Video Splitting techniques for Inverse Multiplexing over GPRS channels

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Video Splitting techniques for Inverse
Multiplexing over GPRS channels

• Roll No 2006-03-0031
• M. Mudassar Nazar

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Roadmap

• Introduction
• Video Splitting Techniques
• Work accomplished
• Challenges Faced
• Future work
• References
• Questions

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IntroductionMajor HurdleMultimedia Apps.

• Scarcity of Bandwidth
• Major hurdle in deployment of multimedia
  applications
• Situation in our country
• In our country, dialup is a major method to
  access the internet
• DSL is limited to specific areas
• In rural areas even dial up access is limited

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Introduction cont. Telecom Revolution
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Introduction cont. Problem Formulation

• What can we do?
• Idea is simple?

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Introduction cont.Problem Formulation

• What can we do?
• Idea is simple?
• Aggregate Bandwidth
• also known as Inverse
• Multiplexing

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Introduction cont.Motivation

• Telemedicine
• Video lecturing
• Video on demand

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Introduction cont. Inverse Multiplexing
S
A
B
Input i.e. video
N network channels
M data packets
M data packets
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Introduction cont. Inverse Multiplexing
S
A
B
Input i.e. video
N network channels
M data packets
M data packets
- Link Layer ML PPP1 - Transport Layer2
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Introduction cont. Schedulingis at core
A
B
N network channels
M data packets
M data packets
Scheduling
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Introduction cont. Schedulingis at core
b
b
A
B
b
b
N network channels
M data packets
M data packets
Scheduling
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Introduction cont. Schedulingis at core
b1
b2
A
B
b3
b4
N network channels
M data packets
M data packets
Scheduling
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Introduction cont. Inverse Multiplexing
S
A
B
Input i.e. video
N network channels
M data packets
M data packets
Scheduler
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Introduction cont. Inverse Multiplexing
S
A
B
Input i.e. video
N network channels
M data packets
M data packets
Scheduler
Splitting
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Video Splitting Techniques

• MobiStream 4 explains four major video
  splitting categories
• Partitioning of video frames into slices
• Multiple Description Coding
• Slice Structured Coding
• Inter-frame/ intra-frame slice interleaving

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Video Splitting TechniquesBlock Interleaving

• Different Block interleaving techniques are
  proposed in 5
• Triangular
• Quadrant
• Coefficient

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Video Splitting TechniquesTriangular Interleaving

• In this, a DCT block is divided into two groups.
  Lower triangular region and the upper triangular
  region.
• Then these groups from different blocks are
  interleaved in such a way that if a lower portion
  of the triangle is lost, then there is high
  probability that higher portion is not lost and
  vice versa.
• DC coefficients are grouped in a separate block
  and can be transmitted on a reliable channel.

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Video Splitting TechniquesQuadrant Interleaving

• In this, a DCT block 8x8 is divided into four
  groups instead of two namely, L, HD, VD, and HI.
• A macro block of 16x16 is made from above blocks
  and number in a clock wise manner from 0 to 3.
• Select Li (i 0,1,2,3) and HDi1, HIi2 and UDi3
  from others to form new interleaved 8x8 blocks
  within the16x16 block.

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Video Splitting TechniquesCoefficient
Interleaving

• This scheme treats each DCT coefficient as a
  group
• Main idea is to shuffle the coefficients.
• Lets say if we have 63 groups in a block. Then we
  take first group from block 1, second from block
  2 to interleave.
• This scheme works on the coefficient level.
  Although this produces high degree of
  interleaving but this also compromises on
  compression efficiency.

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Work Accomplished

• Experiments to check the behavior of real GPRS
  channels (Warid)
• Built an application layer that can
• Identify new GPRS devices and make connection
  with them using Bluetooth
• Maintains a list of available GPRS devices for
  scheduling purpose.
• Provide an interface to outer world to schedule
  packets.
• Note RR Scheduling being used in the layer.

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Work AccomplishedExperiments

• Different experiments for GPRS have been
  performed in order measure
• RTT
• Using ping
• Jitter
• ji ti-ti-1- a
• Where
• ji is the jitter for ith observation
• ti is the receiver time stamp for ith packet

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Work AccomplishedExperiments

• ti-1 is the receiver time stamp for (i-1)th
  packet
• and
• a is the time spacing for generation of two
  consecutive packets at sender.
• and bandwidth estimation
• Using pathload (a bandwidth measurement tool)3

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Work AccomplishedExperimentsRTT Variation
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Work AccomplishedExperimentsJitter (a1s)
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Work AccomplishedExperimentsJitter (a2s)
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Work AccomplishedExperimentsstatistics
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Work AccomplishedExperimentsBandwidth

• Using pathload3, we have measured the
  available bandwidth around 5 times. It was
  ranging from 2kbps to 4kbps depending on the time
  it was measured.
• Horde 2 measurement shows that it was around
  19kbps during day and 25kbps at nightvalidate it
  (a real point to be noted)

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Work AccomplishedExperimentsconcluding remarks

• High variability is giving us a clue that
  whatever is the architecture of inverse
  multiplexer, we need a sophisticated scheduling
  scheme for the best performance. And we need
  video splitting technique that is resilient to
  losses.
• Different levels of jitter is experienced for
  different values of a.
• The bandwidth estimation gap between our and
  Horde is pointing us towards
• Either our measurement methodology has problems
  or
• We need to work on the feasibility of Inverse
  Multiplexing in Pakistan.

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Work AccomplishedScheduling layer

• This layer provides
• Provide an interface to outer world in order to
  schedule packets
• Identify new GPRS devices and make connection
  with them using Bluetooth
• Maintains a list of available GPRS devices for
  scheduling purpose.

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Work AccomplishedScheduling layerMain Components

• Device Discoverer
• Channel Manager
• Scheduler
• Shell Scripts
• Used by the main components

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Work AccomplishedScheduling layerDevice
Discoverer

• Its responsibilities are
• To search new devices after periodic intervals
• To make connection with them
• To create a new routing table and rule for this
  particular interface
• And adding them to devices list

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Work AccomplishedScheduling layerChannel Manager

• Its responsibility is synchronize the device list
  to actual available channels
• It handles
• Removal of devices from the device list that
  disappeared
• Addition of some missing Blue channels

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Work AccomplishedScheduling layerScheduler

• Its responsibility is
• to queue the data transfer requests from above
  layer
• and schedule them to the available blue channels
  in a round robin fashion.

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Work AccomplishedScheduling layerScripts

• These scripts are used by other components to
  perform various tasks
• makeConnection.sh
• To make connection with the device just
  discovered. This is used by the Device Discoverer
• This scripts also releases the unused rfcomm
  devices
• getLastInterfaceDetails.sh
• To get the IP and other parameters of the current
  device we have made connection with. This is also
  used by the Device Discoverer

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Work AccomplishedScheduling layerScripts cont.

• getPPPInterfaces.sh
• This is used by the Channel Manager in order get
  all available blue channels at this particular
  time.
• init_alternate_route.sh
• This is also used by both, the Device Discoverer
  and Channel Manager, to create a separate routing
  table and rule for a blue channel.
• init_route.sh
• This is called at start of the program in order
  to initialize routing table for Ethernet
  interface (if any)

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Challenges Faced

• Following are some the challenges faced during
  the implementation of above layer
• How to make a GPRS connection using API. API
  selection, understanding it and using it for our
  purpose.
• I have used avetana Bluetooth stack and pppd to
  make a connection over rfcomm.
• How to use multiple default routes. As we have
  different links to internet.
• This is accomplished using ip utility in Linux.
  The idea is simple that we create a separate
  routing table for each interface and then make a
  rule to use that table if data originates from
  that particular interface.

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Future Work

• Following areas can be explored
• Experimenting with different video splitting
  techniques described above using the simple
  scheduling layer implemented above.
• Defining a better scheduling scheme that
  maximizes the performance of the inverse
  multiplexer. This include the rate control on
  different links to reduce packet loss

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References

• 1 Alex C. Snoeren, Adaptive Inverse
  Multiplexing for wide-area wireless networks,
  Proceedings of IEEE GlobeCom99
• 2 Qureshi A. and Guttag J., Horde Separating
  Network Striping Policy from Mechanism, ACM
  MOBISYS05
• 3 Manish Jain, Constantinos Dovrolis,
  Pathload A Measurement Tool for End-to-End
  Available Bandwidth, in Proceedings of 3rd
  Passive and Active Measurements Workshop, Fort
  Collins, March 2002.
• 4 Rajiv Chakravorty, Suman Banerjee, Samrat
  Ganguly, MobiStream Error-Resilient Video
  Streaming in Wireless WANs using Virtual
  Channels, Proceedings of IEEE Infocom 2006

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Questionif you still have any?