TAILIEUCHUNG - CCNA Wireless Official Exam Certification Guide part 5

CCNA Wireless Official Exam Certification Guide part 5 is a best of breed Cisco® exam study guide that focuses specifically on the objectives for the CCNA® Wireless IUWNE exam. Senior instructor Brandon Carroll shares preparation hints and test-taking tips, helping you identify areas of weakness and improve both your conceptual knowledge and hands-on skills. Material is presented in a concise manner, focusing on increasing your understanding and retention of exam topics. | 12 CCNA Wireless Official Exam Certification Guide 5 GHz The 5-GHz range is used by the standard and the new draft standard. In the standard data rates can range from 6 Mbps to 54 Mbps. devices were not seen in the market until 2001 so they do not have quite the market penetration as range b devices. The 5-GHz range is also subdivided into channels each being 20-MHz wide. A total of 23 nonoverlapping channels exist in the 5-GHz range. The 5-GHz ranges use Orthogonal Frequency Division Multiplexing OFDM . OFDM is discussed later in this chapter in the section OFDM. Data rates of 6 9 12 18 24 36 48 and 54 Mbps are defined. Modulation Techniques and How They Work In short the process of modulation is the varying in a signal or a tone called a carrier signal. Data is then added to this carrier signal in a process known as encoding. Imagine that you are singing a song. Words are written on a sheet of music. If you just read the words your tone is soft and does not travel far. To convey the words to a large group you use your vocal chords and modulation to send the words farther. While you are singing the song you encode the written words into a waveform and let your vocal cords modulate it. People hear you singing and decode the words to understand the meaning of the song. Modulation is what wireless networks use to send data. It enables the sending of encoded data using radio signals. Wireless networks use modulation as a carrier signal which means that the modulated tones carry data. A modulated waveform consists of three parts Amplitude The volume of the signal Phase The timing of the signal between peaks Frequency The pitch of the signal Wireless networks use a few different modulation techniques including these DSSS OFDM Multiple-Input Multiple-Output MIMO The sections that follow cover these modulation techniques in further detail. DSSS DSSS is the modulation technique that devices use to send the data. In DSSS

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