Network Working Group Scott Bradner Internet-Draft Harvard University Rohan Mahy Cisco Allison Mankin USC/ISI Joerg Ott IPDialog Brian Rosen Marconi Dean Willis dynamicsoft February 2002 SIP Change Process 1. Status of this Memo This document is an Internet-Draft and is subject to all provisions of Section 10 of RFC 2026. 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 Copyright (C) The Internet Society (2002). All Rights Reserved. 2. Abstract The IETF's Session Initiation Protocol (SIP) [RFC2543] is becoming popular for a growing number of applications. One result of this popularity is a continuous flood of suggestions for SIP modifications and extensions. This memo describes how the Transport Area directors along with the SIP and SIPPING working group chairs have decided to deal with such suggestions. Transport ADs and SIP* Chairs [Page 1] Internet-Draft SIP Change Process February 2002 3. The IETF SIP Working Group The IETF Session Initiation Protocol (sip) Working Group is chartered to be the "owner" of the SIP protocol. All changes or extensions to SIP must first exist as SIP Working Group documents. The SIP Working group is charged with being the guardian of the SIP protocol for the Internet. It should only extend or change the SIP protocol when there are compelling reasons to do so. Documents that must be handled by the SIP working group include new SIP methods, new SIP option tags, new reponse codes, and new standards track SIP headers. With the exception of "P-" headers described in Section 6.1, all SIP extensions must be standards track and must be developed in the IETF, from requirements provided by the SIPPING Working Group. SIP event packages [events] are appropriate to develop in the Working Groups that use them, but they will need charter approval to create a SIP event package as a working group effort. The IETF will also require (Individual) RFC publication for registration of event packages developed outside the scope of an IETF working group. Requirements for publishing event packages are described in detail in Section 6.3. 4. The IETF SIPPING Working Group The IETF Session Initiation Protocol Proposal Investigation (sipping) Working Group is chartered to be a filter in front of the SIP Working Group. This working group will investigate requirements for applications of SIP, some of which may lead to requests for extensions to SIP. These requirements may come from the community at large, or from individuals who are reporting the requirements determined by another standards body. The SIPPING Working Group may determine that these requirements can be satisfied by SIP without modifications, that the requirements are not sufficiently general to warrant a change to SIP, that the requirements justify a change to SIP, or that the requirements should be combined with other requirements to solve a more general problem, or to solve the same problem in a more flexible way. Because the SIP protocol gets so much attention, some application designers may want to use it just because it is there, such as for detailing cars using the new SIP BRUSH method. SIPPING should act as a filter, accepting only requirements which are applicable to SIP. When the SIPPING working group decides on a set of requirements, it forwards them to the SIP working group. The SIPPING Working Group may Transport ADs and SIP* Chairs [Page 2] Internet-Draft SIP Change Process February 2002 also document usage or applications of SIP which do not require any protocol extensions. The SIPPING working group also acts as a filter for proposed event packages as described in Section 6.3. 5. SIP Change Process Anyone who thinks that the existing SIP protocol is applicable to their application, yet not sufficient for their task must write an individual ID explaining the problem they are trying to solve, why SIP is the applicable protocol, and why the existing SIP protocol will not work. The Internet-Draft must include a detailed set of requirements (distinct from solutions) that SIP would need to meet to solve the particular problem. The Internet Draft must also describe in detail any security issues that arise from meeting the requirements. After this Internet-Draft is published, the authors should send a note to the SIPPING Working Group mailing list to start discussion on the Internet-Draft. The SIPPING working group chairs in conjunction with the Transport Area Directors will determine if the particular problems raised in the requirements Internet-Draft warrants being added to the SIPPING charter based on the mailing list discussion. The SIPPING working group should consider whether the requirements merge with other requirements from other or related applications, and refine the ID accordingly. If the chairs and the ADs both feel that the particular new problems should be added to the SIPPING Working Group charter, the ADs will present the proposed SIPPING charter modifications to the IESG and IAB, in accordance with the usual process for charter expansion. If the IESG (with IAB advice) approves of the charter changes, the SIPPING working group can then work on the problems described in the Internet-Draft. In a separate Internet-Draft, the authors may describe a set of changes to SIP that would meet the requirements. This Internet-Draft would be passed on to the SIP working group for consideration (if warranted). There is no requirement on the SIP working group that the proposed solution from this additional ID be adopted. The SIPPING working group may also evaluate such proposals for extensions if the requirements are judged to be appropriate to SIP, but the requirements are not sufficiently general for standards track activity. The SIPPING working group will attempt to determine if the new proposal meets the requirements for publication as a "P-" header as described in Section 6.1 within a specific scope of applicability. Transport ADs and SIP* Chairs [Page 3] Internet-Draft SIP Change Process February 2002 The Transport ADs may, on a case by case basis, support a process in which the requirements analysis is implicit and the SIP working group requests addition of a charter item for an extension without a full SIPPING process as described. This will be the exception. With respect to standardization, this process means that SIP extensions (with the exception of P- headers as described in Section 6.1) come only from the SIP Working Group, and only from the IETF, as the body that created SIP. The IETF will not publish a SIP extension RFC outside of the process described here. The SIP Working Group is required to protect the architectural integrity of SIP and must not add features that do not have general use beyond the specific case - they also must not add features just to make a particular function more efficient at the expense of simplicity or robustness. Some working groups besides SIPPING generate requirements for SIP solutions and/or extensions as well. At the time of writing, these include SIP for Instant Messaging and Presence Leveraging Extensions (simple), Service in the PSTN/IN Requesting InTernet Service (spirits), and Telephone Number Mapping (enum). 6. Extensibility and Architecture In an idealized protocol model, extensible design would be self- contained, and it would be inherent that new extensions and new headers would naturally have an architectural coherence with the original protocol. However, this idealized vision has not been attained in the world of standards tracks protocols. While, interopability implications can be addressed by capabilities negotiation rules, the effects of adding features that overlap or that deal with a point solution and are not general are much harder to control with rules. Therefore the Transport Area calls for architectural guardianship and application of Occam's Razor by the SIP Working Group. We encourage other protocol working groups with highly extensible protocols to review whether they need more coordination of extensions (including restricting them to IETF) as in the SIP case. In keeping with the IETF tradition of "running code and rough consensus", it is valid to allow for development of SIP extensions that are either not ready for standards track, but might be understood for that role after some running code; or are private or proprietary in nature, because a characteristic motivating them is usage that is known not to fit the Internet architecture for SIP. We call these Transport ADs and SIP* Chairs [Page 4] Internet-Draft SIP Change Process February 2002 "P-" headers, for "preliminary", "private", or "proprietary". There are two key issues to consider with respect to keeping the "P-" header extension space "safe": 1. Clearly indicating the unarchitected or not-yet understood nature of the extension. 2. Preventing identity conflicts between extensions. 6.1. Indicating a "P-" Header: Use of an "X-" prefix on textual identfiers has been widely used to indicate experimental extensions in other protocols, and this approach is applied in modified form here by use of a "P-" header extension. Informational SIP Headers can be registered as "P-" headers if all of the following conditions are met: 1. A designated expert [RFC2434] MUST review the proposal for applicability to SIP and conformance to these guidelines. The Expert Reviewer will send email to the IESG on this determina- tion. The expert reviewer can cite one or more of the guide- lines that haven't been followed in his/her opinion. 2. The proposed extension MUST NOT define SIP option tags, response codes, or methods. 3. The function of the proposed header MUST NOT overlap with current or planned chartered extensions. 4. The proposed header MUST be of purely an informational nature, and MUST NOT significantly change the behavior of SIP entities which support it. Headers which merely provide addi- tional information pertinent to a request or a response are acceptable. If the headers redefine or contradict normative behavior defined in bis or other standards track documents then the behavior is significantly different. Transport ADs and SIP* Chairs [Page 5] Internet-Draft SIP Change Process February 2002 5. The proposed header MUST NOT undermine SIP security in any sense. The Internet Draft proposing the new header MUST address security issues in detail as if it were a Standards Track document. Note that, if the intended application sce- nario makes certain assumptions regarding security, the secu- rity considerations only need to meet the intended application scenario rather than the general Internet case. In any case, security issues need to be discussed for arbitrary usage sce- narios (including the general Internet case). 6. The proposed header MUST be clearly documented in an (Individual or Working Group) Informational RFC, and regis- tered with IANA. 7. An applicability statement in the Informational RFC MUST clearly document the useful scope of the proposal, and explain its limitations and why it is not suitable for the general use of SIP in the Internet. Any implementation of a "P-" header (meaning "not specified by a standards-track RFC issued through the SIP Working Group") MUST include a "P-" prefix on the header, as in "P-Headername". Note that "P-" extensions are not IETF standards of any kind, and MUST NOT be required by any production deployment considered compliant to IETF specififcations. Specifically, implementations are only SIP compliant if a) they fall back to baseline behavior when they ignore all P- headers, and b) when using P- headers they do not contradict any normative behavior. 6.2. Preventing Identity Conflicts Between P-Extensions: In order to prevent identity conflicts between P-extensions, this document provides an IANA process (See: "IANA Considerations" below) to allow for the registration of private or experimental extension headers. All implemented extension headers SHOULD meet the P-Header requirements in 6.1, and any extension header used outside of a very restricted research or teaching environment (such as a student lab on implementing extensions) MUST meet those requirements and MUST be documented in an RFC and be IANA registered. 6.3. SIP Event Packages SIP events defines two different types of event pacakges: normal event packages, and event template-packages. Event template- Transport ADs and SIP* Chairs [Page 6] Internet-Draft SIP Change Process February 2002 packages can only be created and registered by the publication of a Standards Track RFC (from an IETF Working Group). Normal event packages can be created and registered by the publication of any Working Group RFC (Informational, Standards Track, Experimental), provided that the RFC is a chartered working group item. Individuals may also wish to publish SIP Event packages. Indi- vidual proposals for registration of a SIP event package MUST first be published as internet-drafts for review by the SIPPING Working Group. Proposals should include a strong motivational section, a thorough description of the proposed syntax and seman- tics, event package considerations, security considerations, and examples of usage. The author should submit his or her proposal as an individual Internet Draft, and post an announcement to the working group mailing list to begin discussion. The SIPPING Working Group will determine if the proposed package is a) an inappropriate usage of SIP, b) applicable to SIP but not suffi- ciently interesting, general, or in-scope to adopt as a working group effort, c) contrary to similar work planned in the Working Group, or d) should be adopted as or merged with charted work. The IETF requires (Individual) RFC publication for registration of event packages developed outside the scope of an IETF working group, according to the following guidelines: 1) A designated expert [RFC2434] MUST review the proposal for applicability to SIP and conformance to these guidelines. The Expert Reviewer will send email to the IESG on this determina- tion. The expert reviewer can cite one or more of the guide- lines that haven't been followed in his/her opinion. 2) The proposed extension MUST NOT define an event template- package. 3) The function of the proposed package MUST NOT overlap with current or planned chartered packages. 4) The event package MUST NOT redefine or contradict the nor- mative behavior of [events], [SIP], or related standards track extensions. Transport ADs and SIP* Chairs [Page 7] Internet-Draft SIP Change Process February 2002 5) The proposed package MUST NOT undermine SIP security in any sense. The Internet Draft proposing the new package MUST address security issues in detail as if it were a Standards Track document. Security issues need to be discussed for arbitrary usage scenarios (including the general Internet case). 6) The proposed package MUST be clearly documented in an (Individual) Informational RFC, and registered with IANA. The package MUST document all the package considerations required in Section 5 of [events] 7) If necessary as determined by the expert reviewer or the chairs or ADs of the SIPPING WG, an applicability statement in the Informational RFC MUST clearly document the useful scope of the proposal, and explain its limitations and why it is not suitable for the general use of SIP in the Internet. 7. Security Considerations Complexity and indeterminate or hard to define protocol behavior, depending on which of many extensions operate, is a fine breeding ground for security flaws. All Internet-Drafts that present new requirements for SIP must include a discussion of the security requirements and implica- tions inherent in the proposal. All RFCs that modify or extend SIP must show that they have adequate security and do not worsen SIP's existing security considerations. 8. IANA Considerations RFC XXXX [bis] directs the Internet Assigned Numbers Authority to establish a registry for SIP method names, a registry for SIP option tags, and a registry for SIP response codes, and to amend the practices used for the existing registry for SIP headers. With the exception of P-headers, entries go into these registries only by approval of a draft for standards track RFC (the IESG announcement of approval authorizes IANA to make the registra- tion). For P-headers this requirement is relaxed to allow regis- tration when any RFC is approved by the IESG (non-standards track). Each RFC shall include an IANA Considerations section which Transport ADs and SIP* Chairs [Page 8] Internet-Draft SIP Change Process February 2002 directs IANA to create appropriate registrations. Standard head- ers and messages MUST NOT begin with the leading characters "P-". "P-" header names MUST being with the leading characters "P-". No "P-" header which conflicts with (would, without the "P-" pre- fix have the same name as) an existing standards track header is allowed. Each registration of a "P-" header will also reserve the name of the header as it would appear without the "P-" pre- fix. These "reserved standard names" MUST NOT be used in a SIP implementation prior to standardization of the header. Short forms of headers MUST only be assigned to standards track headers. 9. References [RFC 2543] "SIP: Session Initiation Protocol.", M. Handley, H. Schulzrinne, E. Schooler, J. Rosenberg, RFC 2543, March 1999 [bis] "SIP: Session Initiation Protocol.", J. Rosenberg, et al, Work in progress. [events] "Event Notification in SIP", A. Roach, Internet Draft, Feb 2002. Work in progress. 10. Author's Addresses Scott Bradner Email: sob@harvard.edu Rohan Mahy Email: rohan@cisco.com Allison Mankin Email: mankin@isi.edu Joerg Ott Email: jo@ipdialog.com Brian Rosen Email: brian.rosen@marconi.com Dean Willis Email: dean.willis@softarmor.com 10. Acknowledgements Transport ADs and SIP* Chairs [Page 9] Internet-Draft SIP Change Process February 2002 The Transport ADs thank our IESG and IAB colleagues (especially Randy Bush, Harald Alvestrand and John Klensin) for valuable discussions of extensibility issues in a wide range of protocols, including those that our area brings forward and others, and many members of the SIP community at IETF for dialogue on these issues for SIP. 10. Full Copyright Statement Copyright (C) The Internet Society (2001). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Stan- dards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGI- NEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PUR- POSE. Transport ADs and SIP* Chairs [Page 10]