A separation principle between scheduling and admission control forbroadband switching

A framework for joint scheduling and admission control in broadband switching systems based on a principle of separation between these two levels of control is developed. It is shown that an admission control strategy can be tailored to a particular mix of traffic by using high-level information from the scheduler. This principle is presented in the context of asynchronous time-sharing (ATS) in which explicit guarantees of cell-level and call-level quality of service (QOS) are given to several traffic classes. The separation principle allows the formulation of an optimal admission control policy that maximizes the expected system utility and maintains all QOS guarantees. Several heuristic admission control policies are considered and compared with the optimal policy. The admissible load region is introduced as a means of quantifying the capacity of a switch under the QOS constraints at the cell and call levels. Numerical calculations for a single MAGNET II switching node carrying two classes of real-time traffic are used to illustrate the effects of different scheduling and admission control policies on both the expected utility and the admissable load region     

Evolution and service requirements of CBR applications on ATM networks

Broadband integrated networks based on asynchronous transfer mode (ATM) technology are being proposed to provide a single integrated access to a variety of services and applications. Constant bit rate services will form an important part of this unified networking solution. In this paper, we identify and describe the relevant aspects related to the implementation of CBR services on ATM. First, we identify two broad categories of potential CBR services for broadband ATM networks. The ATM infrastructure for the identified services is then developed along with the required functionalities of different network elements. Finally, end-to-end performance objectives for the ATM network are determined and verified empirically based on results of laboratory experiments. These performance objectives help us determine the minimum QOS required by the highest class of service category offered by an ATM network.     

Wireless Adaptive Framed Pseudo-Bayesian Aloha (AFPBA) Algorithm with Priorities

In this paper, we propose a new priority algorithm to control the access to the wireless ATM MAC uplink frame, for multimedia traffic like wireless ATM, similar to the Pseudo-Bayesian algorithm presented in [1]. The adaptive framed Pseudo-Bayesian Aloha (AFPBA) algorithm ensures minimum access delay for high priority traffic classes with small delay degradation to low priority traffic classes. Control packets are transmitted in each slot according to transmission probabilities based on the history of the channel and in contention with other packets of the same priority class. The number of contention slots assigned for each priority class, on a given frame, changes adaptively according to its priority index and the estimated arrival rate on each frame using an adaptive slot assignment mechanism. Finally, the throughput analysis of the algorithm is presented and the delay performance is evaluated by simulation on a wireless channel in the presence of shadowing, Rayleigh fading and capture. Results show that the wireless channel offers significant delay improvements to all priority packets, especially in the presence of fast fading.     

Resource allocation for multiple classes of DS-CDMA traffic

We consider a packet data direct-sequence code-division multiple-access (DS-CDMA) system which supports integrated services. The services are partitioned into different traffic classes according to information rate (bandwidth) and quality of service (QoS) requirements. Given sufficient bandwidth, QoS requirements can be satisfied by an appropriate assignment of transmitted power and processing gain to users in each class. The effect of this assignment is analyzed for both a single class of data users and two classes of voice and data users. For a single class of data users, we examine the relationship between average delay and processing gain, assuming that ARQ with forward error correction is used to guarantee reliability. The only channel impairment considered is interference, which is modeled as Gaussian noise. A fixed user population is assumed and two models for generation of data packets are considered: (1) each user generates a new packet as soon as the preceding packet is successfully delivered and (2) each user generates packets according to a Poisson process. In each case, the packets enter a buffer which is emptied at the symbol rate. For the second traffic model, lowering the processing gain below a threshold can produce multiple operating points, one of which corresponds to infinite delay. The choice of processing gain which minimizes average delay in that case is the smallest processing gain at which multiple operating points are avoided. Two classes of users (voice/data and two data classes) are then considered. Numerical examples are presented which illustrate, the increase in the two-dimensional (2-D) capacity region achievable by optimizing the assignment of powers and processing gains to each class     

CELL LOSS QUALITY OF SERVICE IN AN INTEGRATED TRAFFIC ATM NETWORK

This paper explores and evaluates several aspects of quality of service (QOS) in an integrated traffic ATM network. Specifically, we consider the relationships between service class definitions, usage parameter control (UPC) or policing of customer traffic, network resource allocation mechanisms, and specific network conditions under which realistic QOS limits on cell loss ratio (CLR) can be met. Traffic consists of a mixture of voice, video, image and data divided into two service classes for UPC and network resource allocation. The block oriented network simulator (BONeS) tool is used for performance evaluations. Limitations associated with evaluating very low CLR values (e.g. 10⁻⁸ and 10⁻⁶) via simulation are overcome by a hybrid simulation and extrapolation technique. It is found that these stringent QOS limits on CLR can be met for most traffic with the techniques used here, reasonable backbone trunk loads (75 per cent) and reasonable buffer sizes (200–250 cell buffers per queue). However, meeting similar limits for extremely bursty traffic (such as our image traffic model) would require extra care in network design and operation, including judicious segregation of traffic.     

A new priority control of ATM output buffer

A new ATM output buffer management strategy with priority control function is proposed, based on four types of cell classes. This strategy can use system resource more effectively, meet the quality of service (QOS) requirements (i.e. cell loss probabilities and delay characteristics) of different services, and also can reduce the complexity of buffer. Furthermore, overload from lower priority traffic doesn't degrade the performance of higher priority traffic (i.e. cell loss rate and cell delay characteristics).     

An ATM queue manager handling multiple delay and loss priorities

The asynchronous transfer mode (ATM) technique has been widely accepted as a flexible and effective scheme to transport various traffic over the future broadband network. To fully utilize network resources while still providing satisfactory quality of service (QOS) to all network users, prioritizing the user's traffic according to their service requirements becomes necessary. During call setup or service provisioning, each service can be assigned a service class determined by a delay priority and a loss priority. A queue manager in ATM network nodes will schedule ATM cells departing and discarding sequence based on their delay and loss priorities. Most queue management schemes proposed so far only consider either one of these two priority types. The queue manager handles multiple delay and loss priorities simultaneously. Moreover, a cell discarding strategy, called push-out, that allows the buffer to be completely shared by all service classes, has been adopted in the queue manager. We propose a practical architecture to implement the queue manager by using available VLSI sequencer chips     

Designing a CORBA-based high performance open programmablesignaling system for ATM switching platforms

ATM switching platforms are well suited for transporting multimedia streams with quality-of-service (QOS) requirements. This paper describes the system design of a high performance connection management system for xbind, a flexible open programmable signaling system for ATM switching platforms. The latency and throughput of call processing is improved by caching, message aggregation, and processing of requests in parallel. Using a set of general purpose UNIX work stations, we are able to attain a maximum throughput of close to 600000 call operations/h (setup and delete) with an average call setup time of 85 ms. With a low traffic load of 3600 call operations/h, an average call setup latency of 11 ms can be obtained. The system is adaptive. By adjusting various control parameters, the connection manager(s) can be dynamically configured to trade off between throughput and call setup time     

多业务DS-CDMA系统的资源分配算法研究

针对提出的业务模型，分析了多业务DS-CDMA系统中各类业务的QoS性能如平均延时、吞吐量及比特差错率等与各类业务的处理增益和功率分配的关系，提出了一种适用于两类业务（一类实时、一类可靠）的优化处理增益和功率分配算法，数据结果表明优化算法可以在保证两类业务QOS的同时提高系统容量及可靠业务的吞吐量。     

ATM优先级队列的质量控制

在ＡＴＭ队列中可以采用恰当的优先级方案对具有不同ＱＯＳ指标的业务进行适当的控制。本文提出了一种综合的ＡＴＭ队列管理方案，建立了相应的系统模型，并给出了理论分析和模拟结果，表明这种方案对ＡＴＭ业务的质量控制是有效的。     

Performance Evaluation of a Logical Link Control Protocol for an ATM Air Interface

The paper deals with error control proceduresbased on repetitions necessary for an ATM air interface,which enables a full integration of wireless (W) ATMterminals into a fixed ATM network. The architecture and functionality of an additional LLC layer atthe air interface are explained. A set of ARQ protocolsfor the different ATM service classes is investigated.The protocol for VBR services is able to control the number of retransmissions depending on therequirements on maximum delay and residual cell lossratio. It also takes into account instantaneousconditions such as channel load from other sources.Furthermore, the protocol is able to discard ATM cells toavoid and resolve congestion. The performance of theprotocol has been evaluated by simulations.     

具有质量控制功能的ATM交换节点的性能分析

本文提出一种用于ＡＴＭ网的质量控制方法－动态到达控制（ＤＡＣ），分析了采用ＤＡＣ的ＡＴＭ交换节点中，各类业务信元的丢失概率和平均时延，分析结果表明，ＤＡＣ是一种有效的质量控制方式，它能够提供多种服务等级以满足不同的需要，减小所有信元的平均时延，提高系统的有效吞吐量。     

Survey of traffic control schemes and protocols in ATM networks

The authors survey a number of important research topics in ATM (asynchronous transfer mode) networks. The topics covered include mathematical modeling of various types of traffic sources, congestion-control and error-control schemes for ATM networks, and priority schemes to support multiple classes of traffic. Standard activity for ATM networks and future research problems in ATM are also presented. It is shown that the cell-arrival process for data sources can be modeled by a simple Poisson process. However, voice sources or video sources require more complex processes because of the correlation among cell arrivals. Due to the effects of high-speed channels, preventive control is more effective in ATM networks than reactive control. Due to the use of optical fibers in ATM networks, the channel error rate is very small. The effects of propagation delay and processing time become significant in such high-speed networks. These fundamental changes trigger the necessity to reexamine the error-control schemes used in existing networks. Due to the diversity of service and performance requirements, the notion of multiple traffic classes is required, and separate control mechanisms should be used according to the traffic classes. The priority scheme is shown to be an effective method to support multiple classes of traffic     

Bandwidth allocation and admission control in ATM networks withservice separation

The statistical multiplexing operation within an ATM network node is considered, with respect to different methods for the allocation of the bandwidth of an outgoing link. Service separation is assumed by dividing the overall traffic flows into classes, homogeneous in terms of performance requirements and statistical characteristics. Which share the bandwidth of a link according to some specified policy. This context allows one to clearly define, by means of several existing approaches, a region in the space of connections of the different classes (call space) where quality of service (QoS) requirements at the cell level are satisfied. Within this region, some criteria for allocating the bandwidth of the link to the service classes are proposed, and the resulting allocation and call admission control (CAC) strategies are defined and analyzed. The goal of these operations is to achieve some desired QoS at the call level. Several numerical simulation results are presented, in order to highlight the different performance characteristics of the various methods     

突发业务环境下CBR业务性能的实验分析

CBR业务是一类极为重要的实时业务,能否有效地传递这类业务关系到从现有网络向ATM的过渡,因此CBR业务的服务质量是一个值得研究的重要课题。本文利用计算机仿真的方法,全面地分析了突发业务环境下,影响CBR业务服务质量的各种因素,指出复接器占有率、缓冲区容量、背景强度、背景流的自相关特征对CBR业务的时延及时延抖动有很大的影响,尤其是背景流具有长时相关性时,CBR业务的服务质量将严重恶化,必须设法加以控制。     

IP Over ATM的QOS探讨

文章对因特网的“集成服务”、ATM的QOS要求以及IPover ATM的QOS要求进行了探讨,并在此基础上提出了运用资源预保留协议将ATM集成到因特网上的实现方案。     

A call admission control scheme for ATM networks using a simplequality estimate

The authors propose a call admission control scheme based on a method of estimating cell loss quality for individual bursty traffic sources. The estimate is expressed in terms of virtual cell loss probability, which may be defined by two traffic characteristic parameters alone: peak and mean rate. The approach is suitable for the estimation of real cell loss probability in heterogeneous and homogeneous traffic models when burst length is larger than buffer capacity. The concept of virtual cell loss probability is extended to the individual call level so as to be able to estimate the quality of service (QOS) provided to individual calls. A virtual bandwidth method is used to develop a practical call admission control system. Quality is ensured by combining a traffic clustering scheme, with a scheme for assigning individual clusters to subcapacities of a link. Priority levels are presented in terms of the class of QOS required, i.e., deterministic or statistical, and the allocation of virtual bandwidth is discussed in terms of both QOS class and traffic characteristics     

Performance of adaptive token allocation in the leaky bucket

The leaky bucket is a popular method that can regulate traffic into an ATM broadband network. This paper examines a simple but innovative modification that would also provide priority to access the network. This is done by requiring cells of different classes to obtain different numbers of tokens before receiving their services. As a step further, a dynamic scheme can be used in which the tokens allocated to each class are changed according to the traffic load. Performance evaluations of mean cell delays and cell loss probabilities are obtained to provide insight into the behaviour of the system and to provide guideline for furture design.     

Incentive pricing in multiclass systems

In modern communication networks which offer multiple classes of services, an appropriate assignment of service classes to users (or applications) will have a key influence on the performance profile. Differentiated pricing is an important tool for guiding the user's choice. We consider a basic model for a multiclass system that offers multiclass services to multiple types of traffic, and propose a pricing framework which is based on the concept of nominal traffic assignment. Users (or their associated traffic) are categorized into a finite number of traffic types, which are distinct in their performance utilities at the different service classes. The system administrator specifies a required traffic assignment, which associates with each traffic type a nominal service class. Users, on the other hand, choose service classes so as to optimize their own performance. Optimal prices should provide incentives for the users to assign each traffic type to its nominal service class. Our goal is to implement a simple pricing scheme that provides such incentives. We establish necessary and sufficient conditions for the existence of optimal prices and provide an algorithm for their computation. We indicate that optimal prices can tolerate fluctuations in the various parameters. Next, we propose a distributed algorithm, which can be used by the system to compute optimal prices even when it does not have sufficient knowledge of traffic characteristics. We then generalize our analysis to an extended model, which explicitly includes congestion effects. This revised version was published online in June 2006 with corrections to the Cover Date.     

Buffer partitioning formula for different traffic classes in ATM

Future telecommunications networks will use ATM core switching, and these switches are now being designed with a certain total amount of buffer space, X, available at each output port. This leaves the network operator to configure each port such that X is partitioned between the different service classes, in such a way as to be consistent with the required cell loss probability (CLP) for each class. This paper reports the development of a formula that partitions X between an arbitrary number of traffic classes, and allows for any scaling of the CLP. Copyright © 1999 John Wiley & Sons, Ltd.