Professor Computer Engineering
Performance modeling, queuing network models of computer systems and
networks, computer architecture and operating systems
Current research interests
solution of systems with large state space
of conditional probability in the solution of performance models
of virtualized systems
subsystem models, optical channels
problems, e.g. optical networks
- Efficient solutions of priority
- B.A. (University of Paris IV Sorbonne), Docteur-Ingénieur, Docteur d'Etat
(University of Paris VI - UPMC)
- Ingénieur Civil des Télécommunications (ENST, Paris)
I started my
research by designing and implementing a load simulator for the ESOPE Operating
System within the operating system research group at I(n)RIA, the French
national research center. Next, I
worked on modeling the performance of virtual memory systems, and, in
particular, on the determination of the optimal multiprogramming degree. During this work I started to build a
general framework for the equivalence and decomposition method which relies on
the use of marginal and conditional state probabilities. This method allows to obtain (in
general, approximate) solutions of complex systems through structured
During my tenure
at the Computer Science department at the ENST in Paris, I formed a research
team in adaptive system architectures.
Among the goals of the project was the dynamic adaptation of the
architecture to changes in load and to component failures. The resulting dynamic reconfiguration
was to allow the addition or removal of system components and devices without
the need to stop and reboot the system, well before "plug and play" systems
became a commercial reality.
Later, I joined a large computer
manufacturer in the Silicon Valley (Amdahl Corporation) where I worked on the
performance modeling of transaction processing systems, large enterprise
systems, storage subsystems, as well as on modeling network performance. The latter resulted in my work (with L.
Jow) on tandem queueing networks with blocking. My work in industry was instrumental in
allowing me to develop an appreciation for the "real world", problems in
model calibration, and, in general, the size of realistic problems.
As a professor of Computer
Engineering at the University of California Santa Cruz, my research topics have
included solution method for large systems, multi-server priority queues,
multicast systems with periodic synchronization and the modeling of optical
networks (during my sabbatical at Telecom Sud Paris). Additionally, I have continued my work
on model calibration. Some of the
ideas of that research led to the PhD work of Thomas Begin at the
University of Paris (UPMC), which incorporated the idea of automated model
calibration and selection.
At the same time, I have continued my work on
the use of conditional probabilities in the solution of queueing models. This idea resulted in the
development of numerically stable efficient recurrent solution of
M/Ph/1-like queues, and more recently, to the development of an
efficient iterative solution for the Ph/Ph/c queue. I continue to be interested
in approaches that allow circumventing the combinatorial explosion of the
size of the state space, in particular, in the context of virtualized systems
and "cloud computing".
T., Brandwajn, A., Baynat, B., Wolfinger, B., S. Fdida,. 2010 "High-level Approach to Modeling of Observed
System Behavior", Performance Evaluation, vol. 67, pp. 386-405.
A. and T. Begin. 2009 "Higher-order distributional
properties in closed queueing networks", Performance Evaluation, vol. 66,
T., Baynat, B., Sourd, F. and A. Brandwajn. 2009 "A DFO technique to calibrate queueing
models", Computers & Operations Research, May 2009.
A., Nguyen, V.H. and T. Atmaca. 2009 "A Conditional
Probability Approach to Performance Analysis of Optical Unslotted Bus-Based
Networks", in Current Research Progress of Optical Networks, Springer
Verlag, edited by Maode.
F., Obraczka, K., Cortés, J. and A. Brandwajn. 2008 "Exploring landmark
placement strategies for topology-based localization in wireless sensor
networks", EURASIP Journal on Advances in Signal Processing 2008, Article ID
A. and H. Wang. 2008 "A Conditional Probability Approach to
M/G/1-like Queues", Performance Evaluation, vol. 65, pp. 366-381.
A. 2003. "A model of periodic
acknowledgment", Performance Evaluation, Vol. 52, pp. 221-235.
A. and A. Sahai. 1993. "Aspects of
the Solution of Some Multiclass Loss Systems", Performance Evaluation,
Vol. 17, pp. 141-159.
A. and A. Sahai. 1989. "A Note on
Approximate Iterative Solution of Open Tandem Networks with Blocking",
Performance Evaluation, vol. 10, pp. 211-218.
A. 1988. "Load Imbalance in DASD Dynamic Reconnection", Information Processing
Letters, vol. 28, pp. 111-119.
A. and L. Jow. 1988. "An Approximation Method for
Tandem Queues with Blocking", Operations Research 36, pp. 73-83.
A. 1985. "Equivalence and Decomposition in
Queueing Systems - A Unified Approach", Performance Evaluation, vol. 5,
A. 1983. "Models of DASD Subsystems with
Multiple Access Paths: A Throughput-Driven Approach", IEEE Transactions on
Computers, vol. C-32, pp. 451-463.
A. 1982. "DASD Subsystem Modeling", Computer Performance, vol. 3, pp.
A. 1982. "A Finite Difference Equations
Approach to a Priority Queue", Operations Research, vol. 30, pp.
A. 1981. "Models of DASD Subsystems: Basic Model of Reconnection", Performance
Evaluation, vol. 1, pp. 263-281.
A. and J.A. Hernandez. 1981. "A Study of
a Mechanism for Controlling Multiprogrammed Memory in an Interactive
System", IEEE Transactions on Software Engineering SE-7, pp. 321-331.
A. and R. Joly. 1980. "A Scheme for Fault-Tolerant Virtual Memory",
Information Processing Letters, vol. 10, pp. 99-103.
A. 1979. "An Iterative Solution of
Two-Dimensional Birth and Death Processes", Operations Research, vol. 27,
A., P. Kruchten, and J.A. Hernandez. 1978. "ARCADE - A System for Research and
Education in Computer Architecture", Information Processing Letters, vol. 7,
A. and B. Mouneix. 1977. "A Study of a Page-on-Demand System", Information
Processing Letters, vol. 6, pp. 125-132.
A. 1977. "A Queueing Model of
Multiprogrammed Computer Systems under Full-Load Conditions", Journal of
the ACM 24, pp. 222-240.
A. 1976. "A Model of a Virtual Memory System", Acta Informatica 6, pp.
Brandwajn, A. 1976. "Simulation de la charge d'un système
conversationnel", R.A.I.R.O. Informatique 10, pp. 25-44.
A. 1976. "Control Schemes in Queueing Networks", Management Science 22, pp.
A. 1974. "A Model of a Time-Sharing Virtual Memory System Solved Using
Equivalence and Decomposition Methods", Acta Informatica 4, pp.
Begin) "Considerations in Workload Characterization for PAVs", CMG 09, Dec.
6-11, 2009, Dallas, TX.
(with T. Begin)
"Preliminary Results on a Simple
Approach to G/G/c-Like Queues", ASMTA 2009, Madrid Spain, pp.
T. Begin) "A Note on the Effects of Service Time
Distribution in the M/G/1 Queue", SPEC Benchmark Workshop 2009, Austin,
TX, pp. 138-144.
(with T. Begin) "Note sur les
temps résiduels dans les systèmes type M/G/c", CFIP 2008, Les Arcs
T. Begin, B. Baynat, B. Wolfinger, and S. Fdida) "High-level Approach to Modeling Observed
System Behavior", poster session in Performance 2007, The 26th International Symposium
on Computer Performance. Modeling, Measurement, and Evaluation, Cologne,
Germany, October 2007.
T. Begin, B. Baynat, B. Wolfinger, and S. Fdida) "Towards an Automatic Modeling Tool
for Observed System Behavior", EPEW '07, Lecture Notes in Computer
Science, Springer Verlag,, Berlin, Germany, pp. 200-212, September
F. Benbadis, K. Obraczka, and J. Cortes) "Exploring Landmark Placement
Strategies for Self-Localization in Wireless Sensor Networks", 18th
Annual International Symposium on Personal, Indoor and Mobile Radio
Communications, Athens, Greece, 2007, electronic proceedings.
T. Begin, B. Baynat, S. Fdida, S. Kedad, and F. Sourd) "Génération automatique de modèles
calibrés", CFIP 2006, Tozeur, Tunisia, October 30-November 3, 2006.
"A Simple Approach to FICON Channel
Performance", Int. CMG Conference, Dallas, TX, December 2003.
"Modeling FICON channels", First International
Working Conference on Performance Modeling and Evaluation of Heterogeneous
Networks, Ilkley, UK, July 2003.
"Insight through simplicity", Int.
CMG Conference 2002: 379-386, December 2002.
on SCSI Bus Waits", Practical Aspects of Performance Analysis, SIGMETRICS
2002, Marina Del Rey, June 2002.
"A Finite-Source Multiserver Queue With
Preemptive Priorities", 4th International Workshop on Queueing Networks with
Finite Capacity, Ilkley, UK, July 2000.
Decomposition in Large Stochastic Models", IEEE International Conference
on Systems, Man and Cybernetics, San Diego, October 1998.
David Levy) "A Study of Cached RAID-5 I/O", Computer Measurement Group
Conference, December 1994,.
"Réflexions sur l'état de l'art", Proceedings
of the CMGF '91 Conference, Paris, pp. 136--146, November 1991.
"Sur Certains Aspects de la modélisation des
E/S", Proceedings of the CMGF '90 Conference, Paris, pp. 57--70, November
"Performance Benefits of Parallelism in Cached
DASD Controllers", CMG'89 International Conference on Management and
Performance Evaluation of Computer Systems, Dec. 11-15, 1989, Reno, NV, pp.
"Modeling DASD and Disk Caches", CMG '86
International Conference on Management and Performance Evaluation of Computer
Systems, Dec. 9-12, 1986, Las Vegas, NV, pp. 206--216.
"Modeling DASD with Load Imbalance", European
Computer Measurement Association, ECOMA-14 Conference, Oct. 7-10, 1986,
Brussels, pp. 396--408.
"Tandem Exponential Queues with Finite
Buffers", International Seminar on Computer Networking and Performance
Evaluation, Sept. 18-20, 1985, Tokyo, pp. 6.2.1--6.2.13.
W.M. McCormack) "Efficient Approximation
for Models of Multiprogramming with Shared Domains", 1984 SIGMETRICS
Conference, August 21-24, Cambridge, MA, Performance Evaluation Review 12, No.
3, pp. 186--194.
of Dynamic Reconnection", 1983 SIGMETRICS Conference, August 29-31,
Minneapolis, MN, Performance Evaluation Review Special Issue, pp. 1--11.
Approximate Solution of Multiprogramming Models", 1982 SIGMETRICS
Conference, August 30 - September 1, 1982, Seattle, WA, Performance Evaluation
Review 11, No. 4, pp. 141--149.
"A Capacity Planning Model of A DASD
Subsystem", 8th International Symposium on Computer Performance Modelling,
Measurement and Evaluation, Nov. 4-6, 1981, Amsterdam, North-Holland Publ.
Co., pp. 401--414.
"Multiple Paths Versus Memory for Improving
DASD Subsystem Performance", 8th International Symposium on Computer
Performance Modelling, Measurement and Evaluation, Nov. 4-6, 1981, Amsterdam,
North-Holland Publ. Co., pp. 415--434.
"Further Results on Equivalence and
Decomposition in Queueing Network Models", 7th International Symposium on
Computer Performance Modelling, Measurement and Evaluation, May 28-30, 1980,
Toronto, Canada, Performance Evaluation Review 9, No. 2, pp. 93--104.
J.A. Hernandez, R. Joly and P. Kruchten) "Overview of the ARCADE System", 6th
Annual Symposium on Computer Architecture, Philadelphia, April 1979, pp.
J.A. Hernandez) "A Study of a Mechanism for Controlling Multiprogrammed Memory
in an Interactive System", 4th International Symposium on Modelling and
Performance Evaluation of Computer Systems, Feb. 6-8, 1979, Vienna,
North-Holland Publ. Co., pp. 487--500.
J.A. Hernandez, R. Joly and P. Kruchten) "Communication in the Fast Universe
of ARCADE - A Loosely-Coupled Adaptive Multiprocessor System," Fourth EURMICRO
Symposium on Microprocessing and Microprogramming, Oct. 17-19, 1978, Munich,
North-Holland Publ. Co., pp. 281--290.
Approach to the Numerical Solution of Some Queueing Problems", International
Symposium on Computer Performance Modeling, Measurement, and Evaluation, IBM
T. J. Watson Research Center, Yorktown Heights, New York, Aug. 16-28, 1977,
K.M. Chandy and M. Reiser (eds.), North-Holland Publ. Co., pp. 83-112.
Study of a Page-on-Demand System", International Workshop on Models of
Computer Systems, Bonn, March 31-April 1, 1977, Informatik - Fachberichte,
vol. 9, Springer Verlag, pp. 163--173.
Study of an Interactive System", ACM Computer Science Conference, Anaheim, CA,
Feb. 10-12, 1976.
Model of a Time-Sharing System with Two Classes of Processes", Gesellschaft
fuer Informatik, 5 Jahrestagung, Dortmund, 8-10 October, 1975, Lecture Notes
in Computer Science, vol. 34, Springer Verlag, pp. 547--566.
with a Simple Adaptive Control of the Multiprogramming Degree Based on a
System Model", International Seminar on Models and Measures for Computer
Science, Bologna, Italy, February 1975.
J. Buzen, E. Gelenbe and D. Potier) "A Model of Performance for Virtual Memory
Systems", 2nd Annual SIGMETRICS Symposium on Measurement and Evaluation,
and Decomposition Methods with Application to a Model of A Time-Sharing
Virtual Memory System", Colloque sur les aspects théoriques et pratiques des
systèmes d'exploitation, IRIA, Rocquencourt, France, April 1974.
E. Gelenbe, D. Potier and J. Lenfant) "Gestion Optimale d'un Système
d'Ordinateur Multiprogrammé à Mémoire Virtuelle", 5th IFIP Conference on
Optimization Techniques, Rome, Lecture Notes in Computer Science, Vol. 4,
Springer Verlag, pp. 132--143 (1973).
(with E. Gelenbe, D. Potier and J. Lenfant) "Modèle de Système
Multiprogrammé à Mémoire Virtuelle Paginée", Compte rendu des Journees
d'Etudes sur les Recherches en Mesure, Simulation, Modélisation des Systèmes
Informatiques, IRIA, Toulouse, France, June
- (with T. Begin) "Performance Evaluation
of a Single Node with General Arrivals and Service",
ASMTA 2011, Venice, Italy.
T. Begin) "Une
solution approchée pour les files Ph/Ph/1 et Ph/Ph/1/N", Algotel 2011, Cap Estérel (France).
- (with T. Begin) "Note sur la
simulation d'une file M/G/1 selon la distribution du temps de service",
Algotel 2010, Belle Dune (France).
Decomposition in Large Stochastic Models", Institut National des
TÃƒÂ©lÃƒÂ©communications, 2005, Evry.
B. McNutt, B. Smith, W. Baker, J. Buzen and M. Friedman) "Central-Server
Design for Storage Benchmarks'', CMG 2002 International Conference, Panel
Model of Periodic Acknowledgment'', PERNET Colloquia, SFSU, 2002, San
Francisco, CA, USA.
of the State of the Art in Performance Modeling'', Graduate School of Computer
Engineering, CEA, Saclay, 1993.
of I/O Performance Modelling", CMG Benelux, February 1990, Antwerp,
of the Art in I/O Subsystem Modelling", CMGF 1989, Nice.
Benefits of Overlap in Modern Cache Controllers", UK CMG Modelling Group
Meeting, 1989, London, UK.
of Path Sharing in I/O", IBM Palo Alto Scientific Center, Palo Alto, CA, USA,
Approximation Method for Tandem Queues with Blocking", ORSA/TIMS Joint
National Meeting, November 1985, Atlanta, GA, USA.
in Mainframe System Modelling - Lessons from Model Development at Amdahl"
International Conference on Modelling Techniques and Tools for Performance
Analysis, Paris, 1984.
of DASD Performance", advanced tutorial, Computer Measurement Group CMG XIV
International Conference, 1983, Washington, D.C., USA.
in DASD Performance", European Computer Measurement Association, ECOMA-11
Conference, 1983, Copenhagen, Denmark.
Decomposition in Operational Analysis", IMACS World Congress on System
Simulation and Modeling, Session on Operational Analysis, August 8-13, 1982,
Decomposition Approaches to Queueing Problems", TIMS Meeting, Session on
Computational Probability, Hawaii, USA, 1979.
Approach to the Solution of Some Queueing Systems", 7th Conference on
Stochastic Processes and Their Applications, 1977, Twente University of
Technology, the Netherlands.
A. and T. Begin, 2010. "A Recurrent Solution
of Ph/M/c/N-like and Ph/M/c-like Queues", INRIA
research report 7321, June 2010, Lyon, France.
A. and S. Fdida. 1996. "Modeling and Analysis of a Transport Multicast
Protocol", UCSC-CRL-96-20, University of California, Computer Research
Laboratory, Santa Cruz, CA.
A. 1993. "An Approach to the Decomposition of Large Stochastic Models",
UCSC-CRL-93-42, University of California, Computer Research Laboratory, Santa
A. 1987. "Aspects of Path Sharing in I/O", Technical Report, UCSC-CRL-87-16,
University of California, Computer Research Laboratory, Santa Cruz, CA.
A. 1987. "A Simple Model of an Automated Library System", Technical Report,
UCSC-CRL-87-14, University of California, Computer Research Laboratory, Santa
A. 1986. "A Model of Cached I/O", Technical Report, UCSC-CRL-86-26, University
of California, Computer Research Laboratory, Santa Cruz, CA.
A. and Y.L. Jow. 1986. "An Approximation Method for Tandem Queues with
Blocking", Technical Report, UCSC-CRL-86-19, University of California, Computer
Research Laboratory, Santa Cruz, CA.
A. 1979. "Equivalence and Decomposition in Queuing Network Models - A Point of
View", Technical Report, CS-1979-6, Duke University, Durham, NC, May 1979.
A. 1979. "A Method for Finding the Roots of Polynomials With Only Real Zeros",
Technical Report, CS-1979-2, Duke University, Durham, NC, February, 1979.
A. 1976. "A Finite-Source Queueing Model with Blocking", Technical Report
ENST-D-76008, Paris, France, June 1976.
A. 1976. "A Note on the Accuracy of the Equivalence and Decomposition Approach",
Technical Report ENST-D-76007, Paris, France, May 1976.
12. Brandwajn, A. 1975. "Equivalence et Decompostion dans les
Modèles à Files d'Attente et leur Application à
l'Evaluation des Performances de Systèmes d'Exploitation", Docteur d'Etat
Thesis, Paris, France, January 1975.
13. Brandwajn, A. 1972. "Procédure d'Exploitation pour une Liaison UC-UC",
Docteur-Ingénieur Thesis, Paris, France.
"Seeking simplicity in complex systems", LINCS Seminar, February 2011,
M. Boksenbaum (HDS), B. McNutt
(IBM), G. Schultz (StorageIO Group), B. Zahavi (EMC)) "Storage Performance
Measurement'', CMG 2006 International Conference., Panel discussion.
Recent Sabbatical Leaves
I spent my Spring 2010
sabbatical at the LIP Laboratory of the Ecole Normale Supérieure de Lyon
continuing my joint work with Dr. Thomas Begin on efficient solutions of general
queues, as well as collaborating with colleagues (Professors Paolo Gonçalves and
Isabelle Guérin Lassous) and graduate students on topics related to modeling TCP
performance and on static versus dynamic network routing protocols. The work on these topics is still under
During my stay in Lyon, I
gave a seminar on my current research interests. I was also the Chair of the doctoral
defense committee for Dinil Mon Divakaran (“Dealing
with Elephants in the Internet: Towards a Flow-Based Internet
I spent my Winter 2011
sabbatical in Paris dividing my time between the Ecole Nationale Supérieure des
Télécommunications (ENST) and the LIP6 laboratory at the University Pierre et
Marie Curie (Paris VI). My main research during this period was
in the area of applicability of state sampling to the solution of models of
large dimension (ENST with Dr. Thomas Bonald), as well as automated model
generation and calibration (LIP6 with Prof. Serge Fdida). During my stay
in Paris, I gave an invited talk at the LINCS Institute in Paris on possible
approaches to cicumvent the intrinsic complexity of standard queueing network
The work on state sampling
expands my previous work on fast solutions with partial state evaluation in
computer and network models. The
question addressed here was the applicability of this method to networks with
strong coupling for which an exact product-form solution exists but is costly to
compute. The preliminary results seem encouraging at least for some classes of
models. The results obtained will
become the subject of a future paper.
work on automatic model generation and calibration was an attempt to apply
methods developed previously during the Ph. D. work of Thomas Begin to the
modeling of the behavior of wireless networks. This work is still ongoing
- Probability and statistics for engineers (upper division undergraduate)
- Computer architecture (upper division undergraduate)
- Performance evaluation (graduate)
- Advanced topics in performance evaluation (graduate)
- Network engineering project (graduate capstone).