Transcript APPLICATION-LAYER MULTICASTING

APPLICATION LAYER MULTICASTING
BY
D.Jayasakthi
Content
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The Evolution of Multicast
Applications of Multicast
IP Multicast
Application Layer Multicast
Application Layer Multicast Protocol Design
Conclusion
The Evolution of Multicast
1988
Std IP Multicast Model
1992
Multicast Backbone (MBone)
1994
Intra-Domain Multicast
1997
Inter-Domain Multicast
Applications of Multicast
Distance Learning
A scene from the famous network game
“Shrine of the Ancient”
Multimedia conferencing
Data Delivery
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Unicast:
 One
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Broadcast:
 One
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source to one destination
source to all destination
Multicast:
 One
source to many destinations(but not all)
 Many source to many destinations
Multi- Unicast
Unicast
Source
Router
Receiver
IP Multicast
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Distribute information to large audiences over an IP
network
IP Multicast
IP Multicast
Source
Router
Receiver
Deployment Issues with IP Muticasting
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IP Multicast-capable routers need to be installed at all levels of the network
(from backbone to edge routers) for the multicasting service to work.
There also exist management and security issues related to the deployment of
IP Multicast:
 The ease of flooding attacks via multicasting
 Unauthorized reception of data from a multicast session
 Preventing allocation of same multicast address for two sessions
 The difficulty of setting up firewalls while allowing multicasting.
The lack of network-level support for multicasting has thus led researchers and
commercial entities to seek alternative ways of multicasting at the application
layer.
Application Layer Multicasting(ALM)
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IP Multicast is not globally deployed.
Application Layer/Level Multicast (or Overlay Multicast) is hence
proposed.
 Multicasting implemented at end hosts instead of network
routers
 Nodes form Unicast channels or tunnels between them
S
E1
Unicast
Unicast
E2
R1
R2
Unicast
E3
ALM Benefits
• Easy to deploy
– No change to network infrastructure
• Programmable end-hosts
– Overlay construction algorithms at end hosts can be easily
applied
– Easier maintenance.
IP Multicast vs. ALM
IP Multicast vs. ALM
APPLICATION LAYER MULTICAST
PROTOCOL DESIGN
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Application Domain
Deployment Level
Group Management
Routing Mechanism
Application Domain
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Different classes of applications have different sets of
requirements regarding Reliability, Latency, Bandwidth, and
Scaling. Such requirements in turn determine the design choices
of ALM protocol regarding the group management mechanism
it deploys.
The application domain therefore influences the ALM protocol.
Deployment Level
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2 levels of Deployment:
 Infrastructure
Level
 End System Level
Group Management
How to manage a group of nodes in a multicast session?
 Basic group management:
 How users find out about multicast sessions?
 How they join a session?
 How they leave?
 Centralized or Distributed way
 Mesh-first approach or a Tree-first approach
 Source Specific Tree or Shared Tree
 Whether the protocol will take advantage of existing IP
Multicast islands?
 Whether it is necessary to refine the multicast tree to improve
performance?
Routing
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Design of the routing mechanism typically involves a (heuristic)
solution to a graph theory problem.
The most important is the routing mechanisms.
Some Common approaches to the routing mechanism are
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1: Shortest Path
2: Minimum Spanning Tree
3: Clustering Structure
4: Peer-to-Peer Structure
Shortest Path
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The aim is to construct degree constraint minimum diameter
spanning tree
A Shortest Path Tree (SPT) constructs a minimum cost path from
a source node to all its receivers.
Minimum Spanning Tree
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Given a graph with a cost associated with each edge (usually
delay), a Minimum Spanning Tree (MST) is a tree with minimum
total cost spanning all the members
2
Clustering Structure
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This group constructs a cluster of nodes that can be
used to construct trees.
Clustering Structure
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In order to better organize the overlay tree and reduce control
message overhead, some ALM protocols such as ZIGZAG and
NICE construct a hierarchical cluster of nodes.
The advantage of a hierarchical clustering approach to
multicast tree routing is the reduction in control overhead and
faster joining.
Peer-to-Peer Structure
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In P2P structure, the routing is simply done through reversepath forwarding or forward- path forwarding or in some cases
a combination of both type.
The advantage of these approaches includes low control
overhead and distributed management of the multicast tree
but they do not restrict the degree of each node and are
suboptimal.
Conclusion
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Compared to IP multicasting, ALM has certain disadvantages such as
longer delays and less efficient traffic generation.
However, due to its overwhelming advantages for certain
applications, such as immediate deploy-ability and applicationspecific adaptation, it can be a practical solution to many of the
existing problems in multi-user communications.
The fact that an ALM protocol can be developed and deployed on
the Internet without the need to make any changes to the existing
network infrastructure, and the ability to evolve and apply
modifications to the protocol quickly and easily at the application
layer has helped the ALM approach to have a quicker start
compared to other multi-user communications solutions.
References
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"A Survey of Application-Layer Multicast Protocols", Mojtaba Hosseini,
Dewan Tanvir Ahmed, Shervin Shirmohammadi, Nicolas D. Georganas, IEEE
Communications Surveys & Tutorials, Vol. 9, no. 3, July 2007, pp. 58-74
S. Deering and D. Cheriton, “Multicast Routing in Datagram Internetworks
and Extended LANS,” ACM Trans. Comp. Syst., vol. 8, no. 2, 1990, pp. 85–
111.
C. Diot et al., “Deployment Issues for the IP Multicast Service and
Architecture,” IEEE Network Mag., vol. 14, no. 1, 2000, pp. 78–88.
Thank You