| 1. |
- Larzon, Lars-Åke, et al.
(författare)
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Efficient transport of voice over IP over cellular links
- 2000
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Ingår i: GLOBECOM '00. - Piscataway, NJ : IEEE Communications Society. - 0780364511 ; , s. 1669-1676
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Konferensbidrag (refereegranskat)abstract
- Internet and cellular technologies are merging to decrease transport costs and enable IP-based applications to hundreds of millions of cellular users. Real time voice services will continue to be dominant in future cellular systems and to reduce system costs it is desirable to base all services, including voice, on IP. However, the radio spectrum must be efficiently used to provide mass-market services at reasonable prices, but Internet protocol headers are large in size. Moreover, data discarding policies are poorly suited to the error-proneness of cellular links. Protocol overhead for IP-based voice services can be reduced by compressing headers, e.g. with the compressed real time protocol (CRTP). CRTP, however, does not perform well over cellular links since it is not robust in the face of errors. ROCCO, a header compression scheme suitable for cellular systems, delivers more packets to the user than CRTP at realistic error rates with a better average compression ratio. Voice services in cellular systems should also be able to use damaged speech data. This can be done using the UDP Lite protocol which provides a more flexible checksumming policy that enables delivery of data possibly usable to the application. This paper shows that CRTP/UDP fails to deliver sufficient service quality at the error rates of a cost-efficient cellular system and that ROCCO combined with UDP Lite can provide an IP-based voice service over such cellular systems.
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| 2. |
- Alfredsson, Stefan, 1976-
(författare)
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TCP in Wireless Networks: Challenges, Optimizations and Evaluations
- 2005
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents research on transport layer behavior in wireless networks. As the Internet is expanding its reach to include mobile devices, it has become apparent that some of the original design assumptions for the dominant transport protocol, TCP, are approaching their limits. A key feature of TCP is the congestion control algorithm, constructed with the assumption that packet loss is normally very low, and that packet loss therefore is a sign of network congestion. This holds true for wired networks, but for mobile wireless networks non-congestion related packet loss may appear. The varying signal power inherent with mobility and handover between base-stations are two example causes of such packet loss. This thesis provides an overview of the challenges for TCP in wireless networks together with a compilation of a number of suggested TCP optimizations for these environments. A TCP modification called TCP-L is proposed. It allows an application to increase its performance, in environments where residual bit errors normally give a degraded throughput, by making a reliability tradeoff. The performance of TCP-L is experimentally evaluated with an implementation in the Linux kernel. The transport layer performance in a 4G scenario is also experimentally investigated, focusing on the impact of the link layer design and its parameterization. Further, for emulation-based protocol evaluations, controlled packet loss and bit error generation is shown to be an important aspect.
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| 3. |
- Bjurefors, Fredrik, et al.
(författare)
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Performance of Pastry in a Heterogeneous System
- 2004
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Ingår i: Proceedings of the Fourth IEEE International Conference on Peer-to-Peer computing.
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Konferensbidrag (refereegranskat)abstract
- In this paper, we study how Pastry performs in a heterogeneous network environment of varying size. The large traffic overhead for management traffic makes the overlay nonfunctional if it grows too large. This can be circumvented by partitioning the routing tables at the cost of increased path lengths and response times.
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| 4. |
- Hermans, Frederik, et al.
(författare)
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A Lightweight Approach to Online Detection and Classification of Interference in 802.15.4-based Sensor Networks
- 2012
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Ingår i: ACM SIGBED Review. - : Association for Computing Machinery (ACM). - 1551-3688. ; 9:3, s. 11-20
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Tidskriftsartikel (refereegranskat)abstract
- With a rapidly increasing number of devices sharing access to the 2.4 GHz ISM band, interference becomes a serious problem for 802.15.4-based, low-power sensor networks. Consequently, interference mitigation strategies are becoming commonplace. In this paper, we consider the step that precedes interference mitigation: interference detection. We have performed extensive measurements to characterize how different types of interferers affect individual 802.15.4 packets. From these measurements, we define a set of features which we use to train a neural network to classify the source of interference of a corrupted packet. Our approach is sufficiently lightweight for online use in a resource constrained sensor network. It does not require additional hardware, nor does it use active spectrum sensing or probing packets. Instead, all information about interferers is gathered from inspecting corrupted packets that are received during the sensor network’s regular operation. Even without considering a history of earlier packets, our approach reaches a mean classification accuracy of 79.8%, with per interferer accuracies of64.9% for WiFi, 82.6% for Bluetooth, 72.1% for microwave ovens, and 99.6% for packets that are corrupted due to insufficient signal strength.
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| 5. |
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| 6. |
- Landström, Sara, et al.
(författare)
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Buffer management for TCP over HS-DSCH
- 2005
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this paper we investigate the influence of buffer management for TCP on performance of the High Speed Downlink Channel (HS-DSCH) introduced in WCDMA release 5. HS-DSCH is a shared channel, but user data is buffered individually prior to the wireless link. Three queue management principles, e.g., passive queuing, the Packet Discard Prevention Counter (PDPC) method and the Random Early Detection (RED) algorithm were evaluated for a number of buffer sizes and scenarios. Also, a buffer large enough to prevent packets from being lost was included for reference. For round robin (RR) scheduling of radio-blocks, PDPC and the passive approach, that both manage to keep the buffer short, gave the best system goodput as well as the shortest average transfer times together with the excessively large buffer. With signal-to-interference ratio (SIR) scheduling, the strategy to avoid all packet losses, resulted in a lower system goodput than for the short buffers. As illustrated in this article, peak transfer rates may not be achieved with very small buffers, but buffers of 10-15 IP packets seem to represent a good trade-off between transfer rates, delay and system goodput. We would like to investigate how to make use of system parameters such as the current amount of data offered for HS-DSCH in total to regulate individual buffer sizes.
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| 7. |
- Landström, Sara, et al.
(författare)
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Congestion control in a high-speed radio environment
- 2004
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Ingår i: Proceedings of the International Conference on Wireless Networks, ICWN '04. - : CSREA Press. - 1932415394 ; , s. 617-623
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Konferensbidrag (refereegranskat)abstract
- This paper explores interactions between congestion control mechanisms at the transport layer and scheduling algorithms at the physical layer in the High-Speed Down-link Packet Access extension to WCDMA. Two different approaches to congestion control - TCP SACK and TFRC - are studied. We find that TCP SACK and TFRC in most respects perform the same way. SIR scheduling give a higher system throughput for both protocols than RR scheduling, but introduces delay variations that lead to spurious timeouts. The no feedback timeout of TFRC was shown to exhibit a similar sensitivity to delay spikes as the retransmit timeout in TCP SACK
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| 8. |
- Landström, Sara, et al.
(författare)
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Properties of TCP-like congestion control
- 2004
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Ingår i: Proceedings of the Swedish National Computer Networking Workshop.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 9. |
- Landström, Sara, et al.
(författare)
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Reducing the TCP Acknowledgment Frequency
- 2007
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Ingår i: Computer communication review. - : Association for Computing Machinery (ACM). - 0146-4833 .- 1943-5819. ; 37:3, s. 5-16
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Tidskriftsartikel (refereegranskat)abstract
- Delayed acknowledgments were introduced to conserve net- work and host resources. Further reduction of the acknowl- edgment frequency can be motivated in the same way. How- ever, reducing the dependency on frequent acknowledgments in TCP is difficult because acknowledgments support reli- able delivery, loss recovery, clock out new segments, and serve as input when determining an appropriate sending rate. Our results show that in scenarios where there are no ob- vious advantages of reducing the acknowledgment frequency, performance can be maintained although fewer acknowledg- ments are sent. Hence, there is a potential for reducing the acknowledgment frequency more than is done through de- layed acknowledgments today. Advancements in TCP loss recovery is one of the key reasons that the dependence on frequent acknowledgments has decreased. We propose and evaluate an end-to-end solution, where four acknowledgments per send window are sent. The sender compensates for the reduced acknowledgment frequency us- ing a form of Appropriate Byte Counting. The proposal also includes a modification of fast loss recovery to avoid frequent timeouts.
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| 10. |
- Landström, Sara, et al.
(författare)
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Revisiting wireless link layers and in-order delivery
- 2008
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Ingår i: Swedish National Computer Networking Workshop. - Karlskrona.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Wireless link layers, which perform retransmissions to hide transmission errors from upper layers, enforce inorder delivery to avoid triggering TCP's congestion control mechanisms. However, new reordering robust TCP flavors make it possible to revisit the design of these link layers. In this paper, we study the effects of the link layer configuration (in-order vs out-of-order) on network layer buffering and transport layer smoothness in a WWAN scenario through simulations. We use a standards-compliant TCP, TCP-Aix, and TCP-NCR. The results show that smoothness is improved and the buffer requirement is reduced when out-of-order delivery is allowed.
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