# QoS-Aware Flexible Handover Management in Software-Defined Mobile Networks
## 2 Related Works  
As explained above, the separation between the control and forwarding planes allows for flexible configuration and provisioning for the network protocols in a centralized way. This means that new protocolsand applications can simply be provided through the control plane functions without the requirement of specific hardware deployment or the independent access and configuration of each hardware device. As a result, the control plane is responsible for configuring and controlling network nodes to provide mobility management through the programmable interfaces. Based on these properties, research works have been undertaken to provide mobility management in SDN-based networks. As an initial SDN work, OpenRoads [15] provided flat mobile wireless networks in which multiple wireless technologies are connected through the unified network substrate. In OpenRoads [15], the flexible mobility management, such as multicasting transmission during handover, can be provided by incorporating dumb wireless terminations and switches controlled by the SDN controller. On the other hand, research efforts have been undertaken to apply existing mobility protocols into SDN-based networks. Among them, several works have been based on the well-known IP mobility protocols; in particular, proxy mobile IPv6 (PMIPv6) standardized by IETF [16]. PMIPv6 is a network-based mobility management protocol where a core entity called the local mobility anchor (LMA) plays the role of the physical mobility anchor point to establish the appropriate tunnel with mobility access gateways (MAGs) after handover based on the binding updates of the user information. Compared to the legacy PMIPv6-based architecture, where LMA and MAG nodes are physically deployed in the forwarding plane, the SDN-based PMIPv6 separates the mobility functions of LMA and MAG from the forwarding plane nodes, which can provide efficient route management in the forwarding plane [17; 18]. In addition, many works have applied the SDN approach into the evolved packet core (EPC) architecture [11; 19; 20; 21; 22; 23; 24]. Compared to the conventional EPC architecture, SDN-based EPC architecture can provide cost-efficient network operation and traffic optimization by reducing the hardware/vendor dependency and flat networking. In order to overcome the limits of current mobility management, such as routing complexity, tunneling overheads, and inefficient resource consumption, enhanced mobility support schemes have been researched using SDN-based flexible traffic engineering and centralized controllability [19; 20; 21; 22; 23; 24]. However, most of these approaches only provided a general handover management procedure, which also has potential limits when the QoS requirements during handover change or new mobile services with different QoS features appear. In addition, it can be noted that an overly strict handover procedure is also utilized in the conventional EPC without the consideration of different QoS requirements. On the other hand, new, optimized mobility management schemes have been researched considering the specific QoS features [20; 21]. For example, SDN-based D2D joint and half handover procedures have been proposed [20] which enhance the performance in terms of the amount of signaling messages, handover latency and missing handover rate. However, those works have focused on specific QoS requirements and provided enhanced or new mobility management schemes for those scenarios. In addition, to the best of our knowledge, there have been no efforts to provide generalized differential mobility management procedures based on the different QoS requirements through the flow path management from the core to access networks taking advantage of SDN's flexibility and controllability. Recently, distributed mobility management (DMM) has emerged, providing a flat mobility architecture that enables traffic to be anchored locally by exploiting different gateways that are closer to the edge. In order to provide DMM, an SDN-based approach is one of the candidate solutions [19].