We propose an efficient network upgrade and expansion method that can make the most of the next generation channel resources to accommodate further increases in traffic. Semi-flexible grid configuration and two cost metrics are introduced to establish a regularity in frequency assignment and minimize disturbance in the upgrade process; both reduce the fragmentation in frequency assignment and the number of fibers necessary. Various investigations of different configurations elucidate that the number of fibers necessary is reduced about 10-15% for any combination of upgrade scenario, channel frequency bandwidth, and topology adopted.

This paper investigates the prospects and challenges of hierarchical optical path networks. The merits and issues of introducing higher order optical paths are elucidated. State of the art of the key enabling technologies are demonstrated including hierarchical optical cross-connect switch architectures, hierarchical optical path network design algorithms, a newly developed waveband filter, and waveband conversion technologies.

Link-level and node-level blocking in photonic networks has been intensively investigated for several decades and the C/D/C approach to OXCs/ROADMs is often emphasized. However, this understanding will have to change in the future large traffic environment. We herein elucidate that exploiting node-level blocking can yield cost-effective large-capacity wavelength routing networks in the near future. We analyze the impact of link-level and node-level blocking in terms of traffic demand and assess the fiber utilization and the amount of hardware needed to develop OXCs/ROADMs, where the necessary number of link fibers and that of WSSs are used as metrics. We clarify that the careful introduction of node-level blocking is the more effective direction in creating future cost effective networks; compared to C/D/C OXCs/ROADMs, it offers a more than 70% reduction in the number of WSSs while the fiber increment is less than ~2%.

This paper presents past and recent trends of optical networks and addresses the future directions. First, we describe path networks with the historical backgrounds and trends. path networks have advanced by using various multiplexing technologies. They include time-division multiplexing (TDM), asynchronous transfer mode (ATM), and wavelength-division multiplexing (WDM). ATM was later succeeded to multi-protocol label switching (MPLS). Second, we present generalized MPLS technologies (GMPLS). In GMPLS, the label concept of MPLS is extended to other labels used in TDM, WDM, and fiber networks. GMPLS enables network operators to serve networks deployed by different technologies with a common protocol suite of GMPLS. Third, we describe multi-layer traffic engineering and a path computation element (PCE). Multi-layer traffic engineering designs and controls networks considering resource usages of more than one layer. This leads to use network resources more efficiently than the single-layer traffic engineering adopted independently for each layer. PCE is defined as a network element that computes paths, which are used for traffic engineering. Then, we address software-defined networks, which put the designed network functions into the programmable data plane by way of the management plane. We describe the evaluation from GMPLS to software defined networking (SDN) and transport SDN. Fifth, we describe the advanced devices and switches for optical networks. Finally, we address advances in networking technologies and future directions on optical networking.

This paper proposes an ATM traffic management method that utilizes a deterministic source traffic descriptor, a deterministic Usage Parameter Control (UPC) algorithm and a conservative statistical bandwidth allocation method all of which were developed considering the Cell Delay Variation (CDV) typically experienced in ATM networks. For the source traffic descriptor, sliding time interval-type descriptors are proposed. A newly-structured UPC method which combines a sliding window-type circuit and a 2-phase credit window type circuit is proposed. The method is precise and accurate and requires only a small amount of hardware. The proposed parameter conversion method considers the CDV generated between User and UPC point. A bandwidth allocation method based on the worst clumping pattern and UPC output pattern is proposed. The network efficiency degradation caused by CDV is calculated. This traffic management method not only guarantees the QOS of all connections but also allows for large statistical multiplexing gains. The proposed method will, therefore, make it possible to create a more effective B-ISDN, one that can offer cost-effective broadband VBR services.

A wavelength division multiplexing (WDM) optical path-based Internet protocol (IP) backbone network is proposed as a cost-effective way of realizing robust IP-over-photonic systems. The WDM optical path is based on WDM transmission and wavelength routing. Between end-to-end IP backbone routers, the WDM optical path, a fat and robust optical pipe, is defined across photonic transport systems (PTS's). Tera-bit class PTS's will be required for the future IP backbone network and this level of performance is achievable. Optical layer routing is done at intermediate nodes, so the electrical packet-by-packet routing required by existing systems is eliminated. An optical signal format that permits cost-effective IP packet transmission is presented. WDM optical paths directly accommodate the IP packets via layer-2 frames. The cost-effectiveness of the proposed system, especially for heavy traffic, is demonstrated from the viewpoint of the overall network traffic transport capability and network node cost. The proposed system is as robust as existing systems; e. g. fault/degradation localization mechanism and optical layer network protection one are implemented. Thus the proposed IP-over-photonic system will create cost-effective and robust IP backbone networks.

This paper describes the requirements for fault recovery on photonic networks and proposes a fast restoration scheme for recovering optical networks. The proposed scheme is a type of pre-assignment restoration. The features of the scheme are that it is suitable for multi-recovery classes aimed at fine control of the optical paths and that it establishes harmonization between restoration control and distributed network control such as in IP networks. The scheme is implemented on Photonic multi protocol label switching (MPLS) routers. A restoration demonstration was performed and recovery was achieved within 500ms in the optical layer.

Recent technical advances in WDM (Wavelength Division Multiplexing) technologies suggest that their practical application is imminent. By adopting WDM technologies in the transport network, a bandwidth abundant B-ISDN could be realized cost-effectively. This requires the introduction of WDM technologies, especially into the path layer. This paper explores optical path cross-connect (OPXC) nodes that offer very high levels of expandability because existing traffic demands, which are rather limited, must be efficiently supported while permitting easy step-wise expansion in capacity. This paper highlights modularity with regard to incoming/outgoing links. The OPXC architecture that offers the highest modularity is elaborated, and its transmission characteristics, optical loss and switching power consumption are evaluated. This paper also examines OPXC architecture considering the interface needed to connect electrical path cross-connects. The proposed OPXC architectures provide flexibility and minimum investment to encourage the early introduction of B-ISDN and also supports incremental network growth to match traffic demand. The design of OPXC parameters in terms of transmission performance is shown to ensure the applicability of the proposed OPXC architecture to long-haul optical fiber transmission networks. This is made possible with the low optical component losses offered by the OPXC. The proposed OPXC architectures will, therefore, be applied not only to regional networks, but also to global area networks. Thus they will play a key role in realizing the optical path infrastructure for the future bandwidth abundant B-ISDN.

The probe used in the conventional SAR measurement is usually calibrated in a well filled with tissue-equivalent liquid surrounded by a rectangular waveguide and a matching dielectric window in the frequency range from 800 MHz to 3 GHz. However, below 800 MHz, the waveguides are too large to be used for the calibration. Therefore, we have developed another technique of calibrating the SAR-probe, that is, relating the output voltage of the probe to the field intensity produced by a reference antenna in the tissue-equivalent liquid by using two-antenna method. In this paper, the calibration system using the reference dipole antennas in the liquid at 450 MHz, 900 MHz and 2450 MHz is presented and far-field gain of the reference antenna and calibration factor of the SAR-probe are measured and compared with those obtained by using the conventional waveguide system.

This paper presents a newly developed analytical method which evaluates the virtual path bandwidth control effects for a general topology ATM (Asynchronous Transfer Mode) transport network. The virtual path concept can enhance the controllability of path bandwidth. Required link capacity to attain a specified call blocking probability can be reduced by applying virtual path bandwidth control. This paper proposes an analytical method to evaluate the call blocking probability of a general topology ATM network, which includes many virtual paths, that is using virtual path bandwidth control. A method for the designing link capacities of the network is also proposed. These methods make it possible to design an optimum transport network with path bandwidth control. Finally, a newly developed approximation technique is used to develop some analytical results on the effects of dynamic path bandwidth control are provided to demonstrate its effectiveness.

One performance limitation of the "Leaky Bucket algorithm" for usage parameter control and traffic management in Asynchronous Transfer Mode (ATM) networks is analyzed. Simulation results show that the conventional statistical bandwidth allocation method, which uses the most bursty pattern permitted by the Leaky Bucket algorithm, can not guarantee the QOS of established Virtual Channels/Paths (VC/VP). As a result, the VC/VP bandwidth allocation method based on the Leaky Bucket algorithm is proven to be unsatisfactory.

This paper presents a fast and large-scale optical circuit-switch architecture for intra-datacenter applications that uses a combination of space switches and wavelength-routing switches are utilized. A 1,440 × 1,440 optical switch is designed with a fast-tunable laser, 8×8 delivery-and-coupling switch, and a 180×180 wavelength-routing switch. We test the bit-error-ratio characteristics of all ports of the wavelength-routing switch using 180-wavelength 10-Gbps signals in the full C-band. The worst switching time, 498 microseconds, is confirmed and all bit-error ratios are acceptable.

We propose an efficient network design algorithm that realizes shared protection. The algorithm iteratively improves the degree of wavelength resource usage and fiber utilization. To achieve this, we newly define two metrics to evaluate the degree of wavelength resource usage of a pair of working/backup paths and the fiber utilization efficiency. The proposed method iteratively redesigns groups of paths that are selected in the order determined by the metrics. A numerical analysis verifies that the proposed algorithm can substantially reduce the required wavelength resources and hence fiber cost. It is also verified that the computational complexity of the proposed algorithm is small enough to terminate within practicable time.

This paper investigates the linearity performance of analog video transmission systems which use semiconductor laser diodes. The main origins of system linearity degradation are shown to be reflected laser light and speckle noise. It is demonstrated that a laser with an external reflector produces a nonlinear response which degrades the laser modulation properties. It is also revealed that in analog video transmission systems using graded-index multimode fibers, speckle noise is so serious that a reduction in laser coherency is essential, and a new technique employing an optical feedback scheme to reduce speckle noise in investigated. The high quality of results obtained from transmission tests employing the proposed method have confirmed the feasibility of analog video transmission using semiconductor laser diodes.

Adaptive and flexible network control technology is considered essential for efficient network resource utilization. Moreover, such technology is becoming a key to cost-effectively meet diverse service requirements and accommodate heavier traffic with limited network resources; demands that conventional static operation cannot satisfy. To address this issue, we previously studied dynamic network control technology for large-capacity network services including on-demand broad bandwidth provisioning services and layer-one VPN. Our previous study introduced a simple weighting function for achieving fairness in terms of path length and proposed two dynamic Make Before Break Routing algorithms for reducing blocking probability. These algorithms enhance network utilization by rerouting existing paths to alternative routes while completely avoiding disruption for highly reliable services. However, the impact of this avoidance of service disruption on blocking probability has not been clarified. In this paper, we propose modified versions of the algorithms that enhance network utilization while slightly increasing disruption by rerouting, which enable us to elucidate the effectiveness of hitless rerouting. We also provide extensive evaluations including a comparison of original and modified algorithms. Numerical examples demonstrate that they achieve not only a high degree of fairness but also low service blocking probability. Hitless rerouting is achieved with a small increase in blocking probability.

We realize a multicore erbium-doped fiber amplifier (MC-EDFA) with 2dB optical gain improvement (average) by recycling the residual 0.98μm pump light from the MC-EDF output. Eight-channel per core wavelength division multiplexed (WDM) Nyquist PM-16QAM optical signal amplification is demonstrated over a 40-minute period. Furthermore, we demonstrate the proposed MC-EDFA's stability by using it to amplify a Nyquist PM-16QAM signal and evaluating the resulting Q-factor variation. We found that our scheme contributes to reducing the total power consumption of MC-EDFAs in spatial division multiplexing (SDM)/WDM networks by up to 33.5%.

The effectiveness of traffic shaping for VBR traffic is analyzed. Evaluation results prove that traffic shaping can improve link efficiency for most forms of bursty VBR traffic and that link efficiency gains of more than 250% can be expected without the shaping delay imposing any significant QOS deterioration. Traffic shaping increases the link efficiency to about 80% for traffic with short burst repetition periods. The traffic shaping techniques and analytical results described herein can be employed in the traffic management of future B-ISDN/ATM networks.

Optical path technology that employs both WDM/FDM and wavelength routing will play a key role in supporting future high bandwidth transport networks. WP/VWP (Wavelength Path/Virtual Wavelength Path) technologies are very effective in realizing optical path networks. In these networks, since photonic wavelengths are scarce resources, the number of wavelengths required to construct the network must be minimized. However, the wavelength assignment problem, minimizing the number of wavelengths, is an NP-complete problem. Solving this problem heuristically is an important issue for designing large-scale WP/VWP based networks that are also practical. To realize optical path networks, we need to develop path accommodation design algorithms that heuristically solve the wavelength assignment problem. This paper proposes novel path accommodation design algorithms for WP/VWP networks that minimize the number of wavelengths required. We numerically elucidate that the numbers of wavelengths required for active WPs and VWPs are almost equal. When link failure restoration is considered, they are different; more wavelengths are needed with the WP scheme than with the VWP scheme. It is also demonstrated that the proposed algorithms are applicable to a large scale network design.

This paper surveys and discusses traffic control in ATM networks. Traffic control can be classified into path level control, call level control and cell level control. The effectiveness and the remaining problems are clarified for each level of control. The emphasis is on research activities in this field in Japan.

This study compares the performances of waveband protection and wavelength path protection in survivable hierarchical optical path networks. Network costs and the number of switching operations necessary are evaluated for different ratios of protected demand. Numerical results demonstrate that waveband protection can drastically decrease the number of switching operations in the case of failure, while both waveband and wavelength path protection effectively reduce the network resources needed compared to single layer optical path networks.