With the explosive growth of the Internet system, demands for broadband communication networks have rapidly increased to provide high quality network services. For this purpose, the IEEE 802.6 MAC standard protocol defines the distributed-queue dual bus (DQDB) for metropolitan area networks (MANs). The isochronous channel reuse problem (ICRP) has been studied for efficient use of DQDB by finding proper channel assignments to incoming connection requests. In this paper, we first define the generalized isochronous channel reuse problem (GICRP) as a generalization of ICRP, to afford demands of simultaneously satisfying plural connection requests such as for multicast applications, where certain sets of connection requests must be assigned channels simultaneously. We prove the NP-completeness of its decision problem. Then, we propose a minimum dead space (MDS) algorithm as a heuristic approach to GICRP. The extensive simulation results show that with shorter computation time, our MDS algorithm can always find better channel assignments reducing the waiting time for packet transmissions than the best existing algorithm for conventional ICRP.

A loop architecture of DQDB with slot reuse (LDQDB-SR) segmented by erasure nodes was studied to overcome the performance limitation due to the nature of the unidirectional bus architecture of DQDB with slot reuse. The LDQDB-SR adopts the destination slot release and an inter-segment bandwidth regulation based on the distributed queuing system of DQDB. This network suffers not only from severe throughput deterioration due to a high regulation cost and an excessive transit delay but also from unfairness in bandwidth sharing, especially under an overload condition. In this paper, we introduce an enhanced loop architecture of DQDB with slot reuse (ELDQDB-SR) to improve the performance of LDQDB-SR. The ELDQDB-SR uses a quota-based inter-segment bandwidth regulation mechanism to effectively control the bandwidth use of each segment. Each station selects the bus that minimizes the number of erasure nodes on the path to destination stations. Fairness control methods of DQDB are reviewed and the alpha-tuning mechanism is modified to achieve a fair bandwidth distribution among stations within each segment. Simulation results show that the ELDQDB-SR gives an enhanced throughput level and also maintains good fairness under overload conditions.

The location of stations on the buses can not be ignored in the analysis of the DQDB protocol, especially when traffic load is heavy. In this paper, we propose a new method to model the DQDB (Distributed Queue Dual Bus) protocol by assuming that the request arrival process depends on both the value of the request counter and the location of a station on the buses. By taking these dependences, we can catch the real behavior of the DQDB stations, which is locationally dependent and unfair under heavy load traffic. Based on this model, we analyze the DQDB system with finite buffer by considering the request counter states and buffer states separately and obtain the throughput, mean packet delay and packet reject probability of individual stations. The throughput in individual stations matches that of simulation very well within the range of traffic up to the channel capacity. Also the delay and packet reject rate performance is good up to moderate traffic load. These numerical results reveal the properties of the location dependence and the unfairness of DQDB system under heavy load condition. The analytic results under heavy load traffic for a general DQDB system has not been reported till now. Therefore we conclude that our model and analysis are valid and effective.

The DQDB MAC Protocol standardized by the IEEE 802.6 Committee is a single segment bandwidth reservation scheme that only reserves bandwidth for one segment in the distributed queue. Recently, multi-segment bandwidth reservation schemes that reserve bandwidth for not only one segment in the distributed queue but also a part of or all segments in the local node queue have been proposed. In this paper, we propose a new multi-segment bandwidth reservation protocol that can quickly react to changes in a node's traffic and can quickly allocate the bandwidth fairly and waste-free. We also evaluate the mean message transmission delay and throughput convergence performance by simulation. As a result, it is shown that the mean message transmission delay can be decreased and the throughput can be quickly converged to fair bandwidth allocation.

Two simple and high performance multichannel distributed queue dual bus (MDQDB) protocols based on the wavelength division multiplexing (WDM) network technology are proposed, and the network architecture and operations are presented. To be suited for a high speed network, they inherit the advantages of the DQDB protocol such as node simplicity, network flexibility and distributed operations of individual nodes. The network capacity can also be greatly increased with marginal increase of node complexity. Simulation has been done to estimate the performances such as throughput and average access delays for individual nodes. The influence of the bandwidth balancing mechanism on the two protocols is considered at medium, high, and overload conditions. We also investigate the fairness characteristics in asymptotic conditions for various initial states.

The Guaranteed Bandwidth Protocol (GBW) is an access scheme being proposed for implementation of connection oriented services in DQDB networks. Connection oriented services are expected to handle both constant bit rate (CBR) and variable bit rate (VBR) traffic that have delay and jitter constraints. It has been reported that the GBW protocol can provide guaranteed bandwidth and lower delays compared to the ordinary DQDB protocol. However, the intensity of the jitter introduced by this scheme has not been made clear. This paper compares the jitter results for the GBW scheme to those obtained by a new access method called Modified Guaranteed Bandwidth (MOD_GBW) protocol, which is proposed here. It is shown through simulation that MOD_GBW also provides guaranteed bandwidth and that its delay and jitter characteristics are significantly better than those of the GBW protocol. In the simulation model, the DQDB stations are divided into two groups: 1)Real-Time (RT) stations that generate either CBR or VBR real-time traffic; and 2)Data stations that generate memoryless type of traffic. Data stations operate according to the ordinary DQDB protocol only. The main performance measure adopted here for the real-time traffic is the interdeparture time distribution of consecutive segments from an RT-station. We define the variance of this distribution as jitter. This paper also shows the impact of GBW/MOD_GBW on the performance of the data stations by evaluating their throughput and average bus access delay. Finally, we show that the network performance is weakly related to the number of RT-stations under MOD_GBW, but it depends strongly on the overall loading.

In this paper, we formulate and solve a discrete-time queueing problem that has two potential applications: ATM multiplexers and DQDB networks. We first consider the modeling of an ATM multiplexer. The object of the analysis is a periodic traffic stream (CBR traffic), which is one of the inputs to the multiplexer. As in previous works of the subject, we consider a memoryless background traffic input. Here, in addition to this background traffic, we take into account the influence of a high-priority traffic, which is time-correlated and requires expedited service. We analyze the influence of these two types of traffic on the statistics of the interdeparture time (jitter process) and the delay of the periodic traffic stream. We obtain their distributions in a form of z-transforms, and from these we derive closed form expressions for the average delay and the variance of the interdeparture time. Our results show that the delay and jitter are very sensitive to the burstiness of the high priority traffic arrival process. We next apply our analytical modeling to a DQDB network when some of its stations are driven by CBR sources. We can obtain interesting results concerning the influence of the physical location of a DQDB station on the jitter.

CDMA cellular land network (CCLN) consists of base stations connected to selector bank subsystem. In the case of considering only the voice traffics, CCLN can be designed based on E1/T1 physical line and HDLC protocol with fixed or variable length. However, it is necessary to support not only voice but also data traffics in CDMA cellular system. Thus, it is needed to use physical lines efficiently to increase bandwidth efficiency and transmission speed. However, the conventional CCLN has some problems that the bandwidth is wasted because each BTS has its own private line. In this paper, the method using Distributed Queue Dual Bus (DQDB) Metropolitan Area Network (MAN) as a CDMA interconnect subsystem (CIS) is considered, and the performances of conventional and proposed methods constructing CIS are analyzed by computer simulation. According to the simulation results, if the traffics from all mobile stations are uniformly distributed among all BTSs, the performances of both conventional and proposed methodology have turned out to be almost equal. However, the performance of methodology using the DQDB MAN is much better than that of conventional method, in the case that the traffics from all mobile stations are nonuniformly distributed.

In this paper we propose a congestion control method for interconnecting connectionless MANs with ATM networks which works at the gateway of DQDB. Since connectionless traffic belong to loss sensitive data, they should experience small cell loss rate. Due to the function of congestion control in the gateway, we can prevent the network from overload which not only introduces serious cell loss at remote destination gateway but also lots of undesirable retransmissions and time delay in the ATM network. It neither needs to modify the slot format of DQDB nor to increase the overhead so the implementation is simple and cost effective. Performance results are also provided to verify the effectiveness.

The Distributed Queue Dual Bus protocol (DQDB) has been adopted as the metropolitan area network (MAN) standard by IEEE802.6 committee. Recently, the unfairness problem in the DQDB protocol, by which head stations benefit, has been pointed out. Although a fair bandwidth distribution among the stations is obtained by adding the so-called bandwidth balancing mechanism into the DQDB protocol (DQDB/BB), the DQDB/BB protocol leaves a portion of the available bandwidth unused, and it takes a considerable amount of time to converge to fair channel assignment. In this study, to overcome the drawbacks in DQDB and DQDB/BB, we introduce a new media access control protocol which is based on assigning each station a level according to some traffic information such as the queueing length, delay time etc. Only the station with the highest level is allowed to transmit. Through the operation of level assignment or the choice of level function, the transmission can be easily controlled in a distributed manner. This protocol is simple compared with DQDB/BB and can be implemented in the DQDB architecture. The simulation results show that the new protocol obtains not only fair throughput regardless of the distance between the stations, but also fair delay performance. In addition, the new protocol can easily provide preempty priority service through level assignment. The new protocol converges to fair distribution of the channel in the time required for only one or two round-trips. This is very fast compared with the DQDB/BB protocol.