The present paper discusses several promising application areas for optical data links based on high-performance vertical-cavity surface-emitting laser diodes (VCSELs). Both 850 and 980 nm emission wavelength devices realized in the GaAs-AlGaAs or InGaAs-AlGaAs material systems are considered. We show data transmission results of 10 Gb/s signals at 830 nm wavelength over a new high-bandwidth multimode silica fiber of up to 1.6 km length. The same fiber type is employed to demonstrate the first 40 Gb/s transport over 300 m distance by means of a 4-channel coarse wavelength-division multiplexing approach. A first 1 10 linear VCSEL array capable of 10 Gb/s per channel operation is presented for use in next generation parallel optical modules. To improve the singlemode emission characteristics for output power in the 5 mW range we introduce a new device concept incorporating a long monolithic cavity. For low-cost short-distance data links we investigate graded-index polymer optical fibers and report on up to 9 Gb/s transmission over a length of 100 m. Polymer waveguides are also used in an optical layer of a hybrid electrical-optical printed circuit board. Transmitted 10 Gb/s optical data over a prototype board show the potential of this new technology. Finally we present two-dimensional VCSEL arrays for highly parallel data transport on a CMOS chip level. Both 980 and 850 nm bottom emitting devices with modulation capabilities up to 12.5 Gb/s are discussed.

Highly reliable and high power weakly index guided buried-stripe type 980 nm pump laser diodes developed for undersea applications are reviewed. The 10,000-hour large scale reliability tests of the first generation LD chips shows that 16.7 FIT for the random failure was confirmed at 10C with 60% confidence level at 120 mW output power. We also fabricated a FBG locked co-axial type module using a can-sealed LD with a two-lens system, which showed a stable FBG locked mode oscillation at 980 nm under the temperature range from 5C to 45C. The 5,000-hour heat cycle test of the modules reveals that the cumulative failure rate after 27 years at 10C is expected to be 0.023%. These first generation LD modules were employed in the transoceanic commercial systems such as Pacific Crossing-1 and the Japan-US cable system projects. We have also succeeded in developing the 980 nm LD for higher output operation with optimizing waveguide design. The 1000 µm long LD showed CW kink-free operation up to 545 mW optical output and a maximum output power of over 650 mW, which was limited by thermal rollover. In addition, a preliminary aging test at 350 mW optical output power at 50C has shown stable operation up to 2,300 h. We also confirmed 300 mW kink-free fiber output power with a co-axial type module with the improved coupling efficiency of approximately 78%. These figures are the highest reported operation levels for 980-nm co-axial type modules.

We have measured the temperature dependence of the gain characteristics in 1.3-µm AlGaInAs/InP strained multiple-quantum-well (MQW) semiconductor lasers using Hakki-Paoli method. By measuring the temperature dependences of the peak gain value and the gain peak wavelength, we evaluated the temperature dependences of the threshold current and the oscillation wavelength, respectively. The small temperature dependence of the threshold current in AlGaInAs/InP lasers is caused by the small temperature dependence of the transparency current density, which is represented by the characteristic temperature TJtr of 116 K. In AlGaInAs/InP high T0 lasers, the temperature dependence of the oscillation wavelength is slightly larger than that in GaInAsP/InP lasers because of the larger temperature dependence of bandgap wavelength 0.55 nm/K.

A new algorithm called core-stateless random-early-detection (CS-RED) is described. This algorithm can improve the fairness characteristics under a wide range of network conditions and is robust in terms of the setting of its control parameters. It can be used in a distributed architecture, as can the core-stateless fair-queuing (CSFQ) algorithm, so it is applicable to large-capacity backbone routers. Through a detailed evaluation, we have identified and clarified the fairness degradation problem in the CSFQ algorithm. We solved this problem by incorporating the congestion notification proposed in the RED algorithm into CSFQ; we call this hybrid CS-RED. Comparison of the fairness characteristics in a computer-simulated network using either the CS-RED or CSFQ algorithm showed that a higher level of fairness is achieved with the CS-RED algorithm under a wide variety of network conditions without degrading link utilization. Furthermore, the CS-RED algorithm uses a treatment that is more general than the penalty box mechanism to penalize unresponsive flows in best-effort networks.

Among several multiprocessor topologies, two-dimensional (2D) mesh topology has become popular due to its simplicity and efficiency. Even though a number of scheduling and processor allocation schemes for 2D meshes have been proposed in the literature, little study has been done aimed for real-time environment. In this paper, we propose an on-line scheduling and allocation scheme for real-time tasks that require the exclusive use of submeshes in 2D mesh system. By effectively manipulating the information on allocated or reserved submeshes, the proposed scheme can quickly identify the earliest available time of a free submesh for a newly arrived task. We employ a limited preemption approach to reduce the complexity of the search for a feasible schedule. Computer simulation reveals that the proposed scheme allows high throughput by decreasing the number of tasks rejected.

Differentiated services (Diffserv) model is one of the possible solutions for providing quality of service (QoS) on the Internet. Most existing approaches assume that the packet loss is an indication of network congestion and thus reduce the sending rates of sources. For wireless networks, the assumption is not proper since packet losses may be caused by other reasons, such as fading and interference of the signal. Therefore, these approaches do not work well in wireless networks. In this paper, we propose an approach which is able to provide service differentiation in wireless environments. In our approach, the rate share of a connection is determined by the associated weight. By keeping a proper amount of extra data in the network, the proposed approach can achieve weighted proportional fairness, which can provide selective QoS without any particular support from the network. We use the ns simulator to evaluate our approach. Simulation results show the validity of the proposed approach.

Due to the lack of support in mobility and quality of service, today's IP-based networks have some inherent limitations for delivering multimedia services in a mobile environment. In the past few years, these issues have been addressed in the research community and the resulting techniques are being standardised. However, these developments have been done in isolation and become incompatible with each other. In addition to these technical issues, the future infrastructure for charging and accounting mobile multimedia services is expected to be increasingly complicated. In this paper we present a home-proxy based framework which can facilitate the integration of mobility support and QoS management. Furthermore, it enables centralised accounting, which simplifies the cost recovery processes of roaming services. To prove the viability of our design, we have built and tested this framework on a DiffServ wide-area backbone using an MP3 streaming application.

We propose a new conditional linearization based on left-right separated conditional term rewriting systems, in which the left-hand side and the right-hand side of a rewrite rule have separate variables. By developing a concept of weight decreasing joinability we first present a sufficient condition for the Church-Rosser property of left-right separated conditional term rewriting systems. Applying this result to conditional linearization, we next show sufficient conditions for the unique normal form property and the Church-Rosser property of non-duplicating (unconditional) term rewriting systems even if they are non-left-linear or overlapping.

We propose middleware which works on widely-used commercial off-the-shelf platforms (UDP/IP, FastEthernet, and Windows NT or commercial real-time kernels) to realize real-time distributed services for plant monitoring and control systems. It is not suitable to use TCP/IP for the systems because of its unpredictable re-transmission, while, as well known, UDP/IP does not guarantee certain arrivals of packets and it is also not acceptable for the systems. With UDP/IP, packets are lost mainly because of collisions in a network and buffer overflows. To avoid these packet losses, the middleware controls scheduling of all the packets transmitted between the nodes in a distributed system and prevents excessive collisions and buffer overflows. The middleware provides a necessary set of functions for plant monitoring and control applications. The middleware on each node in a distributed system consists of library functions and run-time modules. An application program on the node is required to use these library functions according to the rules the middleware provides. In this way the middleware can manage all the traffic among the nodes in the system. Receiving requests from the application via library functions, the run-time module of the middleware schedules transmission of messages to other nodes, avoiding unexpected delivery delays or buffer overflows. The module also guarantees application-to-application quality of service (QoS), such as transmission period and delivery deadline, required by the applications. This is achieved by assigning the resources not shared by other services to each distributed service and scheduling these resources so as not to violate the assignment. Here, resources include maximum numbers of packets which a node can receive or send in a specific period (20 msec, for example). We show implementation of the middleware to make it clear how to guarantee application-to-application QoS with some application examples.

In this paper, a medium access control protocol is proposed for the integrated voice and data services in the local CDMA communication systems. Based on WB-TD/CDMA, uplink channels for the proposed protocol are composed of time slots with multiple spreading codes for each slot. During a talkspurt, a voice terminal transmits its entire packets over a reserved code. On the other hand, a data terminal transmits its packet after sensing the spreading code status. The base station broadcasts the status of spreading codes for each slot. In this protocol, voice packets never contend with data packets. The numerical results show that this protocol increases the system capacity for voice service by applying the reservation scheme. Despite the low access priority of data terminal, the data traffic performance can be increased in proportion to the number of spreading codes.

In this paper, we propose a new location tracking method for pointer forwarding with distributed HLRs schemes to decrease the location tracking cost. Similar to the distributed HLR schemes, the location information is replicated on all HLRs in our scheme. However, unlike the traditional distributed HLR schemes, we propagate the most recent location changes from an HLR to reset the forwarding pointers in other HLRs, and thus reduce the cost of location tracking for call deliveries. The signaling cost of location propagation may be too costly to be practical. Therefore, we allow some inconsistency to exist among the location data of HLRs and defer the propagation of location changes to reduce the propagation cost. Three delay propagation policies are also proposed and analyzed using simulation. The performance result shows that the delay propagation policies reduce the propagation cost and the propagation resetting process degrades the location tracking cost. Our method preserves a low total cost for call deliveries, registrations and propagations in distributed HLRs.

In this paper, we proposed two models, the full multiple MCS (Multicast Server) model and the hybrid multiple MCS model to support multiple MCS over a single large cluster in ATM (Asynchronous Transfer Mode) networks. Also, we presented two methods for MCS assignment which are known as 2PSPMT (2 Phase Shortest Path based on Multicast tree) and hybrid-2PSPMT, and evaluated its performance by simulation. When an ATM host requests joining a specific multicast group, the MARS (Multicast Address Resolution Server) designates a proper MCS among the multiple MCSs for the group member to minimize the average path delay between the sender and the group members. Each method for MCS assignment construct a 2-phase partial multicast tree based on the shortest path algorithm. We reduced the average path delay in the multicast tree using these methods with various cluster topologies and MCS distribution scenarios in addition to distributing the load among multiple MCSs.

The Direct-Sequence Code Division Multiple Access (DS-CDMA) is one of the most likely candidates for the 3rd generation mobile communication systems. On the other hand, a network supporting integrated data transfer and providing predictable qualities of service (QoS) to such application is an attractive issue. This paper proposes several schemes based on the majority rule concerned with resource reservation to investigate the performance of a CDMA cellular system. The admission control is based on the residue capacity and required signal-to-noise ratio (SNR) for multimedia traffic including voice, data and video. The system performance is explored with variable spreading gain and multi-code CDMA systems under the proposed schemes. Moreover, several system parameters including the handoff probability (lifetime in a cell) and the traffic load are investigated to study the impact to system performance. The results show the trade-off between the blocking probability of new calls and dropping probability of handoff calls under diversified situations. However, it is inefficient under resource reservation due to unused capacity. In this paper, we also propose a resource-borrowing scheme to improve system performance. Simulation results show that our proposed algorithm really improves the system performance in a multimedia CDMA cellular system with resource reservation.

Call admission control (CAC) is becoming vital for multimedia services in the ability of wireless/mobile networks to guarantee Quality of Service (QoS) partially due to the network's limited capacity. In this paper, we propose an optimal call admission control scheme with bandwidth reallocation algorithm (multi-class-CAC-BRA) for multi-classes of adaptive multimedia services in wireless/mobile networks. The multi-class-CAC-BRA approach optimizes revenue for service providers and satisfies QoS requirements for service users. The proposed approach adopts semi-Markov Decision Process to model both call admission control and bandwidth reallocation algorithm. In other words, whenever decisions are made, decisions are made for both call admission control and bandwidth reallocation. Since the non-adaptive multimedia traffic is a special case of the adaptive multimedia traffic, the non-adaptive optimal CAC scheme is a special case of our optimal multi-class-CAC-BRA scheme. Furthermore, the Interior-point Method in linear programming is used to solve the optimal decision problem. Simulation results reveal that the proposed multi-class-CAC-BRA scheme adapts itself well to adaptive multi-class multimedia traffic, achieves optimal revenue, and satisfies QoS requirements that are the upper bounds of handoff dropping probabilities. Our approach solves the optimal adaptive multimedia CAC problem. We believe that this work has both theoretical and practical significance.

Off-line state identification methods for a sequential machine using a homing sequence or an adaptive homing sequence (AHS) are well-known in the automata theory. There are, however, so far few studies on the subject of the on-line state estimator such as a state observer (SO) which is used in the linear system theory. In this paper, we shall construct such an SO for a Moore machine based on the state identification process by means of AHSs, and discuss the convergence property of the SO.

In this manuscript, two key agreement protocols which are resistant to a denial-of-service attack are constructed from a key agreement protocol in [9] provably secure against passive and active attacks. The denial-of-service attack considered is the resource-exhaustion attack on a responder. By the resource-exhaustion attack, a malicious initiator executes a key agreement protocol simultaneously as many times as possible to exhaust the responder's resources and to disturb executions of it between honest initiators and the responder. The resources are the storage and the CPU. The proposed protocols are the first protocols resistant to both the storage-exhaustion attack and the CPU-exhaustion attack. The techniques used in the construction are stateless connection, weak key confirmation, and enforcement of heavy computation. The stateless connection is effective to enhancing the resistance to the storage-exhaustion attack. The weak key confirmation and the enforcement of heavy computation are effective to enhancing the resistance to the CPU-exhaustion attack.

To satisfy huge service demand and multi-traffic requirements with limited bandwidth, this paper proposes two different procedures of multi-channel multiple access schemes with the slotted ALOHA operation for both data and voice traffic and presents an exact analysis to numerically evaluate the performance of the systems. In scheme I, there is no limitation on access between data transmissions and voice transmissions, i.e., all channels can be accessed by all transmissions. In scheme II, a channel reservation policy is applied, where a number of channels are used exclusively for voice packets while the remaining channels are used for both data packets and voice packets. We call the system using scheme I "Non-reservation system" and call the system using scheme II "Reservation system. " Performance characteristics we obtained include loss probability for voice traffic, average packet delay for data traffic and channel utilization for both traffic. The performance of the schemes and the effects of the design parameters are numerically evaluated and compared to a wide-bandwidth conventional single-channel slotted ALOHA system with single data traffic. The analysis presented in this paper will be not only useful for the performance evaluation and the optimum design of multi-channel multi-traffic systems in wireless environments, but also applicable to evaluate other performance measures in priority networks, cellular mobile radio networks or multi-hop wireless networks.

This paper reports the field test performance of a base station (BS) equipped with a linear parallel multi-stage interference canceller for uplink of wideband CDMA in a suburban area. The field test was performed with one desired mobile station (MS) moving around the BS, and three fixed interfering MSs having a target SIR 11 dB higher than that of the desired MS. The field test clearly demonstrates that using interference cancellation with a proper suppression factor (or weighting factor), can reduce the transmission power of the desired MS by around 6 dB. This performance was also compared with calculated data and the interference canceller was verified to function as theoretically expected. The receive power capture ratio was estimated at around 96%. This paper therefore establishes that interference cancellation performance of CDMA systems in the field can be found by estimating the receive power capture ratio and the theoretical results of interference cancellation.

For the purpose of equalisation of rapidly time variant multipath channels, we derive a novel adaptive algorithm, the amplitude banded LMS (ABLMS), which implements a non-linear adaptation based on a coefficient matrix. Then we develop the ABLMS algorithm as the adaptation procedure for a linear transversal equaliser (LTE) and a decision feedback equaliser (DFE) where a parallel adaptation scheme is deployed. Computer simulations demonstrate that with a small increase of computational complexity, the ABLMS based parallel equalisers provide a significant improvement related to the conventional LMS DFE and the LMS LTE in the case of a second order Markov communication channel model.

Automatic repeat request (ARQ) for wireless ATM (WATM) operating at 20 Mbit/s or higher is required to achieve high throughput performance as well as high transmission quality, i.e., low CLR (cell loss ratio). Selective Repeat (SR) and Go-Back-N (GBN) are typical ARQ schemes. Though SR-ARQ is superior to GBN-ARQ in throughput performance, the implementation complexity of SR-ARQ's control procedures is disadvantageous to its application to high-speed wireless systems. In addition, when PDU (protocol data unit) length on wireless link is short, the capacity for ARQ control messages can be significantly large. GBN-ARQ, on the other hand, cannot avoid serious throughput degradation due to fairly high BER caused by multipath fading and shadowing, though its implementation is simple. To solve the above-mentioned problems, this paper proposes a novel ARQ scheme named PRIME-ARQ (Partial selective Repeat superIMposEd on gbn ARQ). PRIME-ARQ achieves high throughput performance, almost equal to selective repeat ARQ, with a simple algorithm resulting in reduced implementation complexity for high speed operation. This paper describes the design, implementation, and performance of the proposed PRIME-ARQ. In addition, it shows the experimental results using an experimental PRIME-ARQ hardware processor and proto-type AWA equipment.