QoS Requirements for Data
Collaboration Using T.120
Liane Tarouco
RNP2
Topics
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This presentation will shows results of an
investigation on the T.120 protocol behavior
aimed to diagnose common data conference
failures causes.
Specific quality of services requests, needed
for this kind of applications will be reported as
well as results of experiments using QoS
approached for videoconference and T.120 data
collaboration organized in RNP2
New alternatives on collaboration software will
be discussed
Data collaboration applications
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Data collaboration applications offer very useful
services like application/desktop sharing to
provide real remote collaboration specially for
use in conjunction with videoconferencing.
T.120 based systems are the most used approach
for this kind of applications providing
interoperability between different vendors
T.120 & H.323
CONFERENCING APPLICATIONS & USER INTERFACE
Pre-proc
Post-proc
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Ctrl
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3 point Exch
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BAS
ECS
H.261
H.262
H.263
AEC
AGC
NoiseSuppress
G.711
G.722
G.728
G.723.1
G.729
VIDEO
AUDIO
Time
Critical
Apps
H.281
Far end
camera
control
H.224
H.233 - Encryption
H.221 Multiplex and Framing
Transport Network (ISDN, Switched-56, ...)
Application
Protocols
T.126
T.127
T.124
Generic
Conference
Control
T.122/T.125
MCS
T.123
H.323 components
H.323 components
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Terminal
GK - gatekeeper (control and ‘routing’ )
GW - gateway (access to other environments)
MC - multipoint controller
MP - multipoint processor ( mix ‘n match the
media)
 MCU - multipoint control unit
• contains MC and MP optionally a T.120 MCU
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Multipoint Control Unit MCU
 Manages conference using H.245 and
may use T.120 commands
 Establishes common conference mode
• Common set of media streams
• May provide audio transcoding
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Basic Operation
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Endpoints register with gatekeeper to
provide mapping between physical
address and alias address
Endpoint asks gatekeeper for permission
to place call to another endpoint
Endpoint signals call with other endpoint
Endpoints exchange media
Endpoints disconnect, notify gatekeeper
Messages & procedures
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Admissions & Directory Service
Creation of a connection
Endpoint capabilities exchange
Opening and closing logical channels
Changing modes (point-to-point multipoint)
Real-time transmission over packet
networks
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Standards
 H.323 for architecture, procedures
 H.225.0 more than just a document...
• Q.931 ‘derived’ messages for call setup
• RAS for endpoint-Gatekeeper signaling
 H.245 for capabilities/media control
 RTP/RTCP for media transport
• Endpoint to endpoint after call setup
• Open multiple logical channels (one per one way media)
 T.120 for data
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RAS Functions (H.225)
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Discovery/Registration - find gatekeeper and
provide mapping between physical and alias
addresses
Admission - ask permission to place call with
bandwidth
Bandwidth Changes - ask permission to use more
bandwidth
Status - report on call status
Disengage - report disconnect and release
bandwidth
Registration, Admission, and Status
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Registration, admission, and status (RAS) is
the protocol between endpoints (terminals
and gateways) and gatekeepers.
The RAS is used to perform registration,
admission control, bandwidth changes,
status, and disengage procedures between
endpoints and gatekeepers.
An RAS channel is used to exchange RAS
messages. This signaling channel is opened
between an endpoint and a gatekeeper prior
to the establishment of any other channels.
H.225/Q.931
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Q.931-like
Setup - initiate call from one entity to another
Alerting - called endpoint is “ringing”
Connect - called endpoint answered
Release Complete - disconnect call
others, including Facility, Information,
Progress, Status
H.245
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Capability negotiation - determine compatible
set of media capabilities
Master/slave determination
Logical channel control - indicate desire to
start transmission of specified medium
Multipoint conference control & indication conference rosters, chair control, media
indications
Miscellaneous
H.245 Control Signaling
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H.245 control signaling is used to exchange
end-to-end control messages governing the
operation of the H.323 endpoint.
These control messages carry information
related to the following:
– capabilities exchange
– opening and closing of logical channels used to
carry media streams
– flow-control messages
– general commands and indications
Tools for collaboration
Videoconference needs
complement for supporting
collaboration:
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Whiteboard
Application sharing
Remote control
Chat
File transfer
Printed documents sharing
(document camera)
H.323 e T.120
ITU-T T.120 series
TERMINAL
Reservations
App Sharing
Switching
T.130
A/V Control
File Transfer
Documents
T.127
Photos
Overhead Proj
Whiteboard
T.126
Application Protocols
T.126 - Still Image, T.127 - File Transfer
T.130 - A/V Control, T.SHARE, T.RES
MCU
T.124 - Generic Conference Control
T.122 / T.125 - Multipoint Comm. Service
ISDN
T.123 - Transport Stacks
Voice/
POTS
LAN
Data
ATM
ITU-T T.120 series
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Kinds of data and standards
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Photos and Documents (T.126)
Pointing and Annotating (T.126)
File transfer (T.127)
PC Application Sharing
Virtually any multipoint flow of data
ITU-T T.120 series
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Kinds of control & standadrds
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Conference setup, entry, modify, exit (T.124)
Camera, mic, peripheral control (T.130)
Who sees whom (T.130)
Director control, browsing (T.130)
Reservations
Add site, extend conference time
Protocols T.120
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T.123 - OSI transport protocol
T.122, T.125 - Multipoint Communication Service
(MCS):
T.124 -Generic Conference Control (GCC)
MCS service primitives
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MCS domain management primitives
MCS Channel Management primitives
MCS data transfer primitives
MCS token management primitives
MCS service primitives
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MCS domain management primitives
– MCS-CONNECT-PROVIDER request, indication, response,
confirm
– MCS-DISCONNECT-PROVIDER request, indication
– MCS-ATTACH-USER request, confirm
– MCS-DETACH-USER request, indication
– MCS-DOMAIN-PARAMETERS request, indication, confirm
MCS service primitives
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MCS Channel Management primitives
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MCS-CHANNEL-JOIN request, confirm
MCS-CHANNEL-LEAVE request, indication
MCS-CHANNEL-CONVENE request, confirm
MCS-CHANNEL-DISBAND request, indication
MCS-CHANNEL-ADMIT request, indication
MCS-CHANNEL-EXPEL request, indication
MCS service primitives
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MCS data transfer primitives
– MCS-SEND-DATA request, indication
– MCS-UNIFORM-SEND-DATA request, indication
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MCS token management primitives
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MCS-TOKEN-GRAB request, confirm
MCS-TOKEN-INHIBIT request, confirm
MCS-TOKEN-GIVE request, indication, response, confirm
MCS-TOKEN-PLEASE request, indication
MCS-TOKEN-RELEASE request, confirm
MCS-TOKEN-TEST request, confirm
T.124 - Generic Conference
Control (GCC):
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T.124 - Generic Conference Control
– Provides set of facilities to establish and manage multipoint .
– Centralize an information base (state of serving conferences)
GCC
GCC
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GCC provides a set of services for
establishment and termination of conferences
GCC provides a means to create new
conferences.
GCC provides a means of identifying which
Application Protocol Entities are available at
each node and to provide necessary
information for Peer Application Protocol
Entities to communicate with each other
GCC
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GCC provides a method for allowing a node
to become a conductor for a conference.
A token is used by GCC to determine
whether a conference is conducted or nonconducted.
The Application Registry is an active database residing at the Top GCC Provider that
may be used to manage channels, tokens,
and other shared resources used in a
conference.
GCC - Functional Units
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Conference establishment and termination
Conference roster
Application roster
Application registry
Conference conductorship
Miscellaneous functions
GCC - Conference establishment
and termination
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GCC-Conference-Create request
GCC-Conference-Create indication
GCC-Conference-Create response
GCC-Conference-Create confirm
GCC-Conference-Query request
GCC-Conference-Query indication
GCC-Conference-Query response
GCC-Conference-Query confirm
GCC-Conference-Join request
GCC-Conference-Join indication
GCC-Conference-Join response
GCC-Conference-Join confirm
GCC - Conference establishment
and termination
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GCC-Conference-Disconnect request
GCC-Conference-Disconnect indication
GCC-Conference-Disconnect confirm
GCC-Conference-Terminate request
GCC-Conference-Terminate indication
GCC-Conference-Terminate confirm
GCC-Conference-Eject-User request
GCC-Conference-Eject-User indication
GCC-Conference-Eject-User confirm
GCC-Conference-Transfer request
GCC-Conference-Transfer indication
GCC-Conference-Transfer confirm
GCC - Conference establishment
and termination
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GCC-Conference-Invite request
GCC-Conference-Invite
indication
GCC-Conference-Invite response
GCC-Conference-Invite confirm
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GCC-Conference-Add
GCC-Conference-Add
GCC-Conference-Add
GCC-Conference-Add
request
indication
response
confirm
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GCC-Conference-Lock request
GCC-Conference-Lock indication
GCC-Conference-Lock response
GCC-Conference-Lock confirm
GCC-Conference-Unlock request
GCC-Conference-Unlock
indication
GCC-Conference-Unlock
response
GCC-Conference-Unlock confirm
GCC-Conference-Lock-Report
indication
Conformance for T.120 service
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Transport protocol profile (T.123);
MCS Multipoint Communication Service
(T.125);
Required components of Generic Conference
Control (T.124);
Why are standards important?
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Communication requires standards
Standards stimulate market growth
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Instant credibility for new products
Customer confidence
Multiple vendors
Increased competition
Volume pricing
Standards are critical to interoperability, but
still leave room for product variation
– Many options in each standard
– Audio and video quality depend on encoders, not
decoders
Additional standards
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T.130 series, High level audio/video
control
– Remote cameras & VCRs, video routing,
continuos presence
• How a student request the floor to ask a
question
– Automatic video switching
• Social rules e.g. hand raising are used
• Submit and cancel floor requests
Required services in H.323 & T.120
Teaching and learning environment
data,
video
audio
Application
Sharing
Applications
Broadcast
application
Lecture delivery performance
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T.120 protocols uses a lot of performance
management and when the data channel or
the end station do not perform according
established thresholds unexpected
decision may occur disconnecting one or
more users from the conference or
disabling some data collaboration function.
Monitoring results
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T.120 communication between terminals
(Netmeeting), start before logical channels open
Centralized conference model (tightly coupled)
use intensively MCU resources
Event>
Event>
Event>
Event>
Event>
Event>
Event>
Event>
Event>
Event>
Event>
Event>
Mon Nov 26 17:15:54 2001
Pkts in 25655
Pkts
client Leandro Bertholdo - T.120 session closed
Mon Nov 26 17:16:54 2001
Pkts in 27438
Pkts
Mon Nov 26 17:17:55 2001
Pkts in 1695
Pkts
client Alexei Korb timeout -- holding down
Mon Nov 26 17:18:55 2001
Pkts in 3324
Pkts
client Alexei Korb - T.120 session closed due to insufficient bandwidth
Mon Nov 26 17:19:56 2001
Pkts in 4708
Mon Nov 26 17:20:56 2001
Pkts in 5850
client Liane Tarouco - T.120 session closed due to insufficient bandwidth
Mon Nov 26 17:21:57 2001
Pkts in 7114
Mon Nov 26 17:22:58 2001
Pkts in 8182
QoS
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Quality of Service - needed quality to
attend specific application user request
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telephony
videoconference
file download
TV
QoS
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Usual specifications
– Bandwidth
– Delay
– Jitter
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QoS from user point of view ?
– ITU P800 Perceptual Speech Quality
Measurement (PSQM)
– Mean Opinion Scores (MOS)
MOS - Mean Opinion Scores
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Bad: unintelligible, user do not understand decoded
message. Interruptions due degradation
Poor: signal present interruption due degradations;
user needs considerable effort to understand some
segments
Moderate: voice quality is bad; user fell annoyed with
degradations but there are no interruption and still
can understand the message (requires moderated
effort)
Good: voice is good to listen, user perceive
degradations but do not bother because are minimal
(no big effort is needed)
Excellent: user can not differentiate original
message from corrupted, that means, do not perceive
signal degradation (no effort is required)
Providing QoS
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Rede TCHÊ
– Videoconference QoS service
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UFRGS intranet
– Ftp impact
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RNP
TCHÊ - Videoconference
TCHÊ - Videoconference
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Problems
– Packet dropping high (> 30%)
– Traffic burst impact video transmission even when
normal bandwidth usage was not too high
Tchê
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Used IBM router implementation
of DiffServ together with RSVP
LLQ used to keep compatibility with Cisco
Defined a service called HVIDEO (Expedited
Forwarding) for video originated in the MCU
and in the streaming video server
– Band reservation (19%) for HVIDEO
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Defined a service called CACHE (Assured
Forwarding) for traffic using existing cache
structure
– Band reservation (15%) for CACHE
Collaborative software development
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Add T.120 service to Open H.323
– Protocols and services study and monitoring
Other collaborative work
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Collaboration with Open RCT project
from UCDavis
– Whiteboard
– Java based
– Open Software
T-Lite
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A lightweight T.120 profile that can be
implemented in products requiring minimal
data services.
They also can be implemented with less effort
than traditional T.120 enhanced multimedia
terminals
Lite T.124 profile
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Only a subset of the GCC services needed
– conference establishment and termination
– support for the conference roster
– support for a single application roster
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Neither the application registry or the
conference conductorship services are
needed.
Also, no miscellaneous functions are required
other than the sending of text messages.
Conclusions
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QoS for collaborative services (H.323 &
T.120)
T.120 like protocols are needed but
lightweight versions must be defined,
implemented, tested and standardized