# Configurable Conferencing Server Architectures: Structural Design and Network Management

Yi Du, Johns Hopkins University

In this talk, we describe conference network of servers based on a configurable computing architecture to support creation and maintenance of simultaneous conferences among sets of $$N$$ conferees with on-line conference requests, where a conference realized on conference network by connecting servers assigned to the conferees remains until its termination. A conference network of $$M$$ servers with link capacity $$c$$ is required to support conferencing for $$N$$ users with certain capabilities such as strictly nonblocking where requests can be assigned arbitrarily, and wide-sense nonblocking where a request assignment algorithm is needed. We study the structural design requirement, on number $$M$$ of servers and link capacity $$C$$, for network of certain structure, and connection management for the server architecture.

We consider conference network models with single and multiple link capacity. For single-capacity case, we show the necessary and sufficient conditions such that an $$r$$-dimensional conferencing mesh of $$M$$ servers provides strictly non-blocking conferencing to $$N$$ conferees are $$M = O(N^{(r+1)/r})$$ nodes for fixed $$r$$, while $$M = O(r N^{(r+1)/r})$$ nodes are sufficient for $$r$$-D mesh with arbitrary $$r$$. A fundamental relationship involving isoperimetric ratios is established between $$M$$ and $$N$$ for general graphs; For multi-capacity meshes, we show $$c = O(N^{1/r})$$ capacity is sufficient for $$r$$-D mesh of $$M = N$$ nodes to support $$N$$ users for wide-sense nonblocking. Interesting trade-off between number $$M$$ of servers and link capacity $$c$$ is thus obtained. Greedy algorithm is designed to satisfy on-line conference requests and its performance is evaluated analytically and studied by simulation. The study shows the algorithm performs very well for meshes with small link capacity. The multi-capacity mesh design offers a practical construction for conference networks.

We also consider scalable hierarchical topology aggregation approach for routing management of large scale networks. Topology aggregation schemes are used in hierarchical source routing frameworks such as the ATM PNNI standard for scalability and security reasons. We discuss the design and implementation of a simulation environment which emulates PNNI. Using this simulator, we study by simulation the performance, in terms of network throughput and signaling delay, of link cost metrics and various topology aggregation schemes. Our study results in verification of theoretical superiority of the exponential cost metric for hierarchical routing and identification of aggregation schemes with good performance/representation trade-off. New re-aggregation policy called logarithmic update is studied to achieve reduction on computation overhead.