We are interested in the problem of satisfying a maximum-profit subset of undirected communication requests in an optical ring that uses the Wavelength Division Multiplexing technology. We present four deterministic and purely... more
We are interested in the problem of satisfying a maximum-profit subset of undirected communication requests in an optical ring that uses the Wavelength Division Multiplexing technology. We present four deterministic and purely combinatorial algorithms for this problem, and give theoretical guarantees for their worst-case approximation ratios. Two of these algorithms are novel, whereas the rest are adaptation of earlier approaches. An experimental evaluation of the algorithms in terms of attained profit and execution time reveals that the theoretically best algorithm performs only marginally better than one of the new algorithms, while at the same time being several orders of magnitude slower. Furthermore, an extremely fast greedy heuristic with nonconstant approximation ratio performs reasonably well and may be favored over the other algorithms whenever it is crucial to minimize execution time.
In recent years, various non-linear phenomena of the Internet have been discovered. For instance, it is reported that congestion of a router propagates to neighboring routers like a wave. Several researches on congestion propagation among... more
In recent years, various non-linear phenomena of the Internet have been discovered. For instance, it is reported that congestion of a router propagates to neighboring routers like a wave. Several researches on congestion propagation among routers have been performed. However, in these researches, cause of congestion propagation and condition that congestion propagation occurs have not been sufficiently investigated. In this paper, we reveal a cause of congestion propagation, and also investigate under what conditions congestion propagation is observed. Consequently, we show that speed of congestion propagation is affected by the bandwidth and the propagation delay of links, and that periodicity of congestion propagation becomes less obvious as randomness of network traffic increases.
Prolonging the network lifetime is one of the main challenges in wireless sensor networks (WSNs). This paper proposes a layered-based routing tree called LBRT that solves the energy holes in WSNs. It uses several layers in a ring network... more
Prolonging the network lifetime is one of the main challenges in wireless sensor networks (WSNs). This paper proposes a layered-based routing tree called LBRT that solves the energy holes in WSNs. It uses several layers in a ring network in a way that each layer is composed of four sectors. The number of nodes in first layer is more than that of in other layers. The nodes construct a cluster at each sector, except sectors of first layer, to transmit the data packets via cluster head (CH) nodes. CH nodes are selected based on their remaining energy and average distance to neighboring nodes. They receive data packets from non-cluster head (NCH) nodes and forward them toward the sink through CH nodes located at the lower layer. Simulation results demonstrate that the proposed method surpasses than another routing method in terms of network lifetime, network traffic, system throughput, and delivery time.
