progress bar code in vb.net The Science of Communications in Software

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The Science of Communications
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Data communication is the procedure required to collect, package, and transmit data from one computing device to another, typically (but not always) over a wide area network (WAN). It is a complex process with many layers of functionality. To understand data communications, we
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Protocols
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Protocols
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must break it into its component parts and examine each part individually, relying on the old adage that the only way to eat an elephant is one bite at a time. Like a Russian Matryoshka doll, such as the one shown in Figure 2-1, data communications comprises layer upon layer of operational functionality that work together to accomplish the task at hand, namely, the communication of data. These component parts are known as protocols, and they have one responsibility: to ensure the integrity of the data that they transport from the source device to the receiver. This data integrity is measured in the following ways (see Figure 2-2):
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Bit level integrity Ensures that the bits themselves are not changed in value as they transit the network Data integrity Guarantees that the bits are recognizable as packaged entities called frames or cells Network integrity Provides for the assured delivery of those entities, now in the form of packets, from a source to a destination Message integrity Not only guarantees the delivery of the packets, but in fact their sequenced delivery to ensure the proper arrival of the entire message Application integrity Provides for the proper execution of the responsibilities of each application
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Protocols exist in a variety of forms and are not limited to data communications applications. Military protocols define the rules of engagement that modern armies agree to abide by, diplomatic protocols define
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Figure 2-1 Russian Matryoshka dolls.
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Protocols
Figure 2-2 The various integrity levels of the OSI Model.
Application Integrity
2
Message Integrity
Network Integrity
Data Integrity
Bit level Integrity
the manner in which nations interact and settle their political and geographic differences, and medical protocols document the manner in which medications are used to treat illness. The word protocol is defined as a set of rules that facilitates communication. Data communications, then, is the science built around the protocols that govern the exchange of digital data between computing systems.
Data Communications Networks
Data communications networks are often described in terms of their architectures, as are protocols. Protocol architectures are often said to be layered because they are carefully divided into highly related but nonoverlapping functional entities. This division of labor not only makes it easier to understand how data communications work, but also makes the deployment of complex networks far easier. The amount of code (lines of programming instructions) required to successfully execute the complex task of data transmission is quite large.
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Protocols
Protocols
If the program that carries out all of the functions in that process were written as a single, large, monolithic chunk of code, then it would be difficult to make a change to the program when updates are required, because of the monolithic nature of the program. Now imagine the following: instead of a single set of code, we break the program into functional pieces, each of which handles a particular, specific function required to carry out the transmission task properly. With this model, changes to a particular module of the overall program can be accomplished in a way that only affects that particular module, making the process far more efficient. This modularity is one of the great advantages of layered protocols. Consider the following simple scenario, shown in Figure 2-3. A PC-based e-mail user in Madrid with an account at ISP Terra Networks wants to send a large, confidential message to another user in Marseilles. The Marseilles user is attached to a mainframe-based corporate e-mail system. In order for the two systems to communicate, a complex set of challenges must first be overcome. Let s examine them a bit more closely. The first and most obvious challenge that must be overcome is the difference between the actual user interfaces on the two systems. The PC-based system s screen presents information to the user in a Graphical User Interface (GUI, pronounced gooey ) format that is carefully designed to make it intuitively easy to use. It eliminates the need to rely on the old command-line syntax that was used in DOS environments. The mainframe system was created with intuitive ease of use in mind, but because a different company designed the interface for a mainframe host, under a different design team, it bears minimal resemblance to the PC system s interface. Both are equally capable, but completely different. As a result of these differences, if we were to transmit a screen of information from the PC directly to the mainframe system, it would be unreadable simply because the two interfaces do not share common field names or locations. The next problem that must be addressed is security, illustrated in Figure 2-4. We mentioned earlier that the message that is to be sent from
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