H.323

Jill GemmillUniversity of Alabama at Birmingham

Doug PearsonIndiana University, Bloomington

Tyler JohnsonUniversity of North Carolina, Chapel Hill

Vid

eo D

evel

op

men

t In

itia

tive

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.