Performance modeling, queuing network models of computer systems and
networks, computer architecture and operating systems

Current research interests

- Efficient solution of systems with large state space
- Application of conditional probability in the solution of performance models
- Stable recurrent solutions
- Models of virtualized systems
- I/O subsystem models, optical channels
- Multimedia/networking problems, e.g. optical networks
- Efficient solutions of priority
system

Credentials

- 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
decomposition.

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".

**PUBLICATIONS**

Journal Papers

- Begin, 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.
- Brandwajn, A. and T. Begin. 2009 "Higher-order distributional properties in closed queueing networks", Performance Evaluation, vol. 66, pp. 660-659.
- Begin, T., Baynat, B., Sourd, F. and A. Brandwajn. 2009 "A DFO technique to calibrate queueing models", Computers & Operations Research, May 2009.
- Brandwajn, 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.
- Benbadis, 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 275658.
- Brandwajn, A. and H. Wang. 2008 "A Conditional Probability Approach to M/G/1-like Queues", Performance Evaluation, vol. 65, pp. 366-381.
- Brandwajn, A. 2003. "A model of periodic acknowledgment", Performance Evaluation, Vol. 52, pp. 221-235.
- Brandwajn, A. and A. Sahai. 1993. "Aspects of the Solution of Some Multiclass Loss Systems", Performance Evaluation, Vol. 17, pp. 141-159.
- Brandwajn, A. and A. Sahai. 1989. "A Note on Approximate Iterative Solution of Open Tandem Networks with Blocking", Performance Evaluation, vol. 10, pp. 211-218.
- Brandwajn, A. 1988. "Load Imbalance in DASD Dynamic Reconnection", Information Processing Letters, vol. 28, pp. 111-119.
- Brandwajn, A. and L. Jow. 1988. "An Approximation Method for Tandem Queues with Blocking", Operations Research 36, pp. 73-83.
- Brandwajn, A. 1985. "Equivalence and Decomposition in Queueing Systems - A Unified Approach", Performance Evaluation, vol. 5, pp. 175-186.
- Brandwajn, A. 1983. "Models of DASD Subsystems with Multiple Access Paths: A Throughput-Driven Approach", IEEE Transactions on Computers, vol. C-32, pp. 451-463.
- Brandwajn, A. 1982. "DASD Subsystem Modeling", Computer Performance, vol. 3, pp. 40-44.
- Brandwajn, A. 1982. "A Finite Difference Equations Approach to a Priority Queue", Operations Research, vol. 30, pp. 74-81.
- Brandwajn, A. 1981. "Models of DASD Subsystems: Basic Model of Reconnection", Performance Evaluation, vol. 1, pp. 263-281.
- Brandwajn, 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.
- Brandwajn, A. and R. Joly. 1980. "A Scheme for Fault-Tolerant Virtual Memory", Information Processing Letters, vol. 10, pp. 99-103.
- Brandwajn, A. 1979. "An Iterative Solution of Two-Dimensional Birth and Death Processes", Operations Research, vol. 27, pp. 595-605.
- Brandwajn, A., P. Kruchten, and J.A. Hernandez. 1978. "ARCADE - A System for Research and Education in Computer Architecture", Information Processing Letters, vol. 7, pp. 78-85.
- Brandwajn A. and B. Mouneix. 1977. "A Study of a Page-on-Demand System", Information Processing Letters, vol. 6, pp. 125-132.
- Brandwajn, A. 1977. "A Queueing Model of Multiprogrammed Computer Systems under Full-Load Conditions", Journal of the ACM 24, pp. 222-240.
- Brandwajn, A. 1976. "A Model of a Virtual Memory System", Acta Informatica 6, pp. 365-386.
- Brandwajn, A. 1976. "Simulation de la charge d'un système conversationnel", R.A.I.R.O. Informatique 10, pp. 25-44.
- Brandwajn, A. 1976. "Control Schemes in Queueing Networks", Management Science 22, pp. 810-822.
- Brandwajn, A. 1974. "A Model of a Time-Sharing Virtual Memory System Solved Using Equivalence and Decomposition Methods", Acta Informatica 4, pp. 11-47.

**Conference
Papers**

- (with T. Begin) "Performance Evaluation of a Single Node with General Arrivals and Service", ASMTA 2011, Venice, Italy.
- (with 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).
- (with T. 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. 159-173.
- (with 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 (France).
- (with 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.
- (with 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 2007.
- with 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.
- (with 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.
- "A Note 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.
- "Fast Decomposition in Large Stochastic Models", IEEE International Conference on Systems, Man and Cybernetics, San Diego, October 1998.
- (with 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 1990.
- "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. 123-140.
- "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.
- (with 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.
- "A Study of Dynamic Reconnection", 1983 SIGMETRICS Conference, August 29-31, Minneapolis, MN, Performance Evaluation Review Special Issue, pp. 1--11.
- "Fast 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.
- (with J.A. Hernandez, R. Joly and P. Kruchten) "Overview of the ARCADE System", 6th Annual Symposium on Computer Architecture, Philadelphia, April 1979, pp. 42--49.
- (with 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.
- (with 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.
- "An 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.
- "A 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.
- "A Study of an Interactive System", ACM Computer Science Conference, Anaheim, CA, Feb. 10-12, 1976.
- "A 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.
- "Experiments 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.
- (with J. Buzen, E. Gelenbe and D. Potier) "A Model of Performance for Virtual Memory Systems", 2nd Annual SIGMETRICS Symposium on Measurement and Evaluation, Montreal, 1974.
- "Equivalence 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.
- (with 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
1973.

**Technical
reports**1.
Brandwajn,
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.

2. Brandwajn, 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.

3. Brandwajn, A. 1993. "An Approach to the Decomposition of Large Stochastic Models", UCSC-CRL-93-42, University of California, Computer Research Laboratory, Santa Cruz, CA.

4. Brandwajn, A. 1987. "Aspects of Path Sharing in I/O", Technical Report, UCSC-CRL-87-16, University of California, Computer Research Laboratory, Santa Cruz, CA.

5. Brandwajn, A. 1987. "A Simple Model of an Automated Library System", Technical Report, UCSC-CRL-87-14, University of California, Computer Research Laboratory, Santa Cruz, CA.

6. Brandwajn, A. 1986. "A Model of Cached I/O", Technical Report, UCSC-CRL-86-26, University of California, Computer Research Laboratory, Santa Cruz, CA.

7. Brandwajn, 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.

8. Brandwajn, A. 1979. "Equivalence and Decomposition in Queuing Network Models - A Point of View", Technical Report, CS-1979-6, Duke University, Durham, NC, May 1979.

9. Brandwajn, 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.

10. Brandwajn, A. 1976. "A Finite-Source Queueing Model with Blocking", Technical Report ENST-D-76008, Paris, France, June 1976.

11. Brandwajn, 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.

**Invited
talks**

- "Seeking simplicity in complex systems", LINCS Seminar, February 2011, Paris.
- (with M. Boksenbaum (HDS), B. McNutt (IBM), G. Schultz (StorageIO Group), B. Zahavi (EMC)) "Storage Performance Measurement'', CMG 2006 International Conference., Panel discussion.
- "Fast Decomposition in Large Stochastic Models", Institut National des TÃƒÂ©lÃƒÂ©communications, 2005, Evry.
- (with B. McNutt, B. Smith, W. Baker, J. Buzen and M. Friedman) "Central-Server Design for Storage Benchmarks'', CMG 2002 International Conference, Panel discussion.
- "A Model of Periodic Acknowledgment'', PERNET Colloquia, SFSU, 2002, San Francisco, CA, USA.
- "Overview of the State of the Art in Performance Modeling'', Graduate School of Computer Engineering, CEA, Saclay, 1993.
- "Aspects of I/O Performance Modelling", CMG Benelux, February 1990, Antwerp, Belgium.
- "State of the Art in I/O Subsystem Modelling", CMGF 1989, Nice.
- "Performance Benefits of Overlap in Modern Cache Controllers", UK CMG Modelling Group Meeting, 1989, London, UK.
- "Aspects of Path Sharing in I/O", IBM Palo Alto Scientific Center, Palo Alto, CA, USA, 1987.
- "An Approximation Method for Tandem Queues with Blocking", ORSA/TIMS Joint National Meeting, November 1985, Atlanta, GA, USA.
- "Issues in Mainframe System Modelling - Lessons from Model Development at Amdahl" International Conference on Modelling Techniques and Tools for Performance Analysis, Paris, 1984.
- "Aspects of DASD Performance", advanced tutorial, Computer Measurement Group CMG XIV International Conference, 1983, Washington, D.C., USA.
- "Factors in DASD Performance", European Computer Measurement Association, ECOMA-11 Conference, 1983, Copenhagen, Denmark.
- "On Decomposition in Operational Analysis", IMACS World Congress on System Simulation and Modeling, Session on Operational Analysis, August 8-13, 1982, Montreal, Canada.
- "On Decomposition Approaches to Queueing Problems", TIMS Meeting, Session on Computational Probability, Hawaii, USA, 1979.
- "An Approach to the Solution of Some Queueing Systems", 7th Conference on Stochastic Processes and Their Applications, 1977, Twente University of Technology, the Netherlands.

Recent Sabbatical Leaves

April –June 2010

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
way.

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
Architecture”).

January-March
2011

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 solutions.

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.

The
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

Classes taught
recently

- 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).