Upon completing this chapter, you should be able to: • Define the following terms; transmission lines, circuits, trunks, virtucal circuits, bandwidth, analog transmission, digital transmission, internet governance. • Differentiate between; line and trunks, PVC and SVC, Narrowband, wideband and broadband, analog and digital transmission, codecs and modems and various standards organization bodies. Describe the various circuit types. Describe the allocation of spectrum for use in communication Name and define the functions of various standard organizations locally and internationally
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This chapter from (Goleniewski and Jarrett, 2006) discusses the types of transmission lines and network connections, the electromagnetic spectrum, and what bandwidth is all about in the emerging broadband era. It looks at the differences between analog and digital signals. Finally, this chapter describes the various standards bodies and their roles in shaping aspects of
2.1 Transmission Lines
Two prerequisites must be satisfied to have successful communication. The first prerequisite is understandability. The transmitter and receiver must speak the same language. It doesn't matter how big or how clean the pipe between the two endpoints. If they're not speaking the same language, they will not be able to understand the message. In the case of data communications, we've resolved these issues quite elegantly: We have software and hardware translation devices that can convert between the different languages that individual computing systems speak. In the realm of human communications, we're about to embark on that exciting journey as well. Through the use of advanced voice-processing systems, in the next five to seven years we should have the ability to do real-time foreign language translation as part of the network service. And of course, some search engines, such as Google, already provide Web page translation and do a pretty good job at it. The second prerequisite is the capability to detect errors as they occur and to have some procedure for resolving those errors. In the case of human communications, intelligent terminals at either end human beings can detect noise that may have affected a transmission and request a retransmission, thereby correcting for that error. In the case of data devices, similar logic must be built in to end devices so that they can detect errors and request a retransmission in order to correct for the errors. If these two prerequisites understandability and error control are met, then communication can occur. We communicate by using data devices over what is generically termed a transmission line. There are five main types of transmission lines circuits, channels, lines, trunks, and virtual circuits each of which has a specific meaning. (Keep in mind that these transmission lines can be composed of either wired or wireless media, and in fact, these days, we're seeing more and more use of wireless facilities to accomplish networking, from simple mobile phones to the Interplanetary Internet.) The following sections describe each of these types of transmission lines in detail. 21
EE331 Telecommunication Principles I
2.1.1 Circuits A circuit is the physical path that runs between two or more points. It terminates on a port (i.e., a point of electrical or optical interface), and that port can be in a host computer, on a multiplexer, on a switch, or in another device, as discussed later in this chapter. In and of itself, a circuit does not define the number of simultaneous conversations that can be carried; that is a function of the type of circuit it is. For example, a simple, traditional telephone circuit is designed to carry just one conversation over one physical pathway. (But note that I specifically reference "traditional telephone circuit"; digital broadband facilities, such as DSL, permit multiple channels, such as separate...