Ebook Communication systems principles using MATLAB R: Part 2

Part 2 book "Communication systems principles using MATLAB R" includes content: Internet protocols and packet delivery algorithms; quantization and coding; data transmission and integrity.
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Ebook Communication systems principles using MATLAB R: Part 2 269 4 Internet Protocols and Packet Delivery Algorithms 4.1 Chapter Objectives This chapter examines the defined standards and methods for Internet data communications, the protocols. This encompasses the data formats employed as well as the algorithms that operate on that data in order to facilitate data com- munication between physically separate devices. On completion of this chapter, the reader should: 1) Be able to define IP, TCP, and UDP, the role of protocol layers, and what functions they perform. 2) Be conversant with the key elements of each protocol, such as IP addresses and TCP sockets. 3) Be able to explain potential pitfalls in networking, such as congestion col- lapse, and know the approaches used to mitigate these problems. 4) Be able to explain the principles of routing and calculate the shortest path in a routing graph. There is a vast range of detail concerning the Internet protocols that cannot be discussed in detail in one chapter – the intent here is to explain the salient points and examine some important aspects in depth. In addition to Internet standard RFC documents, a very approachable reference is Kozierok (2005). Detailed explanations of the inner workings of TCP/IP are given in Stevens (1994), while implementation details are covered in Wright and Stevens (1995a). 4.2 Introduction Suppose we wish to connect a number of devices together for the purposes of exchanging data. What is the best way to do this? What do we mean by “best” in this context? We might want a system that uses the available infrastructure in the most efficient manner or can transmit with the highest possible data rate Communication Systems Principles Using MATLAB®, First Edition. John W. Leis. © 2018 John Wiley & Sons, Inc. Published 2018 by John Wiley & Sons, Inc. Companion website: www.wiley.com/go/Leis/communications-principles-using-matlab 270 4 Internet Protocols and Packet Delivery Algorithms and the lowest possible delay. It may have to be expandable to different physi- cal interconnection methods, from wired to optical, wireless, and satellite, each with different characteristics. For example, a wired connection may be fast and have low delay, whereas a satellite link may be fast but experience high delays. On the other hand, a wireless link may experience interference leading to fre- quently lost data. If we want to have many devices interconnected, how do they “discover” each other? Finally, we may want to have a system that is scalable to a large number of interconnected devices. In short, we seek the best way to set up a network for seamless connectivity of many devices. The Internet has become a ubiquitous data communications network. This chapter considers the role of packet switching, network device discovery, data packet routing, and other aspects of what is generally known as Transmission Control Protocol/Internet Protocol (TCP/IP). In the following, reference is made to the Internet Request For Comment (RFC) documents, which define the standards for various functions, data formats, and operational requirements; in short, the protocols for data com- munication. A standardization process is important, so that equipment from different vendors will interoperate without difficulties. Even issues such as byte ordering must be carefully defined. A convenient search facility for RFCs is https://tools.ietf.org/html/ Newer RFCs often update earlier ones, and likewise earlier RFCs are often updated or clarified by later RFCs. In this chapter, we endeavor to provide ref- erence to the original RFC where appropriate. Later RFCs updating a standard are denoted by the wording “updated by.” Another important role of RFCs is to remove ambiguity that may have arisen in the interpretation of a particu- lar protocol. In addition to defining current standards, RFCs may propose new standards or clarify certain operational characteristics – or even just act as a “request for comments” on proposals and new ideas. 4.3 Useful Preliminaries This section introduces some concepts that may be helpful in understanding the remainder of the chapter. These are: the notion of packet switching, binary or digital operations, and some data structure basics with code examples. 4.3.1 Packet Switching One categorization of networks is into either circuit-switched or packet- switched designs. The Internet is a packet-switched network, so it is helpful to define just the what term means initially and why it is a useful concept. In a circuit-switched system, a direct connection is established between devices at the start of data transfer and is maintained until the data transfer 4.3 Useful Preliminaries 271 has completed – usually to the exclusion of all other data on that particular channel. On the other hand, a packet-switched system splits the data up into smaller chunks or packets of information. Each packet is sent separately, from source to destination, and (perhaps surprisingly) different packets may follow different physical paths. Packet switching is arguably more complex and has more overhead, since each data packet comprising a data transfer acts as a separate entity. However, it makes more efficient use of the available bandwidth for typical transmissions. Consider accessing a particular web page: In the time between one page being loaded and the user selecting a different page, is it really necessary to maintain a physical connection, to the exclusion of all other data traffic? Similarly, in ...