Dr' Peter Parnes

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Dr. Peter Parnes

• Associate Professor Luleå University of
  Technology, Media technology
• Co-founder and Chief Scientist Marratech
• Online conferencing since 1992
• Married with Johanna
• Children Tovah (6), Oliver (0)
• Interests Reading, Geomag, Nature, Travel

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Today

• Media Scaling
• Image and TV Compression
• Movie compression
• MPEG
• Image compression
• JPEG

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• Media Scaling of
• IP-Multicast Streams in Heterogeneous Networks
• How to solve the many to many communication
  problem?

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• Which bandwidth should be used when transmitting
  a real-time media stream over heterogeneous
  networks?

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Background

• Broadcasts of real-time media on the Internet
  is becoming more and more important.
• If the used system shall scale, IP-multicast HAS
  to be used!

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Requirements and Restrictions

• Best-effort delivery
• Reliability not required
• Applications have to be adaptive, i.e. have to
  adapt to network congestion and be able to handle
  different configurations.

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Proposed solutions

• Max/Min client bandwidth
• Simulcast
• Network transcoders
• Receiver driven Layered Multicast - RLM
• Bandwidth Guessing - TCP friendly
• Active Networks
• Active Services

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Max/Min client bandwidth

• Just ignore some set of receivers
• Send the stream with high bandwidth
• Ignore low bandwidth receivers
• Send the stream with low bandwidth
• Force high bandwidth receivers to use low quality
• Does not take congestion into account

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Simulcast

• Send the same stream with different encodings
  from the sender and let the receivers choose what
  they want to receive.
• Can be very expensive CPU wise
• Wastes bandwidth on shared links
• Does not take congestion into account in the way
  it is being used today.
• Used in mStar (more later)

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Network Transcoders(Media Gateways)

• A common approach is to deploy transcoders on the
  boundaries between different networks.
• Transcoding
• Mixing
• Downscaling

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Media Gateway
receivers
Transcoding gateways
GW
GW
Internet
GW
GW
R
GW
receivers
Video transmitter
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Transcoding

• Transcoding
• transcode MJPEG to H.261 when the traffic leaves
  a campus (high bandwidth network). -gt high CPU
  requirement!
• Used in SIRAM media gateway

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Downscaling

• Downscaling
• Throw away parts of the media data
• Lower CPU than transcoding but worse result
• Used in mStar mTunnel

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Mixing

• Mixing
• Generate one stream from several active streams.
• Mix audio
• Combine video

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Receiver driven Layered Multicast - RLM

• Divide the stream into a hierarchy of exclusive
  additive layers
• Each layer is multicast to a different group
• loop
• if no_congestion then
• join next group to get higher layer
• else
• leave group to drop highest layer

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RLM Problems

• How to detect congestion caused by my tests or by
  others
• Shared learning proposed
• Does it scale?
• Today long timeout in mcast forwarding trees
• Might lead to false interpretation of the current
  situation
• Is not nice to TCP

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Layered Video
Low quality
GSM
Internet
Medium quality
Low quality
Modem
GRPS
R
Multicast Router
High-speed LAN
Sender
Video
High Quality
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Bandwidth Guessing

• In early 97 a proposal called TCP-Friendly was
  distributed.
• Describes a way of estimating the bandwidth
  between a sender and a receiver based on RTT and
  current packet drop.
• Takes TCP into account and will be a nice
  participant in the network

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BW Guessing Problems

• Hard to calculate RTT accurately
• Works only for broadcast situations
• Not very tested yet

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Active Networks

• A buzzword in the network research area
• Basic idea
• Allow injection of small programs into network
  nodes
• Network nodes perform computations on user data

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Active Networks...

• Two Different Approaches
• Code and control is handled out-of-band
• Each packet carries miniature programs (capsules)
• Allows networks to be modified on-demand
• Opens a completely new area for real-time media
  scaling

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Active Networks...

• Issues
• Safety, fairness, appropriate architecture,
  common programming model, robustness
• Status
• At the very beginning
• A very political problem

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Active Services

• Deploy user controllable programs-pads in the
  network.
• Users can deploy their own transcoding programs
  and can easily up-grade these when needed
• A system for this is currently being deployed and
  tested on Berkeley Campus

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Status in Internet

• Almost all traffic is still sent using Unicast -
  transcoding at the server
• Network transcoders probably most common
• Simulcast less common than one could imagine
  (lack of good support in todays applications).

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Summary

• A number of more or less proposed solutions
• Max/Min client bandwidth
• Simulcast
• Network transcoders
• Receiver driven Layered Multicast - RLM
• Bandwidth Guessing - TCP friendly
• Active Networks
• Active Services
• Still a lot of research needed

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• Questions?