ssage body. Defined values include session, icon, alert, and render. The value session indicates that the message body contains informa- tion to describe a media session. The value render indicates that the message body should be displayed or otherwise rendered for the user. If a message body is present in a request or a 2xx response without a Content-Disposition, the function is assumed to be session. For all other response classes with message bodies, the default function is render. An example is: Content-Function: session 6.4.4 Content-Language The Content-Language header field [2] is used to indicate the language of a message body. It contains a language tag, which identifies the language. Content-Language: en SIP Header Fields 6.4.5 Content-Length The Content-Length is used to indicate the number of octets in the mes- sage body. A Content-Length: 0 indicates no message body. As described in Section 2.4.2, this header field is used to separate multiple messages sent within a TCP stream. If not present in a UDP message, the message body is assumed to continue to the end of the datagram. If not present in a TCP mes- sage, the message body is assumed to continue until the connection is closed. The Content-Length octet count does not include the CRLF that separates the message header fields from the message body. It does, however, include the CRLF at the end of each line of the message body. An example octet calculation is in Chapter 2. The Content-Length header field is not a required header field to allow dynamically generated message bodies, where the Content- Length may not be known a priori. The compact form is l. Examples include: Content-Length: 0 l: 287 6.4.6 Content-Type The Content-Type header field is used to specify the Internet media type [13] in the message body. Media types have the familiar form 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 Unsuppor