- Email: [email protected]
Modeling and performance analysis of networking and collaborative systems
Simulation Modelling Practice and Theory 19 (2011) 1–4
Contents lists available at ScienceDirect
Simulation Modelling Practice and Theory journal homepage: www.elsevier.com/locate/simpat
Modeling and performance analysis of networking and collaborative systems Santi Caballé a,*, Fatos Xhafa b a b
Department of Computer Science, Multimedia and Telecommunication, Open University of Catalonia, Barcelona, Spain Department of Languages & Informatics Systems, Technical University of Catalonia, Barcelona, Spain
a r t i c l e
i n f o
Article history: Available online 15 July 2010 Keywords: Modeling Performance analysis Networking Collaborative systems
a b s t r a c t The special issue on Modeling and Performance Analysis of Networking and Collaborative Systems by leveraging current networks and collaborative applications. In addition, the incorporation of the latest and powerful technologies, based on distributed infrastructure, is also explored for the enhancement of these applications, resulting in complex and entangled systems that pose new issues and challenges, in terms of efficiency, security, mobility, and so on. The goal is to respond to the need for methods and tools for performance analysis and evaluation of current complex collaborative and networking systems and applications. To this direction, this special issue provides latest research on modeling and performance analysis of networking and collaborative systems from different perspectives. Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction With the fast development of the Internet, virtual campuses and organizations strongly exploit intelligent networking and collaborative systems by leveraging current well-known networks and collaborative applications. In addition, latest and powerful technologies based on distributed infrastructure, such as Grid and Cloud computing, are currently enhancing these applications. This has resulted in complex and entangled systems that pose new issues and challenges, in terms of adaptation, security, mobility, and so on, and need to be managed efficiently. The ultimate aim of this special issue is to respond to the need for methods and tools for performance analysis and evaluation of current complex collaborative and networking systems. To pursue this aim, the main focus of the special issue is posed on developing techniques for modeling analysis and performance analysis based on behavior models. These techniques are necessary to handle both current complexity of networks design and collaborative interactions. Indeed, the need for analysis of system-level performance is an essential factor in the design of many of these systems. Validation of the analysis using simulation tools or real testbed infrastructures is thus provided in the contributions to this special issue. This special issue follows the International Conference on Intelligent Networking and Collaborative Systems (INCoS2009), held on November 4–6, 2009 at the Open University of Catalonia, Barcelona, Spain (http://www.uoc.edu/symposia/ incos2009). 2. Organization The special issue comprises 10 papers carefully selected based on their originality, significance, technical soundness, and clarity of exposition. A rigorous research methodology has been required, as well as a review of existing literature and * Corresponding author. Tel.: +34 3263439. E-mail address: [email protected] (S. Caballé). 1569-190X/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.simpat.2010.07.004
2
S. Caballé, F. Xhafa / Simulation Modelling Practice and Theory 19 (2011) 1–4
adequate reference to bibliographical sources. All papers were selected with the aim to make both empirical and theoretical contributions based on models, designs, and experiences on the scope of this special issue. The 10 papers are organized in three sections, as follows: From the methodology perspective, the first four papers present different performance models proposed for networking in distributed systems. The first paper presents a theoretical model and simulation-based approach for increasing the effectiveness and efficiency of job sharing across independent virtual organizations. The second paper proposes a multi-agent based simulation methodology and tool to evaluate the efficiency and effectiveness of collaborative distributed systems. The third paper investigates high-cost effective communications in wireless network infrastructures through the evaluation of different message forward scheduling methods for exchanging large amounts of non-real time data in various simulated scenarios. The fourth and last paper of this section proposes a data-driven model based on the consideration of user-provided input to evaluate quality of service in network systems From the technological perspective, the next two papers provide simulation technology to simulate and monitor certain networking parameters and situations. The fifth paper presents a monitor tool that measures and produces detailed information in order to assess the quality of service (QoS) of diverse applications and services arisen on the Internet. The sixth paper provides a newly developed ad hoc network simulator to investigate the performance of data transmission in dedicated high-speed power line communications with a variety of environmental error patterns. From the application perspective, the last four papers of the special issue propose the application of modeling and analysis techniques to specific contexts. The seventh paper presents an approach to enhance synchronous collaboration occurring in the on-line learning domain by tracing and modeling the learners’ interaction real-time data. The eighth approach proposes the use of knowledge discovery and visualization methods for analyzing data coming from emergency call centers with the aim of detecting anomaly situations as a first step to future automatic emergency call systems. The ninth paper provides an agent-based simulation model for capturing user contribution patterns in open learning object repositories. Finally, the last paper of this special issue proposes a Web services discovery model based on social networks to capture the different interactions that occur between Web services. 3. Contents The 10 papers face the following issues and challenges: In the first paper of this special issue and of the methodology view, Bessis et al. [1] present the design of a novel model entitled the Critical Friend Model (CFM). The CFM considers interconnected nodes, whichever virtual organization they may be in, known via historical collaboration records as nodes, which have passed a threshold test of competence for service delivery, as determined by the node seeking the service. The CFM is integrated together with a novel algorithm that relies on a set of messages to dispatch jobs to available resources within a reachable Grid, in order to increase average job success rate, job response time and resource efficiency. Finally, the paper provides a graph–theoretic foundation for the CFM, and an evaluation of an implementation of the model under various scenarios. Paletta and Herrero [2], in the second paper, investigate new specific collaboration models for distributive systems for enabling effective collaboration processes between users of these dynamic environments. In order to analyze collaboration in distributive systems several elements such as a negotiation mechanism, a load-balancing strategy, a mutual exclusion mechanism, and a learning strategy are analyzed separately in terms of efficiency and effectiveness. In particular, the paper presents a multi-agent based simulation tool and a simulation methodology used to evaluate the efficiency and effectiveness of a collaborative system by analyzing both the global system of each of the strategies or mechanisms involved in the system. Intelligent agents used in the simulation make use of the concept of awareness of interaction for quantifying the degree, nature and quality of the interaction between the agents. Yamamura et al. [3], in the third paper, propose the concept of the Virtual Segment (VS), in which a global communication service is provided by combining a store-carry-forward scheme using vehicles with broadband wireless/wired network infrastructures along roads connected to the Internet. The VS is shown as a practical framework for non-real-time, asynchronous message transfer (especially for large messages) in a cost-effective manner. In this study, a critical implementation design issue, the message forward scheduling, in the VS approach is discussed and investigated through computer simulation by an ad hoc VS simulator that reflect the results of the field experiment for realistic performance evaluation. The fourth paper (Verschae et al. [4]) investigates the incorporation of user-supplied information for the improvement of quality of service (QoS) in network systems. To this end, the authors propose two approaches to derive information about new users in the network design and control processes, where both are based on prototype generation for the answers of former users to a QoS related questionnaire. In the first approach, attempts are made to map user attributes to prototypes. The second approach uses a mapping from partial answers to a prototype. As a result, the first approach appears to be infeasible, while the second shows good results. A case study is presented that demonstrates that the representation of users by such functional prototypes is feasible for the processing of user information towards achievement of QoS. Watabe et al. [5] start the technology perspective with the fifth paper, which addresses the issue of meeting the diverse quality of service (QoS) requirements that must be guaranteed for the diverse and increasing number of new applications and services appeared on the Internet. Accurate measurement tools are needed to produce detailed information and assess QoS. To this end, the authors propose an improvement of a monitor tool called CoMPACT, which is able to overcome the sca-
S. Caballé, F. Xhafa / Simulation Modelling Practice and Theory 19 (2011) 1–4
3
lability problem arisen from the direct measurement of the QoS of the target flow by transforming QoS data obtained by passive measurement into active. The paper investigates how the measurement accuracy of the CoMPACT monitor can be improved by verifying the relation between the stochastic process of probe packet arrivals and the accuracy of this tool. The investigation on CoMPACT is validated by a simulation-based approach. In the sixth paper, Mizutani et al. [6], the authors developed a new module on the NS-2 network simulator that can simulate high-definition high-speed power line communications (HD-PLC) data transmission. This simulator is based on the time-varying packet-level error rate pattern and the physical layer rate under each particular environmental condition through experiments on a real PLC network. The paper shows that the simulator is valid to simulate a real PLC network. To solve the problem on co-existing multiple TCP flows, a novel network-supported TCP rate control that appropriately modifies the advertised-window value in a TCP-ACK packet in response to the PLC network condition is presented and is shown to be effective through simulations. In the seventh paper, Clauzel et al. [7] open the last part of the special issue devoted to the application perspective and address issues related to traces modeling for formally describing human interactions of people engaged into a synchronous collaborative learning activity. The objective is to propose models and tools for representing, transforming, sharing and visualizing traces of users’ experiences. The ultimately aim is to develop an on-line learning platform that uses interaction traces as knowledge sources on, and for, the learners’ learning as individuals or groups. To this direction, this paper proposes a general framework for trace management and sharing, a generic model of synchronous collaborative activity based on the notion of interaction modes specialized for whiteboard sharing and text chatting, and a conceptual framework for modeling the exploitation of modeled traces, in particular for interactive visualization on the user side. Klement and Snásel [8], in the eighth paper, study the collaborative emergency call-taking information system in the Czech Republic, which forms a network of cooperating emergency call centers processing emergency calls to the European 112 emergency number. Large amounts of various incident records are stored in its databases and the data can be used for mining spatial and temporal anomalies, as well as for the monitoring and analysis of the performance of the emergency calltaking system. Based on this data, the authors describe a method for knowledge discovery and visualization targeted at the performance analysis of the system with respect to the organization of the emergency call-taking information system and its data characteristics. The method is based on the Kohonen Self-Organising Map (SOM) algorithm and its extension, the Growing Grid algorithm. In the ninth paper, Sánchez-Alonso et al. [9] investigate Learning Object Repositories (LOR), which are digital collections of educational resources and/or metadata aimed at facilitating reuse of materials worldwide. In open repositories, resources are made available at no cost, representing a case of information sharing with an implicit and diffuse social context. However, there have been numerous repository initiatives and projects and many of them did not reached a significant degree of actual usage and growth that made them sustainable in the long term. To this end, this paper deals with repository research and proposes a partial model for sustainable collections based on existing reported evidence and on the examination of patterns in a large and mature repository. This model accounts for known user contribution patterns and it is coherent with the implicit social network structure found in an existing large LOR. Agent-based simulation is chosen to allow for contrasting configurations with different parameters. Finally, in the last paper of this special issue, Maamar [10] presents LinkedWS, a social networks discovery model to capture the different interactions that occur between Web services. Based on these interactions, specialized relationships are spawned and discerned, such as collaboration and substitution. The discovery of Web services through LinkedWS permits to answer different needs, such as help service engineers expand existing compositions based on the recommendations of some Web services and help make Web services highly available by identifying the most appropriate substitutes in case of failing Web services. Recommendation/robustness-partnership social networks of a Web service are built so that different experiments are completed including the discovery of substitute and partner Web services along with comparing the performance of LinkedWS with an UDDI registry implementation. Acknowledgments The editors of this special issue wish to thank the referees who have carefully reviewed the papers and gave useful suggestions and feedback to the authors. We hope that the readers will find this special issue useful in their research. Finally, we would like to thank Prof. Helen Karatza for the opportunity to edit this special issue. The editors acknowledge that their research has been partially supported by the Spanish MICINN project ‘‘INCoS2009” (Ref: TIN2009-07489-E) and the IN3-UOC HAROSA Knowledge Community Program (http://dpcs.uoc.edu). Fatos Xhafa’s work is partially done at Birkbeck, University of London, on Leave from Technical University of Catalonia (Barcelona, Spain). His research is supported by a grant from the General Secretariat of Universities of the Ministry of Education, Spain. References [1] N. Bessis, Y. Huang, P. Norrington, A. Brown, P. Kuonen, B. Hirsbrunner, Modelling of a Self-led Critical Friend Topology in Inter-cooperative Grid Communities, Simulation Modeling Practice and Theory 19 (1) (2011) 5–16. [2] M. Paletta, P. Herrera, Simulating Collaborative Systems by means of Awareness of Interaction among Intelligent Agents, Simulation Modeling Practice and Theory 19 (1) (2011) 17–29.
4
S. Caballé, F. Xhafa / Simulation Modelling Practice and Theory 19 (2011) 1–4
[3] S. Yamamura, A. Nagata, M. Tsuru, H. Tamura, Virtual Segment: Store-Carry-Forward Relay-based Support for Wide-Area Non-Real-Time Data Exchange, Simulation Modeling Practice and Theory 19 (1) (2011) 30–46. [4] R. Verschae, M. Koeppen, K. Yoshida, Partial User-supplied Information and User Modelling for Improving QoS, Simulation Modeling Practice and Theory 19 (1) (2011) 47–55. [5] K. Watabe, Y. Honma, M. Aida, Probe Interval Designs that Improve Accuracy of CoMPACT Monitor, Simulation Modeling Practice and Theory 19 (1) (2011) 56–68. [6] M. Mizutani, Y. Miyoshi, K. Tsukamoto, K. Tsuru, Y. Oie, Network-supported TCP Rate Control for High-speed Power-line Communications Environment, Simulation Modeling Practice and Theory 19 (1) (2011) 69–83. [7] D. Clauzel, K. Sehaba, Y. Prié, Enhancing Synchronous Collaboration by Using Interactive Visualisation of Modelled Traces, Simulation Modeling Practice and Theory 19 (1) (2011) 84–97. [8] P. Klement, V. Snásel, Using SOM in the Performance Monitoring of the Emergency Call-Taking System, Simulation Modeling Practice and Theory 19 (1) (2011) 98–109. [9] S. Sánchez-Alonso, M.A. Sicilia, E. García-Barriocanal, C. Pagés-Arévalo, L. Lezcano, Social Models in Open Learning Object Repositories. A Simulation Approach for Sustainable Collections, Simulation Modeling Practice and Theory 19 (1) (2011) 110–120. [10] Z. Maamar, LinkedWS: A Novel Web Services Discovery Model Based on Social Networks, Simulation Modeling Practice and Theory 19 (1) (2011) 121– 132.
Contents lists available at ScienceDirect
Simulation Modelling Practice and Theory journal homepage: www.elsevier.com/locate/simpat
Modeling and performance analysis of networking and collaborative systems Santi Caballé a,*, Fatos Xhafa b a b
Department of Computer Science, Multimedia and Telecommunication, Open University of Catalonia, Barcelona, Spain Department of Languages & Informatics Systems, Technical University of Catalonia, Barcelona, Spain
a r t i c l e
i n f o
Article history: Available online 15 July 2010 Keywords: Modeling Performance analysis Networking Collaborative systems
a b s t r a c t The special issue on Modeling and Performance Analysis of Networking and Collaborative Systems by leveraging current networks and collaborative applications. In addition, the incorporation of the latest and powerful technologies, based on distributed infrastructure, is also explored for the enhancement of these applications, resulting in complex and entangled systems that pose new issues and challenges, in terms of efficiency, security, mobility, and so on. The goal is to respond to the need for methods and tools for performance analysis and evaluation of current complex collaborative and networking systems and applications. To this direction, this special issue provides latest research on modeling and performance analysis of networking and collaborative systems from different perspectives. Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction With the fast development of the Internet, virtual campuses and organizations strongly exploit intelligent networking and collaborative systems by leveraging current well-known networks and collaborative applications. In addition, latest and powerful technologies based on distributed infrastructure, such as Grid and Cloud computing, are currently enhancing these applications. This has resulted in complex and entangled systems that pose new issues and challenges, in terms of adaptation, security, mobility, and so on, and need to be managed efficiently. The ultimate aim of this special issue is to respond to the need for methods and tools for performance analysis and evaluation of current complex collaborative and networking systems. To pursue this aim, the main focus of the special issue is posed on developing techniques for modeling analysis and performance analysis based on behavior models. These techniques are necessary to handle both current complexity of networks design and collaborative interactions. Indeed, the need for analysis of system-level performance is an essential factor in the design of many of these systems. Validation of the analysis using simulation tools or real testbed infrastructures is thus provided in the contributions to this special issue. This special issue follows the International Conference on Intelligent Networking and Collaborative Systems (INCoS2009), held on November 4–6, 2009 at the Open University of Catalonia, Barcelona, Spain (http://www.uoc.edu/symposia/ incos2009). 2. Organization The special issue comprises 10 papers carefully selected based on their originality, significance, technical soundness, and clarity of exposition. A rigorous research methodology has been required, as well as a review of existing literature and * Corresponding author. Tel.: +34 3263439. E-mail address: [email protected] (S. Caballé). 1569-190X/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.simpat.2010.07.004
2
S. Caballé, F. Xhafa / Simulation Modelling Practice and Theory 19 (2011) 1–4
adequate reference to bibliographical sources. All papers were selected with the aim to make both empirical and theoretical contributions based on models, designs, and experiences on the scope of this special issue. The 10 papers are organized in three sections, as follows: From the methodology perspective, the first four papers present different performance models proposed for networking in distributed systems. The first paper presents a theoretical model and simulation-based approach for increasing the effectiveness and efficiency of job sharing across independent virtual organizations. The second paper proposes a multi-agent based simulation methodology and tool to evaluate the efficiency and effectiveness of collaborative distributed systems. The third paper investigates high-cost effective communications in wireless network infrastructures through the evaluation of different message forward scheduling methods for exchanging large amounts of non-real time data in various simulated scenarios. The fourth and last paper of this section proposes a data-driven model based on the consideration of user-provided input to evaluate quality of service in network systems From the technological perspective, the next two papers provide simulation technology to simulate and monitor certain networking parameters and situations. The fifth paper presents a monitor tool that measures and produces detailed information in order to assess the quality of service (QoS) of diverse applications and services arisen on the Internet. The sixth paper provides a newly developed ad hoc network simulator to investigate the performance of data transmission in dedicated high-speed power line communications with a variety of environmental error patterns. From the application perspective, the last four papers of the special issue propose the application of modeling and analysis techniques to specific contexts. The seventh paper presents an approach to enhance synchronous collaboration occurring in the on-line learning domain by tracing and modeling the learners’ interaction real-time data. The eighth approach proposes the use of knowledge discovery and visualization methods for analyzing data coming from emergency call centers with the aim of detecting anomaly situations as a first step to future automatic emergency call systems. The ninth paper provides an agent-based simulation model for capturing user contribution patterns in open learning object repositories. Finally, the last paper of this special issue proposes a Web services discovery model based on social networks to capture the different interactions that occur between Web services. 3. Contents The 10 papers face the following issues and challenges: In the first paper of this special issue and of the methodology view, Bessis et al. [1] present the design of a novel model entitled the Critical Friend Model (CFM). The CFM considers interconnected nodes, whichever virtual organization they may be in, known via historical collaboration records as nodes, which have passed a threshold test of competence for service delivery, as determined by the node seeking the service. The CFM is integrated together with a novel algorithm that relies on a set of messages to dispatch jobs to available resources within a reachable Grid, in order to increase average job success rate, job response time and resource efficiency. Finally, the paper provides a graph–theoretic foundation for the CFM, and an evaluation of an implementation of the model under various scenarios. Paletta and Herrero [2], in the second paper, investigate new specific collaboration models for distributive systems for enabling effective collaboration processes between users of these dynamic environments. In order to analyze collaboration in distributive systems several elements such as a negotiation mechanism, a load-balancing strategy, a mutual exclusion mechanism, and a learning strategy are analyzed separately in terms of efficiency and effectiveness. In particular, the paper presents a multi-agent based simulation tool and a simulation methodology used to evaluate the efficiency and effectiveness of a collaborative system by analyzing both the global system of each of the strategies or mechanisms involved in the system. Intelligent agents used in the simulation make use of the concept of awareness of interaction for quantifying the degree, nature and quality of the interaction between the agents. Yamamura et al. [3], in the third paper, propose the concept of the Virtual Segment (VS), in which a global communication service is provided by combining a store-carry-forward scheme using vehicles with broadband wireless/wired network infrastructures along roads connected to the Internet. The VS is shown as a practical framework for non-real-time, asynchronous message transfer (especially for large messages) in a cost-effective manner. In this study, a critical implementation design issue, the message forward scheduling, in the VS approach is discussed and investigated through computer simulation by an ad hoc VS simulator that reflect the results of the field experiment for realistic performance evaluation. The fourth paper (Verschae et al. [4]) investigates the incorporation of user-supplied information for the improvement of quality of service (QoS) in network systems. To this end, the authors propose two approaches to derive information about new users in the network design and control processes, where both are based on prototype generation for the answers of former users to a QoS related questionnaire. In the first approach, attempts are made to map user attributes to prototypes. The second approach uses a mapping from partial answers to a prototype. As a result, the first approach appears to be infeasible, while the second shows good results. A case study is presented that demonstrates that the representation of users by such functional prototypes is feasible for the processing of user information towards achievement of QoS. Watabe et al. [5] start the technology perspective with the fifth paper, which addresses the issue of meeting the diverse quality of service (QoS) requirements that must be guaranteed for the diverse and increasing number of new applications and services appeared on the Internet. Accurate measurement tools are needed to produce detailed information and assess QoS. To this end, the authors propose an improvement of a monitor tool called CoMPACT, which is able to overcome the sca-
S. Caballé, F. Xhafa / Simulation Modelling Practice and Theory 19 (2011) 1–4
3
lability problem arisen from the direct measurement of the QoS of the target flow by transforming QoS data obtained by passive measurement into active. The paper investigates how the measurement accuracy of the CoMPACT monitor can be improved by verifying the relation between the stochastic process of probe packet arrivals and the accuracy of this tool. The investigation on CoMPACT is validated by a simulation-based approach. In the sixth paper, Mizutani et al. [6], the authors developed a new module on the NS-2 network simulator that can simulate high-definition high-speed power line communications (HD-PLC) data transmission. This simulator is based on the time-varying packet-level error rate pattern and the physical layer rate under each particular environmental condition through experiments on a real PLC network. The paper shows that the simulator is valid to simulate a real PLC network. To solve the problem on co-existing multiple TCP flows, a novel network-supported TCP rate control that appropriately modifies the advertised-window value in a TCP-ACK packet in response to the PLC network condition is presented and is shown to be effective through simulations. In the seventh paper, Clauzel et al. [7] open the last part of the special issue devoted to the application perspective and address issues related to traces modeling for formally describing human interactions of people engaged into a synchronous collaborative learning activity. The objective is to propose models and tools for representing, transforming, sharing and visualizing traces of users’ experiences. The ultimately aim is to develop an on-line learning platform that uses interaction traces as knowledge sources on, and for, the learners’ learning as individuals or groups. To this direction, this paper proposes a general framework for trace management and sharing, a generic model of synchronous collaborative activity based on the notion of interaction modes specialized for whiteboard sharing and text chatting, and a conceptual framework for modeling the exploitation of modeled traces, in particular for interactive visualization on the user side. Klement and Snásel [8], in the eighth paper, study the collaborative emergency call-taking information system in the Czech Republic, which forms a network of cooperating emergency call centers processing emergency calls to the European 112 emergency number. Large amounts of various incident records are stored in its databases and the data can be used for mining spatial and temporal anomalies, as well as for the monitoring and analysis of the performance of the emergency calltaking system. Based on this data, the authors describe a method for knowledge discovery and visualization targeted at the performance analysis of the system with respect to the organization of the emergency call-taking information system and its data characteristics. The method is based on the Kohonen Self-Organising Map (SOM) algorithm and its extension, the Growing Grid algorithm. In the ninth paper, Sánchez-Alonso et al. [9] investigate Learning Object Repositories (LOR), which are digital collections of educational resources and/or metadata aimed at facilitating reuse of materials worldwide. In open repositories, resources are made available at no cost, representing a case of information sharing with an implicit and diffuse social context. However, there have been numerous repository initiatives and projects and many of them did not reached a significant degree of actual usage and growth that made them sustainable in the long term. To this end, this paper deals with repository research and proposes a partial model for sustainable collections based on existing reported evidence and on the examination of patterns in a large and mature repository. This model accounts for known user contribution patterns and it is coherent with the implicit social network structure found in an existing large LOR. Agent-based simulation is chosen to allow for contrasting configurations with different parameters. Finally, in the last paper of this special issue, Maamar [10] presents LinkedWS, a social networks discovery model to capture the different interactions that occur between Web services. Based on these interactions, specialized relationships are spawned and discerned, such as collaboration and substitution. The discovery of Web services through LinkedWS permits to answer different needs, such as help service engineers expand existing compositions based on the recommendations of some Web services and help make Web services highly available by identifying the most appropriate substitutes in case of failing Web services. Recommendation/robustness-partnership social networks of a Web service are built so that different experiments are completed including the discovery of substitute and partner Web services along with comparing the performance of LinkedWS with an UDDI registry implementation. Acknowledgments The editors of this special issue wish to thank the referees who have carefully reviewed the papers and gave useful suggestions and feedback to the authors. We hope that the readers will find this special issue useful in their research. Finally, we would like to thank Prof. Helen Karatza for the opportunity to edit this special issue. The editors acknowledge that their research has been partially supported by the Spanish MICINN project ‘‘INCoS2009” (Ref: TIN2009-07489-E) and the IN3-UOC HAROSA Knowledge Community Program (http://dpcs.uoc.edu). Fatos Xhafa’s work is partially done at Birkbeck, University of London, on Leave from Technical University of Catalonia (Barcelona, Spain). His research is supported by a grant from the General Secretariat of Universities of the Ministry of Education, Spain. References [1] N. Bessis, Y. Huang, P. Norrington, A. Brown, P. Kuonen, B. Hirsbrunner, Modelling of a Self-led Critical Friend Topology in Inter-cooperative Grid Communities, Simulation Modeling Practice and Theory 19 (1) (2011) 5–16. [2] M. Paletta, P. Herrera, Simulating Collaborative Systems by means of Awareness of Interaction among Intelligent Agents, Simulation Modeling Practice and Theory 19 (1) (2011) 17–29.
4
S. Caballé, F. Xhafa / Simulation Modelling Practice and Theory 19 (2011) 1–4
[3] S. Yamamura, A. Nagata, M. Tsuru, H. Tamura, Virtual Segment: Store-Carry-Forward Relay-based Support for Wide-Area Non-Real-Time Data Exchange, Simulation Modeling Practice and Theory 19 (1) (2011) 30–46. [4] R. Verschae, M. Koeppen, K. Yoshida, Partial User-supplied Information and User Modelling for Improving QoS, Simulation Modeling Practice and Theory 19 (1) (2011) 47–55. [5] K. Watabe, Y. Honma, M. Aida, Probe Interval Designs that Improve Accuracy of CoMPACT Monitor, Simulation Modeling Practice and Theory 19 (1) (2011) 56–68. [6] M. Mizutani, Y. Miyoshi, K. Tsukamoto, K. Tsuru, Y. Oie, Network-supported TCP Rate Control for High-speed Power-line Communications Environment, Simulation Modeling Practice and Theory 19 (1) (2011) 69–83. [7] D. Clauzel, K. Sehaba, Y. Prié, Enhancing Synchronous Collaboration by Using Interactive Visualisation of Modelled Traces, Simulation Modeling Practice and Theory 19 (1) (2011) 84–97. [8] P. Klement, V. Snásel, Using SOM in the Performance Monitoring of the Emergency Call-Taking System, Simulation Modeling Practice and Theory 19 (1) (2011) 98–109. [9] S. Sánchez-Alonso, M.A. Sicilia, E. García-Barriocanal, C. Pagés-Arévalo, L. Lezcano, Social Models in Open Learning Object Repositories. A Simulation Approach for Sustainable Collections, Simulation Modeling Practice and Theory 19 (1) (2011) 110–120. [10] Z. Maamar, LinkedWS: A Novel Web Services Discovery Model Based on Social Networks, Simulation Modeling Practice and Theory 19 (1) (2011) 121– 132.