SIP - Message Body Header Fields



The Content-Encoding header field is used to indicate that the listed encoding scheme has been applied to the message body. It allows the UAS to determine the decoding scheme necessary to interpret the message body.

  • Only those encoding schemes listed in an Allow-Encoding header field may be used.

  • The compact form is e.

Content-Encoding: text/plain
e: gzip


The Content-Disposition header field is used to describe the function of a message body. Values include session, icon, alert, and render.

The value session indicates that the message body contains information to describe a media session.


The Content-Language header field is used to indicate the language of a message body. It contains a language tag, which identifies the language.

Content-Language: en


The Content-Length is used to indicate the number of octets in the message body.

A Content-Length: 0 indicates no message body.


The Content-Type header field is used to specify the Internet media type in the message body.

  • Media types have the familiar form of type/sub-type.

  • If this header field is not present, application/sdp is assumed.

  • If an Accept header field was present in the request, the response Content-Type must contain a listed type, or a 415 Unsupported Media Type response must be returned.

  • The compact form is c.

Content-Type: application/sdp


The MIME-Version header field is used to indicate the version of MIME protocol used to construct the message body.

SIP, like HTTP, is not considered MIME compliant because parsing and semantics are defined by the SIP standard, not the MIME specification. Version 1.0 is the default value.

MIME-Version: 1.0