Internet DRAFT - draft-romanow-clue-framework
draft-romanow-clue-framework
CLUE WG A. Romanow
Internet-Draft Cisco Systems
Intended status: Informational M. Duckworth
Expires: April 5, 2012 Polycom
A. Pepperell
B. Baldino
Cisco Systems
October 3, 2011
Framework for Telepresence Multi-Streams
draft-romanow-clue-framework-01.txt
Abstract
This memo offers a framework for a protocol that enables devices in a
telepresence conference to interoperate by specifying the
relationships between multiple RTP streams.
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
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 5, 2012.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Framework Features . . . . . . . . . . . . . . . . . . . . . . 7
5. Stream Information . . . . . . . . . . . . . . . . . . . . . . 8
5.1. Media capture -- Audio and Video . . . . . . . . . . . . . 9
5.2. Attributes . . . . . . . . . . . . . . . . . . . . . . . . 9
5.2.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . 10
5.2.2. Audio mixed . . . . . . . . . . . . . . . . . . . . . 10
5.2.3. Audio Channel Format . . . . . . . . . . . . . . . . . 10
5.2.4. Area of capture . . . . . . . . . . . . . . . . . . . 11
5.2.5. Point of capture . . . . . . . . . . . . . . . . . . . 12
5.2.6. Area Scale Millimeters . . . . . . . . . . . . . . . . 12
5.2.7. Video composed . . . . . . . . . . . . . . . . . . . . 12
5.2.8. Auto-switched . . . . . . . . . . . . . . . . . . . . 12
5.3. Capture Set . . . . . . . . . . . . . . . . . . . . . . . 12
6. Choosing Streams . . . . . . . . . . . . . . . . . . . . . . . 14
6.1. Message Flow . . . . . . . . . . . . . . . . . . . . . . . 15
6.1.1. Provider Capabilities Announcement . . . . . . . . . . 15
6.1.2. Consumer Capability Message . . . . . . . . . . . . . 16
6.1.3. Consumer Configure Request . . . . . . . . . . . . . . 16
6.2. Physical Simultaneity . . . . . . . . . . . . . . . . . . 16
6.3. Encoding Groups . . . . . . . . . . . . . . . . . . . . . 18
6.3.1. Encoding Group Structure . . . . . . . . . . . . . . . 19
6.3.2. Individual Encodes . . . . . . . . . . . . . . . . . . 19
6.3.3. More on Encoding Groups . . . . . . . . . . . . . . . 20
6.3.4. Examples of Encoding Groups . . . . . . . . . . . . . 21
7. Using the Framework . . . . . . . . . . . . . . . . . . . . . 23
7.1. The MCU Case . . . . . . . . . . . . . . . . . . . . . . . 27
7.2. Media Consumer Behavior . . . . . . . . . . . . . . . . . 27
7.2.1. One screen consumer . . . . . . . . . . . . . . . . . 28
7.2.2. Two screen consumer configuring the example . . . . . 28
7.2.3. Three screen consumer configuring the example . . . . 29
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 29
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
10. Security Considerations . . . . . . . . . . . . . . . . . . . 29
11. Informative References . . . . . . . . . . . . . . . . . . . . 29
Appendix A. Open Issues . . . . . . . . . . . . . . . . . . . . . 30
A.1. Video layout arrangements and centralized composition . . 30
A.2. Source is selectable . . . . . . . . . . . . . . . . . . . 30
A.3. Media Source Selection . . . . . . . . . . . . . . . . . . 30
A.4. Endpoint requesting many streams from MCU . . . . . . . . 31
A.5. VAD (voice activity detection) tagging of audio streams . 31
A.6. Private Information . . . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 31
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1. Introduction
Current telepresence systems, though based on open standards such as
RTP [RFC3550] and SIP [RFC3261], cannot easily interoperate with each
other. A major factor limiting the interoperability of telepresence
systems is the lack of a standardized way to describe and negotiate
the use of the multiple streams of audio and video comprising the
media flows. This draft provides a framework for a protocol to
enable interoperability by handling multiple streams in a
standardized way. It is intended to support the use cases described
in draft-ietf-clue-telepresence-use-cases-00 and to meet the
requirements in draft-romanow-clue-requirements-xx.
The solution described here is strongly focused on what is being done
today, rather than on a vision of future conferencing. At the same
time, the highest priority has been given to creating an extensible
framework to make it easy to accommodate future conferencing
functionality as it evolves.
The purpose of this effort is to make it possible to handle multiple
streams of media in such a way that a satisfactory user experience is
possible even when participants are on different vendor equipment and
when they are using devices with different types of communication
capabilities. Information about the relationship of media streams
must be communicated so that audio/video rendering can be done in the
best possible manner. In addition, it is necessary to choose which
media streams are sent.
There is no attempt here to dictate to the renderer what it should
do. What the renderer does is up to the renderer.
After the following Definitions, two short sections introduce key
concepts. The body of the text comprises three sections that deal
with in turn stream content, choosing streams and an implementation
example. The media provider and media consumer behavior are
described in separate sections as well. Several appendices describe
further details for using the framework.
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].
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3. Definitions
The definitions marked with an "*" are new; all the others are from
draft-wenger-clue-definitions-00-01.txt.
*Audio Capture: Media Capture for audio. Denoted as ACn.
Capture Device: A device that converts audio and video input into an
electrical signal, in most cases to be fed into a media encoder.
Cameras and microphones are examples for capture devices.
Capture Scene: the scene that is captured by a collection of Capture
Devices. A Capture Scene may be represented by more than one type of
Media. A Capture Scene may include more than one Media Capture of
the same type. An example of a Capture Scene is the video image of a
group of people seated next to each other, along with the sound of
their voices, which could be represented by some number of VCs and
ACs. A middle box may also express Capture Scenes that it constructs
from Media streams it receives.
A Capture Set includes Media Captures that all represent some aspect
of the same Capture Scene. The items (rows) in a Capture Set
represent different alternatives for representing the same Capture
Scene.
Conference: used as defined in [RFC4353], A Framework for
Conferencing within the Session Initiation Protocol (SIP).
Individual Encode: A variable with a set of attributes that describes
the maximum values of a single audio or video capture encoding. The
attributes include: maximum bandwidth- and for video maximum
macroblocks, maximum width, maximum height, maximum frame rate.
[Edt. These are based on H.264.]
*Encoding Group: Encoding group: A set of encoding parameters
representing a device's complete encoding capabilities or a
subdivision of them. Media stream providers formed of multiple
physical units, in each of which resides some encoding capability,
would typically advertise themselves to the remote media stream
consumer as being formed multiple encoding groups. Within each
encoding group, multiple potential actual encodings are possible,
with the sum of those encodings' characteristics constrained to being
less than or equal to the group-wide constraints.
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
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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.
Left: For media captures, left and right is from the point of view of
a person observing the rendered media.
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. [Edt. RFC4353 is
tardy in requiring that media from the mixer be sent to EACH
participant. I think we have practical use cases where this is not
the case. But the bug (if it is one) is in 4353 and not herein.
Media: Any data that, after suitable encoding, can be conveyed over
RTP, including audio, video or timed text.
*Media Capture: a source of Media, such as from one or more Capture
Devices. A Media Capture may be the source of one or more Media
streams. A Media Capture may also be constructed from other Media
streams. A middle box can express Media Captures that it constructs
from Media streams it receives.
*Media Consumer: an Endpoint or middle box that receives Media
streams
*Media Provider: an Endpoint or middle box that sends Media streams
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.
Right: For media captures, left and right is from the point of view
of a person observing the rendered media.
Render: the process of generating a representation from a media, such
as displayed motion video or sound emitted from loudspeakers.
*Simultaneous Transmission Set: a set of media captures that can be
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transmitted simultaneously from a Media Provider.
Spatial Relation: The arrangement in space of two objects, in
contrast to relation in time or other relationships. See also Left
and Right.
*Stream: RTP stream as in [RFC3550].
Stream Characteristics: include media stream attributes commonly used
in non-CLUE SIP/SDP environments (such as: media codec, bit rate,
resolution, profile/level etc.) as well as CLUE specific attributes
(which could include for example and depending on the solution found:
the I-D or spatial location of a capture device a stream originates
from).
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.
*Video Capture: Media Capture for video. Denoted as VCn.
Video composite: A single image that is formed from combining visual
elements from separate sources.
4. Framework Features
Two key functions must be accomplished so that multiple media streams
can be handled in a telepresence conference. These are:
o How to choose which streams the provider should send to the
consumer
o What information needs to be added to the streams to allow a
rendering of the capture scene
The framework/model we present here can be understood as specifying
these two functions.
Media stream providers and consumers are central to the framework.
The provider's job is to advertise its capabilities (as described
here) to the consumer, whose job it is to configure the provider's
encoding capabilities as described below. Both providers and
consumers can each send and receive information, that is, we do not
have one party as the provider and one as the consumer exclusively,
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but all parties have both sending and receiving parts to them. Most
devices function as both a media provider and as a media consumer.
For two devices to communicate bidirectionally, with media flowing in
both directions, both devices act as both a media provider and a
media consumer. The protocol exchange shown later in the "Choosing
Streams" section happens twice independently between the 2
bidirectional devices.
Both endpoints and MCUs, or more generally "middleboxes", can be
media providers and consumers.
Generally, the provider is capable of sending alternate captures of a
capture scene. These are described by the provider as capabilities
and chosen by the consumer.
5. Stream Information
This section describes the structure for communicating information
between providers and consumers. Figure illustrates how information
to be communicated is organized. Each construct illustrated in the
diagram is discussed in the sections below.
Diagram for Stream Content
+---------------+
| |
| Capture Set |
| |
+-------+-------+
_..-' | ``-._
_.-' | ``-._
_.-' | ``-._
+----------------+ +----------------+ +----------------+
| Media Capture | | Media Capture | | Media Capture |
| Audio or Video | | Audio or Video | | Audio or Video |
+----------------+ +----------------+ +----------------+
.' `. `-..__
.' `. ``-..__
,-----. ,---------. ``,----------.
,' Encode`. ,' `. ,'Simultaneous`.
( Group ) ( Attributes ) ( Transmission )
`. ,' `. ,' `. Sets ,'
`-----' `---------' `----------'
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5.1. Media capture -- Audio and Video
A media capture, as defined in definitions, is a fundamental concept
of the model. Media can be captured in different ways, for example
by various arrangements of cameras and microphones. The model uses
the terms "video capture" (VC) and "audio capture" (AC) to refer to
sources of media streams. To distinguish between multiple instances,
they are numbered for example VC1, VC2, and VC3 could refer to three
different video captures which can be used simultaneously.
Media captures are dynamic. They can come and go in a conference -
and their parameters can change. A provider can advertise a new list
of captures at any time. Both the media provider and media consumer
can send "their messages" (i.e., capture set advertisements, stream
configurations) any number of times during a call, and the other end
is always required to act on any new information received (e.g.,
stopping streams it had previously configured that are no longer
valid).
A media capture can be a media source such as video from a specific
camera, or it can be more conceptual such as a composite image from
several cameras, or an automatic dynamically switched capture
choosing from several cameras depending on who is talking or other
factors.
A media capture is described by Attributes and associated with an
Encode Group, and Physical Simultaneity Set.
Audio and video captures are aggregated into Capture Sets as
described below.
5.2. Attributes
Audio and video capture attributes describe information about streams
and their relationships. [Edt: We do not mean to duplicate SDP, if
an SDP description can be used, great.] The attributes of media
captures refer to static aspects of those captures that can be used
by the consumer for selecting the captures offered by the provider.
The mechanism of Attributes make the framework extensible. Although
we are defining some attributes now based on the most common use
cases, new attributes can be added for new use cases as they arise.
In general, the way to extend the solution to handle new features is
by adding attributes and/or values.
We describe attributes by variables and their values. The current
attributes are listed below and then described. The variable is
shown in parentheses, and the values follow after the colon:
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o (Purpose): main, presentation
o (Audio mixed): true, false
o (Audio Channel Format): mono, stereo, tbd
o (Area of Capture): A set of 'Ranges' describing the relevant area
being capture by a capture device
o (Point of Capture): A 'Point' describing the location of the
capture device or pseudo-device
o (Area scale): true, false indicating if area numbers are in
millimeters
o (Video composed): true, false
o (Auto-switched): true, false
5.2.1. Purpose
A variable with enumerated values describing the purpose or role of
the Media Capture. It could be applied to any media type. Possible
values: main, presentation, others TBD.
Main:
The audio or video capture is of one or more people participating in
a conference (or where they would be if they were there). It is of
part or all of the Capture Scene.
Presentation:
The stream provides a presentation, e. g., from a connected laptop or
other input device.
5.2.2. Audio mixed
A Boolean variable to indicate whether the AC is a mix of other ACs
or Streams.
5.2.3. Audio Channel Format
The "channel format" attribute of an Audio Capture indicates how the
meaning of the channels is determined. It is an enumerated variable
describing the type of audio channel or channels in the Audio
Capture. The possible values of the "channel format" attribute are:
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o mono
o stereo
o TBD - other possible future values (to potentially include other
things like 3.0, 3.1, 5.1 surround sound and binaural)
All ACs in the same row of a Capture Set MUST have the same value of
the "channel format" attribute.
There can be multiple ACs of a particular type, or even different
types. These multiple ACs could each have an area of capture
attribute to indicate they represent different areas of the capture
scene.
If there are multiple audio streams, they might be correlated (that
is, someone talking might be heard in multiple captures from the same
room). Echo cancellation and stream synchronization in consumers
should take this into account.
Mono:
An AC with channel format="mono" has one audio channel.
Stereo:
An AC with channel format = "stereo" has exactly two audio channels,
left and right, as part of the same AC. [Edt: should we mention RFC
3551 here? The channel format may be related to how Audio Captures
are mapped to RTP streams. This stereo is not the same as the effect
produced from two mono ACs one from the left and one from the right.
]
5.2.4. Area of capture
The area_of_capture attribute is used to describe the relevant area
of which a media capture is "capturing". By comparing the area of
capture for different media captures, a consumer can determine the
spatial relationships of the captures on the provider so that they
can be rendered correctly. The attribute consists of a set of
'Ranges', one range for each spatial dimension, where each range has
a Begin and End coordinate. It is not necessary to fill out all of
the dimensions if they are not relevant (i.e. if an endpoint's
captures only span a single dimension, only the 'x' coordinate can be
used). There is no need to pre-define a possible range for this
coordinate system; a device may choose what is most appropriate for
describing its captures. However, it is specified that as numbers
move from lower to higher, the location is going from: left to right
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(in the case of the 'x' dimension), front to back (in the case of the
'y' dimension or low to high (in the case of the 'z' dimension).
5.2.5. Point of capture
The point_of_capture attribute can be used to describe the location
of a capture device or pseudo-device. If there are multiple captures
which share the same 'area_of_capture' value, then it is useful to
know the location from which they are capturing that area (e.g. a
device which has multiview). Point of capture is expressed as a
single {x, y, z} coordinate where, as with area_of_capture, only the
necessary dimensions need be expressed.
5.2.6. Area Scale Millimeters
An optional Boolean variable indicating if the numbers used for area
of capture and point of capture are in terms of millimeters. If this
attribute is true, then the x,y,z numbers represent millimeters. If
this attribute is false, then there is no physical scale. The
default value is false.
5.2.7. Video composed
An optional Boolean variable indicating if the VC is constructed by
composing multiple other video captures together. (This could
indicate for example a continuous presence view of multiple images in
a grid, or a large image with smaller picture-in-picture images in
it.)
Note: this attribute is not intended to differentiate between
different ways of composing images. For possible extension of the
framework, additional attributes could be defined to distinguish
between different ways of composing images, with different video
layout arrangements of composing multiple images into one.
5.2.8. Auto-switched
A Boolean variable that may be used or audio and/or video streams.
In this case the offered AC or VC varies depending on some rule; it
is auto-switched between possible VCs, or between possible ACs. The
most common example of this is sending the video capture associated
with the "loudest" speaker according to an audio detection algorithm.
5.3. Capture Set
A capture set describes the alternative media streams that the
provider offers to send to the consumer. As shown in the content
diagram above, the capture set is an aggregation of all audio and
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video captures for a particular scene that a provider is willing to
send.
A provider describes its ability to send alternative media streams in
the capture set, which lists the media captures in rows, as shown
below. Each row of the capture set consists of either a single
capture or a group of captures. A group means the individual
captures in the group are spatially related with the specific
ordering of the captures described through the use of attributes.
Here is an example of a simple capture set with three video captures
and three audio channels:
(VC0, VC1, VC2)
(AC0, AC1, AC2)
The three VCs together in a row indicate those captures are spatially
related to each other. Similarly for the 3 ACs in the second row.
The ACs and VCs in the same capture set are spatially related to each
other.
Multiple Media Captures of the same media type are often spatially
related to each other. Typically multiple Video Captures should be
rendered next to each other in a particular order, or multiple audio
channels should be rendered to match different speakers in a
particular way. Also, media of different types are often associated
with each other, for example a group of Video Captures can be
associated with a group of Audio Captures meaning they should be
rendered together.
Media Captures of the same media type are associated with each other
by grouping them together in a single row of a Capture Set. Media
Captures of different media types are associated with each other by
putting them in different rows of the same Capture Set.
Since all captures have an area_of_capture associated with them, a
consumer can determine the spatial relationships of captures by
comparing the locations of their areas of capture with one another.
Association between audio and video can be made by finding audio and
video captures which share overlapping areas of capture.
The items (rows) in a capture set represent different alternatives
for representing the same Capture Scene. For example the following
are alternative ways of capturing the same Capture Scene - two
cameras each viewing half of a room, or one camera viewing the whole
room, or one stream that automatically captures the person in the
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room who is currently speaking. Each row of the Capture Set contains
either a single media capture or one group of media captures.
The following example shows a capture set for an endpoint media
provider where:
o (VC0, VC1, VC2) - left camera capture, center camera capture,
right camera capture
o (VC3) - capture associated with loudest
o (VC4) - zoomed out view of all people in the room
o (AC0) - main audio
The first item in this capture set example is a group of video
captures with a spatial relationship to each other. These are VC0,
VC1, and VC2. VC3 and VC4 are additional alternatives of how to
capture the same room in different ways. The audio capture is
included in the same capture set to indicate AC0 is associated with
those video captures, meaning the audio should be rendered along with
the video in the same set.
The idea is to have sets of captures that represent the same
information ("information" in this context might be a set of people
and their associated audio / video streams, or might be a
presentation supplied by a laptop, perhaps with an accompanying audio
commentary). Spatial ordering of media captures is described through
the use of attributes.
A media consumer could choose one row of each media type (e.g., audio
and video) from a capture set. For example a three stream consumer
could choose the first video row plus the audio row, while a single
stream consumer could choose the second or third video row plus the
audio row. An MCU consumer might choose to receive multiple rows.
The groupsSimultaneous Transmission Set and Encoding Groups as
discussed in the next section apply to media captures listed in
capture sets. The groupsSimultaneous Transmission Sets and Encoding
Groups MUST allow all the Media Captures in a particular row of the
capture set to be used simultaneously. But media captures in
different rows of the capture set might not be able to be used
simultaneously.
6. Choosing Streams
This section describes the process of choosing which streams the
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provider sends to the consumer. In order for appropriate streams to
be sent from providers to consumers, certain characteristics of the
multiple streams must be understood by both providers and consumers.
Two separate aspects of streams suffice to describe the necessary
information to be shared by providers and consumers. The first
aspect we call "physical simultaneity" and the other aspect we refer
to as "encoding group". These are described in the following
sections, after the message flow is discussed.
6.1. Message Flow
The following diagram shows the flow of messages between a media
provider and a media consumer. The provider sends information about
its capabilities (as specified in this section), then the consumer
chooses which streams it wants, which we refer to as "configure".
The consumer sends its own capability message to the provider which
may contain information about its own capabilities or restrictions,
in which case the provider might tailor its announcements to the
consumer.
Diagram for Message Flow
Media Consumer Media Provider
-------------- ------------
| |
|----- Consumer Capability ---------->|
| |
| |
|<---- Capabilities (announce) -------|
| |
| |
|------ Configure (request) --------->|
| |
6.1.1. Provider Capabilities Announcement
The provider capabilities announce message includes:
o the list of captures and their attributes
o the list of capture sets
o the list of Simultaneous Transmission Sets
o the list of the encoding groups
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6.1.2. Consumer Capability Message
In order for a maximally-capable provider to be able to advertise a
manageable number of video captures to a consumer, there is a
potential use for the consumer being able, at the start of CLUE to be
able to inform the provider of its capabilities. One example here
would be the video capture attribute set - a consumer could tell the
provider the complete set of video capture attributes it is able to
understand and so the provider would be able to reduce the capture
set it advertises to be tailored to the consumer.
TBD - the content of this message needs to be better defined. The
authors believe there is a need for this message, but have not worked
out the details yet.
6.1.3. Consumer Configure Request
After receiving a set of video capture information from a provider
and making its choice of what media streams to receive based on the
consumer's own capabilities and any provider-side simultaneity
restrictions, the consumer needs to essentially configure the
provider to transmit the chosen set.
The expectation is that this message will enumerate each of the
encoding groups and potential encoders within those groups that the
consumer wishes to be active (this may well be a subset of the
complete set available). For each such encoder within an encoding
group, the consumer would specify the video capture (i.e., VC<n> as
described above) along with the specifics of the video encoding
required, i.e. width, height, frame rate and bit rate. At this
stage, the consumer would also provide RTP demultiplexing information
as required to distinguish each stream from the others being
configured by the same mechanism.
6.2. Physical Simultaneity
An endpoint or MCU can send multiple captures simultaneously.
However, there may be constraints that limit which captures can be
sent simultaneously with other captures.
Physical or device simultaneity refers to fact that a device may not
be able to be used in different ways at the same time. This shapes
the way that offers are made from the provider. The offers are made
so that the consumer will choose one of several possible usages of
the device. This type of constraint is expressed in Simultaneous
Transmission Sets. This is easier to show in an example.
Consider the example of a room system where there are 3 cameras each
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of which can send a separate capture covering 2 persons each- VC0,
VC1, VC2. The middle camera can also zoom out and show all 6
persons, VC3. But the middle camera cannot be used in both modes at
the same time - it has to either show the space where 2 participants
sit or the whole 6 seats. We refer to this as a physical device
simultaneity constraint.
The following illustration shows 3 cameras with 4 video streams. The
middle camera can be used as main video zoomed in on 2 people or it
could be used in zoomed out mode and capture the whole endpoint. The
idea here is that the middle camera cannot be used for both zoomed in
and zoomed out captures simultaneously. This is a constraint imposed
by the physical limitations of the devices.
Diagram for Simultaneity
`-. +--------+ VC2
.-'_Camera 3|---------->
.-' +--------+
VC3
-------->
`-. +--------+ /
.-'|Camera 2|<
.-' +--------+ \ VC1
-------->
`-. +--------+ VC0
.-'|Camera 1|---------->
.-' +--------+
VC0- video zoomed in on 2 people VC2- video zoomed in on 2 people
VC1- video zoomed in on 2 people VC3- video zoomed out on 6 people
Simultaneous transmission sets can be expressed as sets of the VCs
that could physically be transmitted at the same time, though it may
not make sense to do so.
In this example the two simultaneous sets are:
{VC0, VC1, VC2}
{VC0, VC3, VC2}
In this example VC0, VC1 and VC2 can be sent OR VC0, VC3 and VC2.
Only one set can be transmitted at a time. These are physical
capabilities describing what can physically be sent at the same time,
not what might make sense to send. For example, in the second set
both VC0 and VC2 are redundant if VC3 is included.
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In describing its capabilities, the provider must take physical
simultaneity into account and send a list of its Simultaneous
Transmission Sets to the consumer, along with the Capture Sets and
Encoding Groups.
6.3. Encoding Groups
The second aspect of multiple streams that must be understood by
providers and consumers in order to create the best experience
possible, i. e., for the "right" or "best" streams to be sent, is the
encoding characteristics of the possible audio and video streams
which can be sent. Just as in the way that a constraint is imposed
on the multiple streams due to the physical limitations, there are
also constraints due to encoding limitations. These are described by
four variables that make up an Encoding Group, as shown in the
following table:
Table: Encoding Group
+----------------+--------------------------------------------------+
| Name | Description |
+----------------+--------------------------------------------------+
| maxBandwidth | Maximum number of bits per second relating to |
| | all encodes combined |
| maxVideoMbps | Maximum number of macroblocks per second |
| | relating to a all video encodes combined ((width |
| | + 15) / 16) * ((height + 15) / 16) * |
| | framesPerSecond |
| videoEncodes[] | Set of potential video encodes can be generated |
| audioEncodes[] | Set of potential encodes that can be generated |
+----------------+--------------------------------------------------+
An encoding group is the basic concept for describing encoding
capability. As shown in the Table, it has an overall maxMbps and
bandwidth limits, as well as being comprised of sets of individual
encodes, which will be described in more detail below.
Each media stream provider includes one or more encoding groups.
There may be multiple encoding groups per endpoint. For example,
each video capture device might have an associated encoding group
that describes the video streams that can result from that capture.
A remote receiver (i. e., stream consumer)configures some or all of
the specific encodings within one or more groups in order to provide
it with media streams to decode.
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6.3.1. Encoding Group Structure
This section shows more detail on the media stream provider's
encoding group structure. The encoding group includes several
individual encodes, each has different encoding values. For example
one may be high definition video 1080p60, and another 720p30, with a
third being CIF. While a typical 3 codec/display system would have
one encoding group per "box", there are many possibilities for the
number of encoding groups a provider may be able offer and for what
encoding values there are in each encoding group.
Diagram for Encoding Group Structure
,-------------------------------------------------.
| Media Provider |
| |
| ,--------------------------------------. |
| | ,--------------------------------------. |
| | | ,--------------------------------------. |
| | | | Encoding Group | |
| | | | ,-----------. | |
| | | | | | ,---------. | |
| | | | | | | | ,---------.| |
| | | | | Encode1 | | Encode2 | | Encode3 || |
| `.| | | | | | `---------'| |
| `.| `-----------' `---------' | |
| `--------------------------------------' |
`-------------------------------------------------'
As shown in the diagram, each encoding group has multiple potential
individual encodes within it. Not all encodes are equally capable,
the stream consumer chooses the encodes it wants by configuring the
provider to send it what it wants to receive.
Some encoding endpoints are fixed, others are flexible, e. g., a
single box with multiple DSPs where the resources are shared.
6.3.2. Individual Encodes
An encoding group is associated with a media capture through the
individual encodes, that is, an audio or video capture is encoded in
one or more individual encodes, as described by the videoEncodes[]
and audioEncodes[]variables.
The following table shows the variables for a Video Encode. (There
is a similar table for audio.)
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Table: Individual Video Encode
+--------------+----------------------------------------------------+
| Name | Description |
+--------------+----------------------------------------------------+
| maxBandwidth | Maximum number of bits per second relating to a |
| | single video encoding |
| maxMbps | Maximum number of macroblocks per second relating |
| | to a single video encoding: ((width + 15) / 16) * |
| | ((height + 15) / 16) * framesPerSecond |
| maxWidth | Video resolution's maximum supported width, |
| | expressed in pixels |
| maxHeight | Video resolution's maximum supported height, |
| | expressed in pixels |
| maxFrameRate | Maximum supported frame rate |
+--------------+----------------------------------------------------+
A remote receiver configures (i. e., instantiates) some or all of the
specific encodes such that:
o The configuration of each active ENC<n> does not exceed that
individual encode's maxWidth, maxHeight, maxFrameRate.
o The total bandwidth of the configured ENC<n>t; does not exceed
the maxBandwidth of the encoding group.
o The sum of the macroblocks per second of each configured encode
does not exceed the maxMbps attribute of the encoding group.
An equivalent set of attributes holds for audio encodes within an
audio encoding group.
6.3.3. More on Encoding Groups
An encoding group EG<n> comprises one or more potential encodings
ENC<n>. For example,
EG0: maxMbps=489600, maxBandwidth=6000000
VIDEO_ENC0: maxWidth=1920, maxHeight=1088, maxFrameRate=60,
maxMbps=244800, maxBandwidth=4000000
VIDEO_ENC1: maxWidth=1920, maxHeight=1088, maxFrameRate=60,
maxMbps=244800, maxBandwidth=4000000
AUDIO_ENC0: maxBandwidth=96000
AUDIO_ENC1: maxBandwidth=96000
AUDIO_ENC2: maxBandwidth=96000
Here, the encoding group is EG0. It can transmit up to two 1080p30
encodings (Mbps for 1080p = 244800), but it is capable of
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transmitting a maxFrameRate of 60 frames per second (fps). To
achieve the maximum resolution (1920 x 1088) the frame rate is
limited to 30 fps. However 60 fps can be achieved at a lower
resolution if required by the consumer. Although the encoding group
is capable of transmitting up to 6Mbit/s, no individual video
encoding can exceed 4Mbit/s.
This encoding group also allows up to 3 audio encodings,
AUDIO_ENC<0-2>. It is not required that audio and video encodings
reside within the same encoding group, but if so then the group's
overall maxBandwidth value is a limit on the sum of all audio and
video encodings configured by the consumer. A system that does not
wish or need to combine bandwidth limitations in this way should
instead use separate encoding groups for audio and video in order for
the bandwidth limitations on audio and video to not interact.
Audio and video can be expressed in separate encode groups, as in
this illustration.
VIDEO_EG0: maxMbps=489600, maxBandwidth=6000000
VIDEO_ENC0: maxWidth=1920, maxHeight=1088, maxFrameRate=60,
maxMbps=244800, maxBandwidth=4000000
VIDEO_ENC1: maxWidth=1920, maxHeight=1088, maxFrameRate=60,
maxMbps=244800, maxBandwidth=4000000
AUDIO_EG0: maxBandwidth=500000
AUDIO_ENC0: maxBandwidth=96000
AUDIO_ENC1: maxBandwidth=96000
AUDIO_ENC2: maxBandwidth=96000
6.3.4. Examples of Encoding Groups
This section illustrates further examples of encoding groups. In the
first example, the capability parameters are the same across ENCs.
In the second example, they vary.
An endpoint that has 3 similar video capture devices would advertise
3 encoding groups that can each transmit up to 2 1080p30 encodings,
as follows:
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EG0: maxMbps = 489600, maxBandwidth=6000000
ENC0: maxWidth=1920, maxHeight=1088, maxFrameRate=60,
maxMbps=244800, maxBandwidth=4000000
ENC1: maxWidth=1920, maxHeight=1088, maxFrameRate=60,
maxMbps=244800, maxBandwidth=4000000
EG1: maxMbps = 489600, maxBandwidth=6000000
ENC0: maxWidth=1920, maxHeight=1088, maxFrameRate=60,
maxMbps=244800, maxBandwidth=4000000
ENC1: maxWidth=1920, maxHeight=1088, maxFrameRate=60,
maxMbps=244800, maxBandwidth=4000000
EG2: maxMbps = 489600, maxBandwidth=6000000
ENC0: maxWidth=1920, maxHeight=1088, maxFrameRate=60,
maxMbps=244800, maxBandwidth=4000000
ENC1: maxWidth=1920, maxHeight=1088, maxFrameRate=60,
maxMbps=244800, maxBandwidth=4000000
A remote consumer configures some or all of the specific encodings
such that:
o The configuration of each active ENC<n> parameter values does not
cause that encoding's maxWidth, maxHeight, maxFrameRate to be
exceeded
o The total bandwidth of the configured ENC <n> encodings does not
exceed the maxBandwidth of the encoding group
o The sum of the "macroblocks per second" values of each configured
encoding does not exceed the maxMbps of the encoding group
There is no requirement for all encodings within an encoding group to
be activated when configured by the consumer.
Depending on the provider's encoding methods, the consumer may be
able to request fixed encode values or choose encode values in the
range less than the maximum offered. We will discuss consumer
behavior in more detail in a section below.
6.3.4.1. Sample video encoding group specification #2
This example specification expresses a system whose encoding groups
can each transmit up to 3 encodings, but with each potential encoding
having a progressively lower specification. In this example, 1080p60
transmission is possible (as ENC0 has a maxMbps value compatible with
that) as long as it is the only active encoding (as maxMbps for the
entire encoding group is also 489600). Significantly, as up to 3
encodings are available per group, some sets of captures which
weren't able to be transmitted simultaneously in example #1 above now
become possible, for instance VC1, VC3 and VC6 together. In common
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with example #1, all encoding groups have an identical specification.
EG0: maxMbps = 489600, maxBandwidth=6000000
ENC0: maxWidth=1920, maxHeight=1088, maxFrameRate=60,
maxMbps=489600, maxBandwidth=4000000
ENC1: maxWidth=1280, maxHeight=720, maxFrameRate=30,
maxMbps=108000, maxBandwidth=4000000
ENC2: maxWidth=960, maxHeight=544, maxFrameRate=30,
maxMbps=61200, maxBandwidth=4000000
EG1: maxMbps = 489600, maxBandwidth=6000000
ENC0: maxWidth=1920, maxHeight=1088, maxFrameRate=60,
maxMbps=489600, maxBandwidth=4000000
ENC1: maxWidth=1280, maxHeight=720, maxFrameRate=30,
maxMbps=108000, maxBandwidth=4000000
ENC2: maxWidth=960, maxHeight=544, maxFrameRate=30,
maxMbps=61200, maxBandwidth=4000000
EG2: maxMbps = 489600, maxBandwidth=6000000
ENC0: maxWidth=1920, maxHeight=1088, maxFrameRate=60,
maxMbps=489600, maxBandwidth=4000000
ENC1: maxWidth=1280, maxHeight=720, maxFrameRate=30,
maxMbps=108000, maxBandwidth=4000000
ENC2: maxWidth=960, maxHeight=544, maxFrameRate=30,
maxMbps=61200, maxBandwidth=4000000
7. Using the Framework
This section shows in more detail how to use the framework to
represent a typical case for telepresence rooms. First an endpoint
is illustrated, then an MCU case is shown.
Consider an endpoint with the following characteristics:
o 3 cameras, 3 displays, a 6 person table
o Each video device can provide one capture for each 1/3 section of
the table
o A single capture representing the active speaker can be provided
o A single capture representing the active speaker with the other 2
captures shown picture in picture within the stream can be
provided
o A capture showing a zoomed out view of all 6 seats in the room can
be provided
The audio and video captures for this endpoint can be described as
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follows. The Encode Group specifications can be found above in
Section 6.3.4.1, Sample video encoding group specification #2.
Video Captures:
o VC0- (the left camera stream), encoding group:EG0, attributes:
purpose=main;auto-switched:no; area_of_capture={xBegin=0, xEnd=33}
o VC1- (the center camera stream), encoding group:EG1, attributes:
purpose=main; auto-switched:no; area_of_capture={xBegin=33,
xEnd=66}
o VC2- (the right camera stream), encoding group:EG2, attributes:
purpose=main;auto-switched:no; area_of_capture={xBegin=66,
xEnd=99}
o VC3- (the loudest panel stream), encoding group:EG1, attributes:
purpose=main;auto-switched:yes; area_of_capture={xBegin=0,
xEnd=99}
o VC4- (the loudest panel stream with PiPs), encoding group:EG1,
attributes: purpose=main; composed=true; auto-switched:yes;
area_of_capture={xBegin=0, xEnd=99}
o VC5- (the zoomed out view of all people in the room), encoding
group:EG1, attributes: purpose=main;auto-switched:no;
area_of_capture={xBegin=0, xEnd=99}
o VC6- (presentation stream), encoding group:EG1, attributes:
purpose=presentation;auto-switched:no; area_of_capture={xBegin=0,
xEnd=99}
Summary of video captures - 3 codecs, center one is used for center
camera stream, presentation stream, auto-switched, and zoomed views.
Note the text in parentheses (e.g. "the left camera stream") is not
explicitly part of the model, it is just explanatory text for this
example, and is not included in the model with the media captures and
attributes.
[edt. It is arbitrary that for this example the alternative views
are on EG1 - they could have been spread out- it was not a necessary
choice.]
Audio Captures:
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o AC0 (left), attributes: purpose=main;channel format=mono;
area_of_capture={xBegin=0, xEnd=33}
o AC1 (right), attributes: purpose=main;channel format=mono;
area_of_capture={xBegin=66, xEnd=99}
o AC2 (center) attributes: purpose=main;channel format=mono;
area_of_capture={xBegin=33, xEnd=66}
o AC3 being a simple pre-mixed audio stream from the room (mono),
attributes: purpose=main;channel format=mono; mixed=true;
area_of_capture={xBegin=0, xEnd=99}
o AC4 audio stream associated with the presentation video (mono)
attributes: purpose=presentation;channel format=mono;
area_of_capture={xBegin=0, xEnd=99}
The physical simultaneity information is:
{VC0, VC1, VC2, VC3, VC4, VC6}
{VC0, VC2, VC5, VC6}
It is possible to select any or all of the rows in a capture set.
This is strictly what is possible from the devices. However, using
every member in the set simultaneously may not make sense- for
example VC3(loudest) and VC4 (loudest with PIP). (In addition, there
are encoding constraints that make choosing all of the VCs in a set
impossible. VC1, VC3, VC4, VC5, VC6 all use EG1 and EG1 has only 3
ENCs. This constraint shows up in the Capture list and encoding
groups, not in the simultaneous transmission sets.)
In this example there are no restrictions on which audio captures can
be sent simultaneously.
The following table represents the capture sets for this provider.
Recall that a capture set is composed of alternative captures
covering the same scene. Capture Set #1 is for the main people
captures, and Capture Set #2 is for presentation.
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+----------------+
| Capture Set #1 |
+----------------+
| VC0, VC1, VC2 |
| VC3 |
| VC4 |
| VC5 |
| AC0, AC1, AC2 |
| AC3 |
+----------------+
+----------------+
| Capture Set #2 |
+----------------+
| VC6 |
| AC4 |
+----------------+
Different capture sets are unique to each other, non-overlapping. A
consumer chooses a capture row from each capture set. In this case
the three captures VC0, VC1, and VC2 are one way of representing the
video from the endpoint. These three captures should appear adjacent
next to each other. Alternatively, another way of representing the
Capture Scene is with the capture VC3, which automatically shows the
person who is talking. Similarly for the VC4 and VC5 alternatives.
As in the video case, the different rows of audio in Capture Set #1
represent the "same thing", in that one way to receive the audio is
with the 3 linear position audio captures (AC0, AC1, AC2), and
another way is with the single channel monaural format AC3. The
Media Consumer would choose the one audio capture row it is capable
of receiving.
The spatial ordering is understood by the media capture attributes
area and point of capture.
The consumer finds a "row" in each capture set #x section of the
table that it wants. It configures the streams according to the
encoding group for the row.
A Media Consumer would likely want to choose a row to receive based
in part on how many streams it can simultaneously receive. A
consumer that can receive three people streams would probably prefer
to receive the first row of Capture Set #1 (VC0, VC1, VC2) and not
receive the other rows. A consumer that can receive only one people
stream would probably choose one of the other rows.
If the consumer can receive a presentation stream too, it would also
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choose to receive the only row from Capture Set #2 (VC6).
7.1. The MCU Case
This section shows how an MCU might express its Capture Sets,
intending to offer different choices for consumers that can handle
different numbers of streams. A single audio capture stream is
provided for all single and multi-screen configurations that can be
associated (e.g. lip-synced) with any combination of video captures
at the consumer.
+--------------------+---------------------------------------------+
| Capture Set #1 | note |
+--------------------+---------------------------------------------+
| VC0 | video capture for single screen consumer |
| VC1, VC2 | video capture for 2 screen consumer |
| VC3, VC4, VC5 | video capture for 3 screen consumer |
| VC6, VC7, VC8, VC9 | video capture for 4 screen consumer |
| AC0 | audio capture representing all participants |
+--------------------+---------------------------------------------+
If / when a presentation stream becomes active within the conference,
the MCU might re-advertise the available media as:
+----------------+--------------------------------------+
| Capture Set #2 | note |
+----------------+--------------------------------------+
| VC10 | video capture for presentation |
| AC1 | presentation audio to accompany VC10 |
+----------------+--------------------------------------+
7.2. Media Consumer Behavior
[Edt. Should this be moved to appendix?]
The receive side of a call needs to balance its requirements, based
on number of screens and speakers, its decoding capabilities and
available bandwidth, and the provider's capabilities in order to
optimally configure the provider's streams. Typically it would want
to receive and decode media from each capture set advertised by the
provider.
A sane, basic, algorithm might be for the consumer to go through each
capture set in turn and find the collection of video captures that
best matches the number of screens it has (this might include
consideration of screens dedicated to presentation video display
rather than "people" video) and then decide between alternative rows
in the video capture sets based either on hard-coded preferences or
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user choice. Once this choice has been made, the consumer would then
decide how to configure the provider's encode groups in order to make
best use of the available network bandwidth and its own decoding
capabilities.
7.2.1. One screen consumer
VC3, VC4 and VC5 are all on different rows by themselves, not in a
group, so the receiving device should choose between one of those.
The choice would come down to whether to see the greatest number of
participants simultaneously at roughly equal precedence (VC5), a
switched view of just the loudest region (VC3) or a switched view
with PiPs (VC4). An endpoint device with a small amount of knowledge
of these differences could offer a dynamic choice of these options,
in-call, to the user.
7.2.2. Two screen consumer configuring the example
Mixing systems with an even number of screens, "2n", and those with
"2n+1" cameras (and vice versa) is always likely to be the
problematic case. In this instance, the behavior is likely to be
determined by whether a "2 screen" system is really a "2 decoder"
system, i.e., whether only one received stream can be displayed per
screen or whether more than 2 streams can be received and spread
across the available screen area. To enumerate 3 possible behaviors
here for the 2 screen system when it learns that the far end is
"ideally" expressed via 3 capture streams:
v
1. Fall back to receiving just a single stream (VC3, VC4 or VC5 as
per the 1 screen consumer case above) and either leave one screen
blank or use it for presentation if / when a presentation becomes
active
2. Receive 3 streams (VC0, VC1 and VC2) and display across 2 screens
(either with each capture being scaled to 2/3 of a screen and the
centre capture being split across 2 screens) or, as would be
necessary if there were large bezels on the screens, with each
stream being scaled to 1/2 the screen width and height and there
being a 4th "blank" panel. This 4th panel could potentially be
used for any presentation that became active during the call.
3. Receive 3 streams, decode all 3, and use control information
indicating which was the most active to switch between showing
the left and centre streams (one per screen) and the centre and
right streams.
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For an endpoint capable of all 3 methods of working described above,
again it might be appropriate to offer the user the choice of display
mode.
7.2.3. Three screen consumer configuring the example
This is the most straightforward case - the consumer would look to
identify a set of streams to receive that best matched its available
screens and so the VC0 plus VC1 plus VC2 should match optimally. The
spatial ordering would give sufficient information for the correct
video capture to be shown on the correct screen, and the consumer
would either need to divide a single encode group's capability by 3
to determine what resolution and frame rate to configure the provider
with or to configure the individual video captures' encode groups
with what makes most sense (taking into account the receive side
decode capabilities, overall call bandwidth, the resolution of the
screens plus any user preferences such as motion vs sharpness).
8. Acknowledgements
Mark Gorzyinski contributed much to the approach. We want to thank
Stephen Botzko for helpful discussions on audio.
9. IANA Considerations
TBD
10. Security Considerations
TBD
11. 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.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
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[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.
Appendix A. Open Issues
A.1. Video layout arrangements and centralized composition
In the context of a conference with a central MCU, there has been
discussion about a consumer requesting the provider to provide a
certain type of layout arrangement or perform a certain composition
algorithm, such as combining some number of most recent talkers, or
producing a video layout using a 2x2 grid or 1 large cell with 5
smaller cells around it. The current framework does not address
this. It isn't clear if this topic should be included in this
framework, or maybe a different part of CLUE, or maybe outside of
CLUE altogether.
A.2. Source is selectable
A Boolean variable. True indicates the media consumer can request a
particular media source be mapped to a media capture. Default is
false.
TBD - how does the consumer make the request for a particular source?
How does the consumer know what is available? Need to explain better
how multiple media captures are different from a single media capture
with choices for the source, and when each concept should be used.
A.3. Media Source Selection
The use cases include a case where the person at a receiving endpoint
can request to receive media from a particular other endpoint, for
example in a multipoint call to request to receive the video from a
certain section of a certain room, whether or not people there are
talking.
TBD - this framework should address this case. Maybe need a roster
list of rooms or people in the conference, with a mechanism to select
from the roster and associate it with media captures. This is
different from selecting a particular media capture from a capture
set. The mechanism to do this will probably need to be different
than selecting media captures based on capture sets and attributes.
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A.4. Endpoint requesting many streams from MCU
TBD - how to do VC selection for a system where the endpoint media
consumers want to receive lots of streams and do their own
composition, rather than MCU doing transcoding and composing.
Example is 3 screen consumer that wants 3 large loudest speaker
streams, and a bunch of small ones to render as PiP. How the small
ones are chosen, which could potentially be chosen by either the
endpoint or MCU. There are other more complicated examples also. Is
the current framework adequate to support this?
A.5. VAD (voice activity detection) tagging of audio streams
TBD - do we want to have VAD be mandatory? All audio streams
originating from a media provider must be tagged with VAD
information. This tagging would include an overall energy value for
the stream plus information on which sections of the capture scene
are "active".
Each audio stream which forms a constituent of a row within a capture
set should include this tagging, and the energy value within it
calculated using a fixed, consistent algorithm.
When a system determines the most active area of a capture scene
(either "loudest", or determined by other means such as a button
press) it should convey that information to the corresponding media
stream consumer via any audio streams being sent within that capture
set. Specifically, there should be a list of active linear positions
and their VAD characteristics within the audio stream in addition to
the overall VAD information for the capture set. This is to ensure
all media stream consumers receive the same, consistent, audio energy
information whichever audio capture or captures they choose to
receive for a capture set. Additionally, linear position information
can be mapped to video captures by a media stream consumer in order
that it can perform "panel switching" if required.
A.6. Private Information
Authors' Addresses
Allyn Romanow
Cisco Systems
San Jose, CA 95134
USA
Email: allyn@cisco.com
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Mark Duckworth
Polycom
Andover, MA 01810
US
Email: mark.duckworth@polycom.com
Andrew Pepperell
Cisco Systems
Langley, England
UK
Email: apeppere@cisco.com
Brian Baldino
Cisco Systems
San Jose, CA 95134
US
Email: bbaldino@cisco.com
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