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  • 301.
    Hall, Tomas
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Hurtig, Per
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Garcia, Johan
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Brunstrom, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Performance Evaluation of KauNet in Physical and Virtual Emulation Environments2012Rapport (Övrigt vetenskapligt)
    Abstract [en]

    Evaluation of applications and protocols in the context of computer networking is often necessary to determine the efficiency and level of service they can provide. In practical testing, three different options are available for the evaluation; using a physical network as a testbed, using an emulator to simplify the infrastructure, or using a simulator to remove reliance on infrastructure entirely. As a real network is costly and difficult or even impossible to create for every scenario, emulation and simulation is often used to approximate the behavior of a network with considerably less resources required. However, while a simulator is limited only by the time required to perform the simulation, an emulator is also limited by the hardware and software used. It is therefore important to evaluate the performance of the emulator itself, to determine its ability to emulate the desired network topologies.

    The focus of this document is the KauNet emulator, an extension of Dummynet that adds several new features, primarily deterministic emulation of various network characteristics through the use of pre-generated patterns. A series of tests were per- formed using a testbed with KauNet in both physical and virtual environments, as well as a hybrid environment with both physical and virtual machines. While virtualization greatly increases the flexbility and utilization of resources compared to a pure physical setup, it may also reduce the overall performance and accuracy of the emulation.

    From the results achieved, KauNet performs well in a physical environment, with a high degree of accuracy even at high traffic loads. Virtualization on the other hand, clearly introduces several issues with both processing and packet loss that may make it undesirable for use in experiments, although it may still be sufficient for scenarios where the requirements for accuracy are lower. The hybrid environment represents a compromise, with both performance and flexibility midway between the physical and fully virtualized testbed. 

  • 302. Hansen, Marit
    et al.
    Fischer Hübner, Simone
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Pettersson, John Sören
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för informatik och projektledning. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Bergmann, Mike
    Transparency Tools for User-Controlled Identity Management2007Konferensbidrag (Refereegranskat)
  • 303.
    Hedbom, Hans
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    A Survey of Transparency Tools for Enhancing Privacy2008Konferensbidrag (Refereegranskat)
  • 304.
    Hedbom, Hans
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    A Survey on Transparency Tools for Enhancing Privacy2009Ingår i: The Future of Identity in the Information Socitety. 4th IFIP WG9.2, 9.6/11.6 11.7/FIDIS International Summer School Brno, Czech Republic, September 2008, Revised Selected Papers / [ed] Vashek Matyas, Simone Fischer-Hübner, Daniel Cvrcek, Peter Svenda, Springer , 2009, s. 67-82Kapitel i bok, del av antologi (Refereegranskat)
  • 305.
    Hedbom, Hans
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    On the Self-Protection of Firewalls and Distributed Intrusion Detection Systems2001Rapport (Refereegranskat)
    Abstract [en]

    Distributed computing is performed by allowing a possibly large number of interconnected

    entities to process distributed information. The complexity of these systems

    increases the risk of exposing information to unauthorized parties and opens up the possibility

    of new threats and new vulnerabilities. Thus, the security of the systems cannot be

    provided by the local computer, but is dependent on the security of all the computers and

    communication channels involved. In order to counter these new threats, security extensions,

    such as firewalls and intrusion detection systems, are often added to the system.

    However, to be more effective the extensions need to reflect the structure of the system

    they should protect, i.e. they must cooperate or wherever appropriate be distributed themselves.

    One aspect which is often neglected in this context is that the introduction of security

    extensions may in itself introduce new vulnerabilities. This comes from the fact that

    the extensions rely on sensitive information in order to work properly. Another aspect is

    that commonly used operating systems do not provide a trustworthy platform for the security extensions, so the security can not be based on the security of the underlying system.

    One way to solve this problem is to let the extension take care of its own protection, i.e. provide self-protection. This thesis addresses the self-protection problem and discusses the avoidance of the risks and dangers associated with the use of security extensions. One specific issue of self-protection is studied in particular, namely that of protecting the detection policy of a distributed intrusion detection system. A protection method using one-way functions is proposed.

  • 306.
    Hedbom, Hans
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    van Alsenoy, Brendan
    FIDIS D19.3 Standardisation report2009Rapport (Övrigt vetenskapligt)
  • 307.
    Hedbom, Hans
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Kvarnström, H.
    Jonsson, E.
    Security Implications of Distributed Instrusion Detection Architectures1999Konferensbidrag (Refereegranskat)
  • 308.
    Hedbom, Hans
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Kvarnström, Håkan
    Jonsson, Erland
    Protecting Stateless Security Policies using One-Way Functions2001Rapport (Refereegranskat)
    Abstract [en]

    This paper addresses the problem of protecting security-related information in security extensions, e.g. the detection policy in an Intrusion Detection System (IDS) or the filtering policy in a firewall. Knowledge of the security policy would potentially facilitate the penetration

    of an intruder into the target system, the short-circuiting of a firewall or the circumvention of the IDSs detection mechanisms. To avoid this risk we suggest that the

    policy be protected using one-way functions and the paper suggests a scheme for protecting stateless policies. A stateless policy is a policy that takes only the current event into consideration when decisions are made and not the preceding chain of events. Thus, the

    process of comparing events towards the policy, i.e. making decisions, can be done in much the same way that passwords are hashed and compared in UNIX systems. However, one important distinction is that security policies contain a certain variability that must be

    managed, and a method for this is discussed. Finally, we discuss an automated tool for compiling a policy into a protected policy.

  • 309.
    Hedbom, Hans
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Lindskog, Stefan
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Axelsson, Stefan
    Jonsson, Erland
    A Comparison of the Security of Windows NT and UNIX1998Ingår i: / [ed] Svein J. Knapskog and Tønnes Brekne, Trondheim, Norway, 1998Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a brief comparison of two operating systems, Windows NT and UNIX. The comparison covers two different aspects. First, we compare the main security features of the two operating systems and then we make a comparison of a selection of vulnerabilities most of which we know have been used for making real intrusions. We found that Windows NT has slightly more rigorous security features than standard UNIX but the two systems display similar vulnerabilities. The conclusion is that there are no significant differences in the real level of security between these systems

  • 310.
    Hedbom, Hans
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Lindskog, Stefan
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Axelsson, Stefan
    Jonsson, Erland
    Analysis of the Security of Windows NT1998Rapport (Refereegranskat)
    Abstract [en]

    This paper presents an analysis of the security in Windows NT 4.0, working in both stand-alone and networking mode. The objective of the work was to find out how secure this operating system actually is. A technical overview of the system, and in particular its security features is given. The system security was analyzed and practical intrusion attempts were made in order to verify vulnerabilities or to find new ones. All vulnerabilities are described in detail and classified according to a classification scheme. A comparison to commonly known UNIX weaknesses was made. It revealed generic similarities between the two systems to a surprisingly high degree. Finally a number of recommendations are given. The paper concludes that there are ample opportunities to improve the security of Windows NT. We have reason to believe that it is probably not higher than that of UNIX

  • 311.
    Hedbom, Hans
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Lindskog, Stefan
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Jonsson, Erland
    A Preliminary Evaluation of the Security of a Non-Distributed Version of Windows NT1997Ingår i: / [ed] Arto Karila and Timo Aalto, Espoo, Finland, 1997Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we present a preliminary evaluation of the security of a non-distributed version of Windows NT. The objectives of the work are twofold: first, to learn more about the security system; and, second, to find out how secure the system actually is. Thus the architecture and security mechanisms of Windows NT have been studied. Furthermore, the paper contains a few examples of successful intrusions on the target system, which was a standard personal computer with Windows NT Workstation 3.51 and one with NT Workstation 4.0, both working in a stand-alone mode. We have also found some evidence that other, more severe security flaws exist in the system

  • 312.
    Hedbom, Hans
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Lindskog, Stefan
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Jonsson, Erland
    A Security Evaluation of a Non-Distributed Version of Windows NT1997Rapport (Refereegranskat)
    Abstract [en]

    In this paper we present an evaluation of the security in Windows NT. The objectives of the work are twofold: first, to learn more about the security system; and, second, to find out how secure the system actually is. To investigate the latter, the authors, have adopted the role of attackers. This paper contains results from several attempts to violate the security of Windows NT. In some cases, the attempts were successful, meaning that we gained access to information or resources that should be protected. The target systems were standard personal computers with Windows NT Workstation 3.51 and Windows NT Workstation 4.0 respectively, both working in stand-alone mode

  • 313.
    Hedbom, Hans
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Lindskog, Stefan
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Jonsson, Erland
    Risks and Dangers of Security Extensions2001Konferensbidrag (Refereegranskat)
    Abstract [en]

    Securing computer systems is an increasing concern as more and more systems are connected together in large networks. Traditional operating system based protection mechanisms have failed to fully meet the demands of this new situation. To overcome some of the shortcomings of these mechanisms new types have been developed with the intention to stop or reduce the impact of the new threats. We would like to call these new mechanisms security extensions, since they are not usually part of the core operating system. However, security extensions often contain sensitive and vital information that also needs to be secured. Usually they are dependent on the security mechanisms of the operating system for their own protection, i.e., they are dependent on the security of a mechanism whose insecurity they are supposed to patch. This is clearly an undesirable situation. We thus argue that security extensions actually add risks and vulnerabilities to the system when the underlying system is insecure or when they are not capable of handling their own security by themselves. In this paper, we discuss and analyze possible vulnerabilities in three types of security extensions, i.e., anti-malware software, firewalls, and intrusion detection systems. We also introduce a crude classification scheme for the different types of risks that the security extensions discussed add to the system.

  • 314.
    Hedbom, Hans
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Pulls, Tobias
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Unlinking Database Entries: Implementation Issues in Privacy Preserving Secure Logging2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper discusses implementation issues related to using relational databases as storage when implementing privacy preserving secure logs. In these types of logs it is important to keep the unlinkability properties of log entries intact when the entries are stored. We briefly describe the concept of privacy preserving secure logging and give the rational for it. The problems of using relational database systems as storage is discussed and we suggest three solutions to the problem. Two of the solutions are analyzed and compared and we show that at least one of the solutions is feasible in a real live setting and that the added overhead of the solution is very small.

  • 315.
    Hedbom, Hans
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Pulls, Tobias
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Hansen, Marit
    Unabhangiges Landeszentrum Datenschutz Schleswig, D-24103 Kiel, Germany..
    Transparency Tools2011Ingår i: Privacy and identity management for life / [ed] Jan Camenisch, Simone Fischer-Hübner, Kai Rannenberg, Berlin, Heidelberg: Springer Berlin/Heidelberg, 2011, 1, s. 135-143Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    The increasing spread of personal information on the Internet calls for new tools and paradigm to complement the concealment and protection paradigms. One such suggested paradigm is transparency and the associated transparency enhancing tools, making it possible for Data Subjects to track an examine how there data have been used, where it originates and what personal data about them that Data Controllers have stored. One such tool needed in order to track events related to personal data is a log system. Such a log system must be constructed in such a way that it does not introduce new privacy problems. This chapter describes such a log system that we call a privacy preserving secure log. It outlines the requirements for the system and describes and specifies a privacy preserving log system that has been developed and implemented within the Prime Life project.

  • 316.
    Hedbom, Hans
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Pulls, Tobias
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Hjartquist, Peter
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Lavén, Andreas
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Adding Secure Transparency Logging to the PRIME Core2010Ingår i: PRIVACY AND IDENTITY MANAGEMENT FOR LIFE, 2010, s. 299-314Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a secure privacy preserving log. These types of logs are useful (if not necessary) when constructing transparency services for privacy enhancement. The solution builds on and extends previous work within the area and tries to address the shortcomings of previous solutions regarding privacy issues.

  • 317.
    Hedbom, Hans
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Schallaboeck, Jan
    Germany.
    Wenning, Rigo
    World Wide Web Consortium W3C, F-06902 Sophia Antipolis, France..
    Hansen, Marit
    Unabhangiges Landeszentrum Datenschutz Schleswig, D-24103 Kiel, Germany..
    Contributions to Standardisation2011Ingår i: PRIVACY AND IDENTITY MANAGEMENT FOR LIFE / [ed] Camenisch, J; FischerHubner, S; Rannenberg, K, Springer Berlin/Heidelberg, 2011, 1, s. 479-492Kapitel i bok, del av antologi (Refereegranskat)
  • 318. Heyer, Tim
    et al.
    Göransson, Mari
    Ross, Donald F
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Exploiting heterogeneity to improve learning2006Konferensbidrag (Refereegranskat)
  • 319.
    Holleboom, Thijs Jan
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Classification and Analysis of Errors in Wide Area Networks2005Konferensbidrag (Refereegranskat)
    Abstract [en]

    The error logs of routers in a WAN contain huge amounts of information about the functioning of individual components in the network. Errors may induce other errors and possibly chains

    of errors. An attempt is made to classify and analyse certain chains of errors. Such a systematic approach will hopefully lead to improved possibilities for detecting malfunctioning components. Test have been performed on log data generated in SUNET. Results are presented and discussed.

  • 320.
    Holleboom, Thijs Jan
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Information Technology and Computational Physics2001Konferensbidrag (Refereegranskat)
  • 321.
    Holleboom, Thijs Jan
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Some notes on public key cryptographic systems2002Konferensbidrag (Refereegranskat)
    Abstract [en]

    Public key cryptography is a very important means of obtaining confidentiality in computer security. There are only a few currently known mathematical functions that have the required properties to allow the implementation of public key cryptography. One of the most widespread public key

    cryptographic systems, RSA, which is based upon the integer factoring problem, will be discussed. It is explained how a quantum computer, if ever constructed, is able to factorize integers into its prime constituents in polynomial time. In that case the RSA cryptosystem will not provide any confidentiality anymore. However, the elliptic curve cryptosystem, which is based upon a different mathematical problem for which currently no efficient algorithm exists, not even for a quantum computer, will, in that case, still be able to provide full computer security

  • 322.
    Holleboom, Thijs Jan
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    The Molecular Electron Propagator1992Doktorsavhandling, monografi (Övrigt vetenskapligt)
  • 323.
    Holleboom, Thijs Jan
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Garcia, Johan
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Fragment Retention Characteristics in Slack Space: Analysis and Measurements2010Ingår i: Proceedings Security and Communication Networks (IWSCN), 2010 2nd International Workshop on  Security and Communication Networks, IEEE Computer Society, 2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    When files are deleted, their information is not removed from the storage media. This is a well known fact, and there exist numerous undelete utilities to recover newly deleted files. When deleted files have been partly overwritten, the data from the part of the file that remains in unallocated space can be readily extracted by file carving. Such carving is often performed in forensic investigations. Furthermore, as a consequence of file system implementation specifics, there additionally exist small remains of the previous files in the space at the end of new files. In this paper we focus on these small remains of previous files, or micro-fragments, that exist even after all the space allocated to the previous file has been reallocated to new files. We derive expressions for modeling the number of micro-fragments that can be expected to be found, and perform experiments to evaluate the analytical model. The obtained results indicate good correspondence between the analytical predictions and the measured results.

  • 324.
    Holleboom, Thijs Jan
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Skantz, H.
    Böhm, M.
    A Log Archiving System for Wide Area Networks2004Konferensbidrag (Refereegranskat)
    Abstract [en]

    Monitoring and maintaining modern Wide Area Networks is a complex and time consuming task. These are networks that are owned by different Internet Service Providers all over the world. The demands for accessibility grow hand in hand with the

    increasing number of services and users. This makes effective troubleshooting more important than ever.

    There is an obvious lack of tools today to support the analysis of the state of these networks. This work is an attempt to make this analysis faster, more accurate, and to reduce the demands on the network technicians. Today a technician has to work his way through a huge amount of log data produced by the routers in the network. Finding the cause of the problems often requires great skill, experience, and intuition.

    The goal of this work is to speed up the process of nailing down the source of errors in the network. The basic approach is to store the data in a database. This allows for fast access, for the possibility of combining different methods of analysis, and for filtering out irrelevant information. Furthermore a database

    also allows for the possibility of presenting statistics and tracking faults over longer periods of time.

  • 325.
    Holleboom, Thijs Jan
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Snijders, J.G.
    A comparison between the Möller-Plesset and Green's function perturbative approaches to the calculation of the correlation energy in the many-electron problem1990Ingår i: J. Chem. Phys. 93, 5826 (1990)Artikel i tidskrift (Refereegranskat)
  • 326.
    Holleboom, Thijs Jan
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Snijders, J.G.
    Green's function calculations using non Hartree-Fock orbitals1992Ingår i: Int. J. Quantum Chem. 43, 259 (1992)Artikel i tidskrift (Refereegranskat)
  • 327.
    Holleboom, Thijs Jan
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Snijders, J.G.
    Baerends, E.J.
    Natural energy orbitals and the One-particle Green's function1988Ingår i: Int. J. Quantum Chem. 34, 289 (1988)Artikel i tidskrift (Refereegranskat)
  • 328.
    Holleboom, Thijs Jan
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Snijders, J.G.
    Baerends, E.J.
    Buijse, M.A.
    A correlation potential for molecular systems from the single particle Green's function1988Ingår i: J. Chem. Phys. 89, 3638 (1988)Artikel i tidskrift (Refereegranskat)
  • 329. Huang, H.
    et al.
    Cai, J.
    Kassler, Andreas
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Load-sharing in Multi-homed System based on Mobile IPv62005Konferensbidrag (Refereegranskat)
    Abstract [en]

    In the field of mobile communications, there coexist various access technologies that support wireless connections, such as Bluetooth, IEEE 802.11 and GPRS. These technologies are diverse in terms of bandwidth, delay, coverage area, etc. It is not uncommon that a mobile device is equipped with multiple wireless network interfaces to achieve efficient and ubiquitous communications. In wireless overlay networks, the mobile node can even utilize multiple network interfaces simultaneously to achieve greater QoS performance. This paper presents the design of such a system that supports multi-homed communications. In particular, we design the policy for mapping different network flows to different interfaces, and propose a load-sharing algorithm based on Weighted-Round-Robin channel selection and Jump-Ahead packet scheduling. Simulation results show that the algorithm can efficiently distribute data packets among multiple channels to achieve bandwidth aggregation

  • 330.
    Hurtig, Per
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Improving the Timeliness of SCTP Message Transfers2008Licentiatavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    Due to the cheap and flexible framework that the underlying IP-technology of the internet provides, IP-networks are becoming popular in more and more contexts. For instance, telecommunication operators have started to replace the fixed legacy telephony networks with IP-networks. To support a smooth transition towards IP-networks, the Stream Control Transmission Protocol (SCTP) was standardized. SCTP is used to carry telephony signaling traffic, and solves a number of problems that would have followed from using the Transmission Control Protocol (TCP) in this context. However, the design of SCTP is still heavily influenced by TCP. In fact, many protocol mechansisms in SCTP are directly inherited from TCP. Unfortunately, many of these mechanisms are not adapted to the kind of traffic that SCTP is intended to transport: time critical message-based traffic, e.g. telephony signaling.





    In this thesis we examine, and adapt some of SCTPs mechanisms to more efficiently transport time critical message-based traffic. More specifically, we adapt SCTPs loss recovery and message bundling for timely message transfers. First, we propose and experimentally evaluate two loss recovery mechanisms: a packet-based Early Retransmit algorithm, and a modified retransmission timeout management algorithm. We show that these enhancements can reduce loss recovery times with at least 30 50%, in some scenarios. In addition, we adapt the message bundling of SCTP to better support timely message delivery. The proposed bundling algorithm can in some situations reduce the transfer time of a message with up to 70%.





    In addition to these proposals we also indentify and report mistakes in some of the most popular SCTP implementations. Furthermore, we have continuously developed the network emulation software KauNet to support our experimental evaluations

  • 331.
    Hurtig, Per
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Improving the Timeliness of SCTP Message Transfers2008Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Due to the cheap and flexible framework that the underlying IP-technology of the internet provides, IP-networks are becoming popular in more and more contexts. For instance, telecommunication operators have started to replace the fixed legacy telephony networks with IP-networks. To support a smooth transition towards IP-networks, the Stream Control Transmission Protocol (SCTP) was standardized. SCTP is used to carry telephony signaling traffic, and solves a number of problems that would have followed from using the Transmission Control Protocol (TCP) in this context. However, the design of SCTP is still heavily influenced by TCP. In fact, many protocol mechansisms in SCTP are directly inherited from TCP. Unfortunately, many of these mechanisms are not adapted to the kind of traffic that SCTP is intended to transport: time critical message-based traffic, e.g. telephony signaling.In this thesis we examine, and adapt some of SCTP's mechanisms to more efficiently transport time critical message-based traffic. More specifically, we adapt SCTP's loss recovery and message bundling for timely message transfers. First, we propose and experimentally evaluate two loss recovery mechanisms: a packet-based Early Retransmit algorithm, and a modified retransmission timeout management algorithm. We show that these enhancements can reduce loss recovery times with at least 30-50%, in some scenarios. In addition, we adapt the message bundling of SCTP to better support timely message delivery. The proposed bundling algorithm can in some situations reduce the transfer time of a message with up to 70%.In addition to these proposals we have also indentified and reported mistakes in some of the most popular SCTP implementations. Furthermore, we have continously developed the network emulation software KauNet to support our experimental evaluations.

  • 332.
    Hurtig, Per
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Transport-Layer Performance for Applications and Technologies of the Future Internet2012Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    To provide Internet applications with good performance, the transport protocol TCP is designed to optimize the throughput of data transfers. Today, however, more and more applications rely on low latency rather than throughput. Such applications can be referred to as data-limited and are not appropriately supported by TCP. Another emerging problem is associated with the use of novel networking techniques that provide infrastructure-less networking. To improve connectivity and performance in such environments, multi-path routing is often used. This form of routing can cause packets to be reordered, which in turn hurts TCP performance.

    To address timeliness issues for data-limited traffic, we propose and experimentally evaluate several transport protocol adaptations. For instance, we adapt the loss recovery mechanisms of both TCP and SCTP to perform faster loss detection for data-limited traffic, while preserving the standard behavior for regular traffic. Evaluations show that the proposed mechanisms are able to reduce loss recovery latency with 30-50%. We also suggest modifications to the TCP state caching mechanisms. The caching mechanisms are used to optimize new TCP connections based on the state of old ones, but do not work properly for data-limited flows. Additionally, we design a SCTP mechanism that reduces overhead by bundling several packets into one packet in a more timely fashion than the bundling normally used in SCTP.

    To address the problem of packet reordering we perform several experimental evaluations, using TCP and state of the art reordering mitigation techniques. Although the studied mitigation techniques are quite good in helping TCP to sustain its performance during pure packet reordering events, they do not help when other impairments like packet loss are present.

  • 333.
    Hurtig, Per
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Alay, Ozgu
    Simula Research Laboratory.
    Ferlin, Simone
    Simula Research Laboratory.
    Yedugundla, Kiran
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för matematik och datavetenskap.
    Reducing Transport Latency using Multipath Protocols2015Konferensbidrag (Refereegranskat)
  • 334.
    Hurtig, Per
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Allman, M
    Avrachenkov, K
    Ayesta, U
    Blanton, J
    Early Retransmit for TCP and Stream Control Transmission Protocol (SCTP)2010Ingår i: Internet Engineering Task Force, ISSN 2070-1721, s. 1-15Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This document proposes a new mechanism for TCP and Stream Control Transmission Protocol (SCTP) that can be used to recover lost segments when a connection's congestion window is small. The "Early Retransmit" mechanism allows the transport to reduce, in certain special circumstances, the number of duplicate acknowledgments required to trigger a fast retransmission. This allows the transport to use fast retransmit to recover segment losses that would otherwise require a lengthy retransmission timeout

  • 335.
    Hurtig, Per
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Brunstrom, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Enhanced Metric Caching for Short TCP Flows2012Ingår i: Proceedings of the IEEE International Conference on Communications (ICC 2012), IEEE Press, 2012, s. 1209-1213Konferensbidrag (Refereegranskat)
    Abstract [en]

    Internet-based applications that require low latency are becoming more common. Such applications typically generate traffic consisting of short, or bursty, TCP flows. As TCP, instead, is designed to optimize the throughput of long bulk flows there is an apparent mismatch. To overcome this, a lot of research has recently focused on optimizing TCP for short flows as well. In this paper, we identify a performance problem for short flows caused by the metric caching conducted by the TCP control block interdependence mechanisms. Using this metric caching, a single packet loss can potentially ruin the performance for all future flows to the same destination by making them start in congestion avoidance instead of slow-start. To solve this, we propose an enhanced selective caching mechanism for short flows. To illustrate the usefulness of our approach, we implement it in both Linux and FreeBSD and experimentally evaluate it in a real test-bed. The experiments show that the selective caching approach is able to reduce the average transmission time of short flows by up to 40%.

  • 336.
    Hurtig, Per
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Brunstrom, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Enhancing SCTP Loss Recovery: An Experimental Evaluation of Early Retransmit2008Ingår i: Computer Communications, ISSN 0140-3664, E-ISSN 1873-703X, Vol. 31, nr 16, s. 3778-3788Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To reduce cost and provide more flexible services, telecommunication operators are currently replacing traditional circuit-switched telephony networks with packet-switched IP networks. To support the stringent requirements of telephony signaling (SS7), the SIGTRAN working group of the IETF specified the transport protocol SCTP. SCTP was developed to overcome a number of problems that follow from using TCP for signaling transport. However, the design of SCTP was to a great extent still based on TCP, and some problems related to signaling transport were inherited. For example, the loss recovery mechanisms in SCTP are almost identical to those of TCP. This is a problem as signaling traffic has stringent requirements on timely message delivery. TCP was not designed to meet stringent requirements on timely message delivery, and therefore the loss recovery was not optimized for it. To optimize SCTP’s loss recovery for signaling traffic, we consider the loss recovery enhancement early retransmit. To make early retransmit even better suited for signaling traffic we propose a packet-based version, which was also recently included in the early retransmit specification. By experimentally evaluating this algorithm, we show that the packet-based early retransmit algorithm, in some cases, can reduce SCTP’s loss recovery time by 62%.

  • 337.
    Hurtig, Per
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Brunstrom, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Improved Loss Detection for Signaling Traffic in SCTP2008Ingår i: IEEE International Conference on Communications (ICC 08), IEEE , 2008, s. 5886-5891Konferensbidrag (Refereegranskat)
    Abstract [en]

    The Stream Control Transmission Protocol (SCTP) was designed by the IETF as a viable solution for transportation of signaling traffic within IP-based networks. Signaling traffic is different from ordinary TCP bulk traffic in many ways. One example is that the requirement of timely delivery usually is much stricter. However, the management of the SCTP retransmission timer is not optimally designed considering this requirement. Basically, the management algorithm, unnecessarily, extends the time needed for loss detection. This paper presents a new management algorithm that is able to maintain a correct state of the retransmission timer, which eliminates this particular problem. In addition, the paper also compares the performance of the two management algorithms in an emulated signaling environment, using the lksctp implementation of SCTP. The results show that the proposed algorithm is able to provide significant reductions in loss recovery time. In some cases, the time needed to recover from packet loss is reduced with as much as 43%.

  • 338.
    Hurtig, Per
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Brunstrom, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Packet Reordering in TCP2011Ingår i: Proceedings of the IEEE GLOBECOM Workshop CCNet, IEEE Press, 2011, s. 136-141Konferensbidrag (Refereegranskat)
    Abstract [en]

    Packet reordering is now considered naturally prevalent within complex networks like the Internet. When packets are reordered, the performance of transport protocols like TCP is severely hurt. To overcome performance issues a number of mitigations have been proposed. While evaluations have shown the success of such mitigations, most have not considered realistic scenarios where other impairments are present. Furthermore, most studies only evaluate the performance of long-lived TCP flows, although short-lived flows are the most common. In this paper we evaluate Linux's built-in reordering mitigations and the TCP-NCR proposal using real protocol implementations. The results show that Linux and TCP-NCR are able to provide good protection against reordering when no other impairments are present. For flows that also experience packet loss, the performance is dominated by the negative effect of these losses. Results also indicate that short-lived flows are sensitive to how reordering mitigation is conducted. Linux was able to improve the performance of short flows slightly, while TCP-NCR performed worse than TCP without reordering protection.

  • 339.
    Hurtig, Per
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Brunstrom, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Petlund, Andreas
    Simula Research Laboratory AS.
    Welzl, Michael
    University of Oslo.
    TCP and Stream Control Transmission Protocol (SCTP) RTO Restart2016Ingår i: Internet RFCs, ISSN 2070-1721, nr 7765Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This document describes a modified sender-side algorithm for managing the TCP and Stream Control Transmission Protocol (SCTP) retransmission timers that provides faster loss recovery when there is a small amount of outstanding data for a connection. The modification, RTO Restart (RTOR), allows the transport to restart its retransmission timer using a smaller timeout duration, so that the effective retransmission timeout (RTO) becomes more aggressive in situations where fast retransmit cannot be used. This enables faster loss detection and recovery for connections that are short lived or application limited.

  • 340.
    Hurtig, Per
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Brunström, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Emulation Support for Advanced Packet Reordering Models2010Ingår i: 2010 IEEE International Conference on Communications, Cape Town, South Africa: IEEE Communications Society, 2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    From being regarded as a pathological event, packet reordering is now considered to be naturally prevalent within the Internet. When packets are reordered, the performance of transport protocols like TCP can be severely hurt. To overcome performance problems a number of mitigations have been proposed. Common for most proposals is, however, the lack of evaluations using real protocol implementations and good models of packet reordering. In this paper we highlight the need for detailed reordering models, and implement support for such models in the KauNet network emulator. To demonstrate the importance of using detailed models we present an experimental example.

  • 341.
    Hurtig, Per
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Brunström, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Packet Loss Recovery of Signaling Traffic in SCTP2007Konferensbidrag (Refereegranskat)
  • 342.
    Hurtig, Per
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Brunström, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    SCTP Retransmission Timer Enhancement for Signaling Traffic2008Konferensbidrag (Refereegranskat)
  • 343.
    Hurtig, Per
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Brunström, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Short Flows and TCP Metric Caching in Linux2011Konferensbidrag (Refereegranskat)
    Abstract

    Internet-based applications that offer (or require) user interaction are becoming more common. Such applications typically generate traffic consisting of short, or bursty, TCP flows. As TCP is designed to work better for long-lived bulk flows, a lot of research have recently focused at optimizing TCP for short flows. In this paper, we identify a performance problem for short flows, caused by the TCP metric caching in Linux. Using the cache, a single packet loss can potentially ruin the performance for all future flows to the same destination by making them start in congestion avoidance instead of slow-start. We illustrate the problem in a number of test-bed experiments and propose a modified caching strategy that explicitly considers flow lengths

  • 344.
    Hurtig, Per
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Brunström, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Hurtig, Per
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Message-Based Traffic Control in SCTP2009Konferensbidrag (Refereegranskat)
    Abstract

    Telecommunication operators are currently replacing traditional telephony networks with IP-networks. To support telephony signaling requirements in IP-networks, SCTP was standardized. SCTP solves a number of problems that follows from using TCP for signaling transport. However, the design of SCTP is based on inherited TCP mechanisms that were designed for bulk traffic, not for message-based traffic like telephony signaling. In this paper, we discuss the implications of this design, and exemplify the negative effects of it. In particular, we show how to adapt the SCTP message-bundling to work better for message-based traffic. Evaluations of our adapted message bundling show average reductions in message transfer times with as much as 50%, for some scenarios

  • 345.
    Hurtig, Per
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Brunström, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Kassler, Andreas
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    MPTCP PathFinder: Datacenter Bandwidth Aggregation2014Konferensbidrag (Refereegranskat)
  • 346.
    Hurtig, Per
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Garcia, Johan
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Brunström, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Loss Recovery in Short TCP/SCTP Flows2006Rapport (Refereegranskat)
    Abstract [en]

    The Transmission Control Protocol (TCP) has been the dominant transport protocol within IP-based networks for many years, mainly due to the reliability it provides to its users and the congestion control it employs. However, as the amount of signaling traffic within IP-based networks have increased significantly in recent years, it has become clear that TCP is not suited for this kind of traffic. In order to meet the requirements of signaling traffic the Stream Control Transmission Protocol (SCTP) was developed by the Internet Engineering Task Force (IETF). SCTP is heavily influenced by TCP and is therefore similar to TCP in many ways. One example is the SCTP loss recovery and congestion control mechanisms which are almost identical to those of TCP. The primary purpose of this work is to study the performance and behavior of the TCP/SCTP loss recovery mechanisms for short flows. Using a simple client/server model, we evaluate the performance of these mechanism over a wide range of bandwidths, link delays and packet loss patterns. The experiments evaluate one TCP implementation and two SCTP implementations, and were conducted using network emulation. The experimental results show that there exist strong dependencies between the position of packet loss and the actual transmission time of the corresponding flow. In addition to these dependencies, we also found a number of implementation mistakes in the examined protocol implementations

  • 347.
    Hurtig, Per
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för matematik och datavetenskap (from 2013).
    Grinnemo, Karl-Johan
    Brunström, Anna
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för matematik och datavetenskap (from 2013).
    Ferlin, Simone
    Ericsson Research, Stockholm.
    Alay, Özgü
    Simula Research Laboratory, Norway.
    Kuhn, Nicolas
    French National Space Centre, France.
    Low-Latency Scheduling in MPTCP2019Ingår i: IEEE/ACM Transactions on Networking, ISSN 1063-6692, E-ISSN 1558-2566, Vol. 1, s. 302-315, artikel-id 8584135Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The demand for mobile communication is continuously increasing, and mobile devices are now the communication device of choice for many people. To guarantee connectivity and performance, mobile devices are typically equipped with multiple interfaces. To this end, exploiting multiple available interfaces is also a crucial aspect of the upcoming 5G standard for reducing costs, easing network management, and providing a good user experience. Multi-path protocols, such as multi-path TCP (MPTCP), can be used to provide performance optimization through load-balancing and resilience to coverage drops and link failures, however, they do not automatically guarantee better performance. For instance, low-latency communication has been proven hard to achieve when a device has network interfaces with asymmetric capacity and delay (e.g., LTE and WLAN). For multi-path communication, the data scheduler is vital to provide low latency, since it decides over which network interface to send individual data segments. In this paper, we focus on the MPTCP scheduler with the goal of providing a good user experience for latency-sensitive applications when interface quality is asymmetric. After an initial assessment of existing scheduling algorithms, we present two novel scheduling techniques: the block estimation (BLEST) scheduler and the shortest transmission time first (STTF) scheduler. BLEST and STTF are compared with existing schedulers in both emulated and real-world environments and are shown to reduce web object transmission times with up to 51% and provide 45% faster communication for interactive applications, compared with MPTCP's default scheduler.

  • 348.
    Hurtig, Per
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    John, Wolfgang
    Department of Computer Science and Engineering, Chalmers University of Technology.
    Brunstrom, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Recent Trends in TCP Packet-Level Characteristics2011Ingår i: Proceedings of the 7th International Conference on Networking and Services (ICNS), Venice/Mestre, Italy: IARIA , 2011, s. 179-195Konferensbidrag (Refereegranskat)
    Abstract [en]

    Up-to-date TCP traffic characteristics are essential for research and development of protocols and applications. This paper presents recent trends observed in 70 measurements on backbone links from 2006 and 2009. First, we provide general characteristics such as packet size distributions and TCP option usage. We confirm previous observations such as the dominance of TCP as transport and higher utilization of TCP options. Next, we look at out-of-sequence (OOS) TCP segments. OOS segments often have negative effects on TCP performance, and therefore require special consideration. While the total fraction of OOS segments is stable in our measurements, we observe a significant decrease in OOS due to packet reordering (from 22.5% to 5.2% of all OOS segments). We verify that this development is a general trend in our measurements and not caused by single hosts/networks or special temporal events. Our findings are surprising as many researchers previously have speculated in an increased amount of reordering.

  • 349.
    Hurtig, Per
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Pérennou, Tanguy
    Université de Toulouse, France.
    Garcia, Johan
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Brunström, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Using Triggers for Emulation of Opportunistic Networking2010Ingår i: Proceedings of the Second International Workshop on Mobile Opportunistic Networking, MobiOpp '10, Pisa, Italy: ACM Press, 2010, s. 155-158Konferensbidrag (Refereegranskat)
    Abstract [en]

    Opportunistic networks do not require the availability of an end-to-end path, but may instead take advantage of temporary connectivity opportunities. Opportunistic networks pose a challenge for network emulation as the traditional emulation setup where application/transport endpoints send/receive packets from the network following a black box approach is no longer applicable. Instead opportunistic networking protocols and applications need to react to the dynamics of the underlying network beyond what is conveyed through the exchange of packets. In order to support emulation evaluations for such challenging applications we in this paper introduce the concept of emulation triggers that can emulate arbitrary cross-layer feedback and that are synchronized with the emulated scenario. The design and implementation of triggers in the KauNet emulator are described. The use of triggers in the context of opportunistic networking is briefly sketched.

  • 350.
    Håkangård, Stig
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Domestication of IT-technology2000Konferensbidrag (Refereegranskat)
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