Requirements for Telepresence Multi-Streams
draft-ietf-clue-telepresence-requirements-01

CLUE WG                                                       A. Romanow
Internet-Draft                                             Cisco Systems
Intended status: Informational                                 S. Botzko
Expires: May 3, 2012                                             Polycom
                                                        October 31, 2011

              Requirements for Telepresence Multi-Streams
            draft-ietf-clue-telepresence-requirements-01.txt

Abstract

   This memo discusses the requirements for a specification that enables
   telepresence interoperability, by describing the relationship between
   multiple RTP streams.  In addition, the problem statement and
   definitions are also covered herein.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on May 3, 2012.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   4.  Problem Statement  . . . . . . . . . . . . . . . . . . . . . .  5
   5.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . .  7
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   9.  Informative References . . . . . . . . . . . . . . . . . . . . 10
   Appendix A.  Open issues . . . . . . . . . . . . . . . . . . . . . 11
   Appendix B.  Changes From Earlier Versions . . . . . . . . . . . . 11
     B.1.  Changes From Draft -00 . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12

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1.  Introduction

   Telepresence systems greatly improve collaboration.  In a
   telepresence conference (as used herein), the goal is to create an
   environment that gives the users a feeling of (co-located) presence -
   the feeling that a local user is in the same room with other local
   users and the remote parties.  Currently, systems from different
   vendors often do not interoperate because they do the same tasks
   differently, as discussed in the Problem Statement section below.

   The approach taken in this memo is to set requirements for a future
   specification that, when fullfilled by an implementation of the
   specification, provide for interoperability between IETF protocol
   based telepresence systems.  It is anticipated that a solution for
   the requirements set out in this memo likely involves the exchange of
   adequate information about participating sites; information that is
   currently not standardized by the IETF.

   The purpose of this document is to describe the requirements for a
   specification that enables interworking between different SIP-based
   [RFC3261] telepresence systems, by exchanging and negotiating
   appropriate information.  Non IETF protocol based systems, such as
   those based on ITU-T Rec. H.323, are out of scope.  These
   requirements are for the specification, they are not requirements on
   the telepresence systems implementing the solution/protocol that will
   be specified.

   Telepresence systems of different vendors, today, can follow
   radically different architectural approaches while offering a similar
   user experience.  It is not the intention of CLUE to dictate
   telepresence architectural and implementation choices.  CLUE enables
   interoperability between telepresence systems by exchanging
   information about the systems' characteristics.  Systems can use this
   information to control their behavior to allow for interoperability
   between those systems.

   In a telepresence session, required are at least one sending and one
   receiving endpoint.  Most telepresence endpoints are full-duplex in
   that they are both sending and receiving.  Some, especially
   multiparty telepresence sessions include more than two endpoints, and
   centralized infrastructure such as Multipoint Control Units (MCUs) or
   equivalent.  CLUE specifies the syntax, semantics, and control flow
   of information to enable the best possible user experience at those
   endpoints.

   Sending endpoints, or MCUs, are not mandated to use any of the CLUE
   specifications that describe their capabilities, attributes, or
   behavior.  Similarly, it is not envisioned that endpoints or MCUs

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   must ever take into account information received.  However, by making
   available as much information as possible, and by taking into account
   as much information as has been received or exchanged, MCUs and
   endpoints are expected to select operation modes that enable the best
   possible user experience under their constraints.

   The document structure is as follows: Definitions are set out,
   followed by a description of the problem of telepresence
   interoperability that led to this work.  Then the requirements to a
   specification addressing the current shortcomings are enumerated and
   discussed.

2.  Terminology

   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 [RFC2119].

3.  Definitions

   The definitions are from draft-wenger-clue-definitions-01.txt.  The
   editor's notes are not included here.

      Audio Mixing: refers to the accumulation of scaled audio signals
      to produce a single audio stream.  See RTP Topologies, [RFC5117].

      Conference: used as defined in [RFC4353], A Framework for
      Conferencing within the Session Initiation Protocol (SIP).

      Endpoint: The logical point of final termination through
      receiving, decoding and rendering, and/or initiation through
      capturing, encoding, and sending of media streams.  An endpoint
      consists of one or more physical devices which source and sink
      media streams, and exactly one [RFC4353] Participant (which, in
      turn, includes exactly one SIP User Agent).  In contrast to an
      endpoint, an MCU may also send and receive media streams, but it
      is not the initiator nor the final terminator in the sense that
      Media is Captured or Rendered.  Endpoints can be anything from
      multiscreen/multicamera rooms to handheld devices.

      Endpoint Characteristics: include placement of Capture and
      Rendering Devices, capture/render angle, resolution of cameras and
      screens, spatial location and mixing parameters of microphones.
      Endpoint characteristics are not specific to individual media
      streams sent by the endpoint.

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      Layout: How rendered media streams are spatially arranged with
      respect to each other on a single screen/mono audio telepresence
      endpoint, and how rendered media streams are arranged with respect
      to each other on a multiple screen/speaker telepresence endpoint.
      Note that audio as well as video is encompassed by the term
      layout--in other words, included is the placement of audio streams
      on speakers as well as video streams on video screens.

      Left: to be interpreted as a stage direction, see also
      [StageDirection(Wikipedia)]

      Local: Sender and/or receiver physically co-located ("local") in
      the context of the discussion.

      MCU: Multipoint Control Unit (MCU) - a device that connects two or
      more endpoints together into one single multimedia conference
      [RFC5117].  An MCU includes an [RFC4353] Mixer.

      Media: Any data that, after suitable encoding, can be conveyed
      over RTP, including audio, video or timed text.

      Model: a set of assumptions a telepresence system of a given
      vendor adheres to and expects the remote telepresence system(s)
      also to adhere to.

      Remote: Sender and/or receiver on the other side of the
      communication channel (depending on context); not Local.  A remote
      can be an Endpoint or an MCU.

      Render: the process of generating a representation from a media,
      such as displayed motion video or sound emitted from loudspeakers.

      Right: to be interpreted as stage direction, see also
      [StageDirection(Wikipedia)]

      Telepresence: an environment that gives non co-located users or
      user groups a feeling of (co-located) presence - the feeling that
      a Local user is in the same room with other Local users and the
      Remote parties.  The inclusion of Remote parties is achieved
      through multimedia communication including at least audio and
      video signals of high fidelity.

4.  Problem Statement

   In order to create the "being there" or telepresence experience,
   media inputs need to be transported, received, and coordinated.
   Different telepresence systems take diverse approaches in crafting a

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   solution.  Or, implement similar solutions quite differently.

   They use disparate techniques, and they describe, control and
   negotiate media in dissimilar fashions.  Such diversity creates an
   interoperability problem.  The same issues are solved in different
   ways by different systems, so that they are not directly
   interoperable.  This makes interworking difficult at best and
   sometimes impossible.

   Worse, many telepresence use proprietry protocol extensions to solve
   telepresence-related problems, even if those extensions are based on
   common standards such as SIP.

   Some degree of interworking between systems from different vendors is
   possible through transcoding and translation.  This requires
   additional devices, which are expensive, often not entirely
   automatic, and sometimes introduce unwelcome side effects such as
   additional delay or degrading performance.  Specialized knowledge is
   currently required to operate a telepresence conference with
   endpoints from different vendors, for example to configure
   transcoding and translating devices.  Often such conferences do not
   commence as planned, or are interrupted by difficulties that arise.

   The general problem that needs to be solved can be described as
   follows.  Today, the transmitting side sends audio and video captures
   based upon an implicitely assumed model for rendering a realistic
   depiction from this information.  If the receiving side belongs to
   the same vendor, it works with the same model and renders the
   information according to the model implicitely assumed by the vendor.
   However, if the receiver and the sender are from different vendors,
   the models they each have for rendering presence can and usually do
   differ.  The result can be that the telepresence systems actually
   connect, but the user experience suffers, for example because one
   system assumes that the first video stream stems from the right
   camera, whereas the other assumes the first video stream stems from
   the left camera.

   It is as if Alice and Bob are at different sites.  Alice needs to
   tell Bob information about what her camera and sound equipment see at
   her site so that Bob's receiver can create a display that will
   capture the important characteristics of her site.  Alice and Bob
   need to agree on what the salient characteristics are as well as how
   to represent and communicate them.  Characteristics include number,
   placement, capture/render angle, resolution of cameras and screens,
   spatial location and audio mixing parameters of microphones.

   The telepresence multi-stream work seeks to describe the sender
   situation in a way that allows the receiver to render it

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   realistically, though it may have a different rendering model than
   the sender; and for the receiver to provide information to the sender
   in order to help the sender create adequate content for interworking.

5.  Requirements

   Although some aspects of these requirements can be met by existing
   technology, such as SDP, or H.264, nonetheless we state them here to
   have a complete record of what the requirements for CLUE are, whether
   new work is needed or they can be met by existing technology.
   Figuring this out will be part of the solution development, rather
   than part of the requirements.

   REQMT-1:   The solution MUST support a description of the spatial
              arrangement of source video images sent in video streams
              which enables a satisfactory reproduction at the receiver
              of the original scene.  This applies to each site in a
              point to point or a multipoint meeting and refers to the
              spatial ordering within a site, not to the ordering of
              images between sites.

              Use case point to point symmetric, and all other use cases.

              REQMT-1a:  The solution MUST support a means of allowing
                         the preservation of the order of images in the
                         captured scene.  For example, if John is to
                         Susan's right in the image capture, John is
                         also to Susan's right in the rendered image.

              REQMT-1b:  The solution MUST support a means of allowing
                         the preservation of order of images in the
                         scene in two dimensions - horizontal and
                         vertical.

   REQMT-2:   The solution MUST support a description of the spatial
              arrangement of captured source audio sent in audio streams
              which enables a satisfactory reproduction at the receiver
              in a spatially correct manner.  This applies to each site
              in a point to point or a multipoint meeting and refers to
              the spatial ordering within a site, not the ordering of
              channels between sites.

                 Use case point to point symmetric, and all use cases,
                 especially heterogeneous.

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              REQMT-2a:  The solution MUST support a means of preserving
                         the spatial order of audio in the captured
                         scene.  For example, if John sounds as if he is
                         at Susan's right in the captured audio, John
                         voice is also placed at Susan's right in the
                         rendered image.

              REQMT-2b:  The solution MUST support a means to identify
                         the number and spatial arrangement of audio
                         channels including monaural, stereophonic
                         (2.0), and 3.0 (left, center, right) audio
                         channels.

              REQMT-2c:  The solution MUST NOT preclude the use of
                         binaural audio.  [Edt. This is an outstanding
                         issue.  Text will be changed when the issue is
                         resolved.]

   REQMT-3:   The solution MUST support a mechanism to enable a
              satisfactory spatial matching between audio and video
              streams coming from the same endpoints.

              Use case is point to point symmetric, and all use cases.

              REQMT-3a:  The solution MUST enable individual audio
                         streams to be associated with one or more video
                         image captures, and individual video image
                         captures to be associated with one or more
                         audio captures, for the purpose of rendering
                         proper position.

              REQMT-3b:  The solution MUST enable individual audio
                         streams to be rendered in any desired spatial
                         position.

                          Edt: Rendering is an open issue. Text will
                          be changed when it is resolved.]

   REQMT-4:   The solution MUST enable interoperability between
              endpoints that have a different number of similar devices.
              For example, one endpoint may have 1 screen, 1 speaker, 1
              camera, 1 mic, and another endpoint may have 3 screens, 2
              speakers, 3 cameras and 2 mics.  Or, in a multi-point
              conference, one endpoint may have one screen, another may
              have 2 screens and a third may have 3 screens.  This
              includes endpoints where the number of devices of a given
              type is zero.

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              Use case is asymmetric point to point and  multipoint.

   REQMT-5:   The solution MUST support means of enabling
              interoperability between telepresence endpoints where
              cameras are of different picture aspect ratios.

   REQMT-6:   The solution MUST provide scaling information which
              enables rendering of a video image at the actual size of
              the captured scene.

   REQMT-7:   The solution MUST support means of enabling
              interoperability between telepresence endpoints where
              displays are of different resolutions.

   REQMT-8:   The solution MUST support methods for handling different
              bit rates in the same conference.

   REQMT-9:   The solution MUST support means of enabling
              interoperability between endpoints that send and receive
              different numbers of media streams.

              Use case heterogeneous and multipoint.

   REQMT-10:  The solution MUST make it possible for endpoints without
              support for telepresence extensions to participate in a
              telepresence session with those that do.

   REQMT-11:  The solution MUST support a mechanism for determining
              whether or not an endpoint or MCU is capable of
              telepresence extensions.

   REQMT-12:  The solution MUST support a means to enable more than two
              sites to participate in a teleconference.

              Use case multipoint.

   REQMT-13:  The solution MUST support both transcoding and switching
              approaches to providing multipoint conferences.

   REQMT-14:  The solution MUST support mechanisms to make possible for
              either or both site switching or segment switching.  [Edt:
              This needs rewording.  Deferred until layout discussion is
              resolved.]

   REQMT-15:  The solution MUST support mechanisms for presentations in
              such a way that:

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              *  Presentations can have different sources

              *  Presentations can be seen by all

              *  There can be variation in placement, number and size of
                 presentations

   REQMT-16:  The solution MUST include extensibility mechanisms.

6.  Acknowledgements

   This draft has benefitted from all the comments on the mailing list
   and a number of discussions.  So many people contributed that it is
   not possible to list them all.

7.  IANA Considerations

   TBD

8.  Security Considerations

   TBD

9.  Informative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3261]  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.

   [RFC4353]  Rosenberg, J., "A Framework for Conferencing with the
              Session Initiation Protocol (SIP)", RFC 4353,
              February 2006.

   [RFC5117]  Westerlund, M. and S. Wenger, "RTP Topologies", RFC 5117,
              January 2008.

   [StageDirection(Wikipedia)]
              Wikipedia, "Blocking (stage), available from http://
              en.wikipedia.org/wiki/Stage_direction#Stage_directions",
              May 2011, <http://en.wikipedia.org/wiki/

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              Stage_direction#Stage_directions>.

Appendix A.  Open issues

   OPEN-1  Binaural Audio [REQMT-2C] The need to support of binaural
           audio is unresolved, and the "MUST NOT preclude" language in
           this requirement is problematic.  The authors believe this
           requirement needs to be either changed or withdrawn,
           depending on how the issue is resolved.

   OPEN-2  Reference to Rendering [REQMT-3b] This is the only
           requirement which refers to rendering.  It may also be empty,
           since receivers can rendering audio captures as they wish.
           This is deferred until broader discussion on rendering
           requirements is concluded.

   OPEN-3  Conference modes [REQMT-14] This wording of this requirement
           is problematic in part because the conference modes (site
           switching and segment switching) are not defined.  It at
           least needs rewording.  This is deferred until broader
           discussion on layout is concluded.

   OPEN-4  Need to capture requirement that attributes can change at any
           time during the call.

   OPEN-5  Need to add requirement for three dimensions in the right
           place

   OPEN-6  Multi-view, is there a requirement needed?

Appendix B.  Changes From Earlier Versions

   Note to the RFC-Editor: please remove this section prior to
   publication as an RFC.

B.1.  Changes From Draft -00

   o  Requirement #2, The solution MUST support a means to identify
      monaural, stereophonic (2.0), and 3.0 (left, center, right) audio
      channels.

       changed to

      The solution MUST support a means to identify the number and
      spatial arrangement of audio channels including monaural,

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      stereophonic (2.0), and 3.0 (left, center, right) audio channels.

   o  Added back references to the Use case document.

      *  Requirement #1 Use case point to point symmetric, and all other
         use cases.

      *  Requirement #2 Use case point to point symmetric, and all use
         cases, especially heterogeneous.

      *  Requirement #3 Use case point to point symmetric, and all use
         cases.

      *  Requirement #4 Use case is asymmetric point to point, and
         multipoint.

      *  Requirement #9 Use case heterogeneous and multipoint.

      *  Requirement #12 Use case multipoint.

Authors' Addresses

   Allyn Romanow
   Cisco Systems
   San Jose, CA  95134
   USA

   Email: allyn@cisco.com

   Stephen Botzko
   Polycom
   Andover, MA  01810
   US

   Email: stephen.botzko@polycom.com

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