2010 Annual Report of Advanced Networked Environment Division, Cybermedia Center, Osaka University, Japan

This web page is the 2010 annual report of Advanced Networked Environment Division, Cybermedia Center, Osaka University (Ubiquitous Network Laboratory, Graduate School of Information Science and Technology, Osaka University / Nakano Laboratory).

Japanese version of this web page is here.

Table of contents

  1. Members
    1. Laboratory staffs
    2. Joint researcher
    3. Students
  2. Achievements
    1. Research on wireless mesh networks
      1. Time slot assignment algorithms to upstream links for decreasing transmission latency in IEEE 802.16j relay networks
      2. Time slot assignment algorithms considering adaptive modulation and coding in IEEE 802.16j relay networks
      3. Node repositioning for performance improvement in IEEE 802.16j relay networks
      4. Performance evaluation of IEEE 802.16j relay networks considering radio wave blocking by obstacles
      5. Parameter tuning of protocol interference model considering SINR for TDMA-based wireless mesh networks
      6. Improving coverage performance for wireless networks based on geometric algorithms
    2. Research on object counting and tracking
      1. Counting pedestrians from video sequences
      2. Counting pedestrians with compound-eye binary sensors
      3. Tracking pedestrians based on scenario-type hypothesis tracking
      4. Short-term precipitation forecasting using an optical flow algorithm
    3. Research on overlay network architectures
      1. Reduction of inter-ISP transit cost caused by overlay routing
      2. Proactive recovery from multiple failures utilizing overlay networking technique
      3. Scalable and density-aware measurement strategies for overlay networks
      4. The implication of overlay routing on ISPs' connecting strategies
    4. Research on architecture of transport layer for next-generation high-speed network
      1. Congestion control mechanisms for alleviating TCP unfairness in wireless LAN environment
      2. Analysis of power consumption in TCP data transmission over a wireless LAN environment
      3. Influence of power saving technique in IEEE 802.11 multi-hop networks on network performance
      4. Study on simultaneous measurements of available bandwidth on multiple parts of end-to-end network path
      5. Design and evaluation of a data transfer mechanism for video streaming over TCP
      6. Applications for inline network measurement technique to adaptive quality cntrol in video conference system
  3. Publications
    1. Journal papers
    2. International conference papers
    3. Theses
      1. Masters' Theses
      2. Bachelors' Theses

1. Members

1.1. Laboratory staffs

Hirotaka Nakano
Hirotaka Nakano
Professor
Go Hasegawa
Go Hasegawa
Associate Professor
Yoshiaki Taniguchi
Yoshiaki Taniguchi
Assistant Professor
Takako Inakagi
Takako Inakagi
Secretary
(until 2011.2)
Mari Onishi
Mari Onishi
Secretary
(from 2011.3)

1.2. Joint researcher

Masayuki Murata
Masayuki Murata
Osaka University
Graduate School of IST
Professor

1.3. Students

Shoji Kurakake
Shoji Kurakake
Doctoral Course 3rd
Yasuhiro Ogiri
Yasuhiro Ogiri
Doctoral Course 2nd
Masafumi Hashimoto
Masafumi Hashimoto
Doctoral Course 1st
Kazuhito Matsuda
Kazuhito Matsuda
Doctoral Course 1st
Xun Shao
Xun Shao
Doctoral Course 1st
Gyeongyeon Kang
Gyeongyeon Kang
Master Course 2nd
Shoichi Takemori
Shoichi Takemori
Master Course 2nd
Shinpei Tanaka
Shimpei Tanaka
Master Course 2nd
Yuki Ise
Yuuki Ise
Master Course 1st
Daisuke Kobayashi
Daisuke Kobayashi
Master Course 1st
Takafumi Shigefuji
Takafumi Shigefuji
Master Course 1st
Shizuka Fujisawa
Shizuka Fujisawa
Master Course 1st
Kentarou Imajou
Kentarou Imajou
Bachelor Course 4th
Tomoya Kitayama
Tomoya Kitayama
Bachelor Course 4th
Kazumasa Koitani
Kazumasa Koitani
Bachelor Course 4th
Ryuta Shohara
Ryuta Shohara
Bachelor Course 4th
Wataru Tourisaka
Wataru Tourisaka
Bachelor Course 4th

2. Achievements

2.1. Research on wireless mesh networks

Time slot assignment algorithms to upstream links for decreasing transmission latency in IEEE 802.16j relay networks

In IEEE 802.16j wireless multihop networks, a relay node transmits data to a gateway node through multihop relaying. The radio interference problem occurs when multiple relay nodes that exist in transmission range of each other communicate simultaneously at the same channel. IEEE 802.16j solves the problem by controlling communication opportunities, called time slots, by the TDMA mechanism. On packet transmissions with the TDMA mechanism, end-to-end transmission latency increases due to accumulation of delay at each relay node on transmission path, that is the duration on the relay node from the time receiving a packet to the time sending the packet. Especially, the increase in transmission latency is one of the serious problems for user clients that connect to the relay node with a large hop count from the gateway node. Therefore, decreasing transmission latency by time slot assignment algorithms is one of the important challenges in IEEE 802.16j networks. However, the most of past researches pay attention only to downstream transmissions in small-scale relay networks.

In this research, we focus on upstream transmissions in IEEE 802.16j and proposes the time slot assignment algorithms to decrease end-to-end transmission latency. One of the proposed algorithms assigns time slots considering the hop count from a gateway node, and the other takes the path from the relay node to the gateway node into account. In addition, the restriction in assigning time slots is introduced to reduce the delay at each relay node. The algorithms with the restriction assign later time slots considering the time slot order of links connecting a relay node. The performance of the proposed algorithms is evaluated through simulation experiments from the viewpoints of frame size and end-to-end transmission latency, and is confirmed that the proposed algorithms achieve small transmission latency regardless of packet generation rate in the network, and decrease the transmission latency by up to 70% compared with the existing algorithm.

[Related papers]

  1. Shimpei Tanaka, ``Time slot assignment algorithms to upstream links for decreasing transmission latency in IEEE 802.16j networks,'' Master’s Thesis, Graduate School of Information Science and Technology, Osaka University, Feb. 2011.
  2. Shimpei Tanaka, Go Hasegawa, Yoshiaki Taniguchi, and Hirotaka Nakano, “Time slot assignment algorithms for reducing upstream latency in IEEE 802.16j networks,” in Proceedings of the 7th Advanced International Conference on Telecommunications (AICT 2011), pp.6-11, Mar. 2011. [paper]

2.1.2. Time slot assignment algorithms considering adaptive modulation and coding in IEEE 802.16j relay networks

Time slot assignment algorithms considering adaptive modulation and coding in IEEE 802.16j relay networks

In multi-hop relay network based on IEEE 802.16j standard, tree-based network with wireless links by nodes provides network access service over the wide range by means of multi-hop communication between nodes in comparison with access point type network. Also, relay nodes can communicate with outside network by communication with gateway node close to outside network. In IEEE 802.16j, by adopting the scheduling scheme called Time Division Multiple Access (TDMA), time slot is assigned to link between nodes. Radio interference can be avoided by assigning different time slots to two or more links where radio interferes when communicating at the same time. The quality of the data transmission in the assigned time slot is influenced from the signal to noise ratio when transmitting. Therefore, it is necessary to consider the signal to noise ratio when the link which the time slot is assigned transmits in time slot assignment of the IEEE 802.16j multihop relay network. There is the adaptive modulation and coding as a communication method that enables the improvement of the amount of the data transmission while maintaining the transmission quality. However, there is no example of the examination concerning the performance evaluation and the performance improvement method in an existing research on time slot assignment on the assumption of the adaptive modulation and coding in the IEEE 802.16j multi-hop relay network. In this research, we propose the time slot assignment method of the IEEE 802.16j multi-hop relay network in consideration of the signal to noise ratio in the data transmission. In the proposal method, after assigning time slot to the link based on the simple interference model, the transmission quality of each link is evaluated based on the interference model which is considered the signal to noise ratio. Afterwards, the number of time slots to assign to the link that is the bottleneck in the network is increased. As a result, because the throughput of the bottleneck link increases, the improvement of the network performance can be expected. We evaluate the performance of the proposal method by a numeric calculation method which uses the data transfer throughput to the outside network and the total number of the time slot assigned to all links as evaluation figure. It is shown that the data transfer throughput improve about the maximum 50% compared to an existing method by the proposal method.

[Related paper]

  1. Tomoya Kitayama, ``Time slot assignment algorithms considering adaptive modulation and coding in IEEE 802.16j relay networks,'' Bachelor's Thesis, School of Engineering Science, Osaka University, Feb. 2011. (in Japanese)

2.1.3. Node repositioning for performance improvement in IEEE 802.16j relay networks

Node repositioning for performance improvement in IEEE 802.16j relay networks

The network based on IEEE 802.16j standard is getting attention as a technology which provides a wireless broadband service for the area where the construction of the wired network is difficult or metropolitan region by the features of the network such as high-speed data transmission, wide-range transmission region, easiness of construction and adaptation to mobile communication system. In IEEE 802.16j, the problem of radio interferences between links is solved by adopting the scheduling scheme called Orthogonal Frequency Division Multiple Access (OFDMA) which combines the time-division system and frequency division system. The time-division system divides channel into the unit of frames for a fixed time, and each link communicates by using the time slot into which the frame is divided for a fixed time. Avoiding radio interferences by assigning different time slots to links with radio interferences enables efficient communication.

In the wireless relay network using the time-division system, frame length, which depends on number of time slots to enable all links in the network to communicate without radio interferences are increased, when radio interferences occur between links which demand huge amounts of traffic and between many links. At this time, repositioning relay nodes in the network may be able to resolve or reduce radio interferences to decrease number of time slots needed in the network. Thus, node repositioning may improve the network throughput. However, there is no example of having examined the throughput improvement by node repositioning in the wireless relay network.

In this research, we evaluate the influence that repositioning relay nodes gives to the communication performance in the IEEE 802.16j relay network. First of all, we define the movement condition of a relay node, and then evaluate the change of the frame length by repositioning relay nodes in networks with various number of nodes, maximum transmission distance and interference ratio. As a result, we show that it is possible to reduce the frame length of about the maximum 16% by repositioning one node and to reduce the frame length of the maximum 22% by repositioning more relay nodes one by one.

[Related papers]

  1. Takafumi Shigefuji, Go Hasegawa, Yoshiaki Taniguchi, and Hirotaka Nakano, ``Node repositioning for network performance improvement of IEEE 802.16j relay networks,'' in Proceedings of the 8th IEICE QoS Workshop (QW8-P-01), Nov. 2010. (in Japanese) [paper]

2.1.4. Performance evaluation of IEEE 802.16j relay networks considering radio wave blocking by obstacles

Performance evaluation of IEEE 802.16j relay networks considering radio wave blocking by obstacles

Nowadays, mobile communication terminals are rapidly widespread and people have accessed Internet all over the world. Wireless radio communications are essential to enable the access. IEEE 802.16j multi hop relay network is attracting attention very much. It is different from star network using by IEEE 802.11. In IEEE 802.16j, nodes configure tree-based network with wireless links and provide communication over the wide range by means of multi hop communication between mesh nodes.

Until now, a network model which defined transmission range and interference range of transmission node as a circle is used when evaluation network throughput or service area of IEEE 802.16j multi hop relay network. In existing evaluation of relay network using the model, it is not assumed obstacles and does not consider the influence of radio waves by obstacles. Typically, radio waves are blocked, reected, or diffracted by obstacles. Therefore, it is possible that network performance decrease because obstacles blocked radio waves of nodes. The influence of interference by nearby nodes becomes small, and then the connection and interference of nodes in relay network may change. The change of connection and interference affect the network throughput because IEEE 802.16j supports Time Division Multiple Access (TDMA). Considering obstacles, some node become isolated nodes which cannot transmit any nodes. It in uences service area which relay network provide to client terminals. Consequently, evaluation of relay network considering obstacles is important in order to examine the possible application of relay network in real world.

This research investigates the performance of IEEE 802.16j relay network considering the in uence of radio waves by obstacles. Specifically, obstacles which only block radio waves set in the existing network model. This research evaluates the service area of the relay network, frame size and path length from gateway node to relay node with simulation using this network model. After simulation, it reveals that service area does not decrease so much when the number of obstacles is comparatively little, and then increase the service area in little increase of frame size by adding relay nodes. This research also evaluates network performance using a model supposed architectural design in Toyonaka campus of Osaka university. It clears up the association of network parameter by comparing to an evaluation result of a model which set obstacle randomly.

[Related papers]

  1. Yuki Ise, Go Hasegawa, Yoshiaki Taniguchi, and Hirotaka Nakano, ``Performance evaluation of IEEE 802.16j relay networks with consideration of blocking radio waves by obstacles,'' IEICE Technical Report (IN2010-54), pp.61-66, Sep. 2010. (in Japanese) [paper]

2.1.5. Parameter tuning of protocol interference model considering SINR for TDMA-based wireless mesh networks

Parameter tuning of protocol interference model considering SINR for TDMA-based wireless mesh networks

In time division multiple access (TDMA)-based wireless mesh networks, time slots should be assigned to links considering interference relationships. In graph theory-based time slot assignment algorithms, the protocol interference model is widely used to determine radio interference information, although this model is inaccurate when compared with actual radio interference. On the other hand, the signal-to-interference-plus-noise-ratio model (SINR model) gives more accurate interference relationships. However, the SINR model is difficult to apply to time slot assignment algorithms since the radio interference information cannot be determined before time slot assignment. In this research, we investigate the effect of parameters of the protocol interference model on the accuracy in determining interference relationships. Specifically, after assigning time slot to links based on the protocol interference model with various interference ratio which is the major parameter of the protocol interference model, we compare the interference relationship among links based on the protocol interference model and that based on the SINR model. Through simulation experiments, we show that accuracy of the protocol interference model is improved by up to 15% by adjusting the interference ratios of the protocol interference model.

[Related papers]

  1. Gyeongyeon Kang, ``A study on parameter tuning of protocol interference model considering SINR for TDMA-based wireless mesh networks,'' Master’s Thesis, Graduate School of Information Science and Technology, Osaka University, Feb. 2011.
  2. Gyeongyeon Kang, Yoshiaki Taniguchi, Go Hasegawa, and Hirotaka Nakano, “Extending the protocol interference model considering SINR for wireless mesh networks,” in Proceedings of the 7th Advanced International Conference on Telecommunications (AICT 2011), pp.26-31, Mar. 2011. (Best Paper Award) [paper]

2.1.6. Improving coverage performance for wireless networks based on geometric algorithms

Improving coverage performance for wireless networks based on geometric algorithms

In wireless mesh networks and some wireless sensor networks, each node has its own coverage area. In wireless mesh networks, the mesh node provides wireless Internet access service to client terminals within its coverage area. In wireless sensor networks, the sensor node monitors its coverage area and collects the obtained data. The performance of such networks, such as communication quality, sensing performance and energy consumption, is significantly affected by the coverage area size and its overlap degree. In order to determine the coverage area size for each node adequately, it is important to use the location information of neighboring nodes. However, due to the environments where the network is deployed, such information is not always available or only partially available.

In this research, we introduce several methods to determine the coverage area size according to the various kind of available information on neighboring nodes. The first contribution of this research is that we propose three methods to determine the coverage area size in WMNs, each of which assumes a different kind of available information of neighboring nodes. The first method is for situations where each node cannot obtain any information. The second method is suitable when each node can obtain the number of its neighboring nodes only. The third method requires precise location information of neighboring nodes. We conduct extensive simulation experiments to evaluate the performance of three methods in terms of total covered ratio, coverage overlap, energy consumption, and utilization efficiency of wireless network resources. We confirm the trade-off relationships between the accuracy of information and performance for these three methods. Furthermore, it is shown that the method which uses Voronoi diagram obtained from precise location information of neighboring nodes can obtain the best performance among these methods.

We next propose another method based on Voronoi diagram for situations where each node can obtain the distance information to its neighboring nodes only, which is the second contribution of this research. Specifically, in the proposed method, each node estimates the relative locations of its neighboring nodes based on the estimated distance information. It then calculates its Voronoi area and sets its coverage area size based on the shape of Voronoi area. Through simulation experiments in terms of total covered ratio, coverage overlap, and energy consumption, we confirm that the method can keep more than 99% coverage of the total area, regardless of the node density. In addition, it can reduce the energy consumption more than 50% when compared to that of the first method. Furthermore, the proposed method can perform well against the distance measurement error.

[Related papers]

  1. Shoichi Takemori, Go Hasegawa, Yoshiaki Taniguchi, and Hirotaka Nakano, ``Service area deployment of IEEE 802.16j wireless relay networks: service area coverage, energy consumption, and resource utilization efficiency,'' International Journal on Advances in Internet Technology, vol.3, no.1-2, pp.43-52, Sep. 2010. [paper]
  2. Shoichi Takemori, ``Improving coverage performance for wireless networks based on geometric algorithms,'' Master’s Thesis, Graduate School of Information Science and Technology, Osaka University, Feb. 2011.
  3. Shoichi Takemori, Go Hasegawa, Yoshiaki Taniguchi, and Hirotaka Nakano, ``Determining coverage area using Voronoi diagram based on local information for wireless networks,'' submitted for publication, Feb. 2011.

2.2. Research on object counting and tracking

2.2.1. Counting pedestrians from video sequences

Counting pedestrians from video sequences

In recent years, the demand for automatically counting pedestrians in event sites, buildings, or streets has been increased. Our research group has proposed a real-time counting method of pedestrians from video sequences where the target region is crowded and pedestrians are overlapping. In our method, the video sequences are retrieved from a stationary camera, and a liner virtual gate is set at appropriate location in the video sequences. When there is a difference of pixel value between the current frame and the background image at a pixel on the virtual gate, an optical flow whose origin is the pixel is detected. Detected optical flows are clustered based on their direction, size, and location. Then, the number of pedestrians passing through virtual gate is estimated for each cluster based on the size of cluster.

In this research, we proposed a detection method of optical flow as the fundamental step of our counting method. We use block matching algorithm to detect an optical flow from video sequences. By limiting the area of search to surrounding the virtual gate, the calculation amount can be decreased and detailed detection can be accomplished in real time. Through evaluations based on actual video sequences, we confirmed that calculation amount of detecting optical flows is decreased one over two-thousands and one-hundred, by comparing proposal method with traditional block matching method, and 92% of optical flows can be detected successfully in real time.

2.2.2. Counting pedestrians with compound-eye binary sensors

Counting pedestrians with compound-eye binary sensors

Recently, object tracking with sensor networks has attracted the attention of many researchers and developers. In our research group, we have proposed an object tracking method. In our proposed object tracking method, a sensor is assumed to be able to detect characteristics of moving objects such as direction. In this research, we think compound-eye binary sensors to realize the sensors of our proposed object tracking method. The compound-eye binary sensors consists of closely located multiple binary sensors which generate 1 bit information regarding objects' presence or absence within its sensing region. We propose a method to detect the moving direction and the velocity by using the compound-eye binary sensors. Through simulation evaluations, we confirm the fundamental characteristics of the compound-eye binary sensors and show that the distance between binary sensors should be carefully configured to achieve high detection ratio. Furthermore, we implement our method using off-the-shelf sensor nodes with passive infrared sensors and verify its practicality.

2.2.3. Tracking pedestrians based on scenario-type hypothesis tracking

Tracking pedestrians based on scenario-type hypothesis tracking

In this research, we propose an object tracking method called scenario-type hypothesis object tracking. In the proposed method, an indoor monitoring region is divided into multiple closed microcells using sensor nodes that can detect objects and their moving directions. Sensor information is accumulated in a tracking server through wireless multihop networks, and object tracking is performed at the tracking server. In order to estimate the trajectory of objects from sensor information, we introduce a novel concept of the virtual world, which consists of virtual micro-cells and virtual objects. Virtual objects are generated, transferred, and deleted in virtual micro-cells according to sensor information. In order to handle specific movements of objects in micro-cells, such as slowdown of passing objects in a narrow passageway, we also consider the generation of virtual objects according to interactions among virtual objects. In addition, virtual objects are generated when the tracking server estimates loss of sensor information in order to decrease the number of object tracking failures. Through simulations, we confirm that the ratio of successful tracking is improved by up to 29% by considering interactions among virtual objects. Furthermore, the tracking performance is improved up to 6% by considering loss of sensor information.

[Related papers]

  1. Masakazu Murata, Yoshiaki Taniguchi, Go Hasegawa, and Hirotaka Nakano, ``SHOT: Scenario-type hypothesis object tracking with indoor sensor networks,'' IEICE Transactions on Information and Systems, vol.E94-D, no.5, May 2011. (to appear)

2.2.4. Short-term precipitation forecasting using an optical flow algorithm

Short-term precipitation forecasting using an optical flow algorithm

For forecasting precipitation within a few hours, extrapolation methods based on the motion of observed rainy areas are generally used. This is because the computational time is shorter than that of simulating atmospheric disturbances based on hydrodynamics, especially for a few-hour forecasting. However, weather radars owned by Japan Meteorological Agency (JMA) cannot observe sudden and short-term downpours causing urban-area flood, since they do not have enough resolution and frequency. Recently, high-performance radars are being deployed to overcome the problem. However, there is no forecasting information provided using observed data by such high-performance radars. In this research, we propose a method to do short-term forecasting of precipitation with the observation data from high-performance radars. The proposed algorithm is based on an optical flow algorithm using block matching algorithm. We evaluated the proposed method and revealed that the proposed method can provide more accurate forecasting results compared with Nowcast provided by JMA, by more than 25% for between 5 and 60 minutes forecasting.

[Related paper]

  1. Kentaro Imajo, Go Hasegawa, Yoshiaki Taniguchi, Hirotaka Nakano, ``Short-term precipitation forecasting using an optical flow algorithm,'' IEICE Technical Report (CQ2010-83), vol.110, no.455, pp.93-98, Mar. 2011. (in Japanese) [paper]

2.3. Research on overlay network architectures

2.3.1. Reduction of inter-ISP transit cost caused by overlay routing

Reduction of inter-ISP transit cost caused by overlay routing

Overlay routing is an application-level routing mechanism and existing research has revealed that overlay routing can improve user-perceived performance. On the other hand, overlay routing may harm the ISPs' cost structure because of the policy mismatch between IP routing and overlay routing. In a previous study, we proposed a method to reduce inter-ISP transit cost caused by overlay routing while maintaining the effectiveness of the overlay routing. However, we evaluated the proposed method only in the PlanetLab environment, the node location of which is biased to North America. In addition, the previous evaluation focused only on limiting the degree of increase in the inter-ISP transit cost and did not explicitly consider the performance of the overlay routing. In the present research, we evaluate the proposed method in more general network environments, which are the generalized PlanetLab environment and the Japanese commercial ISPs network environment. We also evaluate the performance of the proposed method in terms of the trade-off relationships between the overlay routing performance and the inter-ISP transit cost over the entire network. In addition, we discuss the differences in the network properties in both environments, which affect the performance of the proposed method.

[Related papers]

  1. Kazuhito Matsuda, Go Hasegawa, Satoshi Kamei, and Masayuki Murata, ``Performance evaluation of a method to reduce inter-ISP transit cost caused by overlay routing,'' in Proceedings of the 14th International Telecommunications Network Strategy and Planning Symposium (NETWORKS 2010), pp.250-255, Sep. 2010. [paper]
  2. Kazuhito Matsuda, Go Hasegawa, Satoshi Kamei, and Masayuki Murata, ``A method to reduce inter-ISP transit cost caused by overlay routing based on end-to-end measurement,'' submitted for publication, Nov. 2010.

2.3.2. Proactive recovery from multiple failures utilizing overlay networking technique

Proactive recovery from multiple failures utilizing overlay networking technique

In this research, we propose a proactive recovery method against multiple network failures for large-scale packet switching networks. The proposed method exploits the overlay networking technique. Specifically, it constructs multiple logical network topologies from the original overlay network topology by assuming various failure patterns. When a failure is detected, our method selects one topology. Consequently, it can immediately recover from the failure by utilizing the selected topology without waiting for routing convergence in the network. When constructing multiple logical topologies, we take into account the correlation among overlay links in terms of the underlay links, and we merge multiple logical topologies into a single topology to decrease the number of topologies while keeping the recovery efficiency. Through the numerical evaluation results of the network reachability and average path length, we show that our method improves network reachability from 69% to 99% while keeping the path length short, when 5% underlay links are simultaneously down.

[Related papers]

  1. Takuro Horie, Go Hasegawa, and Masayuki Murata, ``Proactive recovery method against multiple network failures with overlay networking technique,'' in Proceedings of the 14th International Telecommunications Network Strategy and Planning Symposium (NETWORKS 2010), pp.89-94, Sep. 2010. [paper]

2.3.3. Scalable and density-aware measurement strategies for overlay networks

Scalable and density-aware measurement strategies for overlay networks

In overlay networks, in order to obtain accurate measurement results, it is important to take care of the measurement conflict problem. The problem occurs when overlapped paths are measured simultaneously. In this research, we propose a measurement method which reduce the number of measurement conflicts without centralized control to schedule the measurement. In this method, an overlay node uses traceroute to get path information to other overlay nodes and exchanges with nearby overlay nodes to estimate path overlaps. Based on the number of overlapped paths, the overlay node calculates an appropriate measurement frequency and a measurement timing to minimize the probability of measurement conflicts among overlapped paths. Furthermore, the overlay node exchanges measurement results with overlay nodes of overlapped paths to statistically obtain more exact measurement results.

[Related papers]

  1. Go Hasegawa and Masayuki Murata, ``Accuracy evaluation of spatial composition of measurement results in overlay networks,'' IEICE Technical Report (NS2010-16), vol.110, no.39, pp.1-6, May 2010. (in Japanese) [paper]
  2. Dinh Tien Hoang, Go Hasegawa, and Masayuki Murata, ``A distributed measurement method for reducing measurement conflict in overlay networks ,'' IEICE Technical Report (CQ2010-57), vol.110, no.287, pp.49-54, Nov. 2010. (in Japanese) [paper]
  3. Ryuta Shohara, Go Hasegawa, and Masayuki Murata, ``Performance evaluation of spatial composition method of measurement results in overlay networks,'' IEICE Technical Report (IN2010-180), vol.110, no.449, pp.217-222, Mar. 2011. (in Japanese) [paper]

2.3.4. The implication of overlay routing on ISPs' connecting strategies

The implication of overlay routing on ISPs' connecting strategies

The Internet is composed of many distinct networks, operated by independent Internet Service Providers (ISPs). There are primarily two kinds of relationships between ISPs: transit and peering. ISPs' traffic and economic relationships are mainly decided by ISPs’ routing policy. However, in today's Internet, overlay routing, which changes traffic routing at the application layer to better satisfy the applications' demands, is rapidly increasing, and brings challenge to the ISPs' settlement interconnection researches. The goal of this research is to study the economic implications of overlay routing on ISPs' peering incentive, costs and strategy choice. For this purpose, we introduce an ISP interconnection business model based on a simple ISPs' network. We then study the overlay traffic patterns in the network in various conditions. Combining the business model with traffic patterns, we study the ISPs' economic issues such as incentive to upgrade peering link and cost reduction conditions with various overlay traffic patterns and settlement methods. We also analyze the bilateral Nash equilibrium (BNE) strategy of ISPs in the network. At last, we give an numerical example to explain our results.

[Related paper]

  1. Xun Shao, Go Hasegawa, Yoshiaki Taniguchi, and Hirotaka Nakano, ``The implication of overlay routing on ISPs' connecting strategies,'' submitted for publications, Feb. 2011.

2.4. Research on architecture of transport layer for next-generation high-speed network

2.4.1. Congestion control mechanisms for alleviating TCP unfairness in wireless LAN environment

Congestion control mechanisms for alleviating TCP unfairness in wireless LAN environment

Per-flow unfairness of TCP throughput in the IEEE 802.11 wireless LAN (WLAN) environment has been reported in past literature. A number of researchers have proposed various methods for alleviating the unfairness; most require modification of MAC protocols or queue management mechanisms in access points. However, the MAC protocols of access points are generally implemented at hardware level, so changing these protocols is costly. As the first contribution of this research, we propose a transport-layer solution for alleviating unfairness among TCP flows, requiring a small modification to TCP congestion control mechanisms only on WLAN stations. In the past literature on fairness issues in the Internet flows, the performance of the proposed solutions for alleviating the unfairness has been evaluated separately from the network bandwidth utilization, meaning that they did not consider the trade-off relationships between fairness and bandwidth utilization. Therefore, as the second contribution of this research, we introduce a novel performance metric for evaluating trade-off relationships between per-flow fairness and bandwidth utilization at the network bottleneck. We confirm the fundamental characteristics of the proposed method through simulation experiments and evaluate the performance of the proposed method through experiments in real WLAN environments. We show that the proposed method can achieve better a trade-off between fairness and bandwidth utilization, regardless of vendor implementations of wireless access points and wireless interface cards.

[Related papers]

  1. Masafumi Hashimoto, Go Hasegawa, and Masayuki Murata, ``Trade-off evaluation between fairness and throughput for TCP congestion control mechanisms in a wireless LAN environment,'' in Proceedings of the 2010 International Symposium on Performance Evaluation of Computer and Telecommunication Systems (SPECTS 2010), pp.22-29, July 2010. [paper]
  2. Masafumi Hashimoto, Go Hasegawa, and Masayuki Murata, ``A transport-layer solution for alleviating TCP unfairness in a wireless LAN environment,'' IEICE Transactions on Communications, vol.E94-B, no.3, pp.765-776, Mar. 2011. [paper]

2.4.2. Analysis of power consumption in TCP data transmission over a wireless LAN environment

Analysis of power consumption in TCP data transmission over a wireless LAN environment

Reduction of power consumption is one of an important issue in wireless communications because most mobile devices are battery-driven. For effective power saving, it is important to understand the behaviors of the transport layer protocols used by upper-layer applications, since packet transmission and reception timing are mainly determined by those behaviors. In this report, we propose a power consumption model based on a treatment of detailed TCP behaviors within a WLAN environment. Comparing the model with and without ideal sleeping, we analyze the power consumption of a single wireless client as it sends data to a wired host by TCP. From the numerical results of our analysis, we show the lower-bound for power consumption in upstream TCP data transfer with ideal sleeping. We also discuss the trade-off between power saving and network performance in TCP data transfer.

[Related paper]

  1. Masafumi Hashimoto, Go Hasegawa, Masayuki Murata, ``Analysis of power consumption in TCP data transmission over a wireless LAN environment,'' IEICE Technical Report (NS2010-105), vol.110, no.339, pp.1-6, Dec. 2010. (in Japanese) [paper]

2.4.3. Influence of power saving technique in IEEE 802.11 multi-hop networks on network performance

Influence of power saving technique in IEEE 802.11 multi-hop networks on network performance

Recently, it's general that we use the Internet with wireless networks because of developing the wireless techniques. One of the strong points of wireless networks is no wiring. While, most of its devices work by battery, so we need control the networks on account of power consumption, and it's important to reduce power consumption and keep the network performance. In addition, not only wireless networks of access point type but also wireless multi-hop networks which are extensible by connecting wireless base station attract a great deal of people's attention. In this research, we focus on the multi-hop networks based on IEEE 802.11 wireless LANs' standard which organize easily with existing devices.

IEEE 802.11 standard has various numerous value of datarates with different encoding methods, electricity consumptions and communicable distances. Various standard in IEEE 802.11 has different features. Moreover, even if it's the same standard, there are different values with different hardware organizations. Because of that, it is necessary that we take specification of hardware into account when we discuss the power consumption in IEEE 802.11 wireless LANs. On the other hand, it is a general feature of wireless techniques that transmission power, communicable distance and frame error rate are related to one another; that is, there are many elements to determine power consumption and they relate variously in wireless multi-hop networks by IEEE 802.11 wireless LANs. Therefore, we should reveal their relation and assess the power consumption in data transmission.

In this research, at first we assessed the power consumption in 1 hop data transmission by CSMA/CA as MAC protocol in IEEE 802.11. Then, we also assessed in multi-hop data transmission. Moreover, we computed the power consumption with the data of existing wireless LANs' network interface devices. As a result, when frame error rate is same value, we can decrease the power consumption by higher datarate, but there are some cases we can use lower datarate to decrease the power consumption.

[Related paper]

  1. Wataru Tourisaka, ``Influence of power saving technique in IEEE 802.11 multi-hop networks on network performance,'' Bachelor's Thesis, School of Engineering Science, Osaka University, Feb. 2011. (in Japanese)

2.4.4. Study on simultaneous measurements of available bandwidth on multiple parts of end-to-end network path

Study on simultaneous measurements of available bandwidth on multiple parts of end-to-end network path

Using an available bandwidth on an end-to-end network path enables to detect congestion on the path, adapt the transmission rate, control a network topology in an overlay networks, control variously about network including route control and multi-pass transmission. Therefore, it is important to measure an available bandwidth on an end-to-end network path. Existing technology to measure an available bandwidth on an end-to-end network path can get only the value of the available bandwidth on bottleneck section on the path, but cannot specify bottleneck section on the path nor measure an available bandwidth on multiple parts of the path. On the other hands, for example, if it is possible to measure an available bandwidth on multiple parts of the end-to-end network path, where network characteristics on the path are various such as wireless network and wired network, considering the property in high packet loss rate environment it is able to make transmission rate lower. Thus, considering network characteristics, it is possible to control about network.

In this research, we study the method to measure available bandwidth on any multiple parts of the end-to-end network path simultaneously. In the existing method, the sender sends probe packets to the receiver, when the sender vary the sending packet interval time. Then, observing receiving packet interval time at the receiver, it can measure available bandwidth on end-to-end network path. In the proposing method, we improve the method of the controlling sending packet interval time, and also the router on the end-to-end network path timestamps packets. Thus, it measure available bandwidth on any part of the end-to-end network path.

Performance assessment in this proposed method is done by simple simulation. As a result, it was indicated that this method can estimate available bandwidth of all of each part of the path in the case available bandwidth in receiver side section is larger than in sender side section.

[Related paper]

  1. Kazumasa Koitani, ``A study on simultaneous measurements of available bandwidth on multiple parts of end-to-end network path,'' Bachelor's Thesis, School of Engineering Science, Osaka University, Feb. 2011. (in Japanese)

2.4.5. Design and evaluation of a data transfer mechanism for video streaming over TCP

Design and evaluation of a data transfer mechanism for video streaming over TCP

In recent years, video streaming services using TCP as a transport layer protocol represented by YouTube have been popular, with rapid increase of the network bandwidth. Congestion control of TCP increases the congestion window until a packet loss is detected. Therefore, the video streaming over TCP sends packets to a network at a higher speed than the video playback speed that takes the bandwidth of other competing traffic unnecessarily.

In this research, we first investigate the data transfer mechanism of existing video streaming services using TCP and show that the existing video streaming services perform data transfer at the extremely higher rate than the video playback speed. Then, we propose the data transfer mechanism for video streaming over TCP that does not take the network bandwidth excessively by controlling the data transfer at an application layer.

The proposed mechanism acquires the TCP state variables from the source host TCP, and estimates network congestion status. Moreover, the amount of buffered video data is acquired from a destination host. By adjusting the amount of data passed to a source host TCP in one round-trip time based on the network congestion status and the amount of buffered video data, the proposed mechanism controls the data transfer speed. Simulation results show that the proposed mechanism decreases the frequency of buffer underflow at the destination host, and does not take the bandwidth of background traffic.

[Related paper]

  1. Hiroyuki Hisamatsu, Go Hasegawa, and Masayuki Murata, ``Design and evaluation of a data transfer mechanism for video streaming over TCP,'' IEICE Technical Report (CQ2010-39), vol.110, no.198, pp.31-36, Sep. 2010. (in Japanese) [paper]

2.4.6. Applications for inline network measurement technique to adaptive quality cntrol in video conference system

Details are available from the following paper.

[Related paper]

  1. Go Hasegawa, Kenji Oike, Katsuhiro Amano, and Masayuki Murata, ``Applications for inline network measurement technique to adaptive quality cntrol in video conference system,'' IEICE Technical Report (IN2010-25), vol.110, no.116, pp.13-18, July 2010. (in Japanese) [paper]

3. Publications

3.1. Journal papers

  1. Shoichi Takemori, Go Hasegawa, Yoshiaki Taniguchi, and Hirotaka Nakano, ``Service area deployment of IEEE 802.16j wireless relay networks: service area coverage, energy consumption, and resource utilization efficiency,'' International Journal on Advances in Internet Technology, vol.3, no.1-2, pp.43-52, Sep. 2010. [paper]
  2. Masafumi Hashimoto, Go Hasegawa, and Masayuki Murata, ``A transport-layer solution for alleviating TCP unfairness in a wireless LAN environment,'' IEICE Transactions on Communications, vol.E94-B, no.3, pp.765-776, Mar. 2011. [paper]

3.2. International conference papers

  1. Masafumi Hashimoto, Go Hasegawa, and Masayuki Murata, ``Trade-off evaluation between fairness and throughput for TCP congestion control mechanisms in a wireless LAN environment,'' in Proceedings of the 2010 International Symposium on Performance Evaluation of Computer and Telecommunication Systems (SPECTS 2010), pp.22-29, July 2010. [paper]
  2. Takuro Horie, Go Hasegawa, and Masayuki Murata, ``Proactive recovery method against multiple network failures with overlay networking technique,'' in Proceedings of the 14th International Telecommunications Network Strategy and Planning Symposium (NETWORKS 2010), pp.89-94, Sep. 2010. [paper]
  3. Kazuhito Matsuda, Go Hasegawa, Satoshi Kamei, and Masayuki Murata, ``Performance evaluation of a method to reduce inter-ISP transit cost caused by overlay routing,'' in Proceedings of the 14th International Telecommunications Network Strategy and Planning Symposium (NETWORKS 2010), pp.250-255, Sep. 2010. [paper]
  4. Yoshiaki Taniguchi, Akimitsu Kanzaki, Naoki Wakamiya, and Takahiro Hara, ``Autonomous data gathering mechanism with transmission reduction for wireless sensor networks,'' in Proceedings of the 2011 International Conference on Communications, Computing and Control Applications (CCCA 2011), Mar. 2011. [paper]
  5. Shimpei Tanaka, Go Hasegawa, Yoshiaki Taniguchi, and Hirotaka Nakano, “Time slot assignment algorithms for reducing upstream latency in IEEE 802.16j networks,” in Proceedings of the 7th Advanced International Conference on Telecommunications (AICT 2011), pp.6-11, Mar. 2011. [paper]
  6. Gyeongyeon Kang, Yoshiaki Taniguchi, Go Hasegawa, and Hirotaka Nakano, “Extending the protocol interference model considering SINR for wireless mesh networks,” in Proceedings of the 7th Advanced International Conference on Telecommunications (AICT 2011), pp.26-31, Mar. 2011. (Best Paper Award) [paper]

3.3. Theses

3.3.1. Masters' Theses

  1. Gyeongyeon Kang, ``A study on parameter tuning of protocol interference model considering SINR for TDMA-based wireless mesh networks,'' Master's Thesis, Graduate School of Information Science and Technology, Osaka University, Feb. 2011.
  2. Shoichi Takemori, ``Improving coverage performance for wireless networks based on geometric algorithms,'' Master's Thesis, Graduate School of Information Science and Technology, Osaka University, Feb. 2011.
  3. Shimpei Tanaka, ``Time slot assignment algorithms to upstream links for decreasing transmission latency in IEEE 802.16j networks,'' Master's Thesis, Graduate School of Information Science and Technology, Osaka University, Feb. 2011.

3.3.2. Bachelors' Theses

  1. Kentarou Imajou, ``Short-term precipitation forecasting using an optical flow algorithm,'' Bachelor's Thesis, School of Engineering Science, Osaka University, Feb. 2011. (in Japanese)
  2. Tomoya Kitayama, ``Time slot assignment algorithms considering adaptive modulation and coding in IEEE 802.16j relay networks,'' Bachelor's Thesis, School of Engineering Science, Osaka University, Feb. 2011. (in Japanese)
  3. Kazumasa Koitani, ``A study on simultaneous measurements of available bandwidth on multiple parts of end-to-end network path,'' Bachelor's Thesis, School of Engineering Science, Osaka University, Feb. 2011. (in Japanese)
  4. Ryuta Shohara, ``Performance evaluation of spatial composition method for overlay network measurement,'' Bachelor's Thesis, School of Engineering Science, Osaka University, Feb. 2011. (in Japanese)
  5. Wataru Tourisaka, ``Influence of power saving technique in IEEE 802.11 multi-hop networks on network performance,'' Bachelor's Thesis, School of Engineering Science, Osaka University, Feb. 2011. (in Japanese)