ABSTRACT
A data service is something that is provided to the end user for a speci†c function, making use of a speci†c program (application program). Examples of data services include the Internet protocol (IP) telephony, web browsing, e-mail, †le transfer, and so on. ˆese services can be provided making use of a variety of application programs. For example, Microsoft Outlook, Microsoft Outlook Express, and Groupwise are three examples of speci†c application programs that can be used to have access to e-mail (service). Web browsing is also a service that can be accessed making use of Internet Explorer, Mozilla Firefox, Google Chrome, and so on.
