what-when-how
In Depth Tutorials and Information
6.4 Content Locality: he Inter-Torrent Level Examination........................... 156
6.4.1 Measurement and Analysis of AS-Level Characteristics ................ 158
6.4.2 Peer Prediction Strategy................................................................162
6.4.3 Summary ......................................................................................164
References ......................................................................................................... 165
Peer-to-peer content delivery has become one of the most popular Internet applica-
tions in recent years. Unlike conventional client/server systems, contents in a peer-
to-peer system are not only downloaded and consumed by users, but also generated
and relayed by them; therefore, interactions among the users play an important
role toward achieving efficient sharing in such systems. In this chapter, we present
a systematic measurement study to understand the peer interactions in BitTorrent,
which is one of the most successful file sharing systems to date. Our measurement
consists of a series of experiments, covering microscope piece-level interactions, to
intra-torrent network topologies, and also inter-torrent localities. Our investigation
provides abundant evidence that explains the success of BitTorrent, but also reveals
significant limitations in its current design, thus opening possible avenues toward
enhancing its performance.
6.1 AnOverviewofBitTorrent
Among all the peer-to-peer Internet applications available, BitTorrent [17] has
become the most popular for the sharing of large files. Recent reports have indicated
that half of all the current Internet traic is due to BitTorrent [1]. his popularity
can be greatly attributed to the efficiency with which BitTorrent can distribute
these large files.
his efficiency is partly obtained by breaking up each large file into hundreds or
thousands of segments, or
pieces
, which, once downloaded by a peer, can be shared
with others while the downloading continues. he sharing of pieces of the down-
load has been shown to be very efficient [28], allowing downloads to scale well with
the size of the downloading population. Another aspect of BitTorrent's efficiency
comes from its resilience to peer departures, peer failures, and misbehaving peers.
Many of these properties have been confirmed through both theoretical and experi-
mental studies; however, one aspect yet to be fully explored is the topology of the
network of peers formed during a download.
We start with an overview of BitTorrent and the terminology used to describe
it in Section 1.1.1. BitTorrent is well described in the literature, so more details can
be found in any of the references from Section 1.2. We then discuss specific areas
of BitTorrent that are relevant to our work, including the networks of peers formed
by BitTorrent in Section 1.1.4.
