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CIS*6650.01 Service-Oriented Computing

CIS*6650.01 Service-Oriented Computing. Qusay H. Mahmoud, Ph.D. qmahmoud@uoguelph.ca. WS-QoS. QoS for Web Services: Requirements and Possible Approaches http://www.w3c.or.kr/kr-office/TR/2003/ws-qos. WS-QoS. Web services provided by different vendors have unpredictable characteristics

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CIS*6650.01 Service-Oriented Computing

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  1. CIS*6650.01Service-Oriented Computing Qusay H. Mahmoud, Ph.D. qmahmoud@uoguelph.ca CIS*6650.01

  2. WS-QoS QoS for Web Services: Requirements and Possible Approaches http://www.w3c.or.kr/kr-office/TR/2003/ws-qos CIS*6650.01

  3. WS-QoS • Web services provided by different vendors have unpredictable characteristics • Different Web services with different QoS requirements will complete for network and system resources (bandwidth, processing time) • An enhanced QoS for Web services will bring competitive advantage to service providers • How to provide the desired QoS to clients? • What are possible QoS requirements? CIS*6650.01

  4. WS-QoS Requirements • Performance • How fast a service request can be completed? It can measure in terms of throughout, response time, latency, execution time, transaction time • Throughput: Number of web service requests served in a given time interval • Response time: Time required to complete a WS request • Latency: round-trip delay between sending a request and receiving the response • Execution time: Time taken by a WS to process its sequence of activities • Transaction time: Time that passes while the WS is completing one complete transaction • WS should provide high throughput, fast response time, low latency, low execution time, fast transaction time CIS*6650.01

  5. WS-QoS Requirements • Reliability • He ability of a WS to perform its required functions under stated conditions for a specified time interval • The overall measure of a WS to maintain its service quality • The overall measure is related to the number of failures per day, week, month, or year • It is also related to the assured and ordered delivery of messages • Scalability • The capability of increasing the computing capacity of service provider’s computer system and ability to process more users’ requests, operations or transaction in a given time interval CIS*6650.01

  6. WS-QoS Requirements • Capacity • The limit of the number of simultaneous requests that should be provided with guaranteed performance • Robustness • The degree to which a web service can function correctly even in the presence of invalid, incomplete or conflicting inputs. Still work if incomplete parameters are provided in a service request? • Exception handling • Should be able to handle exceptions (special cases and unanticipated possibilities) CIS*6650.01

  7. WS-QoS Requirements • Accuracy • The error rate generated by the WS. The number of errors that the service generates over a time interval should be minimized • Integrity • Prevent unauthorized access to, or modification of, programs or data (transferred data modified in transit?) • Accessibility • Represents whether the WS is capable of serving client’s requests CIS*6650.01

  8. WS-QoS Requirements • Availability • Ready for immediate consumption • Probability the system is up (related to reliability) • Time-to-Repair is associated with availability: the time it takes to repair the WS • Interoperability • No need to worry about platforms and languages • Security • Look at the WS-security slides from earlier lectures CIS*6650.01

  9. WS-QoS Requirements • Network-related QoS requirements • QoS mechanisms at the WS application level must operate together with the QoS mechanisms at the transport network layer • Application-level QoS should be mapped to corresponding network level QoS parameters • Basic network level QoS parameters include: network delay, packet loss CIS*6650.01

  10. Approaches for WS-QoS • 1. Extend UDDI • Publish QoS-enabled web services (register them in the UDDI registry) • UDDI data structure needs to be extended to describe specific QoS information for a WS CIS*6650.01

  11. Approaches to WS-QoS • 2. Extend SOAP • Extend the format of SOAP messages • Request: find a car reservation service of which availability is 0.8 CIS*6650.01

  12. Approaches to WS-QoS • …Response CIS*6650.01

  13. Approaches to WS-QoS • QoS-aware SOAP message routing • A sender may want the SOAP message to be handled with specific QoS as it traverses the SOAP message path to include multiple intermediaries • If the SOAP intermediary is QoS-aware, the QoS info can be used; if not QoS-aware, a fault is generated • Challenge: A certification protocol is need to describe how to register and certify the QoS-related information. Also, extensions to HTTP might be required to invoke lower-layer QoS mechanisms CIS*6650.01

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