# A Reliable Routing Algorithm Based on Path Satisfaction in the Energy Internet
## 3 Network Architecture and System Model  
### Network Architecture  
In the EI, the IP layer and the optical layer are separately planned and maintained in the communication subsystem. On the one hand, the two layers do not perceive each other, that is, the IP layer knows nothing about the optical network topology, link protection, resource use, etc. Meanwhile, the optical networks do not identify different kinds of services and specific requirements, and they only negatively provide static and rigid channels to services [28; 29]. Moreover, there is a mismatch in service granularity in the two layers due to independent networking modes and switching approaches. Hence, the opaqueness and inconsistency decrease the resource utilization, degrade the performance, and increase the capital expenditure (CAPEX). SDN based on the OpenFlow protocol is known to be the separation between the control plane and the forwarding plane. The control plane masters a global view of the whole network, which is facilitated by centralized management. Furthermore, an increasing number of studies have extended the OpenFlow protocol from computer networks to optical networks, that is, software-defined optical networking (SDON) [30; 31]. This provides a promising solution to overcome the barriers between the IP layer and the optical layer [32]. The network function virtualization (NFV) paradigm enables us to fulfill the traditional network functions of utilizing virtualization. Here, the physical network is divided into multiple virtual networks through virtualization technology, and different kinds of services are separately transmitted on these virtual networks. Subsequently, the combination of SDN and NFV plays a major role in the implementation of a cross-layer coordinative transmission network framework. This improves the flexibility and the availability of optical resources and enhances network intelligence. Compared with the distributed network architecture, the centralized communication network facilitates network management, resource scheduling, and service differentiation. To address this issue, we put forward a cross-layer network architecture based on SDN to fulfill the centralized management and control of the EI in this section. An evolved intelligent communication architecture considering system stable operation and the economical factor is shown in Figure 1. This is a typical layered structure. It not only leverages the advantages of flexible resource scheduling in the IP network but also the large volume and high rate in the optical networks [33]. Especially, prompted by Optical Orthogonal Frequency Division Multiplexing (O-OFDM) and subcarrier multiplexing technology, we conducted the research based on the EONs. Here, the controller in the top layer exchanges information with the IP controller and the optical controller to obtain the global view of the whole network (e.g., the network topology and bandwidth utilization). After all, traditional routers and configurable SDN switches coexist in the IP layer. Moreover, various optical devices in addition to O-OFDM-based bandwidth-variable transponders (BVTs) and bandwidth-variable optical cross-connects (BV-OXCs), such as the extended OpenFlow Protocol (OFP) based on the bandwidth-variable OpenFlow switch (OF-BVOS), are leveraged in optical networks as well. Here, BVTs transmit/receive data and adjust spectrum resources in terms of service requests. The BV-OXCs are responsible for the setup of lightpaths and spectral resource accommodation. The OF-BVOS at the link of the network often connects the core network with various access terminals. Similar to the BV-OXC, it adjusts the bandwidth rate according to the service requests and determines the appropriate modulation format for bandwidth tuning [34]. Figure 1: Architecture diagram for the Energy Internet. It describes a cross-over architecture involving an IP layer and a transmissions layer, which covers three layers of the communication network from the prospect of Software Defined Networking.