tailieunhanh - Lecture Data communications and networks: Chapter 9 - Forouzan 

Converting digital data to a bandpass analog traditionally called digitalto-analog conversion. Converting a low-pass analog signal to a bandpass analog signal is traditionally called analog-to-analog conversion. In this chapter, we discuss these two types of conversions. | Chapter 9 Using Telephone and Cable Networks for Data Transmission Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9. 9-1 TELEPHONE NETWORK Telephone networks use circuit switching. The telephone network had its beginnings in the late 1800s. The entire network, which is referred to as the plain old telephone system (POTS), was originally an analog system using analog signals to transmit voice. Major Components LATAs Signaling Services Provided by Telephone Networks Topics discussed in this section: 9. Figure A telephone system 9. Intra-LATA services are provided by local exchange carriers. Since 1996, there are two types of LECs: incumbent local exchange carriers and competitive local exchange carriers. Note 9. Figure Switching offices in a LATA 9. Figure Point of presences (POPs) 9. The tasks of data transfer and signaling are separated in modern telephone networks: data transfer is done by one network, signaling by another. Note 9. Figure Data transfer and signaling networks 9. Figure Layers in SS7 9. 9-2 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. Figure Telephone line bandwidth 9. Modem stands for modulator/demodulator. Note 9. Figure Modulation/demodulation 9. Figure The and constellation and bandwidth 9. Figure Uploading and downloading in 56K modems 9. 9-3 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 | Chapter 9 Using Telephone and Cable Networks for Data Transmission Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9. 9-1 TELEPHONE NETWORK Telephone networks use circuit switching. The telephone network had its beginnings in the late 1800s. The entire network, which is referred to as the plain old telephone system (POTS), was originally an analog system using analog signals to transmit voice. Major Components LATAs Signaling Services Provided by Telephone Networks Topics discussed in this section: 9. Figure A telephone system 9. Intra-LATA services are provided by local exchange carriers. Since 1996, there are two types of LECs: incumbent local exchange carriers and competitive local exchange carriers. Note 9. Figure Switching offices in a LATA 9. Figure Point of presences (POPs) 9. The tasks of data transfer and signaling are separated in modern telephone networks: data transfer is done by one .