Assessment and performance analysis of DQDB MAC protocols

Distributed queue dual bus (DQDB) has been adopted as the IEEE 802.6 standard for metropolitan area networks (MANs). The access mechanism is based on an implicit distributed queue maintained at each node. DQDB has been shown to achieve maximal aggregate throughput and minimal access delay independent of the size and speed of the network. However, as the size and load of the network increase, DQDB gives rise to throughput unfairness problems due to the long propagation delay. This paper initially presents a survey and assessment of recently proposed remedial DQDB mechanisms. These approaches are categorized as time division multiplexing (TDM)-oriented versus non-TDM-oriented, and exhaustive versus non-exhaustive operations. Regarding TDM as the most promising mechanism, the paper then provides the performance analysis of one TDM-oriented method, called multiple segment control (MSC), proposed by the authors. In the analysis, the network is modelled as a set of identicalM/G/1 queues, each with different services for transmitting the first and remaining segments in a busy period. The average aggregate access delay is then analyzed via an embedded Markov model. The paper shows simulation results to demonstrate the precision of the performance analysis and the performance superiority of MSC over non-TDM-oriented DQDB mechanisms. Furthermore, as will be shown, the network using the TDM-oriented method may incur bandwidth waste should active stations fail. The paper finally proposes a guardian reliability scheme to ensure the robustness of networks.     

A proof for lack of starvation in DQDB with and without slot reuse

The DQDB is the IEEE 802.6 MAC standard protocol for metropolitan area networks (MANs). It is designed for the slotted, dual bus configuration. A simple way to improve the performance of the DQDB is to perform slot reuse and many methods have been suggested in the past to efficiently incorporate slot reuse with the DQDB. However, some of them can lead to starvation. We improve one of these previous suggestions and the main contribution of the paper is that for the first time we also provide a proof that the improved scheme ensures a lack of starvation. We also specify this proof for the important case of the DQDB without slot reuse     

DQDB城域网实现计算机局域网互连时的性能分析

DQDB城域网是实现现有通信网络向B-ISDN过渡的优选网络。本文分析了DQDB城域网用于计算机局域网互连时的排队性能;研究了报文长度、网络上下游负荷、带宽平衡参数和网络计数器级数对报文在缓存器中停留时间的影响。所得结果可为DQDB城域网的具体实现提供参考。     

Slot reuse in MAC protocols for MAN's

Most of the medium-access control (MAC) sublayer protocols recently proposed for application in very high-speed local and metropolitan area networks (LANs and MANs) are based on a slotted transmission scheme. Slotting guarantees very good throughput efficiencies, but further gains are possible if slots can be freed after reaching their destination, thus being available for repeated use as they propagate in the network. The authors describe a simulation-based quantitative analysis of the performance gains obtained by introducing slot reuse in distributed-queue dual-bus (DQDB) and cyclic reservation multiaccess (CRMA) MANs. CRMA-II, the latest evolution of CRMA, naturally incorporates slot reuse in the MAC protocol operations and is considered in the study for comparison purposes. In the case of the standard DQDB protocol, some existing proposals are considered. In the case of CRMA, both a previous IBM proposal and a novel approach, leading to very good performances, are studied     

S++-a new MAC protocol for Gb/s local area networks

A media access control (MAC) layer protocol called S++, which offers several features that are desirable for gigabit per second local area networks, is described. The performance of the protocol has been investigated by detailed simulations which have been confirmed using an analytical model. A number of results that show how S++ offers consistently lower mean delays than the distributed queue dual bus (DQDB) protocol when used on a folded bus network are presented. Further results illustrate additional properties, which include the provision of pseudopriorities, a reduction in message reassembly time compared with DQDB, and the rapid redistribution of bandwidth under varying loads     

The no slot wasting bandwidth balancing mechanism for dual busarchitectures

A bandwidth balancing (BWB) mechanism has been added to the distributed queueing algorithm of the distributed-queue dual bus (DQDB) network. BWB can provide the requested throughputs by lightly loaded stations and evenly distribute the remaining channel bandwidth among overloaded stations. However, its operation requires the wastage of channel slots. The authors introduce a new bandwidth balancing mechanism for DQDB. The operation of the new mechanism requires one additional bit in the access control field (ACF) of the slot but has the advantage of exhibiting a similar behavior with the current BWB mechanism of DQDB without wasting any channel slots. For this reason, it can converge faster to the steady state in which fair bandwidth allocation is achieved. The authors investigate the throughput and delay performance of the proposed mechanism under one traffic class and examine its capacity to support multiple priority classes of traffic. They also compare its performance with the corresponding performance of the BWB mechanism of DQDB     

B-ISDN and the OSI protocol reference model

The evolution of public telecommunication networks toward broadband integrated services digital networks (B-ISDNs) is presented. The asynchronous transfer mode (ATM), which supports B-ISDNs, and the B-ISDN protocol reference model are discussed. It is shown that the service offered by the ATM layer in the B-ISDN protocol reference model is equivalent to the service offered by the OSI physical layer. It is also shown that the service offered by the ATM adaptation layer (AAL) type 3/4 is similar to an OSI data link service. The emergence of the metropolitan area network (MAN) standard as an intermediate support for broadband services and the similarities between the DQDB MAC and the AAL type 3/4 in its connectionless mode are discussed     

Multicommodity flow models, failure propagation, and reliable lossnetwork design

Multicommodity flow (MF) models are well known and have been widely used in the design of packet-switched networks. They have also been used as approximations in the design of circuit-switched networks with reliability constraints. We investigate the usefulness of multicommodity models both as routing models and as an integral part of design models conceived under the failure propagation strategy. First, we compare the performance measures calculated by the models with results produced by a real-time technique. Next, we study the performance of networks dimensioned with flow models and with known adaptive models under failures of transmission facilities when a real-time routing technique is used. Results obtained using realistic data show that the MF models compare favorably with exact dimensioning algorithms when failures are considered     

High-performance optical local and metropolitan area networks:enhancement of FDDI and IEEE 802.6 DQDB

The fiber distributed data interface (FDDI) and the IEEE 802.6 distributed queueing dual bus (DQDB) are emerging standards for high-speed (45-150-Mb/s) local and metropolitan area networks. The authors describe several ways to build on these emerging standards to significantly increase the achievable throughput and lower th e end-to-end delay. Without increasing the number of transceivers or their rate, substantial throughput increases are obtained by a highly concurrent logical interconnection pattern of user modes, and the end-to-end delay is decreased by the use of more efficient media-access techniques. The most promising architecture is a multiconnected ring having only two transmitters and two receivers per node, where each node needs to handle or process only a small fraction of the network traffic. In one example, the authors describe a 24-node, distributed, packet-switched network, with only two 100-Mb/s transmitters and two 100-Mb/s receivers per node; it has a maximum throughput of 1.5 Gb/s-15 times the 100/Mb/s throughput of FDDI. Such a system has the potential to be a follow-on standard to FDDI (or IEEE 802.6) or to provide a high-performance LAN/MAN that can interwork with standard systems     

A high performance transparent bridge

The high performance transparent bridge (HPTB) is a multiport bridge interconnecting gigabit networks. The provision of specialized hardware support coupled with proper partitioning of bridging protocol entities makes it possible to process frames at very high rates. The HPTB architecture allows concurrent bridging of asynchronous, synchronous and isochronous traffic among heterogeneous networks. It supports both traditional networks, such as variable packet size local area networks (LANs), and cell-based net works, such as distributed queue dual bus (DQDB) and metropolitan area networks (MANs). This device is capable of interconnecting any combination of high speed LANs of rates up to 800 Mbps and/or MANs of rates up to 622 Mbps     

Virtual fully connected WDM network: A high-performance single-hop architecture for metropolitan area networks

With the widespread use of broadband access technologies and the development of high-speed Internet backbones, the requirement for high-performance metropolitan area networks (MANs) is increasing. Traditional ring- or star-based metro networks are costly to scale up to high speed and cannot recover from multiple failures, while backbone solutions are too expensive to fit into the cost-sensitive metro market. This paper proposes a virtual fully connected (VFC) architecture for metro networks to provide high-performance node-to-node all-optical transportation. The architecture emulates a fully connected network by providing optical channels between node pairs without intermediate buffering, and thus realizes single-hop transportation and avoids expensive packet routers. In addition, a scheduling algorithm is developed for medium access control and dynamic bandwidth allocation, which achieves 100% throughput and provides a fairness guarantee. Simulations show that the VFC network achieves good performance under both uniform and non-uniform loads.     

AWG-based metro WDM networking

A plethora of metropolitan area wavelength-division multiplexing networks have been proposed and examined in recent years with the aim to alleviate the bandwidth bottleneck between increasingly higher-speed local/access networks and high-speed backbone networks. Many of the considered metropolitan area networks use the arrayed waveguide grating as an optical building block. As we review in this article, in ring, interconnected ring, and meshed metro WDM networks, the AWG is typically used to realize wavelength multiplexers, demultiplexers, or optical add-drop multiplexers without capitalizing on spatial wavelength reuse. By using the AWG as a wavelength router, highly efficient star metro WDM networks can be realized due to extensive spatial wavelength reuse. We give an overview of star metro WDM networks that are able to meet modular upgradability, transparency, flexibility, efficiency, reliability, and protection requirements of future metro networks. AWG-based star networks also enable an evolution path of ring networks toward highly efficient and fault-tolerant hybrid star-ring metro network solutions.     

Request rate control for QA services in DQDB/SMDS–ATM gateways

By the advancement of B-ISDN, ATM has been accepted as the future technology to integrate a variety of services as it is a fine comprise between circuit switching technology and packet switching technology. A cost-effective and simple way to realize the global network is to implement a backbone such as DQDB to interconnect the existing LANs and MANs to ATM. The major advantages of DQDB are the complete compatibility of different layers, the capability of handling real-time and non-real-time traffic and little degradation in delay performance with increase in network span and density. However, a major issue of concern in the design of a DQDB/SMDS–ATM gateway is the transparent transfer of non-real-time traffic, as ATM is basically connection-oriented in nature. In the absence of flow control schemes in high-speed networking, some sort of congestion control mechanism becomes an absolute necessity to reduce the cell loss ratio to the minimum and thus wastage in the network resources. In this paper we discuss the transfer of connectionless traffic in a DQDB–ATM interconnection. One of the two congestion control mechanisms for DQDB networks that we have proposed is discussed in detail. In the request rate control mechanism the bandwidth utilization in DQDB is restricted by controlling the request rate from the gateway. DQDB networks interconnected by gateways are modelled and simulated. The request rate congestion control mechanism is evaluated. Simplicity in implementation and effectiveness in performance are the highlights. © 1998 John Wiley & Sons, Ltd.     

An approximate performance fairness analysis of thepi-persistent protocol with destination release

Sufficient conditions are derived for achieving the two most important fairness criteria in the design of access protocols for high-speed metropolitan area networks (MAN), the delay and throughput fairness criteria, a probabilistic scheduling scheme, known as the p_i-persistent protocol is considered, which has been shown to be suitable for applications requiring large bandwidth over long repeater-free distances and also amenable to an approximate analytical performance evaluation. It is found that the throughput fairness criterion is easier to achieve than its delay counterpart. The delay fairness, when achieved, induces approximate throughput fairness. The current practice in the field of protocol design for unidirectional bus MANs appears to focus almost exclusively on the throughput fairness. For example, in the DQDB protocol, although a bandwidth balancing function exists, balancing delay performance has never been dealt with     

An approximate analysis of the performance of deflection routing inregular networks

Regular two-dimensional architectures are being considered as alternatives to the linear topology metropolitan area networks (MANs) that are popular today. Deflection routing is an adaptive routing strategy that performs well on such architectures. A general analytic model has been developed to study the performance of buffered deflection routing in regular networks. The Manhattan street network, the ShuffleNet, and the shuffle exchange network have been studied as candidate two-connected networks with different topological characteristics. The results show that deflection routing performs well on both the Manhattan street network and the ShuffleNet, even under heavy loads, while on the shuffle exchange network it does not perform as well. The introduction of just a few buffers provides significant improvement in the delay-throughput performance over unbuffered deflection routing, especially in networks with large propagation delays. The analytic results are found to match the simulations very closely in most cases     

High-reliability topological architectures for networks under stress

In this paper, we consider the design of a physical network topology that meets a high level of reliability using unreliable network elements. We are motivated by the use of networks and, in particular, all-optical networks, for high-reliability applications which involve unusual and catastrophic stresses. Our network model is one in which nodes are invulnerable and links are subject to failure - a good approximation for optical networks with passive nodes and vulnerable fiber under stress of disconnection - and we focus on statistically independent link failures with initial steps taken toward generalization to dependent link failures. Our reliability metrics are the all-terminal connectedness measure and the less commonly considered two-terminal connectedness measure. We compare in the low and high stress regimes, via analytical approximations and simulations, common commercial architectures designed for all-terminal reliability when links are very reliable with alternative architectures which are mindful of both of our reliability metrics and regimes of stress. We derive new results especially for one of these alternative architectures, Harary graphs, which have been shown to possess attractive reliability properties. Furthermore, we show that for independent link failures network design should be optimized with respect to reliability under high stress, as reliability under low stress is less sensitive to graph structure; and that under high stress, very high node degrees and small network diameters are required to achieve moderate reliability performance. Finally, in our discussion of correlated failure models, we show the danger in relying on an independent failure model and the need for the network architect to minimize component failure dependencies.     

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.     

A study of slot reuse in dual bus multiple access networks

In dual unidirectional bus networks, packets usually occupy fixed-length slots form the sending station to the end of the network. An erasure node is a specialized station which recognizes packets which have passed their destination stations and releases the slots for subsequent use. The authors derive the optimal locations for erasure nodes and show analytically, for uniform traffic, that only several erasure nodes are needed to achieve throughput close to twice the nominal network bandwidth. The results are tested by simulation of the DQDB (distributed queue dual bus) protocol, which demonstrates a realistic improvement of 40% with only three erasure nodes. Fair access among the stations is improved as well. The authors generalize the analytic results by providing an algorithm for determining the optimal erasure node locations and the throughput improvement, given any arbitrary traffic pattern. The application of this methodology to the related problem of bridged subnetworks is briefly discussed