Violet R. Syrotiuk

Factor interaction on service delivery in mobile ad hoc networks

Delay sensitive applications are driving the need for the support of quality-of-service (QoS) in mobile ad hoc networks. In this paper, we use statistical design of experiments to study the impact of factors and their interaction on the service delivered. We consider the factors of QoS architecture, routing protocol, medium access control protocol, offered load, and mobility, at mixed levels. Real-time throughput, total throughput, and average delay are used as the measures of service delivery. A statistical analysis of the data collected by simulation using analysis of variance techniques is performed. This allows us to identify both main effects and interactions of factors that best explain the response variables. For average delay several factors of the experiment interact. For both forms of throughput, the impact of the routing protocol is not apparent except as it interacts with other factors, and the factor interactions are not as extensive as for delay. Thus, for all response variables the factors cannot be studied in isolation. As well, the analysis provides a means for a system architect to determine the level to set the factors to optimize a specific service delivery metric, or combination of metrics.

Location aware, dependable multicast for mobile ad hoc networks

Abstract This paper introduces dynamic source multicast (DSM), a new protocol for multi-hop wireless (i.e., ad hoc ) networks for the multicast of a data packet from a source node to a group of mobile nodes in the network. The protocol assumes that, through the use of positioning system devices, each node knows its own geographic location and the current (global) time, and it is able to efficiently spread these measures to all other nodes. When a packet is to be multicast, the source node first locally computes a snapshot of the complete network topology from the collected node measures. A Steiner (i.e., multicast) tree for the addressed multicast group is then computed locally based on the snapshot, rather than maintained in a distributed manner. The resulting Steiner tree is then optimally encoded by using its unique Pr u fer sequence and is included in the packet header as in, and extending the length of the header by no more than, the header of packets in source routing (unicast) techniques. We show that all the local computations are executed in polynomial time. More specifically, the time complexity of the local operation of finding a Steiner tree, and the encoding/decoding procedures of the related Prufer sequence, is proven to be O( n 2 ), where n is the number of nodes in the network. The protocol has been simulated in ad hoc networks with 30 and 60 nodes and with different multicast group sizes. We show that DSM delivers packets to all the nodes in a destination group in more than 90% of the cases. Furthermore, compared to flooding, DSM achieves improvements of up to 50% on multicast completion delay.

Dynamic source routing for ad hoc networks using the global positioning system

This paper proposes a new routing protocol for ad hoc networks built around the source routing technique combined with the location (e.g., GPS coordinates) of nodes obtained by an energy and distance smart dissemination mechanism. The key new observation used is that the location information provides each node with a snapshot of the topology of the complete network from which a source route may be computed locally rather than through route discovery. The resulting protocol has reduced delay, and is more bandwidth and energy efficient, than both traditional (proactive and reactive) ad hoc routing protocols, as well as location based routing protocols.

ADAPT: a dynamically self-adjusting media access control protocol for ad hoc-networks

This paper presents a dynamically adaptive protocol for transmission (ADAPT) for ad hoc networks that combines, in a novel way, a collision-free allocation based protocol and a contention based protocol while retaining the advantages of each. At low loads, ADAPT uses its contention mechanism to reclaim/reuse bandwidth that would otherwise be wasted by a pure allocation based protocol. At high loads, ADAPT provides bounded delay guarantees by dynamically changing its operation to that of its allocation based protocol, avoiding the fundamental problem of instability associated with pure contention based protocols. Thus, ADAPT self-adjusts its behavior according to the prevailing network conditions. Both analysis and simulation results demonstrate that the two protocols interact in a positive way, showing that it is possible to combine the advantages of two fundamentally different design philosophies without suffering from their drawbacks.

Optimizing protocol interaction using response surface methodology

Abstract-Response surface methodology (RSM) is a collection of statistical design and numerical optimization techniques traditionally used to optimize industrial processes. In this paper, we demonstrate that the methodology can be successfully applied to the domain of networking. Specifically, we obtain increased throughput with a significant decrease in delay in a ns-2 simulation model of a mobile ad hoc network (MANET) by using RSM to optimize protocol interaction found by factor screening. Whether the experimentation is with a stochastic simulation model or a physical system, such as a MANET or a wireless sensor network test-bed, RSM provides a general and practical methodology to screen factors and robustly and jointly optimize responses.

Meta-MAC protocols: automatic combination of MAC protocols to optimize performance for unknown conditions

A systematic and automatic method to dynamically combine any set of existing MAC protocols into a single higher layer, or meta-MAC protocol, is presented. The new approach makes it possible to always achieve the performance of the best component protocol, without knowing in advance which protocol will match the potentially changing and unpredictable network conditions. Moreover, this dynamic optimization is entirely automatic and runs without any centralized control or any exchange of messages, using only local network feedback information. We describe the method and prove that the resulting meta-MAC protocol achieves optimal performance in a well-defined sense. Through simulation on different types of networks and with different component MAC protocols, we demonstrate that our simple and practical combination algorithm yields highly adaptive and scalable MAC solutions.

MERIT: a scalable approach for protocol assessment

MERIT is a framework that can be used to assess routing protocols in mobile ad hoc networks (manets). It uses the novel concept of a shortest mobile path (SMP) in a mobile graph, a generalization of the shortest path problem for mobile environments. As a measure for routing protocol assessment, we propose the mean ratio of the cost of the route used by a protocol to the cost of the optimal mobile path for the same network history. The cost reflects that the route used in a session can change over time because of network dynamics such as topology changes. The aim is for the ratio to be an abstract, inherent measure of the protocol that is as implementation-independent as possible. The MERIT spectrum, which is the ratio expressed as the function of some parameters of interest, is a characterization of protocol effectiveness. MERIT, for MEan Real vs. Ideal cosT, provides a scalable assessment framework: rather than comparing performance measures of different protocols directly, we compare a protocol to the optimal solution. That is, rather than forcing the comparison to be in the same system, it is done once for each protocol in its own environment. Furthermore, we show that there is an efficient algorithm to solve the underlying SMP problem for important cases, making the approach practically feasible. We also investigate generalizations of and extensions within the MERIT framework. We show that the MERIT framework is rich, with much wider generality and potential applicability than assessing routing protocols.

An adaptive medium access control (MAC) protocol for reliable broadcast in wireless networks

This paper presents ABROAD, an adaptive medium access control (MAC) protocol for reliable broadcast packet transmission in wireless networks. ABROAD incorporates a collision-avoidance handshake within each slot of a synchronous transmission schedule, allowing nodes to reclaim and/or reuse idle slots while maintaining bounded access delay. Thus, ABROAD provides worst-case performance guarantees while remaining adaptive to local changes in traffic load and node connectivity. We analyze the optimal worst-case performance of ABROAD, and show that there is a strict increase in the number of broadcast packets per second over a pure time division multiple access (TDMA) protocol. Extensive simulation confirms our analysis, and also demonstrates that ABROAD outperforms broadcast protocols based on reliable unicast packet delivery schemes, such as the IEEE 802.11 MAC standard.

Cover-Free Families and Topology-Transparent Scheduling for MANETs

We examine the combinatorial requirements of topology-transparent transmission schedules in a mobile ad hoc network (MANET). Specifically, if each of the N nodes has at most D active neighbors, we require the schedule to guarantee a collision-free transmission to each neighbor. This requirement is met by a cover-free family. We show that existing constructions for topology-transparent schedules correspond to an orthogonal array. Moreover, we show that Steiner systems support the largest number of nodes for a given schedule length. Both of these combinatorial objects are special cases of cover-free families. Analytically and numerically, we examine slot guarantees, expected throughput, and normalized expected throughput for systems of small strength, exploring the sensitivity of the response to D. Expected throughput provides a better performance metric than the minimum throughput results obtained earlier. The impact of a more realistic model of acknowledgments is also examined. The extension of the schedule to multiple frames returns us to the orthogonal arrays. The very density of Steiner systems that afforded an improvement over orthogonal arrays in one frame impedes the best extension to more frames.

An adaptive generalized transmission protocol for ad hoc networks

Wireless networking and group communication in combination allows groups of dispersed mobile users to collaborate. This paper presents AGENT, a medium access control (MAC) protocol that unifies point-to-point and multi-point transmission services to facilitate group communication in ad hoc networks. Analysis and experiments performed in a simulated ad hoc network demonstrate that AGENT exhibits reliable and stable performance with high spatial bandwidth reuse. Moreover, variation in the proportion of point-to-point and multi-point traffic is shown to have little impact on the overall performance of AGENT. Comparison with the other tested MAC protocols reveals that the performance of AGENT is superior, achieving higher channel utilization and lower access delay.