Abstract--We consider the stability and performance of a model for networks supporting services that adapt their transmission to the available bandwidth. Not unlike real networks, in our model, connection arrivals are stochastic, each has a random amount of data to send, and the number of ongoing connections in the system changes over time. Consequently, the bandwidth allocated to, or throughput achieved by, a given connection may change during its lifetime as feedback control mechanisms react to network loads. Ideally, if there were a fixed number of ongoing connections, such feedback mechanisms would reach an equilibrium bandwidth al-location typically characterized in terms of its "fairness " to users, e.g., max-min or proportionally fair. In this paper we prove the sta-bility of such networks when the offered load on each link does not exceed its capacity. We use simulation to investigate performance, in terms of average connection delays, for various fairness criteria. Finally, we pose an architectural problem in TCP/IPs decoupling of the transport and network layer from the point of view of guaran-teeing connection-level stability, which we claim may explain con-gestion phenomena on the Internet. Index Terms--ABR service, bandwidth allocation, Lyapunov functions, performance analysis, proportional fairness, rate control, stability, TCP/IP, weighted max-min fairness. F I.

We study how to improve the throughput of high-bandwidth traffic such as large file transfers in a network where resources are fairly shared among connections. While it is possible to devise priority or reservation-based schemes that give high-bandwidth traffic preferential treatment at the expense of other connections, we focus on the use of routing algorithms that improve resource allocation while maintaining max-min fair share semantics. In our approach, routing is closely coupled with congestion control in the sense that congestion information, such as the rates allocated to existing connections, is used by the routing algorithm. To reduce the amount of routing information that must be distributed, an abstraction of the congestion information is introduced. Using an extensive set of simulation, we identify a link-cost or cost metric for "shortest-path" routing that performs uniformly better than the minimal-hop routing and shortest-widest path routing algorithms. To further improve throughput without reducing the fair share of single-path connections, we propose a novel prioritized multi-path routing algorithm in which low priority paths share the bandwidth left unused by higher priority paths. This leads to a conservative extension of max-min fairness called prioritized multi-level max-min fairness. Simulation results confirm the advantages of our multi-path routing algorithm.

Development of portable network-aware applications demands an interface to the network that allows an application to obtain information about its execution environment. This paper motivates and describes the design of Remos, an API that allows network-aware applications to obtain relevant information. The major challenges in defining a uniform interface are network heterogeneity, diversity in traffic requirements, variability of the information, and resource sharing in the network. Remos addresses these issues with two abstraction levels, explicit management of resource sharing, and statistical measurements. The flows abstraction captures the communication between nodes, and the topologies abstraction provides a logical view of network connectivity. Remos measurements are made at network level, and therefore information to manage sharing of resources is available. Remos is designed to deliver best effort information to applications, and it explicitly adds statistical reliability and variability measures to the core information. The paper also presents preliminary results and experience with a prototype Remos implementation for a high speed IP-based network testbed.

This paper presents a feedback control algorithm for ATM congestion control in which source rates are adjusted according to VC queue lengths at intermediate nodes along the path. The goal is to "fill in" the residual bandwidth, without exceeding a specified queue threshold. In order to obtain this, we propose a simple and classical proportional controller, plus a Smith Predictor to overcome instabilities due to large propagation delays, as well as to avoid cell loss. We propose an effective EPRCA implementation in which each source computes its input rate based on the maximum VC queue length along the path. Theoretical and experimental results show that high throughput is achieved even with queue sizes independent of the round trip delay. 1 Introduction In an ATM network, in order to avoid congestion it is necessary to regulate the input traffic rate of the network such that all entering cells can be completely delivered using the existing network resources (i.e. queues, processing p...

In ATM networks congestion control plays an essential role to support different quality of service guarantees for a large variety of traffic types. While for real-time communications, such as CBR and VBR services, a preventive open-loop congestion control mechanism is applied, a reactive closed-loop mechanism has been suggested for the ABR service class, which was introduced aiming at data communication applications. This paper presents a performance analysis of the ratebased congestion control mechanism developed by the ATM Forum. Using a differential equation approach for the computation of the evolution of the allowed cell rate and the buffer content during steady state, we derive closed-form expressions to estimate the maximum buffer lengths. These expressions can be formulated for steady-state conditions as well as for transient phases. In our approach, scenarios with and without priority for the resource management cells are considered. From numerical examples we conclude that an...

This paper gives a class of flow control algorithms for the adaptive allocation of bandwidths to virtual connections (VC) in high speed, wide area ATM networks. The feedback rate to the source from the network is parsimonious, with each feedback bit indicating whether the buffer at a distant switch is above or below a threshold. The service discipline at the switch is First-Come-First-Served. The important goal of adaptability aims to make all of the network bandwidth available to the active VCs, even though the number of such VCs is variable over a given range. Each VC has two parameters, one giving its minimum guaranteed bandwidth and the other is the weight for determining its share of the uncommitted bandwidth. Judicious selection of these parameters defines distinctive services, such as Best Effort and Best Effort with Minimum Bandwidth. We derive design rules for selecting the parameters of the algorithms such that the appropriate guarantees and fairness properties are exhibited ...

Abstract — There have been numerous studies on congestion control for the ABR service in ATM networks. These studies typically focus on the performance and fairness of the algorithms and make simplistic assumptions regarding the switch architecture and the link scheduling. One central issue of these studies has been the compu-tation of the fair- share of the link bandwidth. On the other hand, newer generation of ATM chipsets and switches now implement per-VC queueingand schedu~mgthat is capable of providing flow isolation as well as fair sharing of the link bandwidth among contending connections. As a result, ABR congestion control algorithms can now focus on solving the congestion control problem without unnecessarily being burdened by fairness considerations. In this paper, we take advantage of the per-VC queueinglscheduling capability of the new generation of ATM switches and develop an AM? rate-based congestion control algorithm. In contrast to most algorithms that appeared in the literature which are heuristics-based, this algorithm extends the work of [4] using a control-theoretic approach and takes advantage of the per-VC queue length information to achieve a simple to implement and yet complete control of the stability, rate of convergence, and performance of ABR service. Simulation results confirm the excellent performance and fairness characteristics achieved by the algorithm.

We present a theoretically justified pricing scheme for ABR services which utilizes mechanisms provided by rate-based flow control as defined by the ATM Forum. As a result, the scheme imposes no additional communication overhead, while the added complexity at the switches and end-systems is minimal. Our approach complements ABR's rate-based flow control and leads to economically efficient utilization of network resources. According to the scheme, a connection is charged based on the sum of the price per unit of bandwidth on all links along its route. Prices depend on the demand for bandwidth and are adjusted in a decentralized and iterative manner. Simulation results show that prices converge reasonably fast and do not have a negative effect on the convergence properties of flow control. 1 Introduction The Available Bit Rate (ABR) service class is one of the five service classes identified by the ATM Forum for ATM-based integrated services networks, [1, 2]. It is intended for "best-e...

Flow control in mobile ad hoc network (MANET) must face many new challenges such as frequent re-routing and bandwidth variation of the wireless links. TCP's implicit AIMD flow control performs poorly in this environment, because it often cannot keep up with the dynamics of the network.

We propose an explicit-rate ABR feedback control scheme, UT, that appears to satisfy the criteria of the ATM Forum. The distinct feature of UT is that it achieves max-min fairness by tracking an effective number of sources; specific constraint information is not required. As a result, its implementation is much simpler than that of other fair control schemes; indeed, its complexity is similar to that of unfair explicit-rate controls. In the thorough simulation study, UT demonstrates its ability to scale with speed, distance, number of users (both persistent and bursty), and number of nodes while remaining robust, efficient, and fair under stressing conditions with MPEG background traffic and multiple propagation delay loops. Key Words: explicit-rate ABR, feedback control, max-min fairness, ATM Forum, traffic management, multimedia 1 Introduction SWITCH SOURCE DESTINATION RM i RM i RM i Figure 1: ABR Feedback Control Basics The ATM Forum Traffic Management Specification currently defi...