Video Conferencing: Jetson’s Technology Today

A Guide to How Video Conferencing Works andCommon Problems

An ITU-T standard for bi-directional exchange of voice, video, and data Applies to an IP networkH.323 is a set of standards for group communication TCP Call setup & controlUDP for audio/video

What is H.323?

• H.225 - call setup, establishment, tear-down

• H.245 - media capability negotiation

Setup Standards

• G711 Audio Codec Required• Optional Codecs: G721, G723, G728, G729

• Bottom Line – Good Audio Requires 64Kb

Audio

• 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)

Video

How does all this work?

( the signaling example )

How does all this work?

Calling party opens H.323 client

Call Seacliff

How does all this work?

Q.931 Setup

Setup

How does all this work?

Q.931 Alerting (ringing)

Alerting

How does all this work?

Q.931 Connect

Connect

How does all this work?

H.245 terminal capabilities

termCapSet

How does all this work?

H.245 terminal capabilities

termCapAck

How does all this work?

H.245 determine Master/Slave

mSDet

How does all this work?

H.245 determine Master/Slave

mSDetAck

How does all this work?

H.245 determine Master/Slave

mSDetConfirm

How does all this work?

H.245 open channel (RTP)

openReq

How does all this work?

H.245 open channel (RTP)

openAck

How does all this work?

RTP connection

connected

How does all this work?

H.245 End Session

endSession

How does all this work?

Q.931 Release Complete

ReleaseComplete

user user

Point-to-Point Dial by IP address ! or alias

user user

user

user

MCU

Gatekeeper

Multipoint Register with Gatekeeper

Connect through MCU

Ways To Connect

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

MCU

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

• 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)

Network

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

• 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

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.

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.

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

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.

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.

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.

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

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”.

QoS Continued

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

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.

Problem: Poor video and/or audio in a conference between campuses

Need: Timely, useful assistance If there’s a firewall, it could take weeks!

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

– >.1% packet loss = unacceptable audio (ITU)

– >.5% renders session unusable

End to End Problem

• 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

Solving E-2-E

• Typically due to router or link congestion– >0.1% packet loss (ITU) = unacceptable audio

– >0.5% renders session unusable

• One-Way Delay:– [ 0 – 150 ms] : Excellent !

– [150 – 300 ms] : OK– [300 – 400 ms] : Bad– [400+ ms] : “Fuggedahboudit”

What we are Shooting For

• Ping• TraceRoute• PingPlot• MRTG• Iperf

GnuPlotPing Sniffer ViDe.net

Tools To Use

• This stuff takes time to setup• Clear communication channels• When we run into problems lets work together to fix it

• Contact info Shawn Brown (916) 204-7194 sbrown@parks.ca.gov

Things To Remember