chapter 9 using telephone and cable networks for data transmission

1. 9.1
Chapter 9
Using Telephone
and Cable Networks
for Data Transmission
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. 9.2
9-1 TELEPHONE NETWORK
Telephone networks use circuit switching.
The telephone network had its beginnings in the late
1800s.

3. 9.3
9-1 TELEPHONE NETWORK
The 19th century telephone network is referred to as
the plain old telephone system (POTS),
was an analog system using analog signals to transmit
voice.

4. 9.4
Figure 9.2 Switching offices in a LATA

5. 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

6. 9.6
Figure 9.4 Data transfer and signaling networks

7. 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.

8. 9.8
Figure 9.6 Telephone line bandwidth

9. 9.9
 Data is noise sensitive
 Voice is not noise sensitve

10. 9.10
Modem
stands for modulator/demodulator.
Note

11. 9.11
Figure 9.6 Telephone line bandwidth

12. 9.12
Figure 9.7 Modulation/demodulation

13. 9.13
Figure 9.8 The V.32 and V.32bis constellation and bandwidth

14. 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)

15. 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

16. 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

17. 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)

18. 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.

19. 9.19
ADSL is an asymmetric communication
technology designed for residential
users; it is not suitable for businesses.
Note

20. 9.20
The existing local loops can handle
bandwidths up to 1.1 MHz.
Note

21. 9.21
A filter is used to limit your phone bandwidth
to 4000Hz, otherwise the copper wire can
go to 1.1MHz.

22. 9.22
ADSL is an adaptive technology.
The system uses a data rate
based on the condition of
the local loop line.
Note

23. 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.

24. 9.24
Figure 9.10 Discrete multitone technique

25. 9.25
256 channels
1 for voice
Up to 255 for data
Each channel is 4312 Hz.

26. 9.26
Figure 9.11 Bandwidth division in ADSL

27. 9.27
Channel Rate
Each data channel has a maximum capacity
of 4000 Hz * 15 bits/buad
Not all the frequency bandwidth is used to
allow for guardbands.

28. 9.28
Upstream - Downstream
25 upstream channels =
24 upstream data channels +
1 data control stream channel
225 downstream channels =
224 downstream data channels +
1 data control stream

29. 9.29
ADSL
Max upstream = 1.44 Mbps
Max downstream = 13.4 Mbps
Sorry, the adaptive capability limits you to
much less due to noise, attenuation, and
distortion.

30. 9.30
Figure 9.12 ADSL modem

31. 9.31
Figure 9.13 DSLAM

32. 9.32
Table 9.2 Summary of DSL technologies

33. 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:

34. 9.34
Figure 9.14 Traditional cable TV network

35. 9.35
Communication in the traditional cable
TV network is unidirectional.
Note

36. 9.36
Figure 9.15 Hybrid fiber-coaxial (HFC) network

37. 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.

38. 9.38
Communication in an HFC cable TV
network can be bidirectional.
Note

39. 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:

40. 9.40
Figure 9.16 Division of coaxial cable band by CATV

41. 9.41
Each tv broadcast uses 6MHz, and cable
provides 80 stations

42. 9.42
Downstream data are modulated using
the 64-QAM modulation technique.
Note

43. 9.43
The theoretical downstream data rate
is 30 Mbps.
Note

44. 9.44
Upstream data are modulated using the
QPSK modulation technique.
Note

45. 9.45
The theoretical upstream data rate
is 12 Mbps.
Note

46. 9.46
Bandwidth Sharing
The bandwidth is shared by 1000s of
subscribers using FDM

47. 9.47
Figure 9.17 Cable modem (CM)

48. 9.48
Cable modem (the user)
Cable modem transmission system (cable
provider)

49. 9.49
Figure 9.18 Cable modem transmission system (CMTS)