PAPER 9 Andrew Cunningham
arc39
    _A_Measurement_Study_of_Peer-to-Peer_File_Sharing_Systems_
    Stefan Saroiu, P. Krishna Gummadi, Steven D. Gribble

    This is an almost psychological study on the profiles of users of
Napster and Gnutella, and of their habits and capabilities. It includes
readings on bottleneck bandwidth between the various hosts and the internet
at large, how often hosts connect and disconnect forom the system, how many
hosts share and download, how much they cooperate, and the correlations
between these various behavior. The end result of this study is that there
is significant heterogeneity and lack of cooperation across peers
participating in these systems, (conjecture:) most likely due to the lack of
reward structure in place to induce cooperation. It is humorous that the
authors feel that four days of Napster activity, and eight of Gnutella, is
sufficient to draw conclusions about the systems: they claim that the main
users of these systems are edge computers on the internet; the problem is
that for such uncoordinated beings, time-of-year can have vastly important
impact. For instance, the period during which they observed the systems is
during Cornell's end-of-year, final, and graduation period; user activity is
likely to be anything other than normal for college students!
    Another odd result (under their Napster study) is that they discover
that high speed connections to the internet users constitute both more of
the peers and more than 3 times more of the upload traffic than modem, low
speed connecting clients. They do not seem to draw the same result from this
as I do, which is that some do choose to identify themselves as possessing a
high speed; they get more downloads and many more uploads, and behave in all
ways slightly utopian. On the down side, there are a large number of
unknown-speed hosts; it is to these that the author's desire for a better
reward structure exists.
    They suggest that to solve the client's deliberate misrepresenting of
connection capability, that the software automatically configure itself;
this is a stopgap measure, but morally reprehensible. Not only does it not
solve the problem (if you rely on these values, it is in the interest of the
community to hack together a version of the client which will underreport)
and make the user suspicious of what their computer is doing against them,
it is in some senses a breach of confidence. Moreover, it's out of the scope
of this paper: better phrasing would be to simply issue a call-to-arms for a
solution, without suggesting a software, versus protocol, solution.


 _Measurement,_Modeling,_and_Analysis_of_a_Peer-to-Peer_File-Sharing_Workload_
    Krishna P. Gummadi, Richard J. Dunn, Stefan Saroiu, Steven D. Gribble,
Henry M. Levy, and John Zahorjan

    Using a much larger trace of Kazaa traffic, this paper analyzes various
file-sharing behavioral hypotheses. Among these are a debunking of the
traditional view of Zipf-like distribution for content (due to specific
filesharing characteristics), and the implications of this datum. Among the
implications are optimizations for using the currently untapped locality of
operations to improve the Kazaa workload, with quantified bandwidth savings.
Fortunately, this paper avoids some of the problems of the previous one, in
that the data-gathering period was much longer, although for a much more
constrained population, and thus took into account human behavioral patterns
(as they determined that a large amount of their campus traffic was P2P
related, studies during the summer will ignore that traffic!).
    One thing that was not considered was the amount of data transferred
over Kazaa; text, portable document format, and executable. The reason that
this is relevant is that these formats are somewhat mutable, and might tend
to combat the non-Zipf nature of Kazaa files; essentially, they form groups
and aggregate their downloads for a general popularity metric. Similarly,
the odd behavior surrounding new object arrival -- that new popular object
crystallize load and thus lead to better network load behavior -- ignores
the actual behaviors of users, who will seeks odd/archaic files regardless
of the general opinion of them. In my experience, of course. The other odd
news from this paper is bad news for consistent hashing schemes: to utilize
locality-aware request routing, it is beneficial for clients to be aware of
files that are within some internet-relevant domain -- perhaps on the same
subnet, etc. However, under the ring based systems that we've studied, the
nodeID of hosts (of objects) are some sort of hash of, say, the IP address
-- and thus likely to be completely disassociated from the ID of the object!
This is not an insurmountable obstacle -- with sufficient indirection,
nothing is insurmountable -- but it is a cause for a pause to think.
    Finally, there is little incentive for peers to use some sort of
locality aware caching scheme. This improves performance on a global sense,
but requires admitting that one is "officially" hosting a file; a better way
would be for the protocol to build some sense of this into itself through
some sort of anonymity routine. This is not a well thought out concept, but
the problem is simple: their specific implementation of the locality
heuristic relied on perfect global knowledge in a central location.
