Internet Engineering Task Force M. Welzl Internet-Draft University of Oslo Intended status: Informational D. Ros Expires: April 12, 2011 Telecom Bretagne October 9, 2010 A Survey of Lower-than-Best-Effort Transport Protocols draft-ietf-ledbat-survey-01.txt Abstract This document provides a survey of transport protocols which are designed to have a smaller bandwidth and/or delay impact on standard TCP than standard TCP itself when they share a bottleneck with it. Such protocols could be used for low-priority "background" traffic, as they provide what is sometimes called a "less than" (or "lower than") best-effort service. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on April 12, 2011. Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of Welzl & Ros Expires April 12, 2011 [Page 1] Internet-Draft LBE Transport Survey October 2010 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Delay-based transport protocols . . . . . . . . . . . . . . . 3 2.1. Accuracy of delay-based congestion predictors . . . . . . 6 2.2. Delay-based congestion control = LBE? . . . . . . . . . . 7 3. Non-delay-based transport protocols . . . . . . . . . . . . . 7 4. Application layer approaches . . . . . . . . . . . . . . . . . 8 5. Orthogonal work . . . . . . . . . . . . . . . . . . . . . . . 9 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 8. Security Considerations . . . . . . . . . . . . . . . . . . . 11 9. Informative References . . . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16 Welzl & Ros Expires April 12, 2011 [Page 2] Internet-Draft LBE Transport Survey October 2010 1. Introduction This document presents a brief survey of proposals to attain a Less than Best Effort (LBE) service without help from routers. We loosely define a LBE service as a service which results in smaller bandwidth and/or delay impact on standard TCP than standard TCP itself when sharing a bottleneck with it. We refer to systems that provide this service as Less than Best Effort (LBE) systems. Generally, LBE behavior can be achieved by reacting to queue growth earlier than standard TCP would, or by changing the congestion avoidance behavior of TCP without utilizing any additional implicit feedback. Some mechanisms achieve a LBE behavior at the application layer, e.g. by changing the receiver window of standard TCP, and there is also a substantial amount of work that is related to the LBE concept but not presenting a solution that can be installed in end hosts or expected to work over the Internet. According to this classification, solutions have been categorized in this document as delay-based transport protocols, non-delay-based transport protocols, application layer approaches and orthogonal work. 2. Delay-based transport protocols It is wrong to generally equate "little impact on standard TCP" with "small sending rate". Unless the sender's maximum window is limited for some reason, and in the absence of ECN support, standard TCP will normally increase its rate until a queue overflows, causing one or more packets to be dropped and the rate to be reduced. A protocol which stops increasing the rate before this event happens can, in principle, achieve a better performance than standard TCP. In the absence of any other traffic, this is even true for TCP itself when its maximum send window is limited to the bandwidth*round-trip time (RTT) product. TCP Vegas [Bra+94] is one of the first protocols that was known to have a smaller sending rate than standard TCP when both protocols share a bottleneck [Kur+00] -- yet it was designed to achieve more, not less throughput than standard TCP. Indeed, when it is the only protocol on the bottleneck, the throughput of TCP Vegas is greater than the throughput of standard TCP. Depending on the bottleneck queue length, TCP Vegas itself can be starved by standard TCP flows. This can be remedied to some degree by the RED Active Queue Management mechanism [RFC2309]. The congestion avoidance behavior is the protocol's most important feature in terms of historical relevance as well as relevance in the context of this document (it has been shown that other elements of the protocol can sometimes play a greater role for its overall Welzl & Ros Expires April 12, 2011 [Page 3] Internet-Draft LBE Transport Survey October 2010 behavior [Hen+00]). In Congestion Avoidance, once per RTT, TCP Vegas calculates the expected throughput as WindowSize / BaseRTT, where WindowSize is the current congestion window and BaseRTT is the minimum of all measured RTTs. The expected throughput is then compared with the actual (measured) throughput. If the actual throughput is smaller than the expected throughput minus a threshold beta, this is taken as a sign of congestion, causing the protocol to linearly decrease its rate. If the actual throughput is greater than the expected throughput minus a threshold alpha (with alpha < beta), this is taken as a sign that the network is underutilized, causing the protocol to linearly increase its rate. TCP Vegas has been analyzed extensively. One of the most prominent properties of TCP Vegas is its fairness between multiple flows of the same kind, which does not penalize flows with large propagation delays in the same way as standard TCP. While it was not the first protocol that uses delay as a congestion indication, its predecessors (which can be found in [Bra+94]) are not discussed here because of the historical "landmark" role that TCP Vegas has taken in the literature. Transport protocols which were designed to be non-intrusive include TCP-LP [Kuz+06] and TCP Nice [Ven+02]. Using a simple analytical model, the authors of [Kuz+06] illustrate the feasibility of this endeavor by showing that, due to the non-linear relationship between throughput and RTT, it is possible to remain transparent to standard TCP even when the flows under consideration have a larger RTT than standard TCP flows. TCP Nice [Ven+02] follows the same basic approach as TCP Vegas but improves upon it in some aspects. Because of its moderate linear- decrease congestion response, TCP Vegas can affect standard TCP despite its ability to detect congestion early. TCP Nice removes this issue by halving the congestion window (at most once per RTT, like standard TCP) instead of linearly reducing it. To avoid being too conservative, this is only done if a fixed predefined fraction of delay-based incipient congestion signals appears within one RTT. Otherwise, TCP Nice falls back to the congestion avoidance rules of TCP Vegas if no packet was lost or standard TCP if a packet was lost. One more feature of TCP Nice is its ability to support a congestion window of less than one packet, by clocking out single packets over more than one RTT. With ns-2 simulations and real-life experiments using a Linux implementation, the authors of [Ven+02] show that TCP Nice achieves its goal of efficiently utilizing spare capacity while being non-intrusive to standard TCP. Other than TCP Vegas and TCP Nice, TCP-LP uses only the one-way delay (OWD) instead of the RTT as an indicator of incipient congestion. Welzl & Ros Expires April 12, 2011 [Page 4] Internet-Draft LBE Transport Survey October 2010 This is done to avoid reacting to delay fluctuations that are caused by reverse cross-traffic. Using the TCP Timestamps option [RFC1323], the OWD is determined as the difference between the receiver's Timestamp value in the ACK and the original Timestamp value that the receiver copied into the ACK. While the result of this subtraction can only precisely represent the OWD if clocks are synchronized, its absolute value is of no concern to TCP-LP and hence clock synchronization is unnecessary. Using a constant smoothing parameter, TCP-LP calculates an Exponentially Weighted Moving Average (EWMA) of the measured OWD and checks whether the result exceeds a threshold within the range of the minimum and maximum OWD that was seen during the connections's lifetime; if it does, this condition is interpreted as an "early congestion indication". The minimum and maximum OWD values are initialized during the slow-start phase. Regarding its reaction to an early congestion indication, TCP-LP tries to strike a middle ground between the overly conservative choice of immediately setting the congestion window to one packet and the presumably too aggressive choice of halving the congestion window like standard TCP. It does so by halving the window at first in response to an early congestion indication, then initializing an "interference time-out timer", and maintaining the window size until this timer fires. If another early congestion indication appeared during this "interference phase", the window is then set to 1; otherwise, the window is maintained and TCP-LP continues to increase it the standard Additive-Increase fashion. This method ensures that it takes at least two RTTs for a TCP-LP flow to decrease its window to 1, and, like standard TCP, TCP-LP reacts to congestion at most once per RTT. With ns-2 simulations and real-life experiments using a Linux implementation, the authors of [Kuz+06] show that TCP-LP is largely non-intrusive to TCP traffic while at the same time enabling it to utilize a large portion of the excess network bandwidth, which is fairly shared among competing TCP-LP flows. They also show that using their protocol for bulk data transfers greatly reduces file transfer times of competing best-effort web traffic. Sync-TCP [Wei+05] follows a similar approach as TCP-LP, by adapting its reaction to congestion according to changes in the OWD. By comparing the estimated (average) forward queuing delay to the maximum observed delay, Sync-TCP adapts the AIMD parameters depending on the trend followed by the average delay over an observation window. Even though the authors of [Wei+05] did not explicitely consider its use as an LBE protocol, Sync-TCP was designed to react early to incipient congestion, while grabbing available bandwidth more aggressively than a standard TCP in congestion-avoidance mode. Welzl & Ros Expires April 12, 2011 [Page 5] Internet-Draft LBE Transport Survey October 2010 Delay-based congestion control is also at the basis of proposals aiming at adapting TCP's congestion avoidance to very high-speed networks. Some of these proposals [Tan+06][Sri+08][Liu+08] are hybrid loss- and delay-based mechanisms, whereas others [Dev+03][Wei+06][Cha+10] are variants of Vegas based solely on delays. 2.1. Accuracy of delay-based congestion predictors The accuracy of delay-based congestion predictors has been the subject of a good deal of research, see e.g. [Bia+03], [Mar+03], [Pra+04], [Rew+06], [McC+08]. The main result of most of these studies is that delays (or, more precisely, round-trip times) are, in general, weakly correlated with congestion. There are several factors that may induce such a poor correlation: o Bottleneck buffer size: in principle, a delay-based mechanism could be made "more than TCP friendly" _if_ buffers are "large enough", so that RTT fluctuations and/or deviations from the minimum RTT can be detected by the end-host with reasonable accuracy. Otherwise, it may be hard to distinguish real delay variations from measurement noise. o RTT measurement issues: in principle, RTT samples may suffer from poor resolution, due to timers which are too coarse-grained with respect to the scale of delay fluctuations. Also, a flow may obtain a very noisy estimate of RTTs due to undersampling, under some circumstances (e.g., the flow rate is much lower than the link bandwidth). For TCP, other potential sources of measurement noise include: TCP segmentation offloading (TSO) and the use of delayed ACKs [Hay10]. o Level of statistical multiplexing and RTT sampling: it may be easy for an individual flow to "miss" loss/queue overflow events, especially if the number of flows sharing a bottleneck buffer is significant. This is nicely illustrated e.g. in Fig. 2 of [McC+08]. o Impact of wireless links: several mechanisms that are typical of wireless links, like link-layer scheduling and error recovery, may induce strong delay fluctuations over short time scales [Gur+04]. Whether a delay-based protocol behaves in its intended manner (e.g., it is "more than TCP friendly", or it grabs available bandwidth in a very aggressive manner) may therefore depend on the accuracy issues listed above. Moreover, protocols like Vegas need to keep an estimate of the minimum ("base") delay; this makes such protocols highly sensitive to eventual changes in the end-to-end route during Welzl & Ros Expires April 12, 2011 [Page 6] Internet-Draft LBE Transport Survey October 2010 the lifetime of the flow [Mo+99]. TODO: incorporate [Bha+07] and any references therein that may be missing. 2.2. Delay-based congestion control = LBE? Regarding the issue of false positives/false negatives with a delay- based congestion detector, most studies focus on the loss of throughput coming from the erroneous detection of queue build-up and of alleviation of congestion. Arguably, for a LBE transport protocol it's better to err on the "more-than-TCP-friendly side", that is, to always yield to _perceived_ congestion whether it is "real" or not; however, failure to detect congestion (due to one of the above accuracy problems) would result in behavior that is not LBE. For instance, consider the case in which the bottleneck buffer is small, so that the contribution of queueing delay at the bottleneck to the global end-to-end delay is small. In such a case, a flow using a delay-based mechanism might end up consuming a good deal of bandwidth with respect to a competing standard TCP flow, unless it also incorporates a suitable reaction to loss. Consider also the case in which the bottleneck link is already (very) congested. In such a scenario, delay variations may be quite small, hence, it may be very difficult to tell an empty queue from a heavily-loaded queue, in terms of delay fluctuation. Therefore, a newly-arriving delay-based flow may start sending faster when there is already heavy congestion, eventually driving away loss-based flows [Sha+05]. 3. Non-delay-based transport protocols 4CP [Liu+07], which stands for "Competitive and Considerate Congestion Control", is a protocol which provides a LBE service by changing the window control rules of standard TCP. A "virtual window" is maintained, which, during a so-called "bad congestion phase" is reduced to less than a predefined minimum value of the actual congestion window. The congestion window is only increased again once the virtual window exceeds this minimum, and in this way the virtual window controls the duration during which the sender transmits with a fixed minimum rate. The 4CP congestion avoidance algorithm allows for setting a target average window and avoids starvation of "background" flows while bounding the impact on "foreground" flows. Its performance was evaluated in ns-2 simulations and in real-life experiments with a kernel-level implementation in Microsoft Windows Vista. Welzl & Ros Expires April 12, 2011 [Page 7] Internet-Draft LBE Transport Survey October 2010 Some work was done on applying weights to congestion control mechanisms, allowing a flow to be as aggressive as a number of parallel TCP flows at the same time. This is usually motivated by the fact that users may want to assign different priorities to different flows. The first, and best known, such protocol is MulTCP [Cro+98], which emulates N TCPs in a rather simple fashion. Improved versions of the parallel-TCP idea are presented in [Hac+04] and [Hac+08], and there is also a variant where only one feedback loop is applied to control a larger traffic aggregate by the name of Probe- Aided (PA-)MulTCP [Kuo+08]. Another protocol, CP [Ott+04], applies the same concept to the TFRC protocol [RFC5348] in order to provide such fairness differentiation for multimedia flows. The general assumption underlying all of the above work is that these protocols are "N-TCP-friendly", i.e. they are as TCP-friendly as N TCPs, where N is a positive (and possibly natural) number which is greater than or equal to 1. The MulTFRC [Dam+09] protocol, another extension of TFRC for multiple flows, is however able to support values between 0 and 1, making it applicable as a mechanism for a LBE service. Since it does not react to delay like the mechanisms above but adjusts its rate like TFRC, it can probably be expected to be more aggressive than mechanisms such as TCP Nice or TCP-LP. This also means that MulTFRC is less likely to be prone to starvation, as its aggression is tunable at a fine granularity even when N is between 0 and 1. 4. Application layer approaches A simplistic, application-level approach to a background transport service may just consist in scheduling automated transfers at times when the network is lightly loaded, as described in e.g. [Dyk+02]. An issue with such a technique is that it may not necessarily be appropriate to applications like peer-to-peer file transfer, since the notion of an "off-peak hour" is not meaningful when end-hosts may be located anywhere in the world. TCP's built-in flow control can be used as a means to achieve a low- priority transport service. For instance, the mechanism described in [Spr+00] controls the bandwidth by letting the receiver intelligently manipulate the receiver window of standard TCP. This is done because the authors assume a client-server setting where the receiver's access link is typically the bottleneck. The scheme incorporates a delay-based calculation of the expected queue length at the bottleneck, which is quite similar to the calculation in the above delay based protocols, e.g. TCP Vegas. Using a Linux implementation, where TCP flows are classified according to their application's needs, it is shown that a significant improvement in Welzl & Ros Expires April 12, 2011 [Page 8] Internet-Draft LBE Transport Survey October 2010 packet latency can be attained over an unmodified system while maintaining good link utilization. A similar method is employed by Mehra et al. [Meh+03], where both the advertised receiver window and the delay in sending ACK messages are dynamically adapted to attain a given rate. As in [Spr+00], Mehra et al. assume that the bottleneck is located at the receiver's access link. However, the latter also propose a bandwidth-sharing system, allowing to control the bandwidth allocated to different flows, as well as to allot a minimum rate to some flows. Receiver window tuning is also done in [Key+04], where choosing the right value for the window is phrased as an optimization problem. On this basis, two algorithms are presented, binary search -- which is faster than the other one at achieving a good operation point but fluctuates -- and stochastic optimization, which does not fluctuate but converges slower than binary search. These algorithms merely use the previous receiver window and the amount of data received during the previous control interval as input. According to [Key+04], the encouraging simulation results suggest that such an application level mechanism can work almost as well as a transport layer scheme like TCP-LP. Another way of dealing with non-interactive flows, like e.g. web prefetching, is to rate-limit the transfer of such bursty traffic [Cro+98b]. Note that one of the techniques used in [Cro+98b] is, precisely, to have the downloading application adapt the TCP receiver window, so as to reduce the data rate to the minimum needed. The so-called Background Intelligent Transfer Service (BITS) [BITS], implemented in several versions of Microsoft Windows, uses a system of application-layer priority levels for file-transfer jobs, together with monitoring of bandwidth usage of the network interface (or, in more recent versions, of the network gateway connected to the end- host), so that low-priority transfers give way to both high-priority (foreground) transfers and traffic from interactive applications. 5. Orthogonal work Various suggestions have been published for realizing a LBE service by influencing the way packets are treated in routers. One example is the Persistent Class Based Queuing (P-CBQ) scheme presented in [Car+01], which is a variant of Class Based Queuing (CBQ) with per- flow accounting. RFC 3662 [RFC3662] defines a DiffServ per-domain behavior called "Lower Effort". Similar Lower-Effort PDBs have been tested and deployed, at least in research networks [Cho+03], [QBSS]. Welzl & Ros Expires April 12, 2011 [Page 9] Internet-Draft LBE Transport Survey October 2010 Harp [Kok+04] realizes a LBE service by dissipating background traffic to less-utilized paths of the network. This is achieved without changing routers by using edge nodes as relays. According to the authors, these edge nodes should be gateways of organizations in order to align their scheme with usage incentives, but the technical solution would also work if Harp was only deployed in end hosts. It detects impending congestion by looking at delay, similar to TCP Nice [Ven+02], and manages to improve utilization and fairness over pure single-path solutions. An entirely different approach is taken in [Egg+05]: here, the priority of a flow is reduced via a generic idletime scheduling strategy in a host's operating system. While results presented in this paper show that the new scheduler can effectively shield regular tasks from low-priority ones (e.g. TCP from greedy UDP) with only a minor performance impact, it is an underlying assumption that all involved end hosts would use the idletime scheduler. In other words, it is not the focus of this work to protect a standard TCP flow which originates from any host where the presented scheduling scheme may not be implemented. In [Ven+08], Venkataraman et al. propose a transport-layer approach to leverage an existing, network-layer LBE service based on priority queueing. The transport protocol, which they call PLT (Priority- Layer Transport), splits a layer-4 connection into two flows, a high- priority one and a low-priority one. The high-priority flow is sent over the higher-priority queueing class (in principle, offering a best-effort service) using an AIMD, TCP-like congestion control mechanism. The low-priority flow, which is mapped to the LBE class, uses a non TCP-friendly congestion control algorithm. The goal of PLT is thus to maximize its aggregate throughput by exploiting unused capacity in an aggressive way, while protecting standard TCP flows carried by the best-effort class. [Ott+03] proposes simple changes to the AIMD parameters of TCP for use over a network-layer LBE service, so that such "filler" traffic may aggressively consume unused bandwidth. Note that [Ven+08] also considers a mechanism for detecting the lack of priority queueing in the network, so that the non-TCP friendly flow may be inhibited. The PLT receiver monitors the loss rate of both flows; if the high-priority flow starts seeing losses while the low-priority one does not experience 100% loss, this is taken as an indication of the absence of strict priority queueing. Another technique is that used by protocols like NF-TCP [Aru+10b], where a bandwidth-estimation module integrated into the transport protocol allows to rapidly take advantage of free capacity. NF-TCP combines this with an early congestion detection based on Explicit Congestion Notification (ECN) [RFC3168] and RED [RFC2309]; when congestion starts building up, appropriate tuning of a RED queue Welzl & Ros Expires April 12, 2011 [Page 10] Internet-Draft LBE Transport Survey October 2010 allows to mark low-priority (i.e., NF-TCP) packets with a much higher probability than high-priority (i.e., standard TCP) packets, so low- priority flows yield up bandwidth before standard TCP flows. 6. Acknowledgements The authors would like to thank Dragana Damjanovic, Melissa Chavez, Yinxia Zhao and Mayutan Arumaithurai for reference pointers. 7. IANA Considerations This memo includes no request to IANA. 8. Security Considerations This document introduces no new security considerations. 9. Informative References [Aru+10b] Arumaithurai, M., Fu, X., and K. Ramakrishnan, "NF-TCP: A Network Friendly TCP Variant for Background Delay- Insensitive Applications", Technical Report No. IFI-TB- 2010-05, Institute of Computer Science, University of Goettingen, Germany, September 2010, . [BITS] Microsoft, "Windows Background Intelligent Transfer Service", . [Bha+07] Bhandarkar, S., Reddy, A., Zhang, Y., and D. Loguinov, "Emulating AQM from end hosts", Proceedings of ACM SIGCOMM 2007, 2007. [Bia+03] Biaz, S. and N. Vaidya, "Is the round-trip time correlated with the number of packets in flight?", Proceedings of the 3rd ACM SIGCOMM conference on Internet measurement (IMC '03) , pages 273-278, 2003. [Bra+94] Brakmo, L., O'Malley, S., and L. Peterson, "TCP Vegas: New techniques for congestion detection and avoidance", Proceedings of SIGCOMM '94, pages 24-35, August 1994. Welzl & Ros Expires April 12, 2011 [Page 11] Internet-Draft LBE Transport Survey October 2010 [Car+01] Carlberg, K., Gevros, P., and J. Crowcroft, "Lower than best effort: a design and implementation", Workshop on Data communication in Latin America and the Caribbean 2001, San Jose, Costa Rica, Pages: 244 - 265, 2001. [Cha+10] Chan, Y., Lin, C., Chan, C., and C. Ho, "CODE TCP: A competitive delay-based TCP", Computer Communications , 33(9):1013-1029, June 2010. [Cho+03] Chown, T., Ferrari, T., Leinen, S., Sabatino, R., Simar, N., and S. Venaas, "Less than Best Effort: Application Scenarios and Experimental Results", Proceedings of QoS-IP , pages 131-144, February 2003. [Cro+98] Crowcroft, J. and P. Oechslin, "Differentiated end-to-end Internet services using a weighted proportional fair sharing TCP", ACM SIGCOMM Computer Communication Review vol. 28, no. 3 (July 1998), pp. 53-69, 1998. [Cro+98b] Crovella, M. and P. Barford, "The network effects of prefetching", Proceedings of Infocom 1998, April 1998. [Dam+09] Damjanovic, D. and M. Welzl, "MulTFRC: Providing Weighted Fairness for Multimedia Applications (and others too!)", ACM Computer Communication Review vol. 39, no. 3 (July 2009), 2009. [Dev+03] De Vendictis, A., Baiocchi, A., and M. Bonacci, "Analysis and enhancement of TCP Vegas congestion control in a mixed TCP Vegas and TCP Reno network scenario", Performance Evaluation , 53(3-4):225-253, 2003. [Dyk+02] Dykes, S. and K. Robbins, "Limitations and benefits of cooperative proxy caching", IEEE Journal on Selected Areas in Communications 20(7):1290-1304, September 2002. [Egg+05] Eggert, L. and J. Touch, "Idletime Scheduling with Preemption Intervals", Proceedings of 20th ACM Symposium on Operating Systems Principles SOSP 2005, Brighton, United Kingdom, pp. 249/262, October 2005. [Gur+04] Gurtov, A. and S. Floyd, "Modeling wireless links for transport protocols", ACM SIGCOMM Computer Communications Review 34(2):85-96, April 2004. [Hac+04] Hacker, T., Noble, B., and B. Athey, "Improving Throughput and Maintaining Fairness using Parallel TCP", Proceedings Welzl & Ros Expires April 12, 2011 [Page 12] Internet-Draft LBE Transport Survey October 2010 of Infocom 2004, March 2004. [Hac+08] Hacker, T. and P. Smith, "Stochastic TCP: A Statistical Approach to Congestion Avoidance", Proceedings of PFLDnet 2008, March 2008. [Hay10] Hayes, D., "Timing enhancements to the FreeBSD kernel to support delay and rate based TCP mechanisms", Technical Report 100219A , Centre for Advanced Internet Architectures, Swinburne University of Technology, February 2010. [Hen+00] Hengartner, U., Bolliger, J., and T. Gross, "TCP Vegas revisited", Proceedings of Infocom 2000, March 2000. [Key+04] Key, P., Massoulie, L., and B. Wang, "Emulating Low- Priority Transport at the Application Layer: a Background Transfer Service", Proceedings of ACM SIGMETRICS 2004, January 2004. [Kok+04] Kokku, R., Bohra, A., Ganguly, S., and A. Venkataramani, "A Multipath Background Network Architecture", Proceedings of Infocom 2007, May 2007. [Kuo+08] Kuo, F. and X. Fu, "Probe-Aided MulTCP: an aggregate congestion control mechanism", ACM SIGCOMM Computer Communication Review vol. 38, no. 1 (January 2008), pp. 17-28, 2008. [Kur+00] Kurata, K., Hasegawa, G., and M. Murata, "Fairness Comparisons Between TCP Reno and TCP Vegas for Future Deployment of TCP Vegas", Proceedings of INET 2000, July 2000. [Kuz+06] Kuzmanovic, A. and E. Knightly, "TCP-LP: low-priority service via end-point congestion control", IEEE/ACM Transactions on Networking (ToN) Volume 14, Issue 4, pp. 739-752., August 2006, . [Liu+07] Liu, S., Vojnovic, M., and D. Gunawardena, "Competitive and Considerate Congestion Control for Bulk Data Transfers", Proceedings of IWQoS 2007, June 2007. [Liu+08] Liu, S., Basar, T., and R. Srikant, "TCP-Illinois: A loss- and delay-based congestion control algorithm for high- speed networks", Performance Evaluation , 65(6-7):417-440, 2008. Welzl & Ros Expires April 12, 2011 [Page 13] Internet-Draft LBE Transport Survey October 2010 [Mar+03] Martin, J., Nilsson, A., and I. Rhee, "Delay-based congestion avoidance for TCP", IEEE/ACM Transactions on Networking , 11(3):356-369, June 2003. [McC+08] McCullagh, G. and D. Leith, "Delay-based congestion control: Sampling and correlation issues revisited", Technical report , Hamilton Institute, 2008. [Meh+03] Mehra, P., Zakhor, A., and C. De Vleeschouwer, "Receiver- Driven Bandwidth Sharing for TCP", Proceedings of Infocom 2003, April 2003. [Mo+99] Mo, J., La, R., Anantharam, V., and J. Walrand, "Analysis and Comparison of TCP Reno and TCP Vegas", Proceedings of Infocom 1999, March 1999. [Ott+03] Ott, B., Warnky, T., and V. Liberatore, "Congestion control for low-priority filler traffic", SPIE QoS 2003 (Quality of Service over Next-Generation Internet), In Proc. SPIE, Vol. 5245, 154, Monterey (CA), USA, July 2003. [Ott+04] Ott, D., Sparks, T., and K. Mayer-Patel, "Aggregate congestion control for distributed multimedia applications", Proceedings of Infocom 2004, March 2004. [Pra+04] Prasad, R., Jain, M., and C. Dovrolis, "On the effectiveness of delay-based congestion avoidance", Proceedings of PFLDnet , 2004. [QBSS] "QBone Scavenger Service (QBSS)", Internet2 QBone Initiative . [RFC1323] Jacobson, V., Braden, B., and D. Borman, "TCP Extensions for High Performance", RFC 1323, May 1992. [RFC2309] Braden, B., Clark, D., Crowcroft, J., Davie, B., Deering, S., Estrin, D., Floyd, S., Jacobson, V., Minshall, G., Partridge, C., Peterson, L., Ramakrishnan, K., Shenker, S., Wroclawski, J., and L. Zhang, "Recommendations on Queue Management and Congestion Avoidance in the Internet", RFC 2309, April 1998. [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition of Explicit Congestion Notification (ECN) to IP", RFC 3168, September 2001. [RFC3662] Bless, R., Nichols, K., and K. Wehrle, "A Lower Effort Per-Domain Behavior (PDB) for Differentiated Services", Welzl & Ros Expires April 12, 2011 [Page 14] Internet-Draft LBE Transport Survey October 2010 RFC 3662, December 2003. [RFC5348] Floyd, S., Handley, M., Padhye, J., and J. Widmer, "TCP Friendly Rate Control (TFRC): Protocol Specification", RFC 5348, September 2008. [Rew+06] Rewaskar, S., Kaur, J., and D. Smith, "Why don't delay- based congestion estimators work in the real-world?", Technical report TR06-001 , University of North Carolina at Chapel Hill, Dept. of Computer Science, January 2006. [Sha+05] Shalunov, S., Dunn, L., Gu, Y., Low, S., Rhee, I., Senger, S., Wydrowski, B., and L. Xu, "Design Space for a Bulk Transport Tool", Technical Report , Internet2 Transport Group, May 2005. [Spr+00] Spring, N., Chesire, M., Berryman, M., Sahasranaman, V., Anderson, T., and B. Bershad, "Receiver based management of low bandwidth access links", Proceedings of Infocom 2000, pp. 245-254, vol.1, 2000. [Sri+08] Sridharan, M., Tan, K., Bansala, D., and D. Thaler, "Compound TCP: A new TCP congestion control for high-speed and long distance networks", Internet Draft draft-sridharan-tcpm-ctcp , work in progress, November 2008. [Tan+06] Tan, K., Song, J., Zhang, Q., and M. Sridharan, "A Compound TCP approach for high-speed and long distance networks", Proceedings of IEEE INFOCOM 2006, Barcelona, Spain, April 2008. [Ven+02] Venkataramani, A., Kokku, R., and M. Dahlin, "TCP Nice: a mechanism for background transfers", Proceedings of OSDI '02, 2002. [Ven+08] Venkataraman, V., Francis, P., Kodialam, M., and T. Lakshman, "A priority-layered approach to transport for high bandwidth-delay product networks", Proceedings of ACM CoNEXT, Madrid, December 2008. [Wei+05] Weigle, M., Jeffay, K., and F. Smith, "Delay-based early congestion detection and adaptation in TCP: impact on web performance", Computer Communications 28(8):837-850, May 2005. [Wei+06] Wei, D., Jin, C., Low, S., and S. Hegde, "FAST TCP: Motivation, architecture, algorithms, performance", IEEE/ Welzl & Ros Expires April 12, 2011 [Page 15] Internet-Draft LBE Transport Survey October 2010 ACM Transactions on Networking , 14(6):1246-1259, December 2006. Authors' Addresses Michael Welzl University of Oslo Department of Informatics, PO Box 1080 Blindern N-0316 Oslo, Norway Phone: +43 512 507 6110 Email: michawe@ifi.uio.no David Ros Telecom Bretagne Rue de la Chataigneraie, CS 17607 35576 Cesson Sevigne cedex, France Phone: +33 2 99 12 70 46 Email: david.ros@telecom-bretagne.eu Welzl & Ros Expires April 12, 2011 [Page 16]