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Network Working Group                                           O. LevinRequest for Comments: 4245                         Microsoft CorporationCategory: Informational                                          R. Even                                                                 Polycom                                                           November 2005High-Level Requirements for Tightly Coupled SIP ConferencingStatus of This Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2005).Abstract   This document examines a wide range of conferencing requirements for   tightly coupled SIP conferences.  Separate documents will map the   requirements to existing protocol primitives, define new protocol   extensions, and introduce new protocols as needed.  Together, these   documents will provide a guide for building interoperable SIP   conferencing applications.Table of Contents1. Introduction ....................................................22. An Overview .....................................................23. High-Level Requirements .........................................33.1. Discovery Phase ............................................33.2. Conference Creation ........................................43.3. Conference Termination .....................................43.4. Participants' Manipulations ................................43.4.1. Participation of a Conference-Unaware User Agent ......53.4.2. Dial-Out Scenarios ....................................53.4.3. Dial-In Scenarios .....................................53.4.4. Third-Party Invitation to a Conference ................63.4.5. Participants' Removal .................................63.4.6. Participants' Privacy .................................63.5. Conference State Information ...............................73.5.1. Description ...........................................73.5.2. Dissemination of Changes ..............................73.5.3. On-demand Information Dissemination ...................83.6. Focus Role Migration .......................................8Levin & Even                 Informational                      [Page 1]

RFC 4245               Conferencing Requirements           November 20053.7. Side-bar Conferences .......................................83.8. Cascading of Conferences ...................................93.9. SIMPLE and SIP Conferencing Coordination ...................94. Security Considerations ........................................105. Contributors ...................................................106. References .....................................................106.1. Normative References ......................................101.  Introduction   This document examines a wide range of conferencing requirements for   tightly coupled SIP (RFC 3261 [2]) conferencing.   The requirements are grouped by subjects in various areas allowing   solutions to progress in parallel.   Separate documents will map the requirements to existing protocol   primitives, define new protocol extensions, and introduce new   protocols as needed.   Together, these documents will provide a guide for building   interoperable SIP conferencing applications.   The terms "MAY", "SHOULD", and "MUST" are to be interpreted as   described inRFC 2119 [1].2.  An Overview   A SIP conference is an association of SIP user agents (i.e.,   conference participants) with a central point (i.e., a conference   focus), where the focus has direct peer-wise relationships with the   participants by maintaining a separate SIP dialog with each.   The focus is a SIP user agent that has abilities to host SIP   conferences including their creation, maintenance, and manipulation   using SIP call control means and potentially other non-SIP means.   In this tightly coupled model, the SIP conference graph is always a   star.  The conference focus maintains the correlation among   conference's dialogs internally.   The conference focus can be implemented either by a participant or by   a separate application server.   In the first case, a focus is typically capable of hosting a simple   ad hoc conference only.  We envision that such basic conference can   be established using SIP call control primitives only.Levin & Even                 Informational                      [Page 2]

RFC 4245               Conferencing Requirements           November 2005   A dedicated conference server, in addition to the basic features,   offers richer functionality including simultaneous conferences, large   scalable conferences, reserved conferences, and managed conferences.   A conferencing server can support any subset of the advanced   conferencing functions presented in this document.   The media graph of a SIP conference can be centralized,   decentralized, or any combination of both, and potentially differ per   media type.  In the centralized case, the media sessions are   established between the focus and each one of the participants.  In   the de-centralized (i.e., distributed) case, the media graph is a   (multicast or multi-unicast) mesh among the participants.   Consequently, the media processing (e.g., mixing) can be performed   either by the focus alone or by the participants.   Conference participants and third parties can have different roles   and privileges in a certain conference.  For example, conferencing   policy can state that the rights to disconnect from and to invite to   a conference are limited to the conference chair only.   Throughout the document, by conference policies we mean a set of   parameters and rules (e.g., maximum number of participants, needs   chair-person supervision or not, password protected or not, duration,   or a way of media mixing) that are defined at the onset of a   conference.  Typically, conference policies would be specified by a   conference creator and need special privileges to be manipulated.   Throughout the document, by a conference state we mean a set of   information describing the conference in progress.  This includes   participants' information (such as dialog identifiers), media   sessions in progress, the current loudest speaker, the current chair,   etc.3.  High-Level Requirements   In addition to the requirements presented in this document,   supplementary requirements for conferencing policy, media mixing and   other manipulations, floor control, privilege control, etc. will be   discussed in separate documents.3.1.  Discovery Phase   Some of the requirements presented in this section can be met either   by configuration means or by using proprietary conventions.   Nevertheless, there is consensus that standard means for implementing   these functions by automata MUST be defined.Levin & Even                 Informational                      [Page 3]

RFC 4245               Conferencing Requirements           November 2005   REQ-1: Discovery of a location of an arbitrary SIP conferencing        server(s).   REQ-2: Given a SIP Address-of-Record (AOR) of a certain entity,        resolution whether the SIP entity has focus capabilities.   REQ-3: Given a global identifier of a particular conference, locating        the conference focus.   REQ-4: Given a global identifier of a particular conference,        obtaining the conference properties.   REQ-5: Given a global identifier of a particular conference,        obtaining the conference state information.3.2.  Conference Creation   Given a focus location, a means MUST be defined for an interested   entity (including a user agent) to implement the procedures below:   REQ-1: Creation of an ad-hoc conference identifier and the conference        with specified properties.   REQ-2: Creation of a reserved conference identifier for a conference        with specified properties.   REQ-3:  Specifying properties upon conference creation in any of the        following ways: default, profiles, and explicitly.3.3.  Conference Termination   REQ-1: Given a conference identifier, a means MUST be defined for a        user agent to disconnect all participants from the conference        and terminate the conference including the release of the        associated resources.   REQ-2: A means MAY be defined for requesting a focus to revert a        two-party conference to a basic SIP point-to-point session        including the release of the associated conferencing resources.3.4.  Participants' Manipulations        Some of the requirements presented in this section can be met by        human intervention, configuration means, or proprietary        conventions.  Nevertheless, there is consensus that standard        means for implementing these functions by automata MUST be        defined.Levin & Even                 Informational                      [Page 4]

RFC 4245               Conferencing Requirements           November 20053.4.1.  Participation of a Conference-Unaware User Agent   REQ-1: Focus MUST be able to invite and disconnect anRFC 3261        compliant only SIP user agent to and from a SIP conference.   REQ-2: AnRFC 3261 compliant only SIP user agent MUST be able to        dial-in to a particular SIP conference.  In this case, only the        human knows that he/she is connected to the conference.3.4.2.  Dial-Out Scenarios   REQ-1: A means MUST be defined for a focus to invite another user        agent to one of the focus' conferences.  This procedure MUST        result in the establishment of a single SIP dialog between the        two.   REQ-2: Given an existing SIP dialog between two user agents, if at        least one user agent has focus capabilities, a means MUST be        defined for the conference focus to invite the other user agent        to one of the focus' conferences without additional SIP dialog        establishment.   REQ-3: An invitation to a user agent to join a conference MUST        include a standard indication that it is a conference and the        conference identifier.3.4.3.  Dial-In Scenarios   REQ-1: A means MUST be defined for a user agent to create an ad hoc        conference with default properties (as per "Conference Creation"        REQ-1 above) and to become a participant using a single SIP        dialog.   REQ-2: Given a reserved conference identifier, a means MUST be        defined for a user agent to activate the conference and to        become a participant using a single SIP dialog.   REQ-3: Given a conference identifier of an active conference, a means        MUST be defined for a user agent to dial-in the conference and        to become a participant using a single SIP dialog between the        two.   REQ-4: Given an identifier of one of the dialogs of a particular        active conference, a means MUST be defined for a user agent to        dial-in the conference and to become a participant.Levin & Even                 Informational                      [Page 5]

RFC 4245               Conferencing Requirements           November 20053.4.4.  Third-Party Invitation to a Conference   REQ-1: Given a conference identifier, a means MUST be defined for a        user agent to invite another user agent to this conference.   REQ-2: Given an identifier of one of the dialogs of a particular        active conference, a means MUST be defined for a user agent to        invite another user agent to this conference.   EQ-3: Given a conference identifier, a means SHOULD be defined for a        user agent to invite a list of user agents to this conference (a        so-called "mass invitation").3.4.5.  Participants' Removal   REQ-1: A means MUST be defined for a conference focus to remove a        conference participant from the conference.   REQ-2: Given a conference identifier, a means MUST be defined for a        user agent to remove a participant from the conference.   REQ-3: Given an identifier of one of the dialogs of a particular        active conference, a means MUST be defined for a user agent to        remove a participant from the conference.   REQ-4: Given a conference identifier, a means MUST be defined for a        user agent to remove all the participants from the conference.   REQ-5: Given a conference identifier and a sub-list of participants,        a means MAY be defined for a user agent to remove the specified        participants from the conference (a so-called "mass ejection").3.4.6.  Participants' Privacy   A conference focus SHOULD support the procedures described in this   section.  A conference participant MAY support the procedures   described in this section.  The requirements imply that "anonymizing"   operations MUST be performed on all: the call control, the media   control, and the media content when appropriate.   REQ-1: A conference participant joins the conference "anonymously";        that is, his/her presence can be announced but without        disclosing his/her identity.   REQ-2: A conference participant requests a focus for anonymous        participation in the conference.Levin & Even                 Informational                      [Page 6]

RFC 4245               Conferencing Requirements           November 2005   REQ-3: A conference participant joins a conference in a "hidden        mode"; that is, his/her presence and identity are not to be        disclosed to other participants.   REQ-4: A conference participant requests a focus for participation in        the conference in a hidden mode.3.5  Conference State Information3.5.1.  Description   By a conference state, we mean a virtual database describing the   conference in progress.  This includes different conference aspects:   participants' information (such as dialog identifiers and state),   media sessions in progress (such as current stream contributing   sources and encoding schemes), the current loudest speaker, the   current chair, etc.  Conference state is the latest conference   snapshot triggered by changes in participants' state, conference   policy changes, etc.   REQ-1: A conference state virtual database MUST have a modular        definition that is, it MUST be possible to access different        conference aspects independently.   REQ-2: It MUST be possible to aggregate information relating to        different conference aspects in a single report.   REQ-3: A mechanism for extensible definition and registration of        conference state evolving aspects MUST be present.   REQ-4: A default conference state report MUST be defined.  It SHOULD        contain a minimal useful set of information (e.g., a list of        current conference participants).3.5.2.  Dissemination of Changes   REQ-1: A means MUST be defined for reporting the conference state        changes to interested parties (including non-conference        participants) in a timely manner.   REQ-2: A means MUST be defined for a SIP user agent to express its        interest in selected state changes only.   REQ-3: A means MUST be defined for a SIP user agent to express the        minimum interval between receiving state change reports.   REQ-4: It MUST be possible to aggregate recent changes in a single        reporting event.Levin & Even                 Informational                      [Page 7]

RFC 4245               Conferencing Requirements           November 2005   REQ-5: Default conference state change reports MUST be defined.  They        SHOULD contain minimal useful to the participants information        (e.g., participants' joining and leaving the conference).3.5.3.  On-demand Information Dissemination   REQ-1: A means MUST be defined to disseminate any conference state        information to interested parties (including SIP user agents)        on-demand.   REQ-2: A means MUST be defined for an interested party (including a        SIP user agent) to request conference state information of a        particular conference defined by the conference identifier.   REQ-3: A means MUST be defined for an interested party (including a        SIP user agent) to specify the subset of the conference state        information it wants and is capable of receiving.3.6.  Focus Role Migration   REQ-1: A procedure for delegating a focus role by the current focus        to another participant MUST be defined.   REQ-2: A procedure for requesting a conference focus to transfer its        role to another participant MUST be defined.   REQ-3: A procedure for on-demand unconditional transfer of the focus        role to a different participant MUST be defined.   REQ-4: A detection procedure for a focus failure condition MUST be        defined.3.7.  Side-bar Conferences   A standard means MUST be defined in order to implement the operations   defined in this section below.   REQ-1: A user agent (not a conference participant) joins a side-bar        within the conference by SIP means.   REQ-2: A user agent (not a conference participant) is invited to a        side-bar within the conference by SIP means.   REQ-3: A conference participant creates a side-bar conference with        one or more participants in a conference by SIP means.   REQ-4: A conference participant joins a side-bar within the        conference by SIP means.Levin & Even                 Informational                      [Page 8]

RFC 4245               Conferencing Requirements           November 2005   REQ-5: A conference participant is invited to a side-bar within the        conference by SIP means.   REQ-6: A conference-unaware user agent (a participant or not) creates        and participates in side-bar conferences.  It MAY be achieved by        non-SIP means.   REQ-7: A conference participant creates side-bar conferences within        the conference without establishing any additional SIP dialogs        with the focus.  It MAY be achieved by non-SIP means.   REQ-8: A conference participant joins any number of side-bars within        the conference without establishing any additional SIP dialogs        with the focus.  It MAY be achieved by non-SIP means.   REQ-9: A conference participant is invited to any number of side-bars        within the conference without establishing any additional SIP        dialogs with the focus.  It MAY be achieved by non-SIP means.3.8.  Cascading of Conferences   "Cascading of Conferences" is a term that has different meanings in   different contexts.  Some examples are listed below:      -    Peer-to-peer chaining of signaling.  (Many ways exist to           build the media graph in this case.)      -    Conferences have hierarchal signaling relations.  (Many ways           exists to build the media graph in this case.)      -    "Cascading" is used to distribute the media "mixing" only.           The distribution of signaling is not required.   As it can be seen from the examples, each will define a different set   of requirements.3.9.  SIMPLE and SIP Conferencing Coordination   REQ-1: SIMPLE-based Presence and Instant Messaging architecture        SHOULD fit into the general SIP Conferencing architecture.   REQ-2: A scenario where a multimedia SIP conference and a multiparty        instant messaging conversation take place among the same group        of participants MUST be addressed.   REQ-3: A scenario where a side-bar and/or a sub-IM-conference is        being held as a part of SIP conference MUST be addressed.Levin & Even                 Informational                      [Page 9]

RFC 4245               Conferencing Requirements           November 20054.  Security Considerations   This document discusses high-level requirements for SIP conferencing.   Conferencing has some specific security requirements, which will be   summarized here at a very high level.   All of the operations and functions described in this document need   to be authorized by a focus or a participant.  It is expected that   conferences will be governed by a set of authorization rules defined   as a part of the conference policy.  In order for the conference   policy to be implemented, the focus needs to be able to authenticate   potential participants.  Normal SIP mechanisms including Digest   authentication and certificates can be used [2].  These conference-   specific security requirements will be discussed in detail in the   protocol documents.   Conferencing also has privacy implications.  Some of these are   discussed in this document.  Standard SIP mechanisms for a user agent   to request privacy should be utilized by a focus and will be detailed   in the protocol documents.5.  Contributors   This work is based on the discussions among the members of the SIP   Conferencing design team.6.  References6.1.  Normative References   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement        Levels",BCP 14,RFC 2119, March 1997.   [2]  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.Levin & Even                 Informational                     [Page 10]

RFC 4245               Conferencing Requirements           November 2005Authors' Addresses   Orit Levin   Microsoft Corporation   One Microsoft Way   Redmond, WA  98052   EMail: oritl@microsoft.com   Roni Even   Polycom   94 Derech Em Hamoshavot   Petach Tikva, Israel   EMail: roni.even@polycom.co.ilLevin & Even                 Informational                     [Page 11]

RFC 4245               Conferencing Requirements           November 2005Full Copyright Statement   Copyright (C) The Internet Society (2005).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET   ENGINEERING TASK FORCE DISCLAIM 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 PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 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 athttp://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.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Levin & Even                 Informational                     [Page 12]