This document defines the high level requirements for a framework and/or one or more mechanisms that support user interaction, via SIP-based user agents, with applications residing on remote network servers. The requirements in this document address the overall features of such a system, without regard to its architecture. SIP currently supports media-based application interactions using methods such as speech, video and end-to-end telephony-related tones; however, it is desired that more general application interaction models are defined, especially those that are not restricted to the media plane. In addition, it is desired that an application be able to present the user with application-specific user interfaces and information. The user agent should also be able to generate activity indications back to an application to communicate actions on physical or logical user interfaces. The document also defines a number of topic-related terms to assist in disambiguating discussions of the issues.