The robustness of content-based search in hierarchical peer to peer networks

Hierarchical <i>peer to peer</i> networks with multiple directory services are an important architecture for large-scale file sharing due to their effectiveness and efficiency. Recent research argues that they are also an effective method of providing large-scale content-based federated search of text-based digital libraries. In both cases the directory services are critical resources that are subject to attack or failure, but the latter architecture may be particularly vulnerable because content is less likely to be replicated throughout the network. This paper studies the robustness, effectiveness and efficiency of content-based federated search in hierarchical <i>peer to peer</i> networks when directory services fail unexpectedly. Several recovery methods are studied using simulations with varying failure rates. Experimental results show that quality of service and efficiency degrade gracefully as the number of directory service failures increases. Furthermore, they show that content-based search mechanisms are more resilient to failures than the match-based search techniques.