Course Matters

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Course Matters
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Recent Papers

• from journals

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Good PostersBad Posters
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Improving I/O Performance of Intermediate
Multimedia Storage Node

• Pal Halvorsen
• Thomas Plagemann
• Vera Goebel
• Multimedia Systems 03

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Problem

• Improve the performance of I/O in integrated
  multimedia storage node
• 3 areas of improvement are identified
• reduce memory copy
• checksum computation
• FEC computation

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Reduce Memory Copy

• File system maintain pointer to an area in memory
• Communication system maintain pointer to same
  area in memory
• Memory copy avoided!

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Network Level Framing

• Packet payloads are stored with checksum
• When packets are retrieved for sending,
  destination address in header is updated
• Checksum is updated with new destination
• No need to recompute checksum for payload

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Integrated Error Management

• Data are stored on RAID-4 (single parity checks)
• Use the same error correcting code for RAID and
  packets
• Avoid multiple computation of error correcting
  code

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Experiment Memory Copy

• Read 28662512B file 38 times in a loop
• The time to transmit data through the storage
  node is reduced by 45-50 when there is no CPU
  load, and by 70-73 when CPU load is high

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Experiment Network Level Framing

• Transmit 255MB file
• Time to calculate checksum is reduced by 95-99
• Time spent in kernel is reduced by 51-61

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Experiment Integrated Error Management

• With encoding FEC, the maximum throughput is
  22-24 Mbps.
• Without encoding FEC, the maximum throughput is
  1Gbps

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Lets try again..
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Improving I/O Performance of Intermediate Media
Storage Node

• Pal Halvorsen
• Thomas Plagemann
• Vera Goebel

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Contributions

• Improve performance by
• reducing memory copy
• reducing checksum computation
• reducing ECC computation

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Reduce Memory Copy

• One shared copy of data for different OS
  component

Memory
Network System
File System
data
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Network Level Framing
store payload with payloads checksum
1
3
update header and checksum
2
read payload with checksum

• Reduce time to packetize data and compute
  checksum for data

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Integrated Error Management
reuse RAID ECC as ECC packet
RAID
ECC
data
data
data
ECC

• Avoid multiple computation of error correcting
  code

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Results Zero Copy
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Results Network Level Framing
Accumulated UDP Protocol Execution Time for
sending 225MB file
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Results Integrated Error Management
With ECC Encoding Without ECC Encoding
22-24 Mbps 1 Gbps
Maximum Throughput with/without Encoding
using Cauchy-based Reed Solomon Erasure Code
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Ad Hoc Networks

• Session 1

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Mobile Ad Hoc Network
Radio
Router
Host
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Animation

• http//www-i4.informatik.rwth-aachen.de/mesut/man
  et/manet_en.html

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Mobile Ad Hoc Network
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Examples

• Battlefield
• Highway
• Disaster Zone

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Challenges

• All the difficulties of wireless LAN
• Plus
• Nodes can move
• Connections can go up/down
• No fix route

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Two Papers

• IEEE JSAC
• Special Issues in Wireless Multimedia
• Baochun Li from U. of Toronto
• Shiwen Mao from Polytechnic U.

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NonStop Continuous Streaming Service on MANET

• Baochun Li
• IEEE JSAC 2004

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Streaming over MANET
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Network Partition Problem
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Only Solution ..

• Predict Partition
• Replicate Service

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Partition Prediction
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Network Partition Problem
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How to Predict Partition?

• given velocity of each node
• cluster nodes into mobile groups
• find mean group velocity

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Clustering Algorithm
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Clustering Algorithm
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Clustering Algorithm
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Clustering Algorithm
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Choosing Server
?
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How to Choose Server?

• find stable group
• choose server within stable group with the most
  similar velocity

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Stable Group
probability
A
B
distance
mean lt radio range and variance is not too large
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Stable Group
B
A
C
H
D
G
E
F
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Stable Group
BCD are in my group
AGH are in my group
B
A
C
H
D
G
E
F
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Stable Group
BCDGH are in my group
ABDGH are in my group
B
A
C
H
D
G
E
F
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How to Choose Server?

• find stable group
• choose server within stable group with the most
  similar velocity

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Summary

• Server construct mobile group by clustering nodes
  using velocity
• Use mean mobile group velocity to predict network
  partition
• Replicate service before partition to ensure
  continuous service

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Summary

• Node construct stable group by comparing distance
  over time
• Choose server within stable group with most
  similar velocity

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Multipath Transport and Multistream Coding for
MANET

• Shiwen Mao et. al.
• IEEE JSAC

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Single Path Transport
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Multipath Transport
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Multipath Transport
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Video Coding 1 of 3
I
P
P
P
P
P
P
P
Typical Frame Dependency
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Video Coding 1 of 3
I
P
P
P
I
P
P
P
Multistream Coding
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Dynamic Reference Frame

• Choose last received frame as reference

believed to be received
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Predict Network States
GOOD )
NACK
ACK
BAD (
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Example
ACK0
ACK2
ACK4
ACK6
0
2
4
6
8
10
1
3
5
7
9
NACK1
NACK3
NACK5
ACK7
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Video Coding 2 of 3
I
P
P
P
Enhancement Layer
I
P
P
P
Base Layer
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Video Coding 2 of 3
BL
S
D
EL
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Video Coding 2 of 3
NACK
NACK
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Video Coding 2 of 3
S
D
BL
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Video Coding 3 of 3

• Multiple Description Coding

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MDMC

• MDMC

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Example of MDMC
359
363
370
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Typical Reference Frame
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Example of MDMC
359
363
370
MDMC Reference Frame
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Example of MDMC
359
363
9
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Example of MDMC
359
?
9
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Example of MDMC
361
359
363
370
9
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Example of MDMC
359
?
9,2
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Comparisons
Reference Frame LayeredCoding MDMC
Feedback
Buffer
Decoding Delay
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Improving Multicast

• Session 2

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Organizing Multicast Receivers

• Brian Neil Levine
• Sanjoy Paul
• JJ Garcia-Luna-Aceves
• Multimedia Systems 03

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Retransmission in Mcast
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Idea

• Ask a neighbour for a missing packet

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Helper Tree
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Pick Helper By Hop
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Pick Helper by Hop

• Not entirely accurate
• Need to consider latency, link condition etc.

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Pick Neighbour By Latency
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Pick Helper by Latency

• How to measure latency?
• unicast?
• multicast?
• shared-tree? per-source tree?

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Ideal Location of Helper

• share a common path, and is closer to source
  (acceptable)

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Idea

• Suppose node A and B know their path back to the
  source, then they can deduce if A is acceptable
  to help B

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MTrace
D
F
A
B
C
H
G
I
E
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ERS
my path is ABCDF
D
F
A
B
C
H
G
I
E
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ERS
D
F
A
B
C
H
G
I
E
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Respond if

• acceptable
• not too many helpee

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Picking Helper

• packet loss measurement

10
30
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Maintenance

• Periodic refresh states (soft-states)
• Periodic repeat procedure

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Summary

• Organized receivers based on common path
• Enable peer-to-peer retransmission

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THE END