Implementation of New Computer Network

Implementation of New Computer Network Here we are going to implement an new computer network for this company that 25 employees have been working in. Suppose you want to build a computer network, one that has potential to grow to global proportions to support applications as diverse as teleconferencing, video-on-demand, electronic commerce, distributed computing, and digital libraries. What available technologies would serve as the underlying building blocks, and what kind of software architecture would you design t integrate these building blocks into an effective communication service? Suppose you want to build a computer network, one that has the potential togrow to global proportions and to support applications as diverse as teleconferencing, video-on-demand, electronic commerce, distributed computing, and digital libraries. What available technologies would serve as the underlying building blocks, and what kind of software architecture would you design to integrate these building blocks into an effective communication service? Answering this question is the overriding goal of — to describe the available building materials and then to show how they can be used to construct a network from the ground up. Before we can understand how to design a computer network, we should first agree on exactly what a computer network is. At one time, the term network meant the set of serial lines used to attach dumb terminals to mainframe computers. To some, the term implies the voice telephone network. To others, the only interesting network is the cable network used to disseminate video signals. The main thing these networks have in common is that they are specialized to handle one particular kind of data (keystrokes, voice, or video) and they typically connect to special-purpose devices (terminals, hand receivers, and television sets). What distinguishes a computer network from these other types of networks? Probably the most important characteristic of a computer network is its generality. Computer networks are built primarily from general-purpose programmable hardware, and they are not optimized for a particular application like making phone calls or delivering television signals. Instead, they are able to carry many different types of data, and they support a wide, and ever-growing, range of applications. This chapter looks at some typical applications of computer networks and discusses the requirements that a network designer who wishes to support such applications must be aware of. Once we understand the requirements, how do we proceed? Fortunately, we will not be building the first network. Others, most notably the community of researchers responsible for the Internet, have gone before us. We will use the wealth of experience generated from the Internet to guide our design. This experience is embodied in a network architecture that identifies the available hardware and software components and shows how they can be arranged to form a complete network system. To start us on the road toward understanding how to build a network, this chapter does four things. First, it explores the requirements that different applications and different communities of people (such as network users and network operators) place on the network. Second, it introduces the idea of a network architecture, which lays the foundation for the rest of the book. Third, it introduces some of the key elements in the implementation of computer networks. Finally, it identifies the key metrics that are used to evaluate the performance of computer networks. 1.1 APPLICATIONS Most people know the Internet through its applications: the World Wide Web, email, streaming audio and video, chat rooms, and music (file) sharing. The Web, for example, presents an intuitively simple interface. Users view pages full of textual and graphical objects, click on objects that they want to learn more about, and a corresponding new page appears. Most people are also aware that just under the covers, each selectable object on a page is bound to an identifier for the next page to be viewed. This identifier, called a Uniform Resource Locator (URL), is used to provide a way of identifying all the possible pages that can be viewed from your web browser. For example, http://www.cs.princeton.edu/~llp/index.html is the URL for a page providing information about one of this books authors: the string http indicates that the HyperText Transfer Protocol (HTTP) should be used to download the page, www.cs.princeton.edu is the name of the machine that serves the page, and /~llp/index.html uniquely identifies Larrys home page at this site. What most Web users are not aware of, however, is that by clicking on just one such URL, as many as 17 messages may be exchanged over the Internet, and this assumes the page itself is small enough to fit in a single message. This number includes up to six messages to translate the server name (www.cs.princeton.edu) into its Internet address (128.112.136.35), three messages to set up a Transmission Control Protocol (TCP) connection between your browser and this server, four messages for your browser to send the HTTP get request and the server to respond with the requested page (and for each side to acknowledge receipt of that message), and four messages to tear down the TCP connection. Of course, this does not include the millions of messages exchanged by Internet nodes throughout the day, just to let each other know that they exist and are ready to serve web pages, translate names to addresses, and forward messages toward their ultim ate destination. Another widespread application of the Internet is the delivery of streaming audio and video. While an entire video file could first be fetched from a remote machine and then played on the local machine, similar to the process of downloading and displaying a web page, this would entail waiting for the last second of the video file to be delivered before starting to look at it. Streaming video implies that the sender and the receiver are, respectively, the source and the sink for the video stream. That is, the source generates a video stream (perhaps using a video capture card), sends it across the Internet in messages, and the sink displays the stream as it arrives. There are a variety of different classes of video applications. One class of video application is video-on-demand, which reads a pre-existing movie from disk and transmits it over the network. Another kind of application is videoconferencing, which is in some ways the more challenging (and, for networking people, interesting) case because it has very tight timing constraints. Just as when using the telephone, the interactions among the participants must be timely. When a person at one end gestures, then that action must be displayed at the other end as quickly as possible. Too much delay makes the system unusable. Contrast this with video-on-demand where, if it takes several seconds from the time the user starts the video until the first image is displayed, the service is still deemed satisfactory. Also, interactive video usually implies that video is flowing in both directions, while a video-on-demand application is most likely sending video in only one direction. One pioneering example of a videoconferencing tool, developed in the early and mid-1990s, is vic. shows the control panel for a vic session. vic is actually one of a suite of conferencing tools designed at Lawrence Berkeley Laboratory and UC Berkeley. The others include a whiteboard application (wb) that allows users to send sketches and slides to each other, a visual audio tool called vat, and a session directory (sdr) that is used to create and advertise videoconferences. All these tools run on Unix—hence their lowercase names—and are freely available on the Internet. Many similar tools are available for other operating systems. It is interesting to note that while video over the Internet is still considered to be in its relative infancy at the time of this writing (2006), that the tools to support video over IP have existed for well over a decade. Although they are just two examples, downloading pages from the Web and participating in a videoconference demonstrate the diversity of applications that can be built on top of the Internet, and hint at the complexity of the Internets design. Starting from the beginning, and addressing one problem at time, the rest of this book explains how to build a network that supports such a wide range of applications. Chapter 9 concludes the book by revisiting these two specific applications, as well as several others that have become popular on todays Internet. 1.2 REQUIREMENTS We have just established an ambitious goal for ourselves: to understand how to build a computer network from the ground up. Our approach to accomplishing this goal will be to start from first principles, and then ask the kinds of questions we would naturally ask if building an actual network. At each step, we will use todays protocols to illustrate various design choices available to us, but we will not accept these existing artifacts as gospel. Instead, we will be asking (and answering) the question of why networks are designed the way they are. While it is tempting to settle for just understanding the way its done today, it is important to recognize the underlying concepts because networks are constantly changing as the technology evolves and new applications are invented. It is our experience that once you understand the fundamental ideas, any new protocol that you are confronted with will be relatively easy to digest. The first step is to identify the set of constraints and requirements that influence network design. Before getting started, however, it is important to understand that the expectations you have of a network depend on your perspective: An application programmer would list the services that his application needs, for example, a guarantee that each message the application sends will be delivered without error within a certain amount of time. A network designer would list the properties of a cost-effective design, for example, that network resources are efficiently utilized and fairly allocated to different users. A network provider would list the characteristics of a system that is easy to administer and manage, for example, in which faults can be easily isolated and whereitiseasytoaccountfor usage. This section attempts to distill these different perspectives into a high-level introduction to the major considerations that drive network design, and in doing so, identifies the challenges addressed throughout the rest of this book. 1.2.1 Connectivity Starting with the obvious, a network must provide connectivity among a set of computers. Sometimes it is enough to build a limited network that connects only a few select machines. In fact, for reasons of privacy and security, many private (corporate) networks have the explicit goal of limiting the set of machines that are connected. In contrast, other networks (of which the Internet is the prime example) are designed to grow in a way that allows them the potential to connect all the computers in the world. A system that is designed to support growth to an arbitrarily large size is said to scale. Using the Internet as a model, this book addresses the challenge of scalability. Links, Nodes, and Clouds Network connectivity occurs at many different levels. At the lowest level, a network can consist of two or more computers directly connected by some physical medium, such as a coaxial cable or an optical fiber. We call such a physical medium a link,and we often refer to the computers it connects as nodes. (Sometimes a node is a more specialized piece of hardware rather than a computer, but we overlook that distinction for the purposes of this discussion.) As illustrated in, physical links are sometimes limited to a pair of nodes (such a link is said to be point-to-point), while in other cases, more than two nodes may share a single physical link (such a link is said to be multiple-access). Whether a given link supports point-to-point or multiple-access connectivity depends on how the node is attached to the link. It is also the case that multiple-access links are often limited in size, in terms of both the geographical distance they can cover and the number of nodes they can connect. If computer networks were limited to situations in which all nodes are directly connected to each other over a common physical medium, then networks would either be very limited in the number of computers they could connect, or the number of wires coming out of the back of each node would quickly become both unmanageable and very expensive. Fortunately, connectivity between two nodes does not necessarily imply a direct physical connection between them—indirect connectivity may be achieved among a set of cooperating nodes. Consider the following two examples of how a collection of computers can be indirectly connected. shows a set of nodes, each of which is attached to one or more point- to-point links. Those nodes that are attached to at least two links run software that forwards data received on one link out on another. If organized in a systematic way, these forwarding nodes form a switched network. There are numerous types of switched networks, of which the two most common are circuit-switched and packet-switched. The former is most notably employed by the telephone system, while the latter is used for the overwhelming majority of computer networks and will be the focus of this book. The important feature of packet-switched networks is that the nodes in such a network send discrete blocks of data to each other. Think of these blocks of data as corresponding to some piece of application data such as a file, a piece of email, or an image. We call each block of data either a packet or a message, and for now we use these terms interchangeably; we discuss the reason they are not always the same in Section 1.2.2. Packet-switched networks typically use a strategy called store-and-forward. As the name suggests, each node in a store-and-forward network first receives a complete packet over some link, stores the packet in its internal memory, and then forwards the complete packet to the next node. In contrast, a circuit-switched network first establishes a dedicated circuit across a sequence of links and then allows the source node to send a stream of bits across this circuit to a destination node. The major reason for using packet switching rather than circuit switching in a computer network is efficiency, discussed in the next subsection. The cloud in distinguishes between the nodes on the inside that implement the network (they are commonly called switches, and their primary function is to store and forward packets) and the nodes on the outside of the cloud that use the network (they are commonly called hosts, and they support users and run application programs). Also note that the cloud in is one of the most important icons of computer networking. In general, we use a cloud to denote any type of network, whether it is a single point-to-point link, a multiple-access link, or a switched network. Thus, whenever you see a cloud used in a figure, you can think of it as a placeholder for any of the networking technologies covered in this book. A second way in which a set of computers can be indirectly connected is shown in . In this situation, a set of independent networks (clouds) are interconnected to form an internetwork, or internet for short. We adopt the Internets convention of referring to a generic internetwork of networks as a lowercase i internet, and the currently operational TCP/IP Internet as the capital I Internet. A node that is connected to two or more networks is commonly called a router or gateway, and it plays much the same role as a switch—it forwards messages from one network to another. Note that an internet can itself be viewed as another kind of network, which means that an internet can be built from an interconnection of internets. Thus, we can recursively build arbitrarily large networks by interconnecting clouds to form larger clouds. Just because a set of hosts are directly or indirectly connected to each other does not mean that we have succeeded in providing host-to-host connectivity. The final requirement is that each node must be able to state which of the other nodes on the network it wants to communicate with. This is done by assigning an address to each node. An address is a byte string that identifies a node; that is, the network can use a nodes address to distinguish it from the other nodes connected to the network. When a source node wants the network to deliver a message to a certain destination node, it specifies the address of the destination node. If the sending and receiving nodes are not directly connected, then the switches and routers of the network use this address to decide how to forward the message toward the destination. The process of determining systematically how to forward messages toward the destination node based on its address is called routing. This brief introduction to addressing and routing has presumed that the source node wants to send a message to a single destination node (unicast). While this is the most common scenario, it is also possible that the source node might want to broadcast a message to all the nodes on the network. Or a source node might want to send a message to some subset of the other nodes, but not all of them, a situation called multicast. Thus, in addition to node-specific addresses, another requirement of a network is that it supports multicast and broadcast addresses. The main idea to take away from this discussion is that we can define a network recursively as consisting of two or more nodes connected by a physical link, or as two or more networks connected by a node. In other words, a network can be constructed from a nesting of networks, where at the bottom level, the network is implemented by some physical medium. One of the key challenges in providing network connectivity is to define an address for each node that is reachable on the network (including support for broadcast and multicast connectivity), and to be able to use this address to route messages toward the appropriate destination node(s). 1.2.2 Cost-Effective Resource Sharing As stated above, this book focuses on packet-switched networks. This section explains the key requirement of computer networks—efficiency—that leads us to packet switching as the strategy of choice. Given a collection of nodes indirectly connected by a nesting of networks, it is possible for any pair of hosts to send messages to each other across a sequence of links and nodes. Of course, we want to do more than support just one pair of communicating hosts—we want to provide all pairs of hosts with the ability to exchange messages. The question, then, is how do all the hosts that want to communicate share the network, especially if they want to use it at the same time? And, as if that problem isnt hard enough, how do several hosts share the same link when they all want to use it at the same time? To understand how hosts share a network, we need to introduce a fundamental concept, multiplexing, which means that a system resource is shared among multiple users. At an intuitive level, multiplexing can be explained by analogy to a timesharing computer system, where a single physical CPU is shared (multiplexed) among multiple jobs, each of which believes it has its own private processor. Similarly, data being sent by multiple users can be multiplexed over the physical links that make up a network. To see how this might work, consider the simple network illustrated in , where the three hosts on the left side of the network (senders S1S3) are sending data to the three hosts on the right (receivers R1R3) by sharing a switched network that contains only one physical link. (For simplicity, assume that host S1 is sending data to host R1, and so on.) In this situation, three flows of data—corresponding to the three pairs of hosts—are multiplexed onto a single physical link by switch 1 and then demultiplexed back into separate flows by switch 2. Note that we are being intentionally vague about exactly what a flow of data corresponds to. For the purposes of this discussion, assume that each host on the left has a large supply of data that it wants to send to its counterpart on the right. There are several different methods for multiplexing multiple flows onto one physical link. One common method is synchronous time-division multiplexing (STDM). The idea of STDM is to divide time into equal-sized quanta and, in a round-robin fashion, give each flow a chance to send its data over the physical link. In other words, during time quantum 1, data from S1 to R1 is transmitted; during time quantum 2, data from S2 to R2 is transmitted; in quantum 3, S3 sends data to R3. At this point, the first flow (S1 to R1) gets to go again, and the process repeats. Another method is frequency-division multiplexing (FDM). The idea of FDM is to transmit each flow over the physical link at a different frequency, much the same way that the signals for different TV stations are transmitted at a different frequency on a physical cable TV link. Although simple to understand, both STDM and FDM are limited in two ways. First, if one of the flows (host pairs) does not have any data to send, its share of the physical link—that is, its time quantum or its frequency—remains idle, even if one of the other flows has data to transmit. For example, S3 had to wait its turn behind S1 and S2 in the previous paragraph, even if S1 and S2 had nothing to send. For computer communication, the amount of time that a link is idle can be very large—for example, consider the amount of time you spend reading a web page (leaving the link idle) compared to the time you spend fetching the page. Second, both STDM and FDM are limited to situations in which the maximum number of flows is fixed and known ahead of time. It is not practical to resize the quantum or to add additional quanta in the case of STDM or to add new frequencies in the case of FDM. The form of multiplexing that we make most use of in this book is called statistical multiplexing. Although the name is not all that helpful for understanding the concept, statistical multiplexing is really quite simple, with two key ideas. First, it is like STDM in that the physical link is shared over time—first data from one flow is transmitted over the physical link, then data from another flow is transmitted, and so on. Unlike STDM, however, data is transmitted from each flow on demand rather than during a predetermined time slot. Thus, if only one flow has data to send, it gets to transmit that data without waiting for its quantum to come around and thus without having to watch the quanta assigned to the other flows go by unused. It is this avoidance of idle time that gives packet switching its efficiency. As defined so far, however, statistical multiplexing has no mechanism to ensure that all the flows eventually get their turn to transmit over the physical link. That is, once a flow begins sending data, we need some way to limit the transmission, so that the other flows can have a turn. To account for this need, statistical multiplexing defines an upper bound on the size of the block of data that each flow is permitted to transmit at a given time. This limited-size block of data is typically referred to as a packet, to distinguish it from the arbitrarily large message that an application program might want to transmit. Because a packet-switched network limits the maximum size of packets, a host may not be able to send a complete message in one packet. The source may need to fragment the message into several packets, with the receiver reassembling the packets back into the original message. In other words, each flow sends a sequence of packets over the physical link, with a decision made on a packet-by-packet basis as to which flows packet to send next. Notice that if only one flow has data to send, then it can send a sequence of packets back-to-back. However, should more than one of the flows have data to send, then their packets are interleaved on the link. depicts a switch multiplexing packets from multiple sources onto a single shared link. The decision as to which packet to send next on a shared link can be made in a number of different ways. For example, in a network consisting of switches interconnected by links such as the one in the decision would be made by the switch that transmits packets onto the shared link. (As we will see later, not all packet-switched networks actually involve switches, and they may use other mechanisms to determine whose packet goes onto the link next.) Each switch in a packet-switched network makes this decision independently, on a packet-by-packet basis. One of the issues that faces a network designer is how to make this decision in a fair manner. For example, a switch could be designed to service packets on a first-in-first-out (FIFO) basis. Another approach would be to transmit the packets from each of the different flows that are currently sending data through the switch in a round-robin manner. This might be done to ensure that certain flows receive a particular share of the links b andwidth, or that they never have their packets delayed in the switch for more than a certain length of time. A network that attempts to allocate bandwidth to particular flows is sometimes said to support quality of service (QoS), a topic that we return to in Chapter 6. Also, notice in that since the switch has to multiplex three incoming packet streams onto one outgoing link, it is possible that the switch will receive packets faster than the shared link can accommodate. In this case, the switch is forced to buffer these packets in its memory. Should a switch receive packets faster than it can send them for an extended period of time, then the switch will eventually run out of buffer space, and some packets will have to be dropped. When a switch is operating in this state, it is said to be congested. The bottom line is that statistical multiplexing defines a cost-effective way for multiple users (e.g., host-to-host flows of data) to share network resources (links and nodes) in a fine-grained manner. It defines the packet as the granularity with which the links of the network are allocated to different flows, with each switch able to schedule the use of the physical links it is connected to on a per-packet basis. Fairly allocating link capacity to different flows and dealing with congestion when it occurs are the key challenges of statistical multiplexing. 1.2.3 Support for Common Services While the previous section outlined the challenges involved in providing costeffective connectivity among a group of hosts, it is overly simplistic to view a computer network as simply delivering packets among a collection of computers. It is more accurate to think of a network as providing the means for a set of application processes that are distributed over those computers to communicate. In other words, the next requirement of a computer network is that the application programs running on the hosts connected to the network must be able to communicate in a meaningful way. When two application programs need to communicate with each other, there are a lot of complicated things that need to happen beyond simply sending a message from one host to another. One option would be for application designers to build all that complicated functionality into each application program. However, since many applications need common services, it is much more logical to implement those common services once and then to let the application designer build the application using those services. The challenge for a network designer is to identify the right set of common services. The goal is to hide the complexity of the network from the application without overly constraining the application designer. Intuitively, we view the network as providing logical channels over which application-level processes can communicate with each other; each channel provides the set of services required by that application. In other words, just as we use a cloud to abstractly represent connectivity among a set of computers, we now think of a channel as connecting one process to another. shows a pair of application-level processes communicating over a logical channel that is, in turn, implemented on top of a cloud that connects a set of hosts. We can think of the channel as being like a pipe connecting two applications, so that a sending application can put data in one end and expect that data to be delivered by the network to the application at the other end of the pipe. Thechallengeistorecognize what functionality the channels should provide to application programs. For example, does the application require a guarantee that messages sent over the channel are delivered, or is it acceptable if some messages fail to arrive? Is it necessary that messages arrive at the recipient process in the same order in which they are sent, or does the recipient not care about the order in which messages arrive? Does the network need to ensure that no third parties are able to eavesdrop on the channel, or is privacy not a concern? In general, a network provides a variety of different types of channels, with each application selecting the type that best meets its needs. The rest of this section illustrates the thinking involved in defining useful channels. Identifying Common Communication Patterns Designing abstract channels involves first understanding the communication needs of a representative collection of applications, then extracting their common communication requirements, and finally incorporating the functionality that meets these requirements in the network. One of the earliest applications supported on any networ Implementation of New Computer Network Implementation of New Computer Network Here we are going to implement an new computer network for this company that 25 employees have been working in. Suppose you want to build a computer network, one that has potential to grow to global proportions to support applications as diverse as teleconferencing, video-on-demand, electronic commerce, distributed computing, and digital libraries. What available technologies would serve as the underlying building blocks, and what kind of software architecture would you design t integrate these building blocks into an effective communication service? Suppose you want to build a computer network, one that has the potential togrow to global proportions and to support applications as diverse as teleconferencing, video-on-demand, electronic commerce, distributed computing, and digital libraries. What available technologies would serve as the underlying building blocks, and what kind of software architecture would you design to integrate these building blocks into an effective communication service? Answering this question is the overriding goal of — to describe the available building materials and then to show how they can be used to construct a network from the ground up. Before we can understand how to design a computer network, we should first agree on exactly what a computer network is. At one time, the term network meant the set of serial lines used to attach dumb terminals to mainframe computers. To some, the term implies the voice telephone network. To others, the only interesting network is the cable network used to disseminate video signals. The main thing these networks have in common is that they are specialized to handle one particular kind of data (keystrokes, voice, or video) and they typically connect to special-purpose devices (terminals, hand receivers, and television sets). What distinguishes a computer network from these other types of networks? Probably the most important characteristic of a computer network is its generality. Computer networks are built primarily from general-purpose programmable hardware, and they are not optimized for a particular application like making phone calls or delivering television signals. Instead, they are able to carry many different types of data, and they support a wide, and ever-growing, range of applications. This chapter looks at some typical applications of computer networks and discusses the requirements that a network designer who wishes to support such applications must be aware of. Once we understand the requirements, how do we proceed? Fortunately, we will not be building the first network. Others, most notably the community of researchers responsible for the Internet, have gone before us. We will use the wealth of experience generated from the Internet to guide our design. This experience is embodied in a network architecture that identifies the available hardware and software components and shows how they can be arranged to form a complete network system. To start us on the road toward understanding how to build a network, this chapter does four things. First, it explores the requirements that different applications and different communities of people (such as network users and network operators) place on the network. Second, it introduces the idea of a network architecture, which lays the foundation for the rest of the book. Third, it introduces some of the key elements in the implementation of computer networks. Finally, it identifies the key metrics that are used to evaluate the performance of computer networks. 1.1 APPLICATIONS Most people know the Internet through its applications: the World Wide Web, email, streaming audio and video, chat rooms, and music (file) sharing. The Web, for example, presents an intuitively simple interface. Users view pages full of textual and graphical objects, click on objects that they want to learn more about, and a corresponding new page appears. Most people are also aware that just under the covers, each selectable object on a page is bound to an identifier for the next page to be viewed. This identifier, called a Uniform Resource Locator (URL), is used to provide a way of identifying all the possible pages that can be viewed from your web browser. For example, http://www.cs.princeton.edu/~llp/index.html is the URL for a page providing information about one of this books authors: the string http indicates that the HyperText Transfer Protocol (HTTP) should be used to download the page, www.cs.princeton.edu is the name of the machine that serves the page, and /~llp/index.html uniquely identifies Larrys home page at this site. What most Web users are not aware of, however, is that by clicking on just one such URL, as many as 17 messages may be exchanged over the Internet, and this assumes the page itself is small enough to fit in a single message. This number includes up to six messages to translate the server name (www.cs.princeton.edu) into its Internet address (128.112.136.35), three messages to set up a Transmission Control Protocol (TCP) connection between your browser and this server, four messages for your browser to send the HTTP get request and the server to respond with the requested page (and for each side to acknowledge receipt of that message), and four messages to tear down the TCP connection. Of course, this does not include the millions of messages exchanged by Internet nodes throughout the day, just to let each other know that they exist and are ready to serve web pages, translate names to addresses, and forward messages toward their ultim ate destination. Another widespread application of the Internet is the delivery of streaming audio and video. While an entire video file could first be fetched from a remote machine and then played on the local machine, similar to the process of downloading and displaying a web page, this would entail waiting for the last second of the video file to be delivered before starting to look at it. Streaming video implies that the sender and the receiver are, respectively, the source and the sink for the video stream. That is, the source generates a video stream (perhaps using a video capture card), sends it across the Internet in messages, and the sink displays the stream as it arrives. There are a variety of different classes of video applications. One class of video application is video-on-demand, which reads a pre-existing movie from disk and transmits it over the network. Another kind of application is videoconferencing, which is in some ways the more challenging (and, for networking people, interesting) case because it has very tight timing constraints. Just as when using the telephone, the interactions among the participants must be timely. When a person at one end gestures, then that action must be displayed at the other end as quickly as possible. Too much delay makes the system unusable. Contrast this with video-on-demand where, if it takes several seconds from the time the user starts the video until the first image is displayed, the service is still deemed satisfactory. Also, interactive video usually implies that video is flowing in both directions, while a video-on-demand application is most likely sending video in only one direction. One pioneering example of a videoconferencing tool, developed in the early and mid-1990s, is vic. shows the control panel for a vic session. vic is actually one of a suite of conferencing tools designed at Lawrence Berkeley Laboratory and UC Berkeley. The others include a whiteboard application (wb) that allows users to send sketches and slides to each other, a visual audio tool called vat, and a session directory (sdr) that is used to create and advertise videoconferences. All these tools run on Unix—hence their lowercase names—and are freely available on the Internet. Many similar tools are available for other operating systems. It is interesting to note that while video over the Internet is still considered to be in its relative infancy at the time of this writing (2006), that the tools to support video over IP have existed for well over a decade. Although they are just two examples, downloading pages from the Web and participating in a videoconference demonstrate the diversity of applications that can be built on top of the Internet, and hint at the complexity of the Internets design. Starting from the beginning, and addressing one problem at time, the rest of this book explains how to build a network that supports such a wide range of applications. Chapter 9 concludes the book by revisiting these two specific applications, as well as several others that have become popular on todays Internet. 1.2 REQUIREMENTS We have just established an ambitious goal for ourselves: to understand how to build a computer network from the ground up. Our approach to accomplishing this goal will be to start from first principles, and then ask the kinds of questions we would naturally ask if building an actual network. At each step, we will use todays protocols to illustrate various design choices available to us, but we will not accept these existing artifacts as gospel. Instead, we will be asking (and answering) the question of why networks are designed the way they are. While it is tempting to settle for just understanding the way its done today, it is important to recognize the underlying concepts because networks are constantly changing as the technology evolves and new applications are invented. It is our experience that once you understand the fundamental ideas, any new protocol that you are confronted with will be relatively easy to digest. The first step is to identify the set of constraints and requirements that influence network design. Before getting started, however, it is important to understand that the expectations you have of a network depend on your perspective: An application programmer would list the services that his application needs, for example, a guarantee that each message the application sends will be delivered without error within a certain amount of time. A network designer would list the properties of a cost-effective design, for example, that network resources are efficiently utilized and fairly allocated to different users. A network provider would list the characteristics of a system that is easy to administer and manage, for example, in which faults can be easily isolated and whereitiseasytoaccountfor usage. This section attempts to distill these different perspectives into a high-level introduction to the major considerations that drive network design, and in doing so, identifies the challenges addressed throughout the rest of this book. 1.2.1 Connectivity Starting with the obvious, a network must provide connectivity among a set of computers. Sometimes it is enough to build a limited network that connects only a few select machines. In fact, for reasons of privacy and security, many private (corporate) networks have the explicit goal of limiting the set of machines that are connected. In contrast, other networks (of which the Internet is the prime example) are designed to grow in a way that allows them the potential to connect all the computers in the world. A system that is designed to support growth to an arbitrarily large size is said to scale. Using the Internet as a model, this book addresses the challenge of scalability. Links, Nodes, and Clouds Network connectivity occurs at many different levels. At the lowest level, a network can consist of two or more computers directly connected by some physical medium, such as a coaxial cable or an optical fiber. We call such a physical medium a link,and we often refer to the computers it connects as nodes. (Sometimes a node is a more specialized piece of hardware rather than a computer, but we overlook that distinction for the purposes of this discussion.) As illustrated in, physical links are sometimes limited to a pair of nodes (such a link is said to be point-to-point), while in other cases, more than two nodes may share a single physical link (such a link is said to be multiple-access). Whether a given link supports point-to-point or multiple-access connectivity depends on how the node is attached to the link. It is also the case that multiple-access links are often limited in size, in terms of both the geographical distance they can cover and the number of nodes they can connect. If computer networks were limited to situations in which all nodes are directly connected to each other over a common physical medium, then networks would either be very limited in the number of computers they could connect, or the number of wires coming out of the back of each node would quickly become both unmanageable and very expensive. Fortunately, connectivity between two nodes does not necessarily imply a direct physical connection between them—indirect connectivity may be achieved among a set of cooperating nodes. Consider the following two examples of how a collection of computers can be indirectly connected. shows a set of nodes, each of which is attached to one or more point- to-point links. Those nodes that are attached to at least two links run software that forwards data received on one link out on another. If organized in a systematic way, these forwarding nodes form a switched network. There are numerous types of switched networks, of which the two most common are circuit-switched and packet-switched. The former is most notably employed by the telephone system, while the latter is used for the overwhelming majority of computer networks and will be the focus of this book. The important feature of packet-switched networks is that the nodes in such a network send discrete blocks of data to each other. Think of these blocks of data as corresponding to some piece of application data such as a file, a piece of email, or an image. We call each block of data either a packet or a message, and for now we use these terms interchangeably; we discuss the reason they are not always the same in Section 1.2.2. Packet-switched networks typically use a strategy called store-and-forward. As the name suggests, each node in a store-and-forward network first receives a complete packet over some link, stores the packet in its internal memory, and then forwards the complete packet to the next node. In contrast, a circuit-switched network first establishes a dedicated circuit across a sequence of links and then allows the source node to send a stream of bits across this circuit to a destination node. The major reason for using packet switching rather than circuit switching in a computer network is efficiency, discussed in the next subsection. The cloud in distinguishes between the nodes on the inside that implement the network (they are commonly called switches, and their primary function is to store and forward packets) and the nodes on the outside of the cloud that use the network (they are commonly called hosts, and they support users and run application programs). Also note that the cloud in is one of the most important icons of computer networking. In general, we use a cloud to denote any type of network, whether it is a single point-to-point link, a multiple-access link, or a switched network. Thus, whenever you see a cloud used in a figure, you can think of it as a placeholder for any of the networking technologies covered in this book. A second way in which a set of computers can be indirectly connected is shown in . In this situation, a set of independent networks (clouds) are interconnected to form an internetwork, or internet for short. We adopt the Internets convention of referring to a generic internetwork of networks as a lowercase i internet, and the currently operational TCP/IP Internet as the capital I Internet. A node that is connected to two or more networks is commonly called a router or gateway, and it plays much the same role as a switch—it forwards messages from one network to another. Note that an internet can itself be viewed as another kind of network, which means that an internet can be built from an interconnection of internets. Thus, we can recursively build arbitrarily large networks by interconnecting clouds to form larger clouds. Just because a set of hosts are directly or indirectly connected to each other does not mean that we have succeeded in providing host-to-host connectivity. The final requirement is that each node must be able to state which of the other nodes on the network it wants to communicate with. This is done by assigning an address to each node. An address is a byte string that identifies a node; that is, the network can use a nodes address to distinguish it from the other nodes connected to the network. When a source node wants the network to deliver a message to a certain destination node, it specifies the address of the destination node. If the sending and receiving nodes are not directly connected, then the switches and routers of the network use this address to decide how to forward the message toward the destination. The process of determining systematically how to forward messages toward the destination node based on its address is called routing. This brief introduction to addressing and routing has presumed that the source node wants to send a message to a single destination node (unicast). While this is the most common scenario, it is also possible that the source node might want to broadcast a message to all the nodes on the network. Or a source node might want to send a message to some subset of the other nodes, but not all of them, a situation called multicast. Thus, in addition to node-specific addresses, another requirement of a network is that it supports multicast and broadcast addresses. The main idea to take away from this discussion is that we can define a network recursively as consisting of two or more nodes connected by a physical link, or as two or more networks connected by a node. In other words, a network can be constructed from a nesting of networks, where at the bottom level, the network is implemented by some physical medium. One of the key challenges in providing network connectivity is to define an address for each node that is reachable on the network (including support for broadcast and multicast connectivity), and to be able to use this address to route messages toward the appropriate destination node(s). 1.2.2 Cost-Effective Resource Sharing As stated above, this book focuses on packet-switched networks. This section explains the key requirement of computer networks—efficiency—that leads us to packet switching as the strategy of choice. Given a collection of nodes indirectly connected by a nesting of networks, it is possible for any pair of hosts to send messages to each other across a sequence of links and nodes. Of course, we want to do more than support just one pair of communicating hosts—we want to provide all pairs of hosts with the ability to exchange messages. The question, then, is how do all the hosts that want to communicate share the network, especially if they want to use it at the same time? And, as if that problem isnt hard enough, how do several hosts share the same link when they all want to use it at the same time? To understand how hosts share a network, we need to introduce a fundamental concept, multiplexing, which means that a system resource is shared among multiple users. At an intuitive level, multiplexing can be explained by analogy to a timesharing computer system, where a single physical CPU is shared (multiplexed) among multiple jobs, each of which believes it has its own private processor. Similarly, data being sent by multiple users can be multiplexed over the physical links that make up a network. To see how this might work, consider the simple network illustrated in , where the three hosts on the left side of the network (senders S1S3) are sending data to the three hosts on the right (receivers R1R3) by sharing a switched network that contains only one physical link. (For simplicity, assume that host S1 is sending data to host R1, and so on.) In this situation, three flows of data—corresponding to the three pairs of hosts—are multiplexed onto a single physical link by switch 1 and then demultiplexed back into separate flows by switch 2. Note that we are being intentionally vague about exactly what a flow of data corresponds to. For the purposes of this discussion, assume that each host on the left has a large supply of data that it wants to send to its counterpart on the right. There are several different methods for multiplexing multiple flows onto one physical link. One common method is synchronous time-division multiplexing (STDM). The idea of STDM is to divide time into equal-sized quanta and, in a round-robin fashion, give each flow a chance to send its data over the physical link. In other words, during time quantum 1, data from S1 to R1 is transmitted; during time quantum 2, data from S2 to R2 is transmitted; in quantum 3, S3 sends data to R3. At this point, the first flow (S1 to R1) gets to go again, and the process repeats. Another method is frequency-division multiplexing (FDM). The idea of FDM is to transmit each flow over the physical link at a different frequency, much the same way that the signals for different TV stations are transmitted at a different frequency on a physical cable TV link. Although simple to understand, both STDM and FDM are limited in two ways. First, if one of the flows (host pairs) does not have any data to send, its share of the physical link—that is, its time quantum or its frequency—remains idle, even if one of the other flows has data to transmit. For example, S3 had to wait its turn behind S1 and S2 in the previous paragraph, even if S1 and S2 had nothing to send. For computer communication, the amount of time that a link is idle can be very large—for example, consider the amount of time you spend reading a web page (leaving the link idle) compared to the time you spend fetching the page. Second, both STDM and FDM are limited to situations in which the maximum number of flows is fixed and known ahead of time. It is not practical to resize the quantum or to add additional quanta in the case of STDM or to add new frequencies in the case of FDM. The form of multiplexing that we make most use of in this book is called statistical multiplexing. Although the name is not all that helpful for understanding the concept, statistical multiplexing is really quite simple, with two key ideas. First, it is like STDM in that the physical link is shared over time—first data from one flow is transmitted over the physical link, then data from another flow is transmitted, and so on. Unlike STDM, however, data is transmitted from each flow on demand rather than during a predetermined time slot. Thus, if only one flow has data to send, it gets to transmit that data without waiting for its quantum to come around and thus without having to watch the quanta assigned to the other flows go by unused. It is this avoidance of idle time that gives packet switching its efficiency. As defined so far, however, statistical multiplexing has no mechanism to ensure that all the flows eventually get their turn to transmit over the physical link. That is, once a flow begins sending data, we need some way to limit the transmission, so that the other flows can have a turn. To account for this need, statistical multiplexing defines an upper bound on the size of the block of data that each flow is permitted to transmit at a given time. This limited-size block of data is typically referred to as a packet, to distinguish it from the arbitrarily large message that an application program might want to transmit. Because a packet-switched network limits the maximum size of packets, a host may not be able to send a complete message in one packet. The source may need to fragment the message into several packets, with the receiver reassembling the packets back into the original message. In other words, each flow sends a sequence of packets over the physical link, with a decision made on a packet-by-packet basis as to which flows packet to send next. Notice that if only one flow has data to send, then it can send a sequence of packets back-to-back. However, should more than one of the flows have data to send, then their packets are interleaved on the link. depicts a switch multiplexing packets from multiple sources onto a single shared link. The decision as to which packet to send next on a shared link can be made in a number of different ways. For example, in a network consisting of switches interconnected by links such as the one in the decision would be made by the switch that transmits packets onto the shared link. (As we will see later, not all packet-switched networks actually involve switches, and they may use other mechanisms to determine whose packet goes onto the link next.) Each switch in a packet-switched network makes this decision independently, on a packet-by-packet basis. One of the issues that faces a network designer is how to make this decision in a fair manner. For example, a switch could be designed to service packets on a first-in-first-out (FIFO) basis. Another approach would be to transmit the packets from each of the different flows that are currently sending data through the switch in a round-robin manner. This might be done to ensure that certain flows receive a particular share of the links b andwidth, or that they never have their packets delayed in the switch for more than a certain length of time. A network that attempts to allocate bandwidth to particular flows is sometimes said to support quality of service (QoS), a topic that we return to in Chapter 6. Also, notice in that since the switch has to multiplex three incoming packet streams onto one outgoing link, it is possible that the switch will receive packets faster than the shared link can accommodate. In this case, the switch is forced to buffer these packets in its memory. Should a switch receive packets faster than it can send them for an extended period of time, then the switch will eventually run out of buffer space, and some packets will have to be dropped. When a switch is operating in this state, it is said to be congested. The bottom line is that statistical multiplexing defines a cost-effective way for multiple users (e.g., host-to-host flows of data) to share network resources (links and nodes) in a fine-grained manner. It defines the packet as the granularity with which the links of the network are allocated to different flows, with each switch able to schedule the use of the physical links it is connected to on a per-packet basis. Fairly allocating link capacity to different flows and dealing with congestion when it occurs are the key challenges of statistical multiplexing. 1.2.3 Support for Common Services While the previous section outlined the challenges involved in providing costeffective connectivity among a group of hosts, it is overly simplistic to view a computer network as simply delivering packets among a collection of computers. It is more accurate to think of a network as providing the means for a set of application processes that are distributed over those computers to communicate. In other words, the next requirement of a computer network is that the application programs running on the hosts connected to the network must be able to communicate in a meaningful way. When two application programs need to communicate with each other, there are a lot of complicated things that need to happen beyond simply sending a message from one host to another. One option would be for application designers to build all that complicated functionality into each application program. However, since many applications need common services, it is much more logical to implement those common services once and then to let the application designer build the application using those services. The challenge for a network designer is to identify the right set of common services. The goal is to hide the complexity of the network from the application without overly constraining the application designer. Intuitively, we view the network as providing logical channels over which application-level processes can communicate with each other; each channel provides the set of services required by that application. In other words, just as we use a cloud to abstractly represent connectivity among a set of computers, we now think of a channel as connecting one process to another. shows a pair of application-level processes communicating over a logical channel that is, in turn, implemented on top of a cloud that connects a set of hosts. We can think of the channel as being like a pipe connecting two applications, so that a sending application can put data in one end and expect that data to be delivered by the network to the application at the other end of the pipe. Thechallengeistorecognize what functionality the channels should provide to application programs. For example, does the application require a guarantee that messages sent over the channel are delivered, or is it acceptable if some messages fail to arrive? Is it necessary that messages arrive at the recipient process in the same order in which they are sent, or does the recipient not care about the order in which messages arrive? Does the network need to ensure that no third parties are able to eavesdrop on the channel, or is privacy not a concern? In general, a network provides a variety of different types of channels, with each application selecting the type that best meets its needs. The rest of this section illustrates the thinking involved in defining useful channels. Identifying Common Communication Patterns Designing abstract channels involves first understanding the communication needs of a representative collection of applications, then extracting their common communication requirements, and finally incorporating the functionality that meets these requirements in the network. One of the earliest applications supported on any networ

Critical Analysis of Edvard Munchs The Scream Essay -- Visual Arts Pa

Critical Analysis of Edvard Munch's The Scream "The Scream", sometimes known as "The Cry" was painted by Edvard Munch in 1893. Some say Munch played a role in the development of German Expressionism, though the Norwegian painter turned down two offers to join the group, and preferred not to be classified, or 'put' into a category. This painting was part of Munch's "The Frieze of Life", a series of paintings each portraying a phase of life - as defined by Munch: Birth of Love, Blossoming and Dissolution of Love, Anguish of Life, and Death. The eleven paintings - "The Kiss", "Madonna", "Ashes", "Dance of Life", "Melancholy", "Red Virginia Creeper", "The Scream", "Death in the Sick-Room", "Puberty", "Moonlight", and "The Sick Child" - are as moving today as they were a hundred years ago when the motifs were first conceived. Munch finished "The Scream" in 1893. It was a work of great personal meaning to him. The painting was like the culmination of all the tragic and harrowing events in his life. When Munch was aged only five years old, his Mother died from Tuberculosis. Nine years later, his favourite sister Sophie dies from tuberculosis also, at the age of 15. Frequent illnesses prevent him from attending Technical college in Christiania (Oslo). In 1889, he is hit with perhaps the biggest blow so far: his beloved father dies. Munch wrote: "And I live with the dead ones; my mother, my sister, my grandfather, my father- he, especially. Every memory, every little thing, they all come back to me in flocks. I can see him again as I saw him for the last time four months ago, when he told me goodbye on the bench; we were a little bit shy, we didn't want to betray the pain that this separation was causing to us. How much we loved each other in spite of everything, how much he worried at night for me, for my life - because I couldn't share his faith" Therefore, it is not surprising that the mood of the painting is so haunting. Munch painted it surrounded by morbidity. The point in the painting where we see the figures, was a road on top of a hill looking over Christiania and the harbour. On one side of the hill was a psychiatric hospital where one of his sisters had been sent, and on the other side, an abattoir. Munch described the feeling he experienced in a diary entry in his literary diary in Nice, on the 22nd January 18... ...e influenced two German expressionist groups, Die Brà ¼ke and Die Blaue Reiter. He had two offers from Die Blaue Reiter to join them, but he turned both down. Painting was for Munch a personal experience, and he did not like to share it, or put his works into any grouping. The painting itself looks quite 'slapdash', as though it was rushed. The thick streaks of oil paint give the effect of a movement blur, like the world was swirling around the figure. It is hard to distinguish between the water and the land, difficult to recognize where the hills in the background stop and the sunset begins. "The Scream" is a painting full of emotion, full of character not understood at the time of its birth. It reflects Munch's life at that time, all the Death and anxiety that makes the painting so mysterious and haunting, whilst also lively. When I look at it, I feel I can hear the scream echoing from it. The screaming figure draws the attention of the onlooker, but other aspects of the painting are just as interesting. Whilst we cannot know what was going through Munch's mind when he painted"The Scream", we can guess that the painting evokes all the pain he was feeling.

The Islamic Worldview

UNGS 2030 THE ISLAMIC WORLDVIEW SEMESTER 1 2012/2013 ASSIGNMENT #1 TITLE| WORLDVIEW:THE MEANINGS,NECESSITY AND ELEMENTS ACCORDING TO MUSLIM SCHOLARS| COURSE TITLE| THE ISLAMIC WORLVIEW| COURSE CODE| UNGS 2030| SUBMISSION DATE| 30 OCTOBER 2012| NAME| NURUL AMALINA BINTI MD ALI| MATRIC. NO| 1215762| SECTION| 2| LECTURER NAME| DR. MD YOUSUF ALI| ACKNOWLEDGEMENT Bismillahirrahmanirrahim Assalamualaikum, First and foremost, I would like to thank to my instructor of this assignment, Dr. Md Yousuf Ali who is my best lecturer of The Islamic Worldview subject for the valuable explanation, guidance and advice especially during lecture session. He inspired me greatly to work in this assignment. His willingness to motivate me contributed tremendously to my assignment. I also would like to thank him for showing me some example that related to the topic of my assignment about The Worldview in term of its meanings, necessity and elements according to Muslim scholars. Besides, an honourable mention goes to my family and friends for their understandings and supports on me in completing this assignment. Without helps of the particular that mentioned above, I would face many difficulties while doing this assignment. During complete this assignment, I faced many difficulties and challenging things especially midterm examination and Eid Adha Celebration was around the corner. I found the information that related to our topic through The Holy Quran, the Internet, magazine, reference book and people in surrounding. However, I had done and can overcome these problem by maximize my effort and pray to Him who is The Most Helpful to His servant. Alhamdulillah. THE MEANINGS THE MEANING OF WORLDVIEWS In this assignment, first and foremost, before us knowing about worldview in Islamic perspectives, we must know the introduction and definition of ‘Worldview’. Where is term come from? And where is it used? The word of ‘Worldview’ is come from many sources. Its meaning is defined by many of scholars either western scholars or Muslim scholars. One of them comes from German’s term which is called as â€Å"Weltanschauung. Meanwhile, in Arabic’s term it is refer as â€Å"Tasawur or Ru’yah al-Islam li al-Wujud â€Å",   *The Meaning of Worldview by Western Scholars In the end of 1700s, Friedrich Schilling who is the German philosopher defined that, worldview (Weltanschauung) is refer as â€Å"The self-realized productive and conscious way of apprehending an d interpreting the universe of beings†. After a century, about in 1868, â€Å"Weltanschauung† was known as â€Å"a comprehensive conception of the world especially from a specific point of view†. Based on German scholars perspectives defined that Worldview is comprises of set of attitudes on basic matters like the way people think about the world. *The Meaning of Worldview by Muslim Scholars Muslim scholars and thinkers started use the precept of â€Å"worldview† during modern period. This percept appeared in the works of a lot of Muslim scholars like Sheikh Badiuzaman Nursi (1877-1960) in â€Å"Rasa’il al Nur† (letters of light) and in some Iranian thinkers such as Ali Shari’ati (1933-1977), al-Mutahari Ayatullah Murtaza (fundamentals of Islamic thought: God, man and the universe), Sayed Husein Naser (1933-) in â€Å" Man and nature: the spiritual crisis in modern man†, â€Å"Islam and the plight of modern man†. Isma’il Raji al-Faruqi (933-1982) â€Å"cultural atlas of Islam†, â€Å"Tawhid: its implications for thought and life†, Muhammad Naqib al-Atas â€Å"Islam and secularism†. In Arabic literature Sayed Qutb (1906-1966) came in the first place in his â€Å"in the shade of the Qur’an† (Fi Zilal al-Qur’an) â€Å"The Islamic Perspective† â€Å"al-Tasawwur al-Islami† occupies a central position. In contemporary period, valuable works have been produced dealing with the issue from Islamic point of view by Sardar Ziauddin (Islamic civilization: history of sciences), Alam Shoudhury (economics) (The Islamic worldview: socio-scientific perspective), al-Messiri (Thought & Political science). The meaning of Worldview by Muslims’ approach stands that the worldview is made from the aspect of both al-Dunya and al-Akhirah, in which the Dunya-aspect must be related in a profound and inseparable way to the Akhirah-aspect which the Akhirah-aspect has ultimate and final significance. In other word, worldview is a set of attitudes on a wide range of fundamental matters. It has a comprehensive set of propositions about various aspects of the world around us and man’s place within it. It is also defined as a basic assumption about the way of thinking about the world, which provides a more or less coherent, though not necessarily accurate. A worldview is a profile of the way the people within a specified culture live, act, think, work and relate. At the same time, it can be act as a â€Å"map† or culture’s social, religious, economic and political views and relationships.THE MEANING OF ISLAMIC WORLDVIEWSBased on Syed Naquib Al-Attas, a great Muslim scholar, he mentioned that Islamic Worldviews is, â€Å"a vision of reality and truth that appears before our mind’s eye revealing what existance is all about†. â€Å"a metaphysical survey of the visible as well as the invisible worlds including the perspective of life as a whole†. According to Al-Attas, worldview is considered as vision of reality and truth (ru’yat  al-Islam  li  al-wujud) from the Islamic point of view. Another Muslim scholar, Professor Kamal Hassan ,Professor  Area of Specialization: Contemporary Islamic Thought IIUM, also stated that, Worldviews is a comprehensive conception of Allah,man and the universe and their relationship from Islamic perspectives. † The worldview of Islam encompasses both al-dunia and al-akhirah in which the dunia aspect must be inextricably linked to the akhirah aspect, and in which the akhirah aspect has ultimate and final significance. Hence, Islamic worldviews concern with this universe (world) and the hereafter or the Day of Judgment as far as Islamic nature of reality is concerned. The belief in dual worldviews has made Islam looks exceptional. Since these views are principally derived from the  Quran, this reflects that Islamic worldviews are identical to  Quranic  worldview. Unlike in the Western, their emphasizing is on logical reasoning as well as rationality. Due to this, Islam has distinguished itself from other available worldviews as mentioned by Khurshid  Ahmad as cited by   Mawdudi. For instances, the Western’s and Christian‘s worldviews are secular and religious respectively. Islamic worldview is about the seen and unseen matter like the universe, creator, prophethood, society, man, and hereafter. Amalgamation or historical concoction or any addition stories of various cultural values are not a worldview that is formed merely. Rather, it is a well established framework derived from the revelation and interpreted by Muslim scholars throughout Islamic history. Then, it is implement by Muslims today. This frame of reference provides us with correct and consistent answers to the ultimate questions pertinent to the issues of God, unseen, man, universe, and life. It also guides man as a vicegerent of Allah to the correct belief system, shari‘ah, and ethical values. THE NECESSITYTHE NECESSITY OF ISLAMIC WORLDVIEWWe all need a certain worldview, even if it is not made fully explicit, to interact with our world. There is a practical need to have at least an implicit and for that reason naive answer for each of the worldview questions. The Islamic worldview is more than a religion. In Islam, it covers all aspects of life for its followers. Many religious scholars treat the Islamic worldview as a monotheistic religion following five simple pillars of faith. In Islamic worldview, it has views about the words like astronomical, spiritual, physical, intellectual and many aspect of life. The outlook of life in this perceptive is highly emphasized which is show us the vision of life to achieve certain goal in world and the ultimate goal in hereafter. Islamic worldview is important in order to provide the Muslims with the true knowledge and explanation about the world seen and unseen as they are explained in the Quran. Quran is the best guidance for all questions about life. This revelation is restricted to deny. The answer from this revelation cannot change and make this worldview become stable due to have ultimate guidance. For instance, if we are question about something, we can refer to Quran to find the solution. This guidance also encourages us to get the answer through the learning and reading. In Surah Al-Alaq, Allah mentioned that: Another that, Islamic worldview helps us to interact with nature, individuals, peoples, nations, cultures and civilizations. It helps us to know them comprehensively and can plan neighborhood among them. After we have relation with certain culture, we have to recognize what is their ethnic and culture. This will helps us to correct our own values, perspectives, attitudes and behaviors. This perceptive guide and teach people the way and method how to achieve the main values of Islam in human life. We can differentiate which one is bad and good. In Islam, the aspects regarding our morality and virtues (akhlaq) are become one of necessity aspect of life although we are struggling to achieve a success in life. As an example, we need to cover aurah during working at workstation. Furthermore, this percept is purposed to establish the fundamental ethical precepts, such as justice, freedom, trust, and dignity of human life and existence. Some of worldview not emphasize ethical aspect very well. By this perception, it will formulate theories of politics, sociology, culture, etc.THE ELEMENTS THE ELEMENTS OF ISLAMIC WORLDVIEWThe fundamental elements of Islamic Worldview are the key terms of this perceptive. These elements act as integrating principles that place all our systems of meaning and standard of life and values in coherent order as a unified system forming the worldview. The highest principle of true reality as stated in Quran is focused on knowledge of the nature of God. The w orldview of Islam is characterized by an authenticity and finality that points to what is ultimate, and it projects a view of reality and truth that encompasses existence and life altogether in total perspective whose fundamental elements are permanently established. Quoted back of Syed Naquib Al Attas word,† A metaphysical survey of seen and unseen world including the perspective of life as a whole†. The element of worldview are include visible anfd visible things. They are: 1. The Nature of God This the supreme principle of Islamic Worldview. This all about the existence of God. 2. The Nature of Revelation- The Qur'an ; Prophethood This element are totally derived from Revelation, the change which is possible in this case is restricted to the manifestation of these elements in different units of time and space. 3. The Nature of Revealed Religion- Islam 4. The Nature of the World and Hereafter (dunya wal akhirah) 5. The Nature of Man The Psychology Of Human Soul (insan) 6. The Nature of Knowledge (‘ilm) As mentioned in Surah Al Alaq which is encourage us to seek knowledge. 7. The Nature of Adab (values and virtues) The aspects regarding our morality and virtues (ahlaq) are become one of necessity aspect of life although we are struggling to achieve a success in life. 8. The Nature of Freedom 9. The Nature of Happiness (sa'adah) 10. The True Meaning of Change, Development, and Progress 1. Concluding Remarks All of them are together with the key terms and concepts that they unfold, have profound bearing upon our ideas about change, development, and progress. These fundamental elements act as integrating principles that place all our system of meaning and standards of life and values in coherent order as a unified system forming the worldview and the supreme principle of true reality that is articulated by these fundamental elements is focused on knowledge of the nature of God as revealed in the Qur'an.CONCLUSIONIt is a high time that the initiative of integrating the Islamic worldview into the planning of neighbourhoods takes off in the Muslim world. Worldviews play the main role in the human being life. Its affect every single action of a man. Different worldviews will certainly shape different qualities of mankind which will eventually lead them to different end means of life as well. This distinction due to man’s aql (intellectual) which is very limited and sometime buyers (not fair). Worldview is a complex and a comprehensive perception. A worldview manifests itself in all aspects of life, social, political, economic, civilization etc. This complex includes the spiritual, cognitive, intellectual and behavioral abilities that Allah has endowed him. Thus, a worldview is at once a mean and a fruit of human spiritual, cognitive, and behavioral efforts. The worldview perceptive can be human-made as well as Revelation based precept. Islamic worldview is a collective and based on ummatic unified. A worldview is similar to any other human ideas which is it develops according to their accumulated knowledge, historical events, and human experience and then it is implemented by the people. However, as far as the Islamic worldview is concerned, the fact of change takes significantly a different position. Although we are busy to achieve world’s mission of life, hereafter’s goal become significant and our priority to achieve it.REFERENCES* Lecture Notes  © Department of General Studies IIUM,2007- 2008. * The Islamic Worldview: Glimpse on Studies and Definitions,Abdelaziz Berghout,Introduction to the Islamic Worldview,Study of Seleceted Essentials,IIUM Press (2010). * Basic Principles of Islamic Worldview ,Sayyid Qutb Islamic Pubns Intl (September 15, 2005). Vidal, C. (2008) Wat is een wereldbeeld? (What is a worldview? ). * David Naugle: Worldview: The History of a Concept (Eerdmans, 2002). * Merriam –Webster 1994 (Britannica Encyclopedia 2001). * Contribution Of The Islamic Worldview Towards Corporate Governance Mohamed Asri, Mohamed Fahmi Msc Accounting Sem 2   2003 IIUM. * http://wikipedia. com/worldview/ * http://www. allaboutworldview. org/is lamic-worldview. htm * http://izat2009. blogspot. com/worldview * http://ungss. blogspot. com * http://web. usm. my/islamicworldview/

Prison Treatments Laws in New York State Essay Essays

Prison Treatments Laws in New York State Essay Essays Prison Treatments Laws in New York State Essay Essay Prison Treatments Laws in New York State Essay Essay Michael E. Deutsch. Dennis Cunningham and Elizabeth M. Fink †Twenty Years Later - Attica Civil Rights Case Finally Cleared for Trial† Social Justice. Vol. 18. No. 3 ( 45 ) . Attica: 1971- 1991 A Commemorative Issue ( Fall 1991 ) . pp. 13-25 This is a journal uses the commissioner. the manager of the correctional. Russel Osward as a halfway function to remember the Attica Riot. reprobating his failure of direction of the prison government and the inhumane assault he had set to stop up the rebellion. The authorities had covered the facts of violent assault of the public violence for old ages. but it had been dug out by the protest of the public violence subsisters 20 old ages after the public violence. and they eventually won the dialogues and gained their civil rights. Citations can be cited for discoursing how the dialogue had gone through. It besides provides me some background information of the public violence. It besides gives a sense of what sort of civil rights had been violated and what had been brought back. I can utilize these rights as mention to seek alterations of the State Torahs. Vicky Munro-Bjorklund â€Å"Popular Cultural Images of Criminals and Prisoners since Attica† Social Justice. Vol. 18. No. 3 ( 45 ) . Attica: 1971- 1991 A Commemorative Issue ( Fall 1991 ) . pp. 48-70 This diary focuses on the popular civilization images that been shaped after the Attica Riot. It argues that the misinterpretation of the captive had been changed since the rebellion. and media is besides a force that pushes the prisons into reform. Because of stereotype. or the popular cultural images of the captives. no 1 had paid that much attending to the captives before the increasing exposure of the existent â€Å"prisoners’ life† after the Attica Riot. The description of the popular cultural images of the captives in Attica is truly a good resource to utilize. This resource is chiefly a statement of the prisoners’ image. I do non necessitate to depict the alteration of the images because I am concentrating on the jurisprudence alterations. so nil will b e quoted. but it makes me believe in a new manner: The fondness of exposure from the populace or societal media. George Edwards. â€Å"Foreword: Penitentiaries Produce No Penitents† forward-penitentiaries produce no penitents. 63 J. Crim. L. Criminology A ; Police Scl. 159 ( 1972 ) : 154-161 This diary focused on how the societal media have done to assist the coloured people inside the US penal system by utilizing the illustration of the media fondness of the Attica Riot. It focuses on and the cultural images that shape the stereotype of the black people so that they are isolated from â€Å"us† . The prisoners’ lives in the prisons have become more crystalline through the societal media after the Attica Riot when the societal media have paid attending to them and cover more about them. Social media is reprobating the barbarous intervention to the captives and the unfairness of the sentence through different ways. This paper is searched after the old 1. it is a good resource for seeing how the societal media had pushed the State to alter their correctional method and give b ack prisoners’ civil rights. Willi The Naturalization Act of 1790 am L. Wilbanks The study of the committee on Attica. 37 Fed. Probation 3 ( 1973 ) : 3-5 This is a premier summery of the national committee study of the Attica Riot published on September 13. 1972. It briefly summarized and explained what is the Attica Riot. recorded the cause of it. reported the dialogue of it. and analyzed the assault and the wake of it. The chief high spot of the public violence from the study is that it happened at a clip when the prison was about to reform for better. and the violent assault was because the prison inmate was inquiring for general forgiveness. but the authorities refused so. yet the consequence was still inhumane. This study is brief and comprehensive ; it is supplying background information for the populace to acquire the general thought of the public violence. Part of it can be quoted for a prof of inhumane intervention after the rebellion. Gerald Benjamin and Stephen P. Rappaport. Attica and Prison Reform. Proceedings of the Academy of Political Science. Vol. 31. No. 3. Regulating New York State: The Rockefeller Years ( May. 1974 ) . pp. 200-213 This diary focuses on describing the inside informations of the dialogue and the assault of the Attica Riot. Informing us assault is because of the failure of the dialogue. This diary besides mentioned that the public violence happened when the reform was merely about to be taken into pattern. After the public violence. the reform began. including the installations alteration and the intervention alterations. Changes are based on the fund from federal and the State. though something still needs to be alteration. it was already a large measure. It is besides demoing some important alterations such as the alteration in the employment of the installations from all Whites to Latinos. the sawed-off clip of locking. Though this diary is truly detail. I need to cite the alterations of Torahs instead than merely physical alterations in this piece. Angela Y. Davis: Are Prisons Obsolete? Seven Stories Press New York. 2003: 10-19. 84-104 Chapter 1 introduces us with an thought of prison reform. which additions the bulk supports of the populace and it is besides the ground for the Attica Riot. It besides reveals the thought that non many people outside the prison are willing to believe about the life inside the prison. which is traveling to be a support of why I said that there is non that much attending had been paid for prison intervention. Chapter 5 Tells us how a mass of private companies and industries are deriving a batch of net income from the captives so that captives are non deriving what they are supposed to be gained. Both chapters are back uping the thought of why prisons should be paid attending and be reformed. Thought the industrial composite of the prison is written late instead than the immediate fact. I would utilize them as mention of things that haven’t been improved after the public violence. Bruce Burgett and Glenn Hendler. Keywords for American Cultural Studies. New York University Press. 2007: 37-42 This piece gives readers a brief history from the ancient Grecian to now of how Citizenship has come to its position in the United State. The civil rights have been violated by the sovereignty. but eventually came to equality through the push of establishments. faiths. every bit good as civil motions. This piece besides introduces us that how the engineering and transits are of import to a new apprehension of citizenship. This piece is of import for analysing the prison rights because I am composing through the chance that prison inmates are besides citizens. that they should hold the same rights as those normal citizens. but prisoners’ rights are somehow ever been valid or even ignored by the U. S. penal system. This article helps to specify the citizen in my paper. Jael Silliman and Anannya Bhattacharjee. Patroling the National Body Sex. Race. and Criminalization. South End Press Cambridge. Massachusetts. 2002: 1-48 Chapter one gives us a general thought on how the US penal setup has been enforced by the engagement of multiple â€Å"relevant† establishments. It is demoing audiences how those institutional officers themselves are piquing the Torahs but still move as a jurisprudence executive. and how they use the name of in-migration jurisprudence to go against the rights. particularly the rights of the adult females with colourss. they offence their organic structures. and utilize them to imprison colored work forces. This helps to analysis the female prison interventions in recent clip. Though it is a good illustration to demo the misdemeanor of the civil rights but it might be a small different from the subject that I am composing about because it is chiefly focused on the recent clip and the in-migration Torahs. Dylan Rodriguez. Forced Passages. Imprisoned Extremist Intellectuals and the U. S. Prison Regime. University of Minnesota Press. Minneapolis. London. 2006 This chapter focuses on the formation of the cardinal word: The War. Though the war is purportedly be the struggle between provinces. the author tells readers that the U. S. authorities is utilizing the war zone as a manner to command the citizens. It talks about how the power is contributed through the usage of the prison government. I would wish to cite the history of the prison government to inform that the prison today has a bondage background and that is what makes the rights of captives been blurred so moderately. U. S. Naturalization Act of 1790. The Transcript of 13th Amendment to the U. S. Constitution: Abolition of Slavery ( 1865 ) The naturalisation act is the cardinal act to the U. S. citizens. It indicated that free white of good moral character that had lived in the U. S. for two old ages and swore commitment. It can be used as a historical accordant to the descriptions of the history of the prison government. The 13th amendment establishes birthright of citizenship due procedure and equal protection. officially extends citizenship to freshly liberate. black work forces. Both of these Torahs can be use as path of the citizenship as proves of the inequality of the civil Torahs roots. Abstraction Citizenship refers to the nexus between province and individual who lives in. Citizens by wide should be within the nexus and should be person who lives in the sate. Prisoners as a particular type of citizen are supposed to hold the same civil rights and be protected by the same Torahs. yet their fortunes set them into a state of affairs where their rights are violated invariably with or without justness. Prison interventions in the US. can been seen as a important illustration of the misdemeanor of the prisoners’ civil rights. It has neer been paid attendings until the four-day rebellion in the Attica Correctional Facility burst out in 1971. Attica Riot was the most violent public violence in the full U. S. history. Through out the rebellion. many inhumane interventions of the captives have been revealed through the exposure of the societal media. As a wonder on the affects of prison rebellions on the New York State authorities. this paper is traveling to detect some important alterations that had been made by the New York State instantly after the public violence through the wake dialogue of the Attica public violence to bespeak that the captive rights are still non hold been treated justly.

Prospectus on family involvment in education essays

Prospectus on family involvment in education essays The research questions addressed in this design will be examined using data from the National Education Longitudinal Study of 1988. The initial NELS research and data collection was done by the National Center for Education Statistics. The data will be used to examine the effects of the family environment on a childs educational attainment. The NELS data set has an extensive list of variables to examine for trends and associations in nearly all aspects of a students life. Not only does the data examine the student but the parents, teachers, learning environment, and everyday life of the student. The problem with the NELS data is successfully wading through the thousands of variables to find the variables of interest and consequence to the researcher. Many of the variables of the NELS data can be used to address the question of the level of affect a familys involvement in a childs educational attainment. The actual hypothesis in the research project is as follows: the family environment in which a child grows up in directly affects the level of educational attainment of the child. The findings and variables of the NELS data have been used by countless researchers and is a wonderful source of reliable educational data. The independent variable of the hypothesis is the family aspect of the statement. The involvement of a family in a childs education can be defined in many different ways. Some may say that how time much a parent spends actually helping his or her child with schoolwork is the determining factor in a childs education. Many others believe the material environment that a parent provides for a child is of more consequence that how much actual time he or she spends with the child. The truth of the matter is that t he true answer more likely is a combination of all aspects of the family and the surroundings that the family sets for a childs education. ...

Effective E-learning To Students Essay Example | Topics and Well Written Essays - 2000 words

Effective E-learning To Students - Essay Example Therefore, this study defines the factors influencing e-learning effectiveness and enforcing quality measures for the consistent effectiveness and how influencing factors and quality measures are observed by various e-learning experts with respect to business and academics and business ones. Keeping all this in mind, this research will be addressing the following questions used for research: 1. How can we measure the e-Learning effectiveness? 2. What factors impact the programs of e-Learning effectiveness? 3. What are the major significance factors and differences between the business and academic e-Learning practitioners? Literature Review Effectiveness of e-Learning The fast pace growth of e-learning industry made the researchers and experts ended up wondering, that how to measure the effectiveness of e-learning programs. Besides, the disparity in between effectiveness and efficiency should be made visible. Effectiveness is related to outputs though efficiency is fraction of output to input (Rumble, 1997). As he quotes, â€Å"An organisation that meets the production outputs that fulfils the demands and needs of their clients is effective. This exhibits the criteria by which the organisation’s success can be measured.† Furthermore, the degree of e-learning programs explaining the enhancement of â€Å"learning† is important. For instance, improving students’ satisfaction, improving learners’ grades and helping learners to perform certain tasks with efficiency and etc. can be interrelated to a successful enhancement of â€Å"learning† experience. In order to make e-Learning more effective and to change the perception of the student with respect to the same, we... This research will be focusing on the outcomes of Hiltz and Johnson’s study which was conducted in 1990, along with some different studies, which will help in the advancement of the measurement of e-Learning effectiveness as well as defining the organism of factors which affect e-Learning, but, modified to the requirements and framework of this research. In 1994, Alavi claimed that previous collaborative learning literature recommended that effectiveness of learning can be measured with respect to the perception of student and their learning and evaluation of experience which the attain from their classrooms. In contrast, in the year 2001 Piccoli, Ives and Ahmad carried out a research to widen the framework of effectiveness of e-Learning. They put forward three major measures for effectiveness, which are, performance, self-efficacy and satisfaction.This research is planned to be conducted in order to share the experience of the e-Learning professionals and to share the knowled ge of the students of e-learning. The research is planned in order to attain firsthand knowledge and experience of planning, preparing and designing and to gauge it with respect to develop better understanding of effectiveness of E-Learning. The purpose of this study is to understand what the benefits of e-Learning are and what are the measure which can be taken in order to enhance the e-Learning effectiveness. People will be asked to share their experience about how much they have benefited by opting towards this field or by choosing e-Learning as their career.

Detailed Research Proposal Example | Topics and Well Written Essays - 1250 words

Detailed - Research Proposal Example These definitions underpin the reason why it tends to wield strong influence on the behavior of teenagers. There are many reasons behind peer pressure but foremost of these is the desire of teenagers to follow people whom they idolize and wish to follow and also to belong and be identified with a group. This is, fundamentally, human nature. Therefore, it is inevitable. Humans are willing to adhere to social mores because it is a requisite in being a member of the community. The dynamics is the same in the case of peer pressure. The school and the social environment of children and adolescents is a microcosm of our society where membership, belongingness and recognition are very important aspects of growing up. The potency of influence of peers has also been attributed to the power of the crowd over its members. It has been said that it â€Å"provides a means of transition from unisexual to heterosexual social relationships by facilitating interclicque activities (Tierney et al., 52) .† Negative peer pressure adversely impacts the psyche of young people and adolescents. The pressure from a group that an adolescent belongs to is very effective because minors are still not capable of completely comprehending the consequences of their actions. Drug abuse, smoking, sex, violence etc. are just few of the activities that teenagers are being forced to do just they could be part of a group (Phelan, Davidson and Thanh 1991). The most extreme outcome of peer pressure is the deviation from established social norms (Berten and Van Rossem 2011). The undesirable behaviors could include drug offences, street violence, theft and burglary, among other crimes. Additionally, several social problems could also result in the process such as teenage pregnancy and bullying. Peer pressure, hence, is an important public issue that needs to be defined, understood and addressed as a problem. By doing so, it is expected that several pressing public concerns can also be dealt with. Fo r instance, it can contribute to solving the problem of juvenile delinquency. This study seeks to contribute to the body of literature on this theme and in the process enrich the extant resources that could ultimately help solve the negative effects of peer pressure. The topic of the research is how to reduce the impact of negative peer pressure on children. Research Hypothesis Peer pressure is an important social phenomenon that intrinsically links human behavior to a cause. Construction of social identities become critical paradigms that are influenced by group representation, ideologies, inter-cultural compulsions etc. and motivate people to adopt specific behavior or activities that would represent their group characteristics. Indeed, Evans & Rilling, (2000) believe that in order to feel secure and connected, individuals adapt themselves to particular situation, setting or people thus, changing their behavior to experience inclusion and consistency. Teenagers especially tend to follow peer group so that they can become part of that particular group and be accepted by the members. Children get attracted by peer groups because they are still trying to find their position in society and assert themselves as individuals. Thus, it is important that adolescents and teenagers must be carefully guided to understand the difference between what is good for them