Post on 27-Mar-2015
H.323
Jill GemmillUniversity of Alabama at Birmingham
Doug PearsonIndiana University, Bloomington
Tyler JohnsonUniversity of North Carolina, Chapel Hill
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Internet2 Commons
Desktop & Room Systems
• USB or Appliance
• Affordable
• User Friendly
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
H.323 Audio Standards
G711 Audio Codec Required
Optional Codecs: G721, G723, G728, G729
Bottom Line – Good Audio Requires 64Kb
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)
Point-to-Point & Multipoint
user user
Point-to-Point Dial by IP address ! or alias
user user
user
user
MCU
Gatekeeper
Multipoint Register with Gatekeeper
Connect through MCU
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 collaboration.
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)
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
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
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.
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.
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
H.323 Network Requirements:
Latency One-Way Delay:
– [ 0 – 150 ms] : Excellent ! – [150 – 300 ms] : OK– [300 – 400 ms] : Bad– [400+ ms] : “Fuggedahboudit”
H.323 Network Requirements: Jitter
Definition: Variation in latency over time.
For switched end-points, the primary source of jitter is variation in the store-and-forward time, resulting from network load.
H.323 is very intolerant of jitter; clients reduce resolution
Rule of thumb?
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
Tools for Diagnosing H.323 Problems
Ping TraceRoute PingPlot MRTG Iperf
GnuPlotPing Sniffer ViDeNet Scout QCheck OARNet H.323
“Beacon”
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/
Scouting Advanced Networks10 minute 384kbs simulated conference
SURFNet (Netherlands) CUDI (Mexico)
THROUGHPUT
PACKET LOSS
JITTER
Scouting Out ProblemsPublic 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
THROUGHPUT
PACKET LOSS
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
Iperf – Example on Intercampus DS3 http://dast.nlanr.net/Projects/Iperf/
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!
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
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
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
What is ViDe? (www.vide.net)
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.