 52 Byte \\ P & 0.1\(\sim\)1 (handoff/s) & L\({}_{\text{RA}}\) & 80 Byte \\ E(T) & 10\(\sim\)100 s & B\({}_{\text{w}}\) & 1 Gbps \\ d\({}_{\text{MN-A2S(1)}}\) & 1 hop & B\({}_{\text{wl}}\) & 100 Mbps \\ d\({}_{\text{A2S(1),3-Ctrl}}\) & 10 hops & \(\alpha\) & 1\(\sim\)10 ms \\ d\({}_{\text{CS-Ctrl}}\) & 7 hops & \(\beta\) & 1\(\sim\)10 ms \\ d\({}_{\text{CS-A2S(1)}}\) & 3 hops & T\({}_{\text{L2}}\) & 100 ms \\ L\({}_{\text{PI}}\) & 32 Bytes & T\({}_{\text{AC}}\) & 15 ms \\ L\({}_{\text{FO}}\) & 24 Bytes & BC\({}_{\text{buff}}\) & 6 \\ L\({}_{\text{FM}}\) & 56 Bytes & L\({}_{\text{Data}}\) & 1518 Bytes \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Parameter values. Figure 3: Signaling cost according to the rate of user mobility **(a)** and the average cell residence time **(b)**. Figure 4a,b show the handover latency according to the wired and wireless link delay, respectively. From both figures, we can see that Class 3 and Class 4 have the same, lower handover latency because both support pre-updates for flow entries. More specifically, compared to the case in which the first data packet after handover can be transmitted through the pre-updated flow path in Class 3 and 4, the packet can be delivered after the last flow-mod message is received in the CS from the SDN controller in Class 1 and 2.