# Context-Based Dynamic Meshed Backhaul Construction for 5G Heterogeneous Networks
## 2 Traffic Adaptive Dynamic Meshed Backhaul Construction For Outdoor Dynamic Crowd
### C-plane for SDN-Based Mesh Construction  
Dynamic control in the conventional wireless mesh network was mainly based on the IEEE 802.11s standard or OLSR (Optimized Link State Routing) protocol. However, in this in-bandmethod as depicted in Figure 4, since C-plane and U-plane share the same media to optimize the network, it may take several tens of seconds to several hundreds of seconds to accomplish a phase of optimization. The performance is further worsen when the size of the network increases and prevents dynamic control of a large scale wireless mesh network like our considered scenario. More specifically, in-band C-plane (using the same small coverage mmWave interface) yields unwanted control latency due to multi-hop communications to the controller, that reduces the resiliency of the networks in adaptation to environment changes significantly. Therefore, this paper employs out-of-band C-plane via direct communication with a large coverage LTE macro as depicted in Figure 5. On contrary to the in-band method, the out-of-band C-plane make the networks more resilient to environment changes owing to faster adaptation rate incurred from lower control latency. It would be more beneficial for SDN technology [33] to be employed in our considered ODC scenario. In fact, the SDN control of the wireless mesh network based on the out-of-band control plane can succeed in making the network more resilient to environment changes as will be shown in Section 3.2. Figure 4: Conventional C-plane (User centric ON). Figure 5: Proposed out-of-band C-plane (Network centric ON). As explained above, the dynamicity of the traffic distribution thus the dynamicity of the meshed network transformation, necessitates the separation of the C-plane (control plane) and the U-plane (data plane) into different frequency bands. Specifically, this paper adopts out-of-band C-plane via macro LTE to support higher C-plane's delay requirement in our study. Here, the macro base station's carrier of 2 GHz band is adopted as the frequency band used for the control plane to guarantee a large coverage in order to centrally manage context information necessary for the C-plane. Also, in general, the load of the control plane is sufficiently smaller than that of the U-plane, so narrow band communications at 2 GHz band is sufficient. Detailed explanation about the signaling over the adopted out-of-band C-plane for operating the functionality of the SDN controller is depicted in Figure 6, where MANO (Management and Network Orchestration) denotes the controller. The controller located behind the C-plane has three functionalities: context management framework, an optimizer and a SDN controller. The context management framework will gather information about traffic distribution etc. The meshed network structure is optimized by the optimizer. SDN controller sends commands to AP and UE via the C-plane downlink to establish the meshed network as well as the association of UE to a SC-BS in a deterministic way. Detailed interaction between different entities in this figure is explained below. First, the user's request e.g., traffic demand is reported to the network via the 2 GHz band C-plane uplink. Furthermore, the network can predict the user's U-plane radio condition as well as position based on measured RSSI (Received Signal Strength Indicator) and GPS (Global Positioning System) etc. Nowadays, there are rigorous research activities to enhance accuracies of such context information and details are our of scope of this paper. The context management framework inside the controller gather such context information i.e., traffic demands, UEs' positions etc. Based on the information, the optimizer analyzes the traffic load of the entire network and calculates the optimum backhaul path as explained in Section 2.3. Again, based on the optimization results, the optimum backhaul path information is then delivered as the commands from the SDN controller to all APs using the 2 GHz band C-plane downlink.