End-to-end Performance Implications of Slow Links

Dawkins, Spencer; Montenegro, Gabriel; Kojo, Markku; Magret, V.

doi:10.17487/rfc3150

Cited by 35 publications

(27 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In the case of long delay paths, a slow upstream link [RFC3150] can lead to another complication when the end host uses TCP large windows [RFC1323] to maximize throughput in the forward direction. Loss of data packets on the forward path, due to congestion, or link loss, common for some wireless links, will generate a large number of back-to-back duplicate ACKs (or TCP SACK packets [RFC2018]), for each correctly received data packet following a loss.…”

Section: Loss In Asymmetric Network Pathsmentioning

confidence: 99%

“…In the form described in [RFC1144], TCP performance is degraded when used over links (or paths) that may exhibit appreciable rates of packet loss [RFC3150]. It may also not provide significant improvement for upstream links with bidirectional traffic.…”

Section: Recommendationmentioning

confidence: 99%

“…Per-flow queuing (e.g., FQ, CBQ) offers benefit when used on any slow link (where the time to transmit a packet forms an appreciable part of the path RTT) [RFC3150]. Type 3 schemes offer additional benefit when used with one of the above techniques.…”

Section: Type 3: Upstream Link Schedulingmentioning

confidence: 99%

“…On a slow upstream link, appreciable jitter may be introduced by sending large data packets ahead of ACKs [RFC3150]. A simple scheme may be implemented using per-flow queuing with a fair scheduler (e.g., round robin service to all flows, or priority scheduling).…”

Section: Per-flow Queuing At the Upstream Bottleneck Linkmentioning

confidence: 99%

“…Bulk (payload) compression, a small MTU, link level transparent fragmentation [RFC1991, RFC2686] or link level suspend/resume capability (where higher priority frames may pre-empt transmission of lower priority frames) may be used to mitigate the impact (jitter) of bidirectional traffic on low speed links [RFC3150]. More advanced schemes (e.g., WFQ) may also be used to improve the performance of transfers with multiple ACK streams such as http [Seg00].…”

Section: Per-flow Queuing At the Upstream Bottleneck Linkmentioning

confidence: 99%

See 4 more Smart Citations

TCP Performance Implications of Network Path Asymmetry

Balakrishnan¹,

Padmanabhan²,

Fairhurst³

et al. 2002

100

View full text Add to dashboard Cite

This document describes TCP performance problems that arise because of asymmetric effects. These problems arise in several access networks, including bandwidth-asymmetric networks and packet radio subnetworks, for different underlying reasons. However, the end result on TCP performance is the same in both cases: performance often degrades significantly because of imperfection and variability in the ACK feedback from the receiver to the sender.The document details several mitigations to these effects, which have either been proposed or evaluated in the literature, or are currently deployed in networks. These solutions use a combination of local link-layer techniques, subnetwork, and end-to-end mechanisms, consisting of: (i) techniques to manage the channel used for the upstream bottleneck link carrying the ACKs, typically using header compression or reducing the frequency of TCP ACKs, (ii) techniques to handle this reduced ACK frequency to retain the TCP sender's acknowledgment-triggered self-clocking and (iii) techniques to schedule the data and ACK packets in the reverse direction to improve performance in the presence of two-way traffic. Each technique is described, together with known issues, and recommendations for use. A summary of the recommendations is provided at the end of the document. , and several packet radio networks. These networks are increasingly being deployed as high-speed Internet access networks, and it is therefore highly desirable to achieve good TCP performance. However, the asymmetry of the network paths often makes this challenging. Examples of some networks that exhibit asymmetry are provided in the Appendix.Asymmetry may manifest itself as a difference in transmit and receive capacity, an imbalance in the packet loss rate, or differences between the transmit and receive paths [RFC3077]. For example, when capacity is asymmetric, such that there is reduced capacity on reverse path used by TCP ACKs, slow or infrequent ACK feedback degrades TCP performance in the forward direction. Similarly, asymmetry in the underlying Medium Access Control (MAC) and Physical (PHY) protocols could make it expensive to transmit TCP ACKs (disproportionately to their size), even when capacity is symmetric. Asymmetry due to Differences in Transmit and Receive CapacityNetwork paths may be asymmetric because the upstream and downstream links operate at different rates and/or are implemented using different technologies. In networks employing centralized multiple access control, asymmetry may be a fundamental consequence of the hub-and-spokes architecture of the network (i.e., a single base node communicating with multiple downstream nodes). The central node often incurs less transmission overhead and does not incur latency in scheduling its own downstream transmissions. In contrast, upstream transmission is subject to additional overhead and latency (e.g., due to guard times between transmission bursts, and contention intervals). This can produce significant network path asymmetry.Upstream capacity ma...

show abstract

Section: Loss In Asymmetric Network Pathsmentioning

confidence: 99%

Section: Recommendationmentioning

confidence: 99%

Section: Type 3: Upstream Link Schedulingmentioning

confidence: 99%

Section: Per-flow Queuing At the Upstream Bottleneck Linkmentioning

confidence: 99%

Section: Per-flow Queuing At the Upstream Bottleneck Linkmentioning

confidence: 99%

See 3 more Smart Citations

TCP Performance Implications of Network Path Asymmetry

Balakrishnan¹,

Padmanabhan²,

Fairhurst³

et al. 2002

100

View full text Add to dashboard Cite

show abstract

Channel‐adaptive techniques in wireless communications: an overview

Cianca¹,

Luise²,

Ruggieri³

et al. 2002

Wireless Communications

View full text Add to dashboard Cite

The concept of adaptivity is of paramount importance in the design of future communication systems, in which a careful exploitation of the limited available resources (bandwidth, power, etc.) is required. The potential of channel‐adaptive transmission has been already recognized 30 years ago, but it did not receive much interest at that time. In the last decade, the advent of feasible software radio systems, and hence, the availability of fast flexible and reconfigurable transceivers has renewed interest in adaptive techniques, which include adaptive modulation and coding, adaptive antennas and adaptive equalization techniques. This paper focuses on adaptive modulation and adaptive error control mechanisms. Basic concepts are highlighted and an overview on the achieved results and new trends in this research area are presented. Some results from information theory are also presented, which show the limitations of these techniques and motivate further research on the practical and design issues that have to be addressed to enable performance to reach close to the theoretical limit. Copyright © 2002 John Wiley & Sons, Ltd.

show abstract