CLUE WG A. Romanow
Internet-Draft Cisco Systems
Intended status: Informational S. Botzko
Expires: July 19, 2013 Polycom
January 15, 2013
Requirements for Telepresence Multi-Streams
draft-ietf-clue-telepresence-requirements-03.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
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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 July 19, 2013.
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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 . . . . . . . . . . . . . . . . . . . . 11
Appendix A. Open issues . . . . . . . . . . . . . . . . . . . . . 11
Appendix B. Changes From Earlier Versions . . . . . . . . . . . . 12
B.1. Changes from draft -02 . . . . . . . . . . . . . . . . . . 12
B.2. Changes from draft -01 . . . . . . . . . . . . . . . . . . 12
B.3. Changes From Draft -00 . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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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(s) that, when fulfilled by an implementation of the
specification(s), 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.
A telepresence session, requires at least one sending and one
receiving endpoint. 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
must ever take into account information received. However, by making
available as much information as possible, and by taking into account
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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 following terms are used throughout this document and serve as
reference for other documents.
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 may include a Mixer [RFC4353].
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 a "being there" experience characteristic of
telepresence, media inputs need to be transported, received, and
coordinated between participating systems. Different telepresence
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systems take diverse approaches in crafting a solution, or, they
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 systems 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 they sometimes introduce unwelcome side effects, such
as additional delay or degraded 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
start as planned, or are interrupted by difficulties that arise.
The general problem that needs to be solved can be described as
follows. Today, each endpoint sends audio and video captures based
upon an implicitly assumed model for rendering a realistic depiction
based on this information. If all endpoints are manufactured by the
same vendor, they work with the same model and render the information
according to the model implicitly assumed by the vendor. However, if
the devices are from different vendors, the models they each use 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 is captured from the right camera, whereas the other assumes
the first video stream is captured from the left camera.
If Alice and Bob are at different sites, Alice needs to tell Bob
about the camera and sound equipment arranement at her site so that
Bob's receiver can create an accurate rendering 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 may
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-1c: The solution MUST support a means to identify
the point of capture of individual video
captures in three dimensions.
REQMT-1d: The solution MUST support a means to identify
the extent of individual video captures in
three dimensions.
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
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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.
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-2d: The solution MUST support a means to identify
the point of capture of individual audio
captures in three dimensions.
REQMT-2e: The solution MUST support a means to identify
the extent of individual audio captures in
three dimensions.
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.
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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.
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.
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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:
* 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.
REQMT-17: The solution must support a mechanism for allowing
information about media captures to change during a
conference.
REQMT-18: The solution MUST provide a mechanism for the secure
exchange of information about the media captures.
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
There are no IANA considerations associated with this specification.
8. Security Considerations
Requirement Paragraph 18 identifies the need to securely transport
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the information about media captures. It is important to note that
session setup for a telepresence session will use SIP for basic
session setup and either SIP or CCMP for a multi-party telepresence
session. Information carried in the SIP signaling can be secured by
the SIP security mechanisms as defined in [RFC3261]. In the case of
conference control using CCMP, the security model and mechanisms as
defined in the XCON Framework [RFC5239] and CCMP [RFC6503] documents
would meet the requirement. Any additional signaling mechanism used
to transport the information about media captures would need to
define the mechanisms by the which the information is secure. These
mechanisms would need to be defined and described in the CLUE
framework document and related solution document(s).
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.
[RFC5239] Barnes, M., Boulton, C., and O. Levin, "A Framework for
Centralized Conferencing", RFC 5239, June 2008.
[RFC6503] Barnes, M., Boulton, C., Romano, S., and H. Schulzrinne,
"Centralized Conferencing Manipulation Protocol",
RFC 6503, March 2012.
[StageDirection(Wikipedia)]
Wikipedia, "Blocking (stage), available from http://
en.wikipedia.org/wiki/Stage_direction#Stage_directions",
May 2011, <http://en.wikipedia.org/wiki/
Stage_direction#Stage_directions>.
Appendix A. Open issues
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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 -02
Updated IANA section - i.e., no IANA registrations required.
Added security requirement Paragraph 18.
Added some initial text to the security section.
B.2. Changes from draft -01
Cleaned up the Problem Statement section, re-worded.
Added Requirement Paragraph 17 in response to WG Issue #4 to make
a requirement for dynamically changing information. Approved by
WG
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Added requirements #1.c and #1.d. Approved by WG
Added requirements #2.d and #2.e. Approved by WG
B.3. 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,
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
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Stephen Botzko
Polycom
Andover, MA 01810
US
Email: stephen.botzko@polycom.com
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