Video Conferencing

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Video Conferencing
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Video Conferencing

• Why?How?Trade offsConclusion

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Applications of VC

• Medical systems
• tele-medicine - allows fast transfer of
  information for the diagnosis and treatment
  purposes
• Distance learning
• opportunity to bring outside resources into the
  classroom
• cuts down on transportation and scheduling
• live experiments from sophisticated labs
• can attend class without being there (illness)

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Pros Cons

• Gestures, expressions, etc improve interpersonal
  communications
• Real time allows for quick feedback
• Guest speakers can speak to multiple classes
  simultaneously

• New technology can impose stresses
• Anxiety about being on camera
• Learning curve
• Invasion into personal space (forgetting to
  switch camera off

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Value of Audio

• Effective communication can not occur without
  intelligible audio, audio delay can make
  interaction difficult
• Audio that is not synchronised with video can be
  distracting
• Some studies suggest however that users prefer
  having audio with minimal delay over having audio
  in sync with video if a noticeable delay is
  imposed

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Value of Video

• Intuitively adds value to a conference
• Enhances communication (sense of presence)
• Allows communication through gesturing
• Objects can be shown to the camera
• Video from auxiliary sources can be used (VCR)
• Explains pauses
• Visual nature helps concentration

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Values of Integrated computer applications

• Shared whiteboard capabilities to supplement
  communications (sketches and annotations)
• Application sharing - i.e. participants
  collaboratively editing a word processed document
  or spreadsheet

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How does it work
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Typically two types

• Room based
• better quality, costly unless good savings in
  travel
• unmovable, relocation is difficult
• requires scheduled bookings
• Desk top
• inexpensive to set up, easy to use maintain
• immediate use, no booking required
• poor quality compared (usually small window)
• lack of standards

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Basic components for DTVC

• PC with min requirements
• 33mhz 486 processor (more recently Pentium)
• a plug in ISA video capture card to handle
  digitisation and compression
• ISA Audio card
• Software (possibly ISDN card and drivers, CODEC)
• Fixed focus camera
• Speakerphone handset with built in microphone
• Extras
• fast modem for ordinary telephone lines
• for ISDN, network termination equipment
• scanner (transferring images to whiteboard)

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UK telephone network

• Early phone network was pure analogue (POTS)
  prone to breakdown and noise
• Modems allow digital info to be transmitted as an
  analogue signal on public phone lines
• Gradual conversion to ISDN digital connectivity
• BTs ISDN network is now available on
  subscription to over 95 of urban households and
  90 of rural households
• Prices are reducing due to the arrival of other
  cable companies and network providers

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ISDN
(Integrated Services Digital Network)

• Success of VC will be built upon the widespread
  availability of low cost, fast digital networks
  based on ISDN
• Only widely available circuit switched digital
  service
• Higher bandwidth, better quality transmissions
• A major advantage against POTS is speed (approx
  384kbps)
• Allows multiple digital channels to be operated
  simultaneously
• Uses an international standard codec (H.320)
• Disadvantage - basically one to one communication

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ISDN - Pros Cons

• Dedicated bandwidth allocated for the exclusive
  use of the session
• Timing of data is predictable
• Widely available

• Sessions are primarily point to point
• Require expensive multi conferencing units (MCU)
  to accommodate multipoint conferences
• Dedicated bandwidth wasteful during periods of
  limited activity

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MBONE
(Multicast Backbone)

• High speed part of the Internet. Operates as a
  separate virtual network
• Often used with one site transmitting many
  receiving
• High degree of networking technical knowledge
  required to set it up
• Needs UNIX workstations and special routers
• Most commonly used within Universities and large
  scientific organisations
• Principal Mbone apps., shared video, audio and
  share drawing whiteboard

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LAN video conferencing

• Currently cannot communicate with users on WAN
  (essentially the ISDN systems)
• ISDN systems use different compression methods
  but this is under current consideration
• LAN is an asynchronous packet based device.
• Video is synchronous so delivery tends to be
  jerky and frames get lost
• Despite attempts to reserve bandwidth, not
  entirely reliable yet (other traffic tends to
  suffer)
• Provides multipoint desktop conferencing within
  an organisation which is cheaper than using ISDN
• Potential market is huge

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Packet switched

• Lan conferencing deploys information by dividing
  it into packets
• Each packet has and ID and destination address
• Packets are sent individually through a network
• Depending on conditions may take different
  routes, may arrive at different times or out of
  order
• Can be buffered at receiver end and reordered,
  but delay detrimental to interactive applications

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ATM
Asynchronous Transfer Mode

• New generation of high speed protocols for fibre
  optic cables
• Provides an answer to problems of running video
  on a LAN, but is expensive
• Good at handling video voice data all at the
  same time
• ATM faster at 45-622Mbps
• Is able to ensure a continuous data transfer rate
• Conventional LANs not well suited and give jerky
  images with lost frames.Multimedia over LANs
  will never be very good

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Compression

• Text data uses narrow bandwidth, can be
  transmitted slowly
• Multimedia needs wider bandwidth and real time
  transmission
• H.261 - video compression standard designed for
  communications bandwidths between 64kbps - 2Mbps
  - designed primarily for VC over ISDN

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Video transmission (example)

• Video image - 300x200 (24bit colour) to transmit
  at 30fps. The size of the video clip that needs
  to be transmitted in 1 second is 5.5 MB
• Using conventional telephone network - bandwidth
  about 2400 bps would take 18,000 secs (5hours) to
  transmit the clip
• Not possible without compression

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CODEC
(COmpressionDECompresssion components)

• CODECs used to perform digitisation as well as
  compression and decompression
• Available in the forms of hardware and software
• Hardware - no burden on CPU
• Software - relies on host PC- easy to install,
  cheaper
• Levels
• DTVC -64kbps
• Group conferencing - between 128 kbps - 2Mbps
  (384 is providing good quality reception)

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DSVD
(Digital Simultaneous Voice Data Technology)

• No video support, still image viewing only
• Can provide a way round the technical
  difficulties that beset motion video systems
• Can be as useful for collaborative work
• Useful for individuals small organisations
• An advantage of other systems of interoperability
  between UNIX and PC users on LAN
• Partial VC fast line out slow return

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Problems to overcome

• It takes time to compress video and audio and
  transmit it
• The lag can contribute to loss of interactivity
  experienced by VC systems
• There is learning curve involved with effectively
  utilising new tools
• Some people are wary of using VC
• Computer can crash during the session

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Conclusion

• The quality of the service provided is limited by
  the amount of bandwidth available in the chosen
  communications channel
• Improved quality can be gained by utilising data
  compression techniques
• Quality of service is largely a function of frame
  rate
• Higher frame rate means the video picture of the
  other person is less jerky and more fluid