# A Hybrid Route Selection Scheme for 5G Network Scenarios: An Experimental Approach
## 2 Related Work
### Hybrid Routing Schemes in Wireless Networks  
Hybrid route selection schemes consist of centralized and distributed mechanisms that cooperate to determine the least cost routes (e.g., with lower traffic loads and the number of hops).  
In [37], a hybrid route selection scheme consists of a centralized mechanism at the control plane and a distributed mechanism at the data plane to shift traffic intensity from congested routes to routes with less traffic. The route update procedure consists of two mechanisms: (a) proactive route updates from the CC with minimum delay; and (b) reactive route updates from the CC after data transmission completes in a node in the data plane. Therefore, the proposed algorithm provides an ingress threshold to determine the congestion level of each node before a route update takes place. The proposed scheme is shown to improve load balancing and increase the network throughput.  
In [38; 39], a hybrid route selection scheme, which consists of proactive and reactive mechanisms, is proposed to establish routes among two types of nodes, namely static and mobile nodes. Firstly, _static nodes_, which have lower dynamicity and energy constraints, perform: (a) proactive route selection to establish backbone routes towards a gateway node for internet access; and (b) reactive route selection to establish routes with mobile nodes. Secondly, _mobile nodes_, which have higher dynamicity and energy constraints, perform reactive route selections to establish better routes (i.e., with lower traffic loads and higher residual energy) towards gateway nodes. The proposed approach is shown to increase throughput, and reduce packet loss rate and end-to-end delay. A similar hybrid route selection scheme was proposed in [39]. The _mobile nodes_ perform the reactive route selection to establish routes with a higher number of static nodes (or a lower number of mobile nodes) in order to improve route stability; the proposed scheme is shown to improve throughput and reduce the delay incurred in the route selection and the energy consumption of mobile nodes.  
In [40; 41], a hybrid route selection scheme, which consists of centralized and distributed mechanisms, is proposed to offload traffic from routes with busier nodes to routes with less occupied nodes. Nodes are segregated into groups, and several nodes in a group are selected as group leaders to communicate with neighboring groups. For intra-group communication, each node selects a route with a lower number of hops and traffic load in a distributed manner. For inter-group communication, with more than a single group leader, a source node can establish more than a single route towards a destination node. The CC selects a route with the lowest number of hops or traffic load and communicates the selected route to the source node. The proposed scheme is shown to increase throughput and channel utilization, as well as reduce the packet loss rate caused by route breakages.  
CenTri is a hybrid route selection scheme that consists of centralized and distributed mechanisms. The centralized mechanism adopts a proactive approach to establish backbone routes using network-wide information in order to search for and use white spaces. In contrast, the distributed mechanism adopts a reactive approach to further improve the routes using local information in order to perform traffic offloading. In comparison with existing works, (a) CenTri considers heterogeneous nodes and networks as seen in 5G, it is different from [37; 38; 39; 40; 41] in terms of the control plane and data plane separation and the platform experimental setup with up to 11 nodes; (b) the traffic offloading mechanism makes it different from [9; 23; 32; 34] as the platform offers a coexistence of proactive-centralized and reactive distributed; (c) the use of D2D communication of the femtocell with a backbone route and the capability of learning the most efficient route with the least presence of PUs and dynamicity of channel availability, which distinguish the platform from [20; 23; 37; 42; 43; 44; 45; 46].