Tokumi Yokohira

A test methodology for interconnect structures of LUT-based FPGAs

In this paper we consider testing for programmable interconnect structures of look-up table based FPGAs. The interconnect structure considered in the paper consists of interconnecting wires and programmable points (switches) to join them. As fault models, stuck-at faults of the wires, and extra-device faults and missing-device faults of the programmable points are considered. We heuristically derive test procedures for the faults and then show their validness and complexity.

Universal test complexity of field-programmable gate arrays

A field-programmable gate array (FPGA) can implement arbitrary logic circuits in the field. In this paper we consider universal test such that when applied to an unprogrammed FPGA, it ensures that all the corresponding programmed logic circuits on the FPGA are fault-free. We focus on testing for look-up tables in FPGAs, and present two types of programming schemes; sequential loading and random access loading. Then we show test procedures for the FPGAs with these programming schemes and their test complexities. In order to make the test complexity for FPGAs independent of the array size of the FPGAs, we propose a programming scheme called block-sliced loading, which makes FPGAs C-testable.

Fault tolerant packet-switched network design and its sensitivity

Reliability and performance for telecommunication networks have traditionally been investigated separately in spite of their close relation. A design method integrating them for a reliable packet switched network, called a proofing method, is presented. Two heuristic design approaches (max-average, max-delay-link) for optimizing network cost in the proofing method are described. To verify their effectiveness and applicability, they are compared numerically for three example network topologies. The sensitivity of these two methods is examined with respect to changes in traffic demand and in link reliability. The design sensitivity to variation of input data is examined by changing the predicted probability of link failure, and by increasing the network traffic over the predicted value. The resulting analysis shows relative insensitivity of solutions generated by the two design methods to input data. >

Testing for the programming circuit of LUT-based FPGAs

The programming circuit of look-up table based FPGAs consists of two shift registers, a control circuit and a configuration memory (SRAM) cell array. Because the configuration memory cell array can be easily tested by conventional test methods for RAMs, we focus on testing for the shift registers. We show that the testing can be done by using only the faculties of the programming circuit, without using additional hardware.

Performance Improvement of TCP using Performance Enhancing Proxies — Effect of Premature ACK Transmission Timing on Throughput —

In order to improve TCP performance, a method using a PEP (performance enhancing proxy) is proposed. The PEP operates on a router along a TCP connection. When a data packet arrives at the PEP, it forwards the packet to the destination host, transmits the corresponding ACK (premature ACK) to the source host in behalf of the destination host and stores the copy of the packet into its own buffer (PEP buffer) in case of the retransmission of the packet. In this paper, under the strategy which keeps the number of packets in the PEP buffer for which premature ACKs have been returned being less than or equal to a fixed threshold value (watermark value), we investigate the relation between the watermark value and the maximum throughput. Extensive simulation runs show that the simulation results are roughly classified into two cases. One case is that the maximum throughput becomes larger for larger watermark value and becomes a constant value when the watermark value is over a value. The other case is that though the maximum throughput becomes larger for lager watermark value in the same way, it reversely decreases when the watermark value is over a value. We also show that the latter (former) case is easier to occur as the propagation delay in the input side network of the PEP becomes smaller (larger) and the propagation delay in the output side network of the PEP becomes larger (smaller) and the PEP buffer capacity becomes smaller (larger)

Analysis of dynamic behavior in p-persistent CSMA/CD using cusp catastrophe

Abstract The dynamic behavior of p-persistent CSMA/CD is considered through application of the cusp catastrophe. Applying the cusp catastrophe, we find that the system state changes from monostable to bistable as the packet arrival rate increases for a given packet retransmission rate but not for another. In order to find an explanation for the sudden performance deterioration for one system state but not another, we examine system performance according to type of transition of the system state - the mean backlog, throughput and mean packet delay. We then consider a control strategy for avoiding drastic performance deterioration. Finally we consider the dependence of the stability of the system state on such system parameters as number of nodes and packet length.

A reroute method to recover fast from network failure

The demand for high Internet availability has increased. As routing methods to recover fast from a single network component (link or node) failure, methods using multiple routing tables have been proposed. In the methods, when a component failure occurs, packets which are supposed to pass through the component in the failure-free state are rerouted using a routing table (backup table) which does not use the component for packet forwarding. Thus, it is important to decrease the increased routing cost (for example, the number of increased hops of rerouted packets if every link cost is one) due to the reroute as much as possible. In this paper, we propose a new routing method to decrease the increased routing cost. In the conventional methods, there are many components that do not fail but are not used for packet forwarding in a backup table. In our proposed method, we use such components as much as possible, and consequently we try to decrease the increased routing cost. Numerical examples show the effectiveness of our proposed method.

Performance evaluation of as-friendly peer selection algorithms for P2P live streaming

In this paper, we evaluate the performance of peer selection algorithms: MLH (Minimum Logical Hop) and MPH (Minimum Physical Hop) to increase the number of joining peers and to decrease inter-AS traffic volume in P2P live streaming, where we assume that every peers logical hop count (the number of providing peers between an origin streaming server and the peer) is limited by a predetermined value in order to keep real-time property of live streaming. In MLH, a newly joining peer selects such providing peers that the logical hop count is minimum to increase the number of joining peers. And then if there are several such providing peers, the newly joining peer selects such providing peers that the number (physical hop count) of ASs between the newly joining peer and each of the providing peers is minimum to decrease the inter-AS traffic volume. In MPH, a newly joining peer selects providing peers in the reverse order of MLH. Simulation results show that MLH achieves about from 20% to 60% more maximum joining peers than MPH, and MPH shows smaller inter-AS traffic volume than MLH when the number of joining peers is small while MLH shows smaller inter-AS traffic volume when the number of joining peers is large.

Performance evaluation of a multi-stage network event detection scheme against DDoS attacks

Change-point detection schemes, which represent one type of anomaly detection schemes, are a promising approach for detecting network anomalies, such as attacks and epidemics by unknown viruses and worms. These events are detected as change-points. However, they generally also detect false-positive change-points caused by other events, such as hardware problems. Therefore there is a requirement for a scheme that detects only true-positive change-points caused by attacks and epidemics by unknown viruses and worms. The true-positive change-points tend to occur simultaneously and intensively in very large numbers, while the false-positive change-points tend to occur independently. We can exclude false-positive change-points by excluding those that occur independently, based on information gathered from the entire network. In this paper, we combine change-point detection schemes with a distributed IDS, and evaluate performance of the combined scheme by a simulation using the parameter values obtained by an experiment using real worms. The simulation results show that the combined scheme detects all the DDoS attacks without any false-positives while we have to tolerate false-positive rate of at least 0.02 to detect all the attacks in a stand-alone IDS scheme.

Performance Improvement of SCTP Communication Using Selective Bicasting on Lossy Multihoming Environment

In recent years, with proliferation of smart phones and tablet PCs, speedup of wireless LAN communication is required for dealing with increase of traffic in wireless networks. However, transmission speed through a wireless network often slows down in comparison with that through a wired network since packets of wireless networks frequently drop due to the influence of surrounding environment such as electromagnetic noise. In this paper, we propose a method to mitigate the impacts caused by packet loss by virtue of SCTP bicasting in lossy multihoming environment with two or more wireless networks. This method bicasts not all packets but only important packets concerning retransmission for efficiency since bicasting all packets would cause congestion. We also implemented a prototype system based on the proposed method. According to the result of performance evaluation experiment, we confirmed the effectiveness of the proposed method by the fact that the prototype system performed faster transmission than normal SCTP transmission even in high packet loss rate environment.