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Level: Introductory
Anbazhagan Mani (manbazha@in.ibm.com), Software engineer, IBM Software Labs, India
Arun Nagarajan (anagaraj@in.ibm.com), Software engineer, IBM Global Services India

01 Jan 2002

With the widespread proliferation of Web services, quality of service (QoS) will become a significant factor in distinguishing the success of service providers. QoS determines the service usability and utility, both of which influence the popularity of the service. In this article, we look at the various Web service QoS requirements, bottlenecks affecting performance of Web services, approaches of providing service quality, transactional services, and a simple method of measuring response time of your Web services using the service proxy.

The dynamic e-business vision calls for a seamless integration of business processes, applications, and Web services over the Internet. Delivering QoS on the Internet is a critical and significant challenge because of its dynamic and unpredictable nature. Applications with very different characteristics and requirements compete for scarce network resources. Changes in traffic patterns, denial-of-service attacks and the effects of infrastructure failures, low performance of Web protocols, and security issues over the Web create a need for Internet QoS standards. Often, unresolved QoS issues cause critical transactional applications to suffer from unacceptable levels of performance degradation.

With standards like SOAP, UDDI, and WSDL being adopted by all major Web service players, a whole range of Web services — covering the financial services, high-tech, and media and entertainment — are being currently developed. As most of the Web services are going to need to establish and adhere to standards, QoS will become an important selling and differentiating point of these services.

QoS covers a whole range of techniques that match the needs of service requestors with those of the service provider’s based on the network resources available. By QoS, we refer to non-functional properties of Web services such as performance, reliability, availability, and security.

Web service QoS requirements

The major requirements for supporting QoS in Web services are as follows:

• Availability: Availability is the quality aspect of whether the Web service is present or ready for immediate use. Availability represents the probability that a service is available. Larger values represent that the service is always ready to use while smaller values indicate unpredictability of whether the service will be available at a particular time. Also associated with availability is time-to-repair (TTR). TTR represents the time it takes to repair a service that has failed. Ideally smaller values of TTR are desirable.
   
• Accessibility: Accessibility is the quality aspect of a service that represents the degree it is capable of serving a Web service request. It may be expressed as a probability measure denoting the success rate or chance of a successful service instantiation at a point in time. There could be situations when a Web service is available but not accessible. High accessibility of Web services can be achieved by building highly scalable systems. Scalability refers to the ability to consistently serve the requests despite variations in the volume of requests.
   
• Integrity: Integrity is the quality aspect of how the Web service maintains the correctness of the interaction in respect to the source. Proper execution of Web service transactions will provide the correctness of interaction. A transaction refers to a sequence of activities to be treated as a single unit of work. All the activities have to be completed to make the transaction successful. When a transaction does not complete, all the changes made are rolled back.