ATM Available Bit Rate Service Research Articles

A simplified approach based on source control for ATM ABR service

The available bit rate (ABR) service is designed to provide efficient support of data traffic in ATM networks. A variety of rate-based flow control approaches have been proposed to support ABR service. Most of these approaches improve both the fairness among active connections and the link utilization by putting more and more complexity into a switch. In this article, we propose a flow control approach in which part of rate-calculation work is moved from switches to end-systems. As a result, the proposed approach reduces the rate-calculation effort in the switch. This may reduce the switch complexity and thus the implementation cost. Furthermore, it mitigates the difficulty for setting the measurement interval in switches, as well as features lower and more stable queue occupancy in the network. Simulation results are presented to demonstrate that the proposed approach achieves better performance than ERICA+, a well-known switch algorithm.

Resource Requirements for ABR Explicit Rate Flow Control: Deterministic and Probabilistic Analyses

ATM Available Bit Rate (ABR) service is intended to offer low cell loss for non-real-time data sources that can respond to closed-loop flow control. ATM Forum Traffic Management Specification Version 4.0 defines the various parameters used in the ABR flow control, as well as the source, destination, and switch behaviors. However, the switch designers and service providers are free to choose the method of congestion control to implement and the ABR Quality of Service (QoS) objective to offer. This paper addresses the interaction among the flow control algorithm, the switch resource requirements, and the resulting QoS characteristics. In this paper we propose and evaluate an Explicit Rate (ER) algorithm. The objective of this algorithm is to maintain the total buffer occupancy of all ABR connections to be close to a given threshold. By maintaining a non-zero queue, the ABR service can achieve a high utilization. The switch periodically determines its desirable ER value, based on the available capacity, the ABR buffer occupancy, and the number of active ABR sources. We develop analyses that relate ABR resources to QoS objectives for this algorithm. The first approach is a deterministic, conservative analysis. It provides formulas for determining the ABR buffer and capacity requirements that can achieve zero buffer overflow. The second analysis determines an upper bound on the buffer overflow probability when the above requirements are not met. The result is most effective when the number of active sources is a small fraction of the total ABR connections. Numerical examples show that by slightly relaxing the loss constraint, resource requirements can be significantly reduced.

Improving goodputs of IP packets under ATM UBR traffic with port-based queueing schemes

ATM networks are widely adopted as backbone networks. TCP/IP are the most popular protocols today and it is quite possible that packets are forwarded by ATM networks. In ATM networks, UBR (unspecified bit rate) service and ABR (available bit rate) service are common in transmitting IP packets. Because TCP has its own flow control mechanism, the flow control of ABR service could become redundant. Moreover, it could interfere with the TCP flow control. In this paper, we will focus on buffer management schemes of ATM switches with UBR service. Researchers have proposed several buffer management schemes for UBR service. However, all schemes do not consider the influence of output rates. In addition, most researchers assume that each port has its own buffers. A basic scheme called dedicated buffers per port is compared with four proposed schemes. The paper considers the situation that switch buffers are shared among all output ports and proposes a scheme called shared buffers among all ports. Then, two schemes, dedicated buffers with early packet discarding (EPD) and shared buffers with EPD, are proposed. The EPD scheme is modified. Instead of using a threshold for each flow, only one threshold is applied to buffers of each output port. The fifth proposed scheme is called shared buffers with EPD + differential buffer allocation (DBA), which also considers the effects of various output rates. Results show that goodputs are increased apparently by applying the DBA scheme. Results also show that for goodputs, when packets pass two or more switches, packet discarding schemes are far more important than whether we adopt schemes of shared buffers or schemes of dedicated buffers. Hence, we can simply adopt schemes of dedicated buffers, which are easy to implement, and incorporate a packet-discarding scheme in most cases.

Weighted fairness with MCR guarantee and a general-purpose explicit rate allocation algorithm for ATM ABR service

In this paper, weighted fair rate allocation for ATM available bit rate (ABR) service is discussed with the concern of the minimum cell rate (MCR). Weighted fairness with MCR guarantee has been discussed recently in the literature. In those studies, each ABR virtual connection (VC) is first allocated its MCR, then the remaining available bandwidth is further shared among ABR VCs according to their weights. For the weighted fairness defined in this paper, the bandwidth is first allocated according to each VC's weight; if a VC's weighted share is less than its MCR, it should be allocated its MCR instead of the weighted share. This weighted fairness with MCR guarantee is referred to as extended weighted (EXW) fairness. Certain theoretical issues related to EXW, such as its global solution and bottleneck structure, are first discussed in the paper. A distributed explicit rate allocation algorithm is then proposed to achieve EXW fairness in ATM networks. The algorithm is a general-purpose explicit rate algorithm in the sense that it can realise almost all the fairness principles proposed for ABR so far whilst only minor modifications may be needed.

A generic weight-proportional bandwidth sharing policy for ATM ABR service

A generic weight-proportional max–min (WPMM) policy has been proposed for the ATM available bit rate (ABR) service. This policy generalizes the classical max–min policy by supporting the minimum cell rate (MCR) requirement, the peak cell rate (PCR) constraint, and a generic weight for each connection. This paper presents a distributed ABR flow control algorithm for the the WPMM policy and gives a formal proof of the distributed algorithm’s convergence to the WPMM policy under any network configuration and any set of link distances. Simulation results on various network configurations demonstrate that the distributed algorithm has a very fast convergence property.

Improving fairness using dynamic weightsin ATM ABR service

A new scheme termed active fairness is proposed that substantially improves fairness in allocating bandwidth among the available bit rate (ABR) connections in ATM networks. In contrast to the one set of weights used in the generalised fairness scheme, active fairness maintains two sets of weights at each link. Simulation results prove the efficacy of the proposed scheme.

QoS and multipoint support for multimedia applications over the ATM ABR service

Multimedia applications with stringent delay requirements are usually supported by the constant bit rate (CBR) or real-time variable bit rate (rt-VBR) service categories of ATM. This article shows that the available bit rate (ABR) service, which was originally designed for data, can also support multimedia applications under certain circumstances. Issues related to the design of proper ABR traffic management algorithms for such support are presented.

WATMnet: a prototype wireless ATM system for multimedia personal communication

A prototype microcellular wireless asynchronous transfer mode network (WATMnet) capable of providing integrated multimedia communication services to mobile terminals is described in this paper. The experimental system's hardware consists of laptop computers (NEC Versa-M) with WATMnet interface cards, multiple VME/i960 processor-based WATMnet base stations, and a mobility-enhanced local-area ATM switch. The prototype wireless network interface cards operate at peak bit-rates up to 8 Mb/s, using low-power 2.4 GHz industrial, scientific, and medical (ISM)-band modems. Wireless network protocols at the portable terminal and base station interfaces support available bit rate (ABR), variable bit rate (VBR), and constant bit rate (CBR) transport services compatible with ATM using a dynamic time-division multiple-access/time-division duplex (TDMA/TDD) MAC protocol for channel sharing and data link control (DLC) protocol for error recovery. A custom wireless control protocol is also implemented between the portable and base units for support of radio link related functions such as user registration and handoff. All network entities including the portable, base and switch use a mobility-enhanced version of ATM ("Q.2931+") signaling for switched virtual circuit (SVC) connection control functions, including handoff. In the first stage of the prototype, the application-level API is TCP/UP over ATM ABR service class using AAL5. Early experiments with the WATMnet prototype have been conducted to validate major protocol and software aspects, including DLC, wireless control, and mobility signaling for handoff, Selected network-based multimedia/video applications requiring moderate bit-rates (/spl sim/0.5-1 Mb/s) in the ABR mode have been successfully demonstrated on the laptop PC.