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Sổ tay của các mạng không dây và điện toán di động P17
The maturity of wireless transmissions and the popularity of portable computing devices have made the dream of “communication anytime and anywhere” possible. Users can move around, while at the same time still remaining connected with the rest of the world.
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Sổ tay của các mạng không dây và điện toán di động P18
The vertices of a geometric network are points on the plane, and its edges straight line segments joining them. A geometric network is called planar if it contains no two edges that intersect other than perhaps at a common endpoint. In the remainder of this paper we will assume that all our graphs, unless otherwise stated, are planar geometric networks. Our main goal here is that of studying routing algorithms that take advantage of the location of the nodes of geometric networks.
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Sổ tay của các mạng không dây và điện toán di động P19
Wireless data networks are increasingly becoming an important part of the next-generation network infrastructure. This is made possible by the availability of inexpensive wireless network devices such as Bluetooth [1] and wireless LANs [20]. The objective of these networks is to provide users with “anytime, anywhere” data access. The end-user devices range from small handheld PDAs to larger laptops.
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Sổ tay của các mạng không dây và điện toán di động P20
An ad hoc wireless network is a special type of wireless network in which a collection of mobile hosts with appropriate interfaces may form a temporary network, without the aid of any established infrastructure or centralized administration. Communication in an ad hoc wireless network is based on multiple hops. Packets are relayed by intermediate hosts between the source and the destination; that is, routes between two hosts may consist of hops through other hosts in the network. Mobility of hosts can cause unpredictable topology changes....
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Sổ tay của các mạng không dây và điện toán di động P21
Mobile ad hoc networks consist of wireless hosts that communicate with each other in the absence of a fixed infrastructure. Some examples of the possible uses of ad hoc networking include soldiers on the battlefield, emergency disaster relief personnel, and networks of laptops. Sensor networks are a similar kind of network that have recently been investigated. Nodes in a sensor network are lighter, computationally less powerful, and more likely to be static compared to nodes in an ad hoc network....
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Sổ tay của các mạng không dây và điện toán di động P22
A low earth orbit (LEO) satellite constellation consists of a set of satellites orbiting the Earth with high constant speed at a relatively low altitude (a few thousand kilometers) [1]. Each satellite is equipped with a fixed number of antennas that allow it to communicate with ground transmitters/receivers and with other satellites. One of the major advantages of LEO satellites (as opposed to geostationary—GEO—satellites) is that they are closer to the Earth’s surface.
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Sổ tay của các mạng không dây và điện toán di động P23
Multicasting can efficiently support a variety of applications that are characterized by the close degree of collaboration typical of many ad hoc applications currently envisioned. Within the wired network, well-established routing protocols exist to offer efficient multicasting service. As nodes become increasingly mobile, these protocols need to evolve to provide similarly efficient service in the new environment.
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Sổ tay của các mạng không dây và điện toán di động P24
Broadcasting is one of the fundamental tasks in network communication. Its goal is to transmit a message from one node of the network, called the source, to all other nodes. Remote nodes get the source message via intermediate nodes, along paths in the network. In this chapter we consider broadcasting in radio networks. (Broadcasting in other types of networks, in particular point-to-point networks, has been extensively studied and is surveyed in [22, 26, 27].)
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Sổ tay của các mạng không dây và điện toán di động P25
The Internet currently offers access to a variety of information worldwide in an efficient and, through the use of web technologies, user-friendly manner. It is based on the Transport Control/Internet Protocol (TCP/IP) protocol stack [6] which has been developed with data communications and fixed access location points in mind. The wide use of wireless technologies for voice communications and the proliferation of handheld and other devices that can provide access to the Internet call for a new paradigm for connecting mobile users to the Internet....
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Sổ tay của các mạng không dây và điện toán di động P26
The need for “information anywhere anytime” has been a driving force for the increasing growth in Web and Internet technology, wireless communication, and portable computing devices. The field of mobile computing is the result of the merger of these advances in computing and communication with the aim of providing a seamless and ubiquitous computing environment for mobile users. In such mobile environments, database applications are enhanced with useful features of wireless technology
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Sổ tay của các mạng không dây và điện toán di động P27
Pervasive computing aims at availability and invisibility. On the one hand, pervasive computing can be defined as availability of software applications and information anywhere and anytime. On the other hand, pervasive computing also means that computers are hidden in numerous so-called information appliances that we use in our day-to-day lives [4, 29, 30]. Personal digital assistants (PDAs) and cell phones are the first widely available and used pervasive computing devices. Next-generation devices are being designed....
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Sổ tay của các mạng không dây và điện toán di động P28
The explosive research in mobile computing in recent years has opened up the field of indoor wireless networks [26]. The rapid expansion in this field is also a result of advances in digital communications, portable devices, semiconductor technology and the availability of license-free frequency bands. Another major factor that presents a real opportunity for data networking in indoor environments is the massive growth and usage of the Internet. Examples include homes, offices, trading floors in stock exchanges, conventions and trade shows, and so on. ...
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Image processing P1
Why do we process images? Image Processing has been developedin response to three major problems concerned with pictures: Picture digitization and coding to facilitate transmission, printing and storage of pictures. Picture enhancement and restoration in order, for example, to interpret more easily pictures of the surface of other planets taken by various probes. Picture segmentation and description as an early stage in Machine Vision.
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Image processing P2
Image Transformations What is this chapter about? This chapter is concerned with the development of some of the most important tools of linear Image Processing, namely the ways by which we express an image as the linear superposition of some elementary images. How can we define an elementary image?
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Image processing P3
In various applications, we often haveto deal with sets of images of a certain type; for example,X-rayimages, traffic sceneimages,etc.Eachimage in the set may be different from all the others, but at the same time all images may share certain common characteristics. We need the statistical description of images so that we capture these common characteristics and use them in order to represent an image with fewer bits and reconstruct it with the minimum error “on average”.
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Image processing P4
Image enhancement is the process by which we try to improve an image so that it looks subjectively better. We do not really know how the image should look, but we can tell whether it has been improved or not, by considering, for example, whether more detail can be seen, or whether unwanted flickering has been removed, or the contrast is better etc.
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Image processing P5
Two-Dimensional Filters What is this chapter about? Manipulation of images often entails omitting or enhancing details of certain spatial frequencies. This is equivalent to multiplying the Fourier transform of the image with a certain function that “kills” or modifies certain frequency components. When we do that, we say that wefilter the image, and the function we use is called a filter. This chapter explores some of the basic properties of 2D filters and presents some methods by which the operation we wish to apply to the Fourier transform of the image can be converted into a simple convolution operation applied to the...
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Image processing P6
Image Restoration What is image restoration? Image restoration is the improvement of an image using objective criteria and prior knowledge as to what the image should look like. What is the difference between image enhancement and image restoration? In image enhancement we try to improve the image usingsubjective criteria, while in image restoration we are trying to reverse a specific damage suffered by the image, using objective criteria. Why may an image require restoration?
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Image processing P7
Image Segmentation and Edge Detection What is this chapter about? This chapter is about those Image Processing techniques that are used in order to prepare an image as an input to an automatic system. These techniques perform vision image segmentation and edge detection, and their purpose is to extract information from an image in such a way that the output image contains much less information than the original one, but the little information it contains is much more relevant to the other modules of an automatic vision system than the discarded information. ...
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Thực hiện chất lượng dịch vụ trong các mạng IP (P1)
Drivers for the Adoption of Multi-service Networks Digitalization of entertainment and other consumer content makes it possible to use available transmission media resources more efficiently, to use universal storage solutions for the content while providing end user quality experience equal to or better than analogue media. This leads to the need for speech, music, pictures and streamed content to be delivered to homes and mobile users in digital form. Content delivery channels of this type exist or are becoming available in the form of digital telephone networks, digital mobile network systems and digital television. ...
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Thực hiện chất lượng dịch vụ trong các mạng IP (P2)
Service Quality Requirements In this chapter, means of assessing and specifying service quality requirements are described. To lay the foundation for discussion, the following questions need to be answered: • What is a service? • What kind of services are there? • What does it mean to provide quality support for a particular service type? • Which form of representation of service quality requirements is the best one? Background for answering the first question will be sought by first studying a few typical Internet services, and then proceeding to define suitable concepts for service definition. The second and third questions will...
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Thực hiện chất lượng dịch vụ trong các mạng IP (P3)
Network Mechanisms for Multi-service Quality Support This chapter deals with service quality support mechanisms in the network. Of particular interest are mechanisms inside an Internet Protocol domain, including edge treatment and service quality support mechanisms in the network core. Requirements for signalling between the endpoint and the network edge will be discussed in Chapter 5. The Internet today is based on the Best Effort (BE) service paradigm in which all IP traffic on a network link is treated alike, or in other words, no service quality support is provided when momentary traffic volume exceeds link capacity....
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Thực hiện chất lượng dịch vụ trong các mạng IP (P4)
Traffic Engineering for Multi-service IP Networks Traffic engineering is a set of techniques and tools that can be used to optimize the performance of an operational IP network. An overarching concept, traffic engineering, broadly interpreted, includes other topics discussed in this chapter: routing control mechanisms such as MPLS, and an advanced configuration in the form of policy-based management. These techniques can also be used without deploying the complete traffic engineering framework, but their optimal use benefits from it....
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Thực hiện chất lượng dịch vụ trong các mạng IP (P5)
Mapping Service Requirements to Network Resources The ability to properly map services to network resources in a multi-service network is highly important both for making the initial configuration of a network domain, and also as a basis for performing network configuration optimization. The basic task in both cases is the same, although in the latter case there is an initial configuration to start with, as well as potentially a larger number of existing boundary conditions for the new configuration. Resource allocation is an optimization problem where the available network resources, SLAs for different parties, and requirements of service types are examples...
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Thực hiện chất lượng dịch vụ trong các mạng IP (P6)
Service Level Management Techniques Service Level Management (SLM) techniques are applicable to a network transport operator – in the parlance of the previous chapter – providing service assurances either to another network transport operator, for a service provider, or an end user. Service level techniques pertain to aggregates of services, and are contractual in nature. The processes and terminology related to this subject are dealt with in this chapter. As in the previous chapters of this book, the terminology and concepts from telecommunications world are when they can be generalized to the multi-service Internet....
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Thực hiện chất lượng dịch vụ trong các mạng IP (P7)
Measurements NO I AYTON (Know thyself; Inscription on the fa¸ ade of Apollo’s temple in Delphi) c The traffic engineering process for IP networks includes obtaining feedback from the network as the basis of assessing the need to modify transport network parameters and to optimize its behaviour. Obtaining information in precise and meaningful form is imperative for being able to make the right adjustments to improve the network performance. This chapter deals with the means of monitoring service quality, the analysis methods applied to measurement data, and examples of network performance optimization based on processed measurement information....
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Thực hiện chất lượng dịch vụ trong các mạng IP (P8)
Mechanisms for Dynamic Service Quality Control The means of dynamically controlling service quality in IP networks is our next topic. There are two primary uses for such methods: dynamic control of resources within an IP domain, and implementation of dynamic SLAs between domains. The generic element handling both of these tasks is often called the “bandwidth broker” (BB), and this convention is followed also within this book. Admission control or service quality instantiation control is not part of the basic DiffServ framework [RFC2475]. Subsequently, the need for IP service quality support mechanisms for DiffServ networks other than edge provisioning and per-hop...
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Thực hiện chất lượng dịch vụ trong các mạng IP (P9)
Case Study: Service Quality Support in an IP-based Cellular RAN In this chapter, we shall study an IP-based Radio Access Network (RAN) as an example of applying the technologies of the preceding chapters. In the framework of preceding chapters, an IP RAN can be considered to be a multi-service Internet access domain supporting endpoint mobility. From the viewpoint of DiffServ, mobility is handled on the link layer. The traffic engineering framework of IETF is used to structure the example. In what follows, we shall first study the motivation for using IP-based transport in cellular radio access network. Next, IP RAN transport...
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Thực hiện chất lượng dịch vụ trong các mạng IP (P10)
Summary It is time to summarize the topics discussed in previous chapters. End users want to have access to different kind of information access and entertainment-related services with as simple technical means as possible and with as understandable a billing as possible. Such a goal not only brings economical benefits, but also means that the customer has smaller number devices and interfaces to master and to maintain. Beneficially, all kinds of services should be available to the end user using a single communication channel only for each context of use. One such context of use is home or corporate use, where...
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Thực hiện tiếng nói qua IP (P1)
Implementation of real-time telephone-quality voice2 transmission using the Internet protocol (IP, the Internet Engineering Task Force’s [IETF’s] request for comment [RFC] 2460 and RFC 791) is no longer as challenging a task as it was a few years ago [1,2]. In this introductory chapter, I define the instances and interfaces of both public switched telephone networks (PSTN) and corporate or enterprise communication networks where voice over IP (VoIP) can be implemented. The goals of VoIP implementation are to achieve (a) significant savings in network maintenance and operations costs and (b) rapid rollout of new services. ...
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