Forward Congestion Research Articles

An Improved Congestion Control Algorithm based on SCPS-TP Protocol

mainly in Vegas agreement by predicting the real-time changes of RTT is to adjust the congestion window, is likely to lead to network to link data congestion has not taken place, but because in the process of reverse echo is sure that the information congestion resulting in RTT value, detection mechanism will default to forward congestion and reduce the congestion window. In order to avoid this situation, RTT acquisition is modified to solve the problem that the forward congestion window may be reduced due to the reverse link congestion, so that the congestion window can be adjusted more accurately, and the network prediction mechanism is added to carry out joint adjustment scheme for the congestion window. Multiple round trip delays are stored at the sending end, and the network information obtained by the original sendRTT is further classified and analyzed through the analysis and processing of the delay by the algorithm, so as to obtain the status of the link more accurately and make accurate adjustments to the congestion window.

Improvement of TCP Vegas algorithm based on forward direction delay

Satellite networks transmit data through the space communications protocol specification transport protocol and uses transmission control protocol (TCP) Vegas as the congestion control algorithm. However, TCP Vegas does not have a suitable solution for the asymmetric bandwidth of satellite networks. Therefore, the reverse link of asymmetric bandwidth frequently causes congestion in satellite networks. This issue is addressed by reducing the congestion window with the occurrence of reverse link congestion, thereby simultaneously reducing the forward link throughput of the satellite network. In this study, a forward congestion control algorithm for the TCP Vegas algorithm based on time delay, which is called Vegas_FDD (forward direction delay), is proposed to mitigate congestion by dividing it into different types (forward and backward) and to improve network bandwidth utilisation. The suitability and effectiveness of the proposed algorithm are verified through simulation on Opnet software.

The DDTCI switch algorithm for ABR traffic control in ATM networks

For the issue of flow control for Available Bit Rate (ABR) traffic in ATM network, a new improved Explicit Rate (ER) algorithm named Dynamic Double Threshold Congestion Indication (DDTCI) algorithm is presented based on the Explicit Forward Congestion Indication (EFCI) Current Cell Rate (CCR) algorithm and Relative Rate (RR) algorithm. Different from the early ER algorithm, both the high-level and the low-level threshold is dynamically changing according to the state of the bottleneck node. We determinate the congestion state with the information of the two dynamic threshold, and control the cell rate of the source by feed back mechanism. Except for the well performance in both link utilization and fairness in distribution of available bandwidth, the improved algorithm can alleviate the fluctuation of sending rate dramatically. The mechanism is modeled by a fluid model, and the useful expressions are derived. Simulation results show up our conclusion.

자기 유사한 트래픽을 이용한 ATM 스위치의 ABR 혼잡제어 알고리즘의 성능분석

네트워크를 설계하고 서비스를 구현하는데 있어서 중요한 변수중의 하나는 트래픽의 특성을 파악하는 것이나 기존의 트래픽 예측과 분석은 포아송(Poisson) 또는 마코비안(Markovian)을 기본으로 하는 모델을 사용하였다. LAN, WAN 및 VBR(Variable Bit Rate) 트래픽 특성에 관한 최근의 실험적 연구들은 기존의 포아송 가정에 의한 모델들이 네트워크 트래픽의 장기간 의존성 및 자기 유사한 특성들을 과소평가 함으로써 실제 트래픽의 특성을 제대로 나타낼 수 없다는 것을 지적해 왔고 최근 실제 트래픽과 유사한 모델로서 자기 유사한 특성을 이용한 접근법이 대두되고 있다. 따라서, 본 논문에서는 실제 트래픽과 유사한 자기 유사 데이터 트래픽을 백그라운드 부하로 발생시켜 기존의 ABR (Available Bit Rate) 혼잡제어 알고리즘 중 대표적인 EFCI(Explicit Forward Congestion Indication), EPRCA(Enhanced Proportional Rate Control Algorithm), ERICA(Explicit Rate Indication for Congestion Avoidance), NIST(National Institute of Standards and Technology) 스위치 알고리즘이 버스트한 트래픽에 대해 효율적으로 반응하는지를 ACR(Allowed Cell Rate), 버퍼 사용율, 셀 폐기율, 전송효율 등으로 나누어 분석을 하였다. One of the most important matters in designing network and realizing service, is to grip on the traffic characteristics. Conventional traffic prediction and analysis used the models which based on the Poisson or Markovian. Recently, experimental research on the LAN, WAN and VBR traffic properties have been pointed rut that they weren't able to display actual real traffic specificities because the models based on the Poisson assumption had been underestimated the long range dependency of network traffic and self-similar peculiarities, it has been lately presented that the new approach method using self-similarity characteristics as similar as the real traffic models. Therefore, in this paper, we generated self-similar data traffic like real traffic as background load. On the existing ABR congestion control algorithm, we analyzed by classify into ACR, buffer utilization. cell drop rate, transmission throughput with the representative EFCI, ERICA, EPRCA and NIST twitch algorithm to show the efficient reaction about the burst traffic.

TCP Explicit Congestion Notification over ATM-UBR: A Simulation Study

The enhancement of Transmission Control Protocol’s (TCP’s) congestion control mechanisms using Explicit Congestion Notification (ECN) over Asynchronous Transfer Mode (ATM) networks is overviewed. TCP’s congestion control is enhanced so that congestion is indicated by not only packet losses as is currently the case but an agent implemented at the ATM network’s edge as well. The novel idea uses EFCI (Explicit Forward Congestion Indication) bits (available in every ATM cell header) to generalize the ECN response to the UBR (Unspecified Bit Rate) service, notify congestion, and adjust the credit-based window size of the TCP. The authors’ simulation experiments show that TCP ECN achieves significantly lower cell loss, packet retransmissions, and buffer utilization, and exhibits better throughput than (non-ECN) TCP Reno.

A performance prediction model for FECN rate-based flow control in ATM networks: a case study

Forward explicit congestion notification (FECN) plays an important role in rate-based flow control for asynchronous transfer mode (ATM) networks. This paper presents a case study in predicting and evaluating the performance of the FECN flow control. Two network models are under investigation; the first model assumes that a target ATM network has no traffic congestion, while the second model assumes that the network has exhibited heavy congestion. For the light-loaded network, we first estimate the number of cells issued by the source during each time interval and then calculate the required number of resource management (RM) cells in the same time interval. A general analytical form to predict allowable cell rate (ACR) at the source can be finally derived. For the heavy-loaded network, RM cells may be delayed and data cells may be discarded due to severe network congestion. Hence, to derive a general form of ACR, we need to estimate the round-trip time (RTT) of RM cells based on the queuing length of the traversed ATM switches. For the purpose of validation, we perform simulation through OPNET. The performance parameters of our interest include the ACR, the RTT of RM cells, the throughput and the cell loss ratio. We have shown that the differences between the analytical and the simulation results are quite small not only in the ACR adjusting rate, but also in the prediction of the system throughput, the CLR, and the RTT of RM cells.

Interoperability of EFCI and ERICA ATM switches for ABR services with VS/VD enhancements

To improve network bandwidth utilization, the asynchronous transfer mode (ATM) forum has standardized available bit rate (ABR) service which requires a number of parameters to be negotiated during connection setup. MCR is the minimum cell rate guaranteed by the network and can be used to provide an acceptable quality of service for applications. In this study, explicit forward congestion indication (EFCI) and explicit rate indication for congestion avoidance (ERICA) switches were adopted in a current transitional ATM network. First, we transfer traffic with ABR service to realize the interoperability of EFCI and ERICA switches. Second, we implemented the virtual source/virtual destination (VS/VD) feature into a homo or heterogeneous EFCI and ERICA switch environment in order to observe the performance. From the simulation results, a smaller queue length was obtained after the VS/VD was introduced into the EFCI and ERICA switches. The high link data transfer utilization with ABR service was also obtained.

Correctness and performance of the ATM ABR rate control scheme

We study both correctness and performance of the source/destination protocols of the available bit rate (ABR) service in asynchronous transfer mode (ATM) networks. Although the basic protocol for rate-based congestion management is relatively simple, the protocol specification has to cope with several “real-world” cases such as failures and delayed/lost feedback which introduce complexity. Rigorous proof of the correct functioning of the protocol based on a formal specification is necessary. We use a formal model to show that the ABR source/destination protocol is free of livelocks, so that under all conditions both resource management (RM) and data cells will be transmitted. Furthermore, if there are data cells available, then the ABR protocol is deadlock free; otherwise, the system goes to a desirable sleep state waiting for data cells, as long as certain parameters are set appropriately at connection setup. We also show that the network options of explicit forward congestion indication (EFCI) and explicit rate (ER) interoperate correctly. In addition to ensuring the correct functioning of the protocol, it is essential that pathological situations do not result in very poor performance, which we view as another form of “incorrect operation”. We derive conditions that ensure that the source's allowed cell rate (ACR) is stable in the presence of delayed or lost feedback RM cells. We arrive at bounds on the number of consecutive RM cell losses tolerated while the ACR rate remains stable. We also provide an asymptotic estimate of ACR and the allowable RM cell loss probability to ensure that ACR is stable, statistically. The ABR protocol contributes to the feedback delay in two ways: the source delay of sending out the probe forward RM (FRM) cells and the destination delay of turning around the backward RM (BRM) cell. We provide a worst-case analysis of the delay in turning around RM cells at the destination station and the worst-case inter-departure time of FRM cells from the source.

Performance evaluation of the rate-based flow control mechanism for ABR service

In this paper we investigate the performances of the EFCI?based (Explicit Forward Congestion Indication) and ER?based (Explicit Rate) algorithms for the rate?based flow control of the ABR (Available Bit Rate) traffic in an ATM network. We consider the case of two switches in tandem. We present several definitions of a bottleneck, and provide conditions that determine whether the first, the second or both queues are bottleneck. We show that it is not necessarily the queue with the slowest transmission rate in which congestion actually occurs. We derive analytic formulas for the maximum queue length. We compare our results to those obtained by approximating a network by a simpler one, containing only the bottleneck switch. We show that the maximum queue lengths under the approximating approach may largely underestimate the ones obtained in the real network.

Interoperability of EFCI and ER switches for ABR services in ATM networks

With the advances in switching technologies, explicit rate (ER) switches are becoming popular since they perform better than explicit forward congestion indication (EFCI) switches. In the transitional period, EFCI and ER switches may coexist in the same ATM network. Hence, the efficiency of various ER schemes should be reevaluated in the mixed EFCI-ER environment, not only in the homogeneous ER environment. Also, some important implications are observed in the heterogeneous environments. Because the location of an ER switch in the topology is critical to its performance, some placement rules, which describe how to place the ER switches for network operators, are developed in order to achieve a better performance of the network. The results presented should serve as an operational reference for service providers.

Comparison of explicit rate and explicit forward congestion indication flow control schemes for ABR service in wide area networks

An adaptive end-to-end rate based congestion control scheme to support a class of best effort service known as available bit rate service (ABR) has been proposed by the ATM Forum. In this paper we investigate two variants of this control scheme. In the first scheme known as the explicit forward congestion indication (EFCI) scheme, a single bit is used to convey to the source the state of the network. In the second scheme, known as the explicit rate (ER) scheme, the network informs the source from time to time, the maximum rate at which they can transmit. We investigate the steady state and transient performance of the controls in a wide area multihop network, including the presence of high priority variable bit rate traffic. To improve the performance of the EFCI scheme in multihop networks, we propose a priority based EFCI scheme. The EFCI scheme exhibits a robust behavior, and ensures fair share of the bandwidth for all virtual channels (VCs) in the long run, regardless of the number of hops they traverse. However, the EFCI mechanism is fundamentally oscillatory in nature and can lead to large cell loss. The ER scheme is very stable, even under extreme loading conditions, and ensures fair sharing of resources.

Performance analysis of reactive congestion control based upon queue length threshold values

Reactive congestion control based upon two thresholds is analyzed. Under the congestion control treated here, a multiplexer or transit node in the network recognizes congestion when its queue length reaches some pre-determined threshold value, denoted by H. The congested node then explicitly informs the sources sharing the node of its congestion in some way to mark a forward congestion notification bit in the header of cells if provided, or to directly send control cells to those sources. The sources then stop the cell transmission according to the feedback information received. The relief of congestion is recognized by the node when its queue length decreases to some low-threshold, L, and informs the sources that the sources can again start the cell transmission. In this paper, we investigate this sort of congestion control by forming a queueing network, in which multiple sources and a single node are explicitly modeled. Through an analysis, we discuss the impact of those two thresholds on performance of the congestion control.

Interoperability between EFCI and ER switch mechanisms for ABR traffic in an ATM network

The rate-based flow control mechanism in Asynchronous Transfer Mode (ATM) networks controls the transmission rate of Available Bit Rate (ABR) traffic sources, based on feedback information contained in the Resource Management (RM) cells coming from the destination and/or the network switching nodes. While the source and destination end systems behavior is fully described in the ATM Forum Traffic Management Specification, the network switch mechanism is implementation dependent. Since there is a variety of algorithms an ATM switch vendor can choose from, different performance characteristics are expected. This paper investigates the interoperability issues in terms of network performance and fairness of bandwidth allocation when an ATM network consists of switches using different rate control mechanisms, namely, the Explicit Forward Congestion Indication (EFCI) mode and the Explicit Rate (ER) mechanism. Simulation results show that these algorithms will interoperate as long as the switch implementation conforms to the end system behavior for congestion notification and usage of RM cells. Moreover, the location of an ER switch in a given topology might be critical to solving the “beat-down” phenomenon, where traffic passing through a larger number of switches might get less bandwidth than single hop traffic.

Performance management issues in ATM networks: traffic and congestion control

The goal is first to introduce performance monitoring aspects of asynchronous transfer mode (ATM) networks and then to focus on traffic and congestion control schemes. To deal with this performance monitoring management, a framework for defining a generic intelligent and integrated model for network management is described. As an example of the efficiency of this intelligent management architecture, we measure the performance of a new congestion control scheme. This scheme uses the cell loss priority (CLP) bit, the explicit forward congestion indicator and the explicit backward congestion indicator. The intelligent management uses different parameters and builds a complex but efficient control scheme. We show that this new control scheme allows performance to be increased by an order of magnitude.

Analysis of Packet Network Congestion Control Using Sparse Matrix Algorithms

The purpose of this study is twofold. First the study illustrates the utility of applying sparse matrix methods to packet network models. Secondly, these methods are used to give new results about the control of store and forward congestion in packet networks. Store and forward congestion (node to node blocking) reduces the effective traffic carrying capacity of the network by unnecessarily idling network resources. This study shows how store and forward congestion can be controlled by a combination of buffer reservation and processor capacity allocation. The scheme presented is analyzed using a Markovian state-space model of two coupled packet switches. The model contains more detail than previous analytic models. It is therefore solved using numerical sparse matrix methods. The results show that the combination of buffer reservation and processor capacity allocation gives strictly nondecreasing network output as a function of increasing network input load, i.e., undesirable store and forward congestion effects are eliminated.