A Comparison of Application-Level and Router-Assisted Hierarchical Schemes for Reliable Multicast Pavlin Radoslavov Christos Papadopoulos Ramesh Govindan Deborah Estrin - PowerPoint PPT Presentation

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A Comparison of Application-Level and Router-Assisted Hierarchical Schemes for Reliable Multicast Pavlin Radoslavov Christos Papadopoulos Ramesh Govindan Deborah Estrin

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Title: A Comparison of Application-Level and Router-Assisted Hierarchical Schemes for Reliable Multicast Pavlin Radoslavov Christos Papadopoulos Ramesh Govindan Deborah Estrin


1
A Comparison of Application-Level and
Router-Assisted Hierarchical Schemes for Reliable
MulticastPavlin RadoslavovChristos
PapadopoulosRamesh GovindanDeborah Estrin
  • Reviewer Jing Lu, Qian Wan

2
Outline
  • Introduction
  • ALH RMTP
  • RAH LMS
  • Metric Space
  • Analysis Using k-ARY Trees
  • Simulation Results
  • Conclusion

3
IP Multicast
  • Send packet from a source to the members of a
    multicast group.
  • Class D IP addresses (250 million)
  • IGMP MOSPF
  • Best-effort packet forwarding
  • Applications multimedia, teleconferencing,
    distributed computing, etc.

4
Reliable IP Multicast
  • Scalability issues
  • Implosion redundant messages triggered by packet
    loss
  • Exposure redundant retransmissions to receivers
    who haven't experienced loss
  • Long recovery latency
  • Hierarchical data recovery schemes
  • ALH (Application-Level Hierarchical) End systems
    assist in hierarchy creation and maintainance.
  • RMTP
  • RAH (Router-Assisted Hierarchical) Routers
    assistance
  • LMS

5
RMTP Data Recovery
  • Static hierarchical scheme
  • Designated Receivers (DRs) are chosen statically
  • A receiver dynamically chooses a closest DR as
    its Ack and retransmission processor
  • A DR collects Nack from its local group members
    and retransmits packet within the group using
    unicast/multicast
  • A DR emits its own Nack to its parent DR in the
    upper hierarchy
  • Sender deals with Nacks from DRs at the top level
    hierarchy

6
ALH Data Recovery
  • Optimal Hierarchy

7
ALH Data Recovery
  • Optimal Hierarchy

8
ALH Data Recovery
  • Sub-optimal Hierarchy

sender
R1
Rx7
Rx1
Rx8
R2
Rx2
R3
R4
Rx3
Rx4
Rx5
Rx6
9
ALH Data Recovery
  • Sub-optimal Hierarchy

sender
R1
Rx7
Rx1
Rx8
R2
Rx2
R3
R4
Rx3
Rx4
Rx5
Rx6
10
Heuristic Dynamic Hierarchy Creation in ALH
  • Each receiver obtains distance info to each other
  • Dynamically create the hierarchy from bottom-up
  • Initially all receivers are eligible to become
    parents
  • A fraction (fracpc) of receivers with the
    smallest sum of distances becomes parents.
  • Receivers that are not elected choose the closest
    parent as its parent.
  • Repeat the selection process among receivers
    chosen from the previous iteration until the
    number of receivers left lt 1/fracpc, so their
    parent is the sender itself.

11
LMS Data Recovery
  • LMS extends router forwarding
  • Enhance routers to
  • Replier selection
  • Forward Nacks to replier and discover root of
    loss subtree
  • Perform DMCAST

12
LMS Replier Selection
sender
  • Router state per-source tree
  • Upstream link
  • List of downstream links
  • Replier link id

R1
Rx7
Rx1
Rx8
R2
Rx2
R3
R4
Rx3
Rx4
Rx5
Rx6
13
LMS Nack Forwarding
LMS router handles Nacks 1
14
LMS DMCAST
  • DMCAST
  • Replier encapsulates a multicast packet into a
    unicast packet and sends to the turning-point
    router
  • LMS router decapsulates and multicasts it on the
    specified link interfaces

15
LMS Enhanced Two-Step DMCAST
  • Nack from a downstream replier specifies reply
    should be unicast back to it rather than to its
    turning point
  • Replier then performs DMCAST when necessary

16
Summary of ALH and RAH
ALH RAH
Automatic creation of data recovery hierarchy End-to-end mechanism and heuristic algorithm Router selects the closest downstream receiver as replier
Retransmission Parent unicasts/multicasts recovery data to its group members Replier unicasts recovery data to turning-point router, router multicasts it directly on specified links
  • RAH is finer-grained with many more internal
    nodes
  • RAH is more congruent to the underlying
    multicast tree
  • RAH doesnt have explicit group concept, so it
    is easily adaptive to membership change
    membership maintenance cost is minimal

17
Metric Space
  • Data Recovery Latency
  • Receiver Exposure
  • Data Traffic Overhead
  • Control Traffic Overhead

18
Data Recovery Latency
Loss Rcvs lat RTT
Rx2 6 8
Rx3 8 10
Rx4 8 10
Rx5 8 10
Rx6 8 10
NormLat 0.79 0.79
19
Receiver Exposure
Loss Rcvs Exposure
Rx2 0
Rx3 0
Rx4 0
Rx5 0
Rx6 0
NormExp 0
20
Data Traffic Overhead
Loss Rcvs Data Subtree
Rx2 3 8
Rx3, Rx4, Rx5, Rx6 7 8
NormDataOverhead 1.25 1.25
21
Control Traffic Overhead
Loss Rcvs Control Subtree
Rx2 3 8
Rx3 3 8
Rx4 3 8
Rx5 3 8
Rx6 3 8
NormLat 1.875 1.875
22
Analysis using k-ARY Tree
  • Purpose
  • Gain initial understanding of the scalability of
    the ALH and RAH schemes
  • Parameters
  • k, L
  • q fraction of leaf nodes that are receivers is
    1/kq-1
  • Assumptions
  • Each parent (ALH) has k-1 children.
  • Single link loss and average per link-loss
    across all links

23
Analysis using k-ARY Tree
  • ALH
  • RAH

24
Control Overhead Analysis
L 10
25
Data Overhead Analysis
L 10
  • RAH is slightly better than ALH
  • In some cases, RAH replier multicast data to all
    receivers within a subtree
  • ALH has to perform multiple multicasts within
    local groups

26
Data Recovery Latency Analysis
27
Data Recovery Latency Analysis
L 10
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