Filippo Rebecchi

A joint multicast/D2D learning-based approach to LTE traffic offloading

Multicast is the obvious choice for disseminating popular data on cellular networks. In spite of having better spectral efficiency than unicast, its performance is bounded by the user with the worst channel in the cell. To overcome this limitation, we propose to combine multicast with device-to-device (D2D) communications over an orthogonal channel. Such a strategy improves the efficiency of the dissemination process while saving resources at the base station. It is quite challenging, however, to decide which users should be served through multicast transmissions and which ones should receive the content via D2D communications. The progress of content dissemination through D2D communications depends on how users meet while on the move. The optimal decision for each content depends both on the status of the LTE channel (when the multicast transmission is executed) and on the evolution of the mobility process of the nodes from there on. We propose a learning solution based on a multi-armed bandit algorithm that dynamically selects the best allocation of users between multicast and D2D to guarantee the timely delivery of data. Numerical evaluations are performed to compare our proposal with the state-of-the-art scheme and an optimal but unfeasible strategy. We confirm that a proper mix of multicast and D2D helps operators save resources at the base station and that the learning algorithm can autonomously find a near-optimal configuration in a reasonable time.

Flooding data in a cell: is cellular multicast better than device-to-device communications?

A natural method to disseminate popular data on cellular networks is to use multicast. Despite having clear advantages over unicast, multicast does not offer any kind of reliability and could result costly in terms of cellular resources in the case at least one of the destinations is at the edge of the cell (i.e., with poor radio conditions). In this paper, we show that, when content dissemination tolerates some delay, providing device-to-device communications over an orthogonal channel increases the efficiency of multicast, concurring also to offload part of the traffic from the infrastructure. Our evaluation simulates an LTE macro-cell with mobile receivers and reveals that the joint utilization of device-to-device communications and multicasting brings significant resource savings while increasing the cellular throughput.

Statesec: Stateful monitoring for DDoS protection in software defined networks

Software-Defined Networking (SDN) allows for fast reactions to security threats by dynamically enforcing simple forwarding rules as counter-measures. However, in classic SDN all the intelligence resides at the controller, with the switches only capable of performing stateless forwarding as ruled by the controller. It follows that the controller, in addition to network management and control duties, must collect and process any piece of information required to take advanced (stateful) forwarding decisions. This threatens both to overload the controller and to congest the control channel. On the other hand, stateful SDN represents a new concept, developed both to improve reactivity and to offload the controller and the control channel by delegating local treatments to the switches. In this paper, we adopt this stateful paradigm to protect end-hosts from Distributed Denial of Service (DDoS). We propose StateSec, a novel approach based on in-switch processing capabilities to detect and mitigate DDoS attacks. StateSec monitors packets matching configurable traffic features (e.g., IP src/dst, port src/dst) without resorting to the controller. By feeding an entropy-based algorithm with such monitoring features, StateSec detects and mitigates several threats such as (D)DoS and port scans with high accuracy. We implemented StateSec and compared it with a state-of-the-art approach to monitor traffic in SDN. We show that StateSec is more efficient: it achieves very accurate detection levels, limiting at the same time the control plane overhead.

Should I seed or should I not: On the remuneration of seeders in D2D offloading

Traffic offloading using opportunistic device-to-device (D2D) communications is a new and exciting opportunity for cellular operators to cope with the unprecedented mobile data growth. A limitation of existing proposals is that they assume that all terminals are, by default, involved in the D2D forwarding process. In particular, they do not capture the need to reward seed users. For this reason, we include a rewarding cost in the design of the opportunistic offloading strategy. In our solution, we make the difference between nodes that receive content through the cellular channel only (leechers) and nodes that take part in the forwarding process (seeders). The key point for an operator is to design a global strategy to select which nodes act as seeders and which ones as leechers, in order to reduce the total dissemination cost. We formulate this question as a stochastic control problem that we solve using an application of Pontryagins Maximum Principle. We provide a mathematical framework to devise the optimal strategy for opportunistic offloading under a generic cost model. First, we show that an optimal solution exists; then, from this policy, we extract some insights to develop heuristics. Finally, we discuss the advantages of the proposed model compared to the classic seeder-only model. We demonstrate that separating seeders/leechers leads to better incentive strategies in the most demanding cases of content with a large span of delivery delays.

Traffic monitoring and DDoS detection using stateful SDN

We propose to showcase the benefits of stateful SDN in the context of DDoS detection and mitigation. By delegating some local tasks to the switch rather than relying always on the controller, it is possible to monitor data-plane traffic efficiently and to detect malicious network behaviours with high accuracy. Stateful SDN concepts are employed both to improve reactivity and to offload the controller and the control channel by delegating local treatments down to the switches. The demo illustrates how to protect end-hosts from Distributed Denial of Service (DDoS) attacks. Our approach, named StateSec, is built on advanced in-switch processing capabilities to detect and mitigate threats swiftly. StateSec relies on a detection loop to: 1) match and count a configurable set of traffic features (e.g., IP source and destination, port source and destination) without resorting to the controller; 2) use an entropy-based detection algorithm with such monitored features, 3) detect several threats such as (D)DoS and port scans with high accuracy, and 4) take countermeasures by installing OpenFlow rules at the switch.

Demo: opportunistic communications to alleviate cellular infrastructures: the FP7-moto approach

Over the latest few years, we have witnessed the widespread diffusion of smartphones, tablets, and other mobile devices with diverse networking and multimedia capabilities. Major operators in the US and Europe are experiencing severe problems in coping with the mobile data traffic generated by their users. The main reason is that the trend of traffic demand is exponentially increasing, while the improvements at the physical layer are bounded by the famous Shannon theorem and by the fact that the licensed spectrum is a limited and scarce resource. The FP7 MOTO project proposes to design, implement, and evaluate an architecture that takes full advantage of the latest advances in opportunistic networking to achieve effi- cient traffic offloading.

Circumventing plateaux in cellular data offloading using adaptive content reinjection

Mobile data offloading is a promising strategy to alleviate the burden on the cellular network by leveraging unused bandwidth across different wireless technologies. In this paper, we focus on hybrid offloading techniques involving both Wi-Fi and device-to-device communications. In this context, designing efficient solutions is challenging, as communication opportunities are, by nature, dependent on both individual mobility patterns and availability of the Wi-Fi infrastructure. We propose, design, and evaluate DROiD (Derivative Re-injection to Offload Data), an efficient strategy to finely control the distribution of popular content in urban scenarios. The idea is to use cellular resources as seldom as possible. To this end, DROiD injects copies using the cellular network only when needed: (i) in the beginning, when the Wi-Fi infrastructure is unable to trigger the dissemination, (ii) if the evolution of the dissemination is below some expected pace, and (iii) when the delivery delay is about to expire, in order to guarantee that all destinations receive the data. Our strategy is particularly efficient in highly dynamic scenarios, where sudden creation and dissolution of clusters of mobile nodes prevent proper content diffusion. We assess the performance of DROiD by simulating a traffic information service over two realistic large-scale vehicular datasets with several thousands of nodes. DROiD substantially outperforms other offloading strategies (opportunistic and AP-based), saving significant amount of cellular traffic even in the case of tight delivery delay constraints and energy limitations.

Demo: D2D Rescue of Overloaded Cellular Channels

Mobile data traffic is set to triple in three years from now according to Cisco. This trend is a real challenge for operators since wireless capacity is bounded. To boost network capacity further, operators think about paradigm-shifting solutions to relieve their infrastructures. Recently, data offloading received increasing attention from the research community. Operators may leverage unused bandwidth across different technologies to shift part of the traffic onto less critical infrastructure (e.g., through Wi-Fi access points). In a further evolution, they can also benefit from the widespread diffusion of smart mobile devices with multiple communication interfaces. Users become the heart of the offloading strategy by employing multi-hop opportunistic communications to improve content dissemination, while reducing the load on the wireless infrastructure. We propose an architecture that takes advantage of the latest advances in opportunistic networking to achieve efficient traffic offloading. In this approach, terminals are under continuous control of the operator - the cellular infrastructure serves as a control channel to track data dissemination. The demonstration builds on DROiD [2] as injection strategy, and Epics [1] to distribute data opportunistically.