Reducing forwarding state overhead of multicast routing protocols
is an important issue towards a scalable global multicast solution. We
propose a new approach, dynamic tunnel multicast, which utilizes
dynamically established tunnels on unbranched links of a multicast
distribution tree to eliminate unnecessary multicast forwarding states.
Analysis and simulation results show promising reduction in the state
overhead of sparse mode multicast routing protocols
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"They proposed a differential flow cache framework that uses a hashbased cache placement and localized Least Recently Used (LRU)-based replacement to reduce the loss of elephant flows. The scalability issue is more serious in multicast, and the previous works , , , ,  have demonstrated that the branch forwarding technique is a promising way since forwarding from a branch node to a neighbor branch node or terminal node can exploit the existing unicast tunneling technique, and tunneling can be facilitated in SDN with logic ports specified in the group table . In other words, the intermediate nodes between two neighbor branch routers no longer need to store a multicast forwarding entry for the tree. "
[Show abstract][Hide abstract] ABSTRACT: Software-Defined Networking (SDN) enables flexible network resource
allocations for traffic engineering, but at the same time the scalability
problem becomes more serious since traffic is more difficult to be aggregated.
Those crucial issues in SDN have been studied for unicast but have not been
explored for multicast traffic, and addressing those issues for multicast is
more challenging since the identities and the number of members in a multicast
group can be arbitrary. In this paper, therefore, we propose a new multicast
tree for SDN, named Branch-aware Steiner Tree (BST). The BST problem is
difficult since it needs to jointly minimize the numbers of the edges and the
branch nodes in a tree, and we prove that it is NP-Hard and inapproximable
within $k$, which denotes the number of group members. We further design an
approximation algorithm, called Branch Aware Edge Reduction Algorithm (BAERA),
to solve the problem. Simulation results demonstrate that the trees obtained by
BAERA are more bandwidth-efficient and scalable than the shortest-path trees
and traditional Steiner trees. Most importantly, BAERA is computation-efficient
to be deployed in SDN since it can generate a tree on massive networks in small
[Show abstract][Hide abstract] ABSTRACT: In this paper, we propose a new multicast scheme, PAM, which as opposed to native IP multicast, does not require all routers to be IP multicast-enabled, and as opposed to existing application-level multicast, does not exclude network support. Instead, PAM relies on partial network support, selects a small subset of routers as PAM-enabled multicast routers that are strategically located to serve group communication, and adapts its selection based on group dynamics. As a result, PAM (1) is suitable for both sparse and dense communication groups, (2) can reduce the network overhead inherent in native IP multicast, and (3) does not suffer the delay stretch and the high stress inherent in application-level multicast. Experimental results on both synthetic and realistic Internet topologies, for both sparse and dense groups, reveal that PAM can achieve efficient group communication with no delay stretch, an average stress of merely 1.25, while using less than 15% of the multicast routers that are needed in native IP multicast.
"Our mechanism is orthogonal to the approach that adopts a single multicast tree to serve multiple multicast groups (for example, , , , and ), and can also be integrated with that approach to further reduce forwarding state stored in each router. Another approach that stores forwarding states only in branching routers of each tree (for example, , , , , , and ) is proved to be a special case of our mechanism, because our mechanism can more flexibly distribute forwarding states among routers. We also show that with the second approach (that is, storing states only in branching routers), forwarding states may be concentrated on backbone routers, which are branching routers in most cases, even when the group size is very small. "
[Show abstract][Hide abstract] ABSTRACT: In this paper, we propose a scalable and adaptive multicast forwarding mechanism based on explicit multicast (Xcast). This mechanism optimizes the allocation of forwarding states in routers and can be used to improve the scalability of traditional IP multicast and source-specific multicast. Compared with previous work, our mechanism needs fewer routers in a multicast tree to store forwarding states and therefore leads to a more balanced distribution of forwarding states among routers. We focus on two problems and formulate each of them as an optimization problem. The first problem, referred to as minstate, minimizes the total number of routers that store forwarding states in a multicast tree. The second problem, referred to as balancestate, minimizes the maximum number of forwarding states stored in a router for all multicast groups, which is proved to be an NP-hard problem. We design a distributed algorithm that obtains the optimal solution to the first problem and propose an approximation algorithm for the second problem. We also prove that the approach adopted by most existing works to allocate forwarding states in the branching routers of a multicast tree is a special case of our mechanism. The simulation results show that the forwarding state allocation provided by previous work is concentrated on the backbone routers in the Internet, which may cause the scalability problem. In contrast, our mechanism can balance forwarding states stored among routers and reduce the number of routers that store the forwarding states for a multicast tree.
Preview · Article · May 2008 · IEEE Transactions on Parallel and Distributed Systems