A%20loss%20detection%20Service%20for%20Active%20Reliable%20Multicast%20Protocols

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A loss detection Service for Active Reliable
Multicast Protocols

• Moufida MAIMOUR C. D. PHAM
• INRIA-RESO
• RESAM UCB-Lyon ENS Lyon

Tuesday, July 16th, 2002
INC02, Plymouth
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Outline

• Introduction
• The DyRAM protocol
• The active loss detection service
• An active-based reliable multicast architecture
• Some results (analysis, simulation,
  implementation)
• Conclusion

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From unicast
Sender

• Problem
• Sending same data to many receivers via unicast
  is inefficient.

data
data
data

data
data
data
Receiver
Receiver
Receiver
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to multicast on the Internet.
Sender

• Problem
• Sending same data to
• many receivers via
• unicast is inefficient.

data
data
data

• Solution
• Using multicast is
• more efficient

data
Receiver
Receiver
Receiver
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Reliable multicast

• At the routing level IP Multicast provides
  efficient delivery without any reliability
  guarantees.
• Many multicast applications require reliability.
• Reliability has to be addressed at a higher level.

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Reliable multicast protocols

• End-to-end solutions
• Only the end hosts (the source and/or the
  receivers) are involved.
• In-network solutions
• Routers are involved in the recovery process.
• Active routers-based solutions

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What are active routers ?

• Active routers are able to perform customized
  computations on the messages flowing through them.

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DyRAM main characteristics

• DyRAM is based on active services
  (router-assisted).
• the recovery is performed from the receivers (no
  data cache at the routers)
• A recovery tree is constructed on a per-packet
  basis via a replier election mechanism.
• Use of NACKs combined with periodic ACKs.

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Main Active Services in DyRAM

• NACK suppression
• Subcast of repair packets
• Dynamic replier election

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NACKs suppression
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Replier election and subcast
D0
DyRAM
0
2
1
D1
DyRAM
Repair 2
R1
1
0
R2
R3
R4
R5
R7
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The active loss detection service
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The active loss detection implementation

• The Track List (TL) structure which maintains for
  each multicast session,
• lastOrdered the sequence number of the last
  received packet in order
• lastReceived the sequence number of the last
  received data packet
• lostList list of not received data packets in
  between.

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The active loss detection implementation (cont.)

• On reception of a data packet with a sequence
  number seq gt TL.lastOrdered1
• for each lost data packet (TL.lastOrdered lt
  lostseq lt seq lostseq ? TL.lostList),
• send a NACK for lostseq toward the source.
• ignore similar NACKs from downstream links for a
  given period.

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Where to place the active routers ?
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ISDN xDSL
PSTN
GSM, UMTS
10Mbits/s
core network Gbits/s
Server
100Mbits/s
wireless LAN 1Mbits/s, 10MBits/s
visio-conferencing
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Location of the loss detection-capable routers

• The loss detection service should be located not
  too far from the source so the corresponding
  overhead is justified !

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Specialized active routers architecture
source
The active router associated to the source can
perform early processing on packets.
core network Gbits rate
A hierarchy of active routers can be used for
processing specific functions at different layers
of the hierarchy NACK suppression, subcast,
replier election.
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Simulation model
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Simulation results
grp 624
4 receivers/group
p0.25
grp 624
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DyRAM implementation

• Tamanoir execution environment
• Java 1.3.1 and a linux kernel 2.4
• A set of receivers and 2 PC-based routers
  (Pentium II 400 MHz 512 KB cache 128MB RAM)
• Active processing cost of a
• data packet 20 micro sec
• NACK packet 135 micro sec
• repair packet 123 micro sec

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Conclusion future work

• Reliability on large-scale multicast session is
  difficult. Active services at the edges can
  provide efficient solutions for reducing
  implosion, recovery delays and exposure problems
  and so achieving scalability.
• Optimizing the replier election based on an
  estimation of the receivers power (by means of
  BW, delay )
• A congestion control is currently under
  evaluation and will be integrated into DyRAM in
  the near future.