On the Role of Helper Peers in P2P Networks

Abstract

Recent studies in peer-to-peer (P2P) networks present surprising new designs that rely on helper peers. Helper peers, sometimes named as Feeders or Support peers are nodes that do not function as direct consumers or providers of content but are used to collaborate with other peers in the network for a growing variety of benefits. In File Sharing networks for instance, due to frequent joins, leaves and the characteristic fluctuating throughput of source peers, clients usually download at an unstable rate. In addition, existing P2P protocols tend to ignore source peers that have relatively low bandwidth to offer and practically miss a potentially huge resource. By employing helper peers that are optimal for availability and throughput stability with the downloading client, it is possible to provide a maximal stable throughput even with extremely weak and unstable sources. Other interesting examples of helper peers in file sharing demonstrated how to integrate helper peers in order to increase the number of sources under flash crowds situations, how to solve the last chunk problem and how to bypass fairness rules for better download rates. In P2P streaming networks such as live IPTV and VOD, helper peers can contribute in preventing glitches and expanding the dissemination of packets, as well as synchronizing and ordering frames for the clients. In this chapter we present novel architectures that embed helper peers in order to solve key problems in P2P networks. We discuss the implications and key techniques in each proposal and point the weaknesses and limitations of mentioned architectures. We present different selection criteria for choosing the optimal helper peers based on theoretic simulations, practical measurements and experiments with popular protocols such as eMule and BitTorrent. We propose an advanced Machine Learning based design that actively learns the behavioural patterns of peers and leverages the performance of clients by collaborating with the ”right” helper peers at the right time. Though helper peers gained popularity in P2P research, different works in this field term the same ideas differently and in some cases do not mention each other; this chapter presents the current state of the art in helper-supported P2P networks. Finally, we present future research directions in this field. 11