Active Reliable Multicast (ARM) is a novel loss recovery scheme for large-scale reliable multicast that employs active routers to protect the sender and network bandwidth from unnecessary feedback and repair traffic. Active routers perform NACKs suppression, cache multicast data for local loss recovery, and use scoped retransmission to avoid exposure. Limited active resources at routers need to be optimized to achieve low loss recovery latency and/or high network throughput. In this paper, we study the cache placement strategies and caching policies for ARM. Several heuristics, namely uniform allocation, proportional allocation, max-min fair share and weighted allocation for cache allocation methods are proposed. To further improve the loss recovery performance, caching policies can be employed in conjunction with the cache allocation strategies. Several caching policies, namely complete caching, random caching and deterministic caching, are proposed. Extensive simulation experiments are conducted to evaluate and compare the performance of the proposed strategies and policies. Numerical results reveal that significant performance gains can be achieved when a proper cache placement strategy and a caching policy are used for a given available cache resource. Another interesting finding is that the contributions of the cache placement scheme and caching policy to the recovery latency performance are roughly independent. The obtained insights in this study will provide some design guidelines for optimal active resource allocation and caching polices for reliable multicast communications.

A large-scale modular multicast ATM switch based on a three-stage Clos network architecture is proposed and its performance is studied in this paper. The complexity of our proposed switch is NN if the switch size is NN. The first stage of the proposed multicast switch consists of n sorting modules, where n=N. Each sorting module has n inputs and n outputs and is responsible for traffic distribution. The second and third stages consist of modified Knockout switches which are responsible for packet replication and switching. Although it is a multipath network, cell sequence is preserved because only output buffers are used in this architecture. The proposed multicast switch has the following advantages: 1) it is modular and suitable for large scale deployment; 2) no dedicated copy network is required since copying and switching are performed simultaneously; 3) two-stage packet replication is used which gives a maximum fan-out of n2; 4) translation tables are distributed which gives manageable table sizes; 5) high throughput performance for both uniform and nonuniform input traffic; 6) self-routing scheme is used. The performance of the switch under uniform and non-uniform input traffic is studied and numerical examples demonstrate that the cell loss probability is significantly improved when the distribution network is used. In a particular example, it is shown that for the largest cell loss probability in the second stage to be less then 10-11, the knockout expander, with the use of the distribution network, needs only be larger than 6. On the other hand, without the distribution network, the knockout expander must be larger than 13.