Distributed Queue Dual Bus Network Research Articles

Isochronous bandwidth utilization improvement in distributed queue dual bus-based personal communication networks

With the expansion of personal communication networks, wireless traffic is expected to grow rapidly. To cope with this situation, we investigate the issue of how to support wireless voice communications efficiently in personal communication networks with distributed queue dual bus networks as backbones. In the backbone networks, pre-arbitrated slots generated at constant intervals are preferred to carry voice traffic with stringent delay requirements. However, they are not utilized as efficiently as queued arbitrated slots, which are allocated on demand. To solve this problem, we propose a new pre-arbitrated slot access scheme, distributed slot reuse with silence detection, which can greatly improve utilization by taking advantage of two features in voice communications, silence detection and source/destination locality. In addition, we prove the scheme's correctness, design an algorithm to solve its related problem of virtual circuit identifier type selection and discuss its implementation details. Simulations are performed to show that the new scheme is much better than two previous schemes in terms of bandwidth utilization and drop rate.

Architecture of multichannel DQDB network

The authors explain the basic architecture of the multichannel DQDB (distributed queue dual bus) network which is a generalisation of the single channel DQDB to the multichannel case by wavelength division multiplexing technology.

Adaptive bandwidth balancing mechanisms for DQDB networks

To improve fairness in distributed queue dual bus (DQDB) metropolitan area networks a mechanism known as bandwidth balancing (BWB) has been introduced in the final version of the IEEE 802.6 standard document. Since then several changes to the basic mechanism, attempting to adhere to different interpretations of the fairness concept and to match the needs of different categories of users, have been proposed. In this paper attention is focused on the adaptive class of fairness control mechanisms and two solutions are analysed and compared. In order to do this, analytical models suited to the study of DQDB networks under overload conditions are introduced. The models are also amenable to the evaluation of the transient behaviour of DQDB networks, thus enabling a thorough investigation of the performance that can be obtained by adopting different fairness control mechanisms. The analytical models have been validated through the use of a software simulator. Numerical indices measuring the performance of the balancing mechanisms mentioned above are also given.

Improving access delay fairness of DQDB MANs under overload condition

The main advantages of Distributed Queue Dual Bus (DQDB) are the simplicity of its medium access control and that it can utilize all of the channel bandwidth independent of data transmission rate and network size. The data transmission rate of DQDB is in the range from DS3 to SONET speeds. Due to the increased ratio of propagation delay to segment transmission time, the information that a station receives about the current state of DQDB network can be out of date in such a high speed environment. This results in the position dependent characteristics of the network, which is the main reason that unfair throughput and access delay appears, especially when network is overloaded to cause unpredictable behavior. Though Bandwidth Balancing Machine (BWBM) is enabled in the IEEE 802.6 DQDB, and the fairness of throughput may be reached, the unfairness of access delay still exists, especially under overloaded condition. In this paper, we propose an efficient modification of REQ Queue Machine (RQM) with an access protection protocol. The modified RQM scheme eliminates longer access delay for downstream stations along the direction of transmission. The utilization of a modified protection scheme prevents the stubborn unfairness for the upstream stations close to the slot generator. Simulations show that our proposed method can reach fairness in terms of throughput and access delay.

DQDB Protocol—A Performance Study

A tutorial view of distributed queue protocol is presented. Some aspects of problems in management of distributed queue dual bus network is considered. A novel algorithm for affiliation of new nodes to such networks without making any significant modification in the network is suggested. The simulation procedure has been summarized in a simple manner. Performance analysis of network has been obtained by extensive simulation studies. Emphasis has been given on increased number of nodes in the DQDB network for performance comparison.

Delay analysis of DQDB networks with slot preuse and reuse

The current IEEE 802.6 standard has defined the distributed queue dual bus (DQDB) as the subnetwork for metropolitan area networks (MAN). However, this standard leaves some latitude in the possibility of slot multiuse. This paper addresses the issue of DQDB network delay performance when special devices called erasure nodes are employed with or without the so-called slot preuse technique, which has been proposed recently. It is shown that introducing this technique into DQDB networks dramatically improves system performance in terms of average segment delay and maximum throughput, especially when there is some locality in traffic patterns or the network consists of a small number of nodes.

Priority promotion DQDB networks to improve fairness

The Distributed Queue Dual Bus (DQDB) network is considered as a Metropolitan Area Network standard. However, it exhibits unfairness problems in bandwidth allocation when the network is overloaded. The bandwidth balancing (BWB) scheme has been recommended by CCITT to improve the fairness of bandwidth allocation, but the price paid is the bandwidth waste. In this paper, we present a different solution, the priority promotion (PP) scheme, to improve the fairness problem of the DQDB network. This solution requires only a minor modification of the current protocol, and wastes negligible bandwidth to solve the unfairness problem. The results indicate that the delay time of each message in the proposed priority promotion scheme is much shorter than that of the BWB scheme: thus the PP scheme has the performance of lower delay time and higher throughput than that of the BWB scheme. When the control parameter in the priority promotion scheme is appropriately chosen, each station in the DQDB network can be allocated a preserved bandwidth, so that the unfairness problem of bandwidth allocation is eliminated.

Heuristic algorithms for constructing optimized structures of linear multihop lightwave networks

The authors exploit the capabilities of lightwave technology in order to construct photonic implementations of adaptive and optimized distributed queue dual bus (DQDB) structures. These (virtual) structures are linear and multihop in nature, and they can be constructed on any physical topology by exploiting the broadcast-and-select property of WDM lightwave networks. The present study is important since it will allow DQDB (IEEE 802.6) networks to scale up by taking advantage of the various attractive properties of lightwave technology when they become available. The specific problem is on topological design, and it can be stated as follows: given that the network nodes must be connected linearly and that the node positions in the network can be adjusted by properly tuning their (optical) transmitters and receivers, what is the best pattern for interconnecting them? Two sets of heuristic optimization algorithms are formulated. The first set is concerned with minimizing the maximum flow in any link. The second set of heuristics requires the knowledge of not only the traffic matrix but also the distance matrix, and these heuristics are aimed at minimizing the network-wide mean packet delay. A dynamic node migration heuristic is also formulated under which neighbouring nodes swap their positions based on local information in order to preserve the optimality criterion in effect when the offered traffic changes. The performance of these heuristics are compared, some of their properties are analyzed, while their other attractive properties are highlighted via numerical examples. >

ATM traffic transfer via queued-arbitrated DQDB

The easy and cost effective interworking of Distributed Queue Dual Bus (DQDB) and Asynchronous Transfer Mode (ATM) protocols is of prime importance for the evolution of the broadband integrated services digital network (B-ISDN) and the long-term success of MANs as tributary networks. In this paper, we study several practically useful scenarios for the interworking of ATM Customer Premises Networks (CPN) through a transit DQDB network. Suitable Interworking Unit (IWU) protocols are presented and compared. It is shown that the most advantageous solution in terms of service quality and IWU simplicity and robustness is the use of a Connection Oriented (CO) DQDB service exploiting the Queued-Arbitrated mode of access. Also, the provisions required in the definition of a CO DQDB service are pointed out. Finally, the implementation of an IWU applying the ideas presented is outlined.

A comparison of linear and mesh topologies-DQDB and the Manhattan street network

The authors make a performance and reliability comparison of two networks that have been proposed for use as high-speed metropolitan area networks (MANs)-the Manhattan street network (MSNet) and the distributed queue dual bus (DQDB) network. Both networks use slotted access protocols and have the same number of links, transmitters, and receivers per node. The DQDB network has been adopted by the IEEE 802.6 committee as the metropolitan area network (MAN) standard. The authors demonstrate the relative superiority of the MSNet over the DQDB network. They show that the MSNet provides a much higher network throughput for a variety of traffic patterns-uniform and nonuniform. They also look at the reliability of both networks and show that the MSNet can survive more failures than the DQDB network and that failures cause a lesser performance degradation in the MSNet. It is also shown that higher-level mechanisms are required in the DQDB network to recover from link failures whereas deflection routing is sufficient in the MSNet.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Alternative strategies for improving the fairness in and an analytical model of the DQDB network

The unfairness problem of the distributed queue dual bus (DQDB) (IEEE Std 802.6) network is addressed, and several alternative solutions that can improve the network's fairness are proposed. Implementation methods that require simple additional hardware on top of the regular DQDB interface are outlined. Simulation examples are employed to compare the performance of the schemes and to gain insight into their characteristics. The performance is also compared with that of the original DQDB and the bandwidth-balancing DQDB. An analytical model of the DQDB network is developed. Some constrained assumptions for analytical tractability are used to obtain a Markov chain model for (an earlier version of) the entire DQDB network, the corresponding state-space explosion problem is highlighted. For reasonably small systems, the analytical model can predict an individual station's throughput and mean segment delay for known (possibly asymmetric) loading patterns. The model is verified via simulation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A General Bandwidth Allocation Scheme for Multi-Priority Traffic on DQDB Networks

The Distributed Queue Dual Bus (DQDB) Media Access Control (MAC) protocol, the current IEEE 802.6 standard for Metropolitan Area Networks, functions well only for one priority level even when three priority levels are designed to support multi-priority traffic. In this paper, a general and flexible bandwidth allocation scheme for handling the multi-priority traffic is proposed. In this scheme, the entire bandwidth can be shared by different priority levels according to a pre-specified ratio. For any absent priority level, the corresponding pre-allocated bandwidth will be automatically reallocated to other priority levels. This scheme is also rather suitable for solving the bandwidth domination problem, the priority domination problem, the priority capturing problem, and the bandwidth allocation problem of the DQDB networks which are unable be effectively solved by the standard DQDB protocol with the bandwidth balancing mechanism.

Incorporating continuation-of-message information, slot reuse, and fairness in DQDB networks

Abstract Several important modifications to the distributed queue dual bus (DQDB) (IEEE 802.6) protocol for metropolitan area networks (MANs) are proposed. These modifications are aimed at improving not only the throughout and delay performance of the network but also its fairness performance. The first proposal exploits the continuation-of-message (COM) information in a DQDB segment in order to minimize the mean overhead for multi-segment messages. Then, a scheme for combining the COM information along with the spatial reuse of slots is proposed, thereby achieving even higher throughput and lower delay. Simulation models are used to study the performance gains achievable by using the COM and the slot reuse approaches. Although slot reuse has been proposed before to improve the DQDB protocol's performance, DQDB's unfairness problem becomes more pronounced when slots are reused. This paper also proposes several schemes to achieve different fairness criteria in a DQDB network employing slot reuse, namely: (a) an individual station's throughput proportional to the number of stations downstream from itself, (b) equal throughput at all stations, and (c) an individual station's throughput proportional to its own offered load. Analytical results corresponding to these schemes are developed, and they are verified via simulation. The proposed schemes can be implemented with just one additional counter and one register (on top of the regular DQDB hardware) at each station.