Yohei Hasegawa

Improved data distribution for multipath TCP communication

Multi-homed environments are increasingly common, especially for mobile users. To efficiently utilize multiple access lines for single file transfer, multipath TCP communication methods have been proposed. A multipath TCP enables simultaneous distributed data transfer between two end-points on multiple TCP connections. However, these methods cannot fully utilize the available bandwidth of multiple paths because they do not properly consider the end-to-end delay of packet transmission, so out-of-order data arrival at a receiver causes a bottleneck in data sort operations. This problem is more severe in environments where the quality of each path is different or unstable, such as in wireless environments. To solve this problem, we propose a multipath TCP communication method that includes a data distribution method to enable in-order delivery at a receiver. We call this arrival-time matching load-balancing (ATLB). ATLB continuously calculates the delay of each path, including the TCP queuing delay at a sender and the network delay, and then sends a data segment through the TCP connection with the lowest end-to-end delay. Simulation results show that ATLB improves end-to-end throughput, especially in heterogeneous environments where the quality of paths differs. For example, ATLB enabled twice the throughput with the conventional multipath TCP. We also report performance evaluation results from our ATLB test bed system in a wireless network environment. Our ATLB test bed system was able to fully utilize the aggregate available bandwidth of unstable multiple wireless links.

Torus-Topology Data Center Network Based on Optical Packet/Agile Circuit Switching with Intelligent Flow Management

We review our work on an intra-data center (DC) network based on co-deployment of optical packet switching (OPS) and optical circuit switching (OCS), conducted within the framework of a five-year-long national R&D program in Japan (~March 2016). For the starter, preceding works relevant to optical switching technologies in intra-DC networks are briefly reviewed. Next, we present the architecture of our torus-topology OPS and agile OCS intra-DC network, together with a new flow management concept, where instantaneous optical path on-demand, so-called Express Path is established. Then, our hybrid optoelectronic packet router (HOPR), which handles 100 Gbps (25 Gbps × 4-wavelength) optical packets and its enabling device and sub-system technologies are presented. The HOPR aims at a high energy-efficiency of 0.09 [W/Gbps] and low-latency of 100 ns regime. Next, we provide the contention resolution strategies in the OPS and agile OCS network and present the performance analysis with the simulation results. It is followed by the discussions on the power consumption of intra-DC networks. We compare the power consumption and the throughput of a conventional fat-tree topology with the N-dimensional torus topology. Finally, for further power saving, we propose a new scheme, which shuts off HOPR buffers according to the server operation status.

Deployable multipath communication scheme with sufficient performance data distribution method

Multi-homed environments are increasingly common, especially for mobile users. And several multipath communication techniques have been proposed, such as multipath TCP communication techniques. Multipath TCP techniques have potential to fully utilize multiple paths, but, these methods have difficulties in implementation and deployment, because users need to modify their applications or operating system or both. In this paper, we propose simple multipath communication technique, which we call Arrival-Time matching Load-Balancing (ATLB). ATLB is designed to be easily implementable on several environments. Besides, we also introduce overlay network approach which implicitly provides parallel data transfer scheme to users. The ATLB continuously calculates transmission delays of each path, including TCP queuing delay at a sender and network delay, and then sends a data segment through the TCP connection with the lowest delay. Simulation results show that ATLB realizes sufficient performance even in heterogeneous environments where the quality of paths differs. Measurement results over our wireless LAN test-bed system suggest that ATLB can fully utilize the aggregate available bandwidth over unstable multiple wireless links.

Fast and Secure Packet Processing Environment for Per-Packet QoS Customization

To allow end users define network behavior and to make communication network evolution service-driven, we propose fast and secure capsule processing environment, dedicated CPU architecture named Stream Code and related mechanisms. In our proposedarc hitecture each packet contains a program for the packet written in Stream Code binary instructions. Every computational resources for packet processing is isolated for each packet and is cleared when execution time limit expires. This prevents malicious programs affecting other packets without virtual machines. Middleware attaches appropriate Stream Code programs considering the user requirements. A sample application, contents-sensitive multicast on our Stream Code emulator, in which a streaming application on a server attaches appropriate multicast program for each contents, optimizes packet loss in multicast in per-user and per-contents basis.

Flexible and automated operational control in SDN transport-base virtual router

We propose and demonstrate a virtual router based on SDN transport which has automatic topology discovery function. We show that the virtual router contributes to flexible and automated operational control.

Performance improvement in LEO-to-ground free space optical communication systems with adaptive distributed frame repetition

We proposed and evaluated the effectiveness of a simple rate control technique of Adaptive Distributed Frame Repetition (ADFR), which achieves both high speed link in the stable condition and suppresses the influence of turbulence-induced fading in the unstable condition. In order to estimate its performance in the LEO-to-Ground link with 10-Gb/s modulation speed, we developed a numerical simulator which enables us to calculate the frame error rate and the throughput under the specific turbulence condition emulated by random phase screens. We confirmed that ADFR can increase the link duration and the capacity by increasing the tolerance to the fading especially in the region of lower elevation angle. In addition, we evaluated its effectiveness through the comparison with the general adaptive rate control, in which the receiver sensitivity can be manipulated in accordance with the link conditions. The results show that ADFR provides similar performances with the sufficient received optical power.

Short-term rainfall attenuation prediction for wireless communication

This paper describes a method for predicting short-term rain attenuation for ground wireless communications. We propose machine learning methods using the k-nearest neighbour (KNN) and artificial neural network (ANN). We used a time-series of link attenuation calculated from a set of high-precision rainfall radar maps as training data. These two methods were verified with data from a different rainfall event. The results show that the two methods provide rainfall attenuation for wireless communications with sufficient accuracy.