A central problem for structured peer-to-peer networks is topology maintenance, that is, how to properly update neighbor variables when nodes join and leave the network, possibly concurrently. In this paper, we first present a protocol that maintains a ring, the basis of several structured peer-to-peer networks. We then present a protocol that maintains Ranch, a topology consisting of multiple rings. The protocols handle both joins and leaves concurrently and actively (i.e., neighbor variables are updated once a join or a leave occurs). We use an assertional method to prove the correctness of the protocols, that is, we first identify a global invariant for a protocol and then show that every action of the protocol preserves the invariant. The protocols are simple and the proofs are rigorous and explicit.

Active and concurrent topology maintenance

Compared with traditional Internet technologies, peer-to-peer technologies has functions to realize resource discovery, resource sharing, and load balancing in a highly distributed manner. In addition to the Internet, new networks such as home network, ad-hoc network and sensor network are emerging. An easy prediction is the emergence of a new environment in which many sensors, people, and many different kinds of devices coexist, move, and communicate with one another over such heterogeneous networks. Peer-to-peer technology is one of the most important and suitable technologies for such ubiquitous networking since it supports discovery mechanisms, simple one-to-one communication, free and extensible distribution of resources, and distributed search to handle the enormous number of resources. The authors have designed and implemented a peer-to-peer networking platform for realizing applications, which include various applications for mobile phones. This chapter presents their peer-to-peer networking architecture, protocols, and applications for mobile phones. Norihiro Ishikawa NTT DOCOMO, Japan

Peer-to-Peer Networking Platform and Its Applications for Mobile Phones

The purpose of this paper is to present the application of distribute mutual exclusion for controlling the text message exchange in a ubiquitous chat named M-SynchroTalk. This chat allows tutors and students to be in contact even on the move. The main issue is to organize the entire communication when several students speak at the same time and about many subjects. All in all, the chat hold the dialog context controlling the message broadcast by means of the distributed mutual exclusion algorithms. In this context, just one student could send a message at a time. To achieve mutual exclusion in the ubiquitous chat, the centralized and the token ring algorithms have been developed. The centralized algorithm was implemented in two versions: human coordinator and computer coordinator. Preliminary results show that this solution provides a well-controlled environment suitable for M-Learning environments.

Using Distributed Mutual Exclusion for Coordinating Virtual Meeting in an Ubiquitous Chat System

The recent desktop versions of Windows (XP SP2 and Vista) include a Peer-to-Peer (P2P) infrastructure that simplifies the development and deployment of true P2P applications. We have ported the latest version of this infrastructure to Windows Embedded CE 5.0, which is the underlying OS for Windows Mobile 5.0. To our knowledge, this is the first native implementation of a P2P infrastructure for Windows Mobile. This paper provides a short overview of the infrastructure and design considerations when running P2P applications on mobile phones. For demonstration purposes, we have developed a community-based photo sharing and chat application that solely uses the P2P infrastructure for communication. We will demonstrate the ease of creating P2P communities in an ad-hoc manner, and the interoperability between Windows Mobile and Windows Vista.

M. Young

Papers

Running the Windows P2P Infrastructure on Mobile Phones