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Chapter 9 Using Telephone and Cable Networks for Data Transmission 9.1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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. Topics discussed in this section: Major Components LATAs: Local Access Transport Areas Signaling Services Provided by Telephone Networks 9.2 Figure 9.1 A telephone system 9.3 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. 9.4 9.5 Service between LATAs are handled by Ineterexchange carriers (IXC) services are provided by long distance company. POP; Point of presence: Each IXC that wants to provide inter-LATA services in a LATA must have a POP in that LATA The local exchange carrier that provides services in that LATA must provide all its customers connections to access all POPs Figure 9.2 Switching offices in a LATA 9.6 Figure 9.3 Point of presences (POPs) 9.7 Note The tasks of data transfer and signaling are separated in modern telephone networks: data transfer is done by one network, signaling by another. SS7: Signaling System Seven is the protocol used in the signaling network 9.8 Figure 9.4 Data transfer and signaling networks 9.9 Figure 9.5 Layers in SS7 9.10 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. Topics discussed in this section: Modem Standards 9.11 Figure 9.6 Telephone line bandwidth 9.12 Modem stands for modulator/demodulator. V.32, V.32bis, V90, V.92: ITU-T standards V.32: 14,400 bps (7 bits with 1 bit for error at a rate of 2400 baud V.90: also called 56K modems( 8bits with 1 bit for error at a rate of 8000): Upload has a max of 33.3kbps Download has a max of 56kbps V.92: Upload at 48Kbps with features such a call-waiting. 9.13 Figure 9.7 Modulation/demodulation 9.14 Figure 9.8 The V.32 and V.32bis constellation and bandwidth 9.15 Figure 9.9 Uploading and downloading in 56K modems 9.16 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 digital communication over the existing local loops. Topics discussed in this section: ADSL ADSL Lite HDSL SDSL VDSL 9.17 ADSL is an asymmetric communication technology designed for residential users; it is not suitable for businesses. 9.18 Note The existing local loops can handle bandwidths up to 1.1 MHz with a filter( 4Khz bandwidth) for voice devices 9.19 Note ADSL is an adaptive technology. The system uses a data rate based on the condition of the local loop line. 9.20 Figure 9.10 ADSL Modulation:Discrete multitone technique 9.21 Upstream: Uses 25 channels (6 to 30), 1 signal, 24 data. Downstream: 225 channels (31-255), 1 for control 9.22 24 x 4000 x 15 = 1.44Mbps. Practically some channels are not used: only 500Kbps, 224 x 4000x 15 = 13.4Mbps Practically: 8Mbps Figure 9.11 Bandwidth division in ADSL 9.23 Figure 9.12 ADSL modem 9.24 Figure 9.13 DSLAM 9.25 Table 9.2 Summary of DSL technologies 9.26 9-4 CABLE TV NETWORKS The 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 Networks Hybrid Fiber-Coaxial (HFC) Network 9.27 Figure 9.14 Traditional cable TV network 9.28 Note Communication in the traditional cable TV network is unidirectional. 9.29 Figure 9.15 Hybrid fiber-coaxial (HFC) network 9.30 Note Communication in an HFC cable TV network can be bidirectional. 9.31 9-5 CABLE TV FOR DATA TRANSFER Cable 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: Bandwidth Sharing CM and CMTS Data Transmission Schemes: DOCSIS 9.32 Competing to provide high speed data transfer. 9.33 Downstream: 30Mbps (5 bits/HZ x6MHz) Upstream: 12Mbps (2bits/Hz x 6Mhz) Shared Media: Timesharing : One channel per group of subscriber ( for downstream, use of multicasting) Figure 9.16 Division of coaxial cable band by CATV 9.34 Note Downstream data are modulated using the 64-QAM modulation technique. 9.35 Note The theoretical downstream data rate is 30 Mbps. 9.36 Note Upstream data are modulated using the QPSK modulation technique. 9.37 Note The theoretical upstream data rate is 12 Mbps. 9.38 Figure 9.17 Cable modem (CM) 9.39 Figure 9.18 Cable modem transmission system (CMTS) 9.40