Efficient Communication Protocols for Non DHT-based Pyramid Tree P2P Architecture

Abstract

In this paper, we have considered a recently reported 2-layer non-DHT-based structured P2P network. Residue Class based on modular arithmetic has been used to realize the overlay topology. At the heart of the architecture (layer-1), there exists a tree like structure, known as pyramid tree. It is not a conventional tree. A node i in this tree represents the cluster-head of a cluster of peers which are interested in a particular resource of type Ri (i.e. peers with a common interest). The cluster-head is the first among these peers to join the system. Root of the tree is assumed to be at level 1. Such a tree is a complete one if at each level j, there are j number of nodes. It is an incomplete one if only at its leaf level, say k, there are less than k number of nodes. Layer 2 consists of the different clusters. The network has some unique structural properties, e.g. each cluster has a diameter of only 1 overlay hop and the diameter of the network is just (2+2d); d being the number of levels of the layer-1 pyramid tree and d depends only on the number of distinct resources. Therefore, the diameter of the network is independent of the number of peers in the whole network. In the present work, we have used some such properties to design low latency intra and inter cluster data lookup protocols. Our choice of considering non-DHT and interest-based overlay networks is justified by the following facts: 1) intra-cluster data lookup protocol has constant complexity and complexity of inter-cluster data lookup is O(d) if tree traversal is used and 2) search latency is independent of the total number of peers present in the overlay network unlike any structured DHT-based network (as a matter fact unlike any existing P2P network, structured or unstructured). Experimental results as well show superiority of the proposed protocols to some noted structured networks from the viewpoints of search latency and complexity involved in it. In addition, we have presented in detail the process of handling churns and proposed a simple yet very effective technique related to cluster partitioning, which, in turn, helps in reducing the number of messages required to be exchanged to handle churns.