We propose a component based methodology for modelling and design of wireless routing protocols. Componentization is a standard methodology for analysis and synthesis of complex systems, or software. The feasibility of the component based design relies heavily on the compositionality property (i.e. system-level properties can be computed from properties of components). To provide a component based design methodology and to test compositionality for routing protocols, we have to develop a component based model of the wireless network. We present the main components of the routing protocol that should be modelled and focus on three main components: neighborhood discovery, selector of topology information to disseminate, and the path selection components. For each component, we identify the inputs, outputs, and a generic methodology for modelling. Throughout the paper, we use the Optimized Link State Routing (OLSR) protocol as a case study to demonstrate the effectiveness of our approach. Using the neighborhood discovery component, we present our design methodology and design a modified enhanced version of this component, and compare its performance to the original OLSR design.

We develop and evaluate a new method for estimating and optimizing various performance metrics for multi- hop wireless networks, including MANETs. We introduce an approximate (throughput) loss model that couples the physical, MAC and routing layers effects. The model provides quantitative statistical relations between the loss parameters that are used to characterize multiuser interference and physical path conditions on the one hand and the traffic rates between origin-destination pairs on the other. The model takes into account effects of the hidden nodes, scheduling algorithms, IEEE 802.11 MAC and PHY layer transmission failures and finite packet transmission retries at the MAC layer in arbitrary network topologies where multiple paths share nodes. We apply automatic differentiation (AD) to these implicit performance models, and develop a methodology for sensitivity analysis, parameter optimization and trade-off analysis for key wireless protocols. Finally, we provide simulation experiments to evaluate the effectiveness and performance estimation accuracy of the proposed models and methodologies.

We consider the problem of joint routing, scheduling and power control in multi-hop wireless networks. We use a linear relation between link capacity and signal to interference noise ratio in our formulation. In a previous work, using a duality approach, the optimal link scheduling and power control that minimizes the total average transmission power is found. We formulate this problem as a linear programming problem with exponential number of constraints. To cope with the exponential number of constraints, we propose an iterative algorithm based on the cutting plane method. The separation oracle for the cutting plane algorithm turns out to be an element-wise concave optimization problem that can be effectively solved using branch and bound algorithm. We extend the same method to find the optimal routing scheduling and power control. Simulation results show that this methodology is more efficient and scalable compare to the previously proposed algorithm.

In this paper, we present an algorithm for intra-domain traffic engineering. We assume that the traffic matrix, which specifies traffic load between every source-destination pair in the network, is unknown and varies with time, but that always lies inside an explicitly defined region. Our goal is to compute a fixed robust routing with best worst case performance for all traffic matrices inside the bounding region. We formulate this problem as a semi-infinite programming problem. Then, we focus on a special case with practical merits, where (1) the traffic matrix region is assumed to be a polytope specified by a finite set of linear inequalities, and (2) our objective is to find the routing that minimizes the maximum link utilization. Under these assumptions, the problem can be formulated as a polynomial size linear programming (LP) problem with finite number of constraints. We further consider two specific set of constraints for the traffic matrix region. The first set is based on the hose model and limits the total traffic rate of network point of presence (PoP) nodes. The second set is based on the pipe model and limits the traffic between source-destination pairs. We study the effectiveness of each set of constraints using extensive simulations.

We present an automated software interference detection methodology for Single Program, Multiple Data (SPMD) parallel applications. Interference comes from the system and unexpected processes. If not detected and corrected such interference may result in performance degradation. Our goal is to provide a reliable metric for software interference that can be used in soft-failure protection and recovery systems. A unique feature of our algorithm is that we measure the relative timing of application events (i.e. time between MPI calls) rather than system level events such as CPU utilization. This approach lets our system automatically accommodate natural variations in an application's utilization of resources. We use performance irregularities and degradation as signs of software interference. However, instead of relying on temporal changes in performance, our system detects spatial performance degradation across multiple processors. We also include a case study that demonstrates our technique's effectiveness, resilience and robustness.

We consider the problem of finding a single-path intra-domain routing for time-varying traffic. We characterize the traffic variations by a finite set of traffic profiles with given non-zero fractions of occurrence. Our goal is to optimize the average performance over all of these traffic profiles. We solve the optimal multi-path version of this problem using linear programming and develop heuristic single-path solutions using randomized rounding and iterated rounding. We analyze our single-path heuristic (finding the optimal single-path routing is NP-hard), and prove that the randomized rounding algorithm has a worst case performance bound of O(log(KN)/log(log(KN))) compared to the optimal multi-path routing with a high probability, where K is the number of traffic profiles, and N the number of nodes in the network. Further, our simulations show the iterated rounding heuristics perform close to the optimal multi-path routing on a wide range of measured ISP topologies, in both the average and the worst-case. Overall, these results are extremely positive since they show that in a wide-range of practical situations, it is not necessary to deploy multi-path routing; instead, an appropriately computed single-path routing is sufficient to provide good performance.

To resolve the high memory bandwidth requirements presented by output-queued switches, several parallel shared-memory architectures have been previously proposed. In this paper, our goal is to extend existing shared-memory architecture results while introducing the notion of Fabric on a Chip (FoC). In taking advantage of recent advancements in integrated circuit technologies, FoC aims to facilitate the consolidation of as many packet switching functions as possible on a single chip. Accordingly, this paper focuses a novel pipelined memory management algorithm which plays a key role in the context of on-chip output-queued switch emulation. We discuss in detail the fundamental properties of the proposed scheme, along with FPGA-based implementation results that illustrate its scalability and performance attributes.

We introduce a new approach for QoS provisioning in packet networks based on the notion of differentiated traffic engineering (DTE). We consider a single AS network capable of source based multi-path routing. We do not require sophisticated queuing or per-class scheduling at individual routers; instead, if a link is used to forward QoS sensitive packets, we maintain its utilization below a threshold. As a consequence, DTE eliminates the need for per-flow (IntServ) or per-class (DiffServ) packet processing tasks such as traffic classification, queueing, shaping, policing and scheduling in the core and hence poses a lower burden on the network management unit. Conversely, DTE utilizes network bandwidth much more efficiently than simple over-provisioning. In this paper, we propose a complete architecture and an algorithmic structure for DTE. We show that our scheme can be formulated as a non-convex optimization problem, and we present an optimal solution framework based on simulated annealing. We present a simulation-based performance evaluation of DTE, and compare our scheme to existing (gradient projection) methods.

In this paper, we present parallel on-line optimization algorithms for parameter tuning of parallel programs. We employ direct search algorithms that update parameters based on real-time performance measurements. We discuss the impact of performance variability on the accuracy and efficiency of the optimization algorithms and proposed modified versions of the direct search algorithms to cope with it. The modified version uses multiple samples instead of single sample to estimate the performance more accurately. We present preliminary results that the performance variability of applications on clusters is heavy tailed. Finally, we studay and demonstrate the performance of the proposed algorithms for real scientific application.

In this paper, we use fluid model techniques to establish some new results for the throughput of input-buffered switches. In particular, we introduce a new class of deterministic maximal size matching algorithms that achieves 100% throughput. Dai and Prabhakar (2000) has shown that any maximal size matching algorithm with speedup of 2 achieves 100% throughput. We introduce a class of maximal size matching algorithms that we call them maximum node containing matching (MNCM) algorithms, and prove that they have 100% throughput with no speedup. We also introduce a new weighted matching algorithm, maximum first matching (MFM) with complexity O(N2.5) that belongs to MNCM. MFM, to the best of our knowledge, is the lowest complexity deterministic algorithm that delivers 100% throughput. The only assumption on the input traffic is that it satisfies the strong law of large numbers. Besides throughput, average delay is the other key performance metric for the input-buffered schedulers. We use simulation results to compare and study the delay performance of MFM. The simulation results demonstrate promising delay performance for MFM.

The concept of tracking fluid policies by packetized policies is extended to input queueing switches. It is considered that the speedup of the switch is one. One of the interesting applications of the tracking policy in TDMA satellite switches is elaborated. For the special case of 2/spl times/2 switches, it is shown that a tracking nonanticipative policy always exists. It is found that, in general, nonanticipative policies do not exist for switches with more than two input and output ports. For the general case of N/spl times/N switches, a heuristic tracking policy is provided. The heuristic algorithm is based on two notions: port tracking and critical links. These notions can be employed in the derivation of other heuristic tracking policies as well. Simulation results show the usefulness of the heuristic algorithm and the two basic concepts it relies on.

The concept of tracking policies for fluid policies is extended to input queueing switches. It is considered that the speed up of the switch is 1. For the special case of 2/spl times/2 switches it is shown that tracking policy always exists. One of the interesting applications of the tracking policy in TDMA satellite switches is elaborated upon. For the general case of N/spl times/N switches a heuristic tracking policy is provided. The heuristic algorithm is based on two notions of port tracking and critical links. These notions can be employed in derivation of other heuristic tracking policies as well. Simulation results present the usefulness of the heuristic algorithm and the two basic concepts it relies upon.