The Session Initiation Protocol (SIP) working group is chartered to maintain and continue the development of SIP, currently specified as proposed standard RFC 3261, and its family of extensions. SIP is a text-based protocol, similar to HTTP and SMTP, for initiating interactive communication sessions between users. Such sessions include voice, video, chat, interactive games, and virtual reality. The main tasks of the group involve bringing SIP from proposed to draft standard and specifying and developing proposed extensions that arise out of strong requirements. The SIP working group will concentrate on the specification of SIP and its extensions, and will not explore the use of SIP for specific environments or applications. It will, however respond to general- purpose requirements for changes to SIP provided by other working groups, including the SIPPING working group, when those requirements are within the scope and charter of SIP. The process and requirements for such extensions are documented in RFC 3427, "Change Process for the Session Initiation Protocol". Throughout its work, the group will strive to maintain the basic model and architecture defined by SIP. In particular: 1. Services and features are provided end-to-end whenever possible. 2. Standards-track extensions and new features must be generally applicable, and not applicable only to a specific set of session types. 3. Simplicity is key. 4. Reuse of existing Internet protocols and architectures and integrating with other Internet applications is crucial. The primary source of change requirements to be considered by the SIP Working Group is the SIPPING working group, which analyzes the requirements for application of SIP to several different tasks, including the tasks of standards-development organizations that are developing systems based on SIP and that may require changes or extensions thereto. Additional requirements are produced by the other IETF working groups that are using SIP, including the SIMPLE WG (which is using SIP for messaging and presence) and the XCON working group (which is using SIP for centralized conferencing). In addition to extending SIP as required to address these externally- derived requirements, the deliverables of the group include assuring capable security and privacy mechanisms within SIP and increasing the stability of the SIP specification. Specific deliverables toward these goals include: 1. Mechanisms for secure expression of identity in requests and responses. 2. Mechanism to securely request services delivery by non-terminal elements ("end-to-middle"). 3. Guidelines for use of existing security mechanisms such as TLS, IPsec, and certificates. 4. Guidelines for the use of descriptive techniques such as SAML (Security Association Markup Language) with SIP. 5. Draft standard versions of SIP and critical supporting specifications. Other deliverables may be agreed upon as extensions are understood to be necessary. Prospective deliverables will be discussed with the Area Director before inclusion on agendas, and new proposed work must be approved via a charter update.