Control Communication in SDN-based Dynamic Multi-hop Wireless Infrastructure-less Networks Ayush Dusia Dept. of Computer & Information Sciences University of Delaware, Newark, DE Email: adusia@udel.edu Vinod K. Mishra US Army Research Lab Aberdeen Proving Ground, MD Email: vinod.k.mishra.civ@mail.mil Adarshpal S. Sethi Dept. of Computer & Information Sciences University of Delaware, Newark, DE Email: sethi@udel.edu Abstract—Nodes in a dynamic wireless network are expected to autonomously self-organize and configure routes for commu- nicating amongst themselves. Such networks have applications in several scenarios, including military, disaster relief, and search and rescue operations. Designing a solution for such networks is challenging because of their unique characteristics. Traditionally, decentralized solutions have been sought-after. In the past few years, Software-Defined Networking (SDN) has emerged as a promising approach for designing effective solutions for different types of networks. In this paper, we present an SDN-based architecture and a control communication protocol for dynamic multi-hop wireless infrastructure-less networks. In particular, the solution is de- signed for networks with 1) node mobility and unreliable con- nectivity, 2) unstructured network topology, 3) limited bandwidth and high interference due to multi-hop communication in a shared channel, 4) no out-of-band communication channel, and 5) no location-tracking services for learning the position of mobile nodes. We evaluate our architecture and control communication protocol in NS-3 and compare the results with two conventional solutions – OLSR and DSDV. The results demonstrate up to 40% reduction in the routing overhead while achieving the same or better throughput than the conventional solutions for networks of size up to 50 nodes. Index Terms—Software-Defined Networks, Multi-hop Wireless Networks, Dynamic Wireless Networks I. I NTRODUCTION A dynamic wireless network is formed by mobile nodes that autonomously self-organize and configure routes for commu- nicating amongst themselves. Node mobility causes dynamic changes to the network topology. Typically, the communica- tion amongst the nodes is multi-hop. Such networks are also called ad hoc networks and support a wide range of applica- tions in non-traditional, sometimes hostile, scenarios. Typical application scenarios include emergency search and rescue operations, military operations, disaster relief efforts, provid- ing connectivity to remote areas, monitoring and collecting environmental measurements, and vehicular communications. Depending on the application, the networks are classified into different categories, such as Wireless Mesh Network (WMN), Vehicular Ad hoc Network (VANET), Wireless Sensor Net- work (WSN), and Mobile Ad hoc Network (MANET). The networks of interest for this paper are MANETs whose distinguishing characteristics include no network infrastructure acting as a gateway or a sink node, unstructured network topology, limited wireless transmission range, and unreliable wireless communication links. Node mobility results in an unstructured network topology. The network experiences high interference caused by nodes in close proximity transmitting at the same time. Nodes have limited power, so efforts are required to optimize the transmissions and minimize the total routing overhead in the network. Wireless links are relatively unstable, mainly due to node mobility, interference, and changes in the environment, causing propagation losses. Link instability makes communication unreliable, especially over multi-hop routes. Designing a solution for such networks is challenging because of all the above reasons. Software-Defined Networking (SDN) has emerged as a promising approach for designing effective solutions for dif- ferent types of networks. The main principle of SDN is to separate the control logic from the forwarding devices and move it to a logically centralized entity, called SDN Controller (SDNC). The SDN architecture allows the behavior of the forwarding devices to be dynamically controlled and managed. It also allows enabling services such as firewall and load balancing without the need of additional devices. SDN was initially designed for wired and datacenter networks, but its application to wireless networks has also proved to be beneficial. A comprehensive survey of the benefits that an SDN architecture can introduce in a wireless network is available in [1]. In addition, an SDN-based architecture also has the potential to improve route selection, spectrum management, and situational awareness in dynamic wireless networks. A basic requirement of an SDN architecture is that IP connectivity should pre-exist for the control communication between SDNC and the forwarding devices. Typically, the control communication is over a secure and reliable channel using a TCP (or TLS) connection. The most widely used protocols for control communication are OpenFlow [2] and ForCES [3]. Depending on the network architecture, the con- trol communication can be either in-band (the same network is used for both data and control communications) or out-of-band (a different network is used for the control communication). A few SDN-based architectures have been proposed in the past for different types of dynamic wireless networks, and their overview is available in [4] and [5]. The proposed architectures are designed with one or more of the following constraints: 1) OpenFlow protocol for the control communication; 2) single hop (direct) wireless link between SDNC and each