(per RFC3420) Media type name: message Media subtype name: sipfrag Required parameters: none Optional parameters: version Version: The SIP-Version number of the enclosed message (e.g., "2.0"). If not present, the version defaults to "2.0". Encoding scheme: SIP messages consist of an 8-bit header optionally followed by a binary MIME data object. As such, SIP messages must be treated as binary. Under normal circumstances SIP messages are transported over binary-capable transports, no special encodings are needed. Security considerations: see Section 6