Title: A Dynamic Ultrapeers Selection Policy for Collaborative Virtual Environments over Mobile Ad Hoc Networks 

Abstract
With the rapid developments in technology, Mobile Collaborative Virtual
Environments (MCVEs) have become an unavoidable application in area such
as military training, health, and education. Unfortunately, as the number
of users grows, nodes may easily become overloaded as they process
messages from other nodes. Most of the existing Ultrapeer systems are
confined to wired network environments and thus preclude collaboration
while users are mobile. In this paper, a Gnutella Ultrapeer system GUS to
improve the performance of MCVEs is proposed. In MANETs, a reconfiguration
process is frequently required in the Ultrapeer system due to node
mobility. In addition, the number of Ultrapeers must be well dispersed
throughout the overlay network. To address these problems, we adopt a
novel selection approach in which we create a hierarchical overlay network
based on the CVE profile in order to reflect the user’s interest in the
virtual environment. We then perform a dynamic Ultrapeer election based on
a score measurement that combines the network behaviors and the user
behaviors in the VE. Thus, not every change in the network topology will
entail an immediate Ultrapeer system reconfiguration. Simulation results
indicate that the proposed GUS is more efficient than popular Ultrapeer
topologies in several important scenarios.