1 Efficient Real–time Content Distribution for Multiple Multicast Groups in SDN–based WLANs Estefan´ ıa Coronado * , Roberto Riggio ‡ , Jos´ e Villal´ on * , Antonio Garrido * * High-Performance Networks and Architectures (RAAP), University of Castilla–La Mancha, Albacete, Spain Email: {Estefania.Coronado, JoseMiguel.Villalon, Antonio.Garrido}@uclm.es ‡ FBK CREATE-NET, Trento, Italy Email: rriggio@fbk.eu Abstract—Wireless networks research and development efforts are largely driven by the increasing interest in multimedia applications. Video streaming services, which often involve strict Quality of Service (QoS) requirements and are very sensitive to delays, represent a significant proportion of these appli- cations. In IEEE 802.11–based WLANs, these services raise several challenges in terms of robustness, reliability and scal- ability, specially when supporting multiple multicast streams at the same time. Nevertheless, traditional network architectures make it difficult to address these problems. In this context, the Software Defined Networking (SDN) paradigm opens new research possibilities by decoupling the control decisions from the data–plane and by improving network management and programmability. In this paper, we present SM-SDN@Play, an SDN–based solution for joint multicast rate selection and group formation in 802.11–based networks. Experimental results show the high performance and reliability capabilities of the scheme, regardless of the application bitrate, the number of clients, and the number of concurrent multicast streams. Furthermore, the channel utilization is greatly reduced with regard to the standard multicast schemes, which allows other applications to be supported without experiencing a performance degradation. We release the entire software implementation under a permissive APACHE 2.0 license for academic use. Keywords—Software Defined Networking, WLANs, IEEE 802.11, multicast, rate adaptation, multimedia, video distribution. I. I NTRODUCTION The emergence of platforms such as Netflix and Youtube has made multimedia content distribution a popular service in the recent years. Furthermore, it is becoming more common that real–time events such as conferences, social events or educa- tional courses are simultaneously transmitted to a wide range of users. In view of this scenario, multicast communications represent an efficient way of delivering the same information to multiple destinations in a scalable fashion. The IEEE 802.11 [1] standard is one of the most widespread technologies for the deployment of Wireless Local Area Net- works (WLANs) and is found in domestic and professional set- tings such as enterprises, campuses and hotels. Nevertheless, multicast communications over 802.11–based WLANs incur in severe reliability issues. In fact, due to the lack of acknowl- edgements and retransmissions, multicast transmissions in 802.11 are performed using the basic Modulation and Coding Scheme (MCS) which results in a high channel occupation. This issue is exacerbated as the applications bitrate increases, and becomes worse in the cases of multiple simultaneous multicast streams. To address these reliability concerns, the IEEE 802.11aa [2] amendment introduces a set of multicast retransmission policies. Nevertheless, no mechanisms for the delivery rate adaptation and multicast group management are specified by the standard. Moreover, due to the widespread use of Wi–Fi compatible devices, IEEE 802.11 amendments aim at maximizing backward compatibility at the expense of inno- vation. In view of this, Software Defined Networking (SDN) changes the traditional network architecture by effectively decoupling the data–plane from the control–plane and by providing network developers with powerful programming abstractions to affect the state of the network. The contribution of this paper is twofold. First, we take advantage of our previous work SDN@Play [3], a multicast MCS selection algorithm, in order to propose a novel multicast group management scheme. This new scheme, named Scalable Multigroup SDN@Play (SM-SDN@Play), jointly drives the multicast MCS selection and the multicast group formation in order to minimize the network–wide airtime utilization and maximize the multicast services reliability. Second, we imple- ment and test SM-SDN@Play over a real world 802.11–based WLAN and we release the entire implementation under a permissive APACHE 2.0 license for academic use 1 . This work extends [3] in three ways. First, as opposed to SDN@Play, the solution presented in this paper indepen- dently selects the optimal MCS for each multicast group. Second, SDN@Play introduced a two–phase algorithm alter- nating unicast and multicast periods, however the duration of such periods was static. SM-SDN@Play, on the other hand, dynamically adapts the duration of the unicast and multicast periods according to the number of active multicast groups. Third, SM-SDN@Play distributes the unicast periods of each multicast group in such a way to minimize the chances that multiple multicast group will operate in unicast mode at the same time. Experimental results show that SM-SDN@Play outperforms the standard IEEE 802.11 multicast schemes in terms of both throughput and channel utilization without requiring any change to the wireless clients. The remainder of this paper is structured as follows. Section II introduces the technical background on multicast communications in 802.11 WLANs. Section III provides an 1 http://empower.create-net.org/