Description
Date depot: 1 janvier 1900
Titre: On the congestion control of Peer-to-peer services
Directeur de thèse:
Dario ROSSI (LTCI (EDMH))
Domaine scientifique: Sciences et technologies de l'information et de la communication
Thématique CNRS : Non defini
Resumé:
1) Context and motivation
The Peer-to-peer approach has emerged as one of themost succesful computing paradigm,
and has survived the Darwinian approach of Internet service evolution, slowly taking
over many of the services traditionally offeret by client-server paradigm. As a result,
the Internet today is populated with a rather large number of P2P applications,
spainning a very wide offer of services: besides the ever-present file-sharing applications
[1, 2], we use P2P application to call our friends with VoIP [3]; for entertainment
purposes, we use P2P based VoD and live TV applications [4–6]; moreover, even operating
system and application are moving toward P2P distribution of their updates [7,8].
Yet, the evolution is far from being completed: for instance consider that while traditional
TV broadcast usually scaled to several million users, P2P-TV based services
have not yet reached that scale yet. Similarly, breakdown of P2P-VoIP systems happened
recently [9], testifying that P2P based application may not be ready yet to fully
support the whole worldwide population unless further effort is pushed in the research
agenda. Worse yet, the breakdown of a given P2P application may affect also all the
rest of the Internet traffic [9], resulting in broadcast storms of Internet messages and
making it necessary to robustly engineer these applications so to avoid these potential
failures. Similarly, even intense P2P usage may congest the network and affect all the
rest of the traffic, which is why some ISPs have been “throttling” P2P traffic: perhaps
the most known case is represented by the Comcast block of BitTorrent traffic, which
was ruled illlegal by the US Federal regulators Federal Communications Commission
(FCC) marking the first time that any U.S. broadband provider has ever been found to
violate Net neutrality rules.
The PhD candidate will have to carry on work in the context of P2P networking,
investigating and evaluating currently deployed solutions, aiming at proposing methods
and mechanism that can be widely accepted and that could push the P2P evolution
even further.
2) P2P Congestion Control
The impact of P2P traffic storm and intese usage of P2P filesharing application as Bit-
Torrent make it necessary to reconsider the standard Internet congestion control mechanism,
which is based on the Transmission Control Protocol (TCP). TCP was originally
designed to counter the congestion collapse of an early Internet [10]. However, TCP is
designed for the transfer of data, and as such multimedia applications typically favor
the unresponsive UDP transport protocol. Moreover, while TCP is designed to maximise
network utilization while at the same time fairly share the bottleneck ressource
in a distributed fashion, TCP has been designed at a time when P2P application did not
exist, and all traffic was mainly client-server.
Now, the typical scenario is that P2P traffic open several parallel connections,
adopting whatever protocol they like at the transport layer, with a current preference
trend toward UDP. For instance, a few months ago, the developers of BitTorrent announced
that the transfer of torrent data in the official client was about to switch to uTP,
an application-layer congestion-control protocol using UDP at the transport-layer. This
announcement immediately raised an unmotivated buzz about a new, imminent congestion
collapse of the whole Internet. Though this reaction was not built on solid technical
foundation, nevertheless a legitimate question remains: i.e., whether this novel
algorithm is a necessary building block for future Internet applications, or whether it
may result in an umpteenth addition to the already well populated world of Internet
congestion control algorithms.
Given these premises, it becomes necessary to evaluate the current spectrum of
P2P congestion control algorithms. To that extent, the PhD candidate should follow
a multi-disciplinary approach, adopting several core analysis tools, such as measurement,
simulation, analysis and prototyping, that we discuss in the following.
2.1 Measurement)
Given that several P2P applications are proprietary, black-box system measurement can
be necessary to understand the internals of P2P applications such as the new, closed and
proprietary BitTorrent release. Work based on black-box experimental measurements,
to unveil closed and proprietary congestion control algorithms include for instance work focusing on Skype [11, 12] and
work focusing on P2P-TV applications [13, 14]
Yet, while BitTorrent is a very popular application, due to its very recent evolution,
previouswork [15–18] focused on complementary aspects to those proposed in this thesis.
For instance, in [15], a fluid model is used to determine the average download time
of a single file. Simulation has instead been used to analyze and improve BitTorrent
performance, as for instance in [16] and [17] where mechanism to prevent free-riding
beyond tit-for-tat
Doctorant.e: Testa Claudio