综合业务光纤DQDB网PABX互连研究

ＤＱＤＢ网具有吞吐量大、网络的可靠性高、抗毁性等优点，它采用电路交换和分组交换相结合的混合交换方式，提供综合业务。文章在对综合业务光纤ＤＱＤＢ网分析的基础 ，重点研究了提供话音业务的ＰＡＢＸ互连问题。     

城域网标准—DQDB

局部网的飞速发展迫切要求在更大区域上进行互连,城域网正是为满足这种需求开发的。本文简要地叙述了IEEE802.6城域网的标准——分布排队双总线(DQDB)网的拓扑结构、网络节点的功能体系、帧格式和网络协议,最后分析了DQDB网的特性及其应用潜力。     

SOJOURN TIME ANALYSIS OF DQDB MAN FOR LANs INTERCONNECTION

The Distributed Queue Dual Bus(DQDB) Metropolitan Area Network(MAN) is a promising solution for the evolution from current networks to B-ISDN. The performance of the DQDB MAN for Local Area Networks(LANs) interconnection is analyzed. The effects of message length, traffic load of upstream and downstream nodes and the parameters of bandwidth balancing mechanism and network counters on the sojourn time of message in the buffer are investigated, which present a valuable reference for the implementation of the DQDB MAN.     

On the approximation of the slot occupancy pattern in a DQDB network

This paper presents a novel approach to DQDB modeling in underload conditions; the innovative aspect lies in the representation of the slot-occupancy-pattern process on the forward bus. In the literature this process has been often modeled as a Bernoulli process, implying that the status (empty/busy) of consecutive slots are independent. Results presented in this paper, however, show that even at light loads the interdependence between slots is significant. Our model captures some of this interdependence by using a discrete-time first-order Markov process for the slot-occupancy-pattern process on the forward bus. In the paper we identify a simplified DQDB network for which we derive a closed formula for the joint probability density function for the slot occupancy pattern of two consecutive slots. The accuracy of our results is investigated via simulation. Finally, an application of our first-order Markov model is shown through an investigation of the performance of a gateway concentrating several DQDB networks in a slotted trunk.     

A journey through the DQDB network literature

The Distributed Queue Dual Bus (DQDB) network has been adopted as the subnetwork for the IEEE 802.6 metropolitan area network (MAN) standard. Since its original proposition a few years back, DQDB has attracted significant attention because of the simplicity of its medium access control (MAC) protocol. The intense scrutiny that DQDB has been subjected to has lead to the identification of a number of its potential problems, and a number of “add-on” strategies have been proposed to “fix” such problems. Moreover, a number of architectural variations have also been proposed to improve the network behavior. Since there has been a literature explosion on DQDB over the past few years, this article is intended to extract the significant features of various DQDB-based investigations, and to present them in an unified manner.     

DQDB综合业务局域网

介绍了一种DQDB综合业务局域网。该网用光纤作传输媒介，拓扑结构为双总线环形，采用DQDB协议，本网可传输数字话音、高／低速计算机数据、高质量静止图像和压缩视频图像等综合业务。文中主要探讨该网结构、访问协议、帧结构等。     

A multiservice GFC protocol

Generic flow control (GFC) is used to provide controlled transmissions from terminals over the BISDN user-network interface. The reason for requiring controlled transmission is to allow for the multiplexing of cells from a number of terminals connected in either a dual bus or star configuration. GFC must provide fair access for each terminal, and the meaning of this is discussed for different services. It must provide a guaranteed minimum bandwidth, meeting the requirement of fair access for constant bit-rate terminals. It must also provide fair access for variable bit-rate (VBR) terminals. It is proposed that all terminals of a given class are given the same percentage reduction of their agreed peak bandwidths during overload conditions, leading to approximately similar delay distributions within the class. GFC can then be considered as providing a given quality of service per terminal (through guaranteed bandwidth) and an additional common quality of service for the unguaranteed cells. Some simulation results are provided for the dual bus configuration.     

ATM DQDB城域网中恒定比特率业务的性能（Ⅱ）;延时分析

本文分析了ＡＴＭ ＤＱＤＢ城域网中恒定比特率业务的时延特性，恒定比特率业务比可变化特率数据业务的优先级高，但两者都采用统一的分组方式进行传输。本文的分析表明，在业务负荷不是非常重的情况下，恒定比特率业务的时延性能还是令人满意的，从而说明了ＡＴＭ ＤＱＤＢ城域网的可行性。     

多优先级DQDB城域网的性能分析

本文分析了多优先级DQDB城域网的性能,得到了采用不同优先级时,报文平均停留时间的表达式。计算机仿真结果与理论分析相吻合。