Internet Engineering Task Force
Internet Draft                                       Koskelainen,Schulzrinne,Wu
draft-koskelainen-sipping-conf-requirements-00.txt            Nokia,Columbia U.
April 29, 2002
Expires: October 2002

                Additional Requirements to Conferencing


   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

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   This document focuses on advanced media-independent conferencing and
   conference control requirements, especially on user management
   related requirements.  Media control and floor control are out of

1 Introduction

   This document is an input document to the IETF SIPPING WG. This
   document complements other conferencing requirements such as [1] and
   focuses more on advanced user management issues.  Floor control and
   media control are totally out of scope.

   This document focuses only on centralized (star-based) conferences in

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   which the server hosts the conference.  Scalable solutions to support
   large conferences are out of scope.  Later standardization may define
   how star-based conference topology can be extended to support really
   large conferences. Work on scalable solutions can be found e.g. in
   [2], which defines a mechanism that can be used to distribute the
   conference across several conference servers using hierarchical,
   distributed server tree (DST) or single source multicast.

   Management functions identified in this document may be utilized for
   other services as well. For example, creating a group list at a
   server (without intension to do conferencing) may utilize same
   operations, such as creating a group list and adding new users into

1.1 Conventions of This Document

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   and "OPTIONAL" are to be interpreted as described in RFC 2119 [3].

2 Overview

   We define conference as a set of members that exchange one or more
   media streams or share some other state, such as an application.
   Conferencing includes two main parts.  First part enables
   participants to join and leave a conference.  Signaling protocols,
   such as SIP, can generally support these operations if conferences
   are addressed like regular endpoints.  The second conferencing part,
   conference control, can be considered as consisting three components:

   - conference management (creating, modifying and
     deleting conferences as a whole),
   - user management (adding and deleting conference participants
     and modifying their properties), and
   - resource contention management, also known as floor control.

   The main function of floor control is to provide safe access to
   shared resources. Controlling permissions to talk is the most typical
   example of floor control. However, as said earlier, floor control is
   out of scope.

   Conferences are addressed like regular endpoints so conference has an
   identifier such as  The conference server has
   a point-to-point relationship with each conference member.

   SIP can control application sessions only between one user and the
   conference server. It cannot change the conference state or the

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   conference-wide media settings at the server so additional management
   operations are needed [2].

3 Example Use Cases

   Use Case 1: (Conference creation and conference control)
   A conference is created at a server, and it is managed during the
   conference lifetime.  Conference may have a lot of properties such as
   member list, access control list (ACL), user privileges, and media

   Use Case 2: (Creating and managing user list without actual
   A group name such as is created. Creator can
   add and remove users. This group name can be used e.g. as an alias
   for multiparty one-shot messaging, or it can be used later for
   conferecing (no need to create new user list for each conference,
   instead, user can utilize existing user lists).

4 General Requirements

   * Tight conference control (in contrast to loose conference control)

   * Centralized architecture (in contrast to fully meshed or multicast)

   * Simplicity:
   Conferencing framework must balance being poweful
   enough for most practical scenarios, yet avoid being too complex to
   be widely accepted and implemented on devices with limited
   computational resources and user interfaces.

   * Mobile-friendliness
   Solution MUST be mobile-friendly, since mobile low-bandwidth devices
   represent large portion of user base. Bandwidth consumption on the
   access link is the most important mobile requirement.  It means that
   unnecessary (frequent) communication SHOULD be minimized.  For
   example, pre-defined definitions (access lists) eliminate the need to
   consult human moderator for every join attempt. Moreover, the
   notification frequency SHOULD be configurable by the user.
   Similarly, partial modifications MUST be supported. This means that
   there is no need to send all parameters if you change only one.  In
   addition, changes in the member lists should be distributed as
   additions and removals (instead of distributing whole list).
   Moreover, the solution MUST NOT assume IP multicast since it is not
   widely available in mobile networks or in residential environments
   (such as PPPoE).

   * Component based

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   The solutions MUST be component-based (in contrast to monolithic).
   This allows clients to implement only relevant components.  It also
   allows more advanced components to be added later (such as floor
   control), or existing components may be changed.

   * Asynchronous commands
   The execution of commands may take a long time, especially if human
   intervention is required so asynchronous commands MUST be supported.

   * Asynchronous notifications
   There MUST be a support for asynchronous notifications (e.g.
   network-initiated notifications without client pull).

   * Media-independency:
   The solution MUST be media-independent since in many cases there is
   no (RTP) media at all.

5 Component Specific Requirements

5.1 Conference Management requirements

   Conference management may include several optional sub-components,
   but it has also a few mandatory top-level requirements:

   * Conference creation: This creates a conference at a server. It may
   have parameters which describe basic conference-wide properties such
   as conference name and subject. Conference may be created for one-
   time use only, or as a permanent conference or group (conference name
   remains reserved).

   * Conference termination: This terminates the conference. The
   conference name may still be left to the server so same conference
   name and parameters may be utilized for later conferences.

   * Modification of conference parameters: This modifies conference
   parameters (e.g. adds video channel).

   * Fetching conference description from the server: User may fetch the
   conference description even before joining the conference.

   * Finding out the status of the conference: Solution MUST NOT be
   based on RTCP.

   * Search conferences at the server (e.g. search all conferences which
   are public and subject line or keywords includes word "soccer")

   * User SHOULD be able to define the level of details it want to
   receive as conference notifications or announcements (e.g. user may

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   not want to receive informational notifications at all)

   It must be possible to create a simple conference using these top-
   level functions. More advanced features can be provided by optional

5.2 User Management component

   This is an optional component.  It must enable at least the following
   operations or features:

   * Managing user right levels:
   Manage user right levels, such as audience, guru, moderator.  It must
   be possible to create and delete a user level, and add (remove) a
   user to (from) a user level. Default user levels may be defined (e.g.
   all new users are audience).

   * Managing privileges for user levels:
   This sets the user level privileges in a conference and defines what
   is allowed for each user level. Managing privileges can be an
   arbitrarily complex, expressible only in a full programming language.
   However, the majority of cases can be handled by defining a few
   simple privileges that are directly tied to conference management and
   giving users rights to those privileges.  The privileges are at least
   invite users, expel members, make real-time authorizations (such as
   accept or deny a join attempt), manage access control list (ACL),
   manage media sessions (e.g. change a user to receive only mode, or
   add video channel into a conference), and manage general parameters
   such as subject, authentication, visibility or start-time.
   Typically, moderator user level has all privileges.

   * Managing ACL:
   Manage ACL and sets allow/block definitions for a list of users.
   Wildcards must be supported (e.g. block sip:*  Add/remove
   operations must be supported.

   * Expelling users:
   This expels list of users from the conference.

   * Mass-invitation:
   Invites a list of users into the conference

   * Real-time authorization operations:
   For unexpected decisions during the conference. For example, "allow
   user X to join the conference".

   * Finding out conference members: It SHOULD be possible to find out
   the identities of current conference members at any given time. Must

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   not assume RTCP.

   * Anonymous participation: It must be possible to participate
   anonymously to the conference (e.g. by creating an anonymous user
   name into the server)

5.3 Other components

   The solution must allow other sub-components to be introduced later
   into the framework (such as SIP/SOAP floor control [4]).

5.4 Group Operations

   * Group name creation, modifications, termination:
   Create/Modify/Terminate a group name which can be later used e.g. for
   conferencing or one-shots.  In many cases, this group name includes
   just a list of users and is used only for one-shot messaging.  (this
   overlaps partly with conference creation..)

6 Notifications

   Following notifications or announcements are required:

   - Occasional user related notifications, such as "Bob and Tom have
   joined", or "Dear moderator, user X wants to join the conference.
   Accept or Deny?", or other general conference notifyications.

   - result for the asynchronous command (e.g. moderator decided - after
   thinking for a while - not to allow Bob to join).

7 Denial-of-Service attacks

   DoS attacks are possible. For example, a large number of join
   attempts may be created. Human moderator should not be automatically
   consulted about each join attempt. Instead, access lists are checked
   first.  Rate-control must be applied in the server so notifications
   are not sent too often. Moreover, this often allows the server to
   include several notification into one message (e.g. 3 join attempts
   are reported in one notification).

8 Examples

   At least the following parameters should be supported:
   - conference name (such as
   - conference subject (such as "IETF interim SIMPLE WG meeting")
   - conference time (e.g. it starts tomorrow 12:00 EST)
   - store conference parameters or not for later use
   - whether conference is public or not (can it be seen/searched)

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   - authentication information
   - application information (such as conference-wide media codecs)
   - list of users to be invited by the server (for mass-invitation)
   - user right levels (such as guru, moderator, audience)
   - user level access rights (such as guru-members are allowed to expel
   - ACL

   Following is a concrete example of the conference creation, and
   conference control during the conference.

   User A creates a conference at a server with following parameters:

   - conference name:
   - subject: Interim Sipping meeting
   - authentication: digest, passwd=''x243DHEDw''
   - media: video channel:H.261.., audio channel:PCM..
   - user levels: default groups (moderator, audience)
       moderator list: user A
       audience list:  (default for all new members)
   - user level rights:
       audience: none
       moderator:expel members, authorize joins, manage ACL, terminate conference)
   - invite users: Tom, Alice, John
   - ACL: block list=Bob, *

   The conference server sends an acknowledgement. It means that the
   command was accepted without an immediate failure.

   The server process the command and makes invitations.

   The server sends occasional notifications to the creator, such as
   "Conference created successfully. Members in a conference: Tom,

   New members try to join the conference. ACL does not include any hint
   how to act so moderator action is required.

   The server waits for a while, and sends a notification to the
   moderator. The notification includes information about 3 join
   attempts. The moderator accepts one of them, and denies two of them.
   The decision is sent to the server in a one message.

9 Conclusions

   There are two kinds of operations needed for conference control and

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   - commands (sent to the server)
   - informative notifications aka announcements

10 Authors' Addresses

   Petri Koskelainen
   Dept. of Computer Science
   Columbia University
   1214 Amsterdam Avenue, MC 0401
   New York, NY 10027
   electronic mail:
   electronic mail:

   Xiaotao Wu
   Dept. of Computer Science
   Columbia University
   1214 Amsterdam Avenue, MC 0401
   New York, NY 10027
   electronic mail:

   Henning Schulzrinne
   Dept. of Computer Science
   Columbia University
   1214 Amsterdam Avenue, MC 0401
   New York, NY 10027
   electronic mail:

11 Bibliography

   [1] O. Levin, A. Zmolek, R. Even, D. Petrie, and P. Koskelainen,
   "Conferencing requirements for sip based systems," Internet Draft,
   Internet Engineering Task Force, April 2002.  Work in progress.

   [2] P. Koskelainen, H. Schulzrinne, and X. Wu, "A sip-based
   conference control framework," in The 12nd International Workshop on
   Network and Operating System Support for Digital Audio and Video
   (NOSSDAV) , (Miami Beach, Florida), May 2002.

   [3] S. Bradner, "Key words for use in RFCs to indicate requirement
   levels," RFC 2119, Internet Engineering Task Force, Mar. 1997.

   [4] X. Wu, P. Koskelainen, H. Schulzrinne, and C. Chen, "Use SIP and
   SOAP for conference floor control," Internet Draft, Internet
   Engineering Task Force, April 2002.  Work in progress.

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   This document and the information contained herein is provided on an

                           Table of Contents

   1          Introduction ........................................    1
   1.1        Conventions of This Document ........................    2
   2          Overview ............................................    2
   3          Example Use Cases ...................................    3
   4          General Requirements ................................    3
   5          Component Specific Requirements .....................    4
   5.1        Conference Management requirements ..................    4
   5.2        User Management component ...........................    5
   5.3        Other components ....................................    6
   5.4        Group Operations ....................................    6
   6          Notifications .......................................    6
   7          Denial-of-Service attacks ...........................    6
   8          Examples ............................................    6

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   9          Conclusions .........................................    7
   10         Authors' Addresses ..................................    8
   11         Bibliography ........................................    8

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