The IEEE token bus-A performance bound on GM MAP

All versions of the General Motors manufacturing automation protocol (GM MAP) specify that MAP's lower-layer services are to be provided by the IEEE 802.4 token bus. An understanding of 802.4 and its performance aspects is therefore a prerequisite to predicting the performance of MAP. It is shown how total bus capacity is divided among data throughput, token traffic, and propagation delays. The relative contributions of access delay and queuing delay to total message delivery time are discussed. The effects on message delivery times of message size and the number of active stations are also reported. As the token cycle time increases beyond the target rotation time for each of the asynchronous access classes, service to the lower-priority classes is curtailed; a formula that can be used to identity the offered load at which the transition from normal to curtailed service begins is presented     

A New CSMA-CD Protocol for Local Area Networks with Dynamic Priorities and Low Collision Probability

This paper reports on the implementation of a local area network (LAN) operating under a new CSMA-CD protocol with dynamic priorities (CSMA-CD-DP). User terminals, host computers, and other servers are connected to a common broad-band channel through N network access stations in a clustered manner. This concept reduces the number of network access stations and enhances the utilization of hardware and software resources greatly. A new protocol has been developed which organizes the decentralized operation of the distributed network access stations and which allows for a number of specific features. In the idle state the channel is operated in the contention mode. After the beginning of a transmission, the channel is operated in a reservation mode. Channel arbitration after a completed transmission is resolved by staggered delays; at any time, each station owns a distinct transmission delay which is changed after every successful transmission by broadcasted acknowledgments. This protocol strictly limits the possibility of collisions and approaches the effectiveness of token and polling protocols with increasing load. Through specific allocations of transmission delays, static priorities or dynamic overload control can be realized easily. The performance of the CSMA-CD-DP protocol has been modeled and analyzed analytically as well as by simulation. Results for normal load and overload reveal high throughput and low transfer times which are basic for a wide range of applications in LAN's.     

Setting target rotation times in an IEEE token bus network

The IEEE standard 802.4 token bus protocol requires each network station to implement a synchronous (highest priority) message class, and permits a station to implement three lower priority classes: urgent asynchronous, normal asynchronous, and time available. Each of the lower three priorities (called access classes) is assigned a target token rotation time that limits the amount of time that a station can use to service lower priority traffic. A formulation of the problem is presented in which messages are transmitted from an access class as long as network throughput remains below a user-specified threshold. Formulas are derived that transform this priority scheme, based on network throughput limits, into the proper target rotation time settings that the token bus protocol actually requires. The analytical model is compared with a computer simulation of the token bus protocol and shows close agreement     

基于令牌总线网络的RS 485应用

应用RS 485物理层标准,构建总线型的控制网络,采用令牌方式实现总线的共享访问,以适应控制网络实时性要求。在进行令牌总线协议设计时,从RS 485特点出发,以特殊的设计来简化协议,提高协议的效率。为了保证网络的可靠性,在协议中采用了有效的错误处理方法,即保证数据传输的正确性,又减小了协议的控制开销,以简单、方便、快捷、高效的方式实现控制网络的介质访问管理,给RS 485网络提供一种较好的连网模型。     

采用动态令牌的MANET多址接入协议

本文设计了一种采用动态令牌算法的MANET多址接入协议,解决了隐藏终端和入侵终端问题.利用这种算法,不再需要为令牌的传递预先建立虚拟的令牌逻辑环路,而是根据当前的网络拓扑结构自动地形成令牌的传递路由,使得令牌的传递能够适应网络拓扑结构动态的动态变化.同时,通过周期性地产生令牌并严格地限制每个令牌的生存时间,简化了令牌的维护过程,并为时延敏感的业务提供良好的QoS保障.另外,该协议采用一种互同步技术,具有成本低廉、运行可靠的特点,可完全独立于其它系统(如GPS等),且已应用于实际的MANET网络.     

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     

Evaluation of the Random Token Protocol for High-Speed and Radio Networks

In high-speed communication networks, the ratio between the end-to-end propagation delay to packet transmission time is large, causing increased scheduling overhead in demand assignment protocols and increased collision probabilities in random access schemes. These lead to rapid degradation of the channel utilization in both channel access control approaches. In this paper, we present a "random token" oriented protocol where channel access is scheduled by random, implicit token passing leading to lower channel access control penalty. By optimally balancing the collision and scheduling penalties, the protocol allows the network to reach better performance than that obtained from random access schemes in networks with and without collision detection, without imposing additional system operational assumptions. Specifically, the random token protocol does not require knowledge of the number of stations, their identities, or synchronization in periods of silence. Therefore, the protocol is also suitable for high-speed networks with frequent reconfiguration and for mobile radio networks.     

A media access and feedback protocol for reliable multicast over wireless channel

A link level reliable multicast requires a channel access protocol to resolve the collision of feedback messages sent by multicast data receivers. Several deterministic media access control protocols have been proposed to attain high reliability, but with large delay. Besides, there are also protocols which can only give probabilistic guarantee about reliability, but have the least delay. In this paper, we propose a virtual token-based channel access and feedback protocol (VTCAF) for link level reliable multicasting. The VTCAF protocol introduces a virtual (implicit) token passing mechanism based on carrier sensing to avoid the collision between feedback messages. The delay performance is improved in VTCAF protocol by reducing the number of feedback messages. Besides, the VTCAF protocol is parametric in nature and can easily trade off reliability with the delay as per the requirement of the underlying application. Such a cross layer design approach would be useful for a variety of multicast applications which require reliable communication with different levels of reliability and delay performance. We have analyzed our protocol to evaluate various performance parameters at different packet loss rate and compared its performance with those of others. Our protocol has also been simulated using Castalia network simulator to evaluate the same performance parameters. Simulation and analytical results together show that the VTCAF protocol is able to considerably reduce average access delay while ensuring very high reliability at the same time.     

R-net: A high speed fibre optics network with reservation access protocol

This paper proposes and describes R-net, a network with a new reservation access protocol that is very suitable for implementation with optical fibre in high speed local area networks. In the operation of R-net, a framing structure with variable length is superimposed on the network bus to bound the network medium access delay which is a highly desirable feature for real time applications. As long as the frame length constraint is not violated, the performance of R-net network is not limited by operating data rate, and the utilization can be set to unity by choosing the appropriate network parameters. The proposed network has the advantage of efficient throughput approaching unity for most practical configurations, bounded delay, and at normal load, the network protocol has fair access for all nodes and allows dynamic bandwidth allocation between the nodes connected to the network bus. A performance (delay and utilization) comparison between R-net and Expressnet is also presented.     

Lookahead Network

This paper formalizes and extends a tree-based local area network, called the lookahead network, proposed by Lipovski, Goyal, and Malek. The leaf nodes in the network are workstations, and the nonleaf nodes consist of pure combinational logic used in carry lookahead circuits of binary adders. Any of the ring or bus access protocols (token passing, contention, etc.) can be used on this network. The first objective of this paper is to give a formal definition of the lookahead logic and show that it can be operated in either a bus or a ring mode. The advantage of using the lookahead logic is that it makes the network operation fail-soft, and since this logic is recursively defined, it simplifies network installation, expansion, and partitioning procedures. The second objective of this paper is to define a new round-robin access protocol on the lookahead network, which has much better throughputdelay characteristics than that of a token ring when the number of active nodes on the network is increased and/or the transmission speed is increased, and/or the average packet size is decreased. Moreover, this new protocol can implement a message-based priority scheme, which makes it useful in integrated voice and data networks.     

RATO-net: a random-access protocol for unidirectionalultra-high-speed optical fiber network

The local network medium is a pair of unidirectional fiber optic buses to which stations are connected via passive taps. For this configuration, a random-access protocol called RATO (random-access time-out) is presented. RATO provides random access, fairness, and bounded delay access to all stations, and is particularly suited for ultra-high-speed transmission when the performance of the popular Ethernet becomes unattractive. Simplicity and ease of hardware implementation of RATO under ultra-high-speed environment is emphasized because the only control requirements are the sensing of activity in the bus and a fixed time delay between consecutive transmissions from the same station. Results of simulation and performance comparisons of RATO with other schemes are given. In ultra-high-speed wide-area networks, RATO outperforms all these other schemes     

Throughput analysis of a timer controlled token passing protocolunder heavy load

An analysis is presented of the throughput performance of some recently proposed token-passing local area network (LAN) protocols under a heavy load assumption. The IEEE 802.4 token bus standard which uses a cycle-dependent timing mechanism to control station access to the channel, is studied. It is shown that the cycle-dependent timing mechanism limits the token circulation times properly. Moreover, priority among different access classes is being implemented. Analytic results for computations of throughputs and cycle lengths are derived. These results provide insights into the cycle-dependent timing mechanism and also guidelines for design. Using the results derived, examples concerning the throughput behavior under different heavy load configurations, the sensitivity to parameters, system optimization with delay and bandwidth constraints, and comparison with the other integrated access schemes are studied     

容错型令牌总线网性能评价算法

本文对符合ＩＥＥＥ８０２．４和ＭＡＰ标准的令牌总线网的性能指标评估给出了一种新的计算方法。文中重点考虑了具有信包重发机制、令牌最大保留时间和信包缓冲区容量有限的令牌网络的性能指标评估问题，克服了以往不能分析同时具有信包重发机制和令牌最大保留时间令牌网性能的局限。文中给出的方法简单易行、计算迅速、精度颇高。最后，本文通过例题说明了此方法的应用。     

Mixed time-constrained and non-time-constrained communications inlocal area networks

It is well known that some time-token medium access protocols for local area networks (LANs) like the IEEE 802.4 token bus and the FDDI token ring can guarantee the medium access delay for time-constrained packets. However, a problem which has been largely overlooked is how these protocols can be made to provide a maximum throughput for nontime-constrained packets while guaranteeing the delay bound of time-constrained packets. The authors first show how the parameters of the IEEE 802.4 token bus and the FDDI token ring can be set to solve the above problem. Then, they design a new timer mechanism for the timed-token protocols which provides the highest guaranteed throughput of nontime-constrained packets among a set of medium access protocols called the token passing protocol, to which most of the existing non-contention LAN protocols belong. They present numerical examples to compare different protocols, all of which have shown the superiority of the proposed protocol to the others     

The effect of bandwidth allocation policies on delay inunidirectional bus networks

We consider the problem of allocating bandwidth fairly to each node in a shared, unidirectional bus network. We focus on the p_i persistent protocol, since these are open loop policies designed to operate well in high speed networks, which have a very large bandwidth-delay product and feedback in the upstream direction is not available in a timely manner. First, we introduce an improvement to the basic p_i persistent protocol, in which we replace random coin tosses with a deterministic counting algorithm, and thereby reduce the delays for all nodes for any given choice of {p_i}. We then describe an exact method for calculating average packet delays and queue lengths in both the p_i persistent and our new deterministic n out of m protocols, based on the regenerative approach of Georgiades et al. (1987). These delay results, together with simulation measurements, show that both of these protocols still waste some bandwidth. After presenting a lower bounding argument to show that some wasted bandwidth is inevitable in all such distributed access control schemes, assuming a passive bus without feedback in the upstream direction, we show that changing the bus to unidirectional point-to-point links between (very simple) active interfaces at each node allows us to construct distributed access schemes that require no upstream feedback and are both work conserving and fair. To illustrate how this can be done, we introduce the p_i preemptive protocol, in which each node randomly inserts its own packets into the traffic arriving from upstream. We derive a simple and effective heuristic for calculating the preemption probability for each node, and use simulation to show how well it equalizes the delays at each node     

Performance Evaluation of Wireless Controller Area Network (WCAN) Using Token Frame Scheme

In this paper, a proposed new wireless protocol so-called wireless controller area network is introduced. WCAN is an adaptation of its wired cousin, controller area network protocol. The proposed WCAN uses token frame scheme in providing channel access to nodes in the system. This token frame method follows the example used in wireless token ring protocol which is a wireless network protocol that reduces the number of retransmissions as a result of collisions. This scheme based on CAN protocol allows nodes to share a common broadcast channel by taking turns in transmitting upon receiving the token frame that circulates around the network for a specified amount of time. The token frame allows nodes to access the network one at a time, giving ‘fair’ chance to all nodes instead of competing against one another. This method provides high throughput in a bounded latency environment. The proposed WCAN protocol has been developed and simulated by means of QualNet simulator. The performances of this proposed protocol are evaluated from the perspective of throughput, end-to-end delay and packet delivery ratio, and are compared against the IEEE 802.11 protocol. Simulation results show that the proposed WCAN outperforms IEEE 802.11 based protocol by 62.5 % in terms of throughput with increasing network size. Also, it shows an improvement of 6 % compared to IEEE 802.11 standard at a higher data interval rate.     

Register insertion bus architecture for fibre optic local area networks

A protocol for fibre optic local area networks, the register insertion bus (RIB), is proposed. RIB uses a folded-bus topology with an access scheme which includes the existence of two buffers in each station to hold packets that would conflict. Simulations have shown the access scheme to efficiently utilise the network with a minimum of overhead. RIB implements a fair access scheme at normal network loads but at high loads a priority scheme is implemented. An enhancement technique is discussed that will implement a fair access scheme by altering the time between transmissions based on the measured network load.<>     

Modeling and performance analysis of a symmetric fast-circuitswitched robust-WDM LAN with the AR/LTP protocol

Robust wavelength division multiplexing (WDM) is a technique to implement WDM local area networks (LAN's) in the presence of laser wavelength drifts. A medium access control (MAC) protocol is used in conjunction with a wavelength-tracking receiver to tolerate the variations of transmission wavelengths. Among the proposed medium access schemes, the aperiodic reservation (AR) scheme with token-passing based control channel gives the best performance. An AR protocol with a lenient token passing policy (AR/LTP) is thus presented. An analytical model is developed to design Robust-WDM AR/LTP LAN's and predict their performance characteristics. The model can be used to evaluate the variation of waiting time and throughput for load and network parameters such as the arrival rate, number of nodes, number of channels and timing parameters. It also addresses the issues related to traffic loss, channel-blocking, token rotation time, network span, and the effect of device parameters     

The pi-persistent protocol for unidirectionalbroadcast bus networks

A protocol for multiaccess communication over unidirectional bus networks is proposed, and its performance capabilities are determined. Under this protocol, time is slotted with a slot equaling a packet's transmission time. A station with a packet to send persists in transmitting its packet in an empty slot with probability p_i until it is successful. Three criteria for fairness in selection of the p_i are modeled using Markov chains, which are solved to obtain the proper p_i that satisfy each fairness criterion. Unlike previous studies of unidirectional bus networks, stations are allowed to buffer more than one packet. The average packet delay for this protocol is bounded, and the maximum achievable throughput approaches unity with increasing buffer size. Further, the protocol provides better delay versus throughput behavior for fixed packet lengths than previous round-robin schemes, its performance is insensitive to bus characteristics, and it appears to be particularly well suited for fiber-optic network applications requiring long distances and high bandwidths. Simulation results that confirm the predicted performance are included