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Topic: Network congestion avoidance

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	Network congestion - Wikipedia, the free encyclopedia
		In data networking and queueing theory, network congestion occurs when incremental increases in offered load lead either only to small increases in network throughput, or to an actual reduction in network throughput.
		Network protocols which use aggressive retransmissions to compensate for packet loss tend to keep systems in a state of network congestion even after the initial load has been reduced to a level which would not normally have induced network congestion.
		Modern networks use congestion control and network congestion avoidance techniques to try to avoid congestion collapse.
	en.wikipedia.org /wiki/Network_congestion (227 words)

	RFC 2001 (rfc2001) - TCP Slow Start, Congestion Avoidance, Fast Retransmit
		The former is based on the sender's assessment of perceived network congestion; the latter is related to the amount of available buffer space at the receiver for this connection.
		Congestion avoidance and slow start require that two variables be maintained for each connection: a congestion window, cwnd, and a slow start threshold size, ssthresh.
		Congestion avoidance dictates that cwnd be incremented by segsize*segsize/cwnd each time an ACK is received, where segsize is the segment size and cwnd is maintained in bytes.
	www.faqs.org /rfcs/rfc2001.html (1753 words)

	New Congestion Avoidance algorithm
		Congestion window is 15 packets but there is one packet that has not been acknowledged yet (packet number 14); then, for TCP, there is one packet traveling through the network.
		The congestion window is set to 7 packets that is exactly one packet more that the number of packets we have outstanding in the pipe (packets number 29, 30, 31, 32, 33, and 34).
		Congestion avoidance is the TCP's steady state algorithm that represent TCP behavior by the TCP response function studied by Sally Floyd, Matthew Mathis, Jeffrey Semke and Jamshid Mahdavi.
	opalsoft.net /qos/TCP-30.htm (2098 words)

	Congestion Avoidance and Control
		Congestion can be understood as the presence of more incoming traffic than network nodes can handle and results in full queues, long delays, and dropped packets.
		Congestion, then, must be a matter of concern in reliable transport protocols, which must strike a balance between congestion and channel underutilization, a problem with perhaps more intuitive drawbacks.
		For a lost packet in slow-start, the congestion window is set to 1 and slow-start begins anew, while a loss during congestion avoidance will cause the congestion window to decrease by a factor of 2.
	www.auburn.edu /~caseykl/research/red/congestion.htm (539 words)

	LWN: Pluggable congestion avoidance modules
		The congestion avoidance problem has grown as well, to the point that there are several competing algorithms seeking to provide the best TCP performance while being fair to other network users.
		As a way of helping those experimenting with congestion avoidance and eliminating the need to patch the TCP code directly, Stephen Hemminger has posted a new infrastructure which allows congestion avoidance algorithms to be written as pluggable modules.
		Congestion avoidance algorithms try to account for the slowest link serving a connection with a "congestion window," which is the maximum amount of data which can be in transit without an acknowledgment from the remote end.
	lwn.net /Articles/128681 (1732 words)

	Network congestion avoidance: Definition and Links by Encyclopedian.com - All about Network congestion avoidance (Site not responding. Last check: 2007-11-06)
		Network congestion avoidance is a process used in networks to avoid Network congestion[?].
		The fundamental problem is that all network resources are limited, including router processing time and link bandwidth.
		There are many different network congestion avoidance processes, since there are a number of different trade-offs available.
	www.encyclopedian.com /ne/Network-congestion-avoidance.html (475 words)

	Congestion Avoidance and Control
		Packet loss is almost always due to congestion and a timeout is almost always due to a lost packet, then a timeout is almost always a signal that the network is congested.
		If network load is measure by average queue length over fixed intervals of time near the round-trip time, an uncongested network can be modeled by saying that queue length changes slowly compared to the sampling time; i.e.
		The network announces, via a dropped packet, when demand is excessive but says nothing if a connection is using less than its fair share; thus a connection has to increase its bandwidth utilization to find out the current limit.
	opalsoft.net /qos/TCP-20.htm (1737 words)

	Congestion Control Mechanisms (Linktionary term)
		Congestion is a problem that occurs on shared networks when multiple users contend for access to the same resources (bandwidth, buffers, and queues).
		In fact, a packet-switched network is often referred to as a "network of queues." A characteristic of packet-switched networks is that packets may arrive in bursts from one or more sources.
		Congestion also occurs at routers in core networks where nodes are subjected to more traffic than they are designed to handle.
	www.linktionary.com /c/congestion.html (3782 words)

	Transmission Control Protocol - Wikipedia, the free encyclopedia
		Applications send streams of 8-bit bytes to TCP for delivery through the network, and TCP divides the byte stream into appropriately sized segments (usually delineated by the maximum transmission unit (MTU) size of the data link layer of the network the computer is attached to).
		RFC 2581, TCP Congestion Control, one of the most important TCP related RFCs in recent years, describes updated algorithms to be used in order to avoid undue congestion.
		In 2001, RFC 3168 was written to describe explicit congestion notification (ECN), a congestion avoidance signalling mechanism.
	en.wikipedia.org /wiki/Transmission_Control_Protocol (2436 words)

	ipedia.com: Network congestion Article (Site not responding. Last check: 2007-11-06)
		Network protocols which use aggressive retries to compensate for packet loss tend to keep systems in a state of network congestion even after the initial load has been reduced to a level which would not normally have induced network congestion.
		The stable state with low throughput is known as congestion collapse, a term which was first defined by John Nagle in RFC 896, written in 1984, when he identified problems with early implementations of the TCP network protocol over parts of the very early Internet.
		Congestion collapse is a condition where a system such as a data network has settled under load into a state where traffic demand is high but little useful throughput is available, with high levels of packet loss, delay, and delay variation.
	www.ipedia.com /network_congestion.html (361 words)

	Analysis of the Increase/Decrease Algorithms for Congestion Avoidance in Computer Networks (Site not responding. Last check: 2007-11-06)
		Congestion avoidance mechanisms allow a network to operate in the optimal region of low delay and high throughput, thereby, preventing the network from becoming congested.
		This is different from the traditional congestion control mechanisms that allow the network to recover from the congested state of high delay and low throughput.
		Both congestion avoidance and congestion control mechanisms are resource management problems in which the system senses its state and feeds this back to its users who adjust their controls.
	www.cse.wustl.edu /~jain/papers/cong_av.htm (234 words)

	Congestion Avoidance and Control (Site not responding. Last check: 2007-11-06)
		One-line summary: Seven new algorithms were put into TCP to make sure that it adhered to the "packet conservation" principle; these congestion avoidance and control algorithms are motivated and described.
		Packet conservation principle: for stability in a network (especially in the face of congestion), a host in equilibrium should only inject one packet into the network for every packet removed from the network, leading to "self-pacing".
		If no congestion, window sizes need to increase (as no indication from network that there is no congestion).
	swig.stanford.edu /pub/summaries/networks/cong_avoid.html (529 words)

	The 3 key main ideas are that the emergence of data computer networks has provided many examples to illuminate the ...
		With congestion avoidance mechanisms, a network can operate in the optimal region of low delay and high throughput (that is at the knee of its throughput/load curve), thereby avoiding being congested.
		The paper focuses on first-order increase/decrease algorithms for congestion avoidance, using metrics such as efficiency, fairness, convergence time, and size of oscillation to compare them.
		By comparison, the authors are able to identify the sort of increase/decrease congestion algorithm that will help the network settle to an efficient and fair state regardless of its starting state.
	zoo.cs.yale.edu /classes/cs633/Reviews/CJ89.sl354.htm (418 words)

	A Framework for Cooperative Congestion Avoidance in TCP Networks
		Current congestion control schemes rely on implicit network feedback from the network to signal congestion events, and they are inherently reactive.
		By keeping a network host informed of upcoming usage by its peers, we give that host the opportunity to decrease its contribution to potential congestion by reducing its sending rate or by signaling the user's application.
		The proactive role offers benefits to both the network and the network hosts that include a reduction of congestion events on the network and improved fairness of capacity sharing between peers.
	www.cs.dal.ca /news/def-1139.shtml (234 words)

	Method and apparatus for packet network congestion avoidance and control - Patent 6477143 (Site not responding. Last check: 2007-11-06)
		When possible future network congestion is predicted, the application of the methods and apparatus of the invention is operative to prevent the development of future congestion altogether or at least to limit the evolving severity level that such future congestion would have otherwise reached.
		When possible future network congestion is predicted, the application of the methods and apparatus described herein is operative to prevent the development of future congestion altogether or at least to limit the evolving severity level that such future congestion would have otherwise reached.
		Other network pathways leading to various nodes 416 are also provided In the illustrated embodiment, intermediate node 418 controls the transmission rate of a network node 410 that is sending information to node 412 and is using pathway 422 in the direction indicated by arrow 424 for the transfer of the information.
	www.freepatentsonline.com /6477143.html (9371 words)

	Congestion avoidance in high-speed network carrying bursty traffic (EP0453355B1)
		A data communication network subject to bursty traffic employs a bandwidth allocation scheme to avoid congestion.
		When the request reaches the destination, it is returned along the same path to the source, and the source then employs the marked-down allocation to select the rate used to send the burst of data.
		The allocation for this source node remains in effect for a limited time, depending upon the amount of data to be sent in the burst, then returns to a "residual" level.
	www.delphion.com /details?pn=EP00453355B1 (355 words)

	Packet Drop Avoidance for High-speed network transmission protocol
		As network bandwidth continues to grow and longer paths are used to exchange large scientific data between storage systems and GRID computation, it has become increasingly obvious that there is a need to deploy a packet drop avoidance mechanism into network transmission protocols.
		Current end-to-end congestion avoidance mechanisms used in Transmission Control Protocol (TCP) have worked well on low bandwidth delay product networks, but with newer high-bandwidth delay networks they have shown to be inefficient and prone to unstable.
		These changes come from a variety of new network applications that are being developed to take advantage of the increased network bandwidth.
	repositories.cdlib.org /lbnl/LBNL-53920 (233 words)

	Binary Feedback Congestion Avoidance (Site not responding. Last check: 2007-11-06)
		Exploration of congestion as an "end to end visible property" of connectionless networks, and of a way to aggregate intermediate-router congestion information (though just 1 bit) by piggybacking on ACKs.
		For small numbers of users on unloaded network, fig 13 seems to show some nontrivial oscillation, indicating that maybe some kind of additional hysteresis would be useful after all.
		Jacobson proposes deducing congestion from timeouts instead, since that info is already available to all packet networks.
	swig.stanford.edu /pub/summaries/networks/binary_fdbk.html (634 words)

	Novell Documentation: Novell Internet Access Server 4.1 - Network Congestion Control Management (Site not responding. Last check: 2007-11-06)
		Congestion avoidance procedures are initiated before the network approaches a moderate congestion state.
		Congestion recovery procedures are usually initiated when the network begins to drop frames because of severe congestion.
		To recover from severe congestion, networks can discard DE-set frames and frames in excess of the CIR agreed upon at subscription time.
	www.novell.com /documentation/nias41/frrlyenu/data/hgpqund6.html (218 words)

	Review of <<Congestion Avoidance and Control>>
		With the explosive growth of computer network, as well as the problem of transport protocol implementation, internet comes severe congestion problems.
		This paper briefly describes several new algorithms dealing with the congestion problem and their implementation in the 4BSD TCP.
		The main idea is that gateway have enough information to control sharing and fair allocation, so it can detect congestion early and small adjustment to the senders’ window can cure it.
	www.cs.berkeley.edu /~hling/courses/cs262a/congestion_control.htm (279 words)

	Paper review: Congestion Avoidance and Control (Site not responding. Last check: 2007-11-06)
		Congestion of a TCP connection is problematic and nearly brought down Internet on October, 1986.
		The packet conservation principle says that for a connection to be in equilibrium and for a packet flow to be conservative, a new packet isn't put into the network until an old packet leaves.
		To deal with congestion, the paper advances the idea of additive increase and multiplicative decrease of the window size.
	zoo.cs.yale.edu /classes/cs633/Reviews/Jac88.hq9.html (330 words)

	Papers in Congestion Control
		NETBLT (NETwork BLock Transfer) is a transport level protocol intended for the rapid transfer of a large quantity of data between computers.
		Effective multiclass service disciplines allow networks to focus resources on performance sensitive applications, while effective pricing policies allow us to spread the benefits of multiple service classes around to all users, rather than just having these benefits remain exclusively with the users of applications that are performance sensitive.
		One congestion avoidance technique is feedback flow control, in which sources adjust their transmission rate in response to congestion signals sent (implicitly or explicitly) by network gateways.
	www.ecse.rpi.edu /Homepages/shivkuma/research/cong-papers.html (3147 words)

	[No title]
		It has become clear that the TCP congestion avoidance mechanisms [RFC2001], while necessary and powerful, are not sufficient to provide good service in all circumstances.
		Others may deliberately be implemented with congestion avoidance algorithms that are more aggressive in their use of bandwidth than other TCP implementations; this would allow a vendor to claim to have a "faster TCP".
		The granularity of flows for congestion management is, at least in part, a policy question that needs to be addressed in the wider IETF community.
	www.ietf.org /rfc/rfc2309.txt (4344 words)

	Computer Science, Rutgers University: (Site not responding. Last check: 2007-11-06)
		However, end-to-end congestion control algorithms alone are incapable of preventing the congestion collapse and unfair bandwidth allocations created by applications which are unresponsive to network congestion.
		NBP relies on the exchange of feedback between routers at the borders of a network in order to detect and restrict unresponsive traffic flows before they enter the network.
		Simulation results show that NBP effectively eliminates congestion collapse, and that, when combined with fair queueing, NBP achieves approximately max-min fair bandwidth allocations for competing network flows.
	www.cs.rutgers.edu /cs/general/colloquia/2000-2001/9.24.99.html (135 words)

	Modeling TCP Behavior in a Differentiated Services Network - Yeom, Reddy (ResearchIndex) (Site not responding. Last check: 2007-11-06)
		Congestion avoidance technique in TCP makes it difficult for flows to achieve performance goal in differentiated services network.
		Our models are developed to estimate TCP throughput as functions in terms of the reservation rate, the probability of packet drop and the round-trip time.
		327 The Macroscopic Behavior of the TCP Congestion Avoidance Alg..
	citeseer.ist.psu.edu /yeom99modeling.html (609 words)

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