9.5 The tasks of data transfer and signaling are separated in modern telephone networks: data transfer is done by one network, signaling by another. Note
9.6 Figure 9.4 Data transfer and signaling networks
9.7 9-2 DIAL-UP MODEMS Traditional analog 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.
9.13 Figure 9.8 The V.32 and V.32bis constellation and bandwidth
9.14 V.32 & V.32 BIS V.32 32 Levels (5 bits per signal) – 1 redundant bit and 4 data bits per baud. (2400Hz * 4 bits/buad) V.32 BIS 128 Levels (7 bits per signal) – 1 redundant bit and 6 data bits per baud (2400Hz * 6 bits/baud)
9.15 V.90 Requires a digital link which came from an ISP The ISP sends a quality signal to the modem, this signal has no quantization error. This allows for 56 Kbps, downstream The signal upstream must be quantized limiting the bandwidth to 33.6 kbps Aka asymmetric V.90
9.16 Downstream Nyquist rate for V.90 Bit-rate = 2 * Bandwidth-Hz * 7bits/signal The phone line provided 4000Hz of bandwidth from the local link to the ISP 1 bit of the 8bit word is for error detection, leaving 7 bits of data per word. 56Kbps total downstream rate
9.17 Upstream V.90 Due to noise introduced by the quantization of the analog signal to the ISP, (refer to Fourier Analysis and Shannon's Sampling Theory)
9.18 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) supports high-speed digital communication over the existing local loops.
9.19 ADSL is an asymmetric communication technology designed for residential users; it is not suitable for businesses. Note
9.20 The existing local loops can handle bandwidths up to 1.1 MHz. Note
9.21 A filter is used to limit your phone bandwidth to 4000Hz, otherwise the copper wire can go to 1.1MHz.
9.22 ADSL is an adaptive technology. The system uses a data rate based on the condition of the local loop line. Note
9.23 Line Condition Factors Length of line, Attenuation Noise Distortion An adaptive technology that adjusts to bandwidth to the quality of the local loop.
9.33 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. Traditional Cable Networks Hybrid Fiber-Coaxial (HFC) Network Topics discussed in this section:
9.37 Regional cable head office can serve up to 400,000 subscribers Each distribution hub can service upto 4000 subscribers. Each coaxial cable can service 1000 subscribers.
9.38 Communication in an HFC cable TV network can be bidirectional. Note
9.39 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. Bandwidth Sharing CM and CMTS Data Transmission Schemes: DOCSIS Topics discussed in this section:
9.40 Figure 9.16 Division of coaxial cable band by CATV
9.41 Each tv broadcast uses 6MHz, and cable provides 80 stations
9.42 Downstream data are modulated using the 64-QAM modulation technique. Note
9.43 The theoretical downstream data rate is 30 Mbps. Note
9.44 Upstream data are modulated using the QPSK modulation technique. Note
9.45 The theoretical upstream data rate is 12 Mbps. Note
9.46 Bandwidth Sharing The bandwidth is shared by 1000s of subscribers using FDM