7. Alert-Info Appearance Parameter Definition

This specification defines a new parameter "appearance" for the Alert-Info header field defined in [RFC3261]. The ABNF [RFC5234] for this parameter is:

appearance = "appearance" EQUAL 1*DIGIT

The Alert-Info header field is used in this specification in INVITE requests to communicate the appearance number to UAs. The "appearance" parameter is only valid in Alert-Info header fields in INVITE requests and responses to INVITE requests. The "appearance" parameter MUST NOT be used in any other SIP method or header field.

The following example shows an INVITE request with an appearance number of "3":

INVITE sip:[email protected] SIP/2.0
Alert-Info: <urn:alert:service:normal>;appearance=3

The Appearance Agent is the only entity that inserts an "appearance" parameter in an Alert-Info header field. UAs MUST NOT insert this parameter.