# An Optimization Framework for Data Collection in Software Defined Vehicular Networks
## 2 Background and Literature Review
**Software defined networking** is an emerging concept that enables network programming by promoting logical centralization of the network control, by separating the basic network control logic from switches and routers [21]. Traditional networking is hardware-based, where the control plane is distributed among network devices like routers. SDN involves the separation of the data plane and control plane compared to traditional network architecture, which encapsulates both data and control plane in the network devices [22]. SDN has three planes: an infrastructure plane, a control plane, and an application plane. Among numerous pros SDN brings in, flexibility and programability stand out compared to conventional networks, as software can be produced via different vendors easily. In SDN, controlling is logically centralized, where a single protocol can be used to communicate between any number of hardware devices. SDN has greater visibility and also has the ability to define secure pathways compared to traditional hardware-based networking [23]. Using SDN, many new capabilities and services have been enabled, such as network virtualization and automation, orchestration for cloud services, traffic engineering, software engineering, etc. [24]. However, it has been noted that SDN faces challenges in terms of security, the inability of the centralized controller to single-handedly control all the traffic, the existence of only a few protocols to communicate between controller and applications, difficulty in integration with old networks that do not support OpenFlow protocol, etc. [25]. Another serious shortcoming of SDN is reliability, as the SDN controller tends to be a single point of failure [26]. Recently, researchers have applied SDN in a VANET, resulting in a new paradigm called **software defined vehicular network** enabling programmability and flexibility in vehicular networks [27]. Due to the inclusion of SDN in VANETs, many advantages are realized, including the improvement in routing, dynamic allocation of radio interfaces, and adaptive allocation of transmission power of the nodes due to network awareness of the SDN controller [28]. Further, due to the use of SDN, SDVN brings out an efficient network management mechanism for VANETs and due to the collection of network statistics, it improves networking applications such as routing, load balancing, and making global optimizations in VANETs. Further, it promotes network innovation, as new protocols for VANETs can be tested and deployed at a lower cost [29]. However, like any paradigm, SDVN also has its own set of challenges. The paper [30] discusses the security vulnerabilities that exist in each of the three planes of SDVNs. Further, network functions such as routing, and transmission control are challenging in SDVNs due to the high mobility of the nodes and dynamic network topology [31; 32]. Based on the degree of control of the SDN controller, there are three architectures for SDVNs [33]. **Centralized architecture**--This is the original architecture of an SDVN, where the control is logically centralized. In this approach, nodes in the data plane will execute actions according to the flow rules given by the SDN controller. This architecture has higher latency for the control plane communication between nodes and the centralized controller [34]. Further, there is a tendency for error when the control plane communication is lost or disrupted, and the scalability is low in this architecture. **Distributed architecture**--In this architecture, control is distributed among the end nodes where the nodes operate without any guidance from the centralized controller where the operation is similar to original VANETs. This architecture prevents the single point of failure and scalability issues found in the centralized control architecture. However, this architecture consumes more time than the centralized architecture to find the optimal routes [35].