McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Physical Layer Summary Data-to-Signal Digital-to-Analog (Modem) Analog-to-Analog (Modem) Digital-to-Digital (line Coding) Analog-Digital (Codec) 1

5.2 DIGITAL-TO-ANALOG CONVERSION DIGITAL-TO-ANALOG CONVERSION Digital-to-analog conversion is the process of changing one of the characteristics of an analog signal based on the information in digital data. Amplitude Shift Keying Frequency Shift Keying Phase Shift Keying Quadrature Amplitude Modulation

5.3 Figure 5.1 Digital-to-analog conversion

5.4 Figure 5.2 Types of digital-to-analog conversion

5.5 Bit rate is the number of bits per second. Baud rate is the number of signal elements per second. In the analog transmission of digital data, the baud rate is less than or equal to the bit rate. Note

5.6 Figure 5.3 Binary amplitude shift keying

5.7 Figure 5.4 Implementation of binary ASK

5.8 Figure 5.6 Binary frequency shift keying

5.9 Figure 5.9 Binary phase shift keying

5.10 Figure 5.11 QPSK and its implementation

5.11 Quadrature amplitude modulation is a combination of ASK and PSK. Note

5.12 ANALOG to ANALOG Conversion ANALOG to ANALOG Conversion Analog-to-analog conversion is the representation of analog information by an analog signal. One may ask why we need to modulate an analog signal; it is already analog. Modulation is needed if the medium is bandpass in nature or if only a bandpass channel is available to us. Amplitude Modulation Frequency Modulation Phase Modulation Topics discussed in this section:

5.13 Figure 5.15 Types of analog-to-analog modulation

5.14 Figure 5.16 Amplitude modulation

5.15 Figure 5.18 Frequency modulation

5.16 Figure 5.20 Phase modulation

9.17 Figure 9.7 Modulation/demodulation

4.18 Digital Transmission -Digital to Digital -Analog to Digital: Codec Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

4.19 DIGITAL-TO-DIGITAL CONVERSION DIGITAL-TO-DIGITAL CONVERSION In this section, we see how we can represent digital data by using digital signals.

4.20 Figure 4.1 Line coding and decoding

4.21 Figure 4.2 Signal element versus data element

4.22 Figure 4.3 Effect of lack of synchronization

4.23 Figure 4.4 Line coding schemes

4.24 Figure 4.5 Unipolar NRZ scheme

4.25 Figure 4.6 Polar NRZ-L and NRZ-I schemes

4.26 Manchester and differential Manchester schemes

4.27 ANALOG-TO-DIGITAL CONVERSION ANALOG-TO-DIGITAL CONVERSION pulse code modulation and …… pulse code modulation and ……

4.28 Figure 4.21 Components of PCM encoder

4.29 According to the Nyquist theorem, the sampling rate must be at least 2 times the highest frequency contained in the signal. Note

4.30 Figure 4.24 Recovery of a sampled sine wave for different sampling rates

4.31 Figure 4.27 Components of a PCM decoder

4.32 TRANSMISSION MODES TRANSMISSION MODES Parallel Transmission Serial Transmission Topics discussed in this section: Topics discussed in this section:

4.33 Figure 4.31 Data transmission and modes

4.34 Figure 4.32 Parallel transmission

4.35 Figure 4.33 Serial transmission

4.36 In asynchronous transmission, we send 1 start bit (0) at the beginning and 1 or more stop bits (1s) at the end of each byte. There may be a gap between each byte. Note

4.37 Asynchronous here means “asynchronous at the byte level,” but the bits are still synchronized; their durations are the same. Note

4.38 Figure 4.34 Asynchronous transmission

4.39 In synchronous transmission, we send bits one after another without start or stop bits or gaps. It is the responsibility of the receiver to group the bits. Note

4.40 Figure 4.35 Synchronous transmission

McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Subscriber Access - Modem - xDSL - Cable Network 41

9.42 Figure 9.1 A telephone system

9.43 Figure 9.2 Switching offices in a LATA

9.44 Figure 9.4 Data transfer and signaling networks

9.45 DIAL-UP MODEMS DIAL-UP MODEMS Traditional telephone lines can carry frequencies between 300 and 3300 Hz, giving them a bandwidth of 3000 Hz. All this range is used for transmitting voice, where a great deal of interference and distortion can be accepted without loss of intelligibility. Modem Standards Topics discussed in this section:

9.46 Modem stands for modulator/demodulator. Note

9.47 DIGITAL SUBSCRIBER LINE DIGITAL SUBSCRIBER LINE After traditional modems reached their peak data rate, telephone companies developed another technology, DSL, to provide higher-speed access to the Internet. Digital subscriber line (DSL) technology is one of the most promising for supporting high-speed digital communication over the existing local loops. ADSL ADSL Lite HDSL SDSL VDSL Topics discussed in this section:

9.48 Figure 9.11 Bandwidth division in ADSL

9.49 Figure 9.12 ADSL modem

9.50 Figure 9.13 DSLAM

9.51 Table 9.2 Summary of DSL technologies

9.52 Figure 9.15 Hybrid fiber-coaxial (HFC) network

9.53 Figure 9.16 Division of coaxial cable band by CATV

9.54 Figure 9.17 Cable modem (CM)