Performance analysis of the timed token protocol of FDDI andFDDI-II

The performance behavior of an FDDI (fiber distributed data interface) system with synchronous traffic as well as an extended FDDI (FDDI-II) system with isochronous and asynchronous traffic is evaluated. Multiple asynchronous priorities are considered, one priority level at each station. an iterative algorithm to calculate the first two moments of the cycle (i.e. token rotation) time is presented, and the major system characteristics are derived from the analysis in terms of queue-length distributions and mean waiting times of the packets. Since the model considers queues with limited buffer size, loss probabilities of data packets can also be calculated. Some results obtained by the approximate analysis are discussed using example configuration, and the accuracy is validated by detailed computer simulations. The complexity and convergence behavior of the algorithm is studied, and it is shown that the algorithm converges very quickly     

The nonoptimality of synchronous bandwidth allocation schemes forthe timed token protocol

This letter examines the optimality of three published “optimal” synchronous bandwidth allocation (SBA) schemes for guaranteeing synchronous message deadlines with the timed token medium access control protocol. It is found that none of these three schemes is optimal. The nonoptimality has been demonstrated by a numerical example and the root cause has been indicated. The development of an optimal SBA scheme remains a challenge     

Performance of the timed token scheme in MAP

Two new analytic approximations are given for the mean delay in the timed token bus network specified in MAP (manufacturing automation protocol). Each station on the network has two kinds of timer for controlling the maximum amount of time for data transfer before giving up the token. High-priority stations would set large values in the token holding timer (THT) and transmit until the timer expires. Low-priority stations compare the elapsed time since the last token arrival (measured cycle time) to the token rotation timer (TRT) setting, and transmit only for the time left in the timer. The first approximation, based on Fuhrmann's bound for the limited-k service discipline, is for the symmetric case where all the stations have the same traffic load and the identical THT or TRT settings. The approximation has been compared to simulation results, and found to be quite accurate for a representation factory network, with THT or TRT set at two and five times the average total walk time. The second approximation is for the asymmetric case where there is one saturated low-priority (limited-TRT) station, and the rest of the stations in the network have high priority with limited-THT service. These two formulas will be useful in the planning and operation of MAP networks by providing guidance in the choice of timer settings for meeting different priority service requirements     

WTRP - wireless token ring protocol

The wireless token ring protocol (WTRP) is a novel medium access control (MAC) protocol for wireless local area networks (WLANs). In contrast with IEEE 802.11 networks, WTRP guarantees quality of service (QoS) in terms of bounded latency and reserved bandwidth, which are critical in many real-time applications. Compared to 802.11, WTRP improves efficiency by reducing the number of retransmissions due to collisions, and it is more fair as all stations use the channel for the same amount of time. Stations take turns transmitting and give up the right to transmit after a specified amount of time. WTRP is a distributed protocol that supports many topologies, as not all stations need to be connected to each other or to a central station. WTRP is robust against single node failures, and recovers gracefully from multiple simultaneous faults. WTRP is suitable for interaccess point coordination in ITS DSRC, safety-critical vehicle-to-vehicle communications, and home networking, and provides extensions to other networks and Mobile IP.     

Determination of LTPB parameters to guarantee message deadlines

A bandwidth allocation scheme for a linear token passing multiplex data bus is proposed based on balancing message transmission time with traffic load to each node. It is proved to provide a network worst case achievable utilization of 50%. Under this allocation scheme, closed-form expressions for the initialized value of token holding timers and token rotation timers in each node are obtained.     

Effect of nodes reordering on the schedulability of real-timemessages in timed token networks

This letter addresses the effect of different ordering patterns of network nodes on the ability to schedule real-time messages in a timed token network where the timed token medium access control protocol is employed. It is found that for any given setting of network parameters, a set of real-time message streams which is unschedulable under one particular nodes-ordering may become schedulable under another different nodes-ordering. Some guidelines for avoiding a possible misjudgement in the schedulability due to inappropriately ordered nodes are discussed     

一种多信道的分簇式短波令牌协议

传统的短波令牌协议( HFTP)调度方式单一,在没有数据传送时,信道资源会被各节点间的令牌传递所占用,且令牌在通信质量较差时易丢失。基于此,提出一种多信道的分簇式短波令牌协议( CHFTP),通过以通信质量评估为标准的分簇算法和基于预约的动态令牌调度,减小了令牌丢失的概率和令牌传递、处理的开销,并给出了仿真分析。仿真结果表明,该协议的端到端平均时延和网络吞吐量明显优于短波令牌协议, CHFTP 的平均时延最多可减少75%,网络吞吐量最多可增加66.7%,适合在短波通信网络中使用。     

Approximate performance analysis of real-time traffic over heavilyloaded networks with timed token protocols

This paper studies timed token protocols with respect to real-time packet traffic in local area networks (LANs), such as FDDI and token bus, employed in distributed control systems. Typically, in such systems, three classes of packet traffic are encountered. The first class consists of packets cyclically generated by data acquisition tasks. The second traffic class is represented by packets generated in a random manner by control tasks and sporadic events. Finally, the third traffic class represents nonreal-time packet streams such as, for example, file transfers. To evaluate protocol performance, three performance measures are taken into account with respect to randomly generated real-time traffic: the mean waiting time, the blocking probability, and the probability that accepted packets will wait for service no longer than a specified time limit. In order to determine the last performance measure, a two-moment approximation of the waiting time distribution is applied. All three performance measures are evaluated at the beginning of the heavy network load region. Two examples of numerical calculations compared with computer simulations done for FDDI-II and token bus networks are given     

基于令牌的无线传感器网络MAC协议

为了更进一步减少信道冲突和网络能耗,提出一种基于令牌的链式无线传感器网络MAC协议.协议自定义信标帧和数据帧,在传感器节点完成时间同步后,以信标帧中的令牌为控制信息对相邻两个传感器节点进行收发控制,实现数据从链尾节点到链头节点的顺序上传.研究表明,该协议不仅能够满足系统的稳定性要求而且能够有效降低功耗.     

Semi-Markov performance model of an extended token bus protocol†

In this paper we present the semi-Markov performance model of a bus protocol (IMAP—Improved token bus Multi-Access Protocol) suitable for embedded networks. IMAP is an improvement over the token bus scheme and is proposed in Sood et al. (1986). The semi-Markov model is developed by considering normal and interrupt modes of operation of IMAP. Performance of IMAP has been compared to token-bus scheme.     

Selection of token holding times in timed-token protocols

Minimum requirements for the high-priority token holding time (HPTHT) in a network using timed token access protocols (such as IEEE 802.4 and FDDI) are derived in order to ensure that the throughput of synchronous messages is no lower than the amount of traffic generated for that class. The minimal value is essential in order to avoid unbounded queue length for the synchronous class as well as to achieve high network responsiveness. The results have been obtained for synchronous messages generated according to a generic periodic pattern with no constraint for the shape and for the period of the pattern. The manner in which the theoretical results obtained can be used to tune the network performance is also shown     

Performance of LAN token passing protocol under asymmetric traffic loads

The nature of the traffic offered to a token passing LAN is shown to be a significant factor affecting the mean delay against traffic throughput performance. A novel asymmetric traffic model with an exponential load distribution is presented, and its effects on the LAN performance are investigated using computer simulation.<>     

Estimation of token bucket parameters for aggregated VoIP sources

The paper presents an analytical study aimed to establish a dimensioning procedure for the token bucket algorithm, used as a meter in a Differentiated Services network architecture, when a stochastic model for the multiplexed traffic is available. In the work, we propose an equivalent queueing system method to ‘on line’ estimate the linear bounded arrival processes (LBAP) parameters when a non‐zero probability of non‐conforming packets is accepted. Then, we validate our approach considering an aggregation of fluidic On‐Off processes with exponentially distributed sojourn time in each state, used to model telephone sources with voice activity detection (VAD). To test the goodness of our analytical results, we employ discrete event simulations, which have highlighted the accuracy of the proposed dimensioning procedure in a voice over IP (VoIP) scenario. Moreover, we investigate the multiplexing gain and the effect of different parameters on the LBAP characterization of the VoIP traffic, taking into account a non‐zero probability of non‐conforming packets. Copyright © 2002 John Wiley & Sons, Ltd.     

QoS-based remote control of networked control systems via Profibus token passing protocol

This paper focuses on a quality-of-service (QoS)-based remote control scheme for networked control systems via the Profibus token passing protocol. Typically, token passing experiences random network delay due to uncertainties in token circulation, but the protocol has in-built upper and lower bounds of network delay. Thus, to ensure the control performance of networked control systems via the Profibus token passing protocol, the network delay should be maintained below the allowable delay level. As the network delay is affected by protocol parameters, such as target rotation time, we present here an algorithm for selection of target rotation time using a genetic algorithm to ensure QoS of control information. We also discuss the performance of the QoS-based remote control scheme under conditions of controlled network delay. To evaluate its feasibility, a networked control system for a feedback control system using a servo motor was implemented on a Profibus-FMS network.     

基于MR-ARQ协议的多业务QoS保证机制研究

针对无线通信中高误码率、高突发误帧、频谱资源紧张等特点,对多拒绝自动请求重传(MR-ARQ)协议相比于传统ARQ协议在提高系统吞吐量、降低系统平均传输时延和时延抖动等方面的优势性能进行了理论分析。在此基础上,针对不同业务传输时对误码率、传输时延和时延抖动的不同要求,研究了基于MR-ARQ协议的宽带无线接入系统(BWA)中多业务混合传输的服务质量保证(QoS)机制,提出了多速率重传策略、基于业务区分的多队列机制以及上行集中带宽分配等3种系统性能优化方案。最后对系统在采用上面3种方案前后的性能进行了仿真和比较分析,验证了方案的可行性和良好效果。     

Fast approximate analysis for token passing LAN protocol with asymmetrically distributed traffic loads

A new approximate analytical expression for the mean packet delay for a non-exhaustive token passing LAN is derived and compared with discrete event computer simulation. The computational problems associated with the exact and other approximate treatments are avoided because the need to solve a system of simultaneous equations is removed.<>     

A new token ring protocol and its performance for single and dual ring lan systems

This paper presents a new protocol for token ring local computer networks and its performance for single and dual ring networks using simulation modelling. The proposed protocol is a modification of the IEEE 802·5 token ring standard. In this protocol, a station can start transmission if it receives a free token or a data packet passing its interface logic. Idle stations are skipped whenever there is at least one station that has a ready packet to transmit. This is achieved by using two of the reserved bits in the frame status (FS) field. The bits used are called transmission reservation bits (TR-bits). The TR-bits are reset by the sending station and set by the first station that has data to transmit during the round trip of the associated packet along the ring. It is found that the proposed modified token ring (MTR) protocol provides better throughput and delay performance for both the single and dual ring networks. The reduction in mean delay of the MTR as compared to the standard token ring (STR) reaches about 45 per cent under heavy traffic conditions. Moreover, it is found that the performance of the MTR decreases as the packet size increases but remains higher than the corresponding performance of the STR for both the single and dual ring networks. The MTR provides a maximum throughput improvement of about 6 per cent over the STR for both dual and single ring cases. Finally, the proposed protocol (MTR) is easy to implement, with no extra hardware and has low cost/performance characteristics.     

Timer selection for satisfying the maximum allowable delay using performance model of profibus token passing protocol

Recently, the Fieldbus has become an indispensable component for many automated systems. In the Fieldbus system, real-time data containing sensor values and control commands have a tendency to rapidly lose their value as time elapses after its creation. In order to deliver these data in time, the fieldbus network should be designed to have a short delay compared to the maximum allowable delay. Because the communication delay is affected by performance parameters such as the target rotation timer of token passing protocol, it is necessary to select proper parameter settings to satisfy the real-time requirement for communication delay. This paper presents the timer selection method for Profibus token passing networks using a genetic algorithm to meet the delay requirements.     

Bayes estimators of exponential parameters utilizing a guessed guarantee with specified confidence

This paper proposes a procedure to modify the conjugate prior for the parameters of an exponential distribution in the light of an available guessed guarantee μ₀ with specified confidence c (0<c<1). The Bayes estimators under modified priors have been obtained. The proposed estimators have been compared with Bayes estimators under conjugate prior, shrinkage estimators and maximum likelihood estimators on the basis of a simulation study.     

不对称令牌总线在分布式控制系统中应用的性能分析与参数设置

建立了实时信息与非实时信息到达模型，并分析了完全不对称令牌总线网络用于控制系统时的性能，主要包括令牌循环时间和网络稳定条件。给出了参数(包括高优先级令牌持有时间和低优先级目标令牌循环时间)设置时应满足的条件。最后给出了收发缓冲器容量的设置方法。