IANA Registration of the 'image' Media Type for the Session Description Protocol (SDP)
Extracted elements (6)
RFC 4566 requested an SDP-specific media type registry separate from the MIME media types namespace used by the earlier RFC 2327. The top-level types registered by RFC 4566 ('audio', 'video', 'text', 'application', 'message') omitted 'image', which was already widely deployed for T.38 fax-over-IP — necessitating this registration.
The 'image' media type is an existing top-level MIME media type widely used in SDP implementations. Registering it as a top-level SDP media type ensures seamless continuity with documentation and previously registered MIME sub-types like 'image/t38' (RFC 3362) used as SDP media descriptors for T.38.
Per RFC 4566 Section 8.2.1, a Standards Track RFC MUST be produced for a new top-level SDP media content type to be registered, and the registration MUST provide good justification why no existing media name is appropriate.
The 'image' media type for SDP is used to describe a media stream whose content consists of one or more separate images. The media subtype further describes the specific format of the image, and it is primarily used to establish T.38 real-time facsimile media streams via SIP.
IANA has registered the 'image' token in the media sub-registry of the Session Description Protocols (SDP) Parameters registry, with type 'media', per the SDP registration procedure in RFC 4566 Section 8.2.8.
The 'image' SDP media type does not introduce security considerations beyond those in RFC 4566 Section 7. However, the ability to exchange images other than T.38 can expose the recipient to potentially malicious executable code.