Published papers

In this paper, we share our experiences with a Trans-Pacific, collaborative mixed-reality (MR) based plant walk tour involving three geographical locations: (i) Dallas, Texas; (ii) Denver, Colorado; and (iii) Yokohama, Japan. The Wide Area Network (WAN) from Japan to Denver and from Denver to Dallas was through 100 Gbps optical links. These links were a mixture of leased and dedicated infrastructure. The average observed latency was around 131 ms and the maximum available bandwidth was 26.6 Gbps. The tour developed using a component-based framework, provided group travel with a leader-follower criterion involving a semi-active travel technique. By applying a 'modified Virtual Reality' (mVR) triangle paradigm, we examined the user experience of this collaborative tour. We considered Visualization, Synchronization, and Exploration design choices as the three key aspects of the mVR triangle. We assessed the user experience of the tour through a Gibbs triangle, with each of the composition of the Gibbs triangle being a key aspect of the mVR triangle. We obtained users' scores on the three aspects of the mVR using a seven-point, Likert scale questionnaire. We conducted 14 sessions of group travel. Overall, we found the user experience of the trans-pacific plant walk tour to be in the Balanced Experience Region (BER) region or the center part of the Gibbs triangle, which conveys that the majority of the participants experienced a balanced influence of mVR aspects throughout the tour.

Optical networks are well suited to enable massive data exchanges between datacenters. Elephant data flows can be routed over custom provisioned and dedicated lightpaths (optical flows) while other (mice) flows, which are routed by electronic switches, are unaffected. In some solutions, wavelength-selective switch (WSS) devices are employed in the optical nodes to physically and individually route each lightpath toward its destination. WSS devices take time to be switched and consequently delay the lightpath setup completion time. In this paper, the authors present three approximate Markov chain models to account for three different WSS service policies. These models estimate the expected lightpath setup and teardown time across an optical node that makes use of WSS devices. The first and more conventional policy (model) assumes that each setup and teardown request is handled individually, while the other two policies (models) assume that groups of setup and/or teardown requests are handled together by the WSS. The models' estimates are compared against the results obtained from a computer-based simulator, where both analytical models and simulator account for experimentally measured WSS response times. The simulator is also used to investigate the end-to-end lightpath setup time across an arbitrary mesh network. Results obtained from the models and simulator show that the group-based service policies outperform the conventional policy at high loads. The group-based policies are especially useful in the presence of lightpaths that are frequently set up and have relatively short holding time (i.e., short duration of elephant-optical flows).

This paper shows the concept of the elastic lambda aggregation network (EλAN) that will achieve an elastic common access infrastructure for the metro-access network. It proposes a service restoration technique that uses optical path switching and intercentral office handover for EλAN to recover from disasters. The feasibility of the proposed service restoration technique is successfully demonstrated for the first time by using a prototype testbed of a metro-access network. By applying both orthogonal frequency division multiplexing and adaptive modulation, the system automatically changes the transmission parameters (modulation level, the number of subcarriers, and symbol rate) according to the service requirements and conditions of the optical distribution network, such as the link's end-to-end optical loss, in order to achieve accommodate multiple services. In the experiment, an optical network unit in a faulted system automatically reconnected within 10 s to another office 20-km away with the same throughput.

The energy consumption of network virtualization environments (NVEs) has become a critical issue. In this paper, we focus on reducing the data switching energy consumption of NVE. We first analyze the data switching energy of NVE. Then, we propose a dynamic energy efficient virtual link resource reallocation (eEVLRR) approach for NVE. eEVLRR dynamically reallocates the energy efficient substrate resources (sresources) for virtual links with dynamic changes of embeddable s-resources to save the data switching energy. In order to avoid traffic interruptions while reallocating, we design a cross layer application-session-based forwarding model for eEVLRR that can identify and forward each data transmission flow along the initial specified substrate data transport path until end without traffic interruptions. The results of performance evaluations show that eEVLRR not only guarantees the allocated s-resources of virtual links are continuously energy efficient to save data switching energy but also has positive impacts on virtual network acceptance rate, revenues and s-resources utilization.

Disaggregation and white-box approaches are useful in expediting disaster recovery of optical transport networks. When an optical network system is damaged by a large disaster, the damaged devices can be replaced by the disaggregated functional devices, while disregarding vendor boundaries. In the light of the disaggregation and white-box approaches, we are developing a prototype of disaggregated portable emergency optical system (EOS) for early and low-cost postdisaster recovery. The EOS is customizable, and different functions can be selected to meet the different requirements in disaster recovery. In addition to replacing the damaged functions of the original optical system with an EOS, we introduce two new disaggregated functions into the EOS for postdisaster recovery. First, we introduce an optical supervisory channel handshake scheme to aid the interconnection of the surviving optical resources. Second, we introduce a scheme to achieve the quick recovery of the damaged control plane with the surviving or first restored wireless access capability. This is highly desired not only for emergency network control, but also for the quick collection of the network damage information. These two new functions have been implemented into the EOS prototype. We experimentally demonstrated the network recovery of the data-plane and the control-plane with the EOS.

An online parameter-tuning method for the energy-efficient data center network (DCN) named HOLST (high-speed optical layer 1 switch system for time-slot-switching-based optical data center networks) is proposed. HOLST comprises an optical circuit switching network, optical slot switching network, and electrical packet switching network for the spine layer. It requires flows to be assigned to optimal switches to achieve high power savings. In this study, first we experimentally confirm that the change in the DCN characteristics in the short term of actual data center traffic downgrades the accuracy of flow classification. Subsequently, we propose a procedure for reconfiguring a flow classification function and a method for online parameter tuning for this function. Finally, the accuracy of the flow classification method using the proposed tuning and estimated switching energy consumption in the spine layer are evaluated. The proposed online parameter-tuning function increases the accuracy of flow classification and reduces switching energy consumption relative to the conventional flow classification function.

The activation time when creating lightpaths is adversely affected by the time optical amplifiers, which are required to adjust the newly added signal power. This shortcoming is particularly true with multicore erbium-doped amplifiers. A fibre span power management scheme is proposed based on the use of dummy wavelength signals, whose function is to alleviate this shortcoming and shorten the required lightpath activation time. An analytical model is developed to estimate the effectiveness of the proposed scheme in achieving this goal.

Software defined networking (SDN) and OpenFlow, which enables the abstraction of vendor/technology-specific attributes, improve the network control and management flexibility of optical transport networks. In this paper, we present an interoperability demonstration of SDN/OpenFlow-based optical path control for multi-domain/multi-technology optical transport networks. We also summarize the abstraction approaches proposed for multi-technology network integration at an SDN controller.

Software defined networking (SDN) and OpenFlow, which enables the abstraction of vendor/technology-specific attributes, improve the network control and management flexibility of optical transport networks. In this paper, we present an interoperability demonstration of SDN/OpenFlow-based optical path control for multi-domain/multi-technology optical transport networks. We also summarize the abstraction approaches proposed for multi-technology network integration at an SDN controller.

Hitless defragmentation has been introduced as an approach to limit the spectrum fragmentation in elastic optical networks without traffic disruption. It facilitates the accommodation of new request by creating large spectrum blocks, as it moves active lightpaths (retuning) to fill in gaps left in the spectrum by expired ones. Nevertheless, hitless defragmentation witnesses limitations for gradual retuning with the conventionally used first fit allocation. The first fit allocation stacks all lightpaths to the lower end of the spectrum. This leads to a large number of lightpaths that need to be retuned and are subject to interfere with each other’s retuning. This paper proposes a route partitioning scheme for hitless defragmentation in order to increase the admissible traffic in elastic optical networks. The proposed scheme uses route partitioning with the first-last fit allocation to increase the possibilities of lightpath retuning by avoiding the retuning interference among lightpaths. The first-last fit allocation is used to set a bipartition with one partition allocated with the first fit and the second with the last fit. Lightpaths that are allocated on different partitions cannot interfere with each other. Thus the route partitioning avoids the interferences among lightpaths when retuning. We define the route partitioning problem as an optimization problem to minimize the total interferences. We then introduce an integer linear programming problem (ILP) that yields an optimal routing and partitioning. We prove that the route partitioning problem is NP-hard. We present a heuristic algorithm for large networks, where the ILP to represent the route partitioning is not tractable. The simulation results show that the proposed route partitioning scheme using first-last fit outperforms the conventional first fit allocation for hitless defragmentation in term of allowable traffic.

Elastic Lambda Aggregation Network (EλAN) is expected to maintain the connectivity between Optical Line Terminal (OLT) and Optical Network Units (ONU) by using reconfigurable Active Optical Distribution Network (ODN) in the case of huge network failure. However, when surviving OLTs are very limited, limited number of ONUs can be accommodated even if restoration paths are available. In this paper, we propose a novel recovery method to maintain the connectivity of a large number of ONUs by virtualizing OLT and switching ONU groups using TDMA. In the proposed method, the effect of large communication intervals on the quality of services is alleviated by inserting a proxy. Numerical results showed that the connectivity of more ONUs can be maintained by using the proposed method compared to the restoration method. We also observed that the insertion of the proxy prevents UDP packet loss and improves TCP throughput by 9.8 Mbps at a maximum by the experiment using the EλAN prototype system.

Elastic Lambda Aggregation Network (EλAN), the next-generation access and aggregation integrated network, has been proposed. In EλAN, Optical Line Terminals (OLTs) are programmable, and Logical-OLTs (L-OLTs) can be migrated between different P-OLTs. L-OLT migration leads to enhance failure resistance and improve power saving. We have experimented L-OLT migration between P-OLTs in our laboratory. However it is necessary to evaluate how L-OLT migration time changes according to physical distance. Therefore we made an experiment of L-OLT migration in wide area network on JGN-X. This paper proposes estimation equation of L-OLT migration time. The equation leads to determine L-OLT arrangements considering time of L-OLT migration for physical distance.