# A Congestion Control Strategy for Power Scale-Free Communication Network
## 2 Power Communication Network Model  
The high reliability power communication network architecture is composed of the core network, backbone network and access network, as shown in Figure 1.  
The provincial control center and the provincial backup control center are set as core nodes; the dispatching stations and core substations are set as backbone nodes; the 110-k  
Figure 1: Power communication network architecture.  
substations are set as access nodes. The links of provincial control center and core substations are ring connection, and the links of dispatching stations and substations are dual homing connection, as shown in Figure 2.  
Power communication network is a typical complex network with the scale-free characteristic. Based on the idea of graph theory, the topology model of the power communication network is built, and the modeling rules are as follows.  
1. The provincial power communication network is set as a unit, and only the communication networks of 110 kV and above are considered, including power plants, substations and dispatching institutions.
2. The communication nodes and dispatch centers of the stations (power plants, substations and converter station) are abstracted as nodes without differences.
3. The communication lines between communication nodes are abstracted as edges. The communication lines are bidirectional communication, and the differences between the communication lines are ignored, that is none of the edges have weights or direction.
4. Multiple communication links in the same direction are merged, and self-loops are eliminated.  
Based on the modeling rules, the power communication network can be built as an undirected graph with N nodes and M edges, that is:  
\[\mathrm{G}\ =\ (\mathrm{V},\ \mathrm{E},\ \mathrm{\Omega}) \tag{1}\]  
where \(\mathrm{V}=\{v_{1},v_{2},...,v_{N}\}\) is the set of nodes in the network and \(\mathrm{E}=\{e_{ij}\}\) is the set of links. When \(\mathrm{e_{ij}}=1\), there is a link between nodes \(\mathrm{v_{i}}\) and \(\mathrm{v_{j}}\) otherwise, \(\mathrm{e_{ij}}=0\). \(\mathrm{\Omega}=\{\omega(e_{ij})\}\) denotes the set of link weights.  
The typical scale-free characteristic is shown in the power communication network, and the degree distribution p(k) follows the power-law distribution, as shown in Equation (2).  
\[\left\{\begin{array}{c}\mathrm{p(k)}=\ \mathrm{N_{k}}/\mathrm{N}\\ \mathrm{p(k)}\sim\mathrm{k^{-\gamma}}\ (2\ \leq\ \gamma\ \leq\ 3)\end{array}\right. \tag{2}\]  
where k is the node degree, \(\mathrm{N_{k}}\) is the number of nodes with the degree k, p(k) is the proportion of nodes with degree \(k\) and \(\gamma\) is the exponent. The power-law distribution shows that the scale-free network has strong heterogeneity, and there are a few hub nodes with very large degrees.  
There is a huge amount of data, and the characteristics of the complex relationship between nodes are shown in the power communication network. In the process of packet delivery, the load distribution is uneven, and the local congestion usually occurs at the hub nodes. If the heavy load on  
Figure 2: Different network architectures of the power communication network.  
hub nodes can be redistributed to the idle nodes when congested, then the hub nodes can avoid being more congested. Therefore, how to improve network throughput, reduce network congestion and ensure the efficient transmission of important packets under the limited condition of nodes' resources have become urgent issues.