Chapter2.Telecommunication Basics

Chapter 2. Telecommunication Basics

The discussion in this chapter covers modulations, line-coding schemes, and techniques for wired, hybrid, wireless, and emerging media. Emerging wireless local-area network (LAN) coding techniques require special attention, and they are covered in detail. The importance of this chapter is to provide you with the fundamental information required for troubleshooting different technical solutions.

Information needs to be transformed into signals to be exchanged over the telecommunication media. When troubleshooting in an enterprise environment, it is important to have a relatively broad understanding of how the information is transformed from one form to another and how the information is carried over the provider's network. This chapter focuses on representing the following:

• Legacy modulations, line-coding schemes, and techniques for the wired media with special attention to the evolving xDSL techniques.

• Extended discussion about some of the emerging wireless modulations and coding schemes because of the expected growth of end-to-end wireless solutions and hybrid solutions.

• Detailed information about clocking, line coding, and framing in the carrier's system, and discussion about T1/Primary Rate Interfaces (PRIs).

In telecommunications, the transfer of information from one point to another is based on signals that can be classified as continuous and discrete, or analog and digital. Analog signals are continuous and carry distinguishable states, called constellations, that can be interpreted as different from each other, such as positive and negative components of the sinusoid, or analog waves with a different amplitude, frequency, or phase. The Public Switched Telephone Network (PSTN), which was developed in the early 1960s, is primarily an analog network. Analog signals are characterized by amplitude, phase, and frequency. The analog transmission can degenerate from changes in the electrical characteristics of the wire that are caused by thunderstorms, snow, rain, and electrical charges.

Discrete, or digital, signals carry the information in defined discrete moments or discrete states. In digital systems, the terminology is based on the base 2 numerical system (1 and 0), where the digital signal has at least two distinguishable states, which are interpreted as 1 or 0. Although the analog transmission's quality can degrade because of interference with other sources, the digital transmission is generally more reliable because error-correcting codes can be applied. Every correction code adds extra bits to the user transmission, and the general rule is that the bigger the correction code, the greater its ability to find and recover from the error. The trade-off is that less user data can be transmitted. The optimum balance must be determined.