APPLICATION LAYER MULTICASTING BY D.Jayasakthi

Content The Evolution of Multicast Applications of Multicast IP Multicast Application Layer Multicast Application Layer Multicast Protocol Design Conclusion

The Evolution of Multicast Std IP Multicast Model 1988 1992 Multicast Backbone (MBone) Intra-Domain Multicast 1994 1997 Inter-Domain Multicast

Applications of Multicast Distance Learning A scene from the famous network game “Shrine of the Ancient” Multimedia conferencing

Data Delivery Unicast: Broadcast: Multicast: One source to one destination Broadcast: One 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 Distribute information to large audiences over an IP network

IP Multicast Source IP Multicast Router Receiver

Deployment Issues with IP Muticasting 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) 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 R1 R2 E1 E2 E3 Unicast

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 Application Domain Deployment Level Group Management Routing Mechanism

Application Domain 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 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 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 1: Shortest Path 2: Minimum Spanning Tree 3: Clustering Structure 4: Peer-to-Peer Structure

Shortest Path 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 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 This group constructs a cluster of nodes that can be used to construct trees.

Clustering Structure 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 In P2P structure, the routing is simply done through reverse- path 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 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 application- specific 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 "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.

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