# A Congestion Control Strategy for Power Scale-Free Communication Network
## 4 Simulation Results  
### Model-Beijing Power Communication Network  
Based on the complex network theory, the model of the Beijing power communication network in 2012 is built, and its topology characteristics are analyzed [22], as shown in Table 3.  
It can be seen from Table 3 that all node degrees of the Beijing power communication network are distributed between two and nine, and the average degree is 3.2. There are only less than 5% of nodes for which the degree is greater than six, which indicates that the number of nodes of a low degree is far more than those of a high degree. The degree distribution in the double logarithmic coordinates is shown in Figure 8.  
The least square method is used to fit the curve, and the degree distribution function p(k) = 1.928 k\({}^{-2.02}\) is obtained, which satisfies Equation (2) and conforms to the power-law distribution. The scale-free network characteristics have been shown for the Beijing power communication network, and the fitting parameter \(\gamma\) = 2.02.  
The topology model of the Beijing power communication network is built, which includes 533 nodes and 876 links in the network. The local topology diagram of 50 nodes is shown in Figure 9.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \(\mathbf{k}\) & \(\mathbf{1}\) & \(\mathbf{2}\) & \(\mathbf{3}\) & \(\mathbf{4}\) & \(\mathbf{5}\) \\ \hline \(\mathbf{N_{k}}\) & 0 & 252 & 111 & 71 & 48 \\ \(\mathbf{p(k)}\) & 0 & 0.432 & 0.208 & 0.133 & 0.090 \\ \hline \(\mathbf{k}\) & \(\mathbf{6}\) & 7 & \(\mathbf{8}\) & \(\mathbf{9}\) & \(\Sigma\) \\ \hline \(\mathbf{N_{k}}\) & 26 & 12 & 8 & 5 & 533 \\ \(\mathbf{p(k)}\) & 0.049 & 0.023 & 0.015 & 0.009 & 1 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Node degree distribution of the Beijing power communication network (2012).  
Figure 8: Degree distribution of the Beijing power communication network.  
All the simulation experiments in this paper were based on MATLAB (R2013b) and OPNET Modeler14.5, and the experimental operation was supported by a cluster server. The Beijing power communication network is set as the network topology based on the topology model in Section 2, including 533 routers and 876 links. The packet arrivals to a node follow the Poisson process. If the amount of packets in the network continues to grow with the time step, i.e., the number of packets entering the network at each time is more than the number of packets leaving the network, network congestion occurs. Simulation parameters are set as follows: power-law index \(\gamma\) = 2.02; node delivery capacity C = 2 \(\times\) N; cache capacity L = 10 \(\times\) N; and the delivery capacity and cache capacity of the nodes are allocated according to Equation (3). Each step generates R packets, and the proportion of I-level packets is \(\lambda\). The packet length is 2000 bits, and pairs of nodes are connected by a bidirectional full duplex link of same capacity. In order to improve the rationality of the simulation experiment, each R value is calculated by 6000 time steps in the simulation process; then it can be considered that the data flow is basically steady, and the average Rc is determined by the last 1000 steps.