## 1 Introduction  
Wireless sensor networks (WSNs) became increasingly adopted in a wide range of application domains, including security, environment, health, and military. These networks consist of sensor nodes with limited resources concerning energy, memory, and processing [1, 2]. However, the development of WSN applications nowadays requires a high level of quality of service (QoS). In this context, software-defined networking (SDN) [3, 4] is applied with WSNs to increase flexibility. Software-defined wireless sensor networks (SDWSNs) facilitate resource sharing and network reconfiguration [5]. They transfer all management and control tasks to a centralized controller, which has an external power supply. IT-SDN [6] is an SDWSN framework example that has been thoroughly analyzed [7], with the results demonstrating that the performance is comparable with that of the routing protocol for low-power and lossy networks (RPL) [8]. Yet, as well as other wireless networks, different traffic types compete for limited resources across the shared wireless medium, making it problematic to ensure the required QoS level [9]. The IEEE 802.15.4e time-slotted channel hopping (TSCH) [10, 11] technology demonstrated its efficacy with the WSNs [12]. TSCH was evaluated [13] using various scheduling approaches, and the results showed that it was capable of improving the data-delivery rate and delay. TSCH was thus employed to address competition for available resources through slicing [9, 14]. TSCH slices the network into slotframes, which are repeated throughout time. Each slotframe is a set of time instants called timeslots. The TSCH schedule specifies when network nodes must send and receive messages during these timeslots [10]. Several issues about SDWSN on top of TSCH were investigated, including interference and multipath fading [15], traffic competition over the wireless medium [9; 14; 16], mobility management [17], and ensuring the application's requirements [18; 19]. Each of these works concentrated on some scheduling approach to handle these issues. However, most of them did not support network scalability since they used dedicated timeslots in the scheduling approach. [PERSON] et al. [20] addressed the scalability issue over SDWSNs. Nonetheless, the proposed approach was based on the creation of virtual sinks, which necessitates the addition of several radio interfaces. The literature review then revealed that there is still a gap in providing the required QoS level for scalable SDWSNs without requiring any extra radio interfaces. Since using shared timeslots allowed for isolating the different traffic types and supported the network scalability [9; 16], we were encouraged to investigate the usage of these timeslots to maintain the required QoS level. The main contribution of this work is the design and evaluation of the application-aware (AA) scheduling approach, which dynamically alters scheduling to ensure the application's QoS requirements in terms of delivery rate and delay. To the best of our knowledge, this is the first paper to address the issue of ensuring the application's QoS requirements for scalable SDWSNs using shared timeslots. The AA approach is evaluated in two different strategies: (i) compared with the application traffic isolation (ATI) approach [16] and (ii) compared with the application's QoS requirements. We adopt the IT-SDN [6] framework and up to four applications with different priorities (QoS requirements). Moreover, we considered a network with up to 225 nodes and 6 different simulation scenarios varying the metric calculation rate (MCR) and the data traffic rate (DTR). The simulations were carried out using Contiki OS [21] and COOJA [22] simulators. The results showed that the AA approach increased the delivery rate by up to 28% and decreased the delay by up to 57% in comparison with the ATI approach. Moreover, it ensured the application's QoS requirements for an increasing number of nodes.