Rohan Sen

Context aware session management for services in ad hoc networks

The increasing ubiquity of wireless mobile devices is promoting unprecedented levels of electronic collaboration among devices interoperating to achieve a common goal. Issues related to host interoperability are addressed partially by the service-oriented computing paradigm. However, certain technical concerns relating to reliable interactions among hosts in ad hoc networks have not yet received much attention. We introduce follow-me sessions, where interactions occur between a client and a service, rather than a specific provider or server. We allow the client to switch service providers, if needed. We exploit strategies involving the use of contextual information, strong process migration, context-sensitive binding, and location-agnostic communication protocols. We show how follow-me sessions mitigate issues related to proxy-based service-oriented architectures in ad hoc networks.

CiAN: a workflow engine for MANETs

The practice of using workflows to model complex activities in stable networks is commonplace and is supported by many commercially available workflow management systems (WfMSs). However, the use of workflows to model collaborative activities in mobile environments, while possible at the model level, has not gained traction due to the lack of a suitable WfMS for mobile networks and devices. This paper seeks to address this need. We present CiAN, a choreography-based workflow engine that is designed with MANETs in mind. We describe the design, architecture, and communication protocols used by CiAN as well as its implementation using Java. An evaluation of the communication protocol used to coordinate among various workflow participants across MANETs is also presented.

Knowledge-driven interactions with services across ad hoc networks

Service oriented computing, with its aim of unhindered interoperability, is an appropriate paradigm for ad hoc networks, which are characterized by physical mobility of heterogenous hosts and by the absence of standardized application level protocols. The decoupled nature of computing in ad hoc networks can result in disconnections at inopportune times during the client-service interaction process. We introduce the notion of a priori selection of services to reduce the likelihood of disconnection during service usage. A client may specify the times when it requires certain services. A knowledge base of the physical motion profiles of various service providers is used to select instances of a service that are co-located with the client at the required time and least likely to disconnect. A system for constructing the knowledge base is presented in this paper, along with the implementation details and the algorithm used to determine the service usage pattern.

MobiWork: Mobile Workflow for MANETs

The workflow model is well suited for scenarios where many entities work collaboratively towards a common goal, and is used widely today to model complex business processes. However, the fundamental workflow model is very powerful and can be applied to a wider variety of application domains. This paper represents an initial investigation into the possibility of using workflows to model collaboration in an ad hoc mobile environment. Moving to a mobile setting introduces many challenges as the mobility of the participants in a workflow imposes constraints on allocation of workflow tasks, coordination among participants, and marshaling of results. We present an algorithm that heuristically allocates tasks to participants based on their capabilities and mobility and discuss the architecture and implementation of MobiWork, our prototype system that allocates and executes workflows in an ad hoc mobile environment. An evaluation of the performance of our heuristic algorithm is also presented. Type of Report: Other Department of Computer Science & Engineering Washington University in St. Louis Campus Box 1045 St. Louis, MO 63130 ph: (314) 935-6160 MobiWork: Mobile Workflow for MANETs Gregory Hackmann, Rohan Sen, Mart Haitjema, Gruia-Catalin Roman, and Christopher Gill Department of Computer Science and Engineering Washington University in St. Louis Campus Box 1045, One Brookings Drive St. Louis, MO 63130, U. S. A. {ghackmann, rohan.sen, mart.haitjema, roman, cdgill}@wustl.edu

Supporting Predictable Service Provision in MANETs Via Context-Aware Session Management

The increasing ubiquity of wireless mobile devices is promoting unprecedented levels of electronic collaboration among devices interoperating to achieve a common goal. Issues related to host interoperability are addressed partially by the principles of the service-oriented computing paradigm. However, certain technical concerns relating to predictable interactions among hosts in mobile ad hoc networks (MANETs) have not yet received much attention. We introduce “follow-me sessions,†where interactions occur between a client and a service, rather than a specific service provider. A client, thus, may exploit several service providers during the course of its interaction with a given service. This redundancy mitigates the effects of mobility-induced disconnections, thereby facilitating reliable communication. The switching of service providers is done using a combination of strong process migration, context-sensitive binding and locationagnostic communication protocols. This paper covers the architecture and implementation of a middleware that supports follow-me sessions and shows how this middleware mitigates issues related to proxy-based service-oriented architectures in mobile ad hoc networks. We support our claims via technical evaluation of our approach.

Coordinating workflow allocation and execution in mobile environments

Workflows have been used successfully to model collaborative activities that have a well-defined structure. Workflow management systems today can execute workflows that range from a simple sequence of tasks to complex business processes, but have a common restriction in that they can only function in settings where the network is stable. This paper represents an initial investigation into the possibility of using workflows in a challenging new domain - that of an ad hoc mobile network - and for a wider purpose - that of supporting arbitary collaborations among groups of people. Moving to a mobile setting introduces many challenges, as the mobility of the participants in a workflow imposes constraints on the allocation of workflow tasks, coordination among participants, and the marshaling of results. We present an algorithm that heuristically allocates tasks to participants based on their capabilities and mobility, and a system that uses spatiotemporal coordination to control and manage workflow execution in a mobile environment.

Opportunistic exploitation of knowledge to increase predictability of agent interactions in MANETs

Mobile Ad hoc Networks (MANETs) are dynamic environments where frequent changes in the network topology due to physical mobility of hosts result in unpredictable, sporadic and transient connectivity. Due to this high level of uncertainty, only limited guarantees can be given for interactions among agents that run on the mobile hosts. This is not desirable as any interaction among agents on different hosts is susceptible to interruption. In this paper, we explore means to alleviate the level of uncertainty in a MANET by having hosts and agents share knowledge of their non-functional attributes such as location, velocity, etc. with each other. This shared knowledge can be used to compute, for example, the points in space and time when two hosts are likely to be within communication range. This information can then be provided to individual agents, making them more aware of the constraints within which they operate and thereby giving them a chance to tailor their behavior so that they are less affected by unpredictable disconnections. The contributions of this paper are a minimalist formalism for knowledge exchange, a software architecture supporting knowledge exchange, and an empirical evaluation of the benefits of exploiting knowledge to increase the predictability of interactions.

An Architecture Supporting Run-Time Upgrade of Proxy-Based Services in Ad Hoc Networks

In the proxy approach to Service Oriented Computing, a service advertises a proxy, which is searched for, retrieved and used by interested clients as a local handle to the service process that runs on a remote host. Due to software evolution, it becomes necessary at times to upgrade the service. Some of these upgrades may require an upgrade of the proxy software, in addition to the server itself. This paper addresses the issue of upgrading both the server and its proxy in a manner transparent to the client, and ensures only momentary interruption during the switching process. The model we propose is designed for ad hoc wireless networks, but can be used in other settings as well. We also describe a Java implementation of our model.

Distributed Allocation of Workflow Tasks in MANETs

When multiple participants work on a workflow that represents a large, collaborative activity, it is important to have a well defined process to determine the portions of the workflow that each participant is responsible for executing. In this paper, we describe a process and related algorithms required to assign tasks in a workflow, to hosts that are willing to carry out the execution of these tasks, and thereby contributing to the completion of the activity. This problem is a stylized form of the multi-processor scheduling algorithm which has been shown to be NP-Hard. Further complicating the issue is that we are targeting our approach to mobile ad hoc networks, where hosts are physically mobile, communication links are frequently interrupted, and spatiotemporal considerations become increasingly important. We describe a distributed approach to task allocation in mobile ad hoc networks that employs heuristics to assign tasks in a workflow to mobile hosts based on their capabilities and their mobility patterns. We have implemented our algorithms in the context of CiAN, a workflow management system (WfMS) supporting collaborations in a mobile environment. In addition, we also present performance data of our algorithm and compare it to naive and brute force approaches. Type of Report: Other Department of Computer Science & Engineering Washington University in St. Louis Campus Box 1045 St. Louis, MO 63130 ph: (314) 935-6160 Distributed Allocation of Workflow Tasks in MANETs Rohan Sen, Gruia-Catalin Roman, and Christopher Gill Department of Computer Science and Engineering Washington University in St. Louis Campus Box 1045, One Brookings Drive St. Louis, MO 63130, U.S.A. Email: {rohan.sen, roman, cdgill}@wustl.edu Abstract—When multiple participants work on a workflow that represents a large, collaborative activity, it is important to have a well defined process to determine the portions of the workflow that each participant is responsible for executing. In this paper, we describe a process and related algorithms required to assign tasks in a workflow, to hosts that are willing to carry out the execution of these tasks, and thereby contributing to the completion of the activity. This problem is a stylized form of the multi-processor scheduling algorithm which has been shown to be NP-Hard. Further complicating the issue is that we are targeting our approach to mobile ad hoc networks, where hosts are physically mobile, communication links are frequently interrupted, and spatiotemporal considerations become increasingly important. We describe a distributed approach to task allocation in mobile ad hoc networks that employs heuristics to assign tasks in a workflow to mobile hosts based on their capabilities and their mobility patterns. We have implemented our algorithms in the context of CiAN, a workflow management system (WfMS) supporting collaborations in a mobile environment. In addition, we also present performance data of our algorithm and compare it to naive and brute force approaches.When multiple participants work on a workflow that represents a large, collaborative activity, it is important to have a well defined process to determine the portions of the workflow that each participant is responsible for executing. In this paper, we describe a process and related algorithms required to assign tasks in a workflow, to hosts that are willing to carry out the execution of these tasks, and thereby contributing to the completion of the activity. This problem is a stylized form of the multi-processor scheduling algorithm which has been shown to be NP-Hard. Further complicating the issue is that we are targeting our approach to mobile ad hoc networks, where hosts are physically mobile, communication links are frequently interrupted, and spatiotemporal considerations become increasingly important. We describe a distributed approach to task allocation in mobile ad hoc networks that employs heuristics to assign tasks in a workflow to mobile hosts based on their capabilities and their mobility patterns. We have implemented our algorithms in the context of CiAN, a workflow management system (WfMS) supporting collaborations in a mobile environment. In addition, we also present performance data of our algorithm and compare it to naive and brute force approaches.

Automated Code Management for Service Oriented Computing in Ad Hoc Networks

Ad hoc networks are dynamic environments where frequent disconnections and transient interactions lead to decoupled computing. Typically, participants in an ad hoc network are small mobile devices such as PDAs or cellular phones that have a limited amount of resources available locally, and must leverage the resources on other colocated devices to provide the user with a richer set of functionalities. Service-oriented computing (SOC), an emerging paradigm that seeks to establish a standard way of making resources and capabilities available for use by others in the form of services, is a useful model for engineering software that seeks to exploit capabilities on remote devices. This paper proposes an automatic code management system supporting SOC in ad hoc networks. The system is responsible for ensuring that the binary code required to use a service on a remote machine is available on the local host only when required. To support this functionality, a local code base is maintained by discovering and installing code from remote hosts. Since the system is specifically designed for ad hoc networks, it incorporates additional features that help it withstand the inherent dynamism of the network. We present an architecture for our system supporting automatic code management and follow it with a discussion of a Javabased implementation.