In this paper, we focus on the problem of tracking a moving target in a wireless sensor network (WSN) in which the capability of each sensor is relatively limited in order to construct large-scale WSNs at a reasonable price. In our prior study, we proposed a simple multi-point surveillance scheme for a moving target in a WSN and demonstrated that the scheme achieved high tracking probability with low power consumption. However, we have not suggested guidelines for designing the WSN to completely satisfy the wide range of user requirements. Therefore, in this study, we examine the relationship between tracking probability and sensor density through simulations, and then derive an approximate expression representing the relationship. As a result, we show guidelines for sensor density, tracking probability, and the number of monitoring sensors that satisfy a variety of application demands.

A huge number of LAN switches are currently in use worldwide, so ways in which they can save energy are of great practical interest. A simple way to save power is to switch the interface to sleep mode when no packets are buffered, and to keep it in active mode while there are packets to be transmitted. This would appear to be the most effective energy saving scheme. However, mode switching gives rise to an in-rush current, which causes electrical damage to devices. This problem arises from over-frequent mode switching, which should be avoided. Thus, the main objective is to develop a way to reduce the number of mode switchings that result in quite short duration sleep modes, as these do not contribute so much to energy saving but lead to damage to the device. To this end, a method is adopted which keeps the interface in active mode for an extra period after all packets are flushed out from the buffer; this is the "extra active period". This scheme protects the device at the expense of energy saving efficiency. In this paper, the scheme is evaluated analytically in terms of its power reduction ratio and the frequency of mode changes, by modifying the M/M/1 and IPP/M/1 queuing models. The numerical results show how the duration of the extra active period degrades the energy saving performance while successfully reducing the number of mode changes. These results will enable LAN switches to be designed with energy saving in mind yet within the constraints of device characteristics.

As the amount of traffic transferee! on the Internet are increasing, dynamic traffic engineering (TE) becomes important to avoid link congestion. In open shortest path fast(OSPF)-based networks, link costs are statically set according to its long-term utilization for reducing traffic on some congested nodes, hence temporary performance degradation may occur due to short-term traffic fluctuation. For dynamic IE on OSPF-based networks, measurement of the utilization of links / nodes, inferring the set of link costs for improving transmission behavior and setting the cost set to routers are necessary and so-called on-line simulation (OLS) system can operate these functions autonomously and periodically. In this paper, we construct the server prototype in OLS system, and evaluate its scalability and control performance in our testbed network. Experimental results show that the server succeeds in providing low-cost network management and real-time control even if there is the large amount of traffic on the network. Furthermore, the total throughput over the network was greatly improved by the OLS.

This paper proposes an analytical model for a delayed reservation scheme, which can be exactly analyzed. By applying it to a server-based QoS management network, we can obtain the related blocking probability and the waiting time distribution of requests, and discuss its performance by means of numerical results. The numerical results show that the delayed scheme can improve the blocking probability by about two orders of magnitude compared with the conventional reservation scheme even with a small acceptable waiting time (e.g. 20% of average flow duration). We can conclude that the delayed reservation scheme can lead to significant improvement in a server-based QoS management network performance.

LSR (label switching router)s in MPLS (multiprotocol label switching) networks map arriving IP flows into some labels on the layer 2 switching fabric and establish LSP (label switching path)s. By using LSPs, LSRs not only transmit IP datagrams fast with a cut-through mechanism, but also solve the traffic engineering issue to optimize the delay of some IP datagram flows. So far, we have analyzed the performance of LSR focusing only on the maximum number of LSPs which can be set on layer 2. We also consider the bandwidth allocated to each LSP and analyze the IP datagram transmission delay and the cut-through rate of LSR. We suppose the label mapping method as the data-driven scheme in the analytical model, so that the physical bandwidth of LSR is shared by both the default LSP for hop-by-hop transmission and the cut-through LSPs. Thus, we investigate the impact of the bandwidth allocation among these LSPs on the performance.

In long haul networks, delay in congestion notification can cause an extended period of congestion which may in turn result in cell loss, and poor utilization of the network. In this regard we investigate various congestion notification strategies and show our results in this paper. Moreover, we identify deficiencies and problems associated with the enhanced proportional rate control algorithm (EPRCA) which is one of the explicit rate control algorithms recommended by the ATM Forum. These deficiencies cause unfairness in bandwidth utilization among contending sources. We suggest modifications in EPRCA and call it the modified enhanced proportional rate control algorithm (EPRCAM). We argue that EPRCAM will lead to better link utilization and fair bandwidth allocation between sources. In our simulation model, EPRCAM results in as high as a 97.5% link utilization without cell loss.

In transport-layer protocols such as TCP over ATM networks, a packet is discarded when one or more cells of that packet are lost, and the destination node then requires its source to retransmit the corrupted packet. Therefore, once one of the cells constituting a packet is lost, its subsequent cells of the corrupted packet waste network resources. Thus, discarding those cells will enable us to efficiently utilize network resources, and will improve the packet loss probability. We focus on tail dropping (TD) and early packet discard (EPD) as selective cell discard schemes which enforce the switches to discard some of the arriving cells instead of relaying them. We exactly analyze the packet loss probability in a system applying these schemes. Their advantages and limits are then discussed based on numerical results derived through the analysis.

In transport-layer protocols such as TCP over ATM networks, a packet is discarded when one or more cells are lost in that packet, and the destination node then requires its source to retransmit the corrupted packet. Therefore, once one of the cells constituting a packet is lost, the subsequent cells of the corrupted packet waste network resources. Thus, discarding those cells will enable us to efficiently utilize the network resources and improve the packet loss probability. We focus on tail dropping (TD) and early packet discard (EPD) as selective cell discard schemes which force the switches to discard some of the arriving cells instead of relaying them. We exactly analyze the packet loss probability in a system applying these schemes. Their advantage and limits are then discussed based on numerical results derived through the analysis.

In ATM networks, preventive congestion control is widely recognized for efficiently avoiding congestion, and it is implemented by a conjunction of connection admission control and usage parameter control. However, congestion may still occur because of unpredictable statistical fluctuation of traffic sources even when preventive control is performed in the network. The authors study another kind of congestion control, i.e., reactive congestion control, in which each source changes its cell emitting rate adaptively to the traffic load at the switching node (or at the multiplexer). The intention is that, by incorporating such a congestion control method in ATM networks, more efficient congestion control is established. They develop an analytical model, and carry out an approximate analysis of reactive congestion control algorithm. Numerical results show that the reactive congestion control algorithms are very effective in avoiding congestion and in achieving the statistical gain. Furthermore, the binary congestion control algorithm with push-out mechanism is shown to provide the best performance among the reactive congestion control algorithms treated.>

In almost all conventional transport protocols, ARQs (automatic repeat request) have been used to recover lost packets, in which receivers would request sources to retransmit lost packets. In these retransmission based error recovery schemes, the transmission delay can reach an unacceptable level for traffic with stringent delay constraints in high speed networks because their propagation delay is very large relative to packet transmission times. On the other hand, FEC (forward error correction) adds redundant packets to data ones, all of which are organized into a group called a block, and hence allows the receivers to correct some of the lost packets without retransmissions. This capability is desirable for high speed networks. The authors exactly analyze the distribution of the number of cells lost within a block in ATM networks with correlated cell arrivals, and examine the benefits due to FEC by means of the analysis.>

The authors consider a three-stage switching configuration with no internal buffers, i.e., bufferless switches are used at the first and second stages, and output buffered switches at the third stage. Short-term cell loss probability is analyzed in order to examine the influence of bursty traffic on the performance of the bufferless switches used at the first two stages. A four-stage switching configuration with traffic distributors added at the first stage is proposed. This switch provides more paths between a pair of input and output ports than the three-stage configuration. Some schemes for distributing cells are compared. It is shown that the distributor successfully reduces cell loss probability due to bursty traffic by splitting incoming cells into several switching modules.>