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Thời gian thực - hệ thống P2
ANALYSIS AND VERIFICATION OF NON-REAL-TIME SYSTEMS A great collection of techniques and tools are available for the reasoning, analysis, and verification of non-real-time systems. This chapter explores the basic foundations of these techniques that include symbolic logic, automata, formal languages, and state transition systems. Many analysis and verification techniques for real-time systems are based on these untimed approaches, as we will see in later chapters.
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Thời gian thực - hệ thống P3
REAL-TIME SCHEDULING AND SCHEDULABILITY ANALYSIS As in preparing a schedule of to-do tasks in everyday life, scheduling a set of computer tasks (also known as processes) is to determine when to execute which task, thus determining the execution order of these tasks; and in the case of a multiprocessor or distributed system, to also determine an assignment of these tasks to specific processors. This task assignment is analogous to assigning tasks to a specific person in a team of people. Scheduling is a central activity of a computer system, usually performed by the operating system....
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Thời gian thực - hệ thống P4
MODEL CHECKING OF FINITE-STATE SYSTEMS One way to show that a program or system meets the designer’s specification is to manually construct a proof using axioms and inference rules in a deductive system such as temporal logic, a first-order logic capable of expressing relative ordering of events. This traditional, manual approach to concurrent program verification is tedious and error-prone even for small programs. For finite-state concurrent systems and systems that can be represented as such, we can use model checking instead of proof construction to check their correctness relative to their specifications....
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Thời gian thực - hệ thống P5
VISUAL FORMALISM, STATECHARTS, AND STATEMATE Finite-state machines (FSMs) have been used extensively in the specification and analysis of many computer-based as well as non-computer-based systems, ranging from electronic circuits to econometric models. They can model in detail the behavior of a system, and several algorithms exist to perform the analysis. Unfortunately, classical state machines such as those employed in the standard, explicit-state CTL model-checking approach [Clarke, Emerson, and Sistla, 1986] lack support for modularity and suffer from exponential-state explosion. ...
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Thời gian thực - hệ thống P6
REAL-TIME LOGIC, GRAPH-THEORETIC ANALYSIS, AND MODECHART A real-time system can be specified in one of two ways. The first is to structurally and functionally describe the system by specifying its mechanical, electrical, and electronic components. This type of specification shows how the components of the system work as well as their functions and operations. The second is to describe the behavior of the system in response to actions and events. Here, the specification tells sequences of events allowed by the system....
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Thời gian thực - hệ thống P7
VERIFICATION USING TIMED AUTOMATA Finite automata and temporal logics have been used extensively to formally verify qualitative properties of concurrent systems. The properties include deadlock- or livelock-freedom, the eventual occurrence of an event, and the satisfaction of a predicate. The need to reason with absolute time is unnecessary in these applications, whose correctness depends only on the relative ordering of the associated events and actions. These automata-theoretic and temporal logic techniques using finitestate graphs are practical in a variety of verification problems in network protocols, electronic circuits, and concurrent programs....
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Thời gian thực - hệ thống P8
TIMED PETRI NETS Petri nets were developed as an operational formalism for specifying untimed concurrent systems. They can show concurrent activities by depicting control and data flows in different parts of the modeled system. As an operational formalism, a Petri net gives a dynamic representation of the state of a system through the use of moving tokens. The original, classical, untimed Petri nets have been used successfully to model a variety of industrial systems. More recently, time extensions of Petri nets have been developed to model and analyze time-dependent or real-time systems....
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Thời gian thực - hệ thống P9
PROCESS ALGEBRA A computer process is a program or section of a program (such as a function) in execution. It may be in one of the following states: ready, running, waiting, or terminated. A process algebra is a concise language for describing the possible execution steps of computer processes. It has a set of operators and syntactic rules for specifying a process using simple, atomic components. It is usually not a logic-based language. Central to process algebras is the notion of equivalence, which is used to show that two processes have the same behavior....
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Thời gian thực - hệ thống P10
DESIGN AND ANALYSIS OF PROPOSITIONAL-LOGIC RULE-BASED SYSTEMS Real-time decision systems are computer-controlled systems that must react to events in the external environment by making decisions based on sensor inputs and state information sufficiently fast to meet environment-imposed timing constraints. They are used in applications that would require human expertise if such decision systems were not available. Human beings tend to be overwhelmed by a transient information overload resulting from an emergency situation, thus expert systems are increasingly used under many circumstances to assist human operators. ...
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Thời gian thực - hệ thống P11
TIMING ANALYSIS OF PREDICATE-LOGIC RULE-BASED SYSTEMS As rule-based expert systems become widely adopted in new application domains such as real-time systems, ensuring that they meet stringent timing constraints in these safety-critical and time-critical environments emerges as a challenging problem. As described in detail in chapter 10, in these systems, a change in the environment may trigger a number of rule firings to compute an appropriate response. If the computation takes too long, the expert system may not have sufficient time to respond to the ongoing changes in the environment, making the result of the computation useless or even harmful to the...
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Thời gian thực - hệ thống P12
OPTIMIZATION OF RULE-BASED SYSTEMS As we have seen in chapters 10 and 11, embedded rule-based expert systems must satisfy stringent timing constraints when applied to real-time environments. We now describe a novel approach to reduce the response time of rule-based expert systems. This optimization is needed when a rule-based system does not meet the specified response-time constraints. Our optimization method is based on a construction of the reduced cycle-free finite-state space-graph.
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Độ tin cậy của hệ thống máy tính và mạng P1
The central theme of this book is the use of reliability and availability computations as a means of comparing fault-tolerant designs. This chapter defines fault-tolerant computer systems and illustrates the prime importance of such techniques in improving the reliability and availability of digital systems that are ubiquitous in the 21st century. The main impetus for complex, digital systems is the microelectronics revolution, which provides engineers and scientists with inexpensive and powerful microprocessors, memories, storage systems, and communication links. ...
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Độ tin cậy của hệ thống máy tính và mạng P2
CODING TECHNIQUES Many errors in a computer system are committed at the bit or byte level when information is either transmitted along communication lines from one computer to another or else within a computer from the memory to the microprocessor or from microprocessor to input/ output device. Such transfers are generally made over high-speed internal buses or sometimes over networks. The simplest technique to protect against such errors is the use of error-detecting and errorcorrecting codes.
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Độ tin cậy của hệ thống máy tính và mạng P3
REDUNDANCY, SPARES, AND REPAIRS This chapter deals with a variety of techniques for improving system reliability and availability. Underlying all these techniques is the basic concept of redundancy, providing alternate paths to allow the system to continue operation even when some components fail. Alternate paths can be provided by parallel components (or systems). The parallel elements can all be continuously operated, in which case all elements are powered up and the term parallel redundancy or hot standby is often used....
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Độ tin cậy của hệ thống máy tính và mạng P4
N-MODULAR REDUNDANCY In the previous chapter, parallel and standby systems were discussed as means of introducing redundancy and ways to improve system reliability. After the concepts were introduced, we saw that one of the complicating design features was that of the coupler in a parallel system and that of the decision unit and switch in a standby system. These complications are present in the design of analog systems as well as digital systems. However, a technique known as voting redundancy eliminates some of these problems by taking advantage of the digital nature of the output of digital elements....
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Độ tin cậy của hệ thống máy tính và mạng P5
SOFTWARE RELIABILITY AND RECOVERY TECHNIQUES The general approach in this book is to treat reliability as a system problem and to decompose the system into a hierarchy of related subsystems or components. The reliability of the entire system is related to the reliability of the components by some sort of structure function in which the components may fail independently or in a dependent manner. The discussion that follows will make it abundantly clear that software is a major “component” of the system reliability,1 R....
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Độ tin cậy của hệ thống máy tính và mạng P6
NETWORKED SYSTEMS RELIABILITY Many physical problems (e.g., computer networks, piping systems, and power grids) can be modeled by a network. In the context of this chapter, the word network means a physical problem that can be modeled as a mathematical graph composed of nodes and links (directed or undirected) where the branches have associated physical parameters such as flow per minute, bandwidth, or megawatts. In many such systems, the physical problem has sources and sinks or inputs and outputs, and the proper operation is based on connection between inputs and outputs....
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Độ tin cậy của hệ thống máy tính và mạng P7
RELIABILITY OPTIMIZATION The preceding chapters of this book discussed a wide range of different techniques for enhancing system or device fault tolerance. In some applications, only one of these techniques is practical, and there is little choice among the methods. However, in a fair number of applications, two or more techniques are feasible, and the question arises regarding which technique is the most cost-effective. To address this problem, if one is given two alternatives, one can always use one technique for design A and use the other technique for design B....
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Digital Communication Systems
Reference subjects of digital information in English and fully understandable. This book was written to be a textbook for seniors or first - year graduate students interested in electrical communication systems. The book departs from the usual formata in two major respects. First, the text does not cover analog or pulse modulation systems.
8/29/2018 6:13:25 PM +00:00
Điện thoại di động mạng lưới Radio P15
UPT—Universal Personal Telecommunication∗ People are becoming more mobile. At the same time they have a greater need to be reachable and to be able to reach others. A variety of different systems that address all the different categories of mobility already exist: • Employees can be reached through a DECT terminal anywhere in their company. • Tradesmen can be called over a Digital Communication System (DCS) within a city. • Business people can be reached over the same telephone number via GSM anywhere in Europe, wherever they are located. ...
8/29/2018 6:10:16 PM +00:00
Điện thoại di động mạng lưới Radio P16
The Future is Wireless A Typical Day in the Year 2000 Joe Mobilus is a manager with a haulage firm in a city 100 km away from his home town; his wife Sue is a nurse at the local hospital. Their son Tom and daughter Ann are still at school. 06:30 The central alarm system wakes Joe and Sue in line with their weekly schedule. 07:00 Joe uses his TETRA terminal to access his firm’s central computer to see if there have been any changes to his diary. 07:15 Joe leaves his house and using his cellular phone in the...
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Điện thoại di động giao thức viễn thông cho các mạng dữ liệu P1
Mobile agent platforms and systems Advanced service provisioning allows for rapid, cost-effective service deployment. Modern mobile telecommunications evolve towards value-added, on-demand services in which the need for communication becomes frequent and ongoing, and the nature of the communication becomes more complex. The services of the future will be available ‘a la carte’, allowing subscribers to receive content and applications when they want it.
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Điện thoại di động giao thức viễn thông cho các mạng dữ liệu P2
Mobile agent-based service implementation, middleware, and configuration There are two agents groups: Intelligent Agents and Mobile Agents (MAs). Intelligent Agents have the ability to learn and react. MAs can migrate between different hosts, execute certain tasks, and collaborate with other agents. In the Intelligent Network (IN) architecture, the control of the network resources is performed by the signaling plane, whereas the service creation, deployment, and provisioning is performed by the service plane....
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Điện thoại di động giao thức viễn thông cho các mạng dữ liệu P3
Wireless local area networks Virtual LANs provide support for workgroups that share the same servers and other resources over the network. A flexible broadcast scope for workgroups is based on Layer 3 (network). This solution uses multicast addressing, mobility support, and the Dynamic Host Configuration Protocol (DHCP) for the IP. The hosts in the network are connected to routers via point-to-point connections. The features used are included in the IPv6 (Internet Protocol version 6) protocol stacks. Security can be achieved by using authentication and encryption mechanisms for the IP....
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Điện thoại di động giao thức viễn thông cho các mạng dữ liệu P4
Wireless protocols A MAC protocol for a wireless LAN provides two types of data-transfer Service Access Points (SAP): network and native. The network SAP offers an access to a legacy network protocol (e.g., IP). The native SAP provides an extended service interface that may be used by custom network protocols or user applications capable of fully exploiting the protocol specific Quality of Service (QoS) parameters within the cell service area. Broadband Radio Access Integrated Network (BRAIN) is used for millimeter wave band multimedia communications....
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Điện thoại di động giao thức viễn thông cho các mạng dữ liệu P5
Protocols for wireless applications Wireless data networks present a more constrained communication environment compared to wired networks. Because of fundamental limitations of power, available spectrum, and mobility, wireless data networks tend to have less bandwidth than traditional networks, more latency than traditional networks, less connection stability than other network technologies, and less predictable availability. Mobile devices have a unique set of features that must be exposed in the Web, in order to enable the creation of advanced telephony services that include location-based services, intelligent network functionality, including integration into the voice network, and voice/data integration. ...
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Điện thoại di động giao thức viễn thông cho các mạng dữ liệu P6
Network architecture supporting wireless applications The Wireless Application Environment (WAE) architecture is designed to support Mobile Terminals (MTs) and network applications using different languages and character sets. WAE user agents have a current language and accept content in a set of well-known character encoding sets. Origin server-side applications can emit content in one or more encoding sets and can accept input from the user agent in one or more encoding sets. Wireless Telephony Application (WTA) is an application framework for telephony services....
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Điện thoại di động giao thức viễn thông cho các mạng dữ liệu P7
XML, RDF, and CC/PP Extensible Markup Language (XML) describes a class of data objects called XML documents and partially describes the behavior of the computer programs that process them. XML is an application profile or restricted form of the Standard Generalized Markup Language (SGML). Resource Description Framework (RDF) can be used to create a general, yet extensible framework for describing user preferences and device capabilities. This information can be provided by the user to servers and content providers. The servers can use this information describing the user’s preferences to customize the service or content provided....
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Điện thoại di động giao thức viễn thông cho các mạng dữ liệu P8
Architecture of wireless LANs In a wireless LAN (WLAN), the connection between the client and user exists through the use of a wireless medium such as Radio Frequency (RF) or Infrared (IR) communications. This allows the mobile user to stay connected to the network. The wireless connection is most usually accomplished by the user having a handheld terminal or a laptop computer that has an RF interface card installed inside the terminal or through the PC Card slot of the laptop. The client connection from the wired LAN to the user is made through an Access Point (AP) that can support...
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Nhiều giao thức truy cập đối với truyền thông di động P1
This book focuses on issues related to multiple access for cellular mobile communications, with a specific interest in access arbitration through multiple access protocols situated at the lower sub-layer of the second OSI layer, namely the medium access control (MAC) layer. In this chapter, first an introduction to cellular mobile communication systems is provided. This introduction will be further expanded upon in Chapter 2, particularly with respect to the features which distinguish the different generations of mobile communication systems, from analogue first generation (1G) systems to possible fourth generation (4G) scenarios....
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