Available Bit Rate Connections Research Articles

Reallocation of paths of ABR services in a multistage interconnection network (MIN)-type ATM switch network

In this paper, we develop algorithms for reallocating paths of available bit rate (ABR) services in an asynchronous transfer mode (ATM) switch network. ATM traffic control for fair share bandwidth allocation is usually performed under the assumption that paths of all services in a switch network are fixed. However, each connection may have multiple paths from an ingress queue to an egress queue since most ATM switch networks have the structure of the multistage interconnection network of switch elements. Therefore, paths already established for ABR connections may have to be changed to enhance throughput of the switch, if the ATM switch has the capability of adjusting paths of ABR connections while they are being served. We present three algorithms, in which throughput for ABR connections is estimated to decide whether or not paths of the connections should be changed. These algorithms are compared with an existing traffic management algorithm through simulation experiments. Results of the experiments show that the suggested algorithms give higher throughput in terms of the number of transmitted ABR cells without increasing the delay time of ABR services as well as quality of service (QoS) guaranteed services or decreasing the number of transmitted cells of QoS guaranteed services.

Centralized Flow Control Scheme for Rate-based Networks

This paper describes the Centralized Flow Control Scheme (CFCS) for a network that uses rate-based flow and congestion control. An example of such a network is an Asynchronous Transfer Mode (ATM) network using the Available Bit Rate (ABR) service. CFCS is a centralized control scheme in which a Network Controller Switch (NCS) maintains the current information of the network such as the number of Virtual Circuits (VCs) active at each switch, available capacity at each switch and rate assigned for each active VC. In order to do this it maintains a Rate Allocation Table (RAT). In our scheme, NCS is the main network controller switch with enough processing power and other switches in the network are the switches without processing power and they do not execute flow control algorithm. We call such switches as Passive Switches (PAS). PAS are controlled by NCS. Thus, in this scheme, the NCS controls the overall operation of the network by allocating rates to ABR connections with the help of RAT. CFCS can achieve zero cell loss, high utilization of links, maintains fairness in allocating bandwidth, it reduces transient response time. Moreover, it needs less feedback information for control and need less parameter to set by users and network administrators. We show the effectiveness of our scheme by simulation experiments.

Modeling and Simulation of an ABR Flow Control Algorithm Using a Virtual Source/Virtual Destination Switch

The Available Bit Rate (ABR) service class of Asynchronous Transfer Mode networks uses a feedback control mechanism to adapt to varying link capacities. The Virtual Source/Virtual Destination (VS/VD) technique offers the possibility to segment the otherwise end-to-end ABR control loop into separate loops. The improved feedback delay and the control of ABR traffic inside closed segments provide a better performance for ABR connections. This article will present the use of classical linear control theory to model and develop an ABR VS/VD flow control algorithm. Discrete event simulations are used to analyze the behavior of the algorithm with respect to transient behavior and correctness of the control model. Linear control theory offers the means to derive correct choices of parameters and to assess performance issues, like stability of the system, during the design phase. The performance goals are a high link utilization, fair bandwidth distribution, and robust operation in various environments, which are verified by discrete event simulations. The major contribution of this work is the use of analytic methods (linear control theory) to model and design an ABR flow control algorithm tailored for the special layout of a VS/VD switch, and the use of simulation techniques to verify the result.

Shaping Aggregate LAN Flows for Transmission over ABR Connections

AbstractIn the current recommendations on Internetworking over Non Broadcasting Medium Access and Multi‐Protocol Over ATM, the issues of ATM bandwidth allocation and flow control for best effort external LAN flows, forwarded to ATM connections, have not been adequately addressed. In this paper, we integrate the above features in the Access Units (i.e., bridges and routers) to smooth the bursty aggregate LAN traffic, to minimize losses due to congestion and consequently to achieve high end‐to‐end performance. The proposed flow control mechanism is based on the knowledge of the bandwidth available in the backbone network. Bandwidth advertising and explicit congestion notification mechanisms are provided by several network technologies such as Frame Relay and ATM. In the latter case the corresponding transfer capability is the Available Bit Rate (ABR). The proposed flow control mechanism, counts the frame delay in the Access Unit, and sends explicit feedback (backpressure) to neighboring legacy LAN sources. Explicit feedback partially absorbs the self‐similar features of the LAN traffic and can extend the ABR flow control to the non‐ATM legacy LAN stations. The shaping performed by the AU can be considered independent to the specific bandwidth advertising mechanism of the backbone network; in our case the ABR. In the performance results, the mechanism is shown to be efficient and adaptive to changes in the ATM available bandwidth and to a variety of LAN traffic characteristics. It is also shown that the flow control mechanism can be easily integrated in the protocol stacks currently met by today's LANs.

Multi-level rate-based flow control for ABR traffic

The rate control mechanism for available-bit-rate (ABR) traffic as defined by the ATM Forum does not distinguish between different types of ABR connections. However, since ABR traffic may result from a heterogeneous set of applications, there is an apparent need for a flow control scheme that can distinguish between and give differential treatment to different classes of ABR connections. In this study, a multi-level flow control scheme for ABR traffic is proposed that performs flow control of ABR traffic simultaneously at three levels: At the first level, the scheme determines the total available ABR bandwidth at a link. At the second level, the ABR bandwidth is distributed to different ABR traffic classes. At the third level, the scheme determines the bandwidth available to connections in same traffic class. It is shown that the multi-level flow control method completely decouples the explicit rate calculation of distinct traffic classes while achieving a high network utilization. Extensive simulations demonstrate that the multi-level flow control quickly adapts to load changes in the network.

Measurement‐based flow control for ABR services in ATM networks

AbstractA distributed explicit‐rate (ER) capacity allocation algorithm for handling available‐bit rate (ABR) services in ATM networks is described. The algorithm uses a measurement‐based approach to achieve max‐min bandwidth fairness and to provide priority service mechanisms for heterogeneous traffic, e.g., constant‐bit rate (CBR), variable‐bit rate (VBR), ABR, etc. Explicit provisions are made for handling minimum cell rate (MCR) guarantees for ABR connections and minimizing RM cell buffering delays at the network switches. It is also proposed that the sources measure their average rates to properly handle variability and to improve bandwidth utilization. An extensive simulation study for a number of network scenarios, which shows that the proposed scheme adapts well to network dynamics and converges to max‐min fairness, is presented.