| 1. |
- Hurtig, Per, 1980-, et al.
(author)
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Early Retransmit for TCP and Stream Control Transmission Protocol (SCTP)
- 2010
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In: Internet Engineering Task Force. - : Internet Engineering Task Force. - 2070-1721. ; , s. 1-15
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Journal article (peer-reviewed)abstract
- 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
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| 2. |
- Hurtig, Per, 1980-, et al.
(author)
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Enhanced Metric Caching for Short TCP Flows
- 2012
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In: Proceedings of the IEEE International Conference on Communications (ICC 2012). - : IEEE Press. - 9781457720512 - 9781457720529 ; , s. 1209-1213
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Conference paper (peer-reviewed)abstract
- 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%.
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| 3. |
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| 4. |
- Hurtig, Per, 1980-, et al.
(author)
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Packet Reordering in TCP
- 2011
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In: Proceedings of the IEEE GLOBECOM Workshop CCNet. - : IEEE Press. - 9781467300384 - 9781467300391 ; , s. 136-141
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Conference paper (peer-reviewed)abstract
- 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.
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| 5. |
- Hurtig, Per, 1980-, et al.
(author)
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Recent Trends in TCP Packet-Level Characteristics
- 2011
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In: International Conference on Networking and Services (ICNS '11). - Venice/Mestre, Italy : IARIA. - 9781612080062 - 9781612081335
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Conference paper (peer-reviewed)abstract
- 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.
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| 6. |
- Hurtig, Per, 1980-, et al.
(author)
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SCTP: Designed for Timely Message Delivery?
- 2011
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In: Telecommunications Systems. - : Springer Science and Business Media LLC. - 1018-4864 .- 1572-9451. ; 47:3-4, s. 323-336
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Journal article (peer-reviewed)abstract
- To reduce cost and provide more flexible services, telecommunication operators are currently replacing traditional telephony networks with IP-networks. To support the requirements of telephony signaling in IP-networks, SCTP was standardized. SCTP solves a number of problems that follows from using TCP for telephony signaling transport. However, the design of SCTP is still largely based on TCP, and most of SCTP's data transmission mechanisms are inherited from TCP. Signaling traffic has stricter requirements of timely delivery than TCP bulk traffic. However, such requirements are not supported optimally by the inherited TCP mechanisms. We therefore argue that SCTP is not fully designed for timely message delivery. In this article we present and evaluate two loss recovery adaptations that enhance the timeliness of SCTP: Early Retransmit and a modified RTO management algorithm. In addition, we evaluate an adapted Nagle-like algorithm. The results from our evaluation show a significant reduction of message delivery times. In many of the experiments, delivery times were reduced with at least 30-50%. Furthermore, in some situations, message delivery times were reduced with up to 70%, using the modified Nagle algorithm.
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| 7. |
- Hurtig, Per, 1980-
(author)
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Transport-Layer Performance for Applications and Technologies of the Future Internet
- 2012
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Doctoral thesis (other academic/artistic)abstract
- 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.
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| 8. |
- Karlsson, Jonas, 1977-, et al.
(author)
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Impact of Multi-path Routing on TCP Performance
- 2012
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In: 2012 IEEE International Symposium on a World of Wireless, Mobile and Multimedia Networks (WoWMoM 2012). - Washington, DC : IEEE Press. - 9781467312387 ; , s. 1-3
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Conference paper (peer-reviewed)abstract
- Routing packets over multiple disjoint paths towards a destination can increase network utilization by load-balancing the traffic over the network. The drawback of load-balancing is that different paths might have different delay properties, causing packets to be reordered. This can reduce TCP performance significantly, as reordering is interpreted as a sign of congestion. Packet reordering can be avoided by letting the network layer route strictly on flow-level. This will, however, also limit the ability to achieve optimal network throughput. There are also several proposals that try to mitigate the effects of reordering at the transport layer. In this paper, we perform an initial evaluation of such TCP reordering mitigations in multi-radio multi-channel wireless mesh networks when using multi-path routing. We evaluate two TCP reordering mitigation techniques implemented in the Linux kernel. The transport layer mitigations are compared using different multi-path routing strategies. Our findings show that, in general, flow-level routing gives the best TCP performance and that transport layer reordering mitigations only marginally can improve performance.
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| 9. |
- Karlsson, Jonas, 1977-, et al.
(author)
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Impact of Multi-path Routing on TCP Performance in Wireless Mesh Networks
- 2012
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In: Proceedings of the 8th Swedish National Computer Networking Workshop (SNCNW 2012).
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Conference paper (peer-reviewed)abstract
- Routing packets over multiple disjoint paths to- wards a destination can increase network utilization by load- balancing the traffic over the network. The drawback of load-balancing is that different paths might have different delay properties, causing packets to be reordered. This can reduce TCP performance significantly, as reordering is interpreted as a sign of congestion. Packet reordering can be avoided by letting the network layer route strictly on flow-level. This will, however, also limit the ability to achieve optimal network throughput. There are also several proposals that try to mitigate the effects of reordering at the transport layer. In this paper, we perform an initial evaluation of such TCP reordering mitigations in multi-radio multi-channel wireless mesh networks when using multi-path routing. We evaluate two TCP reordering mitigation techniques implemented in the Linux kernel. The transport layer mitigations are compared using different multi-path routing strategies. Our findings show that, in general, flow-level routing gives the best TCP performance and that transport layer reordering mitigations only marginally can improve performance.
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| 10. |
- Karlsson, Jonas, 1977-, et al.
(author)
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The Interaction Between TCP Reordering Mechanisms and Multi-path Forwarding in Wireless Mesh Networks
- 2012
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In: 2012 IEEE 8th International Conference on Wireless and Mobile Computing, Networking and Communications (WiMob). - : IEEE Press. - 9781467314299 ; , s. 276-283
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Conference paper (peer-reviewed)abstract
- Routing packets over multiple disjoint paths towards a destination can increase network utilization by load-balancing the traffic over the network. In wireless mesh networks, multi-radio multi-channel nodes are often used to create a larger set of interference-free paths thus increasing the chance of load-balancing. The drawback of load-balancing is that different paths might have different delay properties, causing packets to be reordered. This can reduce TCP performance significantly, as reordering is interpreted as a sign of congestion. Packet reordering can be avoided by letting the network layer forward traffic strictly on flow-level. This would avoid the negative drawbacks of packet reordering, but will also limit the ability to achieve optimal network throughput. On the other hand, there are several proposals that try to mitigate the effects of reordering at the transport layer. In this paper, we perform an in-depth evaluation of such TCP reordering mitigations in multi-radio multi-channel wireless mesh networks when using multi-path forwarding. We evaluate two TCP reordering mitigation techniques implemented in the Linux kernel. The transport layer mitigations are compared using different multi-path forwarding strategies. Our findings show that, in general, flow-level forwarding gives the best TCP performance and that transport layer reordering mitigations only marginally can improve performance
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