Shinya Yamamura

Virtual segment: Store–carry–forward relay-based support for wide-area non-real-time data exchange

Abstract We have proposed the concept of the virtual segment (VS), in which a global communication service is provided by combining a store–carry–forward scheme using vehicles with broadband wireless/wired network infrastructures along roads connected to the Internet. The VS can be a practical framework for non-real-time, asynchronous message transfer (especially for large messages) in a cost-effective manner. In this study, a critical implementation design issue, the message forward scheduling, in the VS approach is discussed and investigated through computer simulation by our developed VS simulator that has reflected the results of the field experiment for realistic performance evaluation.

Data transfer exploiting multiple heterogeneous challenged networks – implementation and application

A concept of integrating multi-path data transfer (IMPDT) is introduced to efficiently transfer a large-sized data if multiple heterogeneous networks are available but none of them has sufficient performance for the requested task. IMPDT integrates heterogeneous networks not simply for bandwidth aggregation but also for providing sustainable control information exchange on a stable but low data rate network path, being handled separately from data transmission on different network paths in different ways. In the present paper, the design of a prototype implementation of IMPDT is discussed especially focusing on retransmission, which is evaluated by field experiments using different types of wireless communication systems. Then the design of a prototype implementation of web access system is discussed as an interactive application over multiple challenged networks by integrating the HTTP protocol and the IMPDT scheme, which implies a potentially wide applicability of our proposed scheme.

Proactive Content Caching for Mobile Video Utilizing Transportation Systems and Evaluation Through Field Experiments

In order to provide high-quality and highly reliable video delivery services for mobile users, especially train passengers, we propose a proactive content caching scheme that uses transportation systems. In our system, we place content servers with cache capability [e.g., content centric networking/named data networking (CCN/NDN)] in every train and station. Video segments encapsulated by MPEG-Dynamic Adaptive Streaming over HTTP (MPEG-DASH) are distributed and pre-cached by the station servers before the trains arrive at the stations. The trains receive content via high-speed wireless transport, such as wireless LANs or millimeter waves, when they stop at the stations. We developed prototype systems based on hypertext transfer protocol and CCN/NDN protocol, evaluate their performance through two field experiments that uses actual trains, and compare with traditional video streaming over cellular networks. Such evaluations indicate that our system can achieve high-quality video delivery without interruption for up to 50 users simultaneously.

Virtual Segment: Store-Carry-Forward Relay-Based Support for Wide-Area Non-Real-time Data Exchange

In the Internet of the future, a flexible, dynamic combination of wireless and wired access networks is expected to be a key driver for enlarging the broadband communication service area. However, in general, the number of broadband wireless access points is limited due to their cost, and hence, they cannot cover the whole network. On the other hand, various message delivery schemes based on store-carry-forward routing with some extensions have been studied to support nonreal- time communication in sparse or intermittent networks. However, communication services based solely on the storecarry- forward schemes covering a large area are inefficient because the delay time for message delivery increases in proportion to the size of the service area. Therefore, to extend the communication service area with controllable performance in a cost-effective manner, the authors have proposed a concept of Virtual Segment (VS) in which global communication service is provided by combining a store-carry-forward scheme with broadband wireless/wired network infrastructures connected to the Internet to deploy the supplementary infrastructure. Along this line, in the present paper, the issues on the addressing and the message transfer methods in VS approach are considered which are essential for designing a practical framework for non-real-time, asynchronous data communication, especially for large-sized message transfer. A logical architecture for implementation is also presented. Finally, the message transmission methods are examined using computer simulation.

Store-Carry-Forward Based Networking Infrastructure: Vision and Potential

In response to the increasing demand for asynchronous mass data exchange even by mobile users, the DTN-related technologies are considered promising for an efficient use of limited network resources and low-cost deployment at the expense of communication delays. The authors previously proposed a Virtual Segment concept aiming at a practical network infrastructure combining Internet-connected broadband wireless network devices, which have high data transmission rates but limited coverage areas, with a store-carry-forward networking by vehicles that is capable of bridging the gaps in broadband service areas in an asynchronous fashion. In this paper, as an extended framework to combine and integrate the wired/wireless communication networks with the transportation networks, Global Information Logistics Infrastructure (GILI) is briefly discussed. A case study of the GILI in a field experiment using school buses is reported with examining its potential. For this experiment, we develop a remote maintenance tool, as an example of store-carry-forward based asynchronous applications, which is shown to be useful in our framework.

The state of DTN evaluation

The most common definition of a challenged network, or Delay-Tolerant Network, is one in which there is no guarantee of a contemporaneous end-to-end path from source to destination. Because of the breadth of of the field, a wide variety of evaluation techniques have been developed and utilized. The goal of this panel is to showcase and discuss an interesting and current selection of evaluation efforts. In this year’s CHANTS submissions over a third used the ONE simulator from Aalto University [1, 2]. Keeping in mind that not all papers were based on simulation, it is fair to say that the ONE is becoming the de-facto simulation tool for certain types of DTN research. This is beneficial in that it facilitates comparisons between routing protocols, and allows researchers to focus their efforts on a single accessible tool. However the growing body of work that compares protocols that exist only in simulation may indicate an over-reliance on simulation and could lead to overlooking important practical technical challenges in the field. Another approach to evaluation is to deploy trial nodes in a real environment. Masato Tsuru has been involved in such field tests in collaboration with Japan’s NIICT and will be able to discuss their reasons for carrying out their experiments and the challenges involved. In addition the DARPA DTN project involved a considerable amount of field testing, and BBN’s Armando Caro will be able to give his perspective on the value and importance of their tests.

Performance Evaluation of Proactive Content Caching for Mobile Video through 50-User Field Experiment

Providing robust content delivery service, such as Video on Demand, with efficient wireless resource usage is important for mobile users. To achieve this, we have proposed a proactive content caching scheme utilizing transportation systems (e.g., train.) Because our previous prototype is immature and has a scalability issue, in this paper, we introduce efficient transmission mechanism of Interest messages in order to improve throughput efficiency in mobile NDN. We develop two prototypes based on HTTP and NDN and then evaluate prototype performance by performing larger-scale field experiments on actual commercial railroad line. Evaluations conclude that our system can achieve high efficient content transfer and fully utilize wireless network bandwidth. Therefore, our system can provide high-quality video streaming for up to 50 users simultaneously.

Web browsing over multiple heterogeneous challenged networks

The authors previously proposed Integrating Multi-Path Data Transfer (IMPDT) that enables an efficient transfer of a large-sized data by integrating multiple heterogeneous wireless access networks, when they are concurrently available but none of them has sufficient performance for a requested task. An important feature is to transmit the control information separately from the transmission of data, where they are flexibly transferred on different types of communication media (network paths) in different ways instead of simple aggregation. In the present work, we develop a prototype of web browsing system that can access web pages over multiple heterogeneous challenged networks by integrating the HTTP and our IMPDT scheme. This is an attempt at extending our scheme from non-interactive bulk transfer to interactive applications, which suggests a potentially wide applicability of our proposed concept.

Case Study on Vehicle-Based Virtual Segment Architecture -- On Application, Field Experiment, and Simulation

Various information delivery schemes based on store-carry-forward routing with extensions have been studied as part of efforts to support non-real-time communications in sparse or intermittent networks. However, communication service schemes that cover large areas based solely on store-carry-forward technology have previously been considered impractical because the delay time for message delivery increases in proportion to the size of the service area. Therefore, in an effort to extend the communication service area of such networks, while providing controllable performance in a cost-effective manner, the authors previously proposed a Virtual Segment (VS) concept in which global communications are provided through a combination of a store-carry-forward service provided by vehicles traveling on roadways along with broadband wireless/wired network devices connected to the Internet. A prototype system has been developed for proof-of-concept implementation. In the present paper, we report a case study evaluation of the VS concept and introduce a sample RSS distribution application of the prototype system. Following a field experiment to validate the system concept, and to obtain realistic data reflecting the geographical features of the segment, a simulation using information obtained from the field experiment was conducted to evaluate the VS concept from realistic and quantitative viewpoints.

Integrating Multiple and Heterogeneous Challenged Networks -- Detailed Design and Experimental Evaluation Using Satellite Link

Motivated by the question of how to quickly transfer large-sized file if multiple and heterogeneous networks are available but each has insufficient performance for the requested task, we propose a research framework for integrating multiple and heterogeneous challenged access networks, in which long delays, heavy packet losses, and frequent disconnections are observed. An important feature of this framework is to treat the transmission of control information separately from the transmission of data information, where they are flexibly transferred on different types of communication media (network paths) in different ways. In the present paper, we describe the design of the mechanisms of this framework such as the retransmission and rate adjustment of each data flow. Then, we report a field experiment with scenarios that are different from those examined in our previous experiments. It validates our prototype implementation.