XCON E. Burger Internet-Draft SnowShore Networks, Inc. Expires: August 8, 2004 February 8, 2004 Centralized Conferencing (XCON) Media Models draft-burger-xcon-mmodels-00 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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 August 8, 2004. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract This document describes various models for endpoint control of media policy for centralized conferencing services. The models include detailed mixer control, as in H.248, individual end-point negotiation, and participant roles, as in MSCML. Burger Expires August 8, 2004 [Page 1] Internet-Draft Centralized Conferencing (XCON) Media Models February 2004 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Low-Level Stream Control . . . . . . . . . . . . . . . . . . . 3 2.1 Decription . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2 Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.3 Drawbacks . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Individual End-Point Negotiation . . . . . . . . . . . . . . . 4 3.1 Decription . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.2 Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.3 Drawbacks . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Role-Directed Control . . . . . . . . . . . . . . . . . . . . 5 4.1 Decription . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.2 Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.3 Drawbacks . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5. Other Thoughts . . . . . . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . 5 Informative References . . . . . . . . . . . . . . . . . . . . 6 Author's Address . . . . . . . . . . . . . . . . . . . . . . . 6 A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6 Intellectual Property and Copyright Statements . . . . . . . . 7 Burger Expires August 8, 2004 [Page 2] Internet-Draft Centralized Conferencing (XCON) Media Models February 2004 1. Introduction There is debate about how one should control the centralized mixing service in the XCON framework. We term this control media policy. Some offer low-level manipulation of media streams and resources on a per-user basis. Others offer models based on end-device negotiation of streams of interest and doing local manipulation. Yet others offer models based on fixed frameworks and user roles to indirectly determine the media policay. In one sense, the different models are isomorphic. One can construct the end-device-centric model from the low-level model. Likewise, one can construct the frameworks-and-roles model from the end-device-centric or the low-level model. Given this, it is important to consider the use cases for media policy manipulation. As this document will assert, the different models impose quite different requirements on the endpoints. Another factor this document will examine is the ease of implementation, both of the server (mixer) and client (endpoint). Everything needs to loop back to and have examples for how to meet the Conferencing Scenarios draft [1]. 2. Low-Level Stream Control 2.1 Decription Low-level stream control is where the endpoint manipulates a direct representation of the media processing resources of the mixer. This representation can be physical, as in terms of directly plumbing DSP resources in the manner of H.248.1. The representation can be logical, as in terms of XML mappings of DSP topologies. 2.2 Benefits This is the most flexible model available. Just as one can construct all logic circuits from an OR gate and a NOT gate, one can construct all possible media mixing scenarios from a two-input mixer and an attinuator. 2.3 Drawbacks Unless the mixer physically maps to the primitives of the device control model, it is very conceivable for a legal mixing request to be unrenderable by the mixing device. For example, an 8-input mixer with the loudest three talkers with four outputs being the full mix, Burger Expires August 8, 2004 [Page 3] Internet-Draft Centralized Conferencing (XCON) Media Models February 2004 the mix less the loudest talker, the mix less the second loudest talker, and the mix less the third loudest talker is a 13-element composition (7x 2-input mixers, 3x loudest talker selectors, and 3x 2-input mixers with "not loudest talkers"). The mixing device must be able to map the representation into primitives it understands, such as an 8-input mixer. Another drawback is the mixer may not be able to globally optimize the mixing resources, as there are many ways of representing the same mix result. For small mixers, this is a denial of service opportunity. For large mixers, properly scaling the system requires minimizing the resource utilization for the average conference. Finally, this model requires the endpoint developer to be an expert in DSP technology. This is because the developer has to manage and manipulate the DSP resources at a fairly low level. 3. Individual End-Point Negotiation 3.1 Decription The individual end-point negotiation model is where the endpoint negotiates directly with other conference endpoints and does any mixing locally. One often finds this model for small audio or multimedia conferences. If the endpoint wants a big video window, it will ask the remote endpoint for a big video transmission. If the endpoint wants a thumbnail, it asks for a thumbnail. With the streams, the endpoint locally composes whatever layout or mixing policy it feels like. This model often relies on the us of silence-suppression codecs to reduce bandwidth to the endpoint and make active talker identification easier. For the most part, only two people will try to talk for more than 500ms. Human protocol usually results on one of the participants to backoff. 3.2 Benefits The main benefit of this model is the user is in complete control of their experience. There are no questions about whether a mixing service can support the user interface, whether because of resource availability, computational complexity, or forsight into the possible media manipulation needs. 3.3 Drawbacks All media must traverse the network from all endpoints to the given Burger Expires August 8, 2004 [Page 4] Internet-Draft Centralized Conferencing (XCON) Media Models February 2004 endpoint. This is not realistic for Internet-scale protocols. There is no centralized control of policy such as floor control. For example, the moderator may wish to mute a particular speaker; the endpoint may still allow that speaker into the mix, ignoring the moderators mute request. The endpoint developer must be able to put together the media manipulation on their own. For example, mixing; video demodulation, mixing, and remodulation; and stream selection are all now endpoint functions. 4. Role-Directed Control 4.1 Decription In role-directed control, the mixing service provides a set of templates for which different users have different roles. The roles in the template dictates the media policy. For example, in a lecture template, there is a lecturer and possibly listeners and questioners. The moderator is the only stream in the mix, unless a user becomes a questioner. As a questioner, their media is added appropriately to the mix. While straightforward for audio, the mix for video is more involved. A likely scenario is to have multiple templates for different preferences, such as video switching to the current speaker, split pane with the lecturer and current questioner, and so on. 4.2 Benefits The endpoint operates at the level of a conference. It only needs to know what role the user wants to be. It does not need to know anything about DSP primitives or plumbing. 4.3 Drawbacks There is unquestionably a loss of generality with role-directed control. However, that loss is made up with an increase in usability. 5. Other Thoughts BOBW: Role-Directed Control with a Framework Markup language? 6. Security Considerations While this document is entirely informative, it is worthwhile to note the above mentioned denial of service opportunities some of the Burger Expires August 8, 2004 [Page 5] Internet-Draft Centralized Conferencing (XCON) Media Models February 2004 methods outlined in the paper present. Informative References [1] Even, R., "Conferencing Scenarios", draft-ietf-xcon-conference-scenarios-00 (work in progress), December 2003. Author's Address Eric Burger SnowShore Networks, Inc. 285 Billerica Rd. Chelmsford, MA 01824-4120 USA EMail: e.burger@ieee.org Appendix A. Acknowledgements If I do this paper for real, there are boatloads of references to do, like Rohan's XML media representation, Jonathan's conferencing framework, Brian's extreamly cool Viper product, and all of Alan and Henry's work in the conferencing space. Please forgive me this -00 done in 00 time at all! Burger Expires August 8, 2004 [Page 6] Internet-Draft Centralized Conferencing (XCON) Media Models February 2004 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property 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; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication 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 implementors or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. Full Copyright Statement Copyright (C) The Internet Society (2004). 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 Standards 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 assignees. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION Burger Expires August 8, 2004 [Page 7] Internet-Draft Centralized Conferencing (XCON) Media Models February 2004 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Burger Expires August 8, 2004 [Page 8]