Scalable messaging methods for IoT services are needed to accommodate a vast number of devices. Skip Graph based topic based pub/sub (SG-TPS), which utilizes multiple brokers composing a structured overlay network, is one of the promising candidates. In SG-TPS, the distribution delay time is widely influenced by a way to assign subscribers to each broker. There are two possible approaches: the intensive assignment by which subscribers having a same topic are accommodated on a same broker, and the extensive assignment by which the subscribers are accommodated on different brokers as far as possible. In this paper, we formulate the difference of the distribution delay time between these two approaches, and discuss about the optimization of subscriber assignment.

Distributed pub/sub messaging has become indispensable for event-driven systems. There are methods for achieving high scalability regarding topic-based pub/sub by using structured overlay networks. However, these methods waste network resources concerning "exhaust data," which have low or no value most of the time. There are at least two problems: each publisher node continues to forward data to a relay node even if there are no subscribers, and multicast trees are constructed which are excessively large for low value data, namely having a small number of subscribers. In this paper, we formulate the requirements of overlay networks by defining a property called "strong relay-free" as an expansion of relay-free property, and propose a practical method satisfying the property by using Skip Graph. The proposed method involves publishers and subscribers composing connected sub graphs to enable detecting the absence of subscribers and autonomously adjusting the tree size. Through simulation experiments, we confirmed that the proposed method can suspend publishing adaptively, and shorten the path length on multicast trees by more than 75% under an experimental condition with 100,000 nodes. The proposed method is competent for decentralized event-driven systems with encouraging the locally produced data to be consumed locally.

In this paper, we propose an efficient video streaming server management scheme for streaming service that minimizes power consumption while satisfying client's requests. In conventional schemes, the power minimizing policy is calculated by means of simple dynamic programming or linear programing systems. However, these schemes may suffer changing the power minimizing policy substantially when the client's requests change even slightly. This increases the cost of changing streaming servers. On the other hand, our approach minimizes power consumption while satisfying client's requests by considering the number of times the policy is changed. To reduce the number of changes, our scheme uses dynamic programming by considering trends in client's requests and the stream length for each server. Evaluations shows that our scheme reduces power consumption by up to 35%-45% of conventional schemes.

An application-cooperative bandwidth on-demand (BoD) network with dynamic adaptive reconfiguration for Gbps-class HDTV transmission applications is presented. For high-bandwidth data transmission, such as HDTV streaming and Tera-byte-class file transfer, the strong application-network cooperation is one of the key components for facilitating stable and high-performance transmission. The BoD network offers flexible use of high performance IP/optical network resource upon application request and dynamic reconfiguration functionality in response to changes in traffic demands. This paper addresses Gbps-class HDTV transmission over a BoD network based on IP-optical networking, which uses PCE/VMTN architecture for network control, in order to examine application-network cooperation. The design of the BoD network service and its cooperation scheme for HDTV transmission are described. Performance evaluation results and issues of the BoD network and video transmission systems are shown.

Integration of a high-resolution video (such as HDTV) delivery system for IP networks with legacy DBMSs and WWW systems, would make it easy to achieve system for a remote video editing, remote education and digital cinema. For this reason, we have developed a streaming server for IP networks is based on the MAPOS link-layer protocol and has a 2.48-Gbps line speed. The MAPOS protocol enables IP networks over SONET/SDH. The streaming server is constructed on a typical PC with Linux. Choosing a PC and Linux provides high performance at low cost to users. Real-time processing is important if we are to send video data at a specified rate. To implement a streaming server that can deliver Gbps video streams, we developed a real-time processing method specifically for this platform. Consequently, we obtained real-time performance for a streaming server in which the method was implemented. To evaluate its performance, we measured the receiving rate and jitter on receiving terminal while the server was delivering video streams at rates from 1.5 to 2.4 Gbps. The jitter indicates the receive-buffer size that is required and the initial delay which should be inserted before playback. For video delivery at 1.5 Gbps, the maximum buffer size was shown to be 936 KBytes (5.1 msec) and initial delay was 3.0 msec. These results show the practicability of constructing a system for ultra high-speed video (including 1.5-Gbps uncompressed HDTV) delivery with a very short response time within one video frame.

Latency, caused by remote memory access and remote procedure call, is one of the most serious problems in massively parallel computers. In order to eliminate the processors' idle time caused by these latencies, processors must perform fast context switching among fine-grain concurrent processes. In this paper, we propose a processor architecture, called Datarol-II, that promotes efficient fine-grain multi-thread execution by performing fast context switching among fine-grain concurrent processes. In the Datarol-II processor, an implicit register load/store mechanism is embedded in the execution pipeline in order to reduce memory access overhead caused by context switching. In order to reduce local memory access latency, a two-level hierarchical memory system and a load control mechanism are also introduced. We describe the Datarol-II processor architecture, and show its evaluation results.>