2.2.2 SIP Extensions to XPIDF Presence Document Format
SIP allows the SIP endpoints to communicate in a P2P mode without requiring an SIP server. The endpoints can also subscribe for presence information and send notifications carrying such information in a P2P manner. Session Initiation Protocol Extensions uses the XPIDF format to exchange presence information when the endpoints are acting in P2P mode.
The XPIDF format was introduced in an IETF draft but was never standardized as an RFC. The details of the format and the schema are included in Appendix B: XPIDF Presence Document Format (section 7).
Session Initiation Protocol Extensions introduces the following extensions to the XPIDF presence document format:
A new element, "display", is defined as a subelement of a presence element. The display element has the attribute name that is a suggested name to identify a contact from other contacts in the client's contact list.
A new element, "msnsubstatus", is defined as a subelement of the address element. This element indicates the availability of the user. The msnsubstatus element has the attribute substatus that can have the following values: unknown, away, online, idle, busy, berightback, onthephone, or outtolunch. The interpretation of these values is as follows:
There is no information about the activity of the user.
User is away.
User is active and available for communication.
User is idle.
User is busy.
User will be right back.
User is on the phone.
User is out to lunch.