Recent attractive high-speed networks require network file servers with high-speed read performance to deliver huge multimedia files, like voice or movie files. This paper proposes new design and implementation techniques that yield high-speed file servers based on UNIX. The techniques are request reduction, in which contiguous blocks on UNIX file system (UFS) are gathered for reducing the number of command requests from the file system to the device driver, and a direct access method for cutting through the buffer cache mechanism. A file server prototype based on a general-purpose personal computer (PC) is constructed and its performance is evaluated. The preliminary results show that the prototype achieves high-speed file read performance in excess of 100 Mbytes/s even on an OpenBSD PC-UNIX system with 3 RAID controllers and 9 hard drives in RAID level 0 configuration.

This paper experimentally confirms the throughput characteristics of TCP and Network Direct Memory Access (Network DMA), our proposed data transfer protocol, over a large delay-band-width link. The experiments clarify that the various problems of TCP over large delay-bandwidth links include limited window size, data retransmission mechanism, and protocol processing overhead. The test results suggest that we must improve not only protocol itself but also the protocol processing architecture to realize Gbit/s class throughput over such links. To avoid these problems, Network DMA realizes high speed memory copy across a network by labeling each packet with its memory address without host CPU intervention; protocol processing is done by firmware on the network interface card. Moreover, it realizes selective retransmission by using the memory addresses. Test results show that Network DMA achieves the sustained throughput of 535Mbit/s over a 10,000km 622Mbit/s ATM link and over 400Mbit/s effective throughput even when the cell loss ratio is 10-4.

This paper proposes a novel universal line termination scheme for the ONUs (optical network units) of fiber-optic local access systems. Its main feature is that only low cost AD/DA converters for Hi-Fi audio are needed. Because audio AD/DA converters are insufficient for ISDN basic rate access (● 320kbaud) and cause waveform distortion, we develop a simple detection algorithm that does not use any equalizing filter. The algorithm can handle plural channels with one general purpose MPU (micro-processing unit). Based on this, a novel architecture for a fiber-optic local access system is presented that removes the MPUs from each optical network unit (ONU) and places them in the central office (CO). The proposed system yields a small, service-uniform ONU that supports a wide range of narrow-band services (POTS & ISDN) with no distinction. To realize this system at the lowest possible cost, a high-speed code division multiplexing (CDM) scheme with novel code word sets is developed.

This paper proposes a novel ultra high-speed file server based on a personal computer (PC) to provide the instantaneous delivery of huge files, like movie files, graphic images and computer programs, over high-speed networks. In order to improve the sustained sequential read speed from arrays of hard drives to host memory in the server, two key techniques are proposed: "multi-stage striping (MSS)" and the "sequential file system (SFS)." An experimental file server based on a general-purpose PC is constructed and its performance is measured. The results show that the server offers ultra high read speeds, up to 105Mbytes/s, with just 8 hard drives.

An optical CDMA (OCDMA) system is a flexible technology for future broadband multiple access networks. A secure OCDMA network in broadband optical access technologies is also becoming an issue of great importance. In this paper, we propose novel reconfigurable wavelength-time (W-T) optical codes that lead to secure transmission in OCDMA networks. The proposed W-T optical codes are constructed by using quasigroups (QGs) for wavelength hopping and one-dimensional optical orthogonal codes (OOCs) for time spreading; we call them QGs/OOCs. Both QGs and OOCs are randomly generated by a computer search to ensure that an eavesdropper could not improve its interception performance by making use of the coding structure. Then, the proposed reconfigurable QGs/OOCs can provide more codewords, and many different code set patterns, which differ in both wavelength and time positions for given code parameters. Moreover, the bit error probability of the proposed codes is analyzed numerically. To realize the proposed codes, a secure system is proposed by employing reconfigurable encoders/decoders based on array waveguide gratings (AWGs), which allow the users to change their codeword patterns to protect against eavesdropping. Finally, the probability of breaking a certain codeword in the proposed system is evaluated analytically. The results show that the proposed codes and system can provide a large codeword pattern, and decrease the probability of breaking a certain codeword, to enhance OCDMA network security.

Future optical code division multiple access (CDMA) networks should be designed for multirate and fully integrated multimedia services. In the conventional schemes, multilength optical orthogonal codes (OOCs) are designed to support multirate systems, while variable-weight OOCs are designed to support differentiated quality of service (QoS) for multimedia applications. In this paper, a novel class of optical signature codes; multiple-length variable-weight optical orthogonal codes (MLVW-OOC) is proposed for supporting multirate and integrated multimedia services in optical CDMA networks. The proposed MLVW-OOC has features that are easy to construct variable-weight codes and expanded to multiple-length codes. A construction method for designing MLVW-OOCs up to three levels of codes is discussed. The designed MLVW-OOCs can support differentiated requirements on data rates and QoS for several types of services in the networks. A code analysis for obtaining the value of cross-correlation constraints or multiple access interference (MAI) computation for several levels of codes is also suggested. The cross-correlation constraints of the proposed codes are better than the conventional codes such as multilength OOCs. Finally, the bit error probability performance of the two-level MLVW-OOC is evaluated analytically. The results show that the proposed MLVW-OOC can provide differentiated bit error probability performances for several combinations of data rates and QoS.