Programmable end system services using SIP

In Internet telephony, end systems can take a much larger role in providing services than in traditional telephony systems. We analyze the importance of end system services and describe the services and the Service Logic Execution Environment (SLEE) implemented in our SIP user agent, SIPC. Since we believe that end system services differ in their requirements from network services, we define a new service creation scripting language called Endpoint Service Markup Language (ESML). Compared with other service creation languages, ESML is extensible, can be easily understood by non-programmers and contains commands and events for direct user interaction and the control of media applications.