Transcript 01-H323-T120Principles

H.323
Liane Tarouco
Leandro Bertholdo
RNP POP/RS
Videoconference solutions
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CuSeeMe
Mbone
H.323
Proprietary solutions
Videoconference with CuSeeme
•Cornel University 1992
•CuSeeMe
•White Pine
•First Virtual Communications
•Reflector - proprietary protocol
•Audio, vídeo, chat
Using CuSeeMe
MBone
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1992
Session reservation
SDR protocol
IP multicast
Mbone tools
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VIC (Video Conference)
RAT (Robust Audio Tool)
WB (White Board)
NTE (Network Text Editor
Standard entities
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Telecommunications standards are set by the United
Nations agency, International Telecommunications
Union (ITU)
– The ITU has developed the H, G and T Series of
standards
Internet Engineering Task Force (IETF) defines
stadards for the Internet
– IETF has developed Real-Time Protocol (RTP),
Real-Time Control Protocol (RTCP) & Resource
Reservation Protocol (RSVP).
Products that adhere to these standards allow users
to participate in a conference, regardless of their
platform.
H.323 became popular
•Microsoft Neteeting
•Application sharing
•File Transfer
• Whiteboard
•Chat
• ILS server
•H.323
Videoconference topology
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Point to point
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Multippoint
Point to point
Group to group
Multipoint
H.323 Architecture
H.323
Terminal
H.323
MCU
H.323
Gatekeeper
H.323
Gateway
H.323
Terminal
H.323
Terminal
GSTN
GQOS
LAN
N-ISDN
B-ISDN
V.70
Terminal
H.324
Terminal
Speech
Terminal
H.322
Terminal
Speech
Terminal
H.320
Terminal
H.321
Terminal
Standards for videoconference
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H.320 ISDN Videoconferencing
groupvideoconferencing
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H.323 Audiovisual communication
desktop videoconferencing
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H.324 High Quality Video and
Audio Compression over POTS
Available Transport Media
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ISDN, LAN, WAN, Internet, ADSL (Asynchronous
Digital Subscriber Lines) and VPN, (Virtual Private
Networks) are the popular transport media used in
desktop video conferencing.
Available Transport Media
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The worldwide availability of the Internet has virtually
stopped the use of POTS (Plain Old Telephone
Service) as a direct means of connecting video
conferencing systems.
Available Transport Media.
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However, the forthcoming media-enabled 3G mobile
phone has caused the creation of a derivative of the
H.324 POTS standard in the form of 3G-324M as well
as next generation Gateways to transcode the new
protocols.
ISDN
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There are two available ISDN connections
– Basic Rate Interface (BRI)
• two 64kbps B-channels and
• one 16kbps D-channel
– Primary Rate Interface (PRI).
• PRI in Europe provides 30 x 64kbps Bchannels and one 64kbps D-channel.
USA PRI
ISDN
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ISDN connections usually aggregate the BRI and
share the same number for both B channels.
– Known as ISDN-2, this provides
a line speed of 128kbps is
typically used in a desktop
conference over ISDN.
– For increased bandwidth, ISDN-6 provides a line
speed of 384kbps and is typically
used in room-based conferences
over ISDN.
ISDN for multipoint conference
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To hold a multipoint conference over ISDN,
participants use a Multipoint Control Unit
(MCU), that connects and manages all the
ISDN lines.
– separate MCU or
– endpoint with an embedded
H.320 multipoint capability
H.320
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H.320 - ITU standard for ISDN conferencing
– Audio: G.711, G.722, G.722.1, G.728
– Video: H.264, H.263, H.261
– Data: H.239, T.120
– Control: H.221, H.231, H.242, H.243
Lan & WAN
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H.323 is the ITU standard for LAN
conferencing and includes:
– Audio: G.711, G.722, G.722.1, G.723.1,
G.728, G.729
– Video: H.264, H.263, H.261
– Data: H.239, T.120
– Control: H.225, H.245
Multipoint conference
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To hold a multipoint conference over IP,
H.323 systems require some form of
Multipoint Conference Server (MCS).
– This is also referred to as an H.323
Multipoint Control Unit (H.323 MCU), which
is not the same as an H.320 MCU;
Cellular Networks.
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The cellular phone network is a readily
available form of wireless multimedia delivery
and with the forthcoming media-enabled 3G
mobile phone or Personal Digital Assistants,
PDAs, that support the CDMA2000 or WCDMA
Air Interface, there is sufficient bandwidth to
enable IP-based multipoint audio and video
conferencing to existing desktop video
conferencing systems when used inconjunction with next generation Gateways
and MCU's that also support these new
protocols.
Cellular networks
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3G-324M is an extension by the 3rd
Generation Partner Project (3GPP) and 3rd
Generation Partner Project2 (3GPP2) to the
ITU H.324M standard for 3G mobile phone
conferencing and includes:
– Audio: G.722.2 (AMR-WB), G.723.1
– Video: MPEG-4, but not H.264
– Control: H.223 A/B, H.245
Internet, VPN & ADSL.
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Internet, VPNs and ADSL are other forms
of TCP/IP networks and hence can be used
as a transport media in desktop
conferencing systems.
Users must get a fixed IP address
Directory services
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Alternatively, users can register their
presence using LDAP with a Directory
Service
Videoconference over Internet
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H.323 is the ITU standard used for Internet
conferencing and includes:
– Audio: G.723.1, G.722.1, G.728
– Video: H.264, H.263, H.261
– Data: H.239, T.120
– Control: H.225, H.245
Codex de Vídeo
H.261 - video codec for >= 64kbps
H.263 - video codec for < 64kbps
Sistema de Captura
Amostras
digitais
Conversor
A/D
Sistema de
transformação de cores
Sistema de
redimensionamento de
frames
Vídeo
analógico
Frames no formato H.261/H.263 não comprimidos
Frames no formato
H.261/H.263 não
comprimidos
Frames
comprimidos
Codificador
Frames
modificados para
exibição
Frames
comprimidos
Rede
Digital
Decodificador
Sistema de Exibição
Sistema de
redimensionamento de
frames
Sistema de
transformação de cores
Video standards
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H.261 - video codec for audiovisual services
at speed > 64Kbps.
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H.263 - video codec for narrow
telecommunications channels at < 64 Kbps.
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H.264/AVC - a new video codec standard
offering major improvements image quality.
Image size
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QCIF - Quarter Common Intermediate Format
– 176x144 pixel image.
– minimum size in H.320
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CIF - optional H.320
full- screen
352x288 pixels
– requires more
computing
capability.
Video Sizes
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NTSC - National Television Standards
Committee, used in USA, Canada & Japan.
640 x 480 pixels.
PAL - Phase Alternation by Line, used in
Europe (except France), Africa & Middle East.
768 x 576 pixels.
Video Sizes
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CIF - Common Intermediate Format
– optional for both H.261 & H.263
– 352 x 288 pixels.
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QCIF - Quarter Common Intermediate Format
– required by both H.261 & H.263
– 176 x 144 pixels.
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SQCIF - Sub Quarter Common Intermediate
Format
– used by 3G mobiles MPEG4 video and H.263,
– 88 x 72 pixels.
PC Window Sizes
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SXGA - 1280 x 1024 pixels - used by high
end graphics workstations.
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XGA - 1024 x 768 pixels - typical PC or laptop
resolution.
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SVGA - 800 x 600 pixels.
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VGA - 640 x 480 pixels.
H.264
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Ratified in late 2003, this new codec standard was a
development between the ITU and ISO/IEC Joint
Video Team, (JVT) and is known as H.264 (ITU
name) or ISO/IEC 14496-10/MPEG-4 AVC (ISO/IEC
name).
This new standard surpasses H.261 and H.263 in
terms of video quality, effective compression and
resilience to transmission losses
Potential to halve the required bandwidth
for digital video services over the Internet
or 3G Wireless networks.
H.264 is likely to be used in applications such as
Video Conferencing, Video Streaming, Mobile
devices, Tele-Medicine etc. Current 3G mobiles use a
derivate of MPEG-4, but not H.264.
Audio standards
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G.711 - Pulse Code Modulation of voice frequencies
(PCM), were 3.1 kHz analogue audio is encoded into a
48, 56 or 64 kbps stream.
– Used when no other standard is equally supported.
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G.722 - 7 kHz audio encoded into a 48, 56 or 64 kbps
stream.
– Provides high quality, but takes bandwidth.
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G.722.1 - 7 kHz audio encoded at 24 and 32 kbps for
hands-free operation in systems with low frame loss.
Audio standards
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G.722.2 - Coding of speech at around 16 kbps using
Adaptive Multi-Rate Wideband, AMR-WB.
– Five mandatory modes, 6.60, 8.85, 12.65, 15.85
and 23.85 kbps.
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G.723.1 - 3.4 kHz dual rate speech codec for
telecommunications at 5.3 kbps & 6.4 kbps.
Audio standards
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G.728 - 3.4 kHz Low Delay Code Excited Linear
Prediction (LD-CELP) were 3.4 kHz analogue audio
is encoded into a 16 kbps stream. This standard
provides good quality results at low bitrates.
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G.729 A/B - 3.4 kHz speech codec that provides near
toll quality audio encoded into an 8 kbps stream
using the AS-CELP method.
Control standards
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H.221 - defines the transmission frame structure for
audovisual teleservices in channels of 64 to 1920
Kbps; used in H.320
H.223 - specifies a packet-orientated multiplexing
protocol for low bit rate multimedia communications;
Annex A & B handles light and medium error prone
channels of the mobile extension as used in 3G324M.
H.224 - defines real-time control protocol for simplex
applications using the H.221 LSD, HSD and HLP
channels.
H.225 - defines the multiplexing transmission formats
for media stream packetisation & synchronisation on
a non-guaranteed QoS LAN.
Control standards
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H.231 - specifies multipoint control units used to
bridge three or more H.320 systems together in a
conference.
H.233 - Confidentiality systems for audiovisual
services, used by H.320 devices.
H.234 - Encryption key management and
authentication system for audiovisual services, used
by H.320 devices.
H.235 - Security and encryption for H.323 and other
H.245 based multimedia terminals.
Control standards
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H.239 - defines role management and additional
media channels for H.300-Series multimedia
terminals.
– How data and web-enabled collaboration work in
parallel with video in a conference, allowing
endpoints that support H.239 to receive and transit
multiple, separate media streams - typically voice,
video and data collaboration.
Control standards
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H.241 - defines extended video procedures and
control signals for H.300-Series multimedia terminal.
H.242 - defines the control procedures and protocol
for establishing communications between audiovisual
terminals on digital channels up to 2 Mbps
– used by H.320.
Control standards
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H.243 - defines the control procedures and protocol
for establishing communications between three or
more audiovisual terminals - H.320 multipoint
conferences.
H.245 - defines the control procedures and protocol
for H.323 & H.324 multimedia communications.
H.246 - Interworking of H-Series multimedia terminal.
H.248 - Gateway Control Protocol.
H.281 - defines the procedures and protocol for far
end camera control (FECC) in H.320 calls.
Control standards
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H.282 - Remote device control protocol for
multimedia applications.
H.283 - Remote device control logical channel
transport.
H.350 - Storing and retrieving video and voice over IP
information from enterprise directories.
Numbers & names
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E.164 Number - (User Number).
– A numeric string given to an H.323 endpoint.
– If this endpoint registers with a Gatekeeper, then
the Gatekeeper can translate the E.164 Number
into the endpoints IP address.
H.323 Alias
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H.323 Alias
– A logical name given to an H.323 endpoint.
– If this endpoint registers with a Gatekeeper, then
the Gatekeeper can translate the H.323 Alias into
the endpoints IP address.
Q.931
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Signalling
protocol for
establishing and
terminating calls.
What is H.323
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H.323* is a multimedia
conferencing protocol,
which includes
– voice,
– video,
– data conferencing
for use over packet-switched networks
H.323 umbrella
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H.323 was first approved in February 1996
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Designed to operate over IP networks
Elements of an H.323 System
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•Terminals
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•Multipoint Control Units (MCUs)
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•Gateways
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•Gatekeeper
Terminals
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Videoconference dedicated units
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“Soft phones” (e.g., NetMeeting®)
Terminals
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H.323 Terminals are the endpoints on the
LAN that provide real-time two way
communications.
The H.323 standard states that all H.323
Terminals must support voice,
– video and data are optional.
– Hence the basic form of an
H.323 Terminal is the IP Phone;
– However most H.323 Terminals are Video
Conferencing Systems.
Terminals
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The H.323 standard specifies what modes
must be supported so that all these endpoints
can work together.
H.323 Terminals must support
– H.245 protocol to control channel usage and
capabilities;
– Q.931 protocol for call setup and signalling;
– RAS (Registration/Admission/Status) protocol to
communicate with the Gatekeeper and
– RTP/RTCP protocol to sequence audio and video
packets.
Terminal identification
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When initiating an H.323 Video Conference, we
need some means of identifying the User or H.323
Endpoint that we wish to conference with.
The thought of having to remember IP addresses is
daunting enough; but the use of DHCP to
dynamically allocate the IP address of an endpoint
means that this method is impractical.
Hence the concept of a Dial Plan and the use of an
H.323 User Number registered to a Gatekeeper.
– A Dial Plan is simply a method of allocating a
unique number to an H.323 Endpoint.
H.323 User Number
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This number is referred to as the H.323 User
Number and when registered with a Gatekeeper,
we have a means of translating this User Number
into an IP address.
The H.323 User Number is often loosely referred to
as the E.164 Number.
Multipoint Control Units
(MCUs):
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To allow three or more participants into a
conference, most H.323 systems usually
require a Multipoint Conference Server
(MCS).
This is also referred to as an H.323 Multipoint
Control Unit (H.323 MCU).
MCUs
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Responsible for managing multipoint
conferences
MCU
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The H.323 MCU's basic function is to
maintain all the audio, video, data and
control streams between all the participants
in the conference.
– hardware based
– software based
MCU
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The main components of an H.323 MCU are
– MC - multipoint controller
• The MC is the conference controller and
handles H.245 negotiations between all
terminals to determine common capabilities for
audio and video processing.
– MP - multipoint processor (optional)
MC
MP
MCU: MC & MP
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The MC also controls conference resources such as
multicasting.
– Most H.323 systems support IP multicast and use
this to send just one audio and one video stream
to the other participants.
– The MC does not actually deal directly with any of
the audio, video and data streams.
This is left to the MP, which does all the audio mixing,
data distribution and video switching/mixing of the
bits.
It also provides the conversion between different
codecs and bit rates.
Switching/mixing
MCU: MC & MP
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Both the MC and MP functions can exist in one unit
or as part of other H.323 components.
Most H.323 MCU's work in conjunction with, or
include a Gatekeeper functionality.
MCU - H.320
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H.320 conferences are essentially a point-to-point
connection and need to use an H.320 MCU to link
and manage all the ISDN lines in order to hold a
conference with three or more participants.
Endpoint with Embedded MCU
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An alternative to using a dedicated MCU for
small conferences involving 3 or 4
participants is to equip one of the endpoints
with an embedded multipoint capability.
– The Polycom VSX 7000s has an embedded multipoint
options that supports itself and up to 3 other sites in a VoiceActivated or Continuous Presence session.
Terminal & MCU
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VSX 7000s has both BRI or PRI ISDN options that
when used in conjunction with the multipoint
capability, allows mixed-mode operation between
both ISDN and IP networks.
In a simplistic manner, it also acts like a Gateway,
bridging between the other 2 or 3 ISDN and IP
endpoints.
Gatekeeper
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The Gatekeeper is an optional component in
the H.323

Primarily used for
– admission control and
– address resolution
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The gatekeeper may allow calls to be placed
directly between endpoints or it may route the
call signaling through itself to perform
functions such as follow-me/find-me and
forward on busy
Gatekeeper
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Although the H.323 standard describes the
Gatekeeper, as an optional component, it is in
practice an essential tool for defining and controlling
how voice and video communications are managed
over the IP network.
Gatekeeper
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Responsible for
– providing address translation between an
endpoints current IP address and its various H.323
aliases,
– call control and
routing services to
H.323 endpoints,
– system management
and security policies.
Gatekeeper
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Registered endpoints can be H.323
Terminals, Gateways or MCU's.
Gatekeeper
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Gatekeeper allow network administrators to
– configure,
– monitor and manage the activities of
registered endpoints,
– set policies and control network resources
such as bandwidth usage within their
H.323 zone.
These services provided by the Gatekeeper
in communicating between H.323 endpoints
are defined in RAS.
Gateway and zone
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Only one Gatekeeper
can manage a H.323
zone, but this zone
could include several
Gateways and
MCU's.
Gatekeeper and zone
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Since a zone is defined and managed by only
one Gatekeeper, endpoints such as Gateways
and MCU's that also have a built-in Gatekeeper
must provide a means for disabling this
functionality.
This ensures that multiple H.323 endpoints that
contain a Gatekeeper can all be configured into
the same zone.
Example of gatekeepers
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The INVISION 100 from RADVISION
combines Gateway and MCU functionality in
one box and has an embedded Gatekeeper
that can be disabled;
– this allows the zone to be controlled by a
more powerful Gatekeeper
Example of gatekeeper
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VCON - Media XchangeManager™, MXM.
Media Xchange Manager™ - VCON
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From a remote console, the administrator can now
perform centralised management functions such as
configure endpoints, monitor the status and
availability of endpoints, control and limit bandwidth
usage and more.
MXM automatically generates Call Detail Reports,
CDR; which can be used for network planning or
billing purposes.
With video telephony services such as Call Forward,
Call Transfer and Call Pickup, MXM provides the
functions that make Video Conferencing as simple as
making a telephone call.
Furthermore, MXM includes an H.323 Gatekeeper.
Interconnected Gatekeeper
Zones:
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Gatekeeper defines the zone and manages the
registered endpoints within.
Calling an endpoint
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To call an endpoint within the same zone, we simply
dial that endpoints H.323 User Number.
Calling na endpoint
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But what happens when we want to call an endpoint
that is located in another zone?
Well, we then also need to know the zone where that
endpoint is registered.
Each Gatekeeper on the same network is identified
by a unique number, its Zone Number.
All the Gatekeepers on the network must
know how they are related to eachother.
Interconnected Gatekeeper
Zones:
Neighbour Gatekeepers
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When Gatekeepers are arranged in a single tier
'Peer-to-Peer' manner with no particular hierarchical
structure, they are termed as being Neighbour
Gatekeepers.
This would typically be on a corporate network within
a multi-site company who has a Gatekeeper at each
site.
Each Gatekeeper manages its own site (Zone), with
inter-zone communications routed directly between
zones and controlled on an individual basis
specifically defined by the direct relationship between
each Gatekeeper
Directory Gatekeepers
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When the Gatekeepers are arranged in a
multi-tier manner with a hierarchical structure,
they are termed as being Directory
Gatekeepers (DGK).
This would typically be within a large scale
deployment such as the national schools
network. Whilst each Gatekeeper still
manages its own zone, inter-zone
communications are routed indirectly on a
Parent-Child basis between zones.
Directory Gatekeeper
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A Directory Gatekeeper only knows
its Parent and Child Gatekeepers.
If the Gatekeeper does not know the Zone of the
dialled number, it routes the call to its Parent DGK,
which then searches its database to see if the Zone
known.
If not known, this Parent routes the call to its Parent
and so on until it eventually reaches a Parent DGK
that has a Child DGK that matches the Zone.
The call is then routed down through each Child DGK
tier until it reaches the specific endpoint.
Gateways

Gateways interface H.323 to other networks,
including the PSTN, H.320 systems, and
other H.323 networks (proxy)
Gateways

The Gateway is composed of a “Media
Gateway Controller” (MGC) and a “Media
Gateway” (MG), which may co-exist or exist
separately
– The MGC handles call signaling and other
non-media-related functions
– The MG handles the media
Gateway
Gateways:
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H.320 and H.323 systems can interoperate with the
use of a Gateway.
Essentially, the Gateway provides translation
between circuit-switched networks ISDN and packetbased networks LAN, enabling the endpoints to
communicate.
To do this, it must translate between the H.225 to
H.221 transmission formats and between the H.245
to H.242 communications control protocols.
The Gateway also has to transcode between the
various audio and video codecs used between the
LAN and ISDN devices.
Gateway
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Most Gateways work in conjunction with, or
include a Gatekeeper functionality
H.323 Stack
The Protocols
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H.323 is a “framework” document that describes how
the various pieces fit together

H.225.0 defines the call signaling between endpoints
and the Gatekeeper
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RTP/RTCP (RFC 3550) is used to transmit media
such as audio and video over IP networks

H.225.0 Annex G and H.501 define the procedures
and protocol for communication within and between
Peer Elements

H.245 is the protocol used to control establishment
and closure of media channels within the context of a
call and to perform conference control
Protocols
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H.450.x is a series of supplementary service
protocols

H.460.x is a series of version-independent extensions
to the base H.323 protocol

T.120 specifies how to do data conferencing
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T.38 defines how to relay fax signals

V.150.1 defines how to relay modem signals

H.235 defines security within H.323 systems
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X.680 defines the ASN.1 syntax used by the
Recommendations

X.691 defines the Packed Encoding Rules (PER)
used to encode messages for transmission on the
network
QoS

H.460.9 allows an endpoint to report Quality
of Service information to the Gatekeeper,
aiding in determine how to route calls

H.323 devices may utilize IETF standards for
providing quality of service, including DiffServ
and RSVP
Data Collaboration Using T.120
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
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)
Standards for Collaboration
Services
Standards
 T.120
– Layered, Network Independent
–
–
–
–

P2P Communications
8K channel
NetMeeting (now dead product)
No development of standard
ITU-T H.239 (July 2003)
– supports one or more parallel streams for sharing
data and presentations
– Defines multiple channels (video, audio, or data.)
and their “role” (Live, Presentation).
– Limited Implementations
ITU-T T.120 series
Reservations
App Sharing
Switching
T.130
A/V Control
File Transfer
Documents
T.127
Photos
Overhead Proj
Whiteboard
T.126
TERMINAL
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
T.123 - Transport Stacks
ISDN
POTS
Voice/
Data
LAN
ATM
H.323 and T.120 components
Terminals may contain T.120
capabilities
MCU - multipoint control unit
contains MC and MP optionally
a T.120 MCU
H.323 e T.120
ITU-T T.120 series
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Kinds of data and standards
– 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
– 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)
T.124 - Generic Conference
Control (GCC):

T.124 - Generic Conference Control
– Provides set of facilities to establish and manage
multipoint .
– Centralize an information base (state of serving
conferences)
Conformance for T.120 service



Transport protocol profile (T.123);
MCS Multipoint Communication Service (T.125);
Required components of Generic Conference
Control (T.124);
Additional standards

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

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.
Some monitoring results


T.120 communication between terminals
(Netmeeting), start before logical channels open
Centralized conference model (tightly coupled) use
intensively MCU resources
Event>
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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

Quality of Service - needed quality to attend
specific application user request
– telephony
– videoconference
– file download
– TV
QoS


Usual specifications
– Bandwidth
– Delay
– Jitter
QoS from user point of view ?
– ITU P800 Perceptual Speech Quality
Measurement (PSQM)
– Mean Opinion Scores (MOS)
MOS - Mean Opinion Scores

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)