A brief biography

I received the Ph.D degree and the "Habilitation à diriger des recherches", both in Computer Science, from the University of Orsay (Paris XI), France, in 1989 and 1993, respectively. I am currently a research director at the performance evaluation group MISTRAL of the national research center on information and automation (INRIA), France. My current research interests are in control and performance analysis of high speed communication networks, scheduling and performance evaluation of parallel and distributed systems. I am also interested in Petri nets and queueing networks.

One of my current activities consists in leading a project on the modeling and the characterization of Web traffic. We have been developing a software tool WAGON (Web trAffic GeneratOr and beNchmark) for generating Web traffic and for the performance evaluation of Web servers and cache.

You are welcome to take a look at my list of publications to have a more general idea of my research activities.

I have been teaching DEA (i.e. Frecnch graduate) courses of Operations Research, Networking and Parallel Computing for more than ten years. These courses are concerned with Queueing Theory, Probabilistic Modeling, Stochastic Scheduling and Quality of Service in Computer Networks. Currently I am involved in the DEA IRO (Informatique et Recherche Opérationnelle, i.e. Computer Science and Operations Research) of the University of Pierre & Marie Curie (Paris VI) and the DEA RSD (Réseaux et Systèmes Distribués, i.e. Computer Networks and Distributed Systems) of the University of Nice - Sophia Antipolis, France.

I am currently supervising two Ph.D. students:

• Cesar Jalpa
• Naceur Malouch

• Lucian Finta (Maître de Conférences, University of Paris XII)
• Nicolas Niclausse (Post-Doc student at ENST, Paris)
• Jerôme Talim (Post-Doc student at Vreije University of Amsterdam)

As a particular application area, I'm interested in the analysis and optimization of the performance of Web servers and Web applications. You can take a look at the page on our activities related to the performance issues of the Web.

We are maintaining a Web page on the literature related to the above mentioned fields. Any comments are welcome and can be mailed to Zhen Liu, Nicolas Niclausse and Cesar Jalpa.

You are welcome to take a look at my list of publications to have a more general idea of my research activities.

• J. Talim, Z. Liu, P. Nain, E. G. Coffman, Jr., ``Optimizing the Number of Robots for Web Search Engines'', to appear in Telecommunication Systems.
  Preliminary version available in http://www.inria.fr/mistral/personnel/Zhen.Liu/Papers/robot_num_ts.ps.gz

• E. G. Coffman, Z. Liu, R. Weber, ``Optimal Robot Scheduling for Web Search Engines'', Journal of Scheduling, Vol. 1, pp. 15-29, 1998.
  Preliminary version available as INRIA RR, No. 3317, 1997.
  http://www.inria.fr/RRRT/RR-3317.html

• G. Koole, Z. Liu, R. Righter, ``Optimal Transmission Policies for Noisy Channels'', Technical Report WS-515, Faculteit der EXacte Wetenschappen, Vrije Universiteit Amsterdam, 1999. to appear in Operations Research.
  Preliminary version available in http://www.inria.fr/mistral/personnel/Zhen.Liu/Papers/noise.ps.gz

• A. Hordijk, Z. Liu, D.Towsley, ``Smoothing Effect of the Superposition of Homogeneous Sources in Tandem Networks'', to appear in the Journal of the Applied Probability, Vol. 37, No.3, september 2000.
  Preliminary version available as INRIA RR, No. 3839, 1999.
  http://www.inria.fr/RRRT/RR-3839.html

• E. Altman, Z. Liu, R. Righter, ``Scheduling of Input-Queued Switch to Achieve Maximal Throughput'', to appear in Probability in the Engineering and Information Sciences.
  Preliminary version available in http://www.inria.fr/mistral/personnel/Zhen.Liu/Papers/input_stab.ps.gz

• Z. Liu, R. Righter, ``The Impact of Cell Dropping Policies in ATM Networks'', to appear in Operations Research.
  Preliminary version available as INRIA RR, No. 3047, 1996.
  http://www.inria.fr/RRRT/RR-3047.html

• Z. Liu, P. Nain, D. Towsley, ``On a Generalization of Kingman's Bounds'', Mathematical Methods of Operations Research, Vol. 49, No. 2, pp. 325-333, 1999.
  Preliminary version available as INRIA RR, No. 2423, 1994.
  http://www.inria.fr/RRRT/RR-2423.html

• Z. Liu, R. Righter, ``Scheduling Multicast Input-Queued ATM Switches'', Journal of Scheduling, Vol. 2, pp. 99-114, 1999.
  Preliminary version available in http://www.inria.fr/mistral/personnel/Zhen.Liu/Papers/multicast.ps.gz

• Z. Liu, P. Nain, D. Towsley, Z.-L. Zhang, ``Asymptotic Behavior of a Multiplexer Fed by a Long-Range Dependent Process'', Journal of Applied Probability, Vol. 36, No. 1, pp. 105-118, March 1999.
  Preliminary version available in http://www.inria.fr/mistral/personnel/Zhen.Liu/Papers/mg_infty.ps.gz

• Z.-L. Zhang, Z. Liu, D. Towsley, ``Closed-Form Deterministic End-to-End Performance Bounds for the Generalized Processor Sharing Scheduling Discipline'', Journal of Combinatorial Optimization, special issue on Scheduling. Vol. 1, No.4, pp. 457-481, 1998.
  Preliminary version available in http://www.inria.fr/mistral/personnel/Zhen.Liu/Papers/gps_e2e.ps.gz

• A. Jean-Marie, Z. Liu, P. Nain, D. Towsley, ``Computational aspects of the workload distribution in the MMPP/GI/1 queue'', IEEE Journal on Selected Areas of Communications, Vol. 16, pp. 640-652, June 1998. Special issue on computational aspects of teletraffic models.
  Preliminary version available in http://www.inria.fr/mistral/personnel/Zhen.Liu/Papers/mmpp_g_1.ps.gz

• G. Koole, Z. Liu, ``Stochastic Bounds for Queueing Systems with Multiple On-Off Sources'', Probability in the Engineering and Information Sciences, Vol. 12, pp. 25-48, Jan. 1998.
  Preliminary version available in http://www.inria.fr/mistral/personnel/Zhen.Liu/Papers/on_off.ps.gz

• Z. Liu, P. Nain, D. Towsley, ``Exponential Bounds with an Application to Call Admission'' Journal of the ACM, Vol. 44, No. 2, 1997.
  Preliminary version available as INRIA RR, No. 2865, 1996.
  http://www.inria.fr/RRRT/RR-2865.html

• J.-C. Bermond, Z. Liu, M. Syska, ``Mean Eccentricities of de Bruijn Networks'', Networks, Vol. 30, pp. 187-203, 1997.
  Preliminary version available as INRIA RR, No. 2114, 1993.
  http://www.inria.fr/RRRT/RR-2114.html

• Z.-L. Zhang, Z. Liu, J. Kurose, D. Towsley, ``Call Admission Control Schemes under the Generalized Processor Sharing Scheduling Discipline'', Telecommunication Systems, Vol. 7, No. 1-3, pp. 125-152, July 1997.
  Preliminary version available as INRIA RR, No. 2711, 1995.
  http://www.inria.fr/RRRT/RR-2711.html

• Z. Liu, T. Y. Sung, ``Routing and Transmitting Problems in de Bruijn Networks'', IEEE Trans. on Computers , Vol. 45, pp. 1056-1062, Sept. 1996.
  Preliminary version available in http://www.inria.fr/mistral/personnel/Zhen.Liu/Papers/debruijn.ps.gz

• E. Altman, Z. Liu, ``Improving the Stability Characteristics of Asynchronous Traffic in FDDI Token Ring'', Performance Evaluation, Vol. 26, pp. 219-234, 1996.
  Preliminary version available as INRIA RR, No. 1934, 1993.
  http://www.inria.fr/RRRT/RR-1934.html

• Z. Liu, D. Towsley, ``Burst Reduction Properties of Rate-Based Flow Control Schemes: Downstream Queue Behavior'', IEEE/ACM Trans. on Networking, Vol. 3, No. 1, pp. 82-90, 1995.
  Preliminary version available as INRIA RR, No. 2117, 1993.
  http://www.inria.fr/RRRT/RR-2117.html

• Z. Liu, ``Dynamic Scheduling of Parallel Computations'', to appear in Theoretical Computer Science.
  Preliminary version available as INRIA RR, No. 3048, 1996.
  http://www.inria.fr/RRRT/RR-3048.html

• Z. Liu, R. Righter, ``Optimal Load Balancing on Distributed Homogeneous Unreliable Processors'', Operations Research, Vol. 46, No. 4, pp. 563-573, August 1998.
  Preliminary version available as INRIA RR, No. 2659, 1995.
  http://www.inria.fr/RRRT/RR-2659.html

• Z. Liu, ``Worst-Case Analysis of Scheduling Heuristics of Parallel Systems'', Parallel Computing, Vol. 24, issue 4-5, pp. 863-891, 1998.
  Preliminary version available as INRIA RR, No. 2710, 1995.
  http://www.inria.fr/RRRT/RR-2710.html

• A. Jean-Marie, S. Lefebvre-Barbaroux, Z. Liu, ``An Analytical Approach to the Performance Evaluation of Master-Slave Computational Models'', Parallel Computing, Vol. 24, issue 4-5, pp. 841-862, 1998.
  Preliminary version available in http://www.inria.fr/mistral/personnel/Zhen.Liu/Papers/master_slave.ps.gz

• L. Finta, Z. Liu, ``Complexity of Task Graph Scheduling with Fixed Communication Capacity'', International Journal of Fondations of Computer Science , Vol. 8, No. 1 (1997), pp. 43-66.
  Preliminary version available as INRIA RR, No. 2959, 1996.
  http://www.inria.fr/RRRT/RR-2959.html

• Z. Liu, E. Sanlaville, ``Stochastic Scheduling with Variable Profile and Precedence Constraints'', SIAM J. on Computing, Vol. 26, No. 1, pp. 173-187, 1997.
  Preliminary version available as INRIA RR, No. 1525, 1991.
  http://www.inria.fr/RRRT/RR-1525.html

• Z. Liu, R. Righter, ``Optimal Scheduling on Parallel Processors under Precedence Constraints for General Costs'', Probability in the Engineering and Information Sciences, Vol. 11, pp. 79-93, Jan. 1997.
  Preliminary version available in http://www.inria.fr/mistral/personnel/Zhen.Liu/Papers/prec_gen.ps.gz

• J. Blazewicz, Z. Liu, ``Scheduling Multiprocessor Tasks with Chain Constraints'', European Journal on Operations Research, Vol. 94, pp. 231-241, 1996.
  Preliminary version available in http://www.inria.fr/mistral/personnel/Zhen.Liu/Papers/chain_task.ps.gz

• L. Finta, Z. Liu, ``Single Machine Scheduling Subject to Precedence Delays'', Discrete Applied Mathematics , Vol. 70, pp. 247-266, 1996.
  Preliminary version available as INRIA RR, No. 2198, 1994.
  http://www.inria.fr/RRRT/RR-2198.html

• L. Finta, Z. Liu, I. Milis, E. Bampis, ``Scheduling UET-UCT Series-Parallel Graphs on Two Processors'', Theoretical Computer Science, special issue on Parallelism and Irregularly Structured Problems, Vol. 162, pp. 323-340, July 1996.
  Preliminary version available as INRIA RR, No. 2566, 1995.
  http://www.inria.fr/RRRT/RR-2566.html

• Z. Liu, E. Sanlaville, ``Preemptive Scheduling with Variable Profile, Precedence Constraints and Due Dates'', Discrete Applied Mathematics , Vol. 58, pp. 253-280, April 1995.
  Preliminary version available as INRIA RR, No. 1622, 1992.
  http://www.inria.fr/RRRT/RR-1622.html

• Z. Liu, ``Performance Analysis of Stochastic Timed Petri Nets using Linear Programming Approach'', IEEE Trans. on Software Engineering, Vol. 24, No. 11, pp. 1014-1030, November 1998.
  Preliminary version available as INRIA RR, No. 2642, 1995.
  http://www.inria.fr/RRRT/RR-2642.html

• Y. Dallery, Z. Liu, D. Towsley, ``Properties of Fork/Join Queueing Networks with Blocking under Various Operating Mechanisms'', IEEE Trans. on Robotics and Automation, Vol. 13, No. 4, pp. 503-518, Aug. 1997.
  Preliminary version available in http://www.inria.fr/mistral/personnel/Zhen.Liu/Papers/bas.ps.gz

• Z. Liu, P. Nain, D. Towsley, ``Sample Path Methods in the Control of Queues'', Queueing Systems, Vol. 21, pp. 293-335, special issue on Optimal Control in Queueing Systems, 1995.
  Preliminary version available as INRIA RR, No. 2457, 1995.
  http://www.inria.fr/RRRT/RR-2457.html

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