Carlo Augusto Grazia

Integration of satellite and LTE for disaster recovery

Wireless communications are critical for public protection and disaster relief (PPDR) professionals during the emergency operations that follow natural or man-made disasters, scenarios in which both commercial and dedicated terrestrial networks often fail to provide the necessary support. The reason is threefold: they simply get destroyed by the disaster, they cannot sustain the sudden surge of network demand or they fail to deliver the necessary bandwidth and/or other QoS guarantees. Because LTE is expected to become the main wireless technology for broadband communication, a lot of studies have been devoted to assess its compliance for PPDR purposes and to find suitable architectural solutions able to meet mission-critical requirements. This approach is surely worthy, but it is based on the assumption that infrastructure-based terrestrial systems are reliable. As a consequence, in worstcase emergency scenarios appropriate guarantees can be provided only in the hypothesis of huge investment costs. Recent developments in satellite technologies are bringing the availability of non-terrestrial high performance channels, with better properties when comparing to LTE for what regards availability and reliability. On this basis, the paper proposes a network architecture based on the integration of satellite and LTE networks for both infrastructure-based and infrastructure-less scenarios. The proposal aims to provide field operators and people in distress with transparent accessibility, coverage guarantees and broadband performance when terrestrial infrastructures are lacking, and to expand their coverage, capacity and resilience otherwise.

A low-latency and high-throughput scheduler for emergency and wireless networks

Providing QoS guarantees, boosting throughput and saving energy over wireless links is a challenging task, especially in emergency networks, where all of these features are crucial during a disaster event. A common solution is using a single, integrated scheduler that deals both with the QoS guarantees and the wireless link issues. Unfortunately, such an approach is not flexible and does not allow any of the existing high-quality schedulers for wired links to be used without modifications. We address these issues through a modular architecture which permits the use of existing packet schedulers for wired links over wireless links, as they are, and at the same time allows the flexibility to adapt to different channel conditions. We validate the effectiveness of our modular architecture by showing, through formal analysis as well as experimental results, that this architecture enables us to get a new scheduler with the following features, by just combining existing schedulers: execution time and energy consumption close to that of just a Deficit Round Robin, accurate fairness and low latency, possibility to set the desired trade-off between throughput-boosting level and granularity of service guarantees, by changing one parameter. In particular, we show that this scheduler, which we named Highth-roughput Twin Fair scheduler (HFS), outperforms one of the most accurate and efficient integrated schedulers available in the literature.

Deadlock Analysis of Concurrent Objects: Theory and Practice

We present a framework for statically detecting deadlocks in a concurrent object language with asynchronous invocations and operations for getting values and releasing the control. Our approach is based on the integration of two static analysis techniques: (i) an inference algorithm to extract abstract descriptions of methods in the form of behavioral types, called contracts, and (ii) an evaluator that computes a fixpoint semantics returning a finite state model of contracts. A potential deadlock is detected when a circular dependency is found in some state of the model. We discuss the theory and the prototype implementation of our framework. Our tool is validated on an industrial case study based on the Fredhopper Access Server (FAS) developed by SDL Fredhoppper. In particular we verify one of the core concurrent components of FAS to be deadlock-free.

Reducing latency in satellite emergency networks through a cooperative transmission control

The vast majority of efforts aimed to improve network performance are focused on the increase of application throughput. The same holds in the context of Emergency Networks, where operators ask for more bandwidth in order to exploit data-intensive services. Following a steady growth in network capacities and number of users, large buffers have been inserted all over the Internet. Their effects on networks are non-trivial: while they may effectively serve the purpose of exploiting the channel potential, they also create unnecessary delays by damaging the behavior of the most common transport protocol, TCP. Nevertheless, they are being assumed by new congestion control algorithms, especially those tailored for high-latency links such as satellite ones. According to the anywhere-anytime paradigm, these channels represents a key technology for both Emergency and General-Purpose networks. In this paper we first show how buffer lengths impact the perceived delay over satellite links that employ a recently proposed burst-based TCP protocol, and then present a cooperative transmission control that reduce buffers usage and latency while keeping high throughput and flow fairness, thus allowing for a better service provision through satellite links.

Integration between terrestrial and satellite networks: the PPDR-TC vision

Wireless communication technologies are critical for public protection and disaster relief (PPDR) professionals during the emergency operations that follow natural or man-made disasters, scenarios in which commercial terrestrial networks often fail to provide the necessary support. The reason is threefold: they simply get disrupted by the disaster, they cannot sustain the sudden surge of network demand or they fail to deliver the necessary bandwidth and/or other QoS guarantees. In every PPDR operation reliable voice communications are critical, especially in the very early stages of the response; nevertheless, there is an increasing demand from the PPDR community for a wider range of data-centric services. While current technologies used for PPDR operations provide a rich set of voice-centric services, they are unable to sustain high-bandwidth data-oriented applications. As the PPDR-TC EU consortium, we propose a hybrid approach to tackle the question of determining the future architecture for Pan-European PPDR networks based on the integration of Terrestrial and Satellite technologies, presenting our first simulation results on the integration of LTE and Satellite Networks.

PINK: Proactive INjection into acK, a queue manager to impose fair resource allocation among TCP flows

This paper presents preliminary work on PINK (Proactive INjection into acK), an AQM algorithm able to enhance TCP congestion control properties without dropping packets. PINK is a completely transparent solution that does not require any modification to the existing protocol stack of end hosts, and it is particularly suitable for high-delay PPDR systems. The algorithm is based on an explicit feedback scheme, able to enforce a fair bandwidth sharing among clients by modifying the Receive Window in TCP acknowledgements returning to them; such a feedback is computed for each flow, and it only needs the number of active connections, the flows RTTs and the shared link bandwidth. Therefore, PINK is a per-flow stateless AQM that works independently from the TCP algorithm used by clients, and it is fair regardless the flows RTTs, which is a key feature for PPDR systems. The effectiveness of the proposed algorithm is demonstrated using the ns-3 simulator.

Performance evaluation and economic modelling of PPDR communication systems

Network-enabled services for public protection and disaster relief (PPDR) professionals have been more than necessary in todays emergency situations. Under the extreme circumstances of an emergency, it is essential to have networks which support the required data throughput as well as high availability in spite of high traffic volume, and which minimize the end-to-end delay for applications: however, the choice between the existing technologies is not so easy for PPDR entities, given the high number of parameters associated to satisfying the stringent PPDR requirements, high investments required to permit desirable availability as well as modernization of the existing services (i.e. voice and data) and design constraints posed by network providers as current deployed network reach their boundaries when emergencies occur. This paper analyzes three different emergency scenarios and then presents a subset of the results obtained in terms of financial and economic recommendations, along with technical reports on throughput and end-to-end delay.

Towards emergency networks security with per-flow queue rate management

When statistical multiplexing is used to provide connectivity to a number of client hosts through a high-delay link, the original TCP as well as TCP variants born to improve performance on those links often provide poor performance and sub-optimal QoS properties. To guarantee intra-protocol fairness, inter-protocol friendliness, low queues utilization and optimal throughput in mission-critical scenarios, Congestion Control Middleware Layer (C2ML) has been proposed as a tool for centralized and collaborative resource management. However, C2ML offers only very limited security guarantees. Because emergencies may be natural or man-provoked, in the latter case there may be interest to cut out legitimate users from the communication networks that support disaster recovery operations. In this paper we present Queue Rate Management (QRM), an Active Queue Management scheme able to provide protection from Resource Exhaustion Attacks in scenarios where access to the shared link is controlled by C2ML; the proposed algorithm checks whether a node is exceeding its allowed rate, and consequently decides whether to keep or drop packets coming from that node. We mathematically prove that with QRM the gateway queue size can never exceed the Bandwidth-Delay Product of the channel. Furthermore, we use the ns-3 simulator to compare QRM with CoDel and RED, showing how QRM provides better performance in terms of both throughput and QoS guarantees when employed with C2ML.

Implementation and validation of TCP options and congestion control algorithms for ns-3

Currently, the ns-3 network simulator include rather limited TCP functionalities. TCP Options are not supported, and it misses models for widely used congestion control algorithms. Thus, simulations can be inadequate for todays standards and unable to represent what happen inside a broad range of networks, from Gigabit Ethernet to high-delay satellite channels. This paper presents an extension of the ns-3 TCP infrastructure, through the addition of the Window Scaling and the Timestamp Options as well as various models of TCP congestion control algorithms, from the widely used TCP Cubic to algorithms tailored for satellite or high Bandwidth-Delay Product links in general, namely TCP Hybla, Highspeed, Bic and Noordwijk. These additions are useful especially for research in high-speed or high-delay networks, filling the gap between real world and ns-3 TCP. Last but not least, this paper also presents some results regarding the validation of the added models, in order to demonstrate their correctness.

An SDN and CPS Based Opportunistic Upload Splitting for Mobile Users

This paper proposes an hybrid approach composed by Software Defined Networking (SDN) and Cyber-Physical Systems (CPS) to boost the upload speed of mobile users in low-bandwidth environments through a next generation Mobile Collaborative Community (MCC). The core idea is to use a high-bandwidth local communication system, like IEEE 802.11 (WiFi), in order to distribute data efficiently through mobile hosts; then, the distributed data may be sent from each mobile node to the original destination through their low-bandwidth mobile interface for wide area network communication. With our solution some drawbacks of MCC are faced. With the use of SDN we defined a flexible and easy-to-configure MCC system which operates in a transparent way for the end hosts. At the same time, the use of CPS creates a feedback for the system regarding the hosts channel status; this way the system is able to fully exploit the MCC potential by increasing the upload speed for both congested and non-congested scenarios. We demonstrate the efficiency of our solution through experimental results obtained using the Mininet network emulator where POX and a Pyretic controller serve as a dynamic data repartition engine.