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
first 3 digits
next 4 digits
9.3
toll offices
intermmediate
switching offices
LATA: Local-Access Transport Area
IXC: Inter-eXchange Carriers (AT&T, MCI, Sprint, Verizon)
POP: Point Of Presence (a switch office)
9.4
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).
9.5
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.
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
Note
Modem
stands for modulator/demodulator.
9.13
Figure 9.7 Modulation/demodulation
9.14
Figure 9.8 The V.32 and V.32bis constellation and bandwidth
V.32
V.32bis
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: 14400 bps
V.34bis:
28.8 Kbps with a 960-point constellation
33.6 Kbps with a 1664-point constellation
9.15
Figure 9.9 Uploading and downloading in 56K modems (V.90)
Quantization
error at user
side
33.6 Kbps
56 Kbps
No quantization error at ISP
(no sampling), higher SNR
8000 * (8-1) = 56000 bps, 8-bit samples, 1 bit for control
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
(often referred to as xDSL)
Note
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.
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 Discrete multitone technique
1 baud / Hz  15 bits / Hz
24 * 15 * 4K = 1.44 Mbps (500K
max. provided normally)
C1-C5 not used, providing a gap
between voice and data
9.21
224 * 15 * 4K = 13.4 Mbps (8 Mbps
max. provided normally)
Figure 9.11 Bandwidth division in ADSL
9.22
Figure 9.12 ADSL modem
Used at the subscriber’s premises
9.23
Figure 9.13 DSLAM
Used at the telephone company site
9.24
Table 9.2 Summary of DSL technologies
9.25
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
9.26
Figure 9.14 Traditional cable TV network
Cable TV office
unidirectional
Up to 35 amplifiers between the head
end and the subscriber premises
9.27
Note
Communication in the traditional cable
TV network is unidirectional.
9.28
Figure 9.15 Hybrid fiber-coaxial (HFC) network
1. Reduces the need for amplifiers to 8 or less
2. Makes the cable network bi-directional
Each cable serves up
to 1,000 subscribers
Modulation
distribution
done here
RCH: Regional cable head, serves
up to 400,000 subscribers
9.29
Note
Communication in an HFC cable TV
network can be bidirectional.
9.30
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
9.31
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
Divide into 6 MHz channels
QPSK used for modulation
2bits / baud, 1baud / Hz
 12 Mbps upstream
> 80 channels
6 MHz each
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
9.32
Note
Downstream data are modulated using
the 64-QAM modulation technique.
9.33
Note
The theoretical downstream data rate
is 30 Mbps.
9.34
Note
Upstream data are modulated using the
QPSK modulation technique.
9.35
Note
The theoretical upstream data rate
is 12 Mbps.
9.36
Figure 9.17 Cable modem (CM)
9.37
Figure 9.18 Cable modem transmission system (CMTS)
9.38