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sdnMAC: A Software-Defined Network Inspired MAC Protocol for Cooperative Safety in VANETs

The performance of a vehicular ad hoc network (VANET) largely depends on the underlying medium access control (MAC), as it determines the schedule utility of physical resources. However, in existing time-division multiple access (TDMA)-based MAC protocols, a node usually acquires slots based on what each node senses, which is typically the coupling of the control and data plane. This coupling makes the TDMA protocols unable to rapidly and agilely deal with the challenges in VANETs, such as high mobility and dynamic network densities. Inspired by the software-defined network (SDN), we propose a novel SDN-based MAC protocol, named sdnMAC, to handle these challenges. A novel roadside openflow switch (ROFS) is designed as the roadside unit, controlled by the openflow controller. The sdnMAC can be divided into two tiers, the management of ROFSes (MA-ROFS) by the controller and the management of vehicles (MA-VEH) by ROFSes. In MA-ROFS, the controller schedules the cooperative sharing of time slot information among ROFSes. In MA-VEH, each ROFS allocates slots based on this shared information, thus decoupling of the control and data plane. This decoupling provides great rapidness and agility to sdnMAC, thus handling the rapid mobility and varying vehicle densities. Extensive simulations using network simulator NS3 and traffic simulator SUMO are performed. It is shown that the sdnMAC protocol can better meet the requirements of cooperative safety in VANETs.