The token grid network

An overwhelming majority of local and metropolitan area network products (LANs and MANs) are based upon linear topologies such as buses and rings. Such networks are economical for high speed operation since the station interfaces are simple and require very little transit buffering. However because of their linear structure, the total throughput is restricted by the transmission rate of the media access channels. In the paper, a token grid network is introduced where media access is performed over a two-dimensional mesh. In the resulting system, each station is two-connected and has the same transmission hardware and small station latency as in a dual token ring. In the token grid however, the total system throughput may be many factors larger than that which is possible in a dual token ring. In a large √N×√N network, the uniform load capacity is approximately √N/2 times that of an N station dual token ring. In addition, the token grid can take advantage of communities-of-interest amongst the stations. It is possible to implement the system in such a way as to achieve robust operation in the presence of station and link failures     

ISO 8802/5 token ring local-area networks

Token ring networks are the second most commonly used type of local-area network (LAN). The second version of the formal token ring multiple access mechanism, ISO 8802/5, was released in late 1995 and this rationalised many of the new developments, e.g. the 16 Mbit/s solutions. The latest innovations are the full duplex dedicated token ring and the development of a 100 Mbit/s high-speed token ring solution. To many people's surprise there is an extensive legacy of token ring installations and the latest innovations, such as token ring switching, are an attempt to maintain and support this significant market presence. Token ring is designed to provide high throughput under heavy loads (something which is normally impossible for Ethernet to sustain) but in most cases it is used in typical office environments where there is infrequent occurrence of heavy loads     

Are priorities useful in an 802.5 token ring?

The IEEE standard 802.5 token ring protocol defines eight packet priorities. The intent is that high-priority packets should be delivered prior to low-priority packets. A series of simulations shows that this expected behavior occurs when there are very few network stations, very short data packets (but still long relative to ring latency), very short token hold times, and very high network loads. In the general case, priorities did not markedly influence packet delivery time. Use of the priority system generally resulted in more overhead and longer average packet delays than when all packets were carried as a single priority. The features of the protocol operation that are the cause of this increased delay and lack of priority discrimination are described mathematically     

A novel fault tolerant token ring network

Token Ring Networks have gained popularity due to their simplicity and ease of maintenance. However, the functioning of the entire network is dependent on the well being of an entity called “token”. The network ceases to function if the token is lost. There are algorithms suggested for improving the fault tolerant capabilities of the network with respect to the token.This paper proposes an algorithm to achieve fault tolerance. The algorithm is implemented on a simulated token ring network.     

Output process from a continuous token ring local area network

A token-ring local area network (LAN) with an infinite number of nodes uniformly distributed around the ring is considered. A token that circulates around the ring at a constant speed stops to serve fixed length packets that are generated by the nodes. It is assumed that the cumulative arrival process of packets constitutes a two-dimensional Poisson process. Given a fixed point on the ring, called the origin, the first-order statistics of the interarrival times of packets at the origin are obtained in the form of their Laplace-Stieltjes transform     

Parallelring: a token ring LAN with concurrent multipletransmissions and message destination removal

A token ring local area network, the parallelring, is introduced. The ability to concurrently support multiple communication paths on a single loop in an efficient and fair manner differentiates the parallelring from earlier ring architectures. This is accomplished by using a message destination removal scheme and, hence, allowing more than one station to transmit a variable-length frame at a time. Simulation studies show that the parallelring exhibits better performance in terms of throughput-delay characteristics than the other token rings. In addition, a priority scheme is used in the parallelring to provide messages of different time constraints with different media access priorities so that it can support media access fairness and real-time services. In the parallelring, error detection and recovery are completely decentralized     

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     

The helical window token ring

An access rule for token ring local-area networks called the helical-window token-ring protocol is introduced. It features the use of a window that limits the allowable messages a token-holding station can send. With the window, the operation of the protocol approaches that of a central single-server queuing system in the sense that messages are delivered in near first-come-first-served order on a network-wide basis. The introduction of the window also makes analysis of the networks tractable. Exact analytical formulas for the capacity and for the mean, variance, and moment-generating function of the message waiting time are derived. Numerical simulation is used to verify the results. Comparisons with continuous polling systems show that the imposition of the windowed access rule can lead to significant reductions in the delay variance (at the cost of increasing the mean system time) when the traffic is heavy and/or the message transmission time is large with respect to the walk time of the ring     

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。     

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.     

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.     

Performance and parameter region for real-time use in IEEE 802.4token bus network

The upper and lower bounds for the mean cycle time and the mean message transmission time of class six and class four in the IEEE 802.4 token bus network, within which the minimum utilization constraint of class four is guaranteed, are derived. Stability conditions for the token bus network are also derived. These bounds and stability conditions are represented in terms of the high-priority token hold time, the token rotation time, the arrival rate, the total number of stations, etc. A parameter-tuning algorithm in a partially symmetric token bus network with two classes is suggested. This algorithm maximizes the utilization of class four for a given high-priority token hold time and at the same time meets the constraints of the stability condition of the network, the real-time constraint, and the minimum utilization of class four     

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     

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     

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。     

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 token schemes supporting delay-constrained prioritytraffic streams

A symmetric priority-based token network is considered. Messages are divided into two priority classes. High-priority messages are assumed to require tight delay constraints. As a result, each station is allowed to establish, at any time, at most a single real-time high-priority access concentration. High-priority messages are guaranteed access onto the channel within a prescribed limited period. In turn, regular priority messages are only served when the system determines, through the repetitive use of circulating tokens (as used by the IEEE 802.5 token-ring-type protocol), that no high-priority messages are currently waiting in the system. Two token schemes employing different service disciplines are used to provide network access. Exact and approximate mean delay formulas for both message classes are derived. Numerical results are then exhibited to illustrate the network performance under various traffic conditions     

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.     

Communication network protocol for real-time distributed controland its LSI implementation

A new token-passing mechanism, priority token passing, which features real-time access and fast detection and recovery of transmission errors, is discussed in detail in comparison with standard token-passing protocols, and its large-scale integration (LSI)-oriented design concept is described. Priority token passing includes only a small performance overhead, due to its switching functions, which can change network topology from ring to broadcast medium. A token-holding node passes the token to another node after determining the successor through priority comparison. Errors occurring during token passing can, thus, be detected and corrected simply and promptly. Priority token passing has a simple hardware implementation, requiring only small additions to the frame control circuitry, and has a small implementation overhead. The priority token-passing protocol and two other important network communication functions, dual ring network reconfiguration and high-level data link control (HDLC) normal response mode-based message transmission, are designed as a single finite-state machine, and implemented into a compact LSI chip. This integrated instrument network (IINET) chip provides complete network communication services and requires only three additional external electronic components for operation     

A token circulation scheme for code assignment and cooperative transmission scheduling in CDMA-based UAV ad hoc networks

Code division multiple access (CDMA) ad hoc networks have been considered a promising multiple-channel networking architecture for connecting tactical platforms in battle fields. In this paper we consider a network of a swarm of unmanned aerial vehicles (UAVs) that are used in a tactical surveillance mission. The UAVs are assumed to have multiuser detection capability and form a CDMA-based ad hoc network. A token circulation scheme is proposed to conduct functions required at the medium access control layer including detection of hidden/lost neighbors, code assignment and schedule-based cooperative transmission scheduling. In the proposed scheme, a token continuously circulates around the network based on the “receive-forward” module. Through circulation of the token, each UAV can detect its hidden and/or lost neighbors in near real-time, assign codes enabling the spatial reuse of code channels without incurring code collision, and schedule data transmissions in a cooperative and distributed manner. In addition, the proposed scheme is able to take advantage of multiuser detection functionality and allows for simultaneous transmissions from multiple transmitters to a same receiver. The performance of the proposed token circulation scheme is evaluated, both analytically and through simulations. It is shown that the latency of the token is at most linearly proportional to the network size, and the average delay of a data packet increases with either the packet generation rate or the network size. The results also show that the proposed token circulation scheme is suitable for large-scale CDMA-based UAV ad hoc networks with even heavy network traffic load.