| Time / Zeit |
Room / Raum |
Type, Speaker, Topic /
Typ, Redner, Thema |
| 1st
quarter of 2009 |
|
9 Mar. 2010
16:00–18:00
|
Auditorium 2
|
In this talk we will give a brief overview on
how to set up a WPA2 Enterprise driven wireless network, a part of
the IEEE 802.11i standard. The WPA2 Enterprise standard combines
the IEEE 802.1X Port-Based Network Access Control and the Advanced
Encryption Standard (AES) for IEEE 802.11 networks. We will
describe the necessary software and procedures to set up and run
a WPA2 Enterprise network by using wpa_supplicant as the entity
that wants to have access, hostapd as the entity that controls the
access and FreeRADIUS, which makes authorization decisions. With
FreeRADIUS, wpa_supplicant and hosted we are using software used
on a reasonable amount of Systems deployed in todays networks.
FreeRADIUS is one of the main used Authentication, Authorization,
and Accounting (AAA) management services used for authentication
in Dial In User services, as well as wpa_supplicant is one of the
major OpenSource supplicant implementations of IEEE 802.11i used
on Systems like Apple Mac OS X, G NU/Linux and
partly on Microsoft Windows.
|
|
2 Mar. 2010
16:00–18:00
|
TEL 1118/19
|
PGT:
Gilles
Trédan
Drawing, embedding, and dissecting Graphs
Studying networks often leads to encounter complex
interaction structures. These structures are often modelled
using graphs. This talks is an informal review of usefull tools
for researchers to gather insights on the phenomenons occurring
in such structures.
More precisely, we will here discuss how and why embed graphs
for visualization purposes. We will also discuss the limits of
these techniques, and present other approaches to circumvent
them, such as clustering analysis.
|
|
24 Feb. 2010
10:00–11:00
|
Auditorium 1
|
PGT:
Michael
Scharf, Alcatel-Lucent, Bell Labs, Stuttgart
Speeding up the Internet: Fast Startup Congestion
Control
The Transmission Control Protocol (TCP) uses the well-known
Slow-Start algorithm at the beginning of a connection and
after idle times, which may cause needless delays. Speeding up
the start of flows is one of the remaining non-trivial open
issues in the Internet. Several new congestion control schemes
have been developed recently in order to realize faster flow
startups. Potential solutions include both end-to-end approaches
and new protocols that use additional feedback from the routers
on the path, such as the Quick-Start TCP extension.
This talk investigates the realization of fast startup
congestion control. We introduce the fundamental challenge of
resource management during flow startups and compare end-to-end
and network-supported solutions. Both simulation studies
and testbed measurements quantify the potential performance
improvement, the robustness and fairness, as well as the
benefit and cost of additional network support. The studies are
performed with new implementations in the Linux network stack.
Our results reveal that end-to-end fast startup mechanisms
are not necessarily overly aggressive and unfair if they are
selectively used. Additional signaling along the path reduces
the risk of congestion at the cost of a higher complexity.
Finally, several case studies prove that fast startup congestion
control can indeed improve the responsiveness of broadband
interactive applications.
Bio:
Michael Scharf is a research scientist at Alcatel-Lucent Bell
Labs Germany. Until 2009, he was a research staff member at the
Institute of Communication Networks and Computer Engineering
(IKR) at the University of Stuttgart, under the supervision
of Prof. Paul J. Kühn. He received his Dipl.-Ing.
in electrical engineering from the University of Stuttgart
in 2003. Since then, he has been an author of more than
20 conference and journal papers and an active IETF/IRTF
contributor. His research interests include future Internet
technologies, transport protocols, congestion control, and
performance evaluation in general.
|
|
23 Feb. 2010
16:00–18:00
|
Auditorium 2
|
Talk:
Amr
Rizk, Univ. Hannover
End-to-end Performance Bounds for Networks under
Long-memory fBm
Cross-traffic
Fractional Brownian motion (fBm) emerged as a useful model
for self-similar and long-range dependent Internet traffic.
Approximate performance measures are known from large deviations
theory for single queuing systems with fBm through traffic.
We derive end-to-end performance bounds for a through flow in
a network of tandem queues under fBm cross traffic. To this
end, we prove a rigorous sample path envelope for fBm that
complements previous approximate results. We find that both
approaches agree in their outcome that overflow probabilities
for fBm traffic have a Weibullian tail. We employ the sample
path envelope and the concept of leftover service curves to
model the remaining service after scheduling fBm cross traffic
at a system. Using composition results for tandem systems
from the stochastic network calculus we derive end-to-end
statistical performance bounds for individual flows in networks
under fBm cross traffic. We discover that these bounds grow
in O(n (log n)^(1/(2-2H)))
for n systems in series where H is the Hurst parameter of the fBm cross traffic and
show numerical results on the impact of the variability and the
correlation of fBm traffic on network performance.
Bio:
Amr Rizk is a PhD student and research assistant at the
Institute for Communications Technology at the Leibniz
University Hannover. He is a member of the Emmy-Noether Research
Group "ProPerBounds" – a DFG funded research project
on the topic "Statistical Performance Bounds for Computer
networks and Communication systems". He received his Diploma
in Electrical Engineering and Business Administration from the
Technical University Darmstadt, Germany in 2008. His research
interests are performance analysis of communication systems,
queuing theory and probabilistic network calculus.
|
|
16 Feb. 2010
16:00–18:00
|
Auditorium 2
|
Talk:
Navid
Ghazisaidi, Optical
Zeitgeist Laboratory, INRS,
Montréal, QC, CANADA
Fiber-Wireless (FiWi) Access
Networks: Challenges and Imperatives
Due to its unique properties, optical fiber
is likely to entirely replace copper wires in the near to
midterm, paving all the way to and penetrating into the homes of
residential and offices of business customers. The final frontier
of optical access networks is the seamless convergence with their
wireless counterparts, giving rise to hybrid fiber-wireless
(FiWi) broadband access networks. By combining the capacity of
optical fiber networks with the ubiquity and mobility of wireless
networks, FiWi networks form a powerful platform for the support
and creation of emerging as well as future unforeseen services
and applications. FiWi networks hold great promise to strengthen
our information society while avoiding its digital divide and
to change the way we live and work by replacing commuting with
teleworking. This not only provides more time for professional and
personal activities for corporate and personal benefit, but also
helps reduce fuel consumption and protect the environment issues
that are becoming increasingly important in our lives. This talk
highlights important challenges and imperatives for the design of
future FiWi network architectures, protocols, and algorithms. A
new proposed Ethernet-based FiWi access-metro network, referred
to as SuperMAN, is introduced which integrates next-generation
WiFi and WiMAX networks with optical access and metro networks.
Finally, a techno-economic analysis of Ethernet passive optical
network (EPON) and WiMAX, as two key FiWi technologies with
similar design goals is described.
|
|
9 Feb. 2010
14:00–15:00
|
tba
|
Thesis talk:
Alexandre
Fiveg
Optimierung des FreeBSD-Packet-Capturing-Stacks
(Improving the FreeBSD Packet Capturing Stack )
Die hohe Datenrate in modernen Netzwerken erschwert die
vollständige Erfassung des Verkehrs. Die Gründe önnen
sowohl in der begrenzten Performance der Hardware, als auch in
der Ineffizienz von Software liegen.
Im Rahmen dieser Diplomarbeit wurden die für die
Verkehrserfassung verantwortlichen Komponenten eines
konventionelles Rechnersystem analysiert mit dem Ziel, die
Engstellen welche die Paketverluste bei Verkehrserfassung
verursachen können zu identifizieren. Dabei wurden sowohl
die Hardware- als auch die Softwareaspekte betrachtet. Aufgrund
der herausgestellten Problemen wurden neue Softwarekomponenten
für das Betriebssystem FreeBSD implementiert. Damit wurden
sowohl Paketverluste als auch die Auslastung des Rechnersystems
bei der Erfassung des Verkehrs deutlich reduziert.
|
|
3 Feb. 2010
10:30–11:30
|
Consilium (TEL 1315)
|
Talk:
Danny Hendler
Randomized Mutual Exclusion in O(log N / log log N)
RMRs.
Mutual exclusion is a fundamental distributed coordination
problem. Shared-memory mutual exclusion research focuses on
local-spin algorithms and uses the remote memory references
(RMRs) metric. An RMR is a shared memory access that cannot be
served from a process' local cache.
A recent proof by Attiya, Hendler and Woelfel established
an Ω(log N) lower bound on the
number of RMRs incurred by processes as they enter and exit the
critical section, matching an upper bound by Yang and Anderson.
Both these bounds apply for N-process
algorithms that only use read and write operations.
The lower bound of Attiya et al. only holds for deterministic
algorithms, however; the question of whether randomized mutual
exclusion algorithms, using reads and writes only, can achieve
sub-logarithmic expected RMR complexity remained open. In this
talk, I will present recent work that answers this question in
the affirmative.
We present two strong-adversary randomized local-spin mutual
exclusion algorithms. In both algorithms, processes incur O(log N / log log N)
expected RMRs per critical section passage. Our first algorithm
has sub-optimal worst-case RMR complexity of O((log N / log log N)²)
. Our second algorithm is a variant of the first that can
be combined with a deterministic algorithm, such as that of
Anderson and Yang, to obtain O(log N)
worst-case RMR complexity. The combined algorithm thus achieves
sub-logarithmic expected RMR complexity while maintaining
optimal worst-case RMR complexity.
The talk will be self-contained and no familiarity with
Distributed Computing theory will be assumed.
This is joint work with Philipp Woelfel.
|
|
2 Feb. 2010
14:00–15:00
|
Consilium (TEL 1315)
|
Talk:
Maximilian Berger
Introduction to the EGEE Grid Infrastructure and the
gLite Middleware
Grid Computing has, over the past few
years, matured sufficiently to make it a viable solution for
real-world problems. However, there are many different toolkits
today that allow to build a Grid environment. The Enableling Grids for E-Science
(EGEE) project is the flagship Grid project sponsored by the
European Union, which brings together more than 140 institutions
to produce a reliable and scalable computing resource available
to the European and global research community. At present, it
consists of approximately 300 sites in 55 countries and gives its
14,000 user's access to 150,000 CPU cores around-the-clock. It
aims at a consolidation of existing efforts and will assist in
the deployment of the resulting next generation Grid middleware
(gLite) by offering support and training to new users, both in
academia and industry. This session gives you an overview of
what the Grid is, the architecture of the gLite middleware,
an introduction to job submission, data management and grid
workflows. It describes in detail the life of a job on the EGEE
Grid, detailing the process of workflow management.
Bio:
Max Berger has received his Diplom at TU München, where he
focused on synchronization of Personal Information Data in his
master thesis. He then attended Texas Tech University, where he
received his Ph.D. for designing a next-generation distributed
file system. Upon his return to Europe he immediately got involved
in the EGEE project, first at the Hungarian Technical Academy of
Science (MTA), then at the Distributed and Parallel Systems Group
at the University of Innsbruck (UIBK), where he became the local
coordinator for the EGEE Project and an EGEE certified trainer.
His research interest are large-scale, autonomous distributed
applications.
|