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  • 251.
    Garcia, Johan
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för matematik och datavetenskap (from 2013).
    Alfredsson, Stefan
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för matematik och datavetenskap (from 2013).
    Brunström, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    A Measurement Based Study of TCP Protocol Efficiency in Cellular Networks2014Ingår i: Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks (WiOpt), 2014 12th International Symposium on, IEEE, 2014, s. 131-136Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper examines the efficiency of resource utilization with respect to short-lived TCP flows in various cellular networks. The examination is done from the vantage point of an end-user who would like to use as much as possible of the cellular transmission resources that are available at any given time, thus minimizing the delays associated with communication. Based on a comprehensive measurement campaign we first derive network characteristics with regards to base RTT, RTT under load, and average throughput. A protocol efficiency metric is introduced to capture how efficiently short TCP flows are in fact able to use the instantaneously available transmission resources in a cellular network. The measurements show that short TCP connections have low efficiency in 3. SG (HSPA+) and 4G (LTE) mobile broadband networks, and that the improved latency and throughput characteristics of 4G in relation to 3. SG nevertheless results in lower short-flow efficiency for 4G.

  • 252.
    Garcia, Johan
    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.
    Asplund, Katarina
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Application and Transport Layer Flexibility - A User-influenced Web Browsing SystemManuskript (preprint) (Övrigt vetenskapligt)
  • 253.
    Garcia, Johan
    et al.
    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.
    A Robust JPEG Coder for a Partially Reliable Transport Service2000Konferensbidrag (Refereegranskat)
  • 254.
    Garcia, Johan
    et al.
    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.
    An Experimental Performance Evaluation of a Partially Reliable Web Application2002Konferensbidrag (Refereegranskat)
  • 255.
    Garcia, Johan
    et al.
    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.
    An Experimental Study on the Performance and Fairness of Loss Differentiation for TCP2004Ingår i: ICETE 3, , INSTICC Press, 2004, s. -419Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper investigates the performance and fairness of receiver-based loss differentiation for TCP. Experimentshave been performed with a FreeBSD kernel implementation. As expected, the results verify theeffectiveness of receiver-based loss differentiation when corruption losses are present. However, if the the corruptinglink is shared with users that do not employ loss differentiation, the performance gain typically comesat the expense of increased unfairness. The results show that a single loss differentiating user may in somecases reduce the bandwidth of users without loss differentiation with up to 35 percent, but there are also cases where loss differentiation has limited fairness implications. The results further show that if a user employs multiple TCP connections over the corrupting link the negative effects of corruption losses are reduced. This is true even if all connections employ regular TCP. Hence, multiple connections at the application level can to some extent be used as a simple mechanism to limit the impact of corruption losses.

  • 256.
    Garcia, Johan
    et al.
    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.
    Checksum-based Loss Differentiation2002Konferensbidrag (Refereegranskat)
    Abstract [en]

    In a wireless environment the common transport protocol assumption that all packet losses are due to congestion no longer holds true. If the transport protocols react identically to both congestion and noncongestion related losses, performance will degrade. To avoid this performance problem, transport protocols must be able to differentiate between losses that are due to congestion and losses that are due to wireless link errors. Suitable congestion avoidance behavior can then be applied as appropriate. This paper overviews previous work on loss differentiation, and proposes a checksumbased scheme. The proposed scheme reuses the checksums already available at various layers in the receiver endhost protocol stack. It is an endtoend solution for the case where the lossy link is the last hop. Header decoding, data integrity and other issues related to the implementation of our cecksumbased scheme are also discussed

  • 257.
    Garcia, Johan
    et al.
    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.
    Effects of Loss Notification and Loss Differentiation on DCCP and TCP Performance2004Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper examines the effects of non-congestion related wireless link errors on transport protocol performance.

    Although link-level retransmissions to a large extent can alleviate this problem for TCP, delay-sensitive applications using DCCP may not be well served by link-level retransmissions. The loss differentiation and loss notification mechanisms in DCCP are discussed, and the TFRC congestion control is numerically evaluated for wireless loss sensitivity. The results show that the use of loss differentiation can be critical for high rate senders.

    The results, however, also show that the blind use of DCCP loss differentiation for low rate senders may be inefficient considering the communications and computational overheads involved. Further, a TCP implementation modified to provide loss differentiation and loss notification is experimentally examined. As expected there are considerable gains from using loss differentiation.

  • 258.
    Garcia, Johan
    et al.
    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.
    Efficient Image Transfer for Wireless Networks2000Konferensbidrag (Refereegranskat)
  • 259.
    Garcia, Johan
    et al.
    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.
    Impact of Partial Reliability on Web Image Transport Performance2002Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper reports on experiments with a web-browsing application using

    PRTP, a new TCP-based protocol. With PRTP it is possible for an application to

    specify, and receive, a more flexible transport service than with TCP or UDP. A web

    application using PRTP is presented, and experiments examining the performance implications

    of using PRTP instead of TCP are discussed. The experiments used actual

    implementations of TCP and PRTP to conduct web page transfers over a network capable

    of emulating different network characteristics. The JPEG part of the web pages

    were recoded using a robust JPEG coding and transmitted using the partially reliable

    transport service made possible by PRTP. A novelty in these experiments was that the

    packet loss could be controlled in detail, allowing specific packets in a stream to be lost as opposed to losing packets with a certain probability. The experiments were performed for five different network characteristics each at six different loss ratios using three different web pages. The results show that using a partially reliable transport service in conjunction with the presented application provides throughput gains in the

    majority of cases, at the expense of slightly degraded image quality. The gains relative to TCP are up to 41% with a mean of 7.2%.

  • 260.
    Garcia, Johan
    et al.
    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.
    Issues with TCP-friendly Rate Control in DCCP2004Konferensbidrag (Refereegranskat)
    Abstract [en]

    TCP-Friendly Rate Control (TFRC) is a congestion control mechanism that is proposed to be used together with the new DCCP protocol. This paper provides an overview of the issues surrounding the use of TFRC for interactive media applications. Most issues are related to speci_c TFRC mechanisms, and to the use of smaller-than-MSS packets. An analytical examination of TFRCs behavior in the presence of wireless bit errors is also presented. The results show that DCCP's builtin loss differentiation can potentially be disabled for resourceconstrained devices in order to reduce overhead

  • 261.
    Garcia, Johan
    et al.
    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.
    Progressive Parsing Transcoding of JPEG Images2000Konferensbidrag (Refereegranskat)
  • 262.
    Garcia, Johan
    et al.
    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.
    Transcoding of Image Data2004Kapitel i bok, del av antologi (Övrigt vetenskapligt)
  • 263.
    Garcia, Johan
    et al.
    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.
    Transport Layer Loss Differentiation and Loss Notification2003Konferensbidrag (Refereegranskat)
  • 264.
    Garcia, Johan
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Conchon, Emmanuel
    LAAS-CNRS / ENSICA, Toulouse, France.
    Perennou, Tanguy
    LAAS-CNRS / ENSICA, Toulouse, France.
    Brunström, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    KauNet: Improving Reproducibility for Wireless and Mobile Research2007Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents the KauNet emulation system that provides pattern-based emulation. KauNet enables bit precise placement of bit-errors, exact and repeatable packet losses, delays and bandwidth variations. The design and performance of KauNet is discussed. An example is also provided of how it can be integrated in a specific emulation framework to enhance emulation for mobile and wireless systems

  • 265.
    Garcia, Johan
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Hjärtquist, Peter
    Hofmann, Johann
    Ulges, Adrian
    Sokolov, Strahil
    FIVES D5.1: Design Specification2009Rapport (Refereegranskat)
  • 266.
    Garcia, Johan
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Hofmann, Johann
    FIVES D4.1: User requirements report with HCI and GUI guidelines2009Rapport (Refereegranskat)
    Abstract

    This user requirements report collects the results from a comprehensive on-line end-user survey that were conducted by the FIVES project. The survey was composed of 50 questions divided into a number of topical areas. In addition to the user survey results, this report also provides guidelines for Human-Computer Interaction (HCI) aspects of systems with a special focus on issues relevant to the task of large volume image classification, which is a major task in many investigations.

    Furthermore, the aspect of Graphical User Interface (GUI) design is also discussed from the context of FIVES needs.

  • 267.
    Garcia, Johan
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Hofmann, Johann
    FIVES D4.2 Test plan for end user tests2010Rapport (Övrigt vetenskapligt)
  • 268.
    Garcia, Johan
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    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.
    Retention of Micro-fragments in Cluster Slack: A First Model2009Ingår i: First IEEE International Workshop on Information Forensics and Security (WIFS 2009), London, UK: IEEE Signal Processing Society, 2009, s. 31-35Konferensbidrag (Refereegranskat)
    Abstract [en]

    In current forensic practice it is regularly needed to determine whether some set of files have been present on a storage medium or not. File carving techniques are readily used as a tool in such examinations. However, if all clusters holding the files searched for have been overwritten, remains of the previous files only resides in the cluster slack. In this work we elaborate on the factors that influence how many such cluster slack ¿micro-fragments¿ that can be expected to be detected. We identify a set of factors that influence the micro-fragment retention characteristics. One such characteristic is the file size distribution of the files overwriting the original files. We derive analytical expressions for three different file size distributions, which allows us to examine the retention characteristics even if the overwriting files come from different sources.

  • 269.
    Garcia, Johan
    et al.
    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.
    Brunström, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    KauNet: A Versatile and Flexible Emulation System2008Konferensbidrag (Refereegranskat)
  • 270.
    Garcia, Johan
    et al.
    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.
    Brunström, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    KauNet: Design and Usage2008Rapport (Refereegranskat)
    Abstract [en]

    KauNet is an emulation system that allows deterministic placement of packet losses and bit-errors as well as more precise control over bandwidth and delay changes. KauNet is an extension to the well-known Dummynet emulator in FreeBSD and allows the use of pattern and scenario files to increase control and repeatability. This report provides a comprehensive description of the usage of KauNet, as well as a technical description of the design and implementation of KauNet

  • 271.
    Garcia, Johan
    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.
    Brunström, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    KauNet: Design and Usage2008Rapport (Övrigt vetenskapligt)
    Abstract [en]

    KauNet is an emulation system that allows deterministic placement of packet losses and bit-errors as well as more precise control over bandwidth and delay changes. KauNet is an extension to the well-known Dummynet emulator in FreeBSD and  allows the use of pattern and scenario files to increase control and repeatability. This report provides a comprehensive description of the usage of KauNet, as well as a technical description of the design and implementation of KauNet.

  • 272.
    Garcia, Johan
    et al.
    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.
    Brunström, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    The Effect of Packet Loss on the Response Times of Web Services2007Ingår i: Proceedings of 3rd International Conference on Web Information Systems and Technologies (WebIST2007), INSTICC Press, 2007Konferensbidrag (Refereegranskat)
  • 273.
    Garcia, Johan
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Ulges, A
    Jansohn, C
    Hofmann, J
    Gluhchev, G
    FIVES M7.1: Image and Video Processing Survey2009Rapport (Refereegranskat)
  • 274.
    Garcia, Johan
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Vermaas, Oscar
    Hofmann, Johann
    FIVES D5.2a Architectural Description and API Description2010Rapport (Refereegranskat)
  • 275. Gilje Jaatun, Martin
    et al.
    Cruzes, Daniela S.
    Angulo, Julio
    Karlstads universitet, Fakulteten för humaniora och samhällsvetenskap (from 2013), Centrum för HumanIT.
    Fischer-Hübner, Simone
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Accountability Through Transparency for Cloud Customers2016Ingår i: CLOUD COMPUTING AND SERVICES SCIENCE, CLOSER 2015, Heidelberg: Springer, 2016, 1, Vol. 581, s. 38-57Konferensbidrag (Refereegranskat)
    Abstract [en]

    Public cloud providers process data on behalf of their customers in data centres that typically are physically remote from their users. This context creates a number of challenges related to data privacy and security, and may hinder the adoption of cloud technology. One of these challenges is how to maintain transparency of the processes and procedures while at the same time providing services that are secure and cost effective. This chapter presents results from an empirical study in which the cloud customers identified a number of transparency requirements to the adoption of cloud providers. We have compared our results with previous studies, and have found that in general, customers are in synchrony with research criteria for cloud service provider transparency, but there are also some extra pieces of information that customers are looking for. We further explain how A4Cloud tools contribute to addressing the customers’ requirements.

  • 276.
    Gineste, Mathieu
    et al.
    LAAS-CNRS, Univ. of Toulouse/ISAE.
    Garcia, Johan
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Programmable active emulation of wireless systems: A DVB-RCS Example2008Ingår i: 6th International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks and Workshops, 2008. WiOPT 2008., IEEE conference proceedings, 2008, s. 2-7Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a DVB-RCS satellite emulation system built using the NPBox programmable network emulation system. NPBox allows system components to be modeled both at a higher abstraction level using a finite-state-machine like abstraction, and also at a lower level using customized event guards and actions. Comparison experiments show that the emulated performance is similar to that of a complex low-level emulator.

  • 277.
    Grahn, Christian
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Implementing Transparency Logging for an Issue Tracking System2012Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    On the Internet today, users are accustomed to disclosing personal information when accessing a new service. When a user does so, there is rarely a system in place which allows the user to monitor how his or her information is actually shared or used by services. One proposed solution to this problem is to have services perform transparency logging on behalf of users, informing them how their data is processed as processing is taking place.

    We have recently participated in a collaboration to develop a privacy-preserving secure logging scheme that can be used for the purpose of transparency logging. As part of that collaboration we created a proof of concept implementation. In this thesis, we elaborate on that implementation and integrate it with a minimalistic open source issue-tracking system. We evaluate the amount of work required to integrate the logging system and attempt to identify potential integration problems. Using this issue-tracking system we then design and implement a scenario that demonstrates the value of the logging system to the average user.

  • 278.
    Grinnemo, Karl-Johan
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    A Study of Partially Reliable Transport Protocols for Soft Real-Time Applications2002Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The profileration of multimedia applications, such as streaming video, teleconferencing, and interactive gaming has created a tremendous challenge for the traditional transport protocols of the Internet – UDP and TCP. Specifically, many multimedia applications are examples of soft real-time applications. They have often relatively stringent require- ments in terms of delay and delay jitter, but typically tolerate a limited packet loss rate.

    In recognition of the transport service requirements of soft real-time applications, this thesis studies the feasibility of using retransmission based, partially reliable trans- port protocols for these applications. The thesis studies ways of designing retransmis- sion based, partially reliable transport protocols that are congestion aware and TCP com- patible. Furthermore, the transport protocols should provide a service that, in terms of performance metrics such as throughput, delay, and delay jitter, are suitable for soft real- time applications. The thesis work comprises the design, analysis, and evaluation of two retransmission based, partially reliable transport protocols: PRTP and PRTP-ECN. Extensive simulations have been carried out on PRTP as well as PRTP-ECN. These sim- ulations have in part been complemented by some theoretical analysis. The results of the simulations and the analysis suggest that substantial reductions in delay jitter and improvements in throughput can indeed be obtained with both PRTP and PRTP-ECN as compared to TCP. While PRTP reacted too slowly to congestion to be TCP-friendly and altogether fair, PRTP-ECN was found to be both TCP-friendly and reasonably fair.

    The thesis work also comprises an extensive survey on retransmission based, par- tially reliable transport protocols. Based on this survey, we have proposed a taxonomy for these protocols. The taxonomy considers two dimensions of retransmission based, partially reliable transport protocols: the transport service, and the error control scheme. 

  • 279.
    Grinnemo, Karl-Johan
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Transport Services for Converged IP Networks Protocols for Soft Real-Time Applications in IP Networks2010Bok (Refereegranskat)
  • 280.
    Grinnemo, Karl-Johan
    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.
    A Simulation Based Performance Analysis of a TCP Extension for Best Effort Multimedia Applications2002Ingår i: Proceedings: 35th Annual Simulation Symposium, IEEE , 2002, s. 327-336Konferensbidrag (Refereegranskat)
    Abstract [en]

    Since TCP is considered unsuitable for the majority of the emerging multimedia applications, these applications primarily use UDP transport together with proprietary congestion control schemes that have better jitter and throughput characteristics. A common problem with these congestion control schemes is that they often exhibit a TCP-unfriendly and unfair behavior. As the number of applications that uses this kind of schemes increases, this could become a serious threat to the stability and performance of the Internet. In an attempt to make TCP a viable alternative to some best-effort multimedia applications, we have proposed an extension to TCP - PRTP-ECN. The performance of PRTP-ECN has been compared with TCP in an extensive factorial simulation experiment. This paper gives a detailed description of this simulation experiment with an emphasis on its statistical design and analysis. The analysis of the experiment includes, among other things, a series of ANOVA tests. These tests indicate that PRTP-ECN gives significant reductions in average interarrival jitter, while at the same time leads to improvements in average throughput and goodput, and better link utilization. In addition, the analysis suggests that PRTP-ECN is almost as fair as TCP and exhibits a TCP-friendly behavior

  • 281.
    Grinnemo, Karl-Johan
    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 TCP for Applications with Soft Real-Time Constraints2001Ingår i: Multimedia systems and applications IV: 21-22 August 2001, Denver, USA / [ed] Andrew G. Tescher, Bhaskaran Vasudev, V. Michael Bove, Jr., Bellingham: SPIE , 2001, s. 18-31Konferensbidrag (Refereegranskat)
    Abstract [en]

    Experiences in the use of the Internet as a delivery medium for multimedia-based applications have revealed serious deficiencies in its ability to provide the QoS of Multimedia Applications. We propose an extension to TCP that addresses the QoS requirements of applications with soft real-time constraints. Although, TCP has been found unsuitable for real-time applications, it can with minor modifications be adjusted to better comply with the QoS needs of applications with soft real-time requirements. Enhancing TCP with support for this group of applications is important since the congestion control mechanism of TCP assures stability of the Internet. In contrast, specialized multimedia protocols that lack appropriate congestion control can never be deployed on a large scale basis. Two factors of great importance for applications with soft real time constraints are jitter and throughput. By relaxing the reliability offered by TCP, the extension gives better jitter characteristics and an improved throughput. The extension only needs to be implemented at the receiving side. The reliability provided is controlled by the receiving application, thereby allowing a flexible tradeoff between different QoS parameters. In this paper, our TCP extension is presented and analyzed. The analysis investigates how the different application-controlled parameters influence performance. Our analysis is supported by a simulation study that investigates the tradeoff between interarrival jitter, throughput, and reliability. The simulation results also confirm that the extended version of TCP still behaves in a TCP-friendly manner

  • 282.
    Grinnemo, Karl-Johan
    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.
    Evaluation of the QoS Offered by PRTP-ECN: A TCP Compliant Partially Reliable Transport Protocol2001Ingår i: Proceedings: IWQoS '01 Proceedings of the 9th International Workshop on Quality of Service, London: Springer , 2001, s. 217-234Konferensbidrag (Refereegranskat)
    Abstract [en]

    The introduction of multimedia in the Internet imposes new QoS requirements on existing transport protocols. Since neither TCP nor UDP comply with these requirements, a common approach today is to use RTP/UDP and to relegate the QoS responsibility to the application. Even though this approach has many advantages, it also entails leaving the responsibility for congestion control to the application. Considering the importance of efficient and reliable congestion control for maintaining stability in the Internet, this approach may prove dangerous. Improved support at the transport layer is therefore needed. In this paper, a partially reliable transport protocol, PRTP-ECN, is presented. PRTP-ECN is a protocol designed to be both TCP-friendly and to better comply with the QoS requirements of applications with soft real-time constraints. This is achieved by trading reliability for better jitter characteristics and improved throughput. A simulation study of PRTP-ECN has been conducted. The outcome of this evaluation suggests that PRTPECN can give applications that tolerate a limited amount of packet loss significant reductions in interarrival jitter and improvements in throughput as compared to TCP. The simulations also verified the TCP-friendly behavior of PRTP-ECN

  • 283.
    Grinnemo, Karl-Johan
    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.
    Impact of Traffic Load on SCTP Failovers in SIGTRAN2005Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    With Voice over IP (VoIP) emerging as a viable alternative to the traditional circuit-switched telephony, it is vital that the two are able to intercommunicate. To this end, the IETF Signaling Transport (SIGTRAN) group has defined an architecture for seamless transportation of SS7 signaling traffic between a VoIP network and a traditional telecom network. However, at present, it is unclear if the SIGTRAN architecture will, in reality, meet the SS7 requirements, especially the stringent availability requirements. The SCTP transport protocol is one of the core components of the SIGTRAN architecture, and its failover mechanism is one of the most important availability mechanisms of SIGTRAN. This paper studies the impact of traffic load on the SCTP failover performance in an M3UA-based SIGTRAN network. The paper shows that cross traffic, especially bursty cross traffic such as SS7 signaling traffic, could indeed significantly deteriorate the SCTP failover performance. Furthermore the paper stresses the importance of configuring routers in a SIGTRAN network with relatively small queues. For example, in tests with bursty cross traffic, and with router queues twice the bandwidth-delay product, failover times were measured which were more than 50% longer than what was measured with no cross traffic at all. Furthermore, the paper also identifies some properties of the SCTP failover mechanism that could, in some cases, significantly degrade its performance

  • 284.
    Grinnemo, Karl-Johan
    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.
    On the Use of CMT-SCTP to Improve the Startup Behavior of PSTN Signaling Traffic2013Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    There is currently work going on at IETF to standardize concurrent multipath transfer, i.e., simultaneous transfer of data over several network paths, for SCTP. This paper studies whether or not SCTP extended with concurrent multipath transfer (CMT-SCTP) could provide a faster startup behavior than standard SCTP. The paper complements previous work on CMT-SCTP, and extends it to PSTN signaling traffic. The paper suggests that CMT-SCTP could give a faster startup behavior over symmetrical paths, i.e., paths with similar bandwidths and round-trip times, but that its behavior is sensitive to differences in round-trip time between the paths. The paper also indicates that signaling traffic properties such as message size and burstiness contribute marginally to the startup behavior of CMT-SCTP. 

  • 285.
    Grinnemo, Karl-Johan
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013).
    Brunstrom, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    On the Use of MPTCP to Reduce Latency for Cloud Applications2014Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    As mobile cloud usage has become more and more prevalent, with more people depending on the cloud for both their work and their leisure, cloud-to-end-user latency have risen to become a key issue. One oft-forgotten way to cost effectively improve the quality of experience is to simultaneously make use of the several network interfaces, e.g., WiFi and 3G/4G interfaces, available on most of todays mobile devices including smartphones and tablets; that is, to employ multihoming. This paper provides an initial evaluation of the latency characteristics of the multipath extensions to TCP, Multipath TCP (MPTCP), that are currently being standardized by IETF. In particular, the paper considers the possible reductions in latency that could be obtained by using MPTCP and multiple network paths between a cloud service and a mobile end user. Traffic from three cloud applications are studied, Netflix, Google Maps, and Google Docs, representing typical high-, mid-, and low- intensity cloud-to-end-user traffic. The result suggests that significant latency reductions are indeed possible, however, primarily for high- intensity video traffic such as Netflix. 

  • 286.
    Grinnemo, Karl-Johan
    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.
    Performance of SCTP-controlled Failovers in M3UA-based SIGTRAN Networks2004Ingår i: Simulations Series, La Jolla, Ca: Society for Computer Simulation , 2004, s. 86-91Konferensbidrag (Refereegranskat)
    Abstract [en]

    There are some large economic, operational, and, to some extent, technicalincentives to replace the traditional telecom network with IP. However,such a large transition will not happen overnight maybe never. Meanwhile,IP-based and traditional TDM-based telephony will have to co-exist. To addressthis situation, the IETF SIGTRAN working group has developed an architecturefor transportation of Signaling System No. 7 (SS7) traffic over IP. Still, itremains to be shown that the introduction of the SIGTRAN architecture will notsignificantly deteriorate the performance of SS7. To this end, this paperevaluates the failover performance in SIGTRAN networks. Specifically, the paperevaluates the performance of SCTP-controlled failovers in M3UA-based SIGTRAN networks.The paper suggests that in order to obtain a failover performance with SCTPcomparable to that obtained in traditional TDM-based SS7 systems, SCTP has to abandonmany of the configuration recommendations of RFC 2960 and become much more aggressivein its failover behavior. Furthermore, the paper suggests that the SCTP parameterPath.Max.Retrans has a major impact on the SCTP failover performance. Our evaluationalso indicates that for those path propagation delays envisioned in future SIGTRAN networks,the impact of the path propagation delay on the failover performance is marginal

  • 287.
    Grinnemo, Karl-Johan
    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.
    Some Observations on the Performance of SCTP-controlled Failovers in M3UA-based SIGTRAN Networks2004Ingår i: Proceedings of the Second Swedish National Computer Networking Workshop: SNCNW2004, Karlstad, 2004Konferensbidrag (Refereegranskat)
    Abstract [en]

    With Voice over IP (VoIP) emerging as a viable alternative totraditional circuit-switched telephony, it is vital that the twoare able to intercommunicate. To this end, the IETF SignalingTransport (SIGTRAN) group has devised an architecture forseamless transportation of SS7 signaling traffic between aVoIP network and a traditional telecom network. However,at present, it is unclear if the SIGTRAN architecture will,in reality, meet the SS7 requirements, especially the stringentavailability requirements.The SCTP transport protocol is one of the core componentsof the SIGTRAN architecture, and its failover mechanism isone of the most important of the availability mechanisms ofSIGTRAN. Currently, we are studying the performance ofSCTP-controlled failovers, and although this study is not yetcompleted some observations have been made on propertiesof the SCTP failover mechanism which could impede on itsperformance. This paper reports on these observations, andexplains their causes.

  • 288.
    Grinnemo, Karl-Johan
    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.
    Andersson, Torbjörn
    Tieto Enator AB, Karlstad.
    Performance Benefits of Avoiding Head-of-Line Blocking in SCTP2005Ingår i: Autonomic and Autonomous Systems and International Conference on Networking and Services, 2005. ICAS-ICNS 2005. Joint International Conference on, IEEE , 2005, s. 44-Konferensbidrag (Refereegranskat)
    Abstract [en]

    Mitigating the effects of head-of-line blocking (HoLB) was one of the major reasons the IETF SIGTRAN working group developed SCTP, a new transport protocol for PSTN signaling traffic, in the first place. However, studies of the impact of HoLB blocking on TCP and SCTP have given ambiguous results as to whether HoLB has, in fact, any significantly deteriorating effect on transmission delay. To this end, we have carried out a detailed experimental study on the quantitative effects of HoLB. Our study suggests that although HoLB could indeed incur a substantial delay penalty on a small fraction of the messages in an SCTP session, it has only a marginal impact on the average end-to-end transmission delay. We only observed improvements in the range of O% to 18% in average message transmission delay of using unordered delivery as compared to ordered delivery. Furthermore, there was a large variability in between different test runs, which often made the impact of HoLB statistically insignificant

  • 289.
    Grinnemo, Karl-Johan
    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.
    Brunström, Anna
    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.
    A First Study on Using MPTCP to Reduce Latency for Cloud Based Mobile Applications2015Ingår i: 2015 IEEE SYMPOSIUM ON COMPUTERS AND COMMUNICATION (ISCC), IEEE, 2015, s. 64-69Konferensbidrag (Refereegranskat)
    Abstract [en]

    Currently, Multipath TCP (MPTCP) – a modifica- tion to standard TCP that enables the concurrent use of several network paths in a single TCP connection – is being standardized by IETF. This paper provides a comprehensive evaluation of the use of MPTCP to reduce latency and thus improve the quality of experience or QoE for cloud-based applications. In particular, the paper considers the possible reductions in latency that could be obtained by using MPTCP and multiple network paths between a cloud service and a mobile end user. To obtain an appreciation of the expected latency performance for different types of cloud traffic, three applications are studied, Netflix, Google Maps, and Google Docs, representing typical applications generating high-, mid-, and low-intensity traffic. The results suggest that MPTCP could provide significant latency reductions for cloud applications, especially for applications such as Netflix and Google Maps. Moreover, the results suggest that MPTCP offers a reduced latency despite a few percent packet loss, and in spite of limited differences in the round-trip times of the network paths in an MPTCP connection. Still, larger differences in the round-trip times seem to significantly increase the application latency, especially for Netflix, Google Maps, and similar applications. Thus, to become an even better alternative to these applications, this paper suggests that the MPTCP packet scheduling policy should be changed: Apart from the round-trip times of the network paths in a connection, it should also consider the difference in round-trip time between the network paths.

  • 290.
    Grinnemo, Karl-Johan
    et al.
    Karlstads universitet, Institutionen för informationsteknologi.
    Brunström, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    A Simulation Based Performance Evaluation of PRTP2002Rapport (Övrigt vetenskapligt)
    Abstract [en]

    PRTP is proposed to address the need of a transport service that is more suitable forapplications with soft real-time requirements, e.g., video broadcasting. It is an extensionfor partial reliability to TCP. The main idea behind PRTP is to exploit the fact thatmany soft real-time applications tolerate a limited amount of packet loss. In particular,PRTP enables an application to trade some of the reliability offered by TCP for improvedthroughput and interarrival jitter. This paper describes the design of PRTP andgives a detailed description of a simulation based performance evaluation. The performanceevaluation involved the performance of PRTP compared to TCP in long- as wellas in short-lived connections and showed that PRTP probably would give significantimprovements in performance, both in terms of throughput and interarrival jitter, for awide range of applications. The performance evaluation also suggested that PRTP is notTCP-friendly and altogether fair against competing flows and thus is not suitable for usein an environment where the main reason for packet loss is congestion, e.g., in a fixedInternet environment. We believe, however, that PRTP could be a viable alternative forwireless applications in error prone environments.

  • 291.
    Grinnemo, Karl-Johan
    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.
    An Easy way to Reduce SCTP Failover Times2005Ingår i: Proceedings of the Third Swedish National Computer Networking Workshop: SNCNW2005, 2005Konferensbidrag (Refereegranskat)
    Abstract [en]

    To enable interoperability between the public switched telephone network and IP, the IETF SIGTRAN working group has developed an architecture for the transportation of SS7 signaling traffic over IP. The architecture is based on a new transport protocol, the Stream Control Transmission Protocol (SCTP), that is designed to meet SS7 requirements. However, recent work suggests that the SCTP failover mechanism has difficulties complying with the SS7 requirements of ITU-T. To this end, this paper suggests using a modified retransmission timeout strategy which involves using a relaxed backoff factor of less than 2, the standard value specified in RFC 2960. Through simulations, it is shown that significant improvements in failover time, and thus in increased permissible network delays, could be obtained with this backoff strategy in well-dimensioned and controlled network environments. However, the simulations also stress the importance of running signaling traffic over managed IP networks. In the simulations where the signaling traffic competed with uncontrolled cross traffic, none of the studied backoff factors made SCTP compliant with ITU-T.

  • 292.
    Grinnemo, Karl-Johan
    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.
    Impact of SCTP-controlled Failovers for M3UA Users in a Dedicated SIGTRAN Network2003Ingår i: Proceedings of the First Swedish National Computer Networking Workshop: SNCNW2003, 2003Konferensbidrag (Refereegranskat)
  • 293.
    Grinnemo, Karl-Johan
    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.
    Brunstrom, Anna
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Taxonomy and Survey of Retransmission-based Partially Reliable Transport Protocols2004Ingår i: Elsevier Computer Communications, ISSN 0140-3664, Vol. 27, nr 15, s. 1441-1452Artikel i tidskrift (Refereegranskat)
  • 294. Guenkova-Luy, T.
    et al.
    Schorr, A.
    Hauck, F.
    Kassler, Andreas
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Wolf, I.
    Feiten, B.
    Timmerer, C.
    Hellwagner, H.
    MPEG-21 DIA based content delivery using SDPng controls and RTP transport2005Konferensbidrag (Refereegranskat)
  • 295. Guenkova-Luy, T.
    et al.
    Schorr, A.
    Kassler, Andreas
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Wolf, I.
    Blaya, J. A.
    Inzerilli, T.
    Gómez, M.
    Mota, T.
    Multimedia Service Provisioning in a B3G Service Creation Platform2005Konferensbidrag (Refereegranskat)
    Abstract [en]

    Future wireless systems will be heterogeneous and highly adaptive. In this environment, it is important to dis-cover, create and adapt (multimedia) services and content and to integrate these processes into a platform so that pervasive systems, application services and other user-centric services can utilise them easily. In this paper, we present a Multimedia Service Provisioning Platform (MMSPP), designed for sys-tems beyond 3G. The MMSPP orchestrates multimedia ses-sion control and content adaptation. Adaptation processes, based on MPEG-21 DIA, are coordinated via SIP/SDPng and guided through user/terminal profiles and network characteris-tics. The platform provides mechanisms for service discovery and interacts with accounting, charging and network QoS mechanisms

  • 296. Guenkova-Luy, Teodora
    et al.
    Schmidt, Holger
    Schorr, Andreas
    Hauck, Franz 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.
    A Session-Initiation-Protocol-based Middleware for Multi-Application Management2007Konferensbidrag (Refereegranskat)
    Abstract [en]

    The deployment of multimedia services in next-generation networks is a challenge due to the high configuration complexity of the streaming process in different stationary and mobile sub-networks and for various user devices. The Session Initiation Protocol (SIP) has proven to be a suitable mechanism to handle the control of multimedia services in such networks. However, the current standardization and implementation of SIP do not allow the simultaneous coordination of multiple concurrent applications on a single device, as the prescribed realization of the SIP state machines (transactions) does not consider mutual access of applications to a single SIP stack. This paper presents a SIP-based mechanism for synchronized management of services in a shared environment. We have developed a middleware that facilitates the uniform access of multiple applications towards one or multiple SIP stacks to enable prioritization of services and centralized resource coordination of concurrent SIP applications on a single terminal or server

  • 297. Guenkova-Luy, Teodora
    et al.
    Schorr, Andreas
    Hauck, Franz
    Gómez, Miguel
    Timmerer, Christian
    Wolf, Ingo
    Kassler, Andreas
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT.
    Advanced Multimedia Management Control Model and Content Adaptation2006Konferensbidrag (Refereegranskat)
    Abstract [en]

    The delivery and adaptation of multimedia content in distributed and heterogeneous environments requires flexible control and management mechanisms in terminals and in control entities inside the network. In the near future, it is important to reach interoperability between the IETF approaches on multimedia session establishment and control and the MPEG-21 efforts for multimedia streaming and adaptation to bring advanced multimedia service provisioning and adaptation services towards the customer. MPEG-21 Digital Item Adaptation (DIA) provides normative descriptions for supporting adaptation of multimedia content, but does not define interactions with transport and control mechanisms. On the other hand, the IETF standardization efforts on multimedia session control provide the necessary transport (e.g. RTP) and control mechanisms (SDP/SDPng). We thus bridge the gap between those approaches by creating a converged XML model that enables the integration of session management and negotiation protocols (e.g. SIP or Megaco) inspired by the XML formats of MPEG-21 DIA and SDPng. We also present preliminary implementation results of the converged model along with concepts and implementation of network-based content adaptation mechanisms through media gateways that enable flexible multimedia management for heterogeneous consumer terminals

  • 298. Gurnett, Michael
    et al.
    Gustafsson, Jörgen
    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.
    Magnusson, Kjell
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för fysik och elektroteknik. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap.
    Widstrand, Susanna
    Johansson, Lars
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för fysik och elektroteknik. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap.
    Johansson, M.K.-J.
    Gray, S.M.
    Core-level spectroscopy study of the Li/Si(111)-3x1, Na/Si(111)-3x1 and K/Si(111)-3x1 surfaces2005Ingår i: Phys. Rev. B 71, 195408 (2005)Artikel i tidskrift (Refereegranskat)
  • 299.
    Gurnett, Michael
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för fysik och elektroteknik.
    Holleboom, Thijs
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Zhang, Hanmin
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för fysik och elektroteknik.
    Johansson, Lars
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för fysik och elektroteknik.
    Photoemission study of the Li/Ge(111)-3×1 reconstruction2009Ingår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, ISSN 0039-6028, Vol. 603, nr 4, s. 727-735Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this article we report our findings on the electronic structure of the Li induced Ge(1 1 1)–3 × 1reconstruction as determined by angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) and core-level spectroscopy using synchrotron radiation. The results are compared to the theoretical honeycomb-chain-channel (HCC) model for the 3 × 1reconstruction as calculated using density functional theory (DFT). ARUPS measurements were performed in both the and directions of the 1 × 1 surface Brillouin zone at photon energies of 17 and 21.2 eV. Three surface related states were observed in the direction. In the direction, at least two surface states were seen. The calculated band structure using the single-domain HCC model for Li/Ge(1 1 1)–3 × 1 was in good agreement with experiment, allowing for the determination of the origin of the experimentally observed surface states. In the Ge core-level spectra, two surface related components were identified, both at lower binding energy with respect to the Ge bulk peak. Our DFT calculations of the surface core-level shifts were found to be in fair agreement with the experimental results. Finally, in contrast to the Li/Si(1 1 1)–3 × 1 case, no double bond between Ge atoms in the top layer was found

  • 300.
    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. 

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