Ryohei Banno

Designing Overlay Networks for Handling Exhaust Data in a Distributed Topic-based Pub/Sub Architecture

To provide event-driven services in IoT, scalable methods of topic-based pub/sub messaging are indispensable. Methods using structured overlay networks are promising candidates. However, existing methods have the problem of wasting network resources, because they lack adaptivity to “exhaust data,” which have low or no value most of the time. The problem contains two aspects. One is that each publisher node continues to forward data to a relay node even if there are no subscribers. The other is that excessively large multicast trees are constructed for low value data, which will be received by only a small number of subscribers. In this paper, we formulate the desirable design of overlay networks by defining a property called “strong relay-free” as an expansion of relay-free property. The property involves publishers and subscribers composing connected subgraphs to enable detecting the absence of subscribers and autonomously adjusting the tree size. We also propose a practical method satisfying the property by using Skip Graph, and evaluate it 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.

SAPS: Software Defined Network Aware Pub/Sub -- A Design of the Hybrid Architecture Utilizing Distributed and Centralized Multicast

Pub/Sub communication model becomes a basis of various applications, e.g. IoT/M2M, SNS. These application domains require new properties of the Pub/Sub infrastructure, for example, supporting a large number of devices with widely distributed manner, handling emergency messaging with priority control and so on. In order to meet the demands, we proposed Software Defined Network Aware Pub/Sub (SAPS) which utilize the both Application Layer Multicast (ALM) and SDN, especially Open Flow based multicast (OFM). A simulation was done for evaluating the hybrid architecture in traffic and transmission delay reduction, and then the issues to be solved in the current design were discussed.

Scalable Pub/Sub System Using OpenFlow Control

Pub/Sub communication model becomes a basis of various applications, e.g., IoT/M2M, SNS. These application domains require new properties of the Pub/Sub infrastructure, for example, supporting a large number of devices in a widely distributed manner. In order to meet the demands, we proposed Scalable Pub/Sub System using OpenFlow Controller, which we call SDN Aware Pub/Sub (SAPS). SAPS utilizes the both Application Layer Multicast (ALM) and OpenFlow based multicast (OFM). A simulation was done for evaluating the hybrid architecture in traffic and transmission delay reduction. The result shows that in the tree topology, even if it has only 100 subscribers, OFM can reduce inter-cluster traffic 71.6% with 16 clusters compared to ALM-LA. It can also reduce maximum intercluster hops 87.5%. On the other hand, with only 100 subscribers, almost all of switches are involved in the OFM tree construction and consume flow table space for the topic. It indicates that our hybrid approach is effective in Pub/Sub optimization considering the resource limitation of OpenFlow switches.

Self-refining skip graph: Skip graph approaching to an ideal topology

In Skip Graph, a structured overlay, each node constructs its routing table by choosing connected nodes based on its membership vector. However, membership vectors are determined randomly; therefore, nodes do not always form an ideal topology. This can cause the route length to be long. Therefore, we propose Self-Refining Skip Graph, a structured overlay where each node refines its routing table toward an ideal Skip Graph topology. Our proposed method has shorter route length as approaching to an ideal topology while maintaining the robustness derived from the mechanism of membership vectors. Our evaluation confirms that the topology approaches to an ideal one and that the route length becomes shorter than that in Skip Graph.

FRT-Skip Graph: A Skip Graph-style structured overlay based on Flexible Routing Tables

Structured overlays enable a number of nodes to construct a logical network autonomously and search each other. Skip Graph, one of the structured overlays, constructs an overlay network based on Skip List structure and supports range queries for keys. Skip Graph manages routing tables based on random digits; therefore, the deviation of them disturbs effective utilization of the routing table entries and increases path length than the ideal value. We therefore propose FRT-Skip Graph, a novel structured overlay that solves the issues of Skip Graph and provides desirable features not in Skip Graph. FRT-Skip Graph is designed based on Flexible Routing Tables and supports range queries similarly to Skip Graph. Furthermore, it provides features derived from FRT, namely, dynamic routing table size and high extensibility.

Self-Refining Skip Graph: A Structured Overlay Approaching to Ideal Skip Graph

In Skip Graph, each node constructs its routing table by choosing neighbor nodes based on its membership vector when a node joins or leaves. However, membership vectors are determined randomly, so nodes do not always compose an ideal topology of Skip Graph. This causes route length to be long. Therefore, we propose Self-Refining Skip Graph, a structured overlay where each node refines its routing table for an ideal topology of Skip Graph. Our proposed method shows shorter route length as approaching to an ideal topology while keeping the robustness caused by membership vectors. We confirmed in the evaluation that the topology approaches to an ideal one and the route length becomes shorter than Skip Graph.

Comparison of subscriber assignment methods on scalable distributed Pub/Sub systems

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.