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ShapeShifter: Scalable, Adaptive EndSystem Multicast

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John Byers, Jeffrey Considine, Nicholas Eskelinen, Stanislav Rost, Dmitriy Zavin. Listed alphabetically. Computer Science. 2. Computer Science. Problem ... – PowerPoint PPT presentation

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Title: ShapeShifter: Scalable, Adaptive EndSystem Multicast


1
ShapeShifter Scalable, Adaptive End-System
Multicast
  • John Byers, Jeffrey Considine, Nicholas
    Eskelinen, Stanislav Rost, Dmitriy Zavin
  • Listed alphabetically

2
Problem
  • Problem efficient delivery of popular bulk
    content
  • Existing Approaches
  • Single-source unicast
  • Forward caching/Content Delivery Networks
  • Reliable IP Multicast
  • End-system multicast
  • Our approach
  • Improving end-system multicast through the use of
    forward error correction and better topologies

3
Network-supported (IP) Multicast
  • Optimal solution duplicates and disseminates
    data only when necessary
  • Relies on network support in the real world, IP
    Multicast lacks deployment
  • Scalability concerns per-group accounting and
    topology management do not scale due to limited
    router resources
  • Reliability many proposals, few solutions

4
End-System Multicast
  • Does not rely on network support builds and
    manages a virtual, overlay topology of unicast
    links on top of the networks physical topology
  • Flexibility optimization of the tree according
    to a richer set of metrics (perhaps specified by
    the application), ability to change topology
    on-demand
  • Improved scalability end-systems are richer
    than routers in terms of dedicated resources
  • Problems increased network resource
    requirements compared to IP Multicast,
    non-optimal mapping of the virtual topology onto
    physical topology

5
Related Work
  • Narada/End-System Multicast Build and maintain
    a mesh of low-latency unicast links and use its
    minimal spanning tree for distribution. Also
    showed costs relative to IP Multicast are not
    excessive.
  • Overcast A core group of well-placed nodes uses
    end-system multicast to distribute bulk content
    internally, in order to eventually provide it to
    clients. A node chooses a parent based on
    bandwidth through the candidate nodes using the
    number of network hops as a tie breaker.

6
Improvements in ShapeShifter
  • Erasure codes improved overlay management, more
    connected graph structure, increased adaptivity
  • Scalable group management a node need only be
    aware of a small portion of the graph but
    achieves coverage through continuous discovery
  • Measurements metrics crucial to optimization of
    the overlay graph, such as shared-link congestion
    (refer to Khaleds presentation)

7
Forward Error Correcting Codes
  • FEC codes a well-known solution to dealing with
    packet loss without using feedback instead of
    retransmitting packets, redundant packets are
    sent combining the original packets to recover
    from losses. e.g. x, y, xy, a, b, abx
  • Efficient codes instead of the traditional slow
    Reed-Solomon codes, we use a variant of Tornado
    codes. This allows fast decoding while only
    requiring a small number of extra packets.
  • Strategy the original server sends out FEC
    packets along the end-system multicast graph (à
    la Digital Fountain).

8
Recoding
  • Problem
  • Correlation client nodes may have a high degree
    of correlation in information received due to
    common sources
  • Duplication given correlation, duplicate
    packets received from client nodes can be
    ineffectual
  • Solution
  • Recoding nodes blend received packets to
    generate new, high utility symbols for other
    nodes
  • Beyond trees recoding allows non-tree
    topologies since duplication is avoided

9
Uncorrelated Loss Compensation
Loss Rate30
Loss Rate5
  • A neighbor node with greater throughput may
    supplement the flow of content to another node,
    circumventing the problematic physical link.

10
Download from Multiple Nodes in Parallel
1 MB/s
1 MB/s
1 MB/s
1 MB/s
Non-uniform dissemination of content
  • Well-connected
  • newcomer scenario

11
Resilience To Partitioning
Partition avoidance through discovery and
awareness of multiple candidates
  • Collaborative
  • Reconstruction

12
Future Work
  • Implementation underway
  • More analysis of
  • Codes and correlation
  • Graph management
  • Security issues
  • Testing
  • WAN, simulated and real
  • Mobile environments
  • Extensions to streaming media
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