From: Steve Arnold (stevearn_at_microsoft.com)
Date: Sun Mar 07 2004 - 22:27:11 PST
In this paper, the researchers aren't designing anything (well there's a
few ideas in there), but rather they are taking a look at peer-to-peer
file sharing workloads. (The scope is quite specific: the use of Kazaa
at the UW.) They started their analysis by collecting a 200 day trace of
internet packet data, where the Kazaa requests were filtered on.
First, they made several key observations based on the data. Kazaa users
will wait a long time just to download files (in contract to web users).
As users are on the system longer, they tend to slow down in their
requests. Most requests are for smaller files. However, given this, "the
majority of bytes transferred are due to the largest objects (video
files)." Perhaps the most key observation is that Kazaa objects are
typically "fetch-at-most-once." In addition, popular objects are usually
short-lived, and, at the same time, most requests are for older objects.
The next section argues that "Kazaa is not Zipf." There have been
previous studies that might indicate this (esp. for the web in general).
However, it is not the case for Kazaa mostly because the objects are
immutable and they are fetch-at-most-once. They show this by modifying
some parameters in a simulation. This does not prove their point, but it
presents a reasonable argument.
Lastly, they explore ways to reduce this bandwidth demand (over half of
internet traffic - it would be interesting to know what effect, if any,
that legal pursuits of the recording industry have had). The natural way
is place caches in certain networks. However, many institutions may not
be willing to do this for legal concerns. Their suggestion is
redirection. When a request goes out for an object that exists within
the sub-network, then the packet is re-directed to that client. They
found that they could achieve between a 37% and 63% hit rate, enough to
reduce external peer-to-peer traffic by over 80%.
This archive was generated by hypermail 2.1.6 : Sun Mar 07 2004 - 22:27:36 PST