Can Self-Organizing P2P File Distribution Provide QoS Guarantees?
Ruchir Bindal and Pei Cao
In this paper, we examine the factors that contribute to the variability in
download time of a self-organizing P2P file distribution application
such as BitTorrent. We conducted a series of side-by-side live experiments,
involving two clients running on the same machine downloading the same file at
the same time.
We found that the download latency varied significantly, sometimes by
a factor of 2. Surprisingly, the main contributing factor isn't the
network bandwidths of the set of neighbors that a client is given.
Rather, it has
to do with the frequency of turn-overs in ``close'' neighbors, i.e. those that
are in a stable data-exchange relationship with the client. Analysis of the logdata shows that a client
obtains over 90% of the file from a small set of close neighbors, and if
a close neighbor leaves the network, it takes the client a long time,
over half an hour, to find another one.
This suggests that self-organizing P2P file distributions indeed need external
help in order to provide QoS guarantees, but such guarantees are achievable
with proper enhancements to the P2P network.
The paper in PDF is here.