# MMNET: A Multi-Modal Network Architecture for Underwater Networking
## 2 Network Architecture
### MMNET Multimodal Routing and Forwarding  
In order to provide personalized underwater network services, MMNET will provide multimodal addressing and routing methods to meet the personalized addressing requirements of applications, provide various addressable and routing capabilities that can be defined, and support multiple converged network addressing and routing considering the complex application scenarios and requirements of underwater applications.  
As shown in the Figure 3, in MMNET, different routing protocols are run on a common hardware platform by using network function virtualization. Different routing protocols run on the same hardware platform in the form of virtual machine (vnf), ignoring the hardware requirements of traditional routing protocols, so that MMNET can better support different routing protocols. With the support of NFV, different routing protocols can run in the same network architecture in parallel. Different routing protocols will not affect each other because of hardware resource occupation. They can provide different routing and forwarding capabilities for different applications in parallel [7; 27]. In MMNET, the virtualization routing protocol communicates with the lower virtualization communication equipment and the upper virtualization application through a fixed interface. At the same time, because MMNET ignores the hardware requirements and connects with the upper and lower layers through fixed interfaces, it can well extend the support of the new architecture.  
Figure 2: Implement of multi-modal access interconnection in MMNET.  
In MMNET, considering the harsh underwater communication environment and tight communication resources, as well as better scheduling routing protocol, the routing control function and forwarding function are concentrated in the same VNF, as shown in Figure 4. As shown in Figure 5, the separation of network control and forwarding can make better use of global information for better routing scheduling in terrestrial networks. However, in UWSNs, the limitations of existing communication modes, such as long propagation delay and valuable communication bandwidth of acoustic communication, and short communication distance between optical and magnetic communication will seriously affect the sending and receiving of control information, so as to affect the actual performance of the whole network. At the same time, compared with the traditional network architecture, the simultaneous operation of multiple routing protocols further increases the exchange of routing control information, which seriously affects the performance of the whole network. If the control function and forwarding function are integrated into VNF, it will lose the guidance of global information on forwarding strategy, but it can effectively save bandwidth resources and improve the response speed of the control algorithm. At the same time, a variety of routing algorithms complement each other, which will effectively reduce the loss of a single routing algorithm due to the lack of global information.  
Figure 3: Implement of MMNET multi-modal routing and forwarding. Each route is organized in the form of virtual machine (vnf), which does not affect each other and runs independently.