Application-Layer Multicast -presented by William Wong

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Application-Layer Multicast-presented by William
Wong
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Outline

• Introduction
• Multicast Tree Formation
• Performance Metrics
• Protocol Examples
• Conclusion

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Outline

• Introduction
• IP Multicast vs. Application-Layer Multicast
• Limitations of IP Multicast
• Advantages of application-Layer Multicast
• Multicast Tree Formation
• Performance Metrics
• Protocol Examples
• Conclusion

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IP Multicast vs. Application-Layer Multicast
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Limitations of IP Multicast

• Difficult to support high level functionalities
  on upper layer
• E.g. congestion control, reliability
• Network and receiver heterogeneities
• Routers need maintain per-group state
• Limited multicast addresses ( class D only)

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Advantages of Application-Layer Multicast

• Easy to support high level functionalities
• Make use of end-host resource (e.g. memory,
  process power) to make a more sophisticated
  decision
• Make use of the existing solutions for unicast
  congestion control and reliability
• Able to modify the content of data
• Does not need router support
• Unlimited multicast addresses

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Outline

• Introduction
• Multicast Tree Formation
• Tree-first approach
• Mesh-first approach
• Others
• Performance Metrics
• Protocol Examples
• Conclusion

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Tree-first Approach

• Constructs a multicast tree directly.
• Members explicitly select their parents.
• Single multicast tree constructed.

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Tree-first Approach Components

• Initial join
• Learn other members locations
• Multicast tree formation
• Loop avoidance and partition avoidance
• Multicast tree maintaince
• Adaptive to network dynamics

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Tree-first Approach Examples

• Overcast
• Build a single source multicast tree that
  maximize the bandwidth from the source to the
  receivers
• Yoid
• A tree is constructed for data delivery, while a
  mesh is constructed for control messages
  exchanging.
• Jungle Monkey
• Build a single source multicast tree for file
  transferring
• ALMI
• Build a single source multicast tree in single
  server and then distributes it.

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Mesh-first Approach

• Members are connected to form a richer connected
  graph, termed a mesh
• Members exchange information on the mesh
• Construct shortest path spanning trees of the
  mesh with routing protocols e.g. DVMRP

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Mesh-first Approach Components

• Initial join
• Learns other members locations
• Mesh formation
• Partition avoidance
• Mesh maintaince
• Adaptive to network dynamics
• Improve the mesh quality
• Multicast tree formation
• Constructs per-source spanning tree with routing
  protocol

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Other Mesh-first Examples

• Narada
• Creates a mesh and then build multicast trees
  with DVMRP algorithm.
• Scattercast
• Proxy servers are placed at strategic location.
  These proxy servers self-organize into multicast
  trees.

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Other Approaches

• Completely ignores the network-layer
  infrastructure.
• Example
• Application-layer Multicast with Delaunay
  Triangulations
• Each nodes route multicast packet based on their
  geometric coordination only.

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Outline

• Introduction
• Protocol Examples
• Performance Metrics
• Application perspectives
• Network perspectives
• Adaptiveness to network dynamics
• Failure Tolerance
• Scalability
• Conclusion

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Application Perspectives

• Directly affect the performance of application
• Examples
• Bandwidth and latency
• Startup time
• End-host resource usages

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Bandwidth and Latency

• Measure the mean and the standard deviation
  versus rank

• Examples
• Experiment 1
• 1200, 1200, 1000, 800.
• Experiment 2
• 1400, 1400, 600, 400.
• Experiment 3
• 1000, 800, 800, 600
• Means
• 1200, 1133, 800, 600

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Startup Time

• Time required to stabilize the multicast tree

Stabilized
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End-host Resource Usages

• Memory
• Disk Storage
• Computation Power

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Network perspectives

• Affect other network user indirectly
• Examples
• Resource usages
• Stresses of physical links
• Protocol overhead

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Resource Usages

• Sum of the costs (e.g. delay) of the overlay
  links

1
2
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1
1
25
A
B
2
2
1
1
4
3
Resource Usages 2 27 2 31
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Stresses of Physical Links

• Number of identical copies of a packet traverse a
  physical link

Stress of physical link 1-A is 2
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Protocol overhead

• Protocol overhead Total non-data traffic /
  total data traffic
• Non-data traffic
• Control messages
• Network measurement messages

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Adaptiveness to Network Dynamics

• When some of the nodes/links are failure, the
  time required to discover, react and repair that

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Discover, React and Repair Time

• Discover
• Duration from nodes/links failure to detection of
  link degradation.
• React
• Duration from detection of link degradation to
  the first change of multicast tree
• Repair
• Duration from the first change of multicast tree
  to the change which fully recover the multicast
  tree quality

Link failure
Detected
First attempt
Last attempt
Discover Time
React Time
Repair Time
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Failure Tolerance

• Single point of failure
• E.g. rendezvous point (RP)
• Impact of large number of nodes/links failure
• The fraction of hosts that correctly receive the
  data packets sent from the source

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Scalability

• Time and resources used to construct a large
  multicast tree
• Scalability maybe limited by
• Routing algorithm
• Control message size
• Protocol overhead

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Outline

• Introduction
• Multicast Tree Formation Protocols
• Performance Metrics
• Existing Protocols
• Overcast
• Narada
• Conclusion

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Overcast Jannotti 88

• It is motivated by real-world problems faced by
  content providers.
• Characteristics of the target applications
• Millions of users
• Requires high bandwidth
• Not latency sensitive

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OvercastMulticast Tree Formation

• Single Source, which located at root
• Always contact the root of multicast tree first
• Use bandwidth as link-cost metric only.
• Move the newly joined node as far way from the
  root as possible without sacrificing bandwidth to
  the root

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OvercastNodes repositioning

• Periodically reevaluates its position in the
  tree.
• Measure the network condition actively

E send 10KB data to D (sibling), B (parent) and
R (grandparent) to find the best parent.
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OvercastNodes repositioning

• Each node keep their ancestor list. These
  ancestors serve as backup parents.

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OvercastLoop avoidance

• Keeps an ancestor list to avoid loop formation

Reject any connection request from nodes in the
ancestor list R,B,E
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OvercastPerformance

• Application prespectives
• High bandwidth, long latency
• Network prespectives
• High protocol overhead due to active measure.
• Not adaptive to network dynamic well
• Node moves locally.
• Low failure tolerance
• Single Point of failure
• High scalability
• Only local information need

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Narada Yang-hua Chu 2000

• It is motivated by real-world problems faced by
  conferencing applications
• Characteristics of the target applications
• Small number of users
• Require high bandwidth
• Latency sensitive

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NaradaMesh Formation

• No rendezvous point
• Contact anyone of group member to join
• Learn the location of our member by exchanging
  control messages
• Randomly select a few group members to be its
  neighbor.

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NaradaMesh Maintance

• Measure the network condition actively and
  passively

The bandwidth and latency are measured actively.
Sent data through the link to determine its
bandwidth and latency
The bandwidth and latency are measured passively
by monitoring the data flow along them.
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NaradaMesh Maintaince

• A mesh is a richer connected graph, such that it
  includes all members with cycles.
• The quality of mesh keep improving by adding
  useful link and drop not useful link.

The link E-G is not very useful, not much
packets would route though it It will be dropped
C
B
D
A
E
The link A-G would be added. It improve the
delay from A/B/C to E/F/G
F
G
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NaradaUtility of a link

• The degree of improvement to tree latency
• Algorithm
• Utility 0
• For each member m (m not i) begin
• CL current latency between i and m along mesh
• NL new latency between I and m along mesh if
  edge i-j were added
• If (NL lt CL) then begin
• utility ( CL NL) / CL
• End
• End
• Return utility

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NaradaConsensus Cost of a link

• Frequency of being used
• Formal definition
• Cost i-j number of members for which i uses j
  as next hopt for forwarding packets.
• Cost j-i number of members for which j uses i
  as next hop for forwarding packets.
• Cost max(cost i-j, cost j-i)

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NaradaMulticast Tree Formation

• Runs a distance vector protocol on top of the mesh

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NaradaMulticast Tree Formation

• Runs a distance vector protocol on top of the
  mesh
• The per-source trees are constructed from the
  reverse shortest paths between each recipient and
  the source.

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NaradaLink Cost

• Use bandwidth and latency as link-cost metric at
  the same time
• Shortest widest path algorithm used
• Pick the widest paths to every other member
• Then choose the shortest path among all widest
  path

This path is selected
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NaradaPerformance

• Application prespectives
• High bandwidth, short latency
• Network prespectives
• Low resource usage, low stress of physical link
• Adaptiveness to network dynamics
• Depends on the probing frequency
• Low scalability
• A global information is need for the routing
  algorithm
• High failure tolerance
• No single-point of failure

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Outline

• Introduction
• Multicast Tree Formation Protocols
• Performance Metrics
• Existing Protocols
• Conclusion

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Conclusion

• Two multicast tree formation approaches
• Tree-first approach
• Mesh-first approach
• Five performance metrics
• Application perspectives
• Network perspectives
• Adaptiveness to network dynamics
• Failure Tolerance
• Scalability

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QA