Asit Dan

Dynamic batching policies for an on-demand video server

In a video-on-demand environment, continuous delivery of video streams to the clients is guaranteed by sufficient reserved network and server resources. This leads to a hard limit on the number of streams that a video server can deliver. Multiple client requests for the same video can be served with a single disk I/O stream by sending (multicasting) the same data blocks to multiple clients (with the multicast facility, if present in the system). This is achieved by batching (grouping) requests for the same video that arrive within a short time. We explore the role of customerwaiting time and reneging behavior in selecting the video to be multicast. We show that a first come, first served (FCFS) policy that schedules the video with the longest outstanding request can perform better than the maximum queue length (MQL) policy that chooses the video with the maximum number of outstanding requests. Additionally, multicasting is better exploited by scheduling playback of the n most popular videos at predetermined, regular intervals (hence, termed FCFS-n). If user reneging can be reduced by guaranteeing that a maximum waiting time will not be exceeded, then performance of FCFS-n is further improved by selecting the regular playback intervals as this maximum waiting time. For an empirical workload, we demonstrate a substantial reduction (of the order of 60%) in the required server capacity by batching.

Web services on demand: WSLA-driven automated management

In this paper we describe a framework for providing customers of Web services differentiated levels of service through the use of automated management and service level agreements (SLAs). The framework comprises the Web Service Level Agreement (WSLA) language, designed to specify SLAs in a flexible and individualized way, a system to provision resources based on service level objectives, a workload management system that prioritizes requests according to the associated SLAs, and a system to monitor compliance with the SLA. This framework was implemented as the utility computing services part of the IBM Emerging Technologies Tool Kit, which is publicly available on the IBM alphaWorksTM Web site.

Service-Oriented Computing – ICSOC 2006

1: Research Track Full Papers.- Requirements and Method for Assessment of Service Interoperability.- An Aspect-Oriented Framework for Service Adaptation.- Automated Generation of BPEL Adapters.- Division of Labor: Tools for Growing and Scaling Grids.- DECO: Data Replication and Execution CO-scheduling for Utility Grids.- Coordinated Co-allocator Model for Data Grid in Multi-sender Environment.- Adaptive Preference Specifications for Application Sessions.- Mobile Ad Hoc Services: Semantic Service Discovery in Mobile Ad Hoc Networks.- Discovering Web Services and JXTA Peer-to-Peer Services in a Unified Manner.- A Hierarchical Framework for Composing Nested Web Processes.- Using Dynamic Asynchronous Aggregate Search for Quality Guarantees of Multiple Web Services Compositions.- Service Composition (re)Binding Driven by Application-1: Research Track Full Papers.- Requirements and Method for Assessment of Service Interoperability.- An Aspect-Oriented Framework for Service Adaptation.- Automated Generation of BPEL Adapters.- Division of Labor: Tools for Growing and Scaling Grids.- DECO: Data Replication and Execution CO-scheduling for Utility Grids.- Coordinated Co-allocator Model for Data Grid in Multi-sender Environment.- Adaptive Preference Specifications for Application Sessions.- Mobile Ad Hoc Services: Semantic Service Discovery in Mobile Ad Hoc Networks.- Discovering Web Services and JXTA Peer-to-Peer Services in a Unified Manner.- A Hierarchical Framework for Composing Nested Web Processes.- Using Dynamic Asynchronous Aggregate Search for Quality Guarantees of Multiple Web Services Compositions.- Service Composition (re)Binding Driven by Application-Specific QoS.- Design of Quality-Based Composite Web Services.- AMPol-Q: Adaptive Middleware Policy to Support QoS.- Adaptive Web Processes Using Value of Changed Information.- SCENE: A Service Composition Execution Environment Supporting Dynamic Changes Disciplined Through Rules.- A Self-healing Web Server Using Differentiated Services.- Quality of Service Enabled Database Applications.- A Model-Based Framework for Developing and Deploying Data Aggregation Services.- A Distributed Approach for the Federation of Heterogeneous Registries.- I-Queue: Smart Queues for Service Management.- Optimizing Differential XML Processing by Leveraging Schema and Statistics.- Optimized Web Services Security Performance with Differential Parsing.- Web Browsers as Service-Oriented Clients Integrated with Web Services.- Interaction Soundness for Service Orchestrations.- Modeling Web Services by Iterative Reformulation of Functional and Non-functional Requirements.- SOCK: A Calculus for Service Oriented Computing.- A Priori Conformance Verification for Guaranteeing Interoperability in Open Environments.- A Business-Aware Web Services Transaction Model.- Licensing Services: Formal Analysis and Implementation.- QoS Assessment of Providers with Complex Behaviours: An Expectation-Based Approach with Confidence.- A QoS-Aware Selection Model for Semantic Web Services.- UML-Based Service Discovery Framework.- BPEL-Unit: JUnit for BPEL Processes.- 2: Research Track Short Papers.- A User Driven Policy Selection Model.- Abstract Transaction Construct: Building a Transaction Framework for Contract-Driven, Service-Oriented Business Processes.- Securing Web Service Compositions: Formalizing Authorization Policies Using Event Calculus.- Supporting QoS Monitoring in Virtual Organisations.- Event Based Service Coordination over Dynamic and Heterogeneous Networks.- Implicit vs. Explicit Data-Flow Requirements in Web Service Composition Goals.- Light-Weight Semantic Service Annotations Through Tagging.- Service-Oriented Model-Driven Development: Filling the Extra-Functional Property Gap.- WSMX: A Semantic Service Oriented Middleware for B2B Integration.- Top Down Versus Bottom Up in Service-Oriented Integration: An MDA-Based Solution for Minimizing Technology Coupling.- Semantic Service Mediation.- Examining Usage Protocols for Service Discovery.- Sliver: A BPEL Workflow Process Execution Engine for Mobile Devices.- Automated Discovery of Compositions of Services Described with Separate Ontologies.- Dynamic Web Service Selection and Composition: An Approach Based on Agent Dialogues.- Leveraging Web Services Discovery with Customizable Hybrid Matching.- 3: Industrial Track Vision and Full Papers.- Assembly of Business Systems Using Service Component Architecture.- The End of Business as Usual: Service-Oriented Business Transformation.- A Service Oriented Reflective Wireless Middleware.- Procedures of Integration of Fragmented Data in a P2P Data Grid Virtual Repository,.- Towards Facilitating Development of SOA Application with Design Metrics.- Dynamic Service Oriented Architectures Through Semantic Technology.- A Service Oriented Architecture Supporting Data Interoperability for Payments Card Processing Systems.- Services-Oriented Computing in a Ubiquitous Computing Platform.- SCA Policy Association Framework.- A Model-Driven Development Approach to Creating Service-Oriented Solutions.- Towards Adaptive Management of QoS-Aware Service Compositions - Functional Architecture.

Cremona: an architecture and library for creation and monitoring of WS-agreents

Using services across domain boundaries, be they organizations or self-managing components of large distributed systs, requires the setup of an agreent between the parties involved, defining the terms of the service including interfaces, security and Quality of Service (QoS) properties. In an on-dand environment in which services are contracted on a short notice, the establishment of an agreent as well as the setup of agreement-fulfilling and monitoring systs of the parties involved must be spontaneous and, partially, automated. WS-Agreent is a standardization effort being conducted in the Global Grid Forum defining a simple agreent establishment protocol, an XML-representation of agreements and agreent tplates as well as a runtime agreement monitoring interface, based on the WSRF set of standards. WS-Agreent standardizes the interaction between the organizational domains. In addition, providers require an infrastructure to manage agreent tplates, implent the interfaces, check availability of service capacity and expose agreement states at runtime. Also, agreent requesters need infrastructure to read tplates, fill in tplates to create suitable agreements, and monitor agreent state at runtime. Crona (Creation and Monitoring of Agreents) proposes an architecture for the WS-Agreent-implenting middleware. In addition, the Crona Java Library implents the WS-Agreent interfaces, provides management functionality for agreement tplates and instances, and defines abstractions of service-providing systs that can be implented in a domain-specific environment.

A service level agreement language for dynamic electronic services

This paper proposes a novel language for Service Level Agreements (SLAs) for dynamic and spontaneous electronic services. In a cross-organizational setting, it is important for customers of a service to obtain, monitor and enforce quality of service (QoS) guarantees by service providers, usually expressed in the form of SLAs. Since the supervision and management of SLAs and the provisioning of corresponding systems should be automated for economic reasons, we need a formal language to define an SLA. If moreover, providers and customers want to sign custom-made SLAs, the SLA language, correspondingly, must provide a large degree of flexibility. The SLA language described in this paper aims at providing the needed flexibility by means of an XML-based representation and a runtime system for SLAs. Using this language, parties to a SLA can describe how parameters are measured and computed from raw metrics, the guarantees they want with respect to those parameters and the involvement of third parties to, e.g., verify independently SLA compliance.

Buffering and caching in large-scale video servers

Video-on-demand servers are characterized by stringent real-time constraints, as each stream requires isochronous data playout. The capacity of the system depends on the acceptable jitter per stream (the number of data blocks that do not meet their real-time constraints). Per-stream read-ahead buffering avoids the disruption in playback caused by variations in disk access time and queuing delays. With heavily skewed access patterns to the stored video data, the system is often disk arm-bound. In such cases, serving video streams from a memory cache can result in a substantial reduction in server cost. In this paper, we study the cost-performance trade-offs of various buffering and caching strategies that can be used in a large-scale video server. We first study the cost impact of varying the buffer size, disk utilization and the disk characteristics on the overall capacity of the system. Subsequently, we study the cost-effectiveness of a technique for memory caching across streams that exploits temporal locality and workload fluctuations.

Resource-based caching for Web servers

The WWW employs a hierarchical data dissemination architecture in which hyper-media objects stored at a remote server are served to clients across the Internet, and cached on disks at intermediate proxy servers. One of the objectives of web caching algorithms is to maximize the data transferred from the proxy servers or cache hierarchies. Current web caching algorithms are designed only for text and image data. Recent studies predict that within the next five years more than half the objects stored at web servers will contain continuous media data. To support these trends, the next generation proxy cache algorithms will need to handle multiple data types, each with different cache resource usage, for a cache limited by both bandwidth and space. In this paper, we present a resource-based caching (RBC) algorithm that manages the heterogeneous requirements of multiple data types. The RBC algorithm (1) characterizes each object by its resource requirement and a caching gain, (2) dynamically selects the granularity of the entity to be cached that minimally uses the limited cache resource (i.e., bandwidth or space), and (3) if required, replaces the cached entities based on their cache resource usage and caching gain. We have performed extensive simulations to evaluate our caching algorithm and present simulation results that show that RBC outperforms other known caching algorithms.

An online video placement policy based on bandwidth to space ratio (BSR)

In a video-on-demand server, resource reservation is required to guarantee continuous delivery. Hence any given storage device (or a striping group treated as a single logical device) can serve only up to a fixed number of client access streams. Each storage device is also limited by the number of video files it can store. For the reasons of availability, incremental growth, and heterogeneity, there may be multiple storage devices in a video server environment. Hence, one or more copies of a particular video may be placed on different storage devices. Since the access rates to different videos are not uniform, there may be load imbalance among the devices. In this paper, we propose a dynamic placement policy (called the Bandwidth to Space Ratio (BSR) Policy) that creates and/or deletes replica of a video, and mixes hot and cold videos so as to make the best use of bandwidth and space of a storage device. The proposed policy is evaluated using a simulation study.

Channel Allocation under Batching and VCR Control in Video-on-Demand Systems

In order to guarantee continuous delivery of a video stream in an on-demand video server environment, a collection of resources (referred to as a logical channel) are reserved in advance. To conserve server resources, multiple client requests for the same video can be batched together and served by a single channel. Increasing the window over which all requests for a particular video are batched results in larger savings in server capacity; however, it also increases the reneging probability of a client. A complication introduced by batching is that if a batched client pauses, a new stream (which may not be immediately available) needs to be started when the client resumes. To provide short response time to resume requests, some channels are set aside and are referred to as contingency channels. To further improve resource utilization, even when a nonbatched client pauses, the channel is released and reacquired upon resume. In this paper, we first develop an analytical model that predicts the reneging probability and expected resume delay, and then use this model to optimally allocate channels for batching, on-demand playback, and contingency. The effectiveness of the proposed policy over a scheme with no contingency channels and no batching is also demonstrated.

A dynamic policy of segment replication for load-balancing in video-on-demand servers

In a video-on-demand server, resource reservation is needed for continuous delivery. Hence, any given server can serve only a fixed maximum of clients. Different videos can be placed on different disks or disk array groups. Since the access rates to various movies are not uniform, load imbalance can occur among the disks in the system. In this paper, we propose a dynamic policy that replicates segments of files to balance the load across the disks. By using simulation, we show that the proposed policy is responsive to quick load surges and is superior to a policy based on the static replication of hot movies.