SIP Working Group G. Camarillo Internet-Draft Ericsson Expires: July 26, 2008 January 23, 2008 Message Body Handling in the Session Initiation Protocol (SIP) draft-ietf-sip-body-handling-01.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on July 26, 2008. Copyright Notice Copyright (C) The IETF Trust (2008). Abstract This document specifies how message bodies are handled in SIP. Additionally, it specifies SIP user agent support for MIME (Multipurpose Internet Mail Extensions) in message bodies. Camarillo Expires July 26, 2008 [Page 1] Internet-Draft Message Body Handling in SIP January 2008 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Message Body Encoding . . . . . . . . . . . . . . . . . . . . 3 3.1. Background on Message Body Encoding . . . . . . . . . . . 3 3.2. UA Behavior to Encode Binary Message Bodies . . . . . . . 5 4. Multipart Message Bodies . . . . . . . . . . . . . . . . . . . 6 4.1. Background on 'multipart' Message Bodies . . . . . . . . . 6 4.2. Mandatory Support for 'multipart' Message Bodies . . . . . 6 4.3. UA Behavior to Generate 'multipart' Message Bodies . . . . 7 5. Multipart/alternative Message Bodies . . . . . . . . . . . . . 7 5.1. Background on 'multipart/alternative' Message Bodies . . . 7 5.2. UA Behavior to Generate 'multipart/alternative' Message Bodies . . . . . . . . . . . . . . . . . . . . . . 8 6. Disposition Types . . . . . . . . . . . . . . . . . . . . . . 8 6.1. Background on Content and Disposition Types in SIP . . . . 8 6.2. UA Behavior to Set the 'handling' Parameter . . . . . . . 10 6.3. UAS Behavior to Report Unsupported Message Bodies . . . . 11 7. Message Body Processing . . . . . . . . . . . . . . . . . . . 11 7.1. Background on References to Message Body Parts . . . . . . 11 7.2. UA Behavior to Generate References to Message Bodies . . . 12 7.3. UA Behavior to Process Message Bodies . . . . . . . . . . 12 7.4. The 'by-reference' Disposition Type . . . . . . . . . . . 12 8. Guidelines to Authors of SIP Extensions . . . . . . . . . . . 13 9. Security Considerations . . . . . . . . . . . . . . . . . . . 14 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 12.1. Normative References . . . . . . . . . . . . . . . . . . . 14 12.2. Informational References . . . . . . . . . . . . . . . . . 15 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 16 Intellectual Property and Copyright Statements . . . . . . . . . . 17 Camarillo Expires July 26, 2008 [Page 2] Internet-Draft Message Body Handling in SIP January 2008 1. Introduction Originally, message body handling in SIP was specified in [RFC3261], which relied on earlier specifications (e.g., MIME) to describe some areas. This document contains background material on how bodies are handled in SIP and normative material on areas that had not been specified before or whose specifications needed to be completed. Sections containing background material are clearly identified as such by their titles. The material on the normative sections is based on experience gained since [RFC3261] was written. 2. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. UA: User Agent UAC: User Agent Client UAS: User Agent Server URL: Uniform Resource Locator 3. Message Body Encoding This section deals with the encoding of message bodies in SIP. 3.1. Background on Message Body Encoding SIP [RFC3261] messages consist of an initial line (request line in requests and status line in responses), a set of header fields, and an optional message body. The message body is described using header fields such as Content-Disposition, Content-Encoding, and Content- Type, which provide information on its contents. Figure 1 shows a SIP message that carries a body. Some of the header fields are not shown for simplicity: Camarillo Expires July 26, 2008 [Page 3] Internet-Draft Message Body Handling in SIP January 2008 INVITE sip:conf-fact@example.com SIP/2.0 Content-Type: application/sdp Content-Length: 192 v=0 o=alice 2890844526 2890842807 IN IP4 atlanta.example.com s=- c=IN IP4 192.0.2.1 t=0 0 m=audio 20000 RTP/AVP 0 a=rtpmap:0 PCMU/8000 m=video 20002 RTP/AVP 31 a=rtpmap:31 H261/90000 Figure 1: SIP message carrying a body The message body of a SIP message can be divided into various body parts. Multipart message bodies are encoded using the MIME (Multipurpose Internet Mail Extensions) [RFC2045] format. Body parts are also described using header fields such as Content-Disposition, Content-Encoding, and Content-Type, which provide information on the contents of a particular body part. Figure 2 shows a SIP message that carries two body parts. Some of the header fields are not shown for simplicity: Camarillo Expires July 26, 2008 [Page 4] Internet-Draft Message Body Handling in SIP January 2008 INVITE sip:conf-fact@example.com SIP/2.0 Content-Type: multipart/mixed;boundary="boundary1" Content-Length: 617 --boundary1 Content-Type: application/sdp v=0 o=alice 2890844526 2890842807 IN IP4 atlanta.example.com s=- c=IN IP4 192.0.2.1 t=0 0 m=audio 20000 RTP/AVP 0 a=rtpmap:0 PCMU/8000 m=video 20002 RTP/AVP 31 a=rtpmap:31 H261/90000 --boundary1 Content-Type: application/resource-lists+xml Content-Disposition: recipient-list --boundary1-- Figure 2: SIP message carrying a body SIP uses S/MIME [RFC3850] to protect message bodies. As specified in [RFC3261], UASs that cannot decrypt a message body or a body part can use the 493 (Undecipherable) response to report the error. 3.2. UA Behavior to Encode Binary Message Bodies SIP messages can carry binary message bodies such as legacy signalling objects [RFC3204]. SIP proxy servers are 8-bit safe. That is, they are able to handle binary bodies. Therefore, there is no need to use encodings such as base64 to transport binary bodies in SIP messages. Consequently, UAs MUST use the binary transfer encoding for binary payloads in SIP. Camarillo Expires July 26, 2008 [Page 5] Internet-Draft Message Body Handling in SIP January 2008 4. Multipart Message Bodies This section deals with 'multipart' message bodies and their handling. 4.1. Background on 'multipart' Message Bodies [RFC3261] did not mandate support for multipart message bodies in MIME format [RFC2046]. However, since [RFC3261] was written, many SIP extensions rely on them. The use of 'multipart/mixed' MIME bodies is a useful tool to build SIP extensions. An example of such an extension could be the inclusion of location information in an INVITE request. Such an INVITE request would use the 'multipart/mixed' MIME type [RFC2046] to carry two body parts: a session description and a location object. An example of an existing extension that uses 'multipart/mixed' to send a session description and a legacy-signalling object is defined in [RFC3204]. Another MIME type that is useful to build SIP extensions is 'multipart/alternative' [RFC2046]. Each body part within a 'multipart/alternative' carries an alternative version of the same information. The transition from SDP to new session description protocols could be implemented using 'multipart/alternative' bodies. SIP messages (e.g., INVITE requests) could carry a 'multipart/alternative' body with two body parts: a session description written in SDP and a session description written in a newer session description format. Legacy recipient UAs would use the session description written in SDP. New recipient UAs would use the one written in the newer format. Nested MIME bodies are yet another useful tool to build and combine SIP extensions. Using the extensions in the previous examples, a UA that supported a new session description format and that needed to include a location object in an INVITE request would include a 'multipart/mixed' body with two body parts: a location object and a 'multipart/alternative'. The 'multipart/alternative' body part would, in turn, have two body parts: a session description written in SDP and a session description written in the newer session description format. 4.2. Mandatory Support for 'multipart' Message Bodies For all MIME-based extensions to work, the recipient needs to be able to decode the multipart bodies. Therefore, SIP UAs MUST be able to Camarillo Expires July 26, 2008 [Page 6] Internet-Draft Message Body Handling in SIP January 2008 parse 'multipart' MIME bodies, including nested body parts. In particular, UAs MUST support the 'multipart/mixed' and 'multipart/ alternative' MIME types. Note that, by default, unknown 'multipart' subtypes are treated as 'multipart/mixed'. Also note that SIP extensions may also include 'multipart' MIME bodies in responses. That is why both UACs and UASs need to support 'multipart' bodies. Legacy SIP UAs without support for 'multipart' bodies generate a 415 (Unsupported Media Type) response when they receive a 'multipart' body. A UAC sending a 'multipart' body may receive such an error response when communicating with a legacy SIP UA that predates this specification. It has been observed on the field that a number of legacy SIP UAs without support for 'multipart' bodies simply ignored those bodies when they were received. These UAs did not return any error response. Unsurprisingly, SIP UAs not being able to report this type of error have caused serious interoperability problems in the past. 4.3. UA Behavior to Generate 'multipart' Message Bodies UAs SHOULD avoid unnecessarily nesting body parts because doing so would, unnecessarily, make processing the body more laborious for the receiver. However, [RFC2046] states that a 'multipart' media type with a single body part is useful in some circumstances (e.g., for sending non-text media types). In any case, UAs SHOULD NOT nest one 'multipart/mixed' within another unless there is a need to reference the nested one (i.e., using the Content ID of the nested body part). Additionally, UAs SHOULD NOT nest one 'multipart/alternative' within another. 5. Multipart/alternative Message Bodies This section deals with 'multipart/alternative' message bodies and their handling. 5.1. Background on 'multipart/alternative' Message Bodies Each body part within a 'multipart/alternative' carries an alternative version of the same information. The body parts are ordered so that the last one is the richest representation of the information. This way, the recipient of a 'multipart/alternative' body chooses the last body part it understands. Camarillo Expires July 26, 2008 [Page 7] Internet-Draft Message Body Handling in SIP January 2008 Note that within a body part encoded in a given format (i.e., of a given content type), there may be optional elements that may provide richer information to the recipient in case the recipient supports them. For example, in SDP (Session Description Protocol) [RFC4566], those optional elements are encoded in 'a' lines. These types of optional elements are internal to a body part and are not visible at the MIME level. That is, a body part is understood if the recipient understands its content type, regardless of whether or not the body part's optional elements are understood. Note as well that each part of a 'multipart/alternative' body represents the same data, but the mapping between any two parts is not necessarily without information loss. For example, information may be lost when translating 'text/html' to 'text/ plain'. [RFC2046] recommends that each part should have a different Content-ID value in the case where the information content of the two parts is not identical. 5.2. UA Behavior to Generate 'multipart/alternative' Message Bodies All the body parts within a 'multipart/alternative' have the same disposition type (see Section 6.2). The 'session' and 'early- session' [RFC3959] disposition types require that all the body parts of a 'multipart/alternative' body have different content types. Consequently, for the 'session' and 'early-session' disposition types, UAs MUST NOT place more than one body part with a given content type in a 'multipart/alternative' body. That is, for 'session' and 'early-session', no body part within a 'multipart/ alternative' can have the same content type as another body part within the same 'multipart/alternative'. 6. Disposition Types This section deals with disposition types in message bodies. 6.1. Background on Content and Disposition Types in SIP The Content-Disposition header field, defined in [RFC2183] and extended by [RFC3261], describes how to handle a SIP message's body or an individual body part. Examples of disposition types used in SIP in the Content-Disposition header field are 'session' and 'render'. [RFC3204] and [RFC3459] define the 'handling' parameter for the Content-Disposition header field. This parameter describes how a UAS should react if it receives a message body whose content type or Camarillo Expires July 26, 2008 [Page 8] Internet-Draft Message Body Handling in SIP January 2008 disposition type it does not understand. If the parameter has the value 'optional', the UAS ignores the message body; if it has the value 'required', the UAS returns a 415 (Unsupported Media Type) response. The default value for the 'handling' parameter is 'required'. The following is an example of a Content-Disposition header field: Content-Disposition: signal; handling=optional [RFC3204] identifies two situations where a UAS (User Agent Server) needs to reject a request with a body part whose handling is required: 1. if it has an unknown content type. 2. if it has an unknown disposition type. If the UAS did not understand the content type of the body part, it can add an Accept header field to its 415 (Unsupported Media Type) response listing the content types that the UAS does understand. Nevertheless, there is no mechanism for a UAS that does not understand the disposition type of a body part to inform the UAC about which disposition type was not understood or about the disposition types that are understood by the UAS. The reason for not having such a mechanism is that disposition types are typically supported within a context. Outside that context, a UA may not support the disposition type. For example, a UA may support the 'session' disposition type for body parts in INVITE and UPDATE requests and their responses. However, the same UA would not support the 'session' disposition type in MESSAGE requests. In another example, a UA may support the 'render' disposition type for 'text/plain' and 'text/html' body parts in MESSAGE requests. Additionally, the UA may support the 'session' disposition type for 'application/sdp' body parts in INVITE and UPDATE requests and their responses. However, the UA may not support the 'render' disposition type for 'application/sdp' body parts in MESSAGE requests, even if, in different contexts, the UA supported all the 'render' disposition type, the 'application/sdp' content type, and the MESSAGE method. A given context is generally (but not necessarily) defined by a method, a disposition type, and a content type. Support for a specific context is usually defined within an extension. For example, the extension for instant messaging in SIP [RFC3428] mandates support for the MESSAGE method, the 'render' disposition type, and the 'text/plain' content type. Camarillo Expires July 26, 2008 [Page 9] Internet-Draft Message Body Handling in SIP January 2008 Note that, effectively, content types are also supported within a context. Therefore, the use of the Accept header field in a 415 (Unsupported Media Type) response is not enough to describe in which contexts a particular content type is supported. Therefore, support for a particular disposition type within a given context is typically signalled by the use of a particular method or an option-tag in a Supported or a Require header field. When support for a particular disposition type within a context is mandated, support for a default content type is also mandated (e.g., a UA that supports the 'session' disposition type in an INVITE request needs to support the 'application/sdp' content type). 6.2. UA Behavior to Set the 'handling' Parameter As stated earlier, the 'handling' Content-Disposition parameter can take two values: 'required' or 'optional'. While it is typically easy for a UA to decide which type of handling an individual body part requires, setting the 'handing' parameter of 'multipart' bodies requires extra considerations. If at least one of the body parts within a 'multipart/mixed' body has a 'handling' value of 'required', the UA MUST set the 'handling' parameter of the 'multipart/mixed' body to 'required'. If all the body parts within a 'multipart/mixed' body have a 'handling' value of 'optional', the UA MUST set the 'handling' parameter of the 'multipart/mixed' body to 'optional'. The 'handling' parameter is a Content-Disposition parameter. Therefore, in order to set this parameter, it is necessary to provide the 'multipart/mixed' body with a disposition type. Per [RFC3261], the default disposition type for 'application/sdp' is 'session' and for other bodies is 'render'. UAs SHOULD assign 'multipart/mixed' bodies a disposition type of 'render'. Note that the fact that 'multipart/mixed' bodies have a default disposition type of 'render' does not imply that they will be rendered to the user. The way the body parts within the 'multipart/mixed' are handled depends on the disposition types of the individual body parts. The actual disposition type of the whole 'multipart/mixed' is irrelevant. The 'render' disposition type has been chosen for 'multipart/mixed' bodies simply because it is the default disposition type in SIP. If the handling of a 'multipart/alternative' body is required, the UA MUST set the 'handling' parameter of the 'multipart/alternative' body to 'required'. The UA MUST also set the 'handling' parameter of the last body part within the 'multipart/alternative' to 'required'. Camarillo Expires July 26, 2008 [Page 10] Internet-Draft Message Body Handling in SIP January 2008 Additionally, the UA MUST set the 'handling' parameter of all body parts within the 'multipart/alternative' except the last one to 'optional'. The UA MUST use the same disposition type for the 'multipart/alternative' body and all its body parts. 6.3. UAS Behavior to Report Unsupported Message Bodies If a UAS cannot process a request because, in the given context, it does not support the content type or the disposition type of a body part whose handling is required, the UAS SHOULD return a 415 (Unsupported Media Type) response even if the UAS supported the content type, the disposition type, or both in a different context. Consequently, it is possible to receive a 415 (Unsupported Media Type) response with an Accept header field containing all the content types used in the request. If a UAS receives a request with a body part whose disposition type is not compatible with the way the body part should be handled according to other parts of the SIP message (e.g., a Refer-To header field with a Content-ID URL pointing to a body part whose disposition type is 'session'), the UAS SHOULD return a 415 (Unsupported Media Type) response. 7. Message Body Processing This section deals with the processing of message bodies and how it is influenced by the presence of references to them. 7.1. Background on References to Message Body Parts Content-ID URLs allow creating references to body parts. A given Content-ID URL [RFC2392], which can appear in a header field or within a body part (e.g., in an SDP attribute), points to a particular body part. The way to handle that body part is defined by the field the Content-ID URL appears. For example, the extension to refer to multiple resources in SIP [I-D.ietf-sip-multiple-refer] places a Content-ID URL in a Refer-To header field. Such a Content-ID URL points to a body part that carries a URI list. In another example, the extension for file transfer in SDP [I-D.ietf-mmusic-file-transfer-mech] places a Content-ID URL in a 'file-icon' SDP attribute. This Content-ID URL points to a body part that carries a (typically small) picture. Camarillo Expires July 26, 2008 [Page 11] Internet-Draft Message Body Handling in SIP January 2008 7.2. UA Behavior to Generate References to Message Bodies UAs MUST only include forward references in the SIP messages they generate. That is, an element in a SIP message can reference a body part only if the body part appears after the element. Consequently, a given body part can only be referenced by another body part that appears before it or by a header field. Having only forward references allows recipients to process body parts as they parse them. They do not need to parse the remainder of the message in order to process a body part. It was considered to only allow (forward) references among body parts that belonged to the same 'multipart/related' [RFC2387] wrapper. However, it was finally decided that this extra constrain was not necessary. 7.3. UA Behavior to Process Message Bodies In order to process a message body or a body part, a UA needs to know whether a SIP header field or another body part contains a reference to it (e.g., a Content-ID URL pointing to it). If the body part is not referenced in any way (e.g., there are no header fields or other body parts with a Content-ID URL pointing to it), the UA processes the body part as indicated by its disposition type and the context in which the body part was received. If the SIP message contains a reference to the body part, the UA processes the body part according to the reference. If the SIP message contains more than one reference to the body part (e.g., two header fields contain Content-ID URLs pointing to the body part), the UA processes the body part as many times as references are. Note that, following the rules in [RFC3204], if a UA does not understand a body part whose handling is optional, it ignores it. Also note that the content indirection mechanism in SIP [RFC4483] allows UAs to point to external bodies. Therefore, a UA receiving a SIP message that uses content indirection may need to fetch a body part (e.g., using HTTP [RFC2616]) in order to process it. 7.4. The 'by-reference' Disposition Type Per the rules in Section 7.3, if a SIP message contains a reference to a body part, the UA processes the body part according to the reference. Since the reference provides the context in which the body part needs to be processed, the disposition type of the body part is irrelevant. However, a UA that missed a reference to a body part (e.g., because the reference was in a header field the UA did not support) would attempt to process the body part according to its Camarillo Expires July 26, 2008 [Page 12] Internet-Draft Message Body Handling in SIP January 2008 disposition type alone. To keep this from happening, we define a new disposition type for the Content-Disposition header field: by- reference. A body part whose disposition type is 'by-reference' needs to be handled according to a reference to the body part that is located in the same SIP message as the body part (given that SIP only allows forward references, the reference will appear in the same SIP message before the body part). A recipient of a body part whose disposition type is 'by-reference' that cannot find any reference to the body part (e.g., the reference was in a header field the recipient does not support and, thus, did not process) MUST NOT process the body part. Consequently, if the handling of the body part was required, the UA needs to report an error. Note that extensions that predate this specifications use references to body parts whose disposition type is not 'by- reference'. Those extensions use option-tags to make sure the recipient understands the whole extension and, thus, cannot miss the reference and attempt to process the body part according to its disposition type alone. 8. Guidelines to Authors of SIP Extensions These guidelines are intended for authors of SIP extensions that involve, in some way, message bodies or body parts. These guidelines discuss aspects authors of such extensions need to consider when design them. This specification mandates support for 'multipart/mixed' and 'multipart/alternative'. At present, there are no SIP extensions that use different 'multipart' subtypes such as parallel [RFC2046] or digest [RFC2046]. If such extensions were to be defined in the future, their authors would need to make sure (e.g., by using an option-tag or by other means) that entities receiving those 'multipart' subtypes were able to process them. As stated earlier, UAs treat unknown 'multipart' subtypes as 'multipart/mixed'. The situation with 'multipart/related' is similar. Per [RFC2387], a UA processing a 'multipart/related' body processes it as a compound object ignoring the disposition types of the body parts within it. However, UAs that do not understand 'multipart/related' will treat it as 'multipart/mixed'. These UAs will not be able to process the body as a compound object. Instead, they will process the body parts according to their disposition type. As stated earlier, SIP extensions may also include 'multipart' MIME Camarillo Expires July 26, 2008 [Page 13] Internet-Draft Message Body Handling in SIP January 2008 bodies in responses. Hence, a response can be extremely complex and the UAC receiving the response might not be able to process it correctly. Because UACs receiving a response cannot report errors to the UAS that generated the response (i.e., error responses can only be generated for requests) authors of SIP extensions need to make sure that requests clearly indicate (e.g., by using an option-tag or by other means) the capabilities of the UAC so that UASs can decide what to include in their responses. 9. Security Considerations This document specifies how SIP entities handle message bodies. [RFC3261] discusses what type of information is encoded in SIP message bodies and how SIP entities can protect that information. In addition to the hop-by-hop security SIP can provide, SIP can also secure information in an end-to-end fashion. SIP message bodies can be end-to-end encrypted and integrity protected using S/MIME [RFC3850], as described in [RFC3261] 10. Acknowledgements The ideas in this document were discussed with Paul Kyzivat. Christer Holmberg, Francois Audet, and Dan Wing provided comments on it. Dave Crocker performed a thorough review on the whole document. 11. IANA Considerations This document defines a new Content-Disposition header field disposition type (by-reference) Section 7.4. This value has been registered in the IANA registry for Content-Dispositions with the following description: by-reference The body needs to be handled according to a reference to the body that is located in the same SIP message as the body. 12. References 12.1. Normative References [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996. Camarillo Expires July 26, 2008 [Page 14] Internet-Draft Message Body Handling in SIP January 2008 [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, November 1996. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2183] Troost, R., Dorner, S., and K. Moore, "Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field", RFC 2183, August 1997. [RFC2387] Levinson, E., "The MIME Multipart/Related Content-type", RFC 2387, August 1998. [RFC2392] Levinson, E., "Content-ID and Message-ID Uniform Resource Locators", RFC 2392, August 1998. [RFC3204] Zimmerer, E., Peterson, J., Vemuri, A., Ong, L., Audet, F., Watson, M., and M. Zonoun, "MIME media types for ISUP and QSIG Objects", RFC 3204, December 2001. [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [RFC3459] Burger, E., "Critical Content Multi-purpose Internet Mail Extensions (MIME) Parameter", RFC 3459, January 2003. [RFC3850] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.1 Certificate Handling", RFC 3850, July 2004. [RFC3959] Camarillo, G., "The Early Session Disposition Type for the Session Initiation Protocol (SIP)", RFC 3959, December 2004. [RFC4483] Burger, E., "A Mechanism for Content Indirection in Session Initiation Protocol (SIP) Messages", RFC 4483, May 2006. 12.2. Informational References [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. [RFC3428] Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C., Camarillo Expires July 26, 2008 [Page 15] Internet-Draft Message Body Handling in SIP January 2008 and D. Gurle, "Session Initiation Protocol (SIP) Extension for Instant Messaging", RFC 3428, December 2002. [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006. [I-D.ietf-sip-multiple-refer] Camarillo, G., "Referring to Multiple Resources in the Session Initiation Protocol (SIP)", draft-ietf-sip-multiple-refer-01 (work in progress), January 2007. [I-D.ietf-mmusic-file-transfer-mech] Garcia-Martin, M., "A Session Description Protocol (SDP) Offer/Answer Mechanism to Enable File Transfer", draft-ietf-mmusic-file-transfer-mech-03 (work in progress), June 2007. Author's Address Gonzalo Camarillo Ericsson Hirsalantie 11 Jorvas 02420 Finland Email: Gonzalo.Camarillo@ericsson.com Camarillo Expires July 26, 2008 [Page 16] Internet-Draft Message Body Handling in SIP January 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Camarillo Expires July 26, 2008 [Page 17]