A Queueing Network Analysis of Computer Communication Networks with Window Flow Control

A computer communication network with window flow control is modeled by a closed multichain queueing network. The severe computational limitation of previous solution algorithms is overcome with a heuristic derived from the recently found mean value analysis. A large numerical example is given.     

Communication Via Decentralized Processing

The problem of a nomadic terminal sending information to a remote destination via agents with lossless connections to the destination is investigated. Such a setting suits, e.g., access points of a wireless network where each access point is connected by a wire to a wireline-based network. The Gaussian codebook capacity for the case where the agents do not have any decoding ability is characterized for the Gaussian channel. This restriction is demonstrated to be severe, and allowing the nomadic transmitter to use other signaling improves the rate. For both general and degraded discrete memoryless channels, lower and upper bounds on the capacity are derived. An achievable rate with unrestricted agents, which are capable of decoding, is also given and then used to characterize the capacity for the deterministic channel.      

Queueing Models for Computer Communications System Analysis

Modeling and performance prediction are becoming increasingly important issues in the design and operation of computer communications systems. Complexities in their configuration and sophistications in resource sharing found in today's computer communications demand our intensive effort to enhance the modeling capability. The present paper is intended to review the state of affairs of analytic methods, queueing analysis techniques in particular, which are essential to modeling of computer communication systems. First we review basic properties of exponential queueing systems, and then give an overview of recent progress made in the areas of queueing network models and discrete-time queueing systems. A unified treatment of buffer storage overflow problems will be discussed as an application example, in which we call attention to the analogy between buffer behavior and waiting time in theGI/G/1queue. Another application deals with the analysis of various multiplexing techniques and network configuration. An extensive reference list of the subject fields is also provided.     

Personal Computer Communications Via Telephone Facilities

Communication from terminals to other terminals and to computing service systems has been an important aspect of data communications since the early 1960's. When personal computers arrived on the scene, in the 1970's, the use of telephone facilities and modems for communications was a natural extension of existing technology. Now, however, many modems have "intelligence" and can be controlled from their electrical interface, communication software is available to facilitate the use of a modem and coordinate the communication process, and there are many uses for personal computer communications. Some of the hardware, software, and computing services for personal computer communications are discussed in this paper.     

Personal Computer Communications Via Ku-Band Small-Earth Stations

This paper describes recent developments in geosynchronous satellite communication with special emphasis on data communication using small inexpensive Earth stations (small-Earth stations or microstations). Recent innovations in design, impacts of regulatory codes and decisions, and an illustrative system design example are all examined. Attention is directed to systems using radio frequency (RF) carriers in theKu-band (14/12 GHz). At some or all of these frequencies terrestrial users are generally considered as secondary to users of fixed satellite services. Because of this relative freedom from terrestrial interference concerns, installation ofKu-band small-Earth stations can be made relatively free of regulatory involvement and coordination procedures. The basic equations governing the noise and interference terms entering link margin calculations are presented. A design example is given, detailing one type of system of practical importance.     

计算机网络通信

本文介绍了目前国内外流行的几种计算机网络、网络拓扑结构、网络互连设备、ＯＳＩ七层标准以及它们相互间的关系。     

计算机通信技术

着重介绍了超高速光通信技术、远距离光通信技术和低成本透明网络光通信技术的最新发展情况     

Asymptotically Optimal Multiple-Access Communication Via Distributed Rate Splitting

We consider the multiple-access communication problem in a distributed setting for both the additive white Gaussian noise channel and the discrete memoryless channel. We propose a scheme called Distributed Rate Splitting to achieve the optimal rates allowed by information theory in a distributed manner. In this scheme, each real user creates a number of virtual users via a power/rate splitting mechanism in the M-user Gaussian channel or via a random switching mechanism in the M-user discrete memoryless channel. At the receiver, all virtual users are successively decoded. Compared with other multiple-access techniques, Distributed Rate Splitting (DRS) can be implemented with lower complexity and less coordination. Furthermore, in a symmetric setting, we show that the rate tuple achieved by this scheme converges to the maximum equal rate point allowed by the information-theoretic bound as the number of virtual users per real user tends to infinity. When the capacity regions are asymmetric, we show that a point on the dominant face can be achieved asymptotically. Finally, when there is an unequal number of virtual users per real user, we show that differential user rate requirements can be accommodated in a distributed fashion     

Pulse Pressure Contour Method Testing Via Hybrid Computer Simulation

A variety of methods have been proposed for determining cardiac output from the shape of the central pulse pressure contour. Each of these methods uses a calibrated constant of proportionality to relate the stroke volume to the specific function of the pulse pressure contour.     

A Queueing Model for Radio Nets--Part II: Results

In Part I of this paper an analytical methodology for quantitatively evaluating radio-communication nets was introduced and the details of the model and mathematics were explained. In this part of the paper the application of the methodology is quantitatively discussed. Results for particular net situations are presented. They are performance of single nets with multiple frequencies, nets with mutual signaling interference resulting from asynchronous signaling and a comparison of dedicated nets with a multiple access-discrete address system. The frequency spectrum savings for the latter use is also considered.     

A Queueing Model for Radio Nets--Part I: Methodology

In voice radio communication nets, digital-frequency assignment patterns and multiple-access discrete address transceivers are being studied to improve grade of service, mean access delay, and other aspects of system performance. An analytical methodology based on a calling system-outer system queueing model is presented. This model permits study of these radio communication problems and system design tradeoffs without computer simulation. In addition, the model utilizes several types of statistics (e.g., Poisson, Erlangian, or hyperexponential). In this paper, the model and the mathematical methodology are explained in detail. Formulas for equilibrium performance measures are derived from their definitions. The concept of station-busy probabilities is introduced and a matrix technique for obtaining numerical results is illustrated.     

The International Telecommunication Union and Broadcasting from Satellites--A Brief Review

The International Telecommunication Union (ITU) conducts a continuing and extensive activity with regard to the broadcasting-satellite service (BSS). First, in appropriate administrative radio conferences, the ITU a) allocates frequency bands for the BSS, sometimes shared with other radiocommunications services, b) establishes the conditions for such frequency sharing, c) plans orbit and frequency assignments within the bands allocated to the BSS, and d) establishes utilization rules, e.g., notification procedures for planned direct broadcast satellite (DBS) systems, coordination with terrestrial stations, resolution of difficulties,etc. Second, through its International Radio Consultative Committee (CCIR), the ITU studies technical and operational matters regarding the BSS, needed by the above conferences and conducive to a smooth international exchange of television and sound programs for the BSS. The paper reviews and explains these activities and their impact on the development of DBS systems in the BSS.     

STD前端通信计算机系统

本文介绍一种已付诸运行的以STD总线模板为主构成的前端通信计算机系统。该系统与主机采用前后台配置,实现了多级分布式计算机测控。     

一种ATM路由器的排队模型及性能分析

简单介绍了一种用于异种网互连的多协议、多接口路由器（multi－protocolrouter，以下简称MPR）的网络互连体制的选择，然后根据MPR对到达数据分组的处理过程建立了排队模型，并提出了一种较好的服务策略：改进的不完全循环服务法，最后利用计算机仿真给出了在此服务策略下的MPR性能分析。     

A Recursive Approximation Technique for a Combined Source Queueing Model

The model studied in this paper captures the combined effects of finite and infinite source traffic-often used to model interactive and batch traffic, respectively-when they contend for a single server resource. The finite source traffic is modeled by heterogeneous finite sources, the infinite source traffic by a stationary Poisson process, and the single server is assumed to have exponentially distributed service times with distinct service rates for the different customer types. All customers share a common queue and are serviced in FIFO order. A special case of this model where theNfinite sources are identical combines two fundamental and widely used models (the repairman andM/M/1models) in a natural manner. Regardless of the homogeneous or heterogeneous nature of the finite sources, the combined source model is not product form due to the realistic assumption that service rates are distinct for different customer types (batch and interactive traffic typically have different CPU processing requirements). In this paper, we show how to recursively calculate all mean quantities of interest in an approximate but quite accurate manner for the general heterogeneous model. The accuracy of the recursive technique is established in part by contrasting the approximate solution to simulation results for a wide parameter range, and in part by studying the asymptotic behavior of the approximation.     

Task-Oriented Queueing: An Analysis Tool for Software Design of Communication Processing Systems

Jobs associated with messages arriving to a communication processing system (CPS) can be described as ordered sets of prioritized tasks, where each task represents the execution of some part of the system's software. The service system of the CPS consists of a collection of queues, one for each distinct priority, serviced by a single server under a preemptive resume discipline. The routing of the job through this collection of queues is defined by a job's priority vector which specifies the priority at which each task in the job is to execute. For example, if a two-task job's priority vector is (3, 2), then the job first joins the priority 3 queue, obtains service for the first task, then joins the priority 2 queue. In a previous paper, the author and a colleague described a method through which average delays in such task-oriented processing systems could be computed for the special case in which all jobs have identical structure. This paper presents a substantially simplified version of the analysis methodology presented previously and extends that work to the case of a finite number of job classes, each job class having a finite number of tasks.     

通过USS协议实现变频调速器与PLC的通讯控制

以前的控制设备中西门子可编程控制器S7-200与变频调速器之间的控制大多是通过并口连接的,西门子S7-200 PLC不能实时读取和设置变频调速器的参数。采用USS协议作为通信链路进行数字化的信息传递,从而实现实时读取和设置变频调速器的相关参数,通讯速率可达187.5 kb/s。通信介质采用RS 485屏蔽双绞线,可有效地减少电缆的数量,提高了系统的自动化水平及运行的可靠性。