Anujan Varma

Asymmetrical multiconnection three-stage Clos networks

The authors study routing problems in a general class of asymmetrical three-stage Clos networks. This class covers many asymmetrical three-stage networks considered by earlier researchers. They derive necessary and sufficient conditions under which this class of networks is rearrangeable with respect to a set of multiconnections, that is, connections where the paired entities are not limited to single terminals but can be arbitrary subsets of the terminals. They model the routing problem in these networks as a network-flow problem. If the number of switching elements in the first and last stages of the network is O(f) and the number of switching elements in the middle stage is m, then the network-flow model yields a routing algorithm with running time O(mf/sup 3/).<<ETX>>

Efficient algorithms for computation of the loss curve of video sources

The loss curve of a video source characterizes the loss rate of the video stream generated by the source as a function of the allocated buffer size for a given transmission rate. The loss curve is useful in the optimal allocation of resources when the video stream is transmitted over a packet network, so that the desired tradeoff can be reached among the loss rate, bandwidth and the buffer space to be allocated in the network. We present an algorithm for computation of the entire loss curve of an elementary video stream. In contrast to earlier algorithms which employ statistical approaches, our algorithm is deterministic and computes the exact loss curve of the video stream. The algorithm exploits the piecewise linearity of the loss curve and computes only the points at which the slope of the loss curve changes. We also present an extension of the algorithm to MPEG-2 transport streams. The efficiency of the algorithm is demonstrated by results from several example video streams. For example, the algorithm was able to compute the entire loss curve of a 2-h elementary video stream in approximately 11 s on a Sun Ultra-2 workstation.

Efficient algorithms for computation of the burstiness curve of video sources

The burstiness of a video source can be characterized by its burstiness curve. The burstiness curve is useful in the optimal allocation of resources to satisfy a desired quality of service for the video stream in a packet network. In this paper, we present deterministic algorithms for exact computation of the burstiness curve of a video source, for both elementary video streams and MPEG-2 Transport Streams. The algorithms exploit the piecewise linearity of the burstiness curve and compute only the points at which the slope of the burstiness curve changes. We also present approximate versions of these algorithms, which save computational effort by considering only a small number of candidate points at which the slope of the burstiness curve may change. The approximate algorithm was able to compute the burstiness curve of a 2-h long elementary video stream in approximately 10 s, as compared to over 6 h for the exact algorithm, with virtually no loss of accuracy in the computation. The efficiency of the proposed algorithms makes them suitable for quality-of-service (QoS) provisioning not only in off-line environments such as in video-on-demand (VoD) servers, but also in real-time applications such as in live TV distribution systems.