Qusay H. Mahmoud CIS* CIS* Service-Oriented Computing Qusay H. Mahmoud, Ph.D.

Qusay H. Mahmoud CIS* WS-QoS QoS for Web Services: Requirements and Possible Approaches

Qusay H. Mahmoud CIS* 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?

Qusay H. Mahmoud CIS* 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

Qusay H. Mahmoud CIS* 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

Qusay H. Mahmoud CIS* 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)

Qusay H. Mahmoud CIS* 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

Qusay H. Mahmoud CIS* 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

Qusay H. Mahmoud CIS* 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

Qusay H. Mahmoud CIS* 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

Qusay H. Mahmoud CIS* 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

Qusay H. Mahmoud CIS* Approaches to WS-QoS …Response

Qusay H. Mahmoud CIS* 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