Real-time optimal multicast routing
Introduction
Multicasting is a communication service that allows an application to efficiently transmit copies of a data packet to a set of receivers that are members of a multicast group. The group is identified by a location independent multicast group address. Senders use this address in the destination field of the packet; multicast routers forward the packet to group members using routing table entries for this address. The entries form a tree, which may be a source-based tree (SBT) or a center-based tree depending on the multicast routing protocol. Multicast group members may be spread across separate physical networks, they may join and leave a group during the life of the group, and they may be members of multiple groups. Multicast routing has been performed by a multicast-capable, virtual network running on top of the Internet called the multicast backbone ‘Mbone’. The Mbone uses the distance vector multicast routing (DVMRP) or the multicast extensions for open shortest path first protocol (MOSPF) to route multicast traffic. Common uses of multicasting include audio and video conferencing, distributed interactive simulation (DIS) activities such as tank battle simulations, and exchanging experimental data and weather maps. DVMRP and MOSPF depend on features of underlying point-to-point (unicast) routing protocols. Efforts to remove this dependency and to develop point-to-multipoint (multicast) routing protocols that operate in a hierarchical manner which subnet multicast routing protocols led to the development of the core-based tree (CBT) protocol [4], [13] and the sparse mode of the protocol independent multicasting (PIM) protocol [22].
In multicast communication, there is a source node s and a set of destination nodes D. The multicast routing is to find a routing tree which is rooted from s and contains all nodes in D. Multicast routing has two important requirements: minimal network cost and shortest network delay. The network cost is the overall network cost of transmitting a message to all destinations; and the network delay is measured by the longest delay from the source to any destinations. In real-time applications, there often exists a real-time constraint and it is required that the communication be done within the constraint. There is no need to achieve the shortest delay to each of the destinations. We propose a real-time multicast routing algorithm, which reduces overall network cost without letting the delay from a source to any destination exceed a real-time constraint. Simulation results have shown that our algorithm has a significant improvement over the original CBT v2.
The rest of the paper is organized as follows. Section 2 presents the previous research in real-time multicast network. Section 3 describes multicast routing background and our proposed protocol. Section 4 describes the simulation demonstrating the capability of our proposed protocol and the paper concludes with Section 5.
Section snippets
Previous work
Optimal algorithms for constructing delay-constrained minimum Steiner trees exist, but their execution times are prohibitively large, because the problem is NP-complete [20]. Several delay-constrained Steiner tree heuristics have been proposed during the past few years. The heuristics proposed in Ref. [23] use a delay-constrained Bellman–Ford shortest path algorithm during the computation of the delay-constrained Steiner tree. Dijkstra [21] presented a delay-constrained heuristic based on
Source-based trees and shared trees
Data packets addressed to a multicast group may be routed on a tree that is specific to the particular sender and group or a tree that is shared by all of the senders to the group. The first approach uses a SBT that is a shortest path tree rooted at a sender. The branches of the tree are the shortest paths from the sender to each of the group members. A separate tree must be constructed for each sender of each active multicast group. A protocol that implements SBT is the dense mode of PIM (PIM
Simulation
In this section, we will describe the simulation results and discuss the performance of our protocol. We adopted the Waxman approach in Ref. [12] to construct our network graph. In our experiments, we used an average node degree of four, which is close to the average node degree of the current Internet. We distributed n nodes randomly across a Cartesian coordinate grid of size 100 by 100. Nodes in the network graph represent the communication endpoints. The edges connecting the nodes represent
Conclusion
In this paper, we proposed a new multicast routing protocol, based on the CBT, whereby, shortest of the shortest paths or a ‘non-core’ scheme has been incorporated. With time delay of real-time traffic imposed as one of the protocol constraint, our proposed approach which is based on the idea of CBT version 2, are built with bounded time delay thus, sustaining the real-time traffic requirements of the applications. In this paper, we also proposed a path selection function which takes into
Acknowledgements
The authors would like to thank the anonymous reviewers of this paper for their insightful comments and suggestions.
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Cited by (1)
Tree network design avoiding congestion
2011, Applied Mathematical ModellingCitation Excerpt :The latter problem has two versions in the literature: the single source tree networks – where we have a true fixed root of the multi-party multi-casting tree – and the core based tree networks – where a single node, the core, is chosen to play the role as the tree root. For further reading, please refer to [12–15]. In the above applications, the fixed cost can be seen as a bandwidth leasing cost, due to the allocation of large capacity links used by multi-casting participants.