The Content-Disposition header field describes how the message body or,
for multipart messages, a message body part is to be interpreted by the
UAC or UAS. This SIP header field extends the MIME Content-Type. Several
new "disposition-types" of the Content-Disposition header are defined by
- session - indicates that the body part describes a session, for either
calls or early (pre-call) media.
- render - indicates that the body part should be displayed or otherwise
rendered to the user.
- icon - indicates that the body part contains an image suitable as an
iconic representation of the caller or callee that could be rendered
informationally by a user agent when a message has been received, or
persistently while a dialog takes place.
- alert - indicates that the body part contains information, such as an
audio clip, that should be rendered by the user agent in an attempt to alert
the user to the receipt of a request, generally a request that initiates a
For backward-compatibility, if the Content-Disposition header field is
missing, the server SHOULD assume bodies of Content-Type application/sdp are
the disposition "session", while other content types are "render".
If this header field is missing, the MIME type determines the default
content disposition. If there is none, "render" is assumed.