Isamu Tsuneizumi

A Scalable Peer-to-Peer Group Communication Protocol

In peer-to-peer (P2P) applications, a group of multiple peer processes (peers) are required to cooperate with each other in a distributed manner. Messages sent by peers have to be causally delivered to every peer in a group. Due to the message overhead O(n) for the number n of peers, the vect. cannot be used to causally deliver messages in a scalable group. On the other hand, the linear clock implies the message length O(1), but some pair of messages are unnecessarily ordered. Recently, more accurate physical clocks can be used in cooperation with the GPS time server. Even if each physical clock is synchronized with a time server, every physical clock does not show the same accurate time. The accuracy of the physical clock depends on distance to the time server, traffic in a network, and type of operating system. In this paper, we reduce the number of messages unnecessarily ordered by taking advantage of the linear time and physical time. In the evaluation, we show the number of messages unnecessarily ordered can be reduced composed with the linear clock.

A scalable group communication protocol with hybrid clocks

In peer‐to‐peer (P2P) applications, messages have to be causally delivered to every peer of a group of n (>1) peers. Owing to the message overhead O(n), the vector clock cannot be used to causally deliver messages in a scalable group. On the other hand, since the message length is O(1) in a linear time (LT) and physical time (PT) protocols, which use the linear clock and physical clock, respectively, the protocols can be adopted to scalable groups. However, some pairs of messages are unnecessarily ordered, i.e. even if a pair of the messages is ordered in the protocols, the messages may not be causally ordered. The more the number of messages unnecessarily ordered, the longer it takes to deliver them. In this paper, we propose a hybrid time (HT) group communication protocol to reduce the number of messages unnecessarily ordered by taking advantage of the LT and PT. We evaluate the HT protocol compared with the PT and LT protocols in terms of the number of unnecessarily ordered messages. We show that the number of unnecessarily ordered messages can be reduced in the HT protocol. Copyright

Hybrid Clock-Based Synchronization in a Scalable Heterogeneous Group

In peer-to-peer (P2P) applications, a group of multiple peer processes (peers) are required to cooperate with each other. In this paper, we discuss a heterogeneous hybrid time group communication (HHT) protocol which takes advantage of the linear time (LT) and physical time (PT) to causally order messages in a scalable heterogeneous group. It depends on accuracy of each physical clock and minimum delay time between a pair of peers how messages can be ordered. In this paper, we consider a heterogeneous type of group where the clock accuracy of each peer and the minimum delay time between every pair of peers are not the same. In group protocols, even if a pair of messages are ordered in the protocol, the messages may not be causally ordered. Thus, some messages are unnecessarily ordered in the protocols. In this paper, we show the number of messages to be unnecessarily ordered can be reduced in the HHT protocol. In a scalable group, it is not easy, maybe impossible for each peer to hold information on the clock accuracy and minimum delay time of every peer. In this paper, we newly consider a two-layered model of a heterogeneous group to reduce the information which each peer has to hold.

Reduction of Messages Unnecessarily Ordered in Scalable Group Communication

In distributed peer-to-peer (P2P) applications, a group of multiple peer processes (peers) are required to cooperate with each other. Messages sent by peers have to be causally delivered. In this paper, we discuss a scalable group communication protocol for a group of multiple peers in P2P overlay networks. Due to the message overhead O(n) for the number n of peers, the vector clock cannot be used to causally deliver messages is a scalable group. On the other hand, the linear clock implies the message length O(1), but some pair of messages are unnecessarily ordered. Recently, more accurate physical clocks can be used with the GPS time server and network time protocol (NTP). In this paper, we consider a group where every member peer can use a physical clock which is synchronized with the time server in the network time protocol (NTP). Even if each physical clock is synchronized with a time server, every physical clock does not show the same accurate time. The accuracy of the physical clock depends on distance to the time server, traffic in a network and operating system. In this paper, we reduce the number of messages unnecessarily ordered by taking advantage of the linear time and physical time.

A flexible group communication protocol with hybrid clocks

In distributed applications, a group of multiple peer processes are required to cooperate with each other. Messages sent by peer processes have to be delivered in some order like causal order and total order. In this paper, we discuss a scalable group communication protocol for a group of multiple peers in peer-to-peer (P2P) overlay networks. Due to the message overhead O(n) for the number n of peer processes, the vector clock cannot be used to causally deliver messages. In this paper, we consider a group where every member peer process can use a physical clock which is synchronized with GPS time server in the network time protocol (NTP). The physical clock can be used to temporally order messages while the linear clock can be used to causally order messages. Even if each physical clock is synchronized with a time server, every physical clock does not show the same accurate time. The accuracy of the physical clock depends on distance, i.e. number of routers and traffic in a network. We discuss how the physical and linear types of clocks can be used to temporally and causally order messages in terms of delay time between peer processes and accuracy of each physical clock. In this paper, we discuss a group communication protocol to deliver messages by taking usage of physical clock and linear clock.

A multi‐layered model for scalable group communication with hybrid clocks

Purpose – A group of n (> 1) peers are required to cooperate with each other in distributed applications on P2P overlay networks. A P2P group is distributed without a centralized controller and is scalable and heterogeneous. The purpose of this paper is to discuss how to realize a scalable group in P2P overlay networks.Design/methodology/approach – In a group, messages have to be causally delivered to every peer. In order to realize a scalable group, messages are ordered by taking advantage of linear time (LT) and physical time (PT) since message length is O(1). Here, each peer has to hold information on the accuracy of physical clock of each peer and minimum delay time among every pair of peers. Since the size of the information is O(n2), it is difficult for each peer to hold the information and so the authors discuss a multi‐layered model to reduce the size of group information.Findings – Through the evaluation studies, it is shown how the size of the group information can be reduced in a multi‐layered ...

A Scalable Hybrid Time Protocol for a Heterogeneous Group

In peer-to-peer (P2P) applications, a scalable group of multiple peer processes (peers) are required to cooperate with each other. In this paper, we discuss a two-layered heterogeneous hybrid time (THHT) protocol which takes advantage of the linear time (LT) and physical time (PT) to causally order messages in a scalable heterogeneous group. In a heterogeneous type of group, the clock accuracy of each peer and the minimum delay time between every pair of peers are not the same. It depends on accuracy of each physical clock and minimum delay time between a pair of peers how messages can be ordered. Each peer has to hold group information on the clock accuracy of every peer and the minimum delay time of every pair of peers. In a scalable group of n peers, it is not easy, maybe impossible for each peer to hold the group information due to storage and computation overhead O(n2 ). In this paper, we newly consider a multi-layered model of a scalable heterogeneous group to reduce the information which each peer has to hold.

A Scalable Communication Protocol for Multi-layered Groups

A group of peers are required to cooperate with each other in distributed applications on P2P overlay networks. In order to realize a scalable P2P group, messages are causally ordered by taking advantage of linear time (LT) and physical time (PT) since message length is O(1) in this paper. In this paper, we newly discuss a multi-layered model to realize a scalable group. A group is hierarchically decomposed into subgroups and every peer is in a leaf peer. We present how to order messages by using PT and LT in a multi-layered group. We evaluate the multi-layered group protocol in terms of the group information size and delay time among peers compared with a flat group.

A Multi-layered Model for Scalable Group Communication in P2P Overlay Networks

A group of n (>1) peers are required to cooperate with each other in distributed applications. In this paper, we consider a distributed group of multiple peers in P2P overlay networks. A P2P group is distributed, i.e. no centralized controller and is scalable and heterogeneous since various types and huge number of computers are interconnected in types of networks. In group communication, messages have to be causally delivered to every peer. In order to realize a scalable group, messages are ordered by linear time (LT) and physical time (PT) since message length is O(1). In order to use the physical time, each peer has to hold information on the accuracy of physical clock of each peer and minimum delay time among every pair of peers. Hence, the size of the information is O (n^2). In this paper, we newly discuss a multi-layered hierarchical model to reduce the size of group information. We evaluate the hierarchical model in terms of the group information size and delay time compared with a flat group model.

Design and Implementation of Hybrid Time HT Group Communication Protocol for Homogeneous Broadcast Groups

To realize the cooperation of a group of multiple peer processes peers, messages sent by peers must be causally delivered to every peer. In a scalable group, it is necessary to reduce the communication overhead to causally deliver messages. In this paper, the authors take advantage of the linear time LT and physical time PT protocols, as the message length is On for the number n of peers. However, some pairs are unnecessarily ordered, that is, even if a pair of messages is ordered in the protocols, the messages may not be causally ordered. The greater the number of messages that are unnecessarily ordered, the larger the overhead is implied since the messages must be kept in a receipt queue if a message is lost or delayed. This paper discusses a hybrid time group communication HT protocol that reduces the number of messages unnecessarily ordered. The HT protocol is evaluated in terms of the number of unnecessarily ordered messages compared with the PT and LT protocols. It is demonstrated that the number of unnecessarily ordered messages can be reduced in the HT protocol compared with the LT and PT protocols.