Floyd, S., TCP and Explicit Congestion Notification. Computer Communication Review, 24(5):10-23, October 1994.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....such as packet marking. It will then be necessary to infer path characteristics by combining sets of local data. Current suggestions for using packet marking for traffic engineering have either been highly conservative such as the IETF s ECN (EXPLICIT CONGESTION NOTIFICATION) proposals [9], or have concentrated on controlling congestion by generating a price based on marked packets received to influence user behaviour [10, 11, 12] These approaches do not directly address the problem of management of traffic within the network. We propose that given the information provided by ....

S. Floyd. TCP and explicit congestion notification. Computer Communication Review, 24(5):10--23, October 1994.

....gentle mode [Flo00] enabled. The two aspects of the RED queue that vary in our simulations are whether the buffering is done in terms of bytes or packets and whether the drop probability is calculated in terms of bytes or packets. Our simulations do not use explicit congestion notification (ECN) [Flo94, RFB01] for marking packets, but instead drop packets to signal incipit congestion, because (i) the number of ECN aware routers in the Internet is currently small and (ii) the marking method does not greatly effect the results . The length of the router buffer is set to 70 packets, and the mean packet ....

Sally Floyd. TCP and Explicit Congestion Notification. Computer Communications Review, 24(5):10--23, October 1994.

....In such a scenario, the limit behavior will become increasingly accurate as the number of users increases. In this paper we extend the model in [10] by incorporating explicitly an additional layer of dynamics, namely the session layer, with TCP in the transport layer and RED gateway [2] with ECN [1] capability in the network layer. As the number of sessions increases, we show that (i) the queue size per session and the workload per session brought in during a round trip time converge to deterministic processes; and (ii) the sessions become asymptotically independent, indicating that the RED ....

....of an idle period is geometrically distributed with parameter P ar (hence with mean 1 P ar ) This attempts to capture the dynamics of connection arrivals, where the interarrival times are reported to be exponentially distributed [9] be a collection of i.i.d. rvs uniformly distributed on [0, 1], and let 1 be the indicator function of the event that a new file object arrives in the time slot [t 1, t 2) for an idle session i. F be a collection of i.i.d. non negative integer valued rvs distributed according to a general probability mass function (pmf) F on 1, 2, ....

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S. Floyd, TCP and explicit congestion notification, Computer Communication Review, vol. 24, no. 5, pp. 10-23, Oct. 1994.

.... that the growing demand for network bandwidth has driven loss rates up across various links in the Internet [23] In order to stem the increasing packet loss rates caused by an exponential increase in network traffic, the IETF is considering the deployment of explicit congestion notification (ECN) [11, 24, 25] along with active queue management techniques such as RED (Random Early Detection) 2, 11] While ECN is necessary for eliminating packet loss in the Internet [10] this paper shows that RED, even when used in conjunction with ECN, is ineffective in preventing packet loss. The basic idea behind ....

.... Internet [23] In order to stem the increasing packet loss rates caused by an exponential increase in network traffic, the IETF is considering the deployment of explicit congestion notification (ECN) 11, 24, 25] along with active queue management techniques such as RED (Random Early Detection) [2, 11]. While ECN is necessary for eliminating packet loss in the Internet [10] this paper shows that RED, even when used in conjunction with ECN, is ineffective in preventing packet loss. The basic idea behind RED queue management is to detect incipient congestion early and to convey congestion ....

S. Floyd. TCP and Explicit Congestion Notification. Computer Communication Review, 24(5):10--23, October 1994.

.... that the growing demand for network bandwidth has driven loss rates up across various links in the Internet [28] In order to stem the increasing packet loss rates caused by an exponential increase in network traffic, the IETF is considering the deployment of explicit congestion notification (ECN) [12, 30, 31] along with active queue management techniques such as RED (Random Early Detection) 3, 14] While ECN is necessary for eliminating packet loss in the Internet [9] we show that RED, even when used in conjunction with ECN, is ineffective in preventing packet loss. The basic idea behind RED queue ....

S. Floyd. TCP and Explicit Congestion Notification. Computer Communication Review, 24(5):10--23, October 1994.

....studies to understand the behavior of Internet applications. In particular, special attention has been paid to modeling TCP friendly protocols in the presence of packet loss, and especially to deriving the throughput of a TCP bulk data transfer. In the absence of timeouts, it was observed in [4, 3, 7] that the throughput of a TCP connection is given by = c ; 1) where c is an empirical constant taking values 1.22 or 1.31, depending on whether the receiver uses delayed acknowledgements or not, R is the round trip time experienced by the packets the connection, and p is the the expected ....

S. Floyd Connections with Multiple Congested Gateways in PacketSwitched Networks Part 1: One-way Traffic. Computer Communication Review, Vol.21, No.5, October 1991, p. 30-47.

....of GREEN against RED and BLUE over the same topology. In the first set of experiments, we simulate all the algorithms using packet dropping rather than marking for congestion notification. In Section V we look at the results with packet marking using Explicit Congestion Notification (ECN) [3]. The queue weight in RED, W q , is set according to the following equation [5] W q = 1 e where C is the link capacity in packets per second. Using a packet size of 1KB and a link capacity of 1Mbps, we set the value of W q to be 0.008. Further in RED, queue sizes tend to stay around Q ....

....quadratically with the number of active flows. This leads to high packet loss rates in heavily congested scenarios such as ours. Although lossrates for GREEN are comparable to RED 5, and queue size stability is achieved, we seek to address this problem throughexplicit congestion notification (ECN) [3] instead of packet dropping as the means for congestion notification. In ECN, the IP header of a packet from an ECN capable host contains a bit that is set by the router when it detects incipient congestion, or in our case, for proactive congestion notification. A host, upon reception of an ECN ....

S. Floyd. TCP and Explicit Congestion Notification. Computer Communication Review, 24(5):10-23, October 1994.

....well known problems characteristic of wireless transmissions. As a result, many modifications and new solutions have been proposed to improve TCP s performance, such as forward error correction schemes, retransmissions at the link layer, split connections like MTCP [11] Explicit Loss Notification [7], link layer TCPAware like Snoop [4] Performance Enhancing Proxies [5] Indirect TCP (I TCP) 2] MAITE [1] etc. Available performance evaluations of TCP over wireless networks are usually incomplete, meaning that the most important TCP versions and the most important solutions are not studied ....

S. Floyd. TCP and Explicit Congestion Notification. Computer Communication Review, Vol. 24, No. 5:10--23, 1994.

....be maintained manually, or by a separate routeing protocol as discussed in Section 2.4. Packet delivery is best effort, with the TOS byte providing only a hint to the router concerning the packet s desired treatment. 2.1. 2 Explicit Congestion Notification ECN (EXPLICIT CONGESTION NOTIFICATION) Floyd94,RFC2481] is a proposed extension to IP and TCP. It allows the network to provide the user with extra feedback concerning its congestion state using two bits in the IP TOS byte. These indicate firstly whether or not the originator of the packet is ECN aware, and secondly whether or not this packet ....

....based on the idea that when the TCP sender notices congestion, it will multiplicatively decrease its transmission rate or back off. Congestion is traditionally detected through loss of a packet, but alternatives where packets are marked to signal the onset of congestion are under consideration [Floyd94,RFC2481, Throughout this dissertation it is noted that loss of a packet might not simply be the packet being dropped in the network either through congestion or error at a lower layer, but also its excessive delay, detected through timeout. Laevens00] as was discussed in Section 2.1.2. The ....

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S. Floyd. TCP and Explicit Congestion Notification. Computer Communication Review, 24(5):10--23, October

....that can cause retransmission timeouts. One possible extension to SHRED is to incorporate an indicator in the cwnd hint when a flow is nearly finished and to avoid dropping the last few packets of a transfer. A second area of future work is integrating SHRED with Adaptive RED [10] and ECN [7]. SHRED combined with Adaptive RED should operate well over a wider range of traffic loads and SHRED with ECN should result in even fewer drops for Web traffic and should further improve Web response times. The effects of AQM on Web traffic performance is dependent on number of Web traffic ....

S. Floyd. TCP and Explicit Congestion Notification. Computer Communication Review, Oct. 1994.

....is higher or lower than available capacity. Furthermore, this 7 feedback about successfully received data and observed congestion needs to be communicated to the sender in some way. The sender s CM uses standard congestion indicators packet losses and Explicit Congestion Notification (ECN) [9, 26] bits set by routers and echoed by the receiver. We now address three issues: feedback frequency, feedback mechanism, and exponential aging to perform well when feedback frequency is lower than optimal. 2.2.1 Feedback frequency TCP s feedback mechanism using ACKs provides the sender with ....

FLOYD, S. TCP and Explicit Congestion Notification. Computer Communications Review 24, 5 (Oct. 1994).

....[14] or RED PD [11] High bandwidth ows could be detected and monitored as in [11] or per packet drop probabilities could be computed based on both the bandwidth used by the ow as well as the RTT. Perhaps the largest bene t of active queue management techniques is in marking packets, using ECN [4], as an indicator of network congestion, rather than dropping them. A new version of Chardonnay, called Chablis, that uses marking instead of dropping, has shown great promise in further enhancing network performance, while even further increasing fairness. We are currently in the process of ....

S. Floyd. TCP and Explicit Congestion Notication. Computer Communication Review, Oct. 1994.

....and LEO satellite links) lossy links (Wireless networks) asymmetric paths (Hybrid satellite networks) and others, are becoming widely embedded in the Internet. Many researchers have studied by experimentations [4, 6, 8, 10, 11, 13, 23] analytical modeling [5, 17, 29, 30, 35] and simulations [1, 16, 18, 25, 24, 33, 41], the performance of TCP in this new environment. Some of the works have focused on the performance of TCP on a general path of a certain characteristic. An example of such works are those aiming to improve the loss recovery capacity of TCP [19, 33, 34] Others have analyzed the protocol in a ....

....this reduces the size of queues in the nodes and thus the end to end delay. Further, the avoidance of losses avoids retransmissions and then gives better service for interactive applications. As solutions, we nd the Vegas version of TCP [9] and the Explicit Congestion Notication (ECN) proposed in [18]. In Vegas, the RTT of the connection and the window size are used to compute the number of packets in network buoeers. The window is decreased when this number exceeds a certain threshold. With ECN, an explicit signal is used by the routers to indicate congestion to TCP sources rather than ....

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S. Floyd, iTCP and Explicit Congestion Noticationj, Computer Communication Review, Vol.24, No.5, October 1994.

....to detect incipient congestion early and convey congestion notification to the end hosts, allowing them to back off before queues overflow and packet loss occur. One of the more promising active queue management schemes being proposed for deployment in the network is RED (Random Early Detection) [7]. A RED gateway maintains an exponentially weighted moving 3 10Mbs 10Mbs 10Mbs 10Mbs 10Mbs 10Mbs 45Mbs 45Mbs RED: MINth=20KB, MAXth=80KB, Qsize=80KB n5 n6 n7 n8 n4 n3 n2 n1 n0 5ms 5ms 5ms 5ms Figure 1: Network Topology average of the queue length as a means for detecting ....

....n5 n6 n7 n8 n4 n3 n2 n1 n0 5ms 5ms 5ms 5ms Figure 1: Network Topology average of the queue length as a means for detecting congestion. When the average queue length exceeds a minimum threshold (min th ) packets are dropped or marked with an explicit congestion notification (ECN) bit [7, 22, 23] at random using a calculated probability. When a TCP sender receives congestion notification in the form of an ECN mark, it halves its congestion window as it would if it had detected a packet loss. The probability that a packet arriving at the RED queue is either dropped or marked depends upon, ....

S. Floyd. TCP and Explicit Congestion Notification. Computer Communication Review, 24(5):10--23, October 1994.

....rst in rst out (FIFO) packet queue shared by all ows. The gateway estimates the overload by monitoring the queue length and starts discarding packets when the queue space is exhausted. This discipline, referred to as DropTail, has been shown to distribute losses among connections arbitrarily [17], to be unfair and to penalize bursty connections. In order to address the de ciencies of DropTail, alternative queue management algorithms have been proposed. One 1 Flows can be shut o by the presence of a very aggressive ow that causes congestion. 2 Backpressure can have a cascading e ect, ....

S. Floyd and V. Jacobson. On trac phase eects in packet-switched gateways. Computer Communication Review, 1991.

....4 Evaluation of ARED In this section, we evaluate ARED by comparing it against drop tail, RED, and BLUE under a wide range of traffic conditions. Drop tail serves as a baseline case in which no active queue management mechanism is employed. All traffic sources are equipped with ECN support [6]. 3 All the simulations were performed in ns 2 [27] which provides accurate packet level implementation for various network protocols, such as TCP UDP, and various buffer management and scheduling algorithms, such as droptail and RED. All algorithms used in the simulation, except ARED and BLUE, ....

....ECN is implement using two bits of TOS field in the IP header and two bits of currently reserved flags field in the TCP header. When a network router experiences congestion, it explicitly signals the sources by setting the bits in the header, instead of dropping their packets. It has been shown in [6] that ECN successfully prevents packet loss. 8 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Throughput( 0 50 100 150 BLUE DropTail RED ARED Figure 4: The performance of drop tail, RED, and ARED. The x axis is the ratio of throughput to link bandwidth, and the y axis is the average queue length in ....

S. Floyd. TCP and explicit congestion notification, Computer Communication Review, Vol. 24, No.5, October 1994, pp. 10--23.

....see the next section) and waiting for the corresponding acknowledgment (ACK) For each ACK received during slow start cwnd is increased by 1 segment. The algorithm ends when congestion is detected (either inferred from observing packet drops or from Explicit Congestion Notification (ECN) Flo94, RF99] or when cwnd reaches the advertised window. 100 1000 10000 100000 1e 06 1e 07 1e 08 1e 09 Dec 1998 May 1999 Oct 1999 Feb 2000 Advertised Window (bytes) Month Month Mean Median Minimum Maximum Figure 12: Advertised windows used by web clients over time. Figure 12 shows ....

....of the first two duplicate ACKs [BPS 98, LK98, ABF00] This will trigger additional duplicate ACKs (if appropriate) and therefore fast retransmit will be invoked. However, the above algorithm does not aid short connections that have no new data to transmit in response to duplicate ACKs. ECN [Flo94, RF99] provides a possible mitigation to this problem. Rather than dropping the segments, the network could simply mark them as experiencing congestion. This would allow the connection to quickly complete without requiring a costly retransmission timeout. Another possibility is for TCP to detect ....

Sally Floyd. TCP and Explicit Congestion Notification. Computer Communications Review, 24(5):10-- 23, October 1994.

....of network efficiency as sources and routers continually generate and forward packets which are then dropped. In order to address the steady rise in packet loss rates in the Internet, the Internet Engineering Task Force (IETF) is considering the deployment of Explicit Congestion Notification (ECN) [23, 55] and active queue management [4, 26] as a means to prevent packet loss. The idea behind ECN is to give the network the ability to explicitly signal TCP sources of congestion and to have the TCP sources reduce their transmission rates in response to the signal. Since TCP sources currently only ....

....is dropped at the router and when the source actually detects the loss. In the meantime, a large number of packets may be dropped as sources continue to transmit at a rate that the network cannot support. Because of this, the IETF is advocating the use of explicit congestion notification (ECN) [23, 55] and active queue management as a means to prevent packet loss. The idea behind ECN is to decouple packet loss from congestion notification. In this proposal, ECN is implemented using two bits of the type of service DS field of the IP header and two bits of the currently reserved flags field of ....

[Article contains additional citation context not shown here]

S. Floyd. TCP and Explicit Congestion Notification. Computer Communication Review, 24(5):10--23, October 1994.

....is higher or lower than available capacity. Furthermore, this feedback about successfully received data and observed congestion needs to be communicated to the sender in a timely manner. The sender s CM uses standard congestion indicators packet losses and Explicit Congestion Noti cation (ECN) [10, 23] bits set by routers and echoed by the receiver. We now address three issues: feedback frequency, feedback mechanism, and exponential aging to perform well when feedback frequency is infrequent. 4.2.1 Feedback frequency TCP s feedback mechanism using ACKs provides the sender with feedback ....

Floyd, S. TCP and Explicit Congestion Notication. Computer Communications Review 24, 5 (Oct. 1994).

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Floyd, S., TCP and Explicit Congestion Notification. Computer Communication Review, 24(5):10-23, October 1994.

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Sally Floyd, TCP and Explicit Congestion Notification," Computer Communications Review, Vol. 24, No. 5, October 1994, pp. 10-23.

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Floyd, S., TCP and Explicit Congestion Notification. Computer Communication Review, 24(5):10-23, October 1994.

....in the past for best effort data networks will not work satisfactorily for multi class IP networks. Recognizing the need for a more direct feedback of congestion information, the Internet Engineering Task Force (IETF) has come up with Explicit Congestion Notification (ECN) method for IP routers [1, 2]. A bit in the IP header is set when the routers are congested. ECN is much more powerful than the simple packet drop indication used by existing routers and is more suitable for high distance bandwidth networks. In this paper we present some enhancement to ECN based on multilevel ECN. Our results ....

Sally Floyd, TCP and Explicit Congestion Notification," Computer Communications Review, Vol. 24, No. 5, October 1994, pp. 10-23.

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Sally Floyd, TCP and Explicit Congestion Notification," Computer Communications Review, Vol. 24, No. 5,October 1994, pp. 10-23.

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S. Floyd, TCP and explicit congestion notification, Computer Communication Review 24(5) (1994) 10--23.

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