| 1. |
- Abrahamsson, H, et al.
(författare)
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TCP over high speed variable capacity links: A simulation study for bandwidth allocation
- 2002
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Konferensbidrag (refereegranskat)abstract
- New optical network technologies provide opportunities for fast, controllable bandwidth management. These technologies can now explicitly provide resources to data paths, creating demand driven bandwidth reservation across networks where an applications bandwidth needs can be meet almost exactly. Dynamic synchronous Transfer Mode (DTM) is a gigabit network technology that provides channels with dynamically adjustable capacity. TCP is a reliable end-to-end transport protocol that adapts its rate to the available capacity. Both TCP and the DTM bandwidth can react to changes in the network load, creating a complex system with inter-dependent feedback mechanisms. The contribution of this work is an assessment of a bandwidth allocation scheme for TCP flows on variable capacity technologies. We have created a simulation environment using ns-2 and our results indicate that the allocation of bandwidth maximises TCP throughput for most flows, thus saving valuable capacity when compared to a scheme such as link over-provisioning. We highlight one situation where the allocation scheme might have some deficiencies against the static reservation of resources, and describe its causes. This type of situation warrants further investigation to understand how the algorithm can be modified to achieve performance similar to that of the fixed bandwidth case.
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| 2. |
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| 3. |
- Ahlgren, Bengt, et al.
(författare)
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Dimensioning links for IP telephony
- 2001. - 1
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Ingår i: Proceedings of the 2nd IP-Telephony Workshop (IPtel 2001), 2-3 April 2001, New York City, New York, USA.
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Konferensbidrag (refereegranskat)abstract
- Packet loss is an important parameter for dimensioning network links or traffic classes carrying IP telephony traffic. We present a model based on the Markov modulated Poisson process (MMPP) which calculates packet loss probabilities for a set of super positioned voice input sources and the specified link properties. We do not introduce another new model to the community, rather try and verify one of the existing models via extensive simulation and a real world implementation. A plethora of excellent research on queuing theory is still in the domain of ATM researchers and we attempt to highlight its validity to the IP Telephony community. Packet level simulations show very good correspondence with the predictions of the model. Our main contribution is the verification of the MMPP model with measurements in a laboratory environment. The loss rates predicted by the model are in general close to the measured loss rates and the loss rates obtained with simulation. The general conclusion is that the MMPP-based model is a tool well suited for dimensioning links carrying packetized voice in a system with limited buffer space.
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| 4. |
- Ahlgren, Bengt, et al.
(författare)
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Dimensioning Links for IP Telephony
- 2000. - 1
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Transmitting telephone calls over the Internet causes problems not present in current telephone technology such as packet loss and delay due to queueing in routers. In this undergraduate thesis we study how a Markov modulated Poisson process is applied as an arrival process to a multiplexer and we study the performance in terms of loss probability. The input consists of the superposition of independent voice sources. The predictions of the model is compared with results obtained with simulations of the multiplexer made with a network simulator. The buffer occupancy distribution is also studied and we see how this distribution changes as the load increases.
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| 5. |
- Backlund, Björn, et al.
(författare)
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A graphical G-LOTOS editor defined by meta-tool LOGGIE
- 1989. - 1
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We present a prototype implementation of a graphical editor for a subset of G-LOTOS. The graphical G-LOTOS syntax is beeing standardized within ISO for the LOTOS specification language. First, we provide a formal definition of the G-LOTOS subset. Then, the specification the editor is derived from this formal definition. Finally, the editor is generated automatically using the LOGGIE meta-tool.
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| 6. |
- Backlund, Björn, et al.
(författare)
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Generation of graphic language-oriented design environments
- 1989. - 1
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We review some results in the area of using meta techniques to generate language-oriented programming environments. We focus on environments for languages having a two-dimensional syntax based on attribute grammars and constraints. We introduce edit-semantic attributes, a new classof attributes which control the user interaction and graphic presentation. We present LOGGIE, a prototype tool implementing some of the meta techniques discussed. The tool generates interactive language-oriented graphical editors.
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| 7. |
- Biyani, Pravesh, et al.
(författare)
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Early Estimation of Voice over IPQuality
- 2003
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Konferensbidrag (refereegranskat)abstract
- Users of Voice over IP (VoIP) applications are sensitive to the quality of an ongoing call. We hypothesize that the quality of a VoIP session can be estimated from the first few seconds of the session and this can be generalized to other VoIP calls. Our approach is an in-band probing mechanism and does not require any external monitoring schemes or network support. We show by post processing VoIP data from globally distributed sites that it is possible to determine the quality after an initial number of seconds. One application is admission control, where it would be possible to reject poor quality calls before they are fully established.
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