Download What is H.323?

CSE679:H.323
“H.323: Video, Voice and Data over IP”
Prasad Calyam,
Systems Developer/Engineer,
ITEC-Ohio, Internet2 E2Epi
Topics of Discussion
 What is H.323?
 H.323 deployment architecture
 Protocols of the H.323 Stack
 H.323 Signaling: Call setup and teardown
 Factors affecting an H.323 system
 My H.323 research!
 Conclusion
What is H.323?
 H.323 is an umbrella standard that defines how
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real-time multimedia communications such as
Videoconferencing can be supported on packet
switched networks (Internet)
Devices: Terminals, Gateways, Gatekeepers and
MCUs
Codecs: H.261, H.263, G.711, G.723.1
Signaling: H.225, H.245
Transport Mechanisms: TCP, UDP, RTP and RTCP
Data collaboration: T.120
Many others…
H.323 Protocol Stack
APPLICATION
G.711
Video Signal
G.728
H.261
H.263
G.722
G.729
Audio Signal
G.723.1
Data
T.127
T.126
PRESENTATION
SESSION
T.124
RTCP
RAS
RTP
TRANSPORT
T.125/
T.122
Supplementary Services
H.450.3
H.235
H.450.2
H.450.1
X.224.0
Control
UDP
NETWORK
DATA LINK
PHYSICAL
H.245
H.225
TCP
H.323 Deployment Architecture
H.323
H.323
Gatekeeper
Corporate LAN
Gateway
Multipoint Control Unit
Switched
Circuit Network
(POTS and ISDN)
router
H.320
(over ISDN)
Internet
H.324
(over POTS)
Speech-Only
(telephones)
Desktop and Room H.323
Videoconferencing Systems
• USB or Appliance
• Affordable
• User Friendly
Basic H.323 Protocols
Gatekeeper H.225/H.245
RAS
H.225/
H.245
Gatekeeper
H.225/
H.245
RAS
Signaling (H.225)
Endpoint
H.245
RTP/RTCP
Gatekeeper Routed Signaling
Direct Routed Signaling
Endpoint
H.323 Call setup and teardown
H.323 Beacon Client
H.323 Beacon Server
Open Socket
SET UP EP, EP2, conf ID
CALL PROCEEDING
CONNECTION
SETUP
ALERTING
Q.931 OVER IP
CONNECT H245 ADDRESS
TERMINAL CAPABILITY SET
TERMINAL CAPABILITY SET
CAPABILITY
EXCHANGE
TERMINAL CAPABILITY SET ACK
TERMINAL CAPABILITY SET ACK
MASTER-SLAVE DETERMINATION
MASTER-SLAVE DETERMINATION
MASTER-SLAVE
DETERMINATION
MSD-ACK
MSD-ACK
OPEN LOGICAL CHANNEL(TYPE)
OPEN LOGICAL CHANNEL(TYPE)
OPEN LOGICAL
CHANNEL
OPEN LOGICAL CHANNELACK (RTP ADDRESS)
OPEN LOGICAL CHANNELACK (RTP ADDRESS)
H.323 Call setup and teardown (Contd.)
RTP STREAM
MEDIA EXCHANGE
TCP CONNECTION
H.245 MESSAGES
CALL TEARDOWN
END SESSION COMMAND
CLOSE LOGICAL CHANNEL
END SESSION COMMAND
CLOSE LOGICAL CHANNEL
RELEASE COMPLETE
RELEASE COMPLETE
Factors affecting an H.323 system
 Human Factors
 Individual perception of audio/video quality
 Excellent: One-way delay between 0-150ms
 Good: One-way delay between 150-300ms
 Intolerable: One-way delay >400ms
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Lack of training to handle the system correctly
 Device Factors
 MCUs, Routers, Firewalls, NATs, Modems, Operating
System, Processor, memory, …
 Network Factors
 Delay, Jitter, Packet loss, Throughput, BER, …
My H.323 research!
Thesis Objectives:
 “To measure the behavior of an H.323
Videoconferencing system with the variations in
the network behavior to suggest a model for
large-scale multipoint H.323 Videoconferencing”
 “To develop a tool that can be used to monitor and
measure the performance of H.323
Videoconference sessions to identify and
troubleshoot performance problems in a H.323
Videoconferencing system”
Performance Evaluation of H.323
Videoconference Traffic
 Bounds Testing
 Testing Environment
 Metrics
 Experiment Criteria
 Results
 End-to-end Delay Testing
 Testing Environment
 Results
 Recommendations for large multipoint H.323
Videoconferencing systems
Why Bounds Testing?
 Every application has many idiosyncrasies and
requires network parameters to be within certain
bounds to achieve acceptable performance
 Regulation of one network parameter influences
other network parameters
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Sharp variations in jitter values leads to a
significant increase in packet loss
 It is necessary to understand application behavior
in an isolated environment with the variations in
the network parameters to make provisions in the
network, without affecting other best-effort
traffic, for enhancing the QoS of H.323
Videoconferencing systems
Bounds Testing: Test Setup
 Point-to-point client test
 Test with multiple clients connected via a single
MCU
 Test with multiple clients cascaded via cascaded
MCUs
NIC
Client
Switch
VLAN-1
Switch
MCU
VLAN-2
Router
running
NISTnet
Software
Appliance
Client
MCU
Multiple clients cascaded via cascaded MCUs
Bounds Testing: Conclusions
 Latency though annoying to users, does not affect the H.323
protocol itself
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Latency may be translated into packet loss and jitter in the buffers and
intermediate routers that handle the H.323 traffic and may result in
the deterioration of the call quality
 Packet Loss is tolerated by the H.323 protocol to a certain extent
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Packet loss must be below 1% in point-to-point and below 0.75% when
using cascaded MCUs for the H.323 audio/video to be acceptable to an
end-user
For the packet loss values above the aforementioned values, the call
was terminated sometimes, showing that the H.323 protocol failed to
maintain the session
 Jitter causes the most distress to the H.323 protocol
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When a single MCU is used to place a call, it was found to smoothen the
jitter
However, in a cascaded MCU scenario, the H.323 audio/video was found
to be more intolerant, as shown by the increase in the events
Why End-to-end Delay Testing?
 To study the effect of the various H.323 Videoconferencing
system components on the overall end-to-end delay and
identify the bottlenecks in the system
 To characterize the end-to-end delay of point-to-point and
multi-point H.323 Videoconferences based on the end-toend delay at different bandwidth settings
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Audio is the reference for end-to-end delay
 Audio is constantly sampled (64kbps) – PCM!
 End-to-end delay for video differs with the scene being captured
by the camera
 Video stream is subjected to lip synchronization with the audio
stream
End-to-end Delay Components
SENDER SIDE
NETWORK
RECEIVER SIDE
Compression
Delay
Propagation
Delay
Resynchronization
Delay
Transmission
Delay
Processing Delay
Decompression
Delay
Electronic
Delay
Queuing
Delay
Presentation
Delay
End-to-end Delay Testing: Test Setup
SWITCH
END POINT-1
END POINT-2
MIC I/P
AUDIO O/P
MCU
METRONOME
(PULSE
GENERATOR)
A
MCU
OSCILLOSCOPE
B
SCOPE I/P A:
METRONOME I/P
SCOPE I/P B:
ENDPOINT 2 AUDIO O/P
End-to-end Delay Testing: Conclusions
 End-system delays are much larger than the network delays
in a H.323 Videoconferencing system
 The encode-decode delay in a point-to-point settings is
~240ms and independent of the dialing speed
 The minimum delay contribution of an MCU is on the order
of ~120ms and the value increases with the increase in the
dialing speed
 The delay introduced by cascaded MCUs is significant to the
overall end-to-end delay of a session
Recommendations for large multipoint
H.323 Videoconferences
 It is favorable to use MCUs with larger ports to host a conference,
rather than cascading MCUs that have lesser number of ports to
support participants in a H.323 Videoconference
 A co-location of all the cascaded MCUs might help in limiting the
effects of latency, packet loss and jitter on the performance of
H.323 audio/video traffic
 Advantages
 This architecture eases the network monitoring and measurement
activity; helps troubleshooting problems easily and quickly
 Shortcomings
 Heavy load on the switch that routes traffic into MCU
concentration
 Single point of failure in case of network distress
H.323 Beacon Overview
 An H.323 Videoconference session monitoring and
measurement tool
 Uses a client/server architecture
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Client is more like an “end-node”
Server is more like a “core-node”
 Can be used to test service availability and call quality,
perform bandwidth management, and to test media
capabilities of H.323 sessions
 H.323 Beacon will serve as a session monitoring tool,
debugging tool and a continuity test tool for an ISP or an
end-user to monitor/trouble shoot H.323 sessions
 No manual intervention is necessary for qualifying a H.323
Videoconference
 Easy to install and use!
Some of the features...
 Multi-threaded Server
 Client and Server interoperability with commercial clients
 Call Status: “In Session”, “Normal Close”, “Exception Close”
Call exception handling Alarms: local client has no Internet
connectivity, network congestion, firewall presence, remote
client/server not online, transport error, insufficient
bandwidth, invalid IP address of remote client or server, …
Call bandwidth selection capability in client
H.323 session statistics: Video Frame Rate, Round Trip Time,
Audio/video jitter and packet loss, packets sent/received, etc..
Excel sheet generation for offline graphical-viewing of statistics!
Real time audio/video feedback: Test audio and video quality of the
end-user as seen on the remote side
Easy to install setup program and help utility!
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H.323 Beacon used as a
quality continuity measurement tool..
End User / Network
Administrator
Network Administrator
located at Los Angeles
wants to have video
conference session with
Network Administrator
located at Chicago
End User / Network
Administrator
(at Los Angeles requests
H.323 session statistics
data from Chicago to Los
Angeles in Web Format)
(at Chicago requests
H.323 session statistics
data from Los Angeles to
Chicago in Web Format)
Beacon Client
Beacon Client
Beacon
Server
(at Sioux
Falls POP)
(at
Chicago
POP)
Beacon
Server
(at Los
Angeles
POP)
Beacon
Server
(at Tampe
POP)
Beacon
Server
(at Austin,
Texas)
H.323 Statistics includes
Video Frame Rate, Round Trip
Time, Throughput, Video
Jitter, Audio Jitter, and Packet
Loss
Beacon
Server
H.323 Beacon Architecture
Dump analyzer:
view capture data, use filters,
message sequence charts, call detail
records, save part or whole trace
Webserver for accessing the data and
dump analyzer via web:
view capture data , use filters,
message sequence charts, call detail
records, save part or whole trace
Determines H.323 session statistics
:frame rate, throughput, interarrival
audio/video jitter, packet loss, etc..
Audio/Video
loop back
ssh and IPTables (filters) for H.323
Beacon server management and
security
Call Set up and TearDown
Statistics log
storage and
graphical view of
change in values
over the session
period
PWLib library
H.323
Beacon
Client
Media Channel
H.323 Beacon
Server
H.323 session statistics
of the channel and traffic
dumps
Central Data
Storage Server
(optional
component)
H.323 session statistics of the
channel and traffic dumps
PTLib library
OpenH323 library
(C++ H.323 stack)
Redirects session statistics
and H.323 traffic
traces(dumps) to client or to
the central data storage server
H.323 Traffic Dump using
H.323 Ethreal
scp for avoiding possible DoS
attack using corrupt data
storage mechanism
Some Screen Shots…
Some Screen Shots…(Contd.)
Questions?