In forthcoming sensor networks, a multitude of sensor nodes deployed over a large geographical area for monitoring traffic, climate, etc. are expected to become an inevitable infrastructure. Clustering algorithms play an important role in aggregating a large volume of data that are produced continuously by the huge number of sensor nodes. In such networks, equal-sized multi-hop clusters which include an equal number of nodes are useful for efficiency and resiliency. In addition, scalability is important in such large-scale networks. In this paper, we mathematically design a decentralized equal-sized clustering algorithm using a partial differential equation based on the Fourier transform technique, and then design its protocol by discretizing the equation. We evaluated through simulations the equality of cluster sizes and the resiliency against packet loss and node failure in two-dimensional perturbed grid topologies.

In ATM Network, the VBR (Variable Bit Rate) service category is used to accommodate TCP/IP traffic. In an international ATM network with large propagation delay, higher TCP throughput can be obtained by use of window scale option. In order to accommodate TCP traffic with window scale option effectively, it is required to select appropriate values of VBR parameters, i. e. SCR (Sustainable Cell Rate) and MBS (Maximum Burst Size), and to evaluate the impact of UPC (Usage Parameter Control) function on TCP throughput. We have studied those technical issues for the conventional TCP, but the results cannot be applied to TCP traffic with the window scale option due to the TCP terminal performance and the large window size. In this paper, we proposed VBR parameter determination method for TCP with the window scale option and evaluated the values in each condition. These results show that the determined MBS is much smaller than the burst length of TCP segments especially using low performance TCP terminals. Furthermore, we also discuss some experimental results of TCP throughput degradation due to UPC function. It shows that the throughput of TCP with large window size is degraded when the SCR and MBS values used in ATM switch are smaller than the determined values.

In the 5G era, centralized mobility management raises the issue of traffic concentration on the mobility anchor. Distributed mobility management is expected to be a solution for this issue, as it moves mobility anchor functions to multiple edge routers. However, it incurs path stretch and redundant traffic on the backhaul links. Although these issues were not considered important in the 3G/4G era, they are expected to be a serious problem in the 5G era. In this paper, we design a routing-based mobility management mechanism to address the above problems. The mechanism integrates distributed routing with Bloom Filters and an anchor-less scheme where edge routers work as mobility anchors. Simulations show that the proposed mechanism achieves a good balance between redundant traffic on the backhaul links and routing overhead.

Internet of Things (IoT) devices deployed in urban areas are seen as data sources for urban sensing IoT applications. Since installing cellular interfaces on a huge number of IoT devices is expensive, we propose to use a user equipment (UE) device with a local wireless interface as a mobile IoT gateway for fixed IoT devices. In this paper, we design a new mobile architecture based on cellular networks to accommodate non-cellular fixed IoT devices by UE devices working as IoT gateways. One key feature is that our architecture leverages proximity services (ProSe) to discover relay UE devices with low overhead in terms of discovery messages. Through simulation studies, we clarify the feasibility of our architecture including the relay UE discovery mechanism in urban areas.

In the gauge of IMT-2000, Mobile IP based location management is standardized. The cellular network of IMT-2000 holds many users and covers a large area. In large-scale Mobile IP networks, such as IMT-2000, a foreign agent may manage many mobile nodes by the visitor list and its forwarding performance degrades owing to the list search overload. In this paper, we propose a fast data transfer method in Mobile IP networks by reducing the load of the search processes on the foreign agent using cooperation between mobility agents. In our experiments, we measured the packet forwarding performance and the packet forwarding process time. The results indicate the possibility of the performance degradation owing to the part of the registered mobile nodes in the visitor list. We verify that the foreign agent using our method can forward all the received packets on Fast Ethernet LAN when one million entries are recorded in the visitor list.

Location-based forwarding is a key driver for location-based services. This paper designs forwarding information data structures for location-based forwarding in Internet Service Provider (ISP) scale networks based on Named Data Networking (NDN). Its important feature is a naming scheme which represents locations by leveraging space-filling curves.

This paper proposes an NDN-based message delivery protocol over a cellular network in disasters. Collaborative communication among cellular devices is integrated into the protocol so that power consumed by battery-operated base stations (BSs) is reduced when a blackout occurs. A key idea is to reduce consumed radio resources by making cellular devices of which radio propagation quality are better forward messages of neighboring devices. The radio resource reduction contributes to reducing power consumed by a battery-operated BS. We empirically and analytically evaluate how the proposed message delivery protocol reduces the power consumption of a BS assuming a densely populated shelter.

In the near future, decentralized network systems consisting of a huge number of sensor nodes are expected to play an important role. In such a network, each node should control itself by means of a local interaction algorithm. Although such local interaction algorithms improve system reliability, how to design a local interaction algorithm has become an issue. In this paper, we describe a local interaction algorithm in a partial differential equation (or PDE) and propose a new design method whereby a PDE is derived from the solution we desire. The solution is considered as a pattern of nodes' control values over the network each of which is used to control the node's behavior. As a result, nodes collectively provide network functions such as clustering, collision and congestion avoidance. In this paper, we focus on a periodic pattern comprising sinusoidal waves and derive the PDE whose solution exhibits such a pattern by exploiting the Fourier method.

It is important to monitor routing protocols to ensure IP networks and their operations can maintain sufficient level of stability and reliability because IP routing is an essential part of such networks. In this paper, we focus on Open Shortest Path First (OSPF), a widely deployed intra-domain routing protocol. Routers running OSPF advertise their link states on Link State Advertisements (LSAs) as soon as they detect changes in their link states. In IP network operations, it is important for operators to ascertain the location and type of a failure in order to deal with failures adequately. We therefore studied IP network failure identification based on the monitoring of OSPF LSAs. There are three issues to consider in regard to identifying network failures by monitoring LSAs. The first is that multiple LSAs are flooded by a single failure. The second is the LSA delay, and the third is that multiple failures may occur simultaneously. In this paper, we propose a method of network failure identification based on a detailed analysis of OSPF LSA flooding that takes into account the above three issues.

As the Asynchronous Transfer Mode (ATM) technology comes to be used widely, the Telecommunications Management Network (TMN) over ATM networks becomes an important issue. Since TMN uses the OSI protocols including the Common Management Information Protocol (CMIP), it is required to implement CMIP communication over ATM networks. In order to realize OSI over ATM, ITU-T SG13 has standardized the Service Specific Coordination Function for Connection Oriented Network Service (SSCF-CONS), Service Specific Connection Oriented Protcol (SSCOP), and the Synchronization and Coordination Function (SCF). We have developed the CMIP software over ATM networks adopting these protocols. The CMIP software is designed so that it achieves both high throughput for large data transfer and short response time for small message exchange. The software adopts the implementation mechanisms commonly applied for protocol modules to reduce the overheads for controlling OSI protocol modules, and some protocol specific mechanisms especially for protocols with heavy processing overheads, i.e. SSCOP and CMIP. The performance evaluation shows that the developed CMIP software achieves more than 200 message exchanges per second for messages whose length is 64 Byte long, and achieves about 36 Mbps throughput for transferring data whose length is more than 100 KByte.

Content-Centric Networking (CCN) employs a hierarchical but location independent content naming scheme. While such a location independent naming brings various benefits including efficient content delivery, mobility, and multihoming, location independent name prefixes are hard to aggregate. This poses a serious scaling issue on the efficiency of looking up content names in a huge Forwarding Information Base (FIB) by longest prefix matching, which requires seeking the longest matching prefix through all candidate prefix lengths. We propose a new scheme for efficiently looking up non-aggregatable name prefixes in a large FIB. The proposed scheme is based on the observation that the bottleneck of FIB lookup is the random accesses to the high-latency off-chip DRAM for prefix seeking and this can be reduced by exploiting the information on the longest matching prefix length in the previous hop. Our evaluation results show that the proposed scheme significantly improves FIB lookup latency with a reasonable traffic parameters observed in today's Internet.

Energy efficiency is an important requirement to forth-coming NDN (Named Data Networking) networks and caching inherent to NDN is a main driver of energy reduction in such networks. This paper addresses the research question “Does caching really reduce the energy consumption of the entire network?”. To answer the question, we precisely estimate how caching reduces energy consumption of forth-coming commercial NDN networks by carefully considering configurations of NDN routers. This estimation reveals that energy reduction due to caching depends on energy-proportionality of NDN routers.

As the Internet has become the infrastructure for the global communication, the quality degradation due to network failures and illegal traffic such as DDoS (Distributed Denial of Service) have become a serious problem. In order to solve the problem, a network monitoring system that monitors the traffic of Internet in real time is strongly desired. Traffic monitors that collect the statistics from captured packets play a key roll in the system; however, they are not flexible enough for being used in the rapidly changing Internet. The traditional approach such that a new traffic monitor is developed for a new requirement results in a long turn around time of the development. Therefore, we have proposed a flexible network monitoring system that consists of programmable traffic monitors. Traffic monitors are made programmable by introducing active network techniques; therefore, we call the network monitoring system as the programmable monitor network. This paper describes the implementation of the programmable monitor network and its application to DDoS (Distributed Denial of Service) attack detection.

In the Mobile IP handoff procedure, mobile node movement is detected from advertisements of foreign agents that differ from previously received advertisement and the new "care-of" address is registered with the home agent. However, user packets are not forwarded to the new foreign agent until a registration is completed and this interruption may degrade the quality of service especially in real-time applications such as audio and video, or may lower the TCP throughput due to retransmission timeout. To tackle these issues, we propose a new low latency handoff method, where access points used in a wireless LAN environment and a dedicated MAC bridge are jointly used to alleviate packet loss without altering the Mobile IP specifications. In this paper, we present design architecture of the proposed method and evaluate its performance in an actual network environment to verify the effectiveness of our approach.

Although TCP is widely used in the Internet, new specifications are still proposed and implemented. In the circumstance above, it is highly possible that some errors are detected on the communication between new and old implementations. Several test tools were developed so far. However, they do not have enough functions to allow test operators to modify test sequences suitable for their test purposes. We have developed a TCP tester which generates test sequence using test scenario. The tester performs exceptional TCP protocol behavior only when the condition specified in the test scenario is satisfied. Otherwise, it performs normal TCP behavior. The tester is implemented by modifying TCP module of NetBSD with SACK code developed by Pittsburgh Supercomputing Center. We have also evaluated implementations of congestion control and SACK algorithms using the tester.

This paper presents a protocol verification method which verifies that the behaviors of a protocol meet requirements. In this method, a protocol specification is expressed as Extended Finite State Machines (EFSM's) that can handle variables, and requirements are expressed using a branching-time temporal logic for a concise and unambiguous description. Using the acyclic expansion algorithm extended such that it can deal with EFSM's, the verification method first generates a state transition graph consisting of executable transitions for each process. Then a branching-time temporal logic formula representing a requirement is evaluated on one of the generated graphs which is relevant to the requirement. An executable state transition graph for each process is much smaller than a global state transition graph which has been used in the conventional verification techniques to represent the behaviors of the whole protocol system consisting of all processes. The computation for generating the graphs is also reduced to much extent for a large complex protocol. As a result, the presented method achieves efficient verification for requirements regarding a state of a process, transmission and reception of messages by a process, varibales of a process and sequences that interact among processes. The validity of the method is illustrated in the paper by the verification of a path-updating protocol for requirements such as process state reachability or fair termination among processes.

Since congestion is very likely to happen in the Internet, locating congested areas (path segments) along a congested path is vital to appropriate actions by Internet Service Providers to mitigate or prevent network performance degradation. We propose a practical method to locate congested segments by actively measuring one-way end-to-end packet losses on appropriate paths from multiple origins to multiple destinations, using a network tomographic approach. Then we conduct a long-term experiment measuring packet losses on multiple paths over the Japanese commercial Internet. The experimental results indicate that the proposed method is able to precisely locate congested segments. Some findings on congestion over the Japan Internet are also given based on the experiment.

It has become more important to reduce the protocol implementation costs as the functions of protocols have become more abundant. The protocol implementation tools which automatically generate a protocol program from a specification described by an FDT (Formal Description Technique) are very promising. Selecting SDL as a target FDT, we have developed an SDL-based protocol implementation tool which consists of a process scheduler and a compiler. Since the efficient SDL process execution is a key to generating the high-speed program, the scheduler is introduced. It provides the mechanism which executes SDL processes concurrently as light-weight-processes. It optimizes so that as few context switches take places as possible. The compiler converts as many kinds of SDL functions whose behaviors can be determined at compile time into programming language statements as possible. These elaborations are so successful that the tool can generate an efficient program. The OSI Transport protocol class 0 program generated by the compiler can process more than 500 packets per second on a 6MIPS workstation.

Internet of Things (IoT) devices, which have different characteristics in mobility and communication patterns from traditional mobile devices such as cellular phones, have come into existence as a new type of mobile devices. A strict mobility management scheme for providing highly mobile devices with seamless access is over-engineered for IoT devices' mobility management. We revisit current mobility management schemes for wireless mobile networks based on identifier/locator separation. In this paper, we focus on IoT communication patterns, and propose a new routing-based mobility scheme for them. Our scheme adopts routing information aggregation scheme using the Bloom Filter as a data structure to store routing information. We clarify the effectiveness of our scheme in IoT environments with a large number of IoT devices, and discuss its deployment issues.