02-06-2012, 11:19 AM
The CoQUOS Approach to Continuous Queries
in Unstructured Overlays
The CoQUOS Approach to Continuous Queries.pdf (Size: 432.89 KB / Downloads: 27)
Abstract—
The current peer-to-peer (P2P) content distribution systems are constricted by their simple on-demand content discovery
mechanism. The utility of these systems can be greatly enhanced by incorporating two capabilities, namely a mechanism through which
peers can register their long term interests with the network so that they can be continuously notied of new data items, and a means
for the peers to advertise their contents. Although researchers have proposed a few unstructured overlay-based publish-subscribe
systems that provide the above capabilities, most of these systems require intricate indexing and routing schemes, which not only
make them highly complex but also render the overlay network less exible towards transient peers.
INTRODUCTION
UNSTRUCTURED peer-to-peer (P2P)-based
content/resource sharing platforms such as
Gnutella [1] and Kazaa [2] have experienced tremendous
growths in the past decade. The popularity of
unstructured P2P networks can be attributed to
the simplicity of their designs and their exibility
towards transient node population. Searching in these
networks is essentially performed by circulating query
messages in an ad-hoc manner and probing individual
peer nodes.
Paper Contributions
The difculties in implementing pub-sub systems on top
of unstructured overlays can be attributed to the inherent
mismatch between the design requirements of pub-sub
systems and the very nature of unstructured P2P systems.
In order to provide strict notication guarantee,
pub-sub systems have to maintain subscription information
in well-organized structures. In contrast, unstructured
overlays, by their very nature, are decentralized,
loosely coupled and, to certain extent, haphazard. This
makes it difcult to build full-edged pub-sub systems
on these platforms.
THE COQUOS SYSTEM
In this section, we present a high-level description of the
CoQUOS system architecture. We begin by introducing
a few concepts that are used in the rest of the paper.
Concepts and Notations
Consider an unstructured P2P system comprising of
peers fP0; P1; : : : ; PN