DyRAM: Dynamic Replier Active reliable Multicast

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DyRAM Dynamic Replier Active reliable Multicast

• Moufida Maimour and C. D. Pham
• INRIA-RESO
• RESAM UCB-Lyon ENS Lyon

ISCC02, Taormina

• Tuesday, July 2nd, 2002

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Outline

• Introduction
• The DyRAM protocol
• Protocol description
• Some simulation results
• Preliminary experimantal measurements
• Conclusions

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Introduction

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

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Local Recovery What and Why

• Packets retransmission is performed by an other
  entity (replier) instead of the source
• It mainly,
• unloads the source from retransmissions,
• reduces the end-to-end delay,
• reduces bandwidth consumption,

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Local Recovery How

• The replier can be
• Any receiver in the neighborhood SRM.
• A parent receiver in a hierarchical structure
  (static RMTP or dynamic TMTP,TRAM ).
• Problem the lack of topology information at the
  end hosts.
• Solution router-assisted schemes

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Active Local Recovery ARM

• routers perform cache of data packets
• repair packets are sent by routers, when
  available

data
data
data5
data1
data2
data1
data3
data2
data4
data3
data5
data4
data5
data4
data1
data2
data3
data5
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However

• Routers caching means are limited.
• Routers have to support many sessions in
  parallel.
• Question
• How the memory usage at the routers can be
  reduced ?
• Answer
• Perform the local recovery from the receivers
  with the help of the routers DyRAM.

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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

• Global 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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Some Simulation results
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Network Model
10 MBytes file transfer
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Local recovery from the receivers (1)
4 receivers/group

• Local recoveries reduces the end-to-end delay
  (per packet)

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Local recovery from the receivers (2)

• As the group size increases, doing the recoveries
  from the receivers greatly reduces the bandwidth
  consumption

48 receivers distributed in g groups ? grp 224
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DyRAM vs ARM

• ARM performs better than DyRAM only for very low
  loss rates and with considerable caching
  requirements

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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 perspectives

• Reliability on large-scale multicast session is
  difficult. Active services at the edges can
  provide efficient solutions for reducing
  implosion 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.

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A reference

• http//www.ens-lyon.fr/LIP/RESAM