IMDEA Networks Institute Digital Repository
Not a member yet
1915 research outputs found
Sort by
Millimeter Wave Networking Challenges
No full textState-of-the-art wireless communication already operates close to Shannon capacity and one of the most promising options to further increase data rates is to increase the communication bandwidth. Very high bandwidth channels are only available in the extremely high frequency part of the radio spectrum, the millimeter wave band (mm-wave). Upcoming communication technologies, such as IEEE 802.11ad, are already starting to exploit this part of the radio spectrum to achieve data rates of several GBit/s. However, communication at such high frequencies also suffers from high attenuation and signal absorption, often restricting communication to line-of-sight (LOS) scenarios and requiring the use of highly directional antennas. This in turn requires a radical rethinking of wireless network design. On the one hand side, such channels experience little interference, allowing for a high degree of spatial reuse and potentially simpler MAC and interference management mechanisms. On the other hand, such an environment is extremely dynamic and channels may appear and disappear over very short time intervals, in particular for mobile devices. It is essential to take these characteristics into account to turn a collection of such very high speed but brittle links into an efficient, low latency, and reliable network. This talk will highlight some of the challenges of and possible approaches for mm-wave networking.FALSEpu
Data Transmission Plan Adaptation for Connected Vehicles
Get PDFConnected vehicles can nowadays be equipped with multiple network interfaces to access the Internet via a number
of networks. Given a network availability map and a vehicle’s route, a joint time-network selection plan could attempt to schedule delay-tolerant data transmission efficiently. Since the networks presence and available capacities change rapidly and in an unforeseen manner (because of changing conditions due the uncertainty in car movement, data transmission needs and network characteristics), the efficiency of such a planning may be
severely compromised. Consequently, mechanisms that determine the deviation from the foreseen conditions are derived in this paper, which modify the transmission plan depending on the type of deviation observed. Simulation results show that the proposed mechanisms help maintain the benefits of a joint time-network planning under changing conditions.TRUEpu
Measurement-based Simulation of Underwater Optical Networks
Get PDFThe increasing interest in the application of optical communications to underwater communications and networks calls for reliable simulation models, that allow a system designer to realistically assess the performance of optical systems before actual deployment in water. In this paper, we present an optical channel model that is based on samples of the total attenuation coefficient and of solar light irradiance taken during the NATO STO CMRE ALOMEX’15 scientific cruise, in different water conditions. The data set includes both strong and mild solar illumination conditions, as well as a number of different settings for the light absorption and scattering coefficients.
We implement the model as part of the DESERT Underwater network simulator, and employ it to show that the throughput of underwater optical links depends not only on the distance between the transmitter and the receiver, but also on the depth at which the devices are deployed. The corresponding insight is empirically validated in dry tests and lake experiments using a proof-of-concept optical modem, and helped drive the next stage of the modem development.TRUEpu
General Ternary Bit Strings on Commodity Longest-Prefix-Match Infrastructures
Get PDFTernary Content-Addressable Memory (TCAM) is a powerful tool to represent network services with line-rate lookup time. There are various software-based approaches to represent multi-field packet classifiers. Unfortunately, all of them either require exponential memory or apply additional constraints on field representations (e.g, prefixes or exact values) to have line-rate lookup time. In this work, we propose alternatives to TCAM and introduce a novel approach to represent packet classifiers based on ternary bit strings (without constraining field representation) on commodity longest-prefix-match (LPM) infrastructures. These representations are built on a novel property, prefix reorderability, that defines how to transform an ordered set of ternary bit strings to prefixes with LPM priorities in linear memory. Our results are supported by evaluations on large-scale packet classifiers with real parameters from ClassBench; moreover, we have developed a prototype in P4 to support these types of transformations.TRUEpu
Crowdsourcing Spectrum Data Decoding
Get PDFCrowdsourced signal monitoring systems are gaining ttention for capturing the wireless spectrum at large geographical scale. Yet, most of the current systems are still limited to simple power spectrum measurements reported by each sensor. Our objective is to enhance such systems with signal decoding capabilities performed in the backend while retaining the original vision of a low-cost and crowdsourced setup. We propose a distributed system architecture for collaborative radio signal monitoring and decoding that builds on $12 low-cost radio frequency (RF) frontends and embedded boards and that takes into consideration the limited network bandwidth from the sensors to the backend. We present a distributed time multiplexing mechanism to sample the spectrum in a coordinated fashion that exploits the similarity of the radio signal received by more than one RF frontend in the same radio coverage. We address the strict time synchronization required among sensors to reconstruct the signal from the samples they receive when in the same radio coverage. We study and implement techniques to identify and overcome errors in the timing information in the presence of noise sources and decode the data in the backend. We provide an evaluation based on simulations and on real signals transmitted by Long-Term Evolution (LTE)
base stations. Our results show that we can reliably reconstruct and decode radio signals received by low-cost crowdsourced sensors.TRUEpu
Multi-Tenant Radio Access Network Slicing: Statistical Multiplexing of Spatial Loads
Get PDFThis paper addresses the slicing of Radio Access Network (RAN) resources by multiple tenants, e.g., virtual wireless operators and service providers. We consider a criterion for dynamic resource allocation amongst tenants, based on a weighted proportionally fair objective, which achieves desirable fairness/protection across the network slices of the different tenants and their associated users. Several key properties are established, including: the Pareto optimality of user association to base stations, the fair allocation of base stations resources, and the gains resulting from dynamic resource sharing across slices, both in terms of utility gains and capacity savings. We then address algorithmic and practical challenges in realizing the proposed criterion. We show that the objective is NP-hard, making an exact solution impractical, and design a distributed semi-online algorithm which meets performance guarantees in equilibrium and can be shown to quickly converge to a region around the equilibrium point. Building on this algorithm, we devise a practical approach with limited computational, information, and handoff overheads. We use detailed simulations to show that our approach is indeed near-optimal and provides substantial gains both to tenants (in terms of capacity savings) and end-users (in terms of improved performance).pu
Content Distribution Networks in the mobile age
No full textMobile applications and websites rely significantly on third party service providers to, among others, accelerate performance and reduce costs. An interesting recent deployment strategy is for content and service providers to leverage the services of multiple CDN providers in order to ensure maximal coverage and uptime. They may further use a managed DNS service, to ensure optimal server selection and load balancing among several CDNs. On top of that, peering agreements may allow some CDNs to deploy their infrastructure inside an ISP, giving them an advantage when serving this ISP’s customers. All of the above create a complex ecosystem, which affects the increasingly popular segment of the mobile apps market, but which thus far has not been studied in-depth. Our main goal is to empirically evaluate, through an active measurement campaign, the robustness and deployment strategies of various CDN providers, as well as their interconnection with ISPs in a mobile scenario. Past measurements have shown that CDN performance is impacted by ISP configuration [1,2]. We currently attempt to dig deeper and investigate questions such as: 1) whether the replica selection strategies of the various players have any inefficiencies, 2) how the choice of mobile technology affects performance and 3) how user mobility affects performance.
In order to answer the above, we first have to identify CDN related addresses that are popular among mobile apps. We make use of the dataset created by Lumen, a crowdsourced mobile app that intercepts and analyzes mobile traffic in user space with real user- and network- stimuli, to identify popular URLs. Then, we use heuristics and third party databases to isolate the CDN related URLs. Each URL is then used as a target of the active measurement campaign which is performed over the MONROE testbed. MONROE is a distributed mobile testbed with hundred of fixed and mobile nodes present in four major European markets (Sweden, Norway, Spain, Italy) and multihomed to up to three mobile operators. It allows for large scale experiments, while being free from the technical and ethical limitations of the current most popular alternative - crowdsourced approaches. For each test URL we periodically perform a series of basic tests, which include traceroutes, pings and attempting to fetch small objects. These are enough to characterize most aspects of the performance of a CDN. Moreover, we can assess mobile specific use cases more closely. For example, mobility scenarios in the city (nodes located in local buses) and country level (nodes located in intercity trains), roaming scenarios (SIM cards of one operator located in the home network and abroad) and study the effect of different technologies (HSPA, LTE, etc.) on CDN performance. Another interesting aspect is how the selection of replicas varies over time in static nodes.
[1] Safari Khatouni, Ali, et al. "Speedtest-like Measurements in 3G/4G Networks: the MONROE Experience." (ITC 2017).
[2] Alay, Özgü, et al. “An Open Platform for Experimentation with Commercial Mobile Broadband Networks” (MOBICOM 2017)TRUEpu
Analysis of TCP Performance in 5G mm-wave Mobile Networks
Get PDFMillimeter-wave (mm-wave) bands are projected to play an essential role in 5G mobile networks in supporting the increasing demands for higher data rates. Communications at mm-wave frequency bands pose unique challenges. The high variability in channel quality due to high propagation loss and unfavorable atmospheric absorption can only be overcome by the use of highly directional antennas. This results in a much higher degree of spatial reuse and lower interference if compared with omni-directional communications at lower frequencies. However, the high directionality may cause communication blockages as the channel may appear and disappear because of beam misalignments. While significant research efforts have investigated challenges and aspects of physical (PHY) and medium access control (MAC) layers, the impact of the unique features of mm-wave systems on transport layer still requires attention. In this article, we focus on analyzing the behavior of congestion control protocols and study their impact on system-level performance. Through extensive simulations, we show the effect of different type of blockages on the design of congestion control protocol in presence of handovers and when small, medium and long flows coexist. Protocols like CUBIC that target high-throughput performance benefit significantly by joint optimization of link layers buffers and timeouts. While the optimization foster prompt reaction to short-term blockages and make them ideal for small and medium flows, their performance significantly decrease when obstacles degrade the channel quality for longer time periods. Hybrid-designs like YeAH are more robust to blockages, but fail to recover fast and achieve the link capacity after timeoutsTelematics EngineeringUniversidad Carlos III de Madrid, Spainpu
Compressive Millimeter-Wave Sector Selection in Off-the-Shelf IEEE 802.11ad Devices
Get PDFDOI:10.1145/3143361.3143384Achieving data-rates of multiple Gbps in 60 GHz millimeter-wave (mm-wave) communication systems requires efficient beam-steering algorithms. To find the optimal steering direction on IEEE 802.11ad compatible devices, state-of-the-art approaches sweep through all predefined antenna sectors. Recently, much more efficient alternatives, such as compressive path tracking, have been proposed, which scale well even with arrays with thousands of antenna elements. However, such have not yet been integrated into consumer devices. In this work, we adapt compressive path tracking for sector selection in o_-the-shelf IEEE 802.11ad devices. In contrast to existing solutions, our compressive sector selection tolerates the imperfections of low-cost hardware, tracks beam directions in 3D and does not rely on pseudo-random beams. We implement our protocol on a commodity router, the TP-Link Talon AD7200, by modifying the sector sweep algorithm in the IEEE 802.11ad chip’s firmware. In particular, we modify the firmware to obtain the signal strength of received frames and to select custom sectors. Using this extension, we precisely measure the device’s sector patterns. We then select the best sector based on the measured patterns and sweep only through a subset of probing sectors. Our results demonstrate, that our protocol outperforms the existing sector sweep, increases stability, and speeds up the sector selection by factor 2.3.TRUEpu
Poster: Integration of WiFi ToF Positioning System in the Open, Flexible and Adaptive WiSHFUL Architecture
Get PDFWe integrate a prototypeWiFi Time-of-Flight (ToF) ranging
and positioning system in the WiSHFUL software platforms
and hardware radios for experimental prototyping. Users
have access to ToF measurements as well as computed positions through unified programming interfaces that make
possible to investigate innovative positioning and networking solutions.TRUEpu