2 Topics discussed in this section: 9-1 TELEPHONE NETWORKTelephone 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.Topics discussed in this section:Major ComponentsLATAs (Local-Access Transport Areas) SignalingServices Provided by Telephone Networks
3 Figure 9.1 A telephone system toll officesfirst 3 digitsintermmediateswitching officesnext 4 digits
4 LATA: Local-Access Transport Area IXC: Inter-eXchange Carriers (AT&T, MCI, Sprint, Verizon)POP: Point Of Presence (a switch office)
5 Intra-LATA services are provided by local exchange carriers (LECs). NoteIntra-LATA services are provided by local exchange carriers (LECs).Since 1996, there are two types of LECs: incumbent local exchange carriers(ILEC) and competitive local exchange carriers (CLEC).
11 Topics discussed in this section: 9-2 DIAL-UP MODEMSTraditional 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.Topics discussed in this section:Modem Standards
15 Figure 9.8 The V.32 and V.32bis constellation and bandwidth Modulation: 32-QAM, 5 bits / baud4 bits for data, 1 extra bit for error detectionBaud rate: 2400, Data rate: 9600 bpsModulation: 128-QAM, 7 bits / baud6 bits for data, 1 extra bit for error detectionBaud rate: 2400, Data rate: bpsV.32bisV.34bis:28.8 Kbps with a 960-point constellation33.6 Kbps with a 1664-point constellation
16 Figure 9.9 Uploading and downloading in 56K modems (V.90) Quantization error at user side33.6 KbpsNo quantization error at ISP (no sampling), higher SNR56 Kbps8000 * (8-1) = bps, 8-bit samples, 1 bit for control
17 Topics discussed in this section: 9-3 DIGITAL SUBSCRIBER LINEAfter 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.Topics discussed in this section:ADSLADSL LiteHDSLSDSL VDSL(often referred to as xDSL)
18 NoteADSL is an asymmetric communication technology designed for residential users; it is not suitable for businesses.
19 The existing local loops can handle bandwidths up to 1.1 MHz. NoteThe existing local loops can handle bandwidths up to 1.1 MHz.
20 ADSL is an adaptive technology. The system uses a data rate NoteADSL is an adaptive technology. The system uses a data ratebased on the condition of the local loop line.
21 Figure 9.10 Discrete multitone technique 1 baud / Hz 15 bits / Hz24 * 15 * 4K = 1.44 Mbps (500K max. provided normally)224 * 15 * 4K = 13.4 Mbps (8 Mbps max. provided normally)C1-C5 not used, providing a gap between voice and data
26 Topics discussed in this section: 9-4 CABLE TV NETWORKSThe cable TV network started as a video service provider, but it has moved to the business of Internet access. In this section, we discuss cable TV networks per se; in Section 9.5 we discuss how this network can be used to provide high-speed access to the Internet.Topics discussed in this section:Traditional Cable NetworksHybrid Fiber-Coaxial (HFC) Network
27 Figure 9.14 Traditional cable TV network Cable TV officeunidirectionalUp to 35 amplifiers between the head end and the subscriber premises
28 Communication in the traditional cable TV network is unidirectional. NoteCommunication in the traditional cable TV network is unidirectional.
29 Figure 9.15 Hybrid fiber-coaxial (HFC) network Reduces the need for amplifiers to 8 or lessMakes the cable network bi-directionalEach cable serves up to 1,000 subscribersEach cable serves up to 1,000 subscribersModulation distribution done hereRCH: Regional cable head, serves up to 400,000 subscribers
30 Communication in an HFC cable TV network can be bidirectional. NoteCommunication in an HFC cable TV network can be bidirectional.
31 Topics discussed in this section: 9-5 CABLE TV FOR DATA TRANSFERCable companies are now competing with telephone companies for the residential customer who wants high-speed data transfer. In this section, we briefly discuss this technology.Topics discussed in this section:BandwidthSharing CM and CMTSData Transmission Schemes: DOCSIS
32 Figure 9.16 Division of coaxial cable band by CATV Frequency range: 5 to 750 MHz (approximate)Divide into 3 bands: video, downstream data, and upstream data> 80 channels 6 MHz eachDivide into 6 MHz channels QPSK used for modulation 2bits / baud, 1baud / Hz 12 Mbps upstream64-QAM, 6 bits/baud,1 baud / Hz 30 Mbps (5 bits/Hz * 6 MHz) 27 Mbps specified by standard6 channels shared by subscribers using timesharing
33 Downstream data are modulated using the 64-QAM modulation technique. NoteDownstream data are modulated using the 64-QAM modulation technique.
34 The theoretical downstream data rate is 30 Mbps. NoteThe theoretical downstream data rate is 30 Mbps.
35 Upstream data are modulated using the QPSK modulation technique. NoteUpstream data are modulated using the QPSK modulation technique.
36 The theoretical upstream data rate is 12 Mbps. NoteThe theoretical upstream data rate is 12 Mbps.
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