Transport Area P. Koskelainen Internet-Draft Nokia Expires:
April 23,July 3, 2005 J. Ott Uni Bremen TZI H. Schulzrinne X. Wu Columbia University October 23, 2004January 2, 2005 Requirements for Floor Control Protocol draft-ietf-xcon-floor-control-req-02.txtdraft-ietf-xcon-floor-control-req-03.txt Status of this Memo This document is an Internet-Draft and is subject to all provisions of section 3 of RFC 3667. 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 become aware will be disclosed, in accordance with RFC 3668. 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 April 23,July 3, 2005. Copyright Notice Copyright (C) The Internet Society (2004).(2005). Abstract Floor control is a means to manage joint or exclusive access to shared resource in a (multiparty) conferencing environment. Thereby, floor control complements other functions -- such as conference and media session setup, conference policy manipulation, and media control -- that are realized by other protocols. This document defines the requirements for a floor control protocol for multiparty conferences in the context of an existing framework. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions Used in This Document . . . . . . . . . . . . . . 4 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5. Integration with Conferencing . . . . . . . . . . . . . . . . 7 6. Assumptions about a Conference Policy . . . . . . . . . . . . 8 7. Floor Control Protocol Requirements . . . . . . . . . . . . . 10 7.1 Communication between Participant and Server . . . . . . . 10 7.2 Communicaton between Chair and Server . . . . . . . . . . 11 7.3 General Protocol Requirements . . . . . . . . . . . . . . 12 8. Security Considerations . . . . . . . . . . . . . . . . . . . 13 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 9.15 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 9.116 10.1 Normative References . . . . . . . . . . . . . . . . . . . . 14 9.216 10.2 Informative References . . . . . . . . . . . . . . . . . . . 1416 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 1517 Intellectual Property and Copyright Statements . . . . . . . . 1618 1. Introduction Conference applications often have shared resources such as the right to talk, input access to a limited-bandwidth video channel, or a pointer or input focus in a shared application. In many cases, it is desirable to be able to control who can provide input (send/write/control, depending on the application) to the shared resource. Floor control enables applications or users to gain safe and mutually exclusive or non-exclusive input access to the shared object or resource. The floor is an individual temporary access or manipulation permission for a specific shared resource (or group of resources) . Floor control is an optional feature for conferencing applications. SIP  conferencing applications may also decide not to support this feature at all. Two-party applications may use floor control outside conferencing, although the usefulness of this kind of scenario is limited. Floor control may be used together with conference policy control protocol (CPCP) , or it may be used as independent standalone protocol, e.g. with SIP but without CPCP. Floor control has been studied extensively over the years, (e.g. , , ) therefore earlier work can be leveraged here. The present document describes the requirements for a floor control protocol. As a requirements specification, the document makes no assumptions about the later implementation of the respective requirements as parts of one or more protocols and about the entities implementing it/them and their roles. This document may be used in conjunction with other documents, such as the Conferencing framework document . In particular, when speaking about a floor control server, this entity may be identical to or co-located with the focus or a conference policy server defined in the framework document, while participants and floor chairs referred to in this specificiation may be regular participants as introduced in the conferencing framework document. The term "floor control protocol" is used in an abstract sense in this specification and may ultimately be mapped to any of the existing conference control or other signaling protocols (including CPCP and SIP). But defining those relationships is left to a concrete floor control protocol specification. 2. Conventions Used in This Document 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 RFC 2119. 3. Terminology This document uses the definitions from . The following additional definitions apply: Floor: A permission to temporarily access or manipulate a specific shared resource or set of resources. Conference owner: A privileged user who controls the conference, creates floors and assigns and deassigns floor chairs. The conference owner does not have to be a member in a conference. Floor chair: A user (or an entity) who manages one floor (grants, denies or revokes a floor). The floor chair does not have to be a member in a conference. Floor control: A mechanism that enables applications or users to gain safe and mutually exclusive or non-exclusive input access to the shared object or resource. Floor control server: A logical entity that maintains the state of the floor(s) including which floors exists, who the floor chairs are, who holds a floor, etc. Requests to manipulate a floor are directed at the floor control server. Floor request set: A logical data structure holding all requests for a particular floor at a given point in time. Floor holder set: A logical data structure identifying all participants who currently hold the floor. 4. Model The model for floor control comprises three logical entities: a single floor control server, one or more floor chairs (moderators), and any number of regular conference participants. A floor control protocol is used to convey the floor control messages among the floor chairs (moderators) of the conference, the floor control server, and the participants of the conference. A centralized architecture is assumed in which all messages go via one point, the floor control server. Processing (granting or rejecting) floor control requests is done by the one or more floor chairs or by the server itself, depending on the policy. Floor requests from the participants are received by the floor control server and kept in an -- at the level of the floor control protocol -- floor request set (i.e. are not ordered in any particular fashion). The current floor holders are reflected in a current floor holder set. Floor chairs are capable of manipulating both sets to e.g. grant, revoke, reject, and pass the floor. The order in which requests are processed, whether they are granted or rejected, how many participants obtain a floor simultaneously, is determined by a higher layer application operating on these sets and is not confined by the floor control protocol. A floor is associated with one or more media sessions. The centralized conference server manages the floors and thus controls access to the media sessions. There are two aspects to this: 1) The server maintains and distributes consistent state information about who has a certain floor at a certain point in time and does so following some rule set. This provides all participants with the necessary information about who is allowed to e.g. speak, but relies on a cooperative behavior among all participants. 2) In addition, to prevent individuals from ignoring the "hints" given by the floor control server, the latter may -- e.g. in cooperation with other functional entities -- enforce compliance with floor status, e.g. by blocking media streams from participants not entitled to speak. The floor control server controls the floors at least at the signaling level (1); actively controlling also the actual (physical) media resources (2) is highly recommended, but beyond the scope of this document. As noted in the introduction, an actual protocol specification fulfilling the requirements defined in this memo may map the components of the above model onto the conferencing components defined in the conferencing framework document. Some of these aspects are discussed briefly in the next subsection. 5. Integration with Conferencing Floor control itself does not support privileges such as creating floors and appointing floor chairs, handing over chair privileges to other users (or taking them away). Instead, some external mechanism, such as conference management (e.g. CPCP or web interface for policy manipulation) is used for that. The conference policy (and thus the conference owner or creator) defines whether floor control is in use or not. Actually enforcing conference media distribution in line with the respective media's floor status (e.g. controlling an audio bridge) is beyond the scope of this document. Floor control itself does not define media enforcement. It is up to the conference and media policies to define which media streams may be used in a conference and which ones are floor controlled. Typically, the conference owner creates the floor(s) using conference policy control protocol (or some other mechanism) and appoints the floor chair. The conference owner can remove the floor anytime (so that a media session is not floor-controlled anymore) or change floor chair or floor parameters. The floor chair just controls the access to the floor(s), according to the conference policy. A floor control server is a separate logical entity, typically co-located with focus and/or conference policy server. Therefore, the floor control server can interact with focus, conference Policy Server and media servers as needed. Communication mechanisms between floor control server and other central conferencing entities are not within the scope of the floor control protocol requirements described in this document. Conferences may be cascaded and hence a single participant in one conference representing a second conference (called subconference). From a floor control perspective there is no difference between a participant (identified by its URI) representing a single person or another (set of) subconference(s). Note: In the latter case, it is the responsibility of the subconference to internally negotiate floor requests before passing on a request to the conference and to internally assign a floor upon receiving a floor grant. This may be done recursively by employing the floor control protocol with a different floor control server in the subconference. 6. Assumptions about a Conference Policy The floor control protocol is supposed to be used to manage access to shared resources in the context of a conference. It is up to this conference -- more precisely: its conference policy  -- to define the rules for the operation of the floor control protocol. Furthermore, a conference policy control protocol  may define mechanisms to alter those rules during the course of a conference. This section briefly outlines the assumptions made by a floor control protocol about the conference policy and means for its modification. The conference policy is expected to define the rules for floor control -- which particularly implies that it is not the responsibility of the floor control protocol to establish or communicate those rules. In general, it is assumed that the conference policy also defines who is allowed to create, change and remove a floor in a conference. Conference participants and floor chairs should be able to get and set floor-related parameters. The conference policy may restrict who may access or alter which parameters. Note that not all parameters maintained for a floor are also interpreted by the floor control protocol (e.g. floor policy descriptions may be stored associated with a floor but may be interpreted by a higher layer application). Note also that changes to the floor control policy outside the scope of the floor control protocol and e.g. to be carried out by a conference policy control protocol. (For example, it may be useful to see who the floor chair is, what kind of policy is in use, time limits, number of simultanous floor holders and current floor holder.) These following requirements on a conference policy related to floor control are identified in : REQ-F1: It MUST be possible to define whether floor control is in use or not. REQ-F2: It MUST be possible to define the algorithm to be used in granting the floor. (Note: Example algorithms might be e.g. moderator-controlled, FCFS, random.) Note: it must be possible to use an automated floor policy where the floor control server decides autonomously about granting, and rejecting floor requests as well as revoking the floor. It must also be possible to use a chair-controlled floor policy in which the floor control server notifies the floor chair and waits for the chair to make a decision. This enables the chair to fully control who has the floor. The server MAY forward all requests immediately to the floor chair, or it may do filtering and send only occasional notifications to the chair. REQ-F3: It MUST be possible to define how many users can have the floor at the same time. REQ-F4: It MUST be possible to have one floor for one or more media types. REQ-F5: It MUST be possible to have multiple floors in a conference. REQ-F6: It MUST be possible to define whether a floor is moderator-controlled or not. REQ-F7: If the floor is moderator-controlled, it MUST be possible to assign and replace the floor moderator. 7. Floor Control Protocol Requirements This section covers the requirements on a floor control protocol. The requirements are grouped as follows: 1) floor control protocol between participant and server; 2) floor control protocol between floor chairs and server; 3) floor control server management, and 4) general protocol requirements. 7.1 Communication between Participant and Server REQ-PS-1: Participants MUST be able to request (claim) a floor. REQ-PS-2: It SHOULD be possible for a participant requesting a floor to give additional information about the request, such as the topic of the question for an audio floor. Note: In some scenarios, the floor control server or the floor chair may use this information when granting the floor to the user, or when making manipulation to the floor sets at the server. REQ-PS-3: It MUST be possible for a participant to modify (e.g. cancel) a previously placed floor request. REQ-PS-4: It SHOULD be possible for a participant to initiate a floor control operation (e.g. floor request, release) on behalf of another participant (third-party floor control) provided that he is authorized to do so. REQ-PS-5: A participant MUST be informed that she has been granted the floor. REQ-PS-6: A participant MUST be informed that his floor request has been rejected. REQ-PS-7: A participant MUST be informed that the floor was revoked from her. REQ-PS-8: A participant SHOULD be informed that her floor request is pending and will be processed later. REQ-PS-9: A floor holder MUST be able to release a floor. REQ-PS-10: It MUST be possible to notify conference participants (changes to) the floor holder(s) REQ-PS-11: It MUST be possible to notify conference participants when a new floor request is being made. RRQ-PS-12: It MUST be possible for a floor requester to request privacy for claiming the floor. anonymous: the participants (including the floor chair) cannot see the floor requester's identity. The floor chairs grant the floor based on the claim id and the topic of the claim. known to the floor chair: only the floor chair is able to see the floor requester's identity; all other participants do not obtain this information. public: all the participants can see the floor requester's identity. REQ-PS-13: It MUST be possible for a participant to request privacy for holding the floor along with a floor request. Note that identity information about the particpant may become available to others through different means (e.g. application/media protocols or the mmedia itself such as the voice). 7.2 Communicaton between Chair and Server REQ-CS-1: It MUST be possible to inform the floor chairs, if present, about a participant's floor request. It SHOULD be possible to convey additional information the participant may have provided along with her request. It MUST be possible to hide the requesting participant's identity from the chair, i.e. not include this identity information in the floor request. REQ-CS-2: It MUST be possible to grant a floor to a participant. REQ-CS-3: It MUST be possible to reject a participant's floor request. REQ-CS-4: The floor chair MUST be able to revoke a floor from (one of) its current holder(s). Note that the floor chair may also remove pending floor requests from the request set (by rejecting them). REQ-CS-5: It MUST be possible to notify floor chairs about changes to the floor holder(s) REQ-CS-6: There SHOULD be operations to manipulate the request set available for floor chair(s). Such request set SHOULD at least include creating, maintaining, and re-ordering floor requests a queue and clearing the floor control queue. RRQ-CS-7: It MUST be possible to hide the identity of a floor chair from a subset or all participants of a conference. REQ-CS-8: It MUST be possible for a newly assigned floor chair to learn about (e.g. inquire) the existing floor request set. 7.3 General Protocol Requirements REQ-GEN-1: Bandwidth and terminal limitations SHOULD be taken into account in order to ensure that floor control can be efficiently used in mobile environments. It should be noted that efficient communication by means of minimal sized messages may contradict the desire to express reasons for requesting a floor along with other information. Therefore, a floor control protocol SHOULD be designed in a way that it allow for expressive as well as minimal messaging, as (negotiable) configuration option and/or selectable on a per-message basis. REQ-GEN-2: The floor control MUST be a reliable client-server protocol. Hence, it MUST provide a positive response indicating that a request has been received or an error response if an error has occurred. REQ-GEN-3: It MUST be possible for the floor control server to authenticate participants and chairs. REQ-GEN-4: It MUST be possible for the participants and chairs to authenticate the server. REQ-GEN-5: It MUST be possible to ensure message integrity between participants and chairs and the floor control server. REQ-GEN-6: It MUST be possible to ensure privacy of messages exchanged between participants and chairs and the floor control server. 8. Security Considerations Floor control messages are exchanged on one hand between regular participants and the floor control server and on the other hand between the floor control server and the floor chair(s). If enabled, floor control mechanisms are used to control who may contribute to a conference in arbitrary ways (speak, be seen, write, etc. as supported by the conferencing applications). It is important that floor control messages be protected because otherwise an attacker could prevent participants from being "heard" in the conference (e.g., in scenarios where silence is considered consent) or make participants be heard in a conference without their knowledge (e.g., eavesdropping on the participant's mike). Such considerations are particularly relevant when floor control is used in conjunction with one or more (central) entities (e.g., a media mixer) controlled by the floor control server to enforce floor control decisions which may allow an attacker to completely "mute" a participant. Communications between a conference participant and the floor control server are vulnerable to all kinds of masquerading attacks. If an attacker can spoof the identity of the participant or inject messages on its behalf, it may generate floor requests (e.g. floor release) and prevent proper participation of the participant. If an attacker can inject messages to the participant, it may generate arbitrary responses and false status information. If an attacker can impersonate the floor control server, a participant's requests may never reach the actual floor control server. If an attacker can intercept either side's messages (and hence become a man in the middle) it may suppress, alter, or inject messages and thus manipulate a participant's view of the conference floor status as well as the floor control server's view of a participant. Similar considerations apply to the communications between the floor control server and the floor chair(s). If an attacker can intercept messages from either side, it may defer or prevent responses to floor control requests (from a particular floor chair). If it can inject messages (particularly in the direction from the floor chair to the floor control server), it may steer the assigment of conference floors. If interception and injection is possible (man in the middle scenario), an attacker can create an arbitrary image of the conference for the floor chair. If an attacker can impersonate a floor chair, it may rule the conference floor assignment (if there is only a single chair) or disrupt the conference course by means of arbitrary and potentially conflicting requests/responses/assignments (if there are multiple floor chairs). In the latter case, the amount of damage a single attacker can do depends on the floor control policy. Finally, attackers may eavesdrop on the floor control communications and learn which participants are present, how active they are, who are the floor chairs, etc. To mitigate the above threats, conference participants, floor control servers, and floor chairs SHOULD be authenticated upon initial contact. All floor control messages SHOULD be authenticated and integrity-protected to prevent third-party intervention and MITM attacks. Floor control messages SHOULD be encrypted to prevent eavesdropping. 9. Acknowledgements The authors would like to thank IETF conferencing design team and Keith Drage, Marcus Brunner, Sanjoy Sen, Eric Burger, Brian Rosen, and Nermeen Ismail for their feedback. 9.10. References 9.110.1 Normative References  Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, BCD 14, March 1997.  Rosenberg et al., J., "SIP: Session Initiation Protocol", RFC 3261, June 2002. 10.2 Informative References  Rosenberg, J., "A Framework for Conferencing with the Session Initiation Protocol", draft-ietf-sipping-conferencing-framework-02.txt (work in progress), June 2004. 9.2 Informative References Koskelainen, P. and H. Khartabil, "Additional Requirements to Conferencing", August 2004.  Wu, X., Schulzrinne, H. and P. Koskelainen, "Use of SIP and SOAP for conference floor control", January 2003.  Koskelainen, P., Schulzrinne, H. and X. Wu, "A sip-based conference control framework", Nossdav'2002 Miami Beach, May 2002.  Dommel, H. and J. Garcia-Luna-Aceves, "Floor control for activity coordination in networked multimedia applications", Proc. of 2nd Asian-pacific Conference on Communications APPC, Osaka Japan, June 1995.  Koskelainen, P., Khartabil, H. and A. Niemi, "The Conference Policy Control Protocol (CPCP)", draft-ietf-xcon-cpcp-01.txt (work in progress), October 2004.  Borman, C., Kutscher, D., Ott, J. and D. Trossen, "Simple conference control protocol service specification", draft-ietf-mmusic-sccp-00.txt (work in progress), March 2001. Authors' Addresses Petri Koskelainen Nokia 5 Wayside Road Burlington 01803 USA EMail: email@example.com Joerg Ott Uni Bremen TZI Bibliothekstr. 1 Bremen D-28359 Germany EMail: firstname.lastname@example.org Henning Schulzrinne Columbia University 1214 Amsterdam Avenue New York 10027 USA EMail: email@example.com Xiaotao Wu Columbia University 1214 Amsterdam Avenue New York 10027 USA EMail: firstname.lastname@example.org Intellectual Property Statement 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 in BCP 78 and BCP 79. 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