TKK 
Tietoverkkolaboratorio
 Tutkimus
COM^{2}  Computational Methods for the Performance Analysis of
Broadband Communication Networks
Note! This project has already ended (31.12.2001).
1. General Information
The COM^{2} is a 3 year project (19982001) funded by the
Academy
of Finland. It is a part of the Research
Programme for Telecommunication Electronics (TELECTRONICS) , which
was initiated by the Academy of Finland in 1997 to further advance scientific
research in the field of tele and data communications.
For results of the project see the following:
2. Background
Telecommunications industry has become one of the key growth factors in
the Finnish economy. Advanced communications also provide the basic infrastructure
which enhances the growth of other industries as well as the development
of the society as a whole. Three technological trends will give new opportunities
for continuous growth in the telecommunications industry:

The emerging broadband networks

The development of the Internet technology and applications

The growth of mobile communications and the introduction of new mobile
systems and services
There are many technological challenges in these areas. One of them is
an appropriate dimensioning of the systems and networks along with adequate
traffic management methods. The importance of these problems has become
evident e.g. in the history of the ATM, where traffical issues, such as
provisioning adequate quality of service to different users in a heterogeneous
environment, have turned out to be a much harder problem than originally
anticipated. Also the congestion problems of the Internet, experienced
by most users, exemplify the reality of the problem. The problem will become
even more pronounced with the introduction of various realtime services,
such as voice over Internet. Finally, in the area of mobile communications,
the scarcity of the available bandwidth makes it important to utilise the
resources to the full extent, which is only possible with adequate dimensioning
methods and design procedures.
The solution to the problems of dimensioning and traffic management
relies on the performance analysis of telecommunications networks. Performance
analysis comprises modelling the system and the traffic offered, and solving
the model by means of various mathematical methods. Despite of the great
advances in the area of performance analysis of multiservice networks over
the past ten years, many problems remain to be solved.
3. Goals and research areas
Goals
The main goal of the project is to develop mathematical and computational
methods for the performance analysis of broadband multiservice networks.
It can be divided into four subgoals:

to further the development of tools needed by the industry

to educate specialists at different levels (M.Sc., Tech.Lic., Tech.Dr.)
in the field

to produce results of high scientific standard

to strengthen the collaboration on the international level
Research areas
The research will be directed to the following three main subfields:

Computational Methods for the Solution of Problems in Scheduling, Dynamic
Resource Allocation, Routing and Network Optimization
The development of computational methods for the solution of queueing
models pertinent to telecommunication networks, e.g. those of advanced
scheduling mechanisms in switches and routers. Similarly, computational
methods for the solution of problems in optimal routing, optimal resource
allocation and network optimisation will be developed. Special attention
will be paid on the robustness of the methods in order to make them as
independent of specific modelling assumptions as possible. The result of
this work will be in the form of mathematical methods as well as efficient
computational algorithms. The potential of extensive use of symbolic computation
in producing the results will also be explored.

Simulation Methods
The multiservice networks pose hard problems for the simulation
approach because of the huge dimensionality of the system and/or the rarity
of the interesting events (e.g. cell loss in an ATM network). The work
on new simulation techniques is currently pursued in a companion project
COST 257 and preliminary
work on a particularly promising approach, so called Markov Chain Monte
Carlo method with Gibbs sampling has been started. In the future, this
work will be done within this project.

Traffic modelling
In particular, the modelling of the data traffic in the Internet
is a central issue. Longrange dependent traffic models have become a hot
topic in the area. The pioneering work by Prof. Ilkka Norros at VTT on
the use of fractional Brownian motion as a model provides basic tools.
The project will address important questions still requiring an adequate
solution, such as the estimation of the parameters of the model on the
basis of measured traffic. Also the use of the model to practical problems
such as the cache design will be studied. As a spinoff application the
model may be utilised in the area of image compression.
5. Persons

Attila Vidács, 1.9.98  31.5.99

Jani Lakkakorpi, 1.9.98  30.4.99

Pasi Lassila, 1.1.99  31.12.01

Vinod Sharma (visiting professor with Tekes funding), 1.9.98  30.6.99
 Hannu Rummukainen, 1.6.99  30.4.00
 Aleksi Penttinen, 1.6.99  15.8.99, 5.6.0031.7.01
 Jan Hlinovsky, 1.6.99  31.8.99, 10.6.00  31.12.00
 Pirkko Kuusela, 18.10.99  31.07.01
 Laura Lignell, 1.2.00  31.8.00
 Elena Siren, 5.6.00  31.8.00
 Jouni Karvo, 1.8.0031.7.01
6. Publications and Reports
Note! Those publications for which the copyright has been transferred to the
publisher may not be available online. If you need a copy of such a paper, simply
contact via email the first author of the paper (firstname.lastname@hut.fi).
All publications of the teletraffic theory group can be found through
our online search engine
Journal Papers
 A. Penttinen and J. Virtamo, Simulation of TwoDimensional Fractional Gaussian Noise, Methodology and Computing in Applied Probability, vol. 6, no. 1, pp. 99107, 2004 (link)(bib)(abstract)
 V. Sharma and J. Virtamo, A finite buffer queue with priorities, Performance Evaluation, vol. 47, no. 1, pp. 122, 2002 (bib)
 V. Sharma, J. Virtamo and P. Lassila, Performance Analysis of the Random Early Detection Algorithm, Probability in the Engineering and Informational Sciences, vol. 16, no. 3, pp. 367388, 2002 (bib)
 J. Karvo, O. Martikainen, J. Virtamo and S. Aalto, Blocking of dynamic multicast connections, Telecommunication Systems, vol. 16, 3,4, pp. 467481, 2001 (link)(bib)(abstract)
 H. Rummukainen and J. Virtamo, Polynomial Cost Approximations in Markov Decision Theory Based Least Cost Routing, IEEE Transactions on Networking, vol. 9, no. 6, pp. 769779, 2001 (link)(bib)
 P. Lassila and J. Virtamo, Nearly Optimal Importance Sampling for Monte Carlo Simulation of Loss Systems, ACM Transactions on Modeling and Computer Simulation, vol. 10, no. 4, pp. 326347, 2000 (link)(bib)
 S. Aalto, Optimal control of batch service queues with finite capacity and linear holding costs, Mathematical Methods of Operations Research, vol. 51, no. 2, pp. 263285, 2000 (link)(bib)(abstract)
 S. Aalto and W. Scheinhardt, Tandem fluid queues fed by homogeneous onoff sources, Operations Research Letters, vol. 27, no. 2, pp. 7382, 2000 (link)(bib)(abstract)
 I. Norros, E. Valkeila and J. Virtamo, An Elementary Approach to a Girsanov Formula and Other Analytical Results on Fractional Brownian Motion, Bernoulli, vol. 5, no. 4, pp. 571587, 1999 (bib)
Conference Papers
 A. Penttinen and J. Virtamo, A packet marking algorithm for congestion pricing, in Proceedings of the 2002 International Symposium on Performance Evaluation of Computer and Telecommunication Systems (SPECTS 2002), pp. 379385, 2002, San Diego, California, USA (bib)(abstract)
 J. Karvo, Efficient simulation of blocking probabilities for multilayer multicast streams, in Proceedings of Networking 2002, pp. 10201031, SpringerVerlag, 2002, Pisa, Italy (bib)(abstract)
 J. Karvo, S. Aalto and J. Virtamo, Blocking probabilities of multilayer multicast streams, in Proc. HPSR 2002, pp. 268277, 2002, Kobe, Japan (bib)(abstract)
 S. Aalto, J. Karvo and J. Virtamo, Calculating blocking probabilities in multicast loss systems, in Proc. SPECTS 2002, pp. 833842, 2002, San Diego, CA (bib)(abstract)
 P. Kuusela, P. Lassila, J. Virtamo and P. Key, Modeling RED with Idealized TCP Sources, in Proceedings of IFIP ATM & IP 2001, pp. 155166, 2001, Budapest, Hungary (bib)
 P. Lassila, J. Karvo and J. Virtamo, Efficient Importance Sampling for Monte Carlo Simulation of Multicast Networks, in Proceedings of IEEE INFOCOM, pp. 432439, 2001, Anchorage, Alaska (bib)
 P. Kuusela, P. Lassila and J. Virtamo, Stability of TCPRED Congestion Control, in Proceedings of ITC17, pp. 655666, Elsevier, 2001, Salvador da Bahia, Brazil (link)(bib)
 A. Penttinen and J. Virtamo, Robust Adaptive Capacity Allocation Algorithm, in Teletraffic Engineering in the Internet Era: Proceedings of the International Teletraffic Congress  ITC17, pp. 223231, North Holland, 2001, Salvador da Bahia, Brazil (bib)(abstract)
 J. Karvo, S. Aalto and J. Virtamo, Blocking probabilities of twolayer statistically indistinguishable multicast streams, in Proceedings of ITC17, pp. 769779, Elsevier, 2001, Salvador da Bahia, Brazil (link)(bib)(abstract)
 A. Vidács and J. Virtamo, Parameter estimation of geometrically sampled fractional Brownian traffic, in Proceedings of IEEE Infocom, pp. 17911796, , 2000, Tel Aviv, Israel (bib)
 P. Lassila and J. Virtamo, Modeling the dynamics of the RED algorithm, in Proceedings of Quality of Future Internet Services (QofIS), pp. 2842, SringerVerlag, 2000, Berlin, Germany (link)(bib)
 P. Kuusela and J. Virtamo, Modeling RED with Two Traffic Classes, in Proceedings of the 15th Nordic Teletraffic Seminar (NTS15), pp. 271282, 2000, Lund, Sweden (bib)
 S. Aalto and J. Virtamo, Combinatorial algorithm for calculating blocking probabilities in multicast networks, in Proceedings of the 15th Nordic Teletraffic Seminar, pp. 2334, 2000, Lund, Sweden (bib)(abstract)
 P. Lassila and J. Virtamo, Inverse convolution approach to importance sampling in Monte Carlo simulation of loss systems, in Proceedings of the 15th Nordic Teletraffic Seminar, pp. 161172, 2000, Lund, Sweden (bib)
 V. Sharma and J. Virtamo, A finite buffer queue, in Proceedings of Globecom, pp. 10531065, 1999, Rio de Janeiro, Brazil (link)(bib)
 A. Vidács and J. Virtamo, ML Estimation of the Parameters of FBM Traffic with Geometrical Sampling, in Proceedings of Broadband Communications'99  Convergence of Network Technologies, pp. 5162, Kluwer, 1999 (bib)
 P. Lassila and J. Virtamo, Efficient Importance Sampling for Monte Carlo Simulation of Loss Systems, in Proceedings of ITC16, pp. 787796, Elsevier, 1999, Edinburgh, England (link)(bib)
 J. Karvo and S. Aalto, Average Signalling Load for Multicast Group Management, in Proceedings of ITC16, pp. 509518, Elsevier, 1999, Edinburgh, UK (link)(bib)(abstract)
 J. Karvo, J. Virtamo, S. Aalto and O. Martikainen, Blocking of dynamic multicast connections, in the 4th INFORMS Telecommunications Conference, 1998, Boca Raton, Florida, published later in Selected Proceedings in Telecommunication Systems (bib)(abstract)
Theses
 A. Penttinen, Mathematical models for marking in congestion pricing, Helsinki University of Technology, 2001, Master's Thesis (bib)
 P. Lassila, Methods for network performance evaluation: fast simulation of loss systems and analysis of Internet congestion control, Ph.D. thesis, Laboratory Report Series, Networking Laboratory, 3/2001, 2001 (link)(bib)
 H. Rummukainen, On approximative Markov control of multiservice telecommunication links, M.Sc. thesis, Laboratory Report Series, Networking Laboratory, 2/2000, 2000 (bib)
Other Documents
 J. Lakkakorpi, Traffic in modem pools of Helsinki University of Technology, Internal report, Networking Laboratory, 1999 (bib)
 J. Lakkakorpi, Traffic Theory Library, Internal report, Networking Laboratory, 1999, (on the basis of an earlier document by A. Pirhonen, 1994) (bib)
 A. Vidács and J. Virtamo, Time Domain MLE of the Parameters of FBM Traffic, Laboratory Report Series, Networking Laboratory, 2/99, 1999 (bib)
 A. Penttinen, Kaksiulotteisesta fraktionaalisesta Brownin liikkeestä ja kuvankoodauksesta, Internal report (in Finnish), Networking Laboratory, 1999 (bib)
 J. Hlinovsky and P. Lassila, Efficient implementation of a loss system simulator in C, Internal report, Networking Laboratory, 1999 (bib)
 M. Alutoin, TCP:n pääsynvalvonnan simulointi, special assignment (in Finnish), Networking Laboratory, 1999 (link)(bib)
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