Department of Electrical and
Intelligent Systems and Networks Group
Imperial College, London
Tuesday, June 3, 8:45-9:15
Title: New Product Form Solutions for Stochastic Models: Discovery or Invention?
In the late seventies, most of us agreed that most of the queuing networks
having product form solutions had already been discovered. Thus much research
was then devoted to explaining why certain queuing networks had such solutions,
and theories about “one step transitions”, the “M=>M property”, “local balance”,
and “quasi-reversibility” were put forth. The G-networks that we introduced in
the late 1980’s and early 1990’s, initially met with incredulity (in particular
at the SIGMETRICS conferences), but proved in a series of papers [3,4,6,7] that
one could have product form solutions (a) without local balance, (b) without one
step transitions, (c) without quasi-reversibility, and (d) with non-linear
traffic equations. These new models established the possibility of
incorporating control primitives into solvable models of queuing
networks. G-networks were inspired by neuronal signalling, and resulted in
interesting parallels between neuronal models [1,2,8], gene regulatory networks
 and queuing networks. We were able to show that (a) they approximate
continuous and bounded functions, and (b) that they have gradient optimisation
algorithms which are O(n3) for an n-queue network [5,8]. In this
lecture we will briefly review these results and summarise recent product form
results that we have discovered.
Gelenbe ``Random neural networks with positive and negative signals and product
form solution'', Neural Computation, 1 (4): 502-510, 1989.
 E. Gelenbe ``Stability of the random neural networks'', Neural
Computation, 2 (2): 239-247, 1990.
 E. Gelenbe ``Product form queueing networks with negative and positive
customers'', J. App. Prob., 28: 656-663, 1991.
 E. Gelenbe ``G-networks with instantaneous customer movement'', J.
App. Prob. , 30 (3): 742-748, 1993.
 E. Gelenbe ``Learning in the recurrent random network'', Neural
Computation, 5: 154-164, 1993.
 Erol Gelenbe ``G-Networks with signals and batch removal'', Probability in
the Engineering and Informational Sciences, 7: 335-342, 1993.
 E. Gelenbe, J.M. Fourneau ``G-Networks with resets'', Performance
Evaluation, 49: 179-192, 2002.
 E. Gelenbe, K. Hussain ``Learning in the multiple class random neural
network'', IEEE Trans. on Neural Networks 13 (6): 1257-1267, 2002.
 E. Gelenbe ``Steady-state solution of probabilistic gene regulatory
networks'', Physical Review E, 76(1), 031903 (2007).
(FACM, FIEEE, FIEE) has been characterized as the single individual who, over a
span of 30 years, has made the greatest overall contribution to the field of
Computer System and Network Performance Evaluation through research, doctoral
training, wide ranging international collaboration, and professional service. He
holds the “Dennis Gabor Chair” at Imperial College, and his papers in 2007-2008
appear in the ACM Trans. on Sensor Networks, ACM Transactions on
Internet Technology, Neural Computation, Performance Evaluation,
Physical Review, Proceedings of the Royal Society A, and The Computer
Journal. He has made decisive contributions to product form networks by
inventing G-networks (Gelenbe-Networks) with totally new types of “negative
customers, triggers, and resets”, and which are characterised by non-linear
traffic equations. He has made seminal contributions to random access
communications, the optimisation of reliability in database systems, the design
of adaptive QoS-aware packet networks, diffusion models in performance analysis,
and the performance of link control protocols.
A native of
Turkey who graduated from the Middle East Technical University in Ankara, he has
authored four books written in English and French, two of which have appeared in
Japanese and Korean translation, and over 115 journal articles in the Journal
of the ACM, Physical Review, Acta Informatica, Proceedings of the Royal Society,
Management Science, IEEE Trans. on Computers, IEEE Trans. on Neural Networks,
IEEE Trans. on Software Engineering, IEEE Trans. on Systems Man and Cybernetics,
IEEE J. on Selected Areas in Communications, ACM Trans. on Sensor
Networks, Communications of the ACM, Journal of Applied Probability, and
Theoretical Computer Science, etc.. His recent work includes path finding
algorithms in noisy and uncertain conditions, networked auctions, the use of
neural networks to control routing in computer networks, as well as theoretical
biology and theoretical chemistry including the analysis of neural networks and
gene regulatory networks. His research is currently funded by industry (GD, BAE
Systems and QinetiQ), and by agencies including EPSRC, MoD and DoD, and the EU.
A founder of
IFIP WG7.3 and of ACM SIGMETRICS, and of the journal Performance Evaluation,
Erol is particularly proud of the 58 PhD students he has graduated, many of whom
are prominent in academia and industry in France, the USA, Turkey, Greece, UK,
Canada, Belgium and Venezuela. Appointed to a chair at the age of 27 at the
University of Liège in Belgium, he founded performance modelling at INRIA and in
French Universities. His professorial posts include the University of Paris-Orsay,
the University of Paris-Descartes, New Jersey Institute of Technology, Duke
University and the University of Central Florida. He is now Editor-in-Chief of
The Computer Journal (British Computer Society), and serves on the
editorial board of several journals. Erol is currently a member of the Science
and Technology Board and of the Executive Board of the UK Defence Technology
Centre on Data and Information Fusion. His experience includes being Department
Head at Duke University (USA), Associate Dean at the University of Central
Florida (USA), and chairing the Technical Advisory Board of the US Army’s
Simulation and Training Command (1999-2003).
include: Commander of Merit of the Republic of Italy, Grand Officer of the Star
of Italy, Officer Order of Merit of France and Chevalier des Palmes Académiques.
Member of the French National Academy of Engineering, Turkish
Academy of Sciences, Academia Europaea. He received the Science Award (1994) of
the Parlar Foundation in Turkey, was the first computer scientist to be awarded
the Grand Prix France Telecom (1996) of the French Academy of Sciences, and
received “honoris causa” doctorates from the University of Rome II (1996),
Bogaziçi University, Istanbul (2004), and the University of Liège, Belgium.
Vice President of Research and Development at Tata Consultancy Services
Tuesday, June 3, 13:00-14:00
Title: Navigating Complexity through Managed Evolution
The complexity of large-scale “information technology (IT) plants”—consisting of
a number of hardware and software components—has been increasing rapidly and is
fast approaching a barrier. Continuous evolution is a key contributor to this
complexity. IT plants evolve to accommodate new software functionality, hardware
technology, application and user requirements, as well as changes in operating
conditions (workload, faults, etc.). To navigate the complexity of IT plants, we
need methodology and
tools for managing evolution. These tools should facilitate designers and
operators of IT plants to reason about the impact of each evolution step on
system-level properties—such as security, privacy, performance, availability,
and reliability--and thereby simplify many tasks such as capacity management,
performance engineering, system testing, and real-time decision making (e.g.,
anomaly detection, alert generation, and root cause analysis). In this talk, I
will briefly describe the overall R&D vision, some of the key challenges, our
approach, and some of the early results from analyzing performance and
operational data collected from large-scale operational systems.
Dr. Harrick Vin is a Vice President (R&D) and a member of the Corporate
Technology Board at Tata Consultancy Services (TCS), India. TCS is the largest
Asian IT Services company. At TCS, he heads the Systems Research Lab (SRL) --
responsible for developing innovative solutions for next-generation enterprise
infrastructure. Prior to TCS, he was a Professor of Computer Sciences at the
University of Texas at Austin. His research interests are in the areas of
networks, operating systems, distributed systems, and multimedia systems.
Harrick received his Ph.D. in Computer Science from the University of California
at San Diego. He has co-authored more than 100 papers in leading international
journals and conferences. He is a recipient of several awards including the
Faculty Fellow in Computer Sciences, Dean's Fellowship, National Science
Foundation CAREER award, IBM Faculty Development Award, Fellow of the IBM Austin
Center for Advanced Studies, AT&T Foundation Award, National Science Foundation
Initiation Award, IBM Doctoral Fellowship, NCR Innovation Award, and San Diego
Supercomputer Center Creative Computing Award. He has served on the Editorial
Board of ACM/Springer Multimedia Systems Journal, IEEE Transactions on
Multimedia, and IEEE Multimedia. He has been a guest editor for IEEE Network. He
has served as the conference and program chairperson for the premier ACM and
IEEE international conferences in the area of multimedia systems and networks;
and served as a technical program committee member for many international
Professor, INRIA (Unité de Recherche de
Rocquencourt) and ENS (Département d'Informatique) France
Wednesday, June 4,
Title: Measurement Based Self-Optimization of Wireless
Networks using Gibbs Fields
The popularity of IEEE 802.11 WLANs has led to dense deployments, either managed
or unmanaged, in urban areas, enterprises and campuses. High density leads
the close proximity of co-channel cells, increased interference and contention
and hence to sub-optimal performance. An efficient use and sharing of the
spectrum requires some form of network-level organization.
This talk surveys a collection of fully distributed self-organization algorithms
applicable within this context
and which allow:
multiple interfering 802.11 Access Points to select their
operating frequency in order to minimize interference throughout the network;
users to choose the Access Point they attach to in order to
optimally share the global network bandwidth;
Access Points to control their transmission power in order to
optimally share the global network bandwidth. This power control problem is
particularly challenging as variable transmit powers result in asymmetric
links in the network and can potentially lead to throughput starvation of some
The proposed algorithms all rely on the Gibbs sampler and its annealed version,
which can be seen as distributed algorithms for minimizing some global
energy function. We analytically prove their convergence:
Algorithm (i) leads to minimal total interference and
Algorithms (ii) and (iii) lead to minimal total potential
delay (when considering elastic traffic on the downlink).
These algorithms do not require global
coordination among the
wireless devices. They only require the participating
wireless nodes to measure such local quantities as
interference or transmission delay and to perform some
local adaptive tuning of the relevant parameters:
Access Point frequency for (i), user Access Point attachment for (ii)
and Access Point transmit power and carrier sensing parameter
We study their performance using both simulation and testbeds and
we show that their incremental deployment is feasible.
This class of algorithms is versatile and can be adapted to
various other contexts. To illustrate this,
some recent extensions to optimal routing in mesh WLANs will also be discussed.
This survey is based
on a series of papers presented
at Infocom 07 (on user association, frequency selection and
on power control) and at CoNext 07 (on routing) which are
based on collaboration
with Vivek Mhatre (Motorola),
Bruno Kauffmann (INRIA-ENS), Augustin Chaintreau (Thomson),
Christophe Diot (Thomson), Konstantina Papagiannaki (INTEL)
and Henrik Lundgren (Thomson).
Francois Baccelli is a specialist of communication network modeling and design.
He got his "doctorat d'etat" from Universite Paris-Sud in
1983. He held positions at INRIA Rocquencourt, AT&T Bell Laboratories and INRIA
Sophia Antipolis. He is currently INRIA "directeur de recherche" in the computer
science department of Ecole Normale Superieure in Paris, where he started the
research group on communication networks in 1999.
He is the co-author of a book on queueing theory with P. Bremaud and on a
book on the max plus algebra with G. Cohen, G.J. Olsder and J.P. Quadrat. His
current research work is focused on two topics: 1) the analysis, the
control and measurements of large IP networks and 2) the development of new
stochastic geometry tools for assessing and exploiting the capacity of wireless
F. Baccelli is a member of the French academy of sciences.
Assistant Director, Computer and Information
Science and Engineering Directorate, National Science Foundation
Thursday, June 5, 14:00-15:00
Title: Computational Thinking and Thinking about
My vision for the 21st Century: Computational thinking will be a fundamental
skill used by everyone in the world. To reading, writing, and arithmetic, let's
add computational thinking to every child's analytical ability. Computational
thinking has already influenced other disciplines, from the sciences to the
arts. Realizing this vision gives the field of computing both exciting research
opportunities and novel educational challenges.
The field of computing is driven by technology innovation, societal demands,
and scientific questions. We are often too easily swept up with the rapid
progress in technology and the surprising uses by society of our technology,
that we forget about the science that underlies our field. In thinking about
computing, I have started a list of "Deep Questions in Computing," with the hope
of encouraging the community to think about the scientific drivers of our
field. One of these questions, “How can we build complex systems simply?” is of
special relevance to the SIGMETRICS community. I will close my talk by posing
some research challenges specific to measuring properties of complex systems.
Dr. Jeannette M. Wing is the President's Professor of Computer Sciencein the
Computer Science Department at Carnegie Mellon University. Shereceived her S.B.
and S.M. degrees in Electrical Engineering and Computer Science in 1979 and her
Ph.D. degree in Computer Science in 1983, all from the Massachusetts Institute
of Technology. From 2004-2007, she was Head of the Computer Science Department
at Carnegie Mellon. Currently on leave from CMU, she is the Assistant Director
of the Computer and Information Science and Engineering Directorate at the
National Science Foundation.
Professor Wing's general research interests are in the areas of specification
and verification, concurrent and distributed systems, and programming languages.
Her current focus is on the foundations of trustworthy computing.
Professor Wing was or is on the editorial board of eleven
journals. She has been a member of many advisory boards, including: the
Networking and Information Technology (NITRD) Technical Advisory Group to the
President's Council of Advisors on Science and Tecbnology (PCAST), the National
Academies of Sciences's Computer Science and Telecommunications Board, ACM
Council, the DARPA Information Science and Technology (ISAT) Board, NSF's CISE
Advisory Committee, Microsoft's Trustworthy Computing Academic Advisory Board,
and the Intel Research Pittsburgh's Advisory Board. She is a member of the Sloan
Research Fellowships Program Committee. She is a member of AAAS, ACM, IEEE,
Sigma Xi, Phi Beta Kappa, Tau Beta Pi, and Eta Kappa Nu. Professor Wing is an
AAAS Fellow, ACM Fellow, and IEEE Fellow.