s a mobile access network evolves from 3G to 4G to accommodate dramatically increased mobile traffic, mobile access network infrastructure becomes increasingly chaotic and dense. Researchers are developing various new technologies to efficiently manage mobile access network resources [1] . A software defined network (SDN) has been proposed to offer scalable and flexible management with a logical centralized control model [2] . Mobile access network topology changes caused by user mobility impose big challenges on rule management [3] which plays an important role in the SDN. When mobile users move after being associated to base stations, they communicate with the Internet along different paths on which the corresponding forwarding rules should be deployed in the backhaul of access networks. Meanwhile, each SDN-enabled switch stores forwarding rules in its local ternary content addressable memory (TCAM), which can compare an incoming packet to patterns in all rules at a line rate simultaneously [4] . However, TCAM is not a cost-effective way to provide high performance with its expensive cost and high energy consumption. A limited TCAM size is a major restriction for adopting policies to support flow-based control in large-scale networks [5] . Rule placement optimization is an existing method to improve the processing capacity of data center networks [6] . The mechanism of this method is that by getting information on the whole network, after some analysis on all existing flows, a proper placement strategy can be found to improve the flow processing capacity. However, these optimizing strategies are usually static with a limited number of flows. Furthermore, when the status of flows changes, such as flow destination movement, traffic variation, and so on, updating the rules in all switches is unafordable. Unlike rule placement optimization, which regards a rule space as a limited resource, rule caching strategies use the space efficiently to store rules and cache the most frequentlyused rules in TCAM as caching [3] . Therefore, all rules can be handled in the network via replacement policies, and the performance can be enhanced in terms of high hit ratio. Compared to rule placement optimization methods, rule caching is a better approach to enable the flow-based control to provide both high performance and scalability, especially in a largescale data center network. In the mobile access network, another problem is that user mobility changes the forwarding path of flows, which invalidates the cache strategies designed for stable network connection. Therefore, except for the prediction of the flow traffic, user mobility can be another issue to consider in mobile access networks. Since it is hard to predict user mobility, and a cache mechanism is online processing rather than traditional static rule placement, a mobile optimized prefetching algorithm is more suitable to mobile access networks. To address these problems on rule management in SDNenabled mobile access networks, in this article we set the TCAM as the rule caching and design a two-layer rule space to support a rule caching mechanism. With the consideration of user mobility, we also model the rule optimization problem and design a caching algorithm of prefetching and replacement strategies. This algorithm achieves a high hit ratio by replacing rules to the flow forwarding paths and replacing them integrally with a prediction of user mobility. The rest of this article is organized as follows. The following section reviews the SDN-enabled mobile access network and rule caching. The design of SRCMN and the caching algorithm are then introduced, followed by results of the performance evaluation. The final section concludes this article.  An SDN enabled mobile access network is a future network with great potential to support scalable and flexible network applications. To support various network applications, the SDN-enabled mobile access network usually uses forwarding rules in SDN devices. With a limited rule space in existing SDN devices, a rule caching mechanism is an efficient way to improve network performance. In this article we propose SRCMN, which is a new caching structure to improve network performance with a limited rule space in the SDN-enabled mobile access network. We design a two-layer rule space in each SDN device, which is managed by the SDN controller. We also design a cache prefetching mechanism with the consideration of user mobility. By conducting extensive simulations, we demonstrate that our proposed structure and mechanism significantly outperform original rule space management under various network settings.  Rule Caching in SDN-Enabled Mobile Access Networks
Dong et al. REF find a new caching device named SRCMN to enhance the network performance under constrained conditions in an SDN-enabled network.
Rule caching in SDN-enabled mobile access networks
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Computer Science