Video Conferencing:

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Video Conferencing Jetsons Technology Today
A Guide to How Video Conferencing Works
and Common Problems
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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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Setup Standards

• H.225 - call setup, establishment, tear-down
• H.245 - media capability negotiation

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Audio

• G711 Audio Codec Required
• Optional Codecs G721, G723, G728, G729
• Bottom Line Good Audio Requires 64Kb

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Video

• 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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How does all this work?
( the signaling example )
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How does all this work?
Call Seacliff
Calling party opens H.323 client
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How does all this work?
Setup
Q.931 Setup
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How does all this work?
Alerting
Q.931 Alerting (ringing)
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How does all this work?
Connect
Q.931 Connect
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How does all this work?
termCapSet
H.245 terminal capabilities
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How does all this work?
termCapAck
H.245 terminal capabilities
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How does all this work?
mSDet
H.245 determine Master/Slave
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How does all this work?
mSDetAck
H.245 determine Master/Slave
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How does all this work?
mSDetConfirm
H.245 determine Master/Slave
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How does all this work?
openReq
H.245 open channel (RTP)
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How does all this work?
openAck
H.245 open channel (RTP)
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How does all this work?
connected
RTP connection
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How does all this work?
endSession
H.245 End Session
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How does all this work?
ReleaseComplete
Q.931 Release Complete
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Ways To Connect
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Gatekeeper

• Purpose is to manage resources in a zone
• Uses RAS signaling
• Provides address resolution
• Alias Address Modification
• Approves calls based on bandwidth
• Dialed Digit Translation (PSTN)
• Directory Services

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MCU

• A computerized switching system that allows
  point-to-multipoint videoconferencing.

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Network

• 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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Duplex Mismatch theSilent 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 doesnt always work, even when
  both sides are set to auto
• Auto-negotiation occurs repeatedly at intervals
  whats 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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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 dont allow unrestricted ports typical
  modern firewalls and H.323 dont get along so
  well.

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What is a Firewall?

• A network firewall protects a computer network
  from unauthorized access. Network firewalls may
  be hardware devices, software programs, or a
  combination of the two.
• Network firewalls guard an internal computer
  network (home, school, business) against
  malicious access from the outside. Network
  firewalls may also be configured to limit access
  to the outside from internal users.

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Why is H.323 tricky with firewalls?

• Requires the use of several ports, both UDP and
  TCP.
• Uses a single fixed TCP port 1720 for call
  control.
• Then uses dynamic TCP ports for capabilities
  exchange and channel control.
• Then uses two dynamic UDP ports for each type of
  media that was negotiated.

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Firewalls and H.323

• In order to use H.323 video conference behind a
  firewall, your firewall needs to open up these
  ports.
• TCP 1720 (Mandatory) H.323 Call setup
• UDP 3230-3235 (Mandatory) H.323 Video Conference
• UDP 1719 (Optional) H.323 GateKeeper
• TCP 1503 (Optional) T.120 Data Sharing
• TCP 1731 (Optional) NetMeeting Audio Call Control
  
• TCP 522 (Optional) NetMeeting ULS User Location
  Services

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Firewalls and Endpoints

• You will also need to setup your video conference
  endpoint to work behind the firewall too.
• So please enable and use ports from 3230 to 3235
  so that it is compatible with your firewall
  configuration.

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What is NAT?

• Network Address Translation, is used to mask the
  true identity of internal computers.
• Computers on the local network use a completely
  different set of IP addresses Private IP. When
  traffic goes out the internal IP address is
  removed and replaced with the public IP address
  of the NAT device or NAT pool Public IP.
• When replies come back to the NAT device it
  determines which internal computer the response
  belongs to and routes it to its proper
  destination.

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NAT and Video Conferencing

• Dynamic NAT Will support outgoing calls only.
• Private IP address is translated into one of the
  available Public IP addresses.
• Static NAT Support both incoming and outgoing
  calls.
• Private IP address is translated into a single
  Public IP address.

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H.323 and Firewall Traversal

• ITU-T ratified extensions to H.323 in August
  2005. Allowing devices to cross NAT Firewall
  devices.
• Software upgrades may be available for endpoints
  to implement these new H.323 extensions.
• H.460.18 and H.460.19

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Quality of Service (QoS)

• QoS enables the network administrator to
  Reserve bandwidth for videoconferencing.
• Methodes RSVP and IP Precedence.
• Without QoS videoconferencing will be Best
  Effort.

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QoS Continued

• Add 20 for IP overhead.
• 384K call, reserve 460K
• 768K call, reserve 922K

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Why implement QoS?

• At any time, if any router along the way becomes
  busy your H.323 data is competing for the same
  bandwidth that all the other data traffic is
  competing for.
• This happens during high traffic times or during
  a denial of service attack.

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End to End Problem

• Problem Poor video and/or audio in a conference
  between campuses
• Need Timely, useful assistance
• If theres a firewall, it could take weeks!

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End to End Problem

• Ongoing, undiagnosed problems with H.323
• Jerky video over uncongested networks why?
• Quality of H.320 vs. H.323 over uncongested
  networks
• gt.1 packet loss unacceptable audio (ITU)
• gt.5 renders session unusable

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Solving E-2-E

• 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

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What we are Shooting For

• One-Way Delay
• 0 150 ms Excellent !
• 150 300 ms OK
• 300 400 ms Bad
• 400 ms Fuggedahboudit

• Typically due to router or link congestion
• gt0.1 packet loss (ITU) unacceptable audio
• gt0.5 renders session unusable

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Tools To Use

• Ping
• TraceRoute
• PingPlot
• MRTG
• Iperf

• GnuPlotPing
• Sniffer
• ViDe.net

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Things To Remember

• This stuff takes time to setup
• Clear communication channels
• When we run into problems lets work together to
  fix it
• Contact info Shawn Brown
• [phone]
• sbrown_at_parks.ca.gov