Sameh Gobriel

A unified interference-collision analysis for power-aware adhoc networks

In this paper we address the issue of controlling transmission power in power-aware ad hoc networks. Previous work that minimizes the transmission power does not consider both the energy consumed in collision resolution and the energy disbursed to overcome the interference resulting from neighboring nodes. We investigate the basic transmission power control for the 802.11 MAC protocols in which the control frames and the data frames can be transmitted at different power levels. A collision model together with an interference model of a uniformly distributed network is constructed. Based on these models, the end-to-end network throughput and the total energy consumption of the network are examined. For a network with a given node density, our results show the optimal transmission power for control messages and for data messages that will yield maximum throughput and minimum energy consumption per message.

Live Baiting for Service-Level DoS Attackers

Denial-of-service (DoS) attacks remain a challenging problem in the Internet. By making resources unavailable to intended legitimate clients, DoS attacks have resulted in significant loss of time and money for many organizations, thus, many DoS defense mechanisms have been proposed. In this paper we propose live baiting, a novel approach for detecting the identities of DoS attackers. Live baiting leverages group-testing theory, which aims at discovering defective members in a population using the minimum number of dasiadasiatestspsilapsila. This leverage allows live baiting to detect attackers using low state overhead without requiring models of legitimate requests nor anomalous behavior. The amount of state needed by live baiting is in the order of number of attackers not number of clients. This saving allows live baiting to scale to large services with millions of clients. We analyzed the coverage, effectiveness (detection time, false positive and false negative probabilities), and efficiency (memory, message overhead, and computational complexity) of our approach. We validated our analysis using NS-2 simulations modeled after real Web traces.

Understanding the bottlenecks in virtualizing cellular core network functions

Network function virtualization (NFV) promises significant cost savings, flexibility and ease of deployment. However, potential challenges in implementing virtualized network elements that can support real-world performance requirements are still an open question. For example, traditional telecom networks have a lot of complex interdependencies that can affect performance. In this paper, we study the potential bottlenecks in virtualizing cellular core network functions. Using a combination of analysis and experimentation, we quantify the impact of software-based EPC elements on various metrics including physical processing, memory, IO, and bandwidth resource requirements. We use production grade, software-based cellular network elements running on general purpose Linux servers, driven by a variety of realistic workloads derived from a realworld cellular network, to examine the combined effects of control and data planes on an LTE enhanced packet core (EPC). In particular, we discover that the SGW handles about 33% of the control plane transactions and is a potential source for performance bottlenecks as a result of the interdependencies between control and data plane processing. Our results indicate that simply replacing existing EPC elements with virtualized equivalents can have severe performance bottlenecks and that virtualized EPC elements need to be carefully designed.

Dynamic rate-selection for extending the lifetime of energy-constrained networks

Wireless networks have a constraint on their functional lifetime. This is due to the limited energy capacity of batteries powering the wireless nodes. For extending the lifetime of such battery-operated networks, we present a scheme for dynamically selecting the transmission rate for each node in the network. The transmission rate is based on the available energy budget in each nodes battery. The goal is to increase the network capability of delivering more packets. The rate selection for each node is subject to satisfying a QoS timing constraint on the packet delivery time. Through adaptively varying each nodes rate, we extended the lifetime 10 times on average more transmitting at a maximum rate and delivered on average 7.5 times more data packets. When compared with a scheme that transmits data at a lower rates independent of the battery levels, our scheme delivers up to 12% more packets for the same available total energy.

Energy-Efficient Thread Assignment Optimization for Heterogeneous Multicore Systems

The current trend to move from homogeneous to heterogeneous multicore systems provides compelling opportunities for achieving performance and energy efficiency goals. Running multiple threads in multicore systems poses challenges on meeting limited shared resources, such as memory bandwidth. We propose an optimization approach that includes an Integer Linear Programming (ILP) optimization model and a scheme to dynamically determine thread-to-core assignment. We present simulation analysis that shows energy savings and performance gains for a variety of workloads compared to state-of-the-art schemes. We implemented and evaluated a prototype of our thread assignment approach at user level, leveraging Linux scheduling and performance-monitoring capabilities.

BLAM: an energy-aware MAC layer enhancement for wireless adhoc networks

In wireless adhoc networks, channel and energy capacities are scarce resources. However, the design of the IEEE 802.11 DCF protocol leads to an inefficient utilization of these resources. We introduce BLAM, a new battery level aware MAC protocol, which is developed from an energy-efficiency point of view to extend the useful lifetime of an adhoc network. We modify the IEEE 802.11 DCF protocol to enable BLAM to tune the random deferring time for fresh and collided data packets dynamically, based on the nodes energy. We show that BLAM can achieve an increase of 15% in network lifetime and an increase of about 35% in the total number of received packets.

A unified interference/collision model for optimal MAC transmission power in ad hoc networks

In this paper we address the issue of controlling transmission power in power-aware ad hoc networks. We argue that minimum transmission power is not always optimal. Previous work that minimises the transmission power does not consider both the energy consumed in collision resolution and the energy disbursed to overcome the interference resulting from neighbouring nodes. We investigate the basic transmission power control for the 802.11 MAC protocol, in which the control frames and the data frames can be transmitted at different power levels. A unified collision and interference model of a uniformly distributed network is constructed. Based on this model, the end-to-end network throughput and the total energy consumption of the network are examined for different network parameters. For a network with a given node density, our results show the optimal transmission power for control messages and for data messages that will yield maximum throughput and minimum energy consumption per message.

Considering Link Qualities in Fault-Tolerant Aggregation in Wireless Sensor Networks

The goal of Wireless Sensor Networks is to extract useful global information from individual sensor readings, which are typically collected and aggregated over a spanning tree. However, the spanning tree structure is not robust against communication errors; a low-quality (i.e., high-error-rate) wireless link close to the tree root may result in a high rate of global information loss. Therefore, many schemes have been proposed to achieve fault-tolerant aggregation. Intuitively, using timely link-quality information, which is gathered by continuous monitoring and error-rate measurement of network links, improves the performance of fault-tolerant aggregation schemes. In this paper, we show that this intuition is not always true. In particular, we show that using link-quality information in an intuitive but wrong way results in degraded performance in some schemes, and therefore, care should be taken in using link-quality information. We also show that some schemes make better usage of link-quality information than others, and some schemes are more robust to errors in link-quality estimation than others. We support our findings by an extensive simulation study, and we focus on the (more general) class of fault-tolerant duplicate-sensitive aggregation schemes.

Self-Configuring Multi-hop Ad-Hoc Wireless Telephony for Small Enterprises

In this paper, the authors motivate the interesting characteristics of small-to-medium enterprises and study the problem of wireless IP telephony for such deployments. While small enterprises are characterized by few network nodes and small deployment areas, they also demand good IP telephony quality, ease of deployment, and low management and configuration overhead. The authors evaluate the feasibility of peer-to-peer telephony over a multi-hop wireless ad-hoc network for such small enterprises. The authors designed a system and built a prototype using off-the-shelf components. In this paper, the authors describe the implementation and deployment of this system. Several fundamental routing protocol issues needed to be resolved to develop a stable system and the authors present them here. The authors also report the results of a simulation study they conducted to establish the configuration and performance parameters for such systems, and identify the limits to the use of multi-hop ad-hoc wireless for peer-to-peer IP telephony for small enterprises.

Load-Based Metrics and Flooding in Wireless Mesh Networks

On-demand routing protocols in wireless ad-hoc (mesh) networks use route requests to search for a routing path. To determine a route that optimizes a metric function, an intermediate node retransmits a route request that has a lower metric value. This can create flooding waves, where a large number of route requests are retransmitted through the network. In this paper, we study different classes of node load-based metric functions that are useful in sensor networks and telephony applications. We tackle the problem of determining optimal routes while minimizing flooding waves. We define a notion of efficient floodingand show that an online algorithm can discover an optimal metric path while achieving efficient flooding for a sum loadmetric, but this is not possible for a min-maxload metric. We simulate an online algorithm that is provably efficient in terms of flooding for some classes of metrics and analyze its performance for different load-based metric functions.