# MPResiSDN: Multipath Resilient Routing Scheme for SDN-Enabled Smart Cities Networks
## 3 Related Work
The results showed that the lightweight SDN architecture outperformed traditional architecture in terms of delivery ratio, latency, and packet overhead. Here, the researchers attempted to improve resilience by improving network performance, which leads to improved availability of network services. However, they only considered normal network operation when no external challenges were presented. Our work differs in that it aims to improve the resilience of smart city networks against external challenges, such as natural disasters. We utilize SDN's programmability feature to implement multipath routing to increase the availability of network services in smart cities, even under difficult circumstances, such as natural disasters. Multipath mechanisms, such as path diversification, are considered effective solutions to obtain high communication reliability between disconnected pairs [51]. The multipath concept has been used by researchers to improve various aspects of smart city networks at different network layers. [PERSON] et al. [52] introduced the potential of integrating Multipath TCP (MPTCP) with SDN in smart cities to improve Vehicle-to-Infrastructure (V2I) communication. They evaluated the performance of MPTCP for V2I connectivity in SDN-controlled small cells of DSRC and Wi-Fi. The results showed that MPTCP improved network resilience to internal failures caused by delays in flow setup or handovers. Other researchers studied utilizing SDN along with multipath mechanisms to achieve resilience outside of the context of smart cities. [PERSON] et al. [53] attempted to improve the resilience of SDNs against security attacks by implementing an algorithm that utilized a network-coding technique together with multipath routing. The results showed that the proposed algorithm improved network resilience to passive security attacks by approximately 20%. In addition, [PERSON] et al. [54] introduced a cross-layer resilient routing protocol stack for survivable network communication during regional challenges. The protocol, which they call GoeDivRP, operates based on SDN, collects network statistics, and calculates multipath communications. The protocol was implemented in the NS-3 network simulator and compared to Multipath TCP. The results showed that the protocol stack provided higher throughput and resilience against regional challenges compared to Multipath TCP. Multipath routing has also been used with SDN to enhance QoS. [PERSON] et al. [55] proposed a general SDN-based framework to route multi-stream transport traffic over multipath networks. The system provides an interface for applications to specify multi-stream rules. Then, it utilizes SDN to ensure that the multiple streams follow the multiple paths based on the specified rules. The framework improved QoS in terms of delay and throughput. To summarize, SDN technology has been used as a foundation to improve different aspects of smart city networks. It has been used to improve smart city network security [31; 32; 33; 34], 5G network performance [35; 36], transferring and processing of big data [37; 38], and to balance sensor loads [39]. In addition, SDN technology has been used to improve surveillance systems in smart cities [40; 41; 56]. It has also been utilized to manage traffic effectively [42; 43; 44; 45; 46]. However, none of these studies addressed utilizing SDN to improve network resilience under challenging external conditions. We note that [PERSON] and [PERSON]. [50] addressed using SDN to improve network resilience; however, they only considered internal challenges, and they only evaluated their system under normal operating conditions with no external challenges present. Moreover, they investigated using a lightweight SDN architecture to achieve network resilience, whereas our study uses multipath routing. Multipath routing has been used to improve resilience with SDN by [PERSON] et al. [52]; however, they did not consider evaluating network performance under external natural challenges. Similarly, [PERSON] et al.