In this paper, we propose the high-level service architecture supporting multimedia multicast. The proposed architecture specifies network-oriented and lightweight communication management, which includes group management, multiparty call control and multicast connection/multiple connections control. Many of the existing approaches handling multimedia multicast applications are dependent on specific transport technologies, such as the Internet and ATM, and lack effective communication management. On the other hand, our approach defines flexible and extensible communication management that can be applied to a variety of multimedia multicast applications, independently of transport technologies. Our architecture supports the separation of control from a terminal, which enables remote control and control mobility, so that a user can use a multicast service in a more various way. The architecture is overlaid above legacy transport networks so that the existing network protocols are used for connection control. This minimizes the modification to a legacy transport network and enhances the practicality of the architecture. In addition, terminal manager and virtual device concepts are introduced that hide the details of physical devices from an application designer. The architecture consists of several service components that effectively interact with each other on a distributed platform. To verify and evaluate our architecture, we have prototyped the high-level service architecture on a CORBA platform and analyzed the architecture using a simulation.

A management of WWW server is still relying on the expertise and heuristic of administrators, because the comprehensive understandings of server behavior are missing. The administrators should maintain the WWW server with good states that they should investigate the WWW server in real time. Therefore, it is exactly desirable to provide a measurement application that enables the WWW server administrators to monitor WWW servers in the actual operational environment. We developed a measurement application called ENMA (Enhanced Network Measurement Agent) which is specially designed for WWW server state analysis. Furthermore, we applied this application to the large scale WWW server operation to show its implementation and advantages. In this paper, we analyze the WWW server states based on precise monitoring of performance indices of WWW system to help the server management.

On the Internet, a Quality of Service (QoS) guaranteed services are increasingly being demanded, and the Internet Engineering Task Force (IETF) is developing the specification documents for the QoS services intensively. This overview details the technical rationales underlining the contents of the specification documents developed by the IETF for Differentiated Services (DiffServ)--to provide QoS guarantee services in the large IP networks-- and Policy Framework--to manage DiffServ compliant networks. The IP networks with DiffServ consist of boundary routers and interior routers. These routers are composed of packet classifiers and marker, shaper, and policing function. Many vendors have developed DiffServ-compliant routers with gigabit interfaces. An example of an implementation of a DiffServ-compliant router and a demonstration of a QoS service using this router are presented here. The Policy Framework is expected to be one of the promising management solutions to co-operate with and manage many DiffServ-compliant routers. An experiment that adopts the Policy Framework to a DiffServ compliant network is also outlined.

Internet Key Exchange (IKE) is very important as an entrance to secure communication over the Internet. The first phase of IKE is based on Diffie-Hellman (DH) key-agreement protocol. Since DH protocol on its own is vulnerable to man-in-the-middle (MIM) attack, IKE provides authentication to protect the protocol from MIM. This authentication owes a lot to public-key primitives whose implementation includes modular exponentiation. Since modular exponentiation is computationally expensive, attackers are motivated to abuse it for Denial-of-Service (DoS) attacks; computational burden caused by malicious requests may exhaust the CPU resource of the target. DoS attackers can also abuse inappropriate use of Cookies in IKE; as an anti-clogging token, Cookie must eliminate the responder's state during initial exchanges of the protocol while IKE Cookies do not. Thus a large number of malicious requests may exhaust the memory resource of the target. In search of resistance against those DoS attacks, this paper first reviews DoS-resistance of the current version of IKE and basic ideas on DoS-protection. The paper then proposes a DoS-resistant version of three-pass IKE Phase 1 where attackers are discouraged by heavy stateful computation they must do before the attack really burdens the target. DoS-resistance is evaluated in terms of the computational cost and the memory cost caused by bogus requests. The result shows that the proposed version gives the largest ratio of the attacker's cost to the responder's cost.

We introduce the characteristics for continuous wave operation at room temperature of InGaN laser diodes fabricated on SiC substrates. The threshold current was 60 mA, the threshold voltage was 8.3 V, and the oscillation wavelength was 404.4 nm. The lifetime of the laser diodes with a constant light output of 1 mW at 25 was 57 hours. The heat dissipation of the devices mounted p-side-up on a stem without using a heat sink was shown to be as good as that of devices mounted p-side-down with an external heat sink, owing to the high thermal conductivity of SiC substrates.

Optical transverse-mode properties of the GaN-based semiconductor laser-diode is characterized by effective refractive index method. In order to stabilize a transverse-mode in the conventional ridge-waveguide structure, very precise control of ridge-height is found to be necessary. On the contrary, a novel 2-step grown structure with 2-dimensional index guiding has wide feasibility for device parameter, excellent stability of large confinement factor in transverse-mode, and small aspect ratio of beam divergence, under the condition that AlN molar fraction of 0.08 in AlGaN current blocking layer and stripe width of 1.5 µm are used.

Biological object could be trapped by a single laser beam from an optical fiber end inserted at an angle to a sample chamber. Separation/coupling of an individual biological cell was easily achieved using plural optical fibers. From these experimental results, we verify that fiber optic trapping technology can provide new and novel tools for the manipulation of microorganisms and cells without physical contact.

A per-connection end-to-end call admission control (CAC) problem is solved in this paper to allocate network resources to an input session to guarantee its quality of service (Qos) requirements. In conjunction with the solution of the CAC problem, a traffic descriptor is proposed to describe the loss rate and the delay bound Qos requirements of the connection to be set up as well as the statistical characteristics of the associated input traffic which is modeled as a linear mean function plus a (zero-mean) fractional Brownian motion. The information in the traffic descriptor is sufficient to determine the allocation of channel bandwidth and buffer space to the input traffic in a network which employs leaky bucket shapers and scheduling algorithms to guarantee the Qos requirements. The CAC problem is solved by an iterative algorithm of which there are two stages in each iteration: one is responsible for the search of a candidate end-to-end routing path and the other for the verification of the legitimacy of this candidate path to meet the Qos requirements and for the allocation of resources in such a legitimate path.

We present an architecture of a VOD system employing proxy servers. The proposed VOD system provides efficient and reliable VOD services and solves the problems caused by traditional VOD systems of centralized, hierarchical or distributed architecture. The proxy servers are placed between video servers and user systems. The proxy server is a small size video server that has not only caching function but also intelligence such as VCR-like video stream control or navigation of other proxy/video servers to search for a selected video program. Using a VOD system of the proposed architecture, the VOD services can be provided to more users because it reduces the workload of video servers and network traffic. We provide the performance model of the system. Service availability is also analyzed. The proposed architecture shows better performance and availability than the traditional VOD architectures.

In this paper, we analytically study the effects of overlap and overlay structure on the quality of service (QoS) of Low Earth-Orbital Satellite (LEOS) communication systems. We consider two-layered overlay of cells and intentional overlap of neighboring small cells. In order to measure the QoS, the probabilities of rejection of a newly arrived call (blocking) and forced termination due to failure of a handover (call dropping) are derived. In addition to these measures, the largest traffic intensity which guarantees the required blocking and dropping probabilities is also used.

This work presents a scalable and high performance prediction protocol for optical networks. In the proposed protocol, we develop a mathematical model to maintain the stability of a network system by prediction based on the traffic temporal locality property. All the critical factors, including transceiver tuning time, propagation delay, and processing time for dealing with control packets, are considered in the proposed prediction protocol. Furthermore, our protocol can resolve the bottlenecks attributed to control signaling and electronics processing. The performance evaluation reveals that the proposed scheme can yield the higher bandwidth efficiency and incur a lower packet delay than those of the TDM and conventional reservation schemes. Also, the proposed protocol can flexibly support any scaled network system such as MANs or LANs.

UV/blue/green InGaN and GaN single-quantum-well structure light-emitting diodes (LEDs) were grown on epitaxially laterally overgrown GaN (ELOG) and sapphire substrates. The external quantum efficiency (EQE) of the UV InGaN LED on ELOG was much higher than that on sapphire only at high-current operation. At low-current operation, both LEDs had the same EQE. When the active layer was GaN, EQE of the LED on sapphire was much lower than that on ELOG even at low- and high-current operations due to the lack of localized energy states formed by alloy composition fluctuations. In order to improve the lifetime of laser diode (LD), ELOG had to be used because the operating current density of the LD is much higher than that of LED. A violet InGaN multi-quantum-well/GaN/AlGaN separate-confinement-heterostructure LD was grown on ELOG on sapphire. The LDs with cleaved mirror facets showed an output power as high as 40 mW under room-temperature continuous-wave (CW) operation. The stable fundamental transverse mode was observed at an output power of up to 40 mW. The estimated lifetime of the LDs at a constant output power of 10 mW was more than 2,000 hours under CW operation at an ambient temperature of 60.

Continuous-wave operation at room-tempera-ture has been demonstrated for InGaN multi-quantum-well (MQW) laser diodes (LDs) grown on FIELO GaN substrates with a backside n-contact. This was made possible by introducing important new concept of reducing threading dislocations that occur during the growth of the GaN substrates. We found that InGaN active layers grown on FIELO GaN are superior to those grown on conventional sapphire substrates in terms of their growth mode and the resultant In compositional fluctuation. The fabricated laser diode shows the threshold current, the threshold current density and the threshold voltage were 36 mA, 5.4 kA/cm2 and 7.5 V, respectively, with the lasing wavelength of 412 nm and internal quantum efficiency as high as 98%.

Laser diodes in the (Al, Ga, In) N system are attractive for many applications. Due to the wurtzite crystal structure, cleaved facets are not easily produced. We have investigated distributed feedback (DFB) laser diodes employing embedded dielectric gratings with the grating located above the active region. The dielectric gratings are incorporated via epitaxial lateral overgrowth. The DFB laser diodes had reduced threshold current densities over the etched cavity devices, with a minimum of 15 kA/cm2. The spectral emission width was considerably reduced for the DFB devices. Voltages for the DFB devices were high due to the presence of the Si3N4 grating within the p-type material.

Coding scheme for a noisy multiple-access adder channel is proposed. When a T-user δ-decodable affine code C is given a priori, a qT-user λ δ-decodable affine code C* is produced by using a q q matrix B satisfying BA=λ Iq q, e. g. , a Hadamard matrix or a conference matrix. In particular, the case of δ=1 is considered for the practical purposes. A (2n-1)-user uniquely decodable (δ=1) affine code Cn with arbitrary code length n is recursively constructed. When Cn plays a role of C, a q(2n-1)-user λ-decodable affine code C* is obtained. The code length and the number of users of C* are more flexible than those of the Wilson's code. The total rate of the λ-decodable code in this paper tends to be higher than that of the λ-decodable code by Wilson as the number of users increases.

A reliable and automatic parameter extraction technique for DFB lasers is developed. The parameter extraction program which is named "LAPAREX" is able to determine many device parameters from a measured sub-threshold spectrum only, including gain- and index-coupling coefficients, and spatial phases of the grating at front and rear facets. Injection current dependence of coupling coefficients in a gain-coupled DFBlaser is observed, for the first time, by making use of it.

Signal conservation logic (SCL) is a model of logic for the physical world subject to the matter conservation law. This letter proves that replication, complementary replication, and computational universality called elemental universality are equivalent in SCL. Since intelligence has a close relation to computational universality, the presented theorem may mean that life under the matter conservation law eventually acquires some kind of intelligence.

This letter proposes a congestion control scheme for the ABR service of ATM networks which have non-responding connections. The control scheme is robust with respect to both the round trip delay and the loss of control information caused by non-responding connections. Thus, it is shown that the proposed control scheme guarantees the QoS of the network.

In this paper, we propose a new secure server-aided RSA secret computation protocol which guards against not only the attacks in [1],[2],[15],[18] but also the new powerful active attacks in [3],[4]. The new protocol is also efficient to support high security level.

It is well known that the electromagnetic interference (EMI) radiated from industrial, scientific and medical (ISM) apparatus seriously degrades the performance of wireless communication systems. In this paper, an ISM-band wireless local area network (WLAN) which employs a direct sequence-spread spectrum (DS-SS) system is designed to be sufficiently robust and reliable to operate in the presence of this EMI. To satisfy this goal, a technique to suppress EMI in the DS-SS system using a multicode transmission and an EMI observation channel is proposed. In the study, the EMI radiated from switching-type microwave ovens (MWO interference) which are ISM apparatus is concerned, and for a tractable investigation, a statistical model to represent MWO interference based on experimental measurement results is employed. As well known that MWO interference exhibits a bursty impulsive characteristic in time, a technique to transmit multiple long spreading codes (multicode transmission) is introduced for the DS-SS system to overcome the burstness of the interference. Moreover, inspired by the broadband in frequency of MWO interference, a technique to estimate the channel MWO interference by means of observing its levels in an adjacent channel is proposed, and this technique is applied to construct a multicode DS-SS receiver which can suppress the channel MWO interference. An evaluation of the bit error rate performance of the proposed multicode DS-SS system is conducted by computer simulation, and the numerical results demonstrate that the proposed DS-SS system can operate effectively even in the presence of MWO interference.