Prithwish Basu

Networked parking spaces: architecture and applications

Finding a parking space is a common challenge faced by millions of city-dwellers every day. As common is the revenue generation by fee and fine collection in these municipalities. Wireless ad hoc networking technologies offer a new and efficient means to both simplify the process of parking and find collection as well as extending the convenience for drivers. In this paper we describe a multi-hop wireless parking meter network (PMNET) that, when coupled with a GPS receiver, allows a user (driver) to quickly locate and navigate to an available parking space. Our solution is achieved by equipping existing parking meters with wireless radio frequency (RF) transceivers and auxiliary hardware and software. We believe that this is a compelling application that applies wireless ad hoc networking and low-power, short range RF technologies. The attractiveness of the proposal stems from the fact that such a network of nodes can function without any fixed wired or wireless infrastructure such as cellular or satellite networks. In this work, we model a PMNET as a special class of ad hoc networks characterized by a combination of static, immobile nodes (parking meters) and mobile nodes (vehicles). We propose scalable techniques for satisfying a mobile users query in a distributed fashion. In particular, we make use of the static nature of the parking meters for efficient discovery and location based routing of information between them and users.

Dynamic task-based anycasting in mobile ad hoc networks

Mobile ad hoc networks (MANETs) have received significant attention in the recent past owing to the proliferation in the numbers of tetherless portable devices, and rapid growth in popularity of wireless networking. Most of the MANET research community has remained focused on developing lower layer mechanisms such as channel access and routing for making MANETs operational. However, little focus has been applied on higher layer issues, such as application modeling in dynamic MANET environments. In this paper, we present a novel distributed application framework based on task graphs that enables a large class of resource discovery based applications on MANETs. A distributed application is represented as a complex task comprised of smaller sub-tasks that need to be performed on different classes of computing devices with specialized roles. Execution of a particular task on a MANET involves several logical patterns of data flow between classes of such specialized devices. These data flow patterns induce dependencies between the different classes of devices that need to cooperate to execute the application. Such dependencies yield a task graph (TG) representation of the application.We focus on the problem of executing distributed tasks on a MANET by means of dynamic selection of specific devices that are needed to complete the tasks. In this paper, we present simple and efficient algorithms for dynamic discovery and selection (instantiation) of suitable devices in a MANET from among a number of them providing the same functionality. This is carried out with respect to the proposed task graph representation of the application, and we call this process Dynamic Task-Based Anycasting. Our algorithm periodically monitors the logical associations between the selected devices, and in the event of a disruption in the application owing to failures in any component in the network, it adapts to the situation and dynamically rediscovers the affected parts of the task graph, if possible. We propose metrics for evaluating the performance of these algorithms and report simulation results for a variety of application scenarios differing in complexity, traffic, and device mobility patterns. From our simulation studies, we observed that our protocol was able to instantiate and re-instantiate TG nodes quickly and yielded high effective throughput at low to medium degrees of mobility and not much below 70% effective throughput for high mobility scenarios.

A novel approach for execution of distributed tasks on mobile ad hoc networks

A novel distributed approach for executing distributed tasks on mobile ad hoc networks (MANETs) is presented. A distributed application is represented as a complex task comprised of simpler sub-tasks that need to be performed on different categories of computing devices with specialized roles. The dependencies induced by logical patterns of data flow between these specialized devices which are responsible for performing the aforementioned sub-tasks, yield a task graph representation for a given application. We present a simple and efficient distributed algorithm for dynamic discovery and selection of suitable devices in a MANET from among a number of them providing the same functionality. We refer to this process as instantiation which is carried out with respect to the proposed task graph representation of the application. We also present a distributed algorithm for detecting disruptions in application execution that can occur due to device mobility. The algorithm then recovers quickly from the situation by re-instantiating affected parts of the task graph, if possible. Finally, we propose metrics for evaluating the performance of these algorithms and report simulation results for a variety of application scenarios.

A task graph based application framework for mobile ad hoc networks

We propose a task graph based framework for modeling and execution of distributed applications in mobile ad hoc networks. Our framework represents a distributed application by a graph composed of nodes and edges in which the nodes logically represent application sub-tasks that need to be completed and the edges represent associations, with certain attributes, between nodes. During application run-time, suitable devices that can complete the sub-tasks and can satisfy the attributes of the associations between them are selected on-the-fly to execute the application. New devices are selected to continue application execution if old devices become unavailable due to mobility. Thus, we decouple the application from a specific set of devices and allow its execution if there is at least one suitable device in the network for carrying out each of the required sub-tasks. We propose an application execution protocol to realize this vision and show simulation results which indicate that our approach is practical for environments with low user/device mobility.

Persistent delivery with deferred binding to descriptively named destinations

Disruption-tolerant networks aim at reliable delivery of messages to their intended destinations even when continuous end-to-end paths are not available. Frequent network disruptions result in poor connectivity to name servers that can resolve destination names to specific network identifiers such as DNS names, IP addresses, or phone numbers. Disruptions also make it virtually impossible to keep dynamic distributed name databases residing on such name servers synchronized. Furthermore, in increasingly heterogeneous and multi-modal DTNs with a plethora of name spaces, a message source may not always be able to pre-determine the specific network address for a destination (as with DNS) or the mode of communication to reach it. In this paper, we describe a disruption-tolerant architecture and use cases for persistent message delivery to descriptively named destinations. We propose an intentional naming scheme that allows destinations to be described by their attributes (e.g., roles, services, or location) and predicates on them rather than by specific network identifiers. An intentional name denotes, in essence, a query on one or more namespaces which can result in specific endpoint identifiers (EID) of appropriate destination nodes. In our architecture, since it may not be possible to bind an intentional name to specific EID(s) at source, its resolution is deferred until the message is routed to one or more nodes that can successfully complete the process. We present a distributed progressive resolution procedure called GRAIN that persistently delivers messages to intentional names with geographic and role attributes, e.g., ldquoFirst responders within a kilometer of a specified locationrdquo. We describe results from a demonstration of GRAIN at a military facility.

Pricing considerations in video-on-demand systems (poster session)

Video-on-demand (VoD) has been an active area of research for the past few years in the multimedia research community. However, there have not been many significant commercial deployments of VoD owing to the inadequacy of per user bandwidth and the lack of a good business model.1 Significant research efforts have been directed towards reduction of network bandwidth requirements, improvement of server utilization, and minimization of start-up latency. In this paper, we investigate another aspect of VoD systems which has been largely neglected by the research community, namely, pricing models for VoD systems. We believe that the price charged to a user for an on-demand video stream should influence the rate of user arrivals into the VoD system and in turn should depend upon quality-of-service (QoS) factors such as initial start-up latency. We briefly describe some simple pricing models and analyze the tradeoffs involved in such scenarios from a profit maximization point of view. We further explore secondary content insertion (ad-insertion) which was proposed elsewhere [1] not only as a technique for reducing the resource requirements at the server and the network, but also as a means of subsidizing VoD content to the end user. We treat the rate of ad insertion as another QoS factor and demonstrate how it can influence the price of movie delivery.

Optimal scheduling of secondary content for aggregation in video-on-demand systems

We present and evaluate an optimal scheduling algorithm for inserting secondary content for improving resource utilization in VoD systems. The algorithm runs in polynomial time, and is optimal with respect to the total bandwidth usage over the merging interval. We present constraints on content insertion which make the overall QoS of the delivered stream acceptable, and show how our algorithm can satisfy these constraints. We discuss dynamic scenarios with user arrivals and interactions, and show by simulations that content insertion reduces the channel bandwidth requirement to almost half.

Implementation of dynamic service aggregation for interactive video delivery

Conventional video-on-demand (VoD) servers providing VCR-like interactivity allocate a separate channel for each user. Various schemes have been proposed for aggregating users into groups to improve resource utilization. By bridging the temporal skew between users viewing the same content, multiple users can be served from a single channel. Dynamic aggregation techniques such as rate adaptation and content insertion attempt to optimize resource utilization on-the-fly, thus improving their performance in interactive situations. In this paper, we describe a VoD system which delivers continuous media content to multiple clients using dynamic service aggregation to reduce bandwidth requirements. MPEG-1 system streams are used as the content format and IP multicast is used for video delivery. To the best of our knowledge, we are the first to demonstrate the viability of dynamic service aggregation using rate-adaptive merging in a VoD system. We present our experiences with building the system and address some important issues relating to aggregation in video servers including server directed channel switching in the client and stream merging by acceleration. We show simulations of our clustering and merging algorithms for large user populations and report the piggybacking of over 2.5 users on average per physical channel.

A new task-based approach for supporting distributed applications on mobile ad hoc networks

Mobile ad hoc networks (MANETs) have received significant attention recently owing to the increasing popularity of tetherless computing and the rapid growth of wireless networking technology. In this paper, we present a novel application framework for dynamic execution of distributed tasks on potentially mobile devices which form a MANET. In this framework, logical patterns of interaction between simpler components of a distributed application are exploited for the discovery of suitable devices/resources on which the application is actually executed. Our application framework is adaptive to network partitions caused by mobility of devices as it enables users to obtain a required service from several devices (providing the same service) over the lifetime of an application. This work helps enable new applications in diverse areas such as smart offices/homes, sensor networks, distributed computing, and disaster relief. A distributed application is represented as a task comprised of smaller, less complex sub-tasks that need to be performed on different types of computing resources/devices with specialized roles. Dependencies are induced by logical patterns of data flow between different categories of devices responsible for performing the aforementioned sub-tasks. Such dependencies yield an abstract task graph (TG) representation for a given application. We focus on the problem of efficiently executing distributed tasks on a MANET by means of dynamic discovery and selection of devices/resources for completion of simpler subtasks. The discovery of devices is carried out with respect to the underlying TG representation from among a multitude of candidate devices offering similar functionality. We refer to this process as task embedding. A task graph TG = (VT , ET ) is composed of a set of nodes, VT , and a set of edges, ET . The nodes represent classes of devices, resources or services (e.g. Printer, Speaker, Camera etc.) needed for processing data related to the task, whereas the edges represent necessary logical associations between different nodes for performing the task†. The process of embedding a task graph TG onto a MANET G = (VG, EG) involves mapping or instantiation of logical TG nodes and edges onto physical devices/resources and shortest paths between them, respectively. This is equivalent to finding a pair of mappings φ : VT → VG and ψ : ET → PG, where the class of v ∈ VT is the same as that of φ(v), and PG is the set of all source-destination paths in G. The quality of a mapping (φ,ψ) can be measured by a metric called average dilation which is the average over all edges in TG

Time-domain modeling of batching under user interaction and dynamic adaptive piggybacking schemes

Provision of Video-on-Demand (VoD) services may require high network bandwidth and server capacity for sustained periods of time. Aggregation schemes can be used to increase the supported customer population under the constraints of these resources, but due to system behavioral complexity, these schemes have been difficult to model in the large scale. We present in this paper a time-domain analysis modeling technique that yields satisfactory performance estimation results. We show that our analysis is analogous to finding the time response of linear systems using the well known convolution theorem. We model two aggregation schemes using this technique: (1) batching by time-out and (2) adaptive piggybacking employing Snapshot-RSMA. Both schemes are server based aggregation schemes, and their importance increases as pervasive computing, with possibly many capacity-limited devices (such as PDAs) connected as potential recipients of streaming VoD, becomes closer to reality. Since such schemes do not assume any end client capacity requirements, they are the logical candidates for enabling efficient VoD service in a pervasive computing environment. We delineate the requirements of the VoD system under which this modeling technique can be employed and also propose a sampling methodology which gives good estimation results when modeling becomes too complex mathematically.