| 31. |
- Arvidsson, Åke, et al.
(författare)
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Profit Optimal Congestion Control in Intelligent Networks
- 1997
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Ingår i: 15th International Teletraffic Congress on Teletraffic Contributions for the Information. - WASHINGTON, DC : ELSEVIER SCIENCE PUBL B V. - 0444825983 ; , s. 911-920
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Bokkapitel (refereegranskat)abstract
- Current developments in technologies and markets stress the importance of exible and robust performance optimisation and congestion control. In intelligent networks, conges- tion control has traditionally taken a mainly technical view and focused on protecting individual nodes from harmful overloads. We take a profit oriented, network wide view and develop a congestion control mechanism to ensure profit maximisation under real time performance. Numerical studies in a simulator show that the proposed mechanism is robust and, in particular in overloaded states, provides a substantial improvement in comparison to conventional load control mechanisms.
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| 32. |
- Arvidsson, Åke
(författare)
-
Real Time Traffic Management by Dynamic Bandwidth Allocation
- 1995
-
Konferensbidrag (refereegranskat)abstract
- We introduce a six layer model of traffic variations and a corresponding model of management actions. In particular, we traffic study real time traffic management on the traffic and session levels which correspond to variations on the hour and minute levels. Using virtual paths (VPs) and virtual channels (VCs) as the managed entities on the two levels respectively, we put forward a simple and robust strategy for traffic management in real time: For slow variations, i.e. on the traffic level, all nodes simultaneously monitor offered traffics and forward the result to a network management centre (NMC); The NMC computes a new set of optimal VPs compares the result to the existing network; If a change appears profitable, the necessary information is sent back to the nodes and the new design is implemented. For fast variations, i.e. on the session level, dynamic routing schemes similar to those of public switched telephone networks are employed. Applying our strategy to control general networks subject to traffics which in advance are known only as expectations, we develop simple methods for traffic observation, derive the optimal observation interval, brie y review algorithms to compute VP networks, develop a cost optimal test to determine whether to implement a new design or not, and derive the optimal updating interval. Running our strategy in a simulator, we discover a considerable adaptivity and a performance far better than obtained by alternative methods.
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| 33. |
- Arvidsson, Åke, et al.
(författare)
-
Reduction of Routing Complexity in Telecommunication Networks by a Novel Decomposition Method
- 1996
-
Konferensbidrag (refereegranskat)abstract
- Routing problems are often encountered when designing and managing telecommuni- cation networks. Today, routing problems are affected by the growing sizes of networks, which increase the complexity, and by introduction of new services and technologies, which rise the demands. Rather than resorting to entirely heuristic algorithms and/or large data bases with off-line precomputed routing information for various situations, we propose a a new decomposition method whereby any routing algorithm is speeded up considerably, thus permitting the deployment of well founded routing algorithms even for real time purposes. In our paper, we present this new method in formal terms, and apply it to a real routing problem. Finally, investigating the performance of our fast implementation by comparing it to the optimal, non-accelerated solution, we find that considerable time savings can be made at a limited cost in terms of non-optimality of the final solution. It is also emphasised that in real-time applications with non-constant traffics, this nominal degradation might be more than compensated for by the prompt delivery.
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| 34. |
- Arvidsson, Åke
(författare)
-
Traffic Management in ATM Networks : A Proposal for Imperfect Traffic Information
- 1995
-
Konferensbidrag (refereegranskat)abstract
- Traffic in ATM networks can be described by numerous parameters. On a per session basis, one may use peak rate, average rate, sustainable rate, average burst duration, average silence duration, and others. In a longer time scale, parameters like the average and peakedness of connection request arrivals, the average and variance of session holding times, and so on are proposed. Theoretically, users should provide the former parameters and network operators the latter. In reality, however, few users can be expected to provide all sorts of statistical information about their traffic in advance, and operators do not have enough experience to prepare traffic forecasts for new services and applications. Moreover, even if the information could be provided, the lack of simple yet valid traffic models for ATM networks means that it is far from clear how it should be used. Realising that ATM networks, which are already being built, at least for the next few years will have to operate under these uncertain conditions, we focus on robust and forgiving strategies for traffic management. The idea is to use only little information about offered traffics and then dynamically control resource allocations, so as to provide acceptable quality of service combined with high utilisation. We give some draft proposals in this direction and point at some open research issues.
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| 35. |
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| 36. |
- Ayani, Rassul, et al.
(författare)
-
Modeling and Simulation of a High Speed LAN
- 1995
-
Ingår i: Simulation (San Diego, Calif.). - San Diego : Simulation Councils Inc.. - 0037-5497 .- 1741-3133. ; 64:1, s. 7-14
-
Tidskriftsartikel (refereegranskat)abstract
- Simulation is a tool that can be used to assess functionality and performance of communication networks and protocols. However, efficient simulation of complex communication systems is not a trivial task. In this paper, we discuss modeling and simulation of bus-based communication networks and present the results of modeling and simulation of a multigigabit/s LAN. We used parallel simulation techniques to reduce the simulation time of the LAN and implemented both an optimistic and a conservative parallel simulation scheme. Our experimental results on a shared memory multiprocessor indicate that the conservative parallel simulation scheme is superior to the optimistic one for this specific application. The parallel simulator based on the conservative scheme demonstates a linear speedup for large networks.
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| 37. |
- Bengtsson, PerOlof, et al.
(författare)
-
An Experiment on Creating Scenario Profiles for Software Change
- 1999
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Scenario profiles are used increasingly often for the assessment of quality attributes during the architectural design of software systems. However, the definition of scenario profiles is subjective and no data is available on the effects of individuals on scenario profiles. In this paper we present the design, analysis and results of a controlled experiment on the effect of individuals on scenario profiles, so that others can replicate the experiments on other projects and people. Both scenario profiles created by individuals and by groups are studied. The findings from the experiment showed that groups with prepared members proved to be the best method for creating scenario profiles. Unprepared groups did not perform better than individuals when creating scenario profiles.
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| 38. |
- Bengtsson, PerOlof, et al.
(författare)
-
Architecture level prediction of software maintenance
- 1999
-
Konferensbidrag (refereegranskat)abstract
- A method for the prediction of software maintainability during software architecture design is presented. The method rakes (1) the requirement specification (2) the design of the architecture (3) expertise from software engineers and, possibly, (4) historical data as input and generates a prediction of the average effort for a maintenance task. Scenarios are used by the method to concretize the maintainability requirements and to analyze the architecture for the prediction of the maintainability. The method is formulated based on extensive experience in software architecture design and detailed design and exemplified using the design of software architecture for a haemo dialysis machine. Experiments for evaluation and validation of the method are ongoing and future work.
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| 39. |
- Bengtsson, PerOlof
(författare)
-
Design and Evaluation of Software Architecture
- 1999
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The challenge in software development is to develop software with the right quality levels. The main problem is not to know if a project is technically feasible concerning functionality, but if a solution exists that meet the software quality requirements. It is therefore desired to get an early indication of the qualities of the resulting software. Software architecture is concerned with what modules are used to compose a system and how these modules are related to each other, i.e. the structure of system. The software architecture of a system sets the boundaries for these qualities. Hence, to design the software architec-ture to meet the quality requirements is to reduce the risks of not achieving the required quality levels. In this thesis we present the experiences from a software architecture design project with two industry partners. Based on these we propose a method for reengineering architectures and exemplify by an applying the method on a real world example. The method is based on architec-ture transformations and software quality evaluation of the architecture. Further, we present a method for predicting software maintenance effort from the software architecture, for use in the design and reengineering method. The method uses change scenario profiles to describe future changes to the system and architecture impact analysis provide knowl-edge of the modification volume required for the realization of each sce-nario. The results from a quasi experiment supports that groups consisting of prepared members create better scenario profiles. Also, the results suggest that there is a large room for variation between scenario profiles created by individual persons.
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| 40. |
- Bengtsson, PerOlof, et al.
(författare)
-
Scenario-based software architecture reengineering
- 1998
-
Konferensbidrag (refereegranskat)abstract
- This paper presents a method for reengineering software architectures. The method explicitly addresses the quality attributes of the software architecture. Assessment of quality attributes is performed primarily using scenarios. Design transformations are done to improve quality attributes that do not satisfy the requirements. Assessment and design transformation can be performed for several iterations until all requirements are met. To illustrate the method we use the reengineering of a prototypical measurement system into a domain-specific software architecture as an example.
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