Transcript H.323

Video Development Initiative
H.323
Jill Gemmill
University of Alabama at Birmingham
Doug Pearson
Indiana University, Bloomington
Tyler Johnson
University of North Carolina, Chapel Hill
NLANR Techs Workshop
January 2002
Internet2
Commons


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Desktop & Room Systems

• USB or Appliance
• Affordable
• User Friendly
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January 2002
What is H.323 ?
 An ITU-T standard for bi-directional
exchange of voice, video, and data
 Applies to an IP network
 H.323 is a set of standards for group
communication
 TCP Call setup & control
 UDP for audio/video
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January 2002
H.323 Audio Standards
 G711 Audio Codec Required
 Optional Codecs: G721, G723, G728,
G729
 Bottom Line – Good Audio Requires
64Kb
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January 2002
H.323 Video Standards
 Video is optional; H.261 required
 H.261 Picture Size
– QCIF (176x44 pixels) is required
– CIF (352x288 pixels) optional
 H.261 Compressed Data Rate
– 64kbs – 1.9 kbs
 H.263 SQCIF, 4CIF, up to 16CIF
(1408x1152 pixels)
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Point-to-Point & Multipoint
Point-to-Point
Dial by IP address ! or alias
user
user
Gatekeeper
user
user
user
MCU
user
Multipoint
Register with Gatekeeper
Connect through MCU
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What is ViDe.Net?
 An international virtual network providing
video teleconferencing, telephone and
collaboration services over advanced
networks. Architecture used in I2 Commons
 A voluntary collaboration and open forum
 A mesh of interconnected 75+ H.323 zones
 Zone: a collection of users administered by
the site.
 RESULT: individual campuses and network
providers interconnect, creating a seamless
global environment for teleconferencing and
Techs Workshop
collaboration. NLANRJanuary
2002
Network Requirements
 Please use switched Ethernet
 Category 5 wiring is part of the above
 10Mb/sec should be adequate for end
points
 Much higher bandwidth at MCU
(multiple 100Mb/sec cards in some
systems)
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January 2002
Duplex Mismatch: the
“Silent Performance Killer”
 A connection set for auto-negotiation,
failing to see auto-negotiation at the
other end, sets itself to the default –
half-duplex.
 Auto-negotiation doesn’t always work,
even when both sides are set to auto
 Auto-negotiation occurs repeatedly at
intervals; what’s right the first time
can be wrong later
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Detecting Duplex Mismatch
 Show switch port stats; if
mismatched:
– High CRC or Alignment errors at full
duplex end
– Late collisions at half duplex end
 UAB sets all user ports to 10/half by
default
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January 2002
Firewalls
 H.323 uses these IP ports:
– Statically-assigned TCP ports 1718 –
1720 and 1731 for call setup and control.
– Dynamically-assigned UDP ports in the
range of 1024 – 65535 for video and
audio data streams.
 Firewalls don’t allow unrestricted
ports: typical modern firewalls and
H.323 don’t get along so well.
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January 2002
Firewalls – Solutions for H.323
• [bad; non-scaleable] Allow unrestricted ports
for specific, known, external IP-addresses.
• [better, but still not so good] Use feature of
some videoconferencing clients to confine
dynamic ports to a specific, narrow range.
• [OK, but extra admin work and cost] Use an
H.323 application proxy.
• [best] Use a firewall that snoops on the H.323
call set-up channels (static ports) and opens
ports for the audio/video (dynamic ports) as
needed.
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January 2002
Network Issues
 Ongoing, undiagnosed problems with
H.323
– Jerky video over uncongested networks;
why?
– Quality of H.320 vs. H.323 over
uncongested networks
– >.1% packet loss = unacceptable audio
(ITU)
– >.5% renders session unusable
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January 2002
H.323 Network Requirements:
Latency
 One-Way Delay:
– [ 0 – 150 ms]
– [150 – 300 ms]
– [300 – 400 ms]
– [400+ ms]
:
:
:
:
Excellent !
OK
Bad
“Fuggedahboudit”
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January 2002
H.323 Network Requirements:
Jitter
 Definition: Variation in latency over
time.
 For switched end-points, the primary
source of jitter is variation in the storeand-forward time, resulting from
network load.
 H.323 is very intolerant of jitter; clients
reduce resolution
 Rule of thumb?
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January 2002
H.323 Network Requirements:
Packet Loss
 Typically due to router or link
congestion
– >0.1% packet loss (ITU) = unacceptable
audio
– >0.5% renders session unusable
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January 2002
Tools for Diagnosing
H.323 Problems





Ping
TraceRoute
PingPlot
MRTG
Iperf
 GnuPlotPing




Sniffer
ViDeNet Scout
QCheck
OARNet H.323
“Beacon”
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January 2002
Tools: ViDe.Net Scout
 Scout is a web-based distributed
network performance analysis tool
developed at the University of North
Carolina at Chapel Hill.
 Scout makes use of the NetIQ Chariot
performance testing engine
 http://scout.video.unc.edu/
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Scouting Advanced Networks
10 minute 384kbs simulated conference
SURFNet (Netherlands)
CUDI (Mexico)
THROUGHPUT
PACKET LOSS
JITTER
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Scouting Out Problems
Public Health Outreach Project
 Remote Health Clinic
connected to Internet2
via xDSL
 Original diagnosis was
h.323 problem
 ISP refused problem
ownership until
presented with Scout
results
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January 2002
THROUGHPUT
PACKET LOSS
Iperf – Example on Intercampus DS3
http://dast.nlanr.net/Projects/Iperf/
MRTG utilization graph
showed bandwidth peaking
at capacity ~ 10:00am –
2:00pm
As utilization peaked on
the DS3, jitter measured by
Iperf rose to unacceptable
level
Iperf also reported periodic
high packet loss, with no
apparent correlation to the
low-resolution MRTG
utilization reports
The End-to-End Problem
 Problem: Poor video and/or audio in
a conference between campuses
 Need: Timely, useful assistance
 If there’s a firewall, it could take
weeks!
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Suggested Solutions
 Articulate the E-2-E problem to network
management and engineers
 Bring all engineers together in a place and
time to share information.
 Establish and use reliable communication
tools
 Improve diagnostic tools
 Have good network documentation for all
networks
NLANR Techs Workshop
January 2002
Future ViDe.Net Direction:
Middleware for Video
 Directories : key enabler of video
teleconferencing.
 Directories : management tool for tracking
and supporting users
 Directory : a portal for account requests,
support, user information updates, etc.
 Goal: Directory lookup, authenticated click
& dial
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Middleware for Video: NSF
National Middleware Initiative
 NMI Release 1 due this Spring
 h323Identify and h323Zone object
classes will enable h.323 attributes to be
added to campus LDAP directories
 Coordination with Internet2 Middleware
activities will create a globally searchable
directory of video users
 Will allow automatic user account
management by integration with enterprise
directories
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January 2002
What is ViDe? (www.vide.net)
NLANR Techs Workshop
January 2002
SURA/ViDe Digital Video
Workshop April 23-25, 2002
 4th Annual Workshop
 Birmingham, Alabama UAB Campus
 Digital Video Applications: collaborative
conferencing, streaming video, and
storing/serving video-on-demand
 Technical Training & Discussion
 Program/Technical/Vendor Advisory
Committee – please volunteer.
NLANR Techs Workshop
January 2002