Multicast Protocols for Publish Subscribe Systems

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Multicast Protocols for Publish Subscribe Systems

• Ashwin R. Bharambe
• Hemamalini Manickavasagam

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Outline

• What is publish-subscribe ?
• Multicast in publish-subscribe systems
• Small Group Multicast
• Evaluation Methodology
• Results
• Conclusions

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What is publish-subscribe ?
Publications
Subscription

• Publishers produce events or publications
• Subscribers register their interests via
  subscriptions
• Network performs routing such that
• Publications meet subscriptions
• Publications get delivered to appropriate
  subscribers

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Why do we care ?

• De-coupling between senders receivers
• Advantages
• Permits heterogeneous components
• Interoperability
• Ideal for evolving software
• Fits many applications
• Stock tickers, instant messengers, etc.
• Multiplayer games!

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Architectures

• Centralized
• Rendezvous point based
• Core components
• Routing of publications and subscriptions
• Matching
• Delivery of publications

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Efficient publication delivery

• Publication needs to be delivered to some subset
  of subscribers
• Multicast!
• Problem
• Could be any subset
• Exponential multicast groups!
• How about the most naïve multicast strategy ?

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Small Group Multicast (SGM)

• Idea
• Send list of recipients along with every packet!
• High overhead if list is large, but
• More efficient than maintaining multicast group,
  if list is usually small
• Use Narada overlay as the backbone

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SGM

• SGM might send data to uninterested people
• Use Narada mesh to get a rough sense of direction
• Use recursive unicast starting from the closest
  guy

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Evaluation methodology

• Internet games as example of a publish subscribe
  system
• Workload
• Quake-II real life traces hard to find
• Introduced BOTs into Quake-II
• Supposed to be human-like
• Visibility box used as subscription

10
Simulation Infrastructure

• ns-2 all the way
• Ported Narada simulator to ns-2
• Implemented SGM, SGM over Narada

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Results (1/2)

• SGM overhead prop. to delivery group size
• Hovers around 4.5
• Very high fraction of packets are routed through
  nodes who are not interested!

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Results (2/2)

• Scaled with respect to Unicast
• As group size increases, SGM performs better
• Publication delivery group is usually small!

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Conclusions

• SGM
• Gives good resource usage
• Low overhead since delivery group sizes in games
  are typically small
• Well suited for games!
• Need workloads for characterizing other
  publish-subscribe systems