1. Using Telephone and Cable Networks
Chapter 9
Using Telephone and Cable Networks
for Data Transmission
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Topics discussed in this section:
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

3. Figure 9.1 A telephone system
toll offices
first 3 digits
intermmediate
switching offices
next 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).
Note
Intra-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).

6. Figure 9.2 Switching offices in a LATA

7. Figure 9.3 Point of presences (POPs)

8. Note
The tasks of data transfer and signaling are separated in modern telephone networks: data transfer is done by one network, signaling by another.

9. Figure 9.4 Data transfer and signaling networks

10. Figure 9.5 Layers in SS7

11. Topics discussed in this section:
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

12. Figure 9.6 Telephone line bandwidth

13. stands for modulator/demodulator.
Note
Modem
stands for modulator/demodulator.

14. Figure 9.7 Modulation/demodulation

15. Figure 9.8 The V.32 and V.32bis constellation and bandwidth
Modulation: 32-QAM, 5 bits / baud
4 bits for data, 1 extra bit for error detection
Baud rate: 2400, Data rate: 9600 bps
Modulation: 128-QAM, 7 bits / baud
6 bits for data, 1 extra bit for error detection
Baud rate: 2400, Data rate: bps
V.32bis
V.34bis:
28.8 Kbps with a 960-point constellation
33.6 Kbps with a 1664-point constellation

16. Figure 9.9 Uploading and downloading in 56K modems (V.90)
Quantization error at user side
33.6 Kbps
No quantization error at ISP (no sampling), higher SNR
56 Kbps
8000 * (8-1) = bps, 8-bit samples, 1 bit for control

17. Topics discussed in this section:
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
(often referred to as xDSL)

18. Note
ADSL 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.
Note
The existing local loops can handle bandwidths up to 1.1 MHz.

20. ADSL is an adaptive technology. The system uses a data rate
Note
ADSL is an adaptive technology. The system uses a data rate
based on the condition of the local loop line.

21. Figure 9.10 Discrete multitone technique
1 baud / Hz  15 bits / Hz
24 * 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

22. Figure 9.11 Bandwidth division in ADSL

23. Figure ADSL modem
Used at the subscriber’s premises

24. Figure DSLAM
Used at the telephone company site

25. Table 9.2 Summary of DSL technologies

26. Topics discussed in this section:
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

27. Figure 9.14 Traditional cable TV network
Cable TV office
unidirectional
Up to 35 amplifiers between the head end and the subscriber premises

28. Communication in the traditional cable TV network is unidirectional.
Note
Communication 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 less
Makes the cable network bi-directional
Each cable serves up to 1,000 subscribers
Each cable serves up to 1,000 subscribers
Modulation distribution done here
RCH: Regional cable head, serves up to 400,000 subscribers

30. Communication in an HFC cable TV network can be bidirectional.
Note
Communication in an HFC cable TV network can be bidirectional.

31. Topics discussed in this section:
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

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 each
Divide into 6 MHz channels QPSK used for modulation 2bits / baud, 1baud / Hz  12 Mbps upstream
64-QAM, 6 bits/baud,1 baud / Hz  30 Mbps (5 bits/Hz * 6 MHz)  27 Mbps specified by standard
6 channels shared by subscribers using timesharing

33. Downstream data are modulated using the 64-QAM modulation technique.
Note
Downstream data are modulated using the 64-QAM modulation technique.

34. The theoretical downstream data rate is 30 Mbps.
Note
The theoretical downstream data rate is 30 Mbps.

35. Upstream data are modulated using the QPSK modulation technique.
Note
Upstream data are modulated using the QPSK modulation technique.

36. The theoretical upstream data rate is 12 Mbps.
Note
The theoretical upstream data rate is 12 Mbps.

37. Figure 9.17 Cable modem (CM)

38. Figure 9.18 Cable modem transmission system (CMTS)