  Swarming peer-to-peer systems play an increasingly instrumental role in
Internet content distribution. It is therefore important to better understand
how these systems behave in practice. Recent research efforts have looked at
various protocol parameters and have measured how they affect system
performance and robustness. However, the importance of the strategy based on
which peers establish connections has been largely overlooked. This work
utilizes extensive simulations to examine the default overlay construction
strategy in BitTorrent systems. Based on the results, we identify a critical
parameter, the maximum allowable number of outgoing connections at each peer,
and evaluate its impact on the robustness of the generated overlay. We find
that there is no single optimal value for this parameter using the default
strategy. We then propose an alternative strategy that allows certain new peer
connection requests to replace existing connections. Further experiments with
the new strategy demonstrate that it outperforms the default one for all
considered metrics by creating an overlay more robust to churn. Additionally,
our proposed strategy exhibits optimal behavior for a well-defined value of the
maximum number of outgoing connections, thereby removing the need to set this
parameter in an ad-hoc manner.
