Synchronous Time Division Research Articles

Firmness Analysis of Real-time Tasks

( m , k )-firm real-time tasks require meeting the deadline of at least m jobs out of any k consecutive jobs. When compared to hard real-time tasks, ( m , k )$-firm tasks open up the possibility of tighter resource-dimensioning in implementations. Firmness analysis verifies the satisfaction of ( m , k )-firmness conditions. Scheduling policies under which a set of periodic tasks runs on a resource influence the number of deadline missed jobs. Therefore, the nature of the firmness analysis problem depends on scheduling policies. In this work, we present Firmness Analysis (FAn) methods for three common scheduling policies—synchronous and asynchronous Static Priority Preemptive (SPP) policies and Time Division Multiple Access (TDMA). We first introduce the Balloon and Rake problem—the problem of striking the maximum number of balloons in a balloon line with a rake. We show that the common core of firmness analysis problems can be abstracted as the Balloon and Rake problem. Next, we prove that the Finite Point method is a solution to the Balloon and Rake problem. We illustrate how existing FAn methods for the TDMA and asynchronous SPP policies can be adapted to use the same solution framework for the Balloon and Rake problem. Using the solution of the Balloon and Rake problem, we adapt the existing FAn methods to synchronous SPP scheduling policies. The scalability of the FAn methods is compared with that of a timed-automata approach, a brute-force approach, and a Mixed Integer Linear Programing method. The FAn methods scale substantially better to firmness analysis problem instances with a large k and a high number of tasks.

SFSW Time Transfer Over Branching Fiber-Optic Networks With Synchronous TDMA

In this letter, we design and demonstrate a single-fiber and same-wavelength (SFSW) time transfer over branching fiber-optic networks with a synchronous time-division multiple access. After pre-synchronization, the transmission collisions among multiple nodes over an SFSW link in branching fiber-optic networks are avoided in the time domain. The two-way time transfer between a master node and multiple slave nodes is then completed within each timing duration over the branching fiber-optic network. A $1\times8$ experimental system with a 50-km single-mode fiber in each sub-path is demonstrated. Experimental results show that the stabilities of better than 45 ps/s and 10 ps/d can be achieved. The measured average clock differences over two branches with a 50-km fiber are 58 and 73 ps, respectively, which are within the calculated expanded uncertainty (with the coverage factor of 2) of 103 ps.

An Autonomous Satellite Time Synchronization System Using Remotely Disciplined VC-OCXOs

An autonomous remote clock control system is proposed to provide time synchronization and frequency syntonization for satellite to satellite or ground to satellite time transfer, with the system comprising on-board voltage controlled oven controlled crystal oscillators (VC-OCXOs) that are disciplined to a remote master atomic clock or oscillator. The synchronization loop aims to provide autonomous operation over extended periods, be widely applicable to a variety of scenarios and robust. A new architecture comprising the use of frequency division duplex (FDD), synchronous time division (STDD) duplex and code division multiple access (CDMA) with a centralized topology is employed. This new design utilizes dual one-way ranging methods to precisely measure the clock error, adopts least square (LS) methods to predict the clock error and employs a third-order phase lock loop (PLL) to generate the voltage control signal. A general functional model for this system is proposed and the error sources and delays that affect the time synchronization are discussed. Related algorithms for estimating and correcting these errors are also proposed. The performance of the proposed system is simulated and guidance for selecting the clock is provided.

One-channel networked data fusion with communication constraint

Multi-sensor data fusion over one channel is studied in this paper. The communication constraint considered here is medium access constraint. When the synchronous time division multiplexing (STDM) mechanism is used to address this problem, collective delay emerges. Collective delay time depends upon the channel capacity and traffic flow assigned to the communication channel, causing contradiction between traffic flow and delay time (the number of transmitted sensors and delay steps). A new model is developed that can truly reflect this contradiction by introducing a stochastic process θ. Based on the obtained system model, the optimal data fusion filter is designed. It also gives the upper bounds of the expected estimation error covariance and estimation error covariance with one-step delay. Two illustrative examples are given in the last section to show the influence of θ on estimation performance.

Channel statistical multiplexing in SDH∕SONET networks

The new technologies of virtual concatenation, the link capacity adjustment scheme and the generic framing protocol make SDH/SONET survivable in the next-generation transport networks. However, based on synchronous time-division multiplexing, SDH/SONET only creates a private point-to-point path for a particular user that cannot be shared by other users when the path is in the idle state. Therefore it results in bandwidth inefficiency for accommodating bursty services. A new scheme called ‘channel statistical multiplexing’ is proposed. It is simple and practical for use when there are several data streams from the same source node to the same destination node in SDH/SONET networks.

Analysis of random polling system with an infinite number of coupled servers and correlated input process

We introduce a simple approach for modeling and analyzing a random polling system with infinite servers. We assume that the infinite number of servers is coupled together and they visit the queues as one processing unit. It is assumed that the customer arrival processes at all queues are correlated. Two classes of service disciplines, exhaustive and gated, are considered. We will derive several performance measures of the system. These performance measures include the mean cycle time and the expected delay observed by a customer. For the special case of M/ D/∞ vacation queue, we also provide a new proof of a known result. The numerical results indicate that when the expected number of busy servers is high gated service produces mean waiting times less than those given by exhaustive service discipline. This result differs significantly from the known result for single server polling system and it is due to the assumption of coupled servers. Scope and purpose The Information Community's insatiable appetite for timely information has led to a number of new services: voice, data, teleconferencing, entertainment video, local area networks bridging, and distributed data processing. For both economic reasons and sophistication of services provided, a multicast feature must be provided. An essential component of multicasting is communication link sharing, an example of which is a self-routing network. Furthermore, the dramatic increase in transmission speed due to advancing technology has significantly altered many of the operating assumptions of communication systems. In particular, the quality of services provided by these communication systems can be improved by redesigning the access control mechanisms. Thus, the design and analysis of high-speed communication networks is drawing increasing attention. As a result, a number of approaches has been proposed for controlling the high-speed communication systems typified by parallel communication in fixed time synchronous mode. The parallel communication aspect is a result of advancing technology. For example, widespread use of fiber optics in parallel buses, parallel rings and star topology networks using frequency or wavelength division multiplexing have made high-speed parallel communication a reality. Furthermore, it has been demonstrated that by using parallel high-speed communication systems the total system capacity can be increased beyond that given by the single channel high-speed communication system. The use of fixed synchronous time division control in high-speed parallel communication systems is dictated by the speed limitations of electronics. However, the implementation of fixed synchronous time division control in high-speed parallel communication systems at fiber optics communication rates has been shown to be feasible. Although a number of performance studies on parallel high-speed communication systems has appeared in the literature; the performance of parallel high-speed communication system is not well understood. Therefore, there is a need to develop models of parallel high-speed communication systems that enable one to analyze their performance. Furthermore, from the perspectives of design and control of the communication system, there is a need for medium access control protocols that will allow designers to prioritize the different stations and thus improve the overall system performance. Motivated by these observations, the objective of this paper is to introduce a new approach to modeling and analyzing parallel high-speed communication systems.

Pipelined asynchronous time-division multiplexing optical bus

S. Q. ZhengLouisiana State UniversityDepartment of Computer Science,andDepartment of Electrical and ComputerEngineeringBaton Rouge, Louisiana 70803E-mail: zheng@bit.csc.lsu.eduYueming LiLouisiana State UniversityDepartment of Computer ScienceBaton Rouge, Louisiana 70803Abstract. We propose a pipelined asynchronous time-division multi-plexing optical bus. Such a bus can use one of two hardwared priorityschemes: the linear priority scheme and the round-robin priority scheme.Our simulation results show that the performance of the proposed bus issignificantly better than the performances of known pipelined synchro-nous time-division multiplexing optical buses. The possibilities of usingour buses to construct multichannel switches and multidimensional pro-cessor arrays are also discussed.

A Hierarchical Neural Optimization Structure for Access Control and Resource Sharing in Integrated Communication Networks

The access to a multiservice broadband synchronous time division multiplexer is considered, where hybrid frames are used to carry two basic traffic types: a circuit-switched isochronous and a packet-switched asynchronous one, generated by several users. Each user has an assigned portion of the total available bandwidth, in terms of slots/frame, which is dynamically allocated between the two traffic types at the user premise, by means of a local randomized decision rule. Its structure is determined by a neural network of the nonlinear perceptron type. A two-level optimization problem is defined, through which the users independently adjust their local parameter values (i.e., the synaptic weights of the neural networks) and a central controller reassigns the bandwidth partitions, that play the role of coordination variables. At the end some simulation results and conclusions on the usefulness of nonstationary and stationary neural networks to feedback control of ISDN are provided.

Architecture and Analysis of Fast Packet Switches Based on Time-Multiplexed Photonic Fabrics

This paper proposes and evaluates two fast packet switching architectures based on time-division multiplexed integrated photonic fabrics. The architectures are targeted towards low-latency inter-node switching and intra-node routing in high-speed networks. The inter-node switch achieves output packet queueing via asynchronous time-division multiplexing a strictly-nonblocking photonic fabric. Buffer behavior is analyzed at both input and output stages to.determine the effect of varying the switching bandwidth on the performance metrics (delay, throughput, and packet loss probability). Analysis is performed for finite switch dimensions by obtaining upper and lower bounds on the packet loss at input. The dependence of finite output buffer latency and overflow probability on the normalized switching bandwidth is examined. The intra-node trunk traffic router consists of a passive optical coupler followed by an active routing stage. For this architecture, both synchronous and asynchronous time-division multiplexing modes are modeled and analyzed to obtain expressions for corresponding packet buffering delay and total switching latency. The router is shown to saturate at the waiting time singularity of its input (or output) buffers, given by the ratio of the switching bandwidth to the dimension.

Performance analysis of the communication architecture of the Connection Machine

The performance of the interprocessor communication architecture of the CM-2 is analyzed. A discrete-time Markov chain model of its network architecture is developed to compute the message delay introduced by the network architecture. Due to the synchronous time-division multiplexing nature of the network operation, it is amenable to a discrete-time Markov chain modeling. The analysis yields formulas for response time and several other related performance measures, showing how the performance of the network degrades with the message arrival rate and other parameters. Since the communication delays affect interprocess communication, knowledge of the sensitivity of the delays to the parameters can be a useful aid in designing a high performance parallel system. To keep the analysis tractable, an approximate Markov model is used that requires the use of fixed-point iteration for its solution. Validation of the results against a simulation study reveals that the analysis predicts the performance of the network with high accuracy. >

A number theoretic approach to time division multiplexing

A systematic approach to synchronous time division multiplexing (TDM) in embedded systems employing TDM as a switching fabric in the form of a bus is presented. The benefits of this approach are increased system capacity, individual and unrestricted circuit creation for all channels regardless of their bandwidth, latency ranging from a fraction of a bit to several bits, and independent tracking of timing and control signals for all interfaces requiring such service. The method divides time in such a way that every circuit receives a quantum of time equal to its nominal bandwidth, thus allowing all circuits to be explicitly identified on the switching fabric. The procedure that accomplishes this type of TDM is based on solutions to sets of linear congruences, also known as linear Diophantine equations. This scheme significantly reduces the cost of an embedded interface and allows flexibility for unbundling the subrate channels, thus permitting easy implementation of subrate multiplexing. It also simplifies design of switching fabrics which must carry voice mixed with subrate bit-interleaved or packet mode data and with ISDN nodes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

P1396: a proposed standard communications bus

P1396 is a standards effort to develop a ‘hybrid’ backplane bus that combines synchronous time division multiplexing for circuit switching with a scheme that allows multiple users to access the bus for the transfer of variable-length packet data. The bus is intended to operate at speeds up to 20 Mbyte s −1 and to be synchronized either to the telephony rate of 8000 frames or to a video frame for image processing applications. The paper introduces the P1396 specification and reviews the standards work that has been done, and that remains to be done, by the IEEE P1396 working group. Applications such as metropolitan area networks and distributed office communications are discussed, as is the functional design of the bus.

Design of transmission and multiplexing systems for broadband packet networks

Dynamic time-division multiplexing (DTDM) is a flexible network transport technique capable of handling both continuous and bursty traffic effectively. By using three different multiplexing architectures in the network, DTDM permits graceful evolution of the existing circuit switching network into a flexible broadband packet communications network supporting integrated voice, data, and video traffic. The first multiplexing stage uses a packet assembler to multiplex different broadband services into a common DTDM-format serial bit stream. The second multiplexing stage uses a statistical packet multiplexer to concentrate network traffic for more efficient use of transmission facilities. The third multiplexing stage uses a synchronous time-division multiplexer for high-speed point-to-point transparent transmission. The multiplexer uses a simple tributary synchronization scheme based on positive and negative block justification, which combines the concept of controlled-slip and bit-stuffing techniques while maintaining information integrity. A generic CMOS LSI chip has been designed for use in the three-stage multiplexing system. >

A Multirate Switching Network for Broadband Channels

A broadband ISDN switching network model is presented, switching the channel types H2, H3, and H4 envisaged by the CCITT. The synchronous time division multiplex technique is applied. The switching network operates at the basic bit rate of the H2-channel; H3and H4-connections are established via multichannel connections of up to four basic channels. H2-connections which are part of one H3- or H4-connection always have to use common interconnection links. This is a favorable solution to keep digit sequence integrity for multichannel connections, but influences blocking characteristics of the switching network. The implementation of an optimal path selection method plays a fundamental role. In such a multichannel switching network, blocking probabilities for H2-, H3-, and H4-connections must be distinguished. They do not only depend on the total offered load, but also on the proportions of H2-, H3-, and H4-connections (traffic mix). The simulation results presented in this paper prove that multirate switching via multichannel connections is feasible for the broadband channel types H2, H3, and H4, and that the proposed switching network has a sufficiently high traffic capacity whatever the traffic mix may be.

Simulation Studies for Data Multiplexing in Speech with Stdm or Tasi

A simulation model of a finite buffer queueing system with Erlang arrivals and multiple random servers is presented. The number of active servers in a service interval vary through a birth and death process derived from the speech samples in synchronous time division multiplexing (STDM) or time assignment speech interpolation (TASI) system. The results of this study show that the TASI system requires a larger buffer than the STDM system for a specified overflow probability.

A Method for Modeling and Analysis of the Reframing Performance of Multilevel Synchronous Time Division Multiplex Hierarchies

This paper presents a method for modeling the operation of the frame synchronization algorithms of the several levels of a synchronous time division multiplex hierarchy as a Markov chain. A method, discussed elsewhere by one of the authors, is used to drastically reduce the number of states in the Markov chain and make a numerical calculation of the mean first passage times possible. The mean reframing times as a function of appropriate parameters are determined for three examples, with one approaching the complexity of a practical system. A determination of the same quantities by methods unrelated to the proposed approach gives results which are in excellent agreement.

Buffer Behavior for Mixed Arrivals and Single Server with Random Interruptions

A queueing model with finite buffer size, mixed input traffic (Poisson and burst Poisson arrivals), synchronous transmission and server interruptions through a Bernoulli sequence of independent random variables is studied. Using average burst length, traffic intensity and input traffic mixture ratio as parameters, the relationships among buffer size, overflow probability and expected message queueing delay are obtained. An integrated digital voice-data system with synchronous time division multiplexing (STDM) for a large number of voice sources and mixed arrival process for data messages is considered as an application for this model. The results of this study are portrayed on graphs and may be used as guidelines in buffer design problems in digital voice-data systems. The queueing model developed is quite general in a sense that it covers pure Poisson and burst Poisson arrival processes and the mixture of the two as well.

Satellite Packet Switching with Global Assignments and Batch Poisson Arrivals

A satellite packet switching multiaccess model which employs a global scheduling assignment scheme is described and analyzed for batch Poisson arrivals. System performance in terms of buffer overflow probability and system delay is analyzed and simulated. The numerical results, presented in graphical form, indicate that the performance improves as the population size M increases. For large value of M the queueing delay decays approximately exponentially as the buffer length increases. Our results indicate that the system delay performance of our dynamic assignment (DA) algorithm is significantly better than that of a synchronous time-division multiplexing scheme.

Global Scheduling Approach to Conflict-Free Multiaccess via a Data Bus

A global scheduling multiple access (GSMA) scheme for data communication via a high speed bus is described. The GSMA scheme, which has a variable length frame format and the desirable property of guaranteeing each active user a minimum service per frame, attains conflict-free multiaccess and has the flexibility of providing more channel capacity to the large users. An expression for the mean system delay under a Poisson arrival law and an imbalanced loading (multi-rate) environment is derived. Numerical results indicate that the GSMA scheme offers substantially higher channel utilization compared to the synchronous time-division multiple access (STDMA) scheme, particularly at the low throughput region. It is shown also that the GSMA system offers superior delaythroughput performance to an STDMA or POLLING system.

Finite Buffer Behavior with Poisson Arrivals and Random Server Interruptions

A queueing model with finite buffer size, Poisson arrival process, synchronous transmission and server interruptions is studied through a Bernoulli sequence of independent random variables. An integrated digital voice-data system with Synchronous Time-Division Multiplexing (STDM) for voice sources and Poisson arrival process for data messages is considered as an application for this model. The relationships among overflow probabilities, buffer size and expected queueing delay due to buffering for various traffic intensities are obtained. The results of this study are portrayed on graphs and may be used as guide lines for the buffer design in digital voice-data systems. Although this study arose in the design of a buffer for digital voice-data systems, the queueing model developed is quite general and may be useful for other industrial applications.