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
Signaling
Services Provided by Telephone Networks
9.2
Switched Network
9.3
Circuit Switching


uses a dedicated path between two stations
has three phases




inefficient

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

9.4
establish
transfer
disconnect
channel capacity dedicated for duration of connection
if no data, capacity wasted
set up (connection) takes time
once connected, transfer is transparent
Public Circuit Switched Network
9.5
Circuit Establishment
9.6
Circuit
Switch
Elements
9.7
Blocking or Non-blocking

blocking network
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non-blocking network


9.8
may be unable to connect stations because all
paths are in use
used on voice systems
permits all stations to connect at once
used for some data connections
Figure 9.1 A telephone system
9.9
Figure 9.2 Switching offices in a LATA
9.10
Note
Intra-LATA (local access transport area)
services are provided by local exchange
carriers (LECs).
Since 1996, there are two
types of LECs: incumbent local
exchange carriers and competitive
local exchange carriers.
IXC (Interexchange carrier, long distance company)
9.11
Figure 9.3 Point of presences (POPs)
Normally digitized data
9.12
Note
The tasks of data transfer and signaling
are separated in modern telephone
networks: data transfer is done by one
network, signaling by another.
9.13
Traditional Circuit Switching
9.14
Figure 9.4 Data transfer and signaling networks
Packet-switch
Packet-switch or circuit-switch
9.15
Figure 9.5 Layers in SS7 (signaling system seven)
9.16
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
9.17
Digital Data, Analog Signal:
Modulation Techniques
9.18
Figure 9.6 Traditional Telephone line bandwidth
Modern phone line has higher bandwidth
9.19
Note
Modem
stands for modulator/demodulator.
9.20
Figure 9.7 Modulation/demodulation
TELCO: telephone company
(unnecessary acronyms! I think)
9.21
Quadrature Amplitude Modulation



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QAM used on asymmetric digital subscriber line
(ADSL) and some wireless
combination of ASK and PSK
logical extension of QPSK
send two different signals simultaneously on
same carrier frequency




9.22
use two copies of carrier, one shifted 90°
each carrier is ASK modulated
two independent signals over same medium
demodulate and combine for original binary output
QPSK Illustration
This figure copied from wikipedia
9.23
Modem Standards
9.24
V-series
standard
Modulation
Data Rate
Baud Rate
V.32
32-QAM
9600 bps
2400 baud
Only 4 bits
represent
data
V.32 bis
128-QAM
14,400 bps
2400 baud
Only 6 bits
represent
data
V.34 bis
M-QAM
28,80033,600 bps
V.90
M-QAM
56 Kbps
(downstream)
33.6 Kbps
(upstream)
V.92
M-QAM
56 Kbps
(downstream)
48 Kbps
(upstream)
A modem
adjusts its
speed
Figure 9.9 Uploading and downloading in 56K modems
SNR explains why upload speed is higher
9.25
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
9.26
Note
ADSL is an asymmetric communication
technology designed for residential
users; it is not suitable for businesses.
9.27
Note
The existing local loops (twisted-pair
lines) can handle bandwidths up to
1.1 MHz.
9.28
Note
ADSL is an adaptive technology.
The system uses a data rate
based on the condition of
the local loop line.
9.29
Figure 9.10 Discrete multitone technique (QAM + FDM)
9.30
Figure 9.11 Bandwidth division in ADSL
9.31
Figure 9.12 Customer site: ADSL modem
Splitter and data line need installation
(maybe expensive)
9.32
Figure 9.13 telephone company site
9.33
Table 9.2 Summary of DSL technologies
ADSL Lite: does not need additional installation
from telephone company
9.34
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
9.35
Figure 9.14 Traditional cable TV network
9.36
Note
Communication in the traditional cable
TV network is unidirectional.
9.37
Figure 9.15 Hybrid fiber-coaxial (HFC) network
9.38
Note
Communication in an HFC cable TV
network can be bidirectional.
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.
Topics discussed in this section:
Bandwidth
Sharing
CM and CMTS
Data Transmission Schemes: DOCSIS
9.40
Figure 9.16 Division of coaxial cable band by CATV
9.41
Note
Downstream data are modulated using
the 64-QAM modulation technique.
9.42
Note
The theoretical downstream data rate
is 30 Mbps.
9.43
Note
Upstream data are modulated using the
QPSK modulation technique.
This figure copied from wikipedia
9.44
Note
The theoretical upstream data rate
is 12 Mbps.
9.45
Sharing: Upstream sharing
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9.46
The upstream bandwidth is 37 MHz.
There are six 6-MHz channels available.
How can the channels be shared in an
area with 1000,2000 or even 200,000
subscribers?
Using FDM/timesharing.
Subscribers have to contend for the
channels with others.
Sharing: Downstream sharing



9.47
The downstream band has 33 channels of
6 MHz.
We have a multicast situation.
If there is data for any of subscribers in
the group, the data are sent to that
channel.
Figure 9.17 Cable modem (CM)
9.48
Figure 9.18 In cable company: Cable modem transmission system (CMTS)
9.49
Data Transmission Schemes: Data Over Cable
System Interface Specification


Defines all the protocols necessary to
transport data from a CMTS to a Cable
Modem.
Upstream Communication

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
9.50
CM checks for specific packets sent by CMTS.
The CMTS sends a packet to CM, defining its
allocated downstream and upstream
channels.
The CM starts ranging process (to determine
the distance for synchronization).
Data Transmission Schemes: Data Over Cable
System Interface Specification


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
9.51
The CM sends a packet to the ISP, asking for
the IP address.
The CM and CMTS exchange some packets to
establish security parameters.
The CM sends its unique identifier to the
CMTS.
Upstream communication can start in the
allocated upstream channel.
Data Transmission Schemes: Data Over Cable
System Interface Specification (DOCSIS)

Downstream Communication


9.52
No contention because only one sender.
The CMTS sends the packet with the address
of the receiving CM, using the allocated
downstream channel.