Koichi Asatani

Access network architectural issues for future telecommunication networks

This article discusses the evolution of access networks to support future multimedia services, with emphasis on the role of Working Party 3 of ITU-T Study Group 13. An overview of the access network is given, and the interfaces between the access network and other portions of the telecommunications network such as the user-network interface (UNI), service node interface (SNI), and telecommunication management (Q3) interface are described. The major functions of the access network are summarized, and various examples of multimedia access architectures are discussed. Fundamental principles for the broadband service node interface (VB5) standard are reviewed.

A new estimation method using RTT for available bandwidth of a bottleneck link

The Internet real-time applications are growing rapidly, and available bandwidth estimation is required. Available bandwidth estimation methods by end host have been studied e.g. Pathload and pathChirp. These methods parameterize probe packets volume and observe the delay variation to estimate available bandwidth. In these methods, probe packets give heavy overhead loads on the network. In this paper, we propose a new available bandwidth estimation method based on frequency of minimum RTT of probe packets in multi hop links. This method estimates bandwidth utilization and available bandwidth of a bottleneck link without severe network loads. Estimation accuracies are evaluated for available bandwidth by implementing the proposed method. The proposed method shows better performance than those of pathChirp and Pathload, requiring smaller number of probe packets and less estimation time simultaneously.

Mitigation of atmospheric effects on terrestrial FSO communication systems by using high-speed beam tracking antenna

When a free-space optical beam propagates through the atmosphere it experiences deterioration and deformation of its wave-front caused from small scale, randomly localized changes in the atmospheric index of refraction. This results in beam wander and scintillation effects which can reduce the link availability and may introduce burst errors. This paper outlines experimental work on a free-space optical (FSO) communication system which connects an optical beam directly to a single-mode fiber (SMF) without any optical-to-electrical (O-E) conversion. In order to effectively couple the 1550 nm transmitted optical beam to a SMF it is necessary to be able to track and control the beam angle-of-arrival (AOA) changes. To achieve this, we have developed an optical antenna which uses a fine positioning mirror (FPM) capable of performing high-speed beam tracking and steering thus reducing to a great extent the optical power fluctuations of the received beam coupled to the SMF. This optical power fluctuation is partly a result of beam angle-of-arrival fluctuations caused by atmospheric turbulence. In our experiments we have tried to measure and quantify the magnitude of atmospheric turbulence experienced by an optical beam propagating through the atmosphere. First we demonstrate the relation between the AOA fluctuations and the frequency characteristics of the scintillation effects for a free-space optical beam propagating through a turbulent atmosphere. We use this information to determine the optimum antenna FPM tracking speed for improved performance and error free transmission. The results in the improved fiber received power as well as continuous error free transmission are presented.

Standardization on multimedia communications: computer-telephony-integration-related issues

Computer-telephony integration (CTI) has been developed since the 1960s. It is one of the major emerging multimedia communications applications. It provides enhanced telecommunications services controlled by a computer, that is by integrating the call handling capabilities of PBXs and the data processing capabilities of computers. CTI applications have become more popular and widespread with the rapid and deep penetration of personal computers and the dramatic growth of the Internet since the mid-1990s. CTI applications are being enhanced by means of more integration with Internet capabilities. Several standardization organizations and fora/consortia are developing standards/specifications for CTI in order to cope with the growing demand for multimedia communications. This article describes a brief historical sketch and the state of the art of CTI-related standards and specifications, which are still being developed.

Experimental demonstration of next-generation FSO communication system

Free-space optical communication has emerged as a competitive and viable technology for offering high data rates, improved capacity, cost-effective and an easy to deploy solution for providing connectivity between two points which are up to a few kilometers apart. In this paper we present experimental work which demonstrates the practicality of next generation free-space optical (FSO) communication systems suitable for short-haul, high-speed and robust data links. This experimental system is placed between two buildings in the Waseda University campus area for a communication link spanning a distance of 1 km. We outline the design of the optical antenna which uses 1550 nm wavelength and directly coupling a freespace optical beam to a single-mode fiber without the need for OE/EO conversion, to offer a communication link with data rates from 2.5 Gbps to 10 Gbps. The antenna is capable of overcoming most common limitations inherent in FSO communication systems, such as atmospheric induced beam wander and scintillation effects. A high-speed tracking mechanism which utilizes a fine positioning mirror (FPM) capable of tracking and controlling the received beam and focusing/steering most of beam power into the fiber is presented. This FPM is capable of suppressing the frequent power fluctuations caused by beam angle-of-arrival (AOA) variations. This paper presents experimental results of the FSO communication system capable offering stable performance in terms of measured bit-error-rate (BER). Performance results showing increasing the systems data rate from 2.5 Gbps to 10 Gpbs are also presented.

A new VoIP call admission control scheme with use of alternate routing for low call loss probability

Call admission control (CAC) is essential for the QoS guarantee communications. VoIP services require QoS guarantee in the existing telephony services. This paper proposes a new CAC scheme for VoIP to achieve an efficient use of network resources by adopting a dynamic routing and a routing history table. This scheme chooses the better route out of the two candidate routes where the admission conditions are satisfied. Two candidate routes are randomly chosen from all the available candidate routes. The routing history table memorizes the resulting routing information for the fixed time interval for the succeeding calls. Within the fixed time interval, the succeeding calls are assigned to the same route. After the fixed time interval, the memorized routing information is cleared, and the call admission control algorithm starts again from the beginning. It is confirmed by simulations that the proposed scheme achieves better performance than the existing CAC with alternate routing scheme.

A routing-aware handover scheme for mobile IP

One of the main issues of mobile IPv6 is handover latency that causes service disruption time. Although plenty of proposals significantly reduce the service disruption time, they suffer from redundant routing that causes packet misordering and bandwidth consumption during the process of inter-domain handover. In this paper, we propose R-MIP, a routing-aware handover scheme for mobile IP, that minimizes the redundant routing during the process of inter-domain handover by utilizing forwarding routers. R-MIP consists of forwarding router discovery and proactive handover. We evaluate R-MIP in the view of packet misordering and bandwidth consumption, and clarify its efficiency. We also evaluate the impact of the forwarding routers capacity since routers have limited resources. By strategically locating forwarding routers, e.g. next to the router that has peering to another domain, the redundant routing caused by inter-domain handover will be efficiently suppressed.

Inter-domain handover scheme based on forwarding router discovery for mobile IP networks

One of the main issues of mobile IPv6 is handover latency that causes service disruption time. Although plenty of proposals significantly reduce the service disruption time, they suffer from redundant routing that causes packet misordering and excess bandwidth consumption. In this paper, we propose a new scheme that minimizes the redundant routing during the process of inter-domain handover by utilizing forwarding routers. Our proposed scheme consists of forwarding router discovery and proactive handover. Furthermore, we evaluate the proposed scheme in the view of packet misordering and bandwidth consumption, and clarify the effectiveness of the proposed scheme.

Rate control on correlation coefficient of network delay

The demand to access multimedia data such as live video is increasing due to the spread of broadband access network. However, the Internet only provides so called best-effort service. The network condition of the Internet shows fluctuation. Delivering video without any control causes degradation of the final video quality. In this paper we propose a stream-rate control algorithm RC/sup 3/ that uses correlation of network delay to evaluate available bandwidth. We show performance of RC/sup 3/ derived from simulations.

IP and telecommunication integration: de jure and de facto standards have entered a new era

The remarkable growth of the Internet draws the attention of de jure and de facto standardization organizations which used to have few activities on IP technology. This article provides the new trends in standards/specifications of such organizations-including ITU-T, ATM-F, DAVIC, TIPHON, and others-on IP-related technologies. These organizations primarily focus on IP and telecommunication integration. IP technology itself is still the main focus of the IETF. The harmonized approach of these organizations is indispensable.